QUARTERLY

Volume 6, Number 4 

A M P T I AC is a DOD Info rmation An alys is Ce nte r Adm inis te re d by th e De fense In fo rmation Syste ms Age n c y, De fe nse Te chn ica l Inform atio n Cent er a nd Opera ted by Alion S cience an d Te ch n o l o g y

Special 

Issue:

P ro t e c t i n g

People at Risk:

How DOD Research Reduces

the Impact of Terrorism
About the Cover: 

The cover photo captures the fireball from an explosive test of a full size building

employing various structural retrofits designed to reduce masonry wall debris from

entering a building. The test series, called Divine Camel, was part of a joint

US/Israeli/UK project to study the performance of blast mitigation technologies.

This simulated car bomb explosion was conducted in May of 1998 in Israel. Two

of the inset photos provide before and after views of the building’s front wall. The

top inset on the cover shows an exterior wall of the Pentagon in Washington DC,

after the terrorist attack on September 11, 2001. The windows on the right had

been replaced with blast resistant units, while the ones on the left had not. 

(The plane crashed approximately 135 feet to the right of this photo location.) 

All images courtesy the US Army Corps of Engineers, Engineer Research and

Development Center, Vicksburg, MS. The series of insets on the back cover

(counter clockwise from upper left) capture a different test explosion.

A few months ago, while watching one of the many television documentaries detailing the demise of the World Trade

Center, I was struck by how the seemingly innocuous decisions of a structural engineer can have drastic ramifications.

All types of engineers are often faced with difficult choices

during their work. Factors such as cost, weight, strength, reliability, and ease of fabrication have to be weighed, balanced,

and optimized in such a way as to meet production goals. It

is these design parameters that establish baselines for our

work, and guide us each and every day.

In the case of the World Trade Center, the decision to use

spray-on fire insulation addressed all the fire safety parameters designers and engineers had set forth. A study by the

Federal Emergency Management Agency and the American

Society of Civil Engineers released this year revealed that the

spray-on insulation would later prove to be a flaw in the

building’s resilience. The insulation had spalled-off of structural members due to time, adhesion failure, maintenance,

and most critically, due to the flying debris from the crashing

aircraft. The building was able to handle two separate events: 

its structure was tough enough to survive the impact of an

aircraft, and the spray-on insulation was designed to protect

the structural steel from the heat of a fire. But when the two

were combined on September 11th, the steel was left unprotected in the subsequent fire. The towers, which were

designed to stand for at least four hours in the event of catastrophic fire, fell in less than 100 minutes. Thus a decision

made more than 30 years ago, which was correct by every

engineering standard and design practice of the time, was

proven inadequate in this unimaginable incident.

All things in life teach us something and some of our greatest lessons come from tragedy. The majority of our decisions

will not carry the weight of a single human life, much less

those of thousands. But when designers of government, civilian, and military buildings put pen to paper today, they are

taking human lives in their hands. Events of the last ten years

have shown that all buildings, from the most prominent to

the very mundane, are exposed to sophisticated threats.

Within this issue of the AMPTIAC Quarterly, we have

brought together some of the Defense community’s most

respected researchers and practitioners of structural protection. They describe the resources and methods that save lives.

I encourage everyone picking up this issue to consider the

larger picture that it paints: the subtleties, the strengths, the

structural and operational techniques that serve to protect us

everyday. Perhaps also you will find application for some of

these resources in your own work.

Wade Babcock

Editor in Chief

Editorial: Serious 

Ramifications for Otherwise 

Innocuous Decisions
Issue focus: 

How DOD Research Protects 

People and Buildings

US Government Initiatives Reduce Terrorist Threat to Personnel and Structures ... 5

Wade Babcock and David Rose, AMPTIAC, Rome, NY

The US Government has been addressing the issue of protecting people and stru c t u res from terrorist attacks for many years. T h i s

a rticle provides an introduction to the federal coordinating group which directs these activities, and the DOD agency that focuses

on military issues. This article also features insight from some of the key people within DOD who direct and take part in these effort s .

The TSWG – Closeup ... 8

Protecting Personnel at Risk:

DOD Writes Anti-Terrorism Standards to Protect People in Buildings ... 11

Colonel Joel C. Bradshaw III, PE, Chief of Military Construction Programs, Office of Deputy Under Secretary of Defense 

(Installations and Environment), The Pentagon, Washington, DC

The DOD takes the issue of protecting its personnel very seriously and has recently completed the codified anti-terrorism standards which began a few years ago as guidance and interim directives. Colonel Bradshaw is in a unique position to explain some

of the critical steps and policy issues that drove this process, as well as the top-level directives and initiatives that are contained in

the document.

DOD Protective Design Manuals Have Wide Application ... 17

Patrick Lindsey, PE, Protective Design Center, US Army Corps of Engineers, Omaha, NE

Factors such as site selection, building location on the site, use of fences and clear space, as well as vegetation and structural reinforcements are all critical to protecting a building and its occupants from various threats. Incorporating protection into a facility’s

design is the best way to achieve a desired level of protection at a reasonable cost. Patrick Lindsey of the Protective Design Center

summarizes many of the key features and considerations to be accounted for, and introduces the DOD resources available. 

Homeland Security vs. Homeland Defense... Is there a difference? ... 24

Polymer Composite Retrofits Strengthen Concrete Structures ... 25

Robert Odello, Director, Waterfront Structures Division, Naval Facilities Engineering Services Center, Port Hueneme, CA

The Navy is using composite materials to strengthen pier decks and support columns. Some of these structures were not designed

for current load requirements and therefore need to be upgraded while others are deteriorating and the retrofits can bring them

back to full service. The systems outlined in this article are also being considered for use in buildings to increase both dynamic

shock-induced load capability and the ability to withstand negative loading. Robert Odello describes a program that is proving that

composite systems offer viable, serviceable, and cost effective ways of strengthening real-world concrete structures. These programs

are also educating both the government and industry on how to specify, install and maintain them. Lessons learned in these Navy

projects will help further advance the protection and hardening of land-based structures.

Blast Retrofit Research and Development:

Protection for Walls and Windows ... 31

David Coltharp and Dr. Robert L. Hall, Geotechnical and Structures Laboratory, US Army Corps of Engineers, 

Engineer Research and Development Center, Vicksburg, MS

Conventional building components are highly vulnerable to terrorist vehicle bomb attack. Common annealed glass windows break

at very low blast pressures and the resulting flying glass fragments are a major cause of injuries in many bombing incidents. Masonry

in-fill walls are also weak elements and another source of hazardous debris. Through the combined research and development efforts

of multiple DOD agencies and the State Department, significant advances have been made since 1996 in improving methods 

for protection of conventional military and government facilities. David Coltharp presents some of the unique and innovative

methods that have been developed for retrofitting windows and walls, and describes how they increase the blast capacity of these

vulnerable components, decrease standoff requirements, and improve protection for personnel.

Mark Your Calendar ... 38

The AMPTIAC Quarterly, Volume 6, Number 4

A M P T I AC is a DOD Information Analysis Center Administe red by the Defense Information Systems Age n c y, 

D e fense Te chnical Information Center and Opera ted by Alion Science and Te ch n o l o g y
MaterialEASE: Materials for Blast and Penetration Resistance ... 39

Richard Lane, Benjamin Craig, and Wade Babcock, AMPTIAC, Rome, NY

In 2001 AMPTIAC was tasked by the Office of the Secretary of Defense to summarize the research efforts and data compiled on

blast and penetration resistant materials (BPRM), including monolithic materials and novel combinations of materials. As a 

service to the uninitiated, we have provided this “primer” so that those less familiar with material and security matters may 

develop a well-rounded perspective of the topic. In turn, this may afford you, the reader, a greater appreciation of the relevance and

importance of the topics discussed within this issue of the AMPTIAC Quarterly.

Polymer Coatings Increase Blast Resistance of Existing and Temporary Structures ... 47

Dr. Jonathan Porter and Robert Dinan, Materials and Manufacturing Directorate, Air Force Research Laboratory, Tyndall AFB, FL

Dr. Michael Hammons and Dr. Kenneth Knox, Applied Research Associates, Inc.

The DOD has banned the use of selected concrete masonry infill building techniques because they don’t hold up to blast 

overpressures and present a serious risk to occupants in the event of a blast. Additionally, the extensive use of temporary, portable

structures presents another unique blast protection problem. This Air Force program is looking for ways to retrofit these thousands

of structures in a quick and cost effective manner, while adding a significant level of fragmentation protection.

Designing Blast Hardened Structures for Military and Civilian Use ... 53

Bruce Walton, PE, Protective Design Center, US Army Corps of Engineers, Omaha, NE

Centuries ago castles and moats addressed the need to keep a facility safe from an attacker. From those massive stone and wood

structures, to the hardened reinforced concrete and sophisticated intrusion detection systems of the present, the principles of 

hardened structures have fundamentally remained the same: Identify the baseline threat and keep it at a safe distance, or create a

structure as impervious as possible to that threat. Bruce Walton provides a broad, overall perspective on the problem of designing

a hardened structure, and describes some of the techniques, fundamentals, and resources available.

Design Example – Exterior Blast Upgrade ... 56

IAC Program Addresses Homeland Security ... 60

Very-High-Strength Concretes for Use in Blast- and Penetration-Resistant Structures ... 61

Dr. J. Donald Cargile, Impact and Explosion Effects Branch; Ed F. O’Neil and Billy D. Neeley, Concrete and Materials Division;

Geotechnical and Structures Laboratory, US Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS

You may be thinking that there is nothing we can tell you about concrete that won’t cure insomnia, but you’d be wrong. How does

advanced concrete 4 to 5 times stronger than standard concrete sound? The folks at ERDC are working to drastically improve this

ubiquitous material, both in its general compressive strength and its resistance to fragmentation in impact events. Donald Cargile

and his colleagues present the experimental data and demonstrate that concrete has a lot of development potential left in it.

The AMPTIAC Quarterly is published by the Advanced Materials and Processes Technology Information

Analysis Center (AMPTIAC). AMPTIAC is a DOD sponsored Information Analysis Center, operated 

by Alion Science and Technology and administratively managed by the Defense Information Systems Agency

(DISA), Defense Technical Information Center (DTIC). The AMPTIAC Quarterly is distributed to more

than 25,000 materials professionals around the world.

Inquiries about AMPTIAC capabilities, products and services may be addressed to 

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E M A I L : a mp t i a c @ a l i o n s c i e n c e . c o m

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ATTN: WADE G. BABCOCK

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Editor-in-Chief

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Christian E. Grethlein, P.E.

CLARIFICATION: The cover story for our last issue described the Army’s exciting Mobile Parts Hospital project. Within that

article, a technology called Laser Engineered Net ShapingTM was presented which can fabricate replacement parts using a

combination of computational design templates, a computer-controlled laser, and powder metallurgy. Laser Engineering Net

ShapingTM and the LENS® acronym are registered trademarks and service marks of Sandia National Laboratories and

Sandia Corporation.
The AMPTIAC Quarterly, Volume 6, Number 4 5

INTRODUCTION

One important consideration when enhancing the capabilities

of the US and its allies in the War on Terrorism is the ability to

rapidly develop and apply technology to meet the challenges

posed by terrorists. The Technical Support Working Group

(TSWG) is the US Government’s focused response to this

problem, and acts to coordinate the efforts of multiple departments and agencies to maximize our investment in combating

terrorism. (Please see the TSWG sidebar on page 8 for more

details.) Within the Department of Defense (DOD), the

Defense Threat Reduction Agency (DTRA) takes the lead in

reducing the threat of weapons of mass destruction; both in

preventing their spread and use, as well as reducing the impact

of their effects if they are used.

DTRA also provides operational and analytical support for

nuclear stockpile stewardship duties and technical support for

nuclear weapons in Defense Department custody. In addition

it focuses DOD efforts to prepare for, and respond to chemical

or biological attacks on US or friendly forces, including overseeing the development and implementation of special

weapons technologies. These technologies provide US military

commanders options for effective targeting against underground or hardened structures and enhanced capabilities to

assess battle damage. The agency also implements on-site arms

control inspection, escort and monitoring activities, and develops treaty verification monitoring technologies.

The main DOD thrust to develop protective technologies

which protect people in buildings from terrorist bomb attacks

is sponsored by the TSWG and managed DTRA. The program

seeks to develop blast mitigation techniques for both retrofitting existing buildings and designing new ones. Many of

these techniques are covered elsewhere in this Special Issue.

While these methods and solutions have direct application to

our military forces, they can also be applied to federal and commercial buildings, both domestic and abroad.

The various Government-sponsored blast mitigation projects

have many goals, one of which is developing a much better

understanding of vulnerability and survivability of buildings

and their occupants. This involves a multi-pronged approach of

characterizing blast effects, quantifying structural response, and

classifying human injuries due to those factors. These are

accomplished through various means, including evaluation of

existing buildings, experimentation with test structures under

controlled explosive events, and computational modeling. A

key analytical tool to understand structural damage and injuries

is to study terrorist events such as the Khobar Towers bombing

in Saudi Arabia (See Figure 1) and the attack on the Murrah

Federal building in Oklahoma City. Much of this work results

in design guidance, which is incorporated into DOD documents for both new construction and retrofits to existing structures. Some of the most notable examples include the Pentagon

in Virginia and the Ronald Reagan Building and International

Trade Center in Washington, DC.

THE ORIGINS OF, AND POLICIES REGARDING, 

BLAST MITIGATION

The actual process of protecting people from blast effects is

more a balancing act of money vs. protection, than it is of

developing technology. “There are no real technology issues

that can’t be worked out,” said Mr. Douglas Sunshine, the

Program Manager at DTRA running many of the blast mitigation research efforts under DTRA and TSWG. “Most often, it’s

about money,” he said, and balancing the need for protection

with its cost, by using the various tools that structural engineers

have available to them, like standoff and hardening.

In the mid-70’s there was a string of Embassy bombings,

encouraging Government planners to place more emphasis on

structural protection. Then, the October 1983 bombing of the

Marine Barracks in Beruit put a sharp point on all US efforts

to protect its personnel both at home and abroad. Mr. David

Coltharp, Technical Director for the Joint Antiterrorist/Force

Protection Re s e a rch program of the US Army Corps of

En g i n e e r s’ Engineer Re s e a rch and De velopment Center

(USACE/ERDC) in Vicksburg, MS said that this event truly

marked the beginning of a whole new thrust within the

Government to address structural protection. “The [USACE]

Pro t e c t i ve Design Center was stood-up at the Corps of

Engineers’ Omaha District and initial drafts of the security

engineering manual were published. The State Department got

involved, and stringent guidelines for new embassies were produced in the following ten years.”

But protection of DOD facilities from terrorists was still not

Wade Babcock and David Rose

AMPTIAC

Rome, NY
6 The AMPTIAC Quarterly, Volume 6, Number 4

a pressing issue, until the Khobar Towers bombing in June of

1996. In this instance, 19 US servicemen were killed when terrorists detonated a tanker truck containing an estimated

15,000 pounds of plastic explosive at a US military complex in

Saudi Arabia. (See Figures 1 & 2) The event highlighted the

vulnerability of military targets to the terrorist threat. Dr.

Robert Hall, Chief of the Geosciences and Structures Division

of the Geotechnical and Structures Laboratory at ERDC said,

“This was where the lack of antiterrorism standards (for military installations) was made clear.” Prior to the Khobar Towers

incident, military installations were thought to be fairly safe

from terrorist actions, due to security perimeters, vehicle and

personnel entry screening, and any number of other measures

employed at specific locations. Coltharp explained that the

responsibility of protecting troops was contained in the established chain of command for a particular location.

“Commander[s] would protect [their] troops, along with

[their] other tasks and responsibilities.”

In the mid-nineties, guidelines and standards for DOD

installations were established to counter the terrorist threat.

Hall said the key at any site is to “balance security and strengthening.” Providing stand-off from a potential threat is much less

expensive and intrusive than thick concrete walls and bullet

proof glass. But where stand-off is not available, the structure

must be hardened to the assumed threat, he said. Coltharp

added, “The antiterrorist construction standards address balancing these factors. Where stand-off is available, it is used.

Where urban settings limit stand-off, hardening is employed.

Base commanders now have other tools available to them, as

well as guidance from the chain of command.” The Joint

Antiterrorism/Force Protection (JAT/FP) program Hall said,

“provides a web-based site to train a commander on protection

techniques. This gives commanders better tools, so that they

can make the best decisions,” he added.

There is, however, a strong need to balance available funding

with eventual safety. Since the late 80’s, antiterrorism has been

identified in budgeting, and is a critical feature of new construction projects. Existing buildings are being prioritized for

blast mitigation retrofits, or retrofits are being incorporated

into major renovations. Sometimes the retrofits are as simple as

choosing a blast resistant window during a scheduled window

replacement in a building, but often these decisions are much

more complex. Coltharp points out that for new construction,

the added cost of most structural protection measures will often

be less than 5% of the total cost, and the cost of protection can

be much lower if careful site planning is employe d .

Additionally, Sunshine said that beyond meeting the safety criteria, engineers also have to balance hardening measures, cost,

and in particular, aesthetics. “It turns out that [protection solutions] have to look good also,” he said. 

THE ROLE OF DTRA AND THE TSWG CONNECTION

DTRA places most of its emphasis on DOD issues like

weapons of mass destruction, dismantling nuclear arsenals in

the former Soviet States, and force protection. Within the area

of force protection, DTRA sponsors work in all three services

including ERDC, the Protective Design Center, the Naval

Facilities Engineering Service Center at Port Hueneme, CA,

and the Air Force Research Lab/Materials and Manufacturing

Directorate at Tyndall AFB, FL. Many of these projects are feat u red elsew h e re in this Special Issue of the A M P T I AC

Quarterly. The two key areas that Sunshine directs research in

are the methodologies to do structural assessments, and the

eventual solutions to protect the structures. The results of these

research efforts are then transitioned to Government agencies

and industry. Often this work is conducted very closely with

industry, as in the case of window systems.

Sunshine is also DTRA’s representative to the TSWG, which

Figure1. Terrorists Killed 19 US Servicemen in the Khobar Towers Bombing.
The AMPTIAC Quarterly, Volume 6, Number 4 7

has a mandate as a requirements-driven, multi-agency working

group, and relies on experts in particular fields. This assures

that in addition to the more fundamental research projects that

it directs, there are plenty of avenues to solve members’ problems. Sunshine says that often agencies come to him with specific questions about structural/force protection. In one case, a

specific type of building common on many foreign US

Government installations was under scrutiny for what type of

hardening measures it would require. About $500,000 was

spent looking at the issue and recommendations were made.

The agency later said that the research investment resulted in a

cost savings of $10-15 Million. “Results from the research program not only increase the protection of people in buildings,

but save significant amounts of money,” said Sunshine.

FUTURE DIRECTIONS FOR BLAST MITIGATION RESEARCH

So, what does the future hold? Hall and Coltharp agree that

there are a number of critical issues facing the Government.

First is placing facilities in campus-like settings, instead of

downtown locations. Next is dealing with leased buildings that

the government utilizes, and how that impacts local businesses,

landlords, and other tenants who currently share space in a

building with the government. These local impacts are often

very difficult to fully characterize. In some cases it is simply a

matter of commercial entities who share building space with

the Government, and are therefore put at risk. In other cases,

the effect is economic. For instance, leased floor space vacated

by the Government can dramatically hurt landlords, as well as

support businesses like restaurants, services and local vendors in

the area.

Sunshine pointed out that the vast majority of blast mitigation research has been conducted on reinforced concrete 

and masonry buildings. There are many existing and planned

buildings which utilize steel, therefore a lot of attention will be

paid to steel frame structures in the near future, he said.

One of the most critical issues facing the military in general

and the Government in particular is the patience of terrorists.

Coltharp says that the enemy “is devious and patient. He

attacks the ‘soft spot,’ and he doesn’t really care where that spot

is. If we secure the military base, he targets the Federal building. If we harden that, then he targets the Post Office, or the

school.” Coltharp adds that placing the emphasis for structural

protection on many more types and classes of buildings that

have rarely been considered as likely targets before will be one

of the most critical issues facing us in the future, and one of the

most expensive. Hall points out that while ERDC and similar

DOD labs have well-defined roles in military force and infrastructure protection, their role in Homeland Security is still

very much in flux. “We are still figuring that out,” he said.

CONCLUSION

Protecting people from the threat of terrorism is one of the most

challenging problems we currently face. While our response to

the threat is still taking shape, agencies and groups like DTRA

and TS WG are leading the fight. The re s e a rch into blast mitigation, including structural hardening, structural re t rofits, and

site planning, obviously has importance to DOD, but is also

critical in domestic pre p a redness measures. Much of this technology may be transitioned directly to many types of stru c t u re s

in all parts of the United States and around the world.

The Army, Navy, and Air Force are actively involved in developing the tools and technologies needed to harden buildings.

They maintain close coordination between research activities

that are developing novel approaches to employ materials in

ways never envisioned when the materials were first developed.

This Special Issue highlights how newer materials, such as polymers or composites, can be used in buildings to help protect

them and their inhabitants from terrorist bombings.

Figure 2. The Khobar Towers Truck Bomb Left a Crater More Than 15 Feet Deep.
8 The AMPTIAC Quarterly, Volume 6, Number 4

THE TECHNICAL SUPPORT WORKING GROUP (TSWG)

The April 1982, National Security Decision Directive (NSDD) 30 assigned responsibility

for the development of overall US policy on terrorism to the Interdepartmental Working

Group on Terrorism (IG/T) chaired by the Department of State (DOS). The TSWG was an

original subgroup of the IG/T, which later became the Interagency Working Group on

C o u n t e rt e r rorism. In its Fe b ru a ry 1986 re p o rt, a cabinet level Task Fo rce on

Counterterrorism led by then Vice-President George H.W. Bush cited the TSWG as assuring “the development of appropriate counterterrorism technological efforts.”

Today, TSWG still performs that counterterrorism technology development function as a

stand-alone interagency working group. TSWG’s mission is to conduct the national interagency research and development (R&D) program for combating terrorism requirements. It

also has commenced efforts to conduct and influence longer-term R&D initiatives and,

reflecting the shift to a more offensive strategy, balance its technology and capability development efforts among the four pillars of combating terrorism: intelligence support, counterterrorism, antiterrorism, and consequence management.

Structure

TSWG operates under the policy oversight of the Department of State’s Coordinator for

Counterterrorism, and the management and technical oversight of the DOD Assistant

Secretary of Defense for Special Operations and Low-Intensity Conflict (ASD (SO/LIC)).

Participation is open to all federal departments and agencies, and current membership

includes representatives from over eighty organizations across the Federal Government.

While the TSWG’s core funds are derived principally from DOD’s Combating Terrorism

Technology Support (CTTS) Program, and the DOS, other departments and agencies contribute additional funding. They also provide personnel to act as project managers and technical advisors. TSWG conducts cooperative R&D with the United Kingdom, Canada, and

Israel through separate bilateral agreements.

Member departments and agencies work together by participating in one or more TSWG

subgroups. The nine subgroups, each focusing on a specific area of technology, are as follows:

The TSWG – Closeup

This sidebar presents a brief introduction to the Technical Su p p o rt

Working Group, or TSWG. Many

government agencies participate in it

and form the core of the US’s development effort for counterterrorism

technologies.

TSWG Organization • Chemical, Biological, Radiological and Nuclear Countermeasures

• Explosives Detection

• Improvised Device Defeat

• Infrastructure Protection

• Investigative Support and Forensics

• Personnel Protection

• Physical Security

• Surveillance, Collection and Operations Support

• Tactical Operations Support

Program Management

Combating Terrorism Technology Support Office

(DOD)

Coordinator for

Counterterrorism

Multi-Agency Member Subgroups

Chemical, Biological,

Radiological & Nuclear

Countermeasures

FBI/IC

Improvised Device

Defeat 

FBI/ATF

Investigative Support

& Forensics 

FBI/USSS

Physical Security 

DOD

Tactical Operations

Support

DOD

Explosives Detection 

TSA

Infrastructure

Protection 

FBI/DOD

Personnel Protection 

USSS

Surveillance,

Collection &

Operations Support

IC

Oversight

DOS

Executive Program

Direction ASD (SO/LIC)

Technical Chairs

DOD DOE FBI
RELEVANT PROGRAM AREAS

One can see that the mission of TSWG crosses many technical areas and scientific disciplines. The areas of most relevance to the structural protection community are presented

below in more detail. More information on the complete activities of TSWG may be found

at www.tswg.gov.

Infrastructure Protection

The Infrastructure Protection (IP) Subgroup’s mission is to identify, prioritize, and execute

research and development projects that satisfy interagency requirements for the protection

and assurance of critical Government, public, and private infrastructure systems required to

maintain the national and economic security of the United States. These critical systems

include control systems for electric power, natural gas, petroleum products, and water; telephone, radio, and television communications systems; ground, rail, and air transportation

facilities; and cyber communications networks. 

Physical Security

The Physical Security (PS) subgroup identifies the physical security requirements of federal

agencies, both within the United States and abroad, and then develops the technology 

to protect their personnel and property from terrorist attack. The technology is developed by creating prototype hardware, software, or

systems for technical and operational evaluation by user

agencies. 

Focus Areas The PS Subgroup focus areas reflect

the prioritized re q u i rements of the physical 

protection community. The following are some

of the topics explored in FY 2002: 

• Blast Mitigation - Develop building construction and retrofit techniques that better protect

people and facilities from the two main causes of

injuries resulting from terrorist bomb blasts - flying

debris and structural collapse. 

• Entry Point Screening - Develop multiple technologies and 

techniques to detect explosives, weapons, chemical and radiological

material, and other contraband on or in personnel, vehicles, vessels, cargo, and mail.

Solutions will increase the detection rate, throughput, and safety while reducing the

number of security forces required to perform the screening process.

• Perimeter Protection - Develop advanced perimeter intrusion detection and surveillance

systems that have a higher probability of detection, a lower false alarm rate, and the 

ability to operate continuously in demanding operational environments. These systems

will provide security forces with improved early warning and response capabilities on land

and at sea.

(Compiled from US Government-supplied information.)

The AMPTIAC Quarterly, Volume 6, Number 4 9

Chemical, Biological,

Radiological and Nuclear

Countermeasures

26%

TSWG FY 2002 

Program Funding

Explosives Detection 5%

Improvised

Device Defeat 

13%

Infrastructure

Protection 

2%

Investigative

Support and

Forensics 

4%

Physical

Security 19%

Personnel

Protection

6%

Surveillance,

Collection and

Operations Support

22%

Tactical

Operations

Support

3%
10 The AMPTIAC Quarterly, Volume 6, Number 4

COMPLETED

Structural Retrofit Methods

Retrofit design concepts and guidelines for strengthening existing reinforced concrete buildings against terrorist bomb attacks were developed.

Retrofit techniques, such as spray-on polymers and composite wraps for

structural columns have been evaluated and design guidance written. These

techniques have been used to upgrade embassies and military facilities.

Quick Reaction Perimeter Intrusion Detection Sensor (QUPID)

QUPID is an ultra-wide impulse radar system with adjustable range gates

that projects a “virtual fence” beyond the perimeter to detect intruders at

distances up to 100 meters. TSWG successfully developed two prototype

versions of the sensor in FY 2002: the first is compatible with the USAF

Tactical Automated Security System and the second works with a commercial intrusion detection system. The Air Force transitioned QUPID into an

acquisition program in July 2002 with fielding planned for FY 2003.

Military Mobile Vehicle and Cargo Inspection System (MMVACIS)

MMVACIS, a mobile gamma radiation imaging system, was developed for

the inspection of vehicles and cargo. The system provides rapid deployment

capability to established bases or with US expeditionary forces. It has been

employed by the DOD since Fall 2001, and has been integrated into contraband interdiction and force protection operations.

ONGOING

Blast Effects Estimation Model (BEEM)

BEEM will be a single model capable of estimating the effects of blasts, fragmentation, building damage and personal injury. BEEM will incorporate

the best features of two existing models, the Force Protection Tool (FPT)

and the Anti-Terrorism Planner (AT-Planner) tool.

Glass Penetration Model

A human injury prediction model based on multi-hit glass penetration is

being developed. The model inputs will be window characteristics, blast

parameters, and the location of a person relative to the window. The model

will output the severity of the injuries to that person. The final product will

be a software model that will complement BEEM.

Lightweight Portable Boom and Underwater Sentry System

A lightweight boom, equipped with fiber optic and acoustic sensors to provide standoff detection of intruders for US Navy ships, is being developed.

It is designed for easy deployment and redeployment by the ship’s crew

dockside or at anchor in transit ports. It will provide a temporary legal

perimeter barrier as well as surface and subsurface intrusion detection 

capabilities against attacks by small boats and swimmers. The prototype 

system will continue developmental testing and evaluation during FY 2003,

and will begin operational testing in FY 2004.

Advanced Vehicle Driver Identification System

The Advanced Vehicle Driver Identification System (AVIDS) is being developed to expedite the screening process at vehicle entry points by providing

force protection personnel with near real-time access to control databases.

This modular system allows users to select only those components needed

at their facility. AVIDS has been installed at a DOD facility, enabling 

verification of the occupants of a vehicle in less than three seconds over a

secure wireless LAN that covers eighteen square miles and five vehicle entry

points. Weigh-in-motion, RF tags, and license plate reader modules were

expected to be integrated by the end of 2002, with biometrics modules 

integrated in 2003.

Example TSWG Projects
The AMPTIAC Quarterly, Volume 6, Number 4 11

Editor’s Note: The following article describes the development of

and basis for the Department of Defense’s antiterrorism and force

protection policy. Many of the topics presented here are discussed in

much finer detail within other articles in this special issue. We feel

Colonel Bradshaw’s summarization of the DOD policy builds a

framework in which to better understand those research

efforts, and thus helps to fill-in the “big picture” of how all

the pieces eventually come together.

Protecting people in De p a rtment of De f e n s e

(DOD) buildings has always been a high priority,

but after the Khobar Towers terrorist act in 1996,

the Department put more emphasis on protecting its people from terrorism. In 1999, DOD

published its “Interim Antiterro r i s m

( AT) / Fo rce Protection (FP) Constru c t i o n

Standards.” This was the result of a threemonth intense effort by a DOD-wide team

led by the Office of the Se c re t a ry of

Defense (OSD) and the US Army Corps

of Engineers (USACE) Pro t e c t i ve De s i g n

Center in Omaha, Nebraska. As a result, buildings on mili t a ry installations, beginning with Fiscal Year (FY) 2002

Military Construction (MilCon) funding, are now being constructed or renovated with features to protect people in the

event of a terrorist attack. 

After publication of the “Interim Standards,” the DOD

team, known as the Security Engineering Working Group, or

SEWG, began to write the final standards. This was a collaborative effort of engineers and antiterrorism experts from the

Services and Defense Agencies, as well as other government

agencies, such as the General Services Administration and the

State Department. The SEWG was co-chaired by Colonel

Debra Lewis of the Joint Staff J-3 Deputy Directorate for

AT/FP and Mr. Curt Betts of the USACE Protective Design

Center. (See also Patrick Lindsey’s article in this Special Issue.)

In addition to USACE, the Navy’s and Air Force’s engineers

we re re p resented by the US Na val Facilities En g i n e e r i n g

Command and the US Air Force Civil Engineer

Support Agency, respectively. The Office

of Deputy Under Secretary of Defense for

Installations and Environment is responsible for the AT Building Standards and now

co-chairs the SEWG along with USACE.

The Assistant Se c re t a ry of Defense for

Special Operations and Low - In t e n s i t y

Conflict (SOLIC) has the overall responsibility for antiterrorism policy within DOD.

The SEWG began development of the new

standards as soon as the Interim Standards were

published. After eighteen months, the final draft

document was published in August 2001 for coordination among numerous offices within DOD.

More than 400 comments were incorporated into

the final version of the standards which were completed in

December 2001. The higher-level coordination within OSD

took longer than expected because of a decision to publish the

standards as a Unified Facilities Criteria (UFC). The new

DOD system of UFCs was approved in May 2002, and the AT

UFC went out for coordination in June. There was concern

within OSD leadership over the rigid requirements for standoff distance and for the applicability of the standards to leased

Colonel Joel C. Bradshaw III, PE

Chief of Military Construction Programs

Office of Deputy Under Secretary of Defense (Installations and Environment)

The Pentagon, Washington, DC
facilities. Eventually both issues were resolved; an “effective

stand off” requirement was incorporated and it was agreed that

DOD personnel in leased facilities should be given the same

protection as those in DOD-owned buildings. The effective

stand-off requirement enables the minimum stand-off distance

to be reduced if the building can be hardened to give an equivalent level of protection. This can result in a much more expensive solution, but it does give an alternative in cases of restrictive land availability. This also encourages development of new

technologies for building hardening.

On September 20, 2002, the “DOD Mi n i m u m

Antiterrorism Standards for Buildings” was published as UFC

4-010-01. This UFC is part of the Whole Building Design

Guide (WBDG), which is maintained by the National Institute

of Building Sciences (NIBS), and is available to the general

public. It can be found on the WBDG web site

( w w w.wbdg.org) or the DOD site (www. a c q . o s d / i e / i r m ) .

Specific AT designs for DOD construction projects will not be

releasable to the public.

The new UFC supercedes the Interim Standards, which were

used for design of FY2002 and FY2003 MilCon projects. The

new criteria however, are applicable to more than just MilCon.

In addition to construction projects beginning in FY2004, they

also apply to new leases in FY2006 and lease renewals by

FY2010. The standards greatly improve the original guidance

and ability to enhance protection. They expand to influence all

funding sources and investments, and they make it easier to

leverage new technology and engineering developments.

Although specific standards may change, the overarching

strategy described in the new standards (Table 1) is designed to

enhance protection of DOD personnel no matter what threats

they may face in the future. The main goal is to increase survival rates in buildings targeted by terrorists, realizing that it

would be cost prohibitive to achieve complete protection

against all potential threats. 

The final AT/FP standards (Figure 1) in the new UFC

describe minimum criteria for protecting against terrorist

12 The AMPTIAC Quarterly, Volume 6, Number 4

Table 2. Building Definitions.

• DOD Building

– Any building or portion of a building owned, leased, privatized, or otherwise occupied, managed, or controlled by or

for DOD

• Inhabited Building

– Buildings or portions occupied by 11 or more DOD personnel

– Population density greater than one person per 430 sq ft

• Primary Gathering Building

– Inhabited buildings occupied by 50 or more DOD personnel

– Family housing with 13 or more family units per building. 

• Billeting

– Building or portion where 11 or more unaccompanied DOD

personnel are routinely housed

Table 1. Guiding Principles for Minimum

Anti-terrorism Standards.

• Maximize standoff distance

• Prevent building collapse

• Minimize hazardous flying debris

• Limit airborne contamination

• Provide mass notification

Figure 1. Building Standards.

Floors designed 

to resist uplift

Installation perimeter

Air intakes

above 3 meters Emergency 

shutoff of HVAC

6mm laminated glass windows

Control roof

access Superstructure

designed to limit 

progressive collapse

(3 stories and above)

Mailroom on

building perimeter Avoid parking 

underneath or on roof

Brace overhead utilities

Doors positioned to minimize targeting

Exterior doors open outwards

Unreinforced exterior

masonry walls 

prohibited
The AMPTIAC Quarterly, Volume 6, Number 4 13

attacks when certain funding thresholds or other identified

triggers are met. For example, the standards are applied to new

construction or to significant renovation of buildings when the

cost estimate exceeds 50% of the building replacement cost.

The definitions in Table 2 illustrate other triggers that may

invoke use of the standards. Recognizing the standards cannot

be applied to every possible type of facility; there are several

exemptions (Table 3), such as low-density family housing, 

franchised food operations, mini marts, gas stations, etc. The

standards (Table 4) apply to most facilities, and will not need

to be supplemented unless a specific terrorist threat is identified, or when an installation commander sees a need for 

additional protective measures. 

The most cost-effective solution, if land is available, is allowing for a stand-off distance (Figure 2). Minimum standoff 

distances identified in Table 5 will ensure survivable structures

for a wide range of conventionally constructed buildings and

expeditionary or temporary structures. These buildings range

from tents and wood framed buildings to reinforced concrete

buildings. Standoff distances in the “Conve n t i o n a l

Construction Standoff Distance” column in Table 5 are based

on explosive safety considerations that have been developed as

Table 3. Exemptions to the DOD AT/FP Standards.

• Family housing with 12 units or fewer per building

• Stand alone franchised food operations

• Stand alone shopettes, mini marts, and small commissaries

• Gas stations and car care centers

• Medical transitional structures and spaces

• Transitional structures and spaces occupied less than one year

• Recruiting stations in leased spaces

Table 4. Summary of Design Strategies from UFC 4-010-01.

Standard 1: Minimum Standoff Distance. 

Applies to new and existing buildings, when triggered.

Standard 2. Building Separation. 

New buildings must be separated to minimize collateral damage.

Standard 3. Unobstructed Space. 

Ensure that obstructions within 10 meters (33 feet) of inhabited

buildings do not allow for concealment of explosive devices 150

mm (6 inches) or greater in height.

Standard 4. Drive-Up/Drop-Off Areas. 

Do not allow drive-through lanes or drive-up/drop-off to be located under any inhabited portion of a building. 

Standard 5. Access Roads. 

Ensure that access control measures are implemented.

Standard 6. Parking Beneath Buildings or on Rooftops. 

No parking underneath or on roof tops. 

Standard 7. Progressive Collapse Avoidance. 

For all new and existing inhabited buildings of three stories or

more, design the superstructure to sustain local damage with

the structural system as a whole remaining stable and not being

damaged to an extent disproportionate to the original local 

damage. 

Standard 8. Structural Isolation. 

Additions to existing buildings must be structurally independent

from the adjacent existing building

Standard 9. Building Overhangs. 

Avoid building overhangs with inhabited spaces above them

where people could gain access to the area underneath the 

overhang. 

Standard 10. Exterior Masonry Walls. 

Unreinforced masonry walls are prohibited.

Standard 11. Windows and Glazed Doors. 

Use a minimum of 6-mm (1/4-in) nominal laminated glass for all

exterior windows and glazed doors. Frames and mullions must be

aluminum or steel.

Standard 12. Building Entrance Layout. 

The main entrance to a building must not face an installation

perimeter or other uncontrolled vantage point.

Standard 13. Exterior Doors. 

Ensure that exterior doors into inhabited areas open outward.

Standard 14. Mailrooms. 

Locate rooms where mail is delivered or handled, to limit collateral

damage.

Standard 15. Roof Access. 

Control access to roofs to minimize the possibility of placing

explosives or chemical, biological, or radiological agents where

they would threaten occupants or infrastructure. 

Standard 16. Overhead Mounted Architectural Features. 

Ensure that overhead mounted features weighing 14 kilograms (31

pounds) or more are securely mounted. 

Standard 17. Air Intakes. 

Locate air intakes at least 3 meters (10 feet) above the ground.

Standard 18. Mailroom Ventilation. 

Provide separate, dedicated air ventilation systems for mailrooms.

Standard 19. Emergency Air Distribution Shutoff. 

Provide an emergency shutoff switch in the HVAC control system.

Standard 20. Utility Distribution and Installation. 

Route critical or fragile utilities so they are not on exterior walls or

on walls shared with mailrooms. 

Standard 21. Equipment Bracing. 

Mount overhead utilities and other fixtures weighing 14 kilograms

(31 pounds) or more to minimize the likelihood that they will fall

and injure building occupants. 

Standard 22. Under-Building Access. 

Ensure that access to crawl spaces, utility tunnels, and other

means of under-building access is controlled.

Standard 23. Mass Notification. 

All inhabited buildings must have a timely means to notify occupants of threats and instruct them what to do in response to those

threats.
14 The AMPTIAC Quarterly, Volume 6, Number 4

a result of years of experience and testing. Because these distances may be conservative for some construction types, the

standards allow for adjustment of standoff distances based on

the results of a structural analysis considering the applicable

explosive weights. For new buildings, even if such an analysis

yields a shorter standoff distance than those shown in Table 5,

the minimum specified standoff distance must be used to allow

for future upgrades as a result of emerging threats. For existing

buildings, lesser standoff distances may be allowed where the

required level of protection can be achieved through building

hardening or other mitigating construction or retrofit. The

standoff distance may also be reduced if analysis proves the

existing structure is sufficiently hardened.

Other agencies, such as GSA and the Department of State,

have been developing antiterrorism standards for facilities.

There are many similar criteria; however, there are several differences. All deal with multiple threats, but to differing degrees,

and all include requirements for windows. The biggest point of

contention is the issue of standoff distance. DOD has been

insistent on standoff as the primary strategy, where others lean

toward building hardening and less emphasis on standoff.

Incorporating AT/FP standards into new buildings, where

required standoff distances are available, increases construction

cost by three to five percent. Costs vary considerably where sufficient standoff is not available or when upgrading existing

buildings. Cost increases are generally based on upgraded windows, structural detailing for the prevention of progressive collapse, and modifications of the building interior to minimize

hazardous flying debris. 

Although the DOD standards have been published, there are

still several challenges. One of the biggest challenges is the cost

to enhance or relocate from leased facilities. Lack of standoff

distance is a big concern, especially on installations overseas

where land is not available in many locations and in urban areas

where leased facilities are downtown. Installations without

standoff distances will rely on other construction techniques or

mitigating measures. The issue of leased facilities will have to be

resolved by October 2009 for lease renewals, but some of the

alternatives may be expensive. Compliance with the standards

will be managed by the Services and Defense Agency heads.

The ultimate responsibility lies with the In s t a l l a t i o n

Commanders, who must notify senior commanders of noncompliance.

Figure 2. Standoff Distances and Building Separations – Controlled Perimeter.

45m = 148 ft

25m = 82 ft

10m = 33 f t

150mm = 6 in

Trash

Containers

Parking Roadways

Unobstructed Space

(150mm Height)

Primary Structures

Inhabited

Structures

Uninhabited Building

10m 25m 10m

10m 10m

Note: Standoff 

distances indicated

are for conventional

construction without

computational

analysis

Fence, Earthen Berm, or Similar Barrier
The AMPTIAC Quarterly, Volume 6, Number 4 15

Joel C. Bradshaw III, PE, Colonel, USAF, is the Chief of Military Construction Programs, Office of Deputy

Under Secretary of Defense (Installations and Environment), The Pentagon, Washington, DC. He serves as

principal advisor on the Military Construction program and on facilities investment matters. He is the DOD

lead for facilities criteria and anti-terrorism standards for buildings. He earned a Bachelor of Science Degree

in Civil Engineering in 1973 and a Master of Science Degree in Structural Engineering in 1975 from Virginia

Tech. Colonel Bradshaw is a registered professional engineer, has commanded a civil engineer squadron,

and served in a wide range of civil engineering positions at base level, major command, and at the Air Staff.

He has experience in research and development and in military construction projects both overseas and

CONUS. Colonel Bradshaw is a member of the American Society of Civil Engineers and a Fellow and Life

Member of the Society of American Military Engineers.

Table 5. Minimum Standoff Distances and Separation for New and Existing Buildings[1].

Location Building Category Minimum Standoff Distances or Separation Requirements

Applicable Level Standoff Distances Effective Standoff

of Protection For Conventional Construction Distances[2]

meters (feet) meters (feet)

Controlled Perimeter Billeting and Primary Low 45 (148) 25 (82)

or Roads & Parking Gathering Buildings

without 

Controlled Perimeter Inhabited Buildings Very Low 25 (82) 10 (33)

Roads & Parking Billeting and Primary Low 25 (82) 10 (33)

within a Gathering Buildings

Controlled 

Perimeter Inhabited Buildings Very Low 10 (33) 10 (33)

Trash Containers Billeting and Primary Low 25 (82) 10 (33)

Gathering Buildings

Inhabited Buildings Very Low 10 (33) 10 (33)

Building Separation Billeting and Primary Low 10 (33) No minimum

(New Bldgs) Gathering Buildings

Inhabited Buildings Very Low No minimum No minimum

[1] This table is derived from Table B-1, UFC 4-010-01, “DOD Minimum Antiterrorism Standards for Buildings,” dated July 31, 2002

[2] Even with analysis, standoff distances less than those in this column are not allowed for new buildings (even when constructed in accordance with AT standards),

but are allowed for existing buildings if constructed/retrofitted to provide the required level of protection at the reduced standoff distance.
16 The AMPTIAC Quarterly, Volume 6, Number 4

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The AMPTIAC Quarterly, Volume 6, Number 4 17

INTRODUCTION

Many manuals are available within the DOD to aid engineers

in the design of facilities subjected to blast loadings from

bombs. Facility design in consideration of exterior blast loadings starts with locating a site that is adequate for the facility

and level of protection required. The design basis threat (as

defined by the installation master planning team) identifies the

weapons, tools and tactics that could be used in an attack

against the facility. The site or master planners then review the

site plan and the design basis threat to determine if the amount

of standoff distance that is available can provide a proper level

of protection. The planners will then incorporate the use of

controlled and non-controlled perimeters, locate appropriate

exclusion or non-exclusion zones, define the standoff distances,

and identify facility clear zones. They will also locate the facility’s entry control points for vehicles and personnel. Should the

site be inadequate for a structure built with standard construction techniques, then blast loadings will need to be accounted

for to give the facility the same level of protection at the

reduced standoff distance. 

BACKGROUND HISTORY OF STANDARDS

Military Hardened Structures Progression

Since the invention of dynamite by Alfred Nobel in 1866, blast

effects on structures have been observed. In 1870, Rankine and

Hugoniot published their analytical solution to normal shocks

in an ideal gas and these relationships have formed the foundation for studying gas dynamics and the interaction of shock

waves with structures. It is well known that internal blasts are

more damaging than exterior blast effects as the shock and gas

pressure combine to act on the structure. 

In the last 50 years, the engineering units within the Mi l i t a ry

d e veloped many mathematical models to capture the stru c t u r a l

interaction with blast waves. After World War II, these models

s t a rted to show development when damage levels for masonry

s t ru c t u res we re correlated to crater size, crater location, and

e x p l o s i ve weights used in bombing runs. Damage level was a

m e a s u re of the amount of stru c t u re remaining based on the blast

p re s s u re and impulse the stru c t u re experienced from those

bombs. From those early days of the 1950’s other observa t i o n s

we re noted that relate the many blast parameters to scaling laws,

thus making it easy for engineers to develop models for pre d i c ting categories of damage based on: weight of explosive, range,

and type of stru c t u re. The 1950’s we re also the beginning of the

nuclear age, and many design ideas we re developed during this

era. A lot of the bunker mentality commonly associated with

e x p l o s i ve effects came from this time period. 

Anybody who has handled explosives knows the dangers

associated with that endeavor, as many accidents have occurred

as a result of their handling. A vast amount of knowledge was

acquired from accident investigations of catastrophic events. To

protect personnel, a Tri-Service group from the Army, Navy

and Air Force was formed to develop a manual to give engineers

a procedure that lets them design “Structures to Resist the

Effects of Accidental Explosions” (commonly known as technical manual TM 5-1300). The primary purpose of the manual

is to present methods for protective construction used in facilities for the development, testing, production, storage, maintenance, modification, inspection, demilitarization, and disposal

of explosive materials. This manual was used as the standard for

explosive effects for about thirty years. By using this manual,

engineers could design structures to resist the effects of blast

waves and fragments preventing the propagation of explosive

effects from one structure to the next, or to prevent the mass

detonation of explosives and provide protection to personnel

and valuable equipment. Instrumental to this approach was a

well-developed understanding of:

• the blast load parameters

• the response of structures to blast loads

• how to establish proper details for construction to develop

the proper structural response

• establishing guidelines for siting explosives facilities.

Technical manual TM 5-855-1, “Fundamentals of Protective

Design for Conventional Weapons” also came out of the postWorld War II era. While this manual is dedicated to the design

of structures to resist conventional weapons, during the 1970’s

great advances were made in the area of numerical modeling of

nuclear weapon effects. These include the effects of dynamic

response of aboveground, and belowground structures to airblast, blast-induced ground shock, cratering, and the response

of various materials to these effects. These modeling techniques

were then applied to the conventional weapons arena and the

Patrick Lindsey, PE

Protective Design Center

US Army Corps of Engineers (USACE)

Omaha, NE
manual has been updated several times since its original printing. This manual and TM 5-1300 deal with primarily concrete

and steel structures, but not everybody works in those types of

structures. Additional work has produced more data on how

conventional construction responds to blast loads and that data

has been incorporated into the new design guidance. 

After the Marine barracks bombing in Beirut, Lebanon in

1983, the DOD looked for a group to develop procedures that

could be implemented to prevent this type of incident from

recurring. The Army established the Corps of En g i n e e r s

Protective Design Center to take on this mission and its main

purpose was to provide physical security and antiterrorism protection to military assets. The first document created by this

group was called the Security Engineering Manual, which

became the TM 5-853 series of manuals on security engineering. Much of the blast and fragment technology developed for

TM 5-1300 and TM 5-855-1 had direct application to the area

of security engineering. Within this series of manuals, aggressors, weapons, tools and explosives are defined to develop a

design basis threat against specific assets. With this information

protective measures are designed to counter these threats and

protect the defined assets.

The physical security portion is that part of security concerned with physical measures designed to safeguard personnel;

prevent or delay unauthorized access to equipment, installations, material, and documents; and to safeguard against 

espionage, damage, and theft. Prior to this period, many of the

regulations were not interrelated or tied to design procedures,

and at times it was difficult to determine what level of protection was being provided for an asset. This manual brought

threats and protective measures together as a security engineering design procedure, balancing the design basis threat against

the level of protection. 

The antiterrorism aspects of facility design are the defensive

measures used to reduce the vulnerability of individuals and

p ro p e rty to terrorist attacks and often include a limited

response and containment of the aggressor by local military

forces, or a response force. Therefore, security engineering is

the process of identifying practical, risk-managed short and

long-term solutions to reduce and/or mitigate dynamic manmade hazards by integrating multiple factors, including 

construction, equipment, manpower, and procedures.

Application of DOD Manuals to Antiterrorism

The DOD manuals use the blast analysis and design tools 

created for the military and apply them to normal or civilian

type structures. These are referred to in the security engineering

process as conventional construction and include typical building systems including doors, windows, or manufacturers’ components, which are not designed to resist tools, weapons, or

explosives but are designed to resist common environmental

conditions such as gravity, wind, and seismic loads. Two cases

present themselves when blast loads are considered: external

and internal blasts. While an external blast load is very devastating, it is easier to handle if a standoff distance is available.

Standoff is the distance or open space placed between the external surface of the structure and the center of an explosive

device. For a known or assumed explosive weight with a given

standoff distance, the blast pressure, loading duration, and blast

impulse can be calculated using TM 5-855-1, TM 5-1300, or

TM 5-853-1 and applied to the facility components for design

or evaluation.

Should an internal blast occur, blast shock and gas loadings

reverse the normal loading direction of structural components:

the compression side of a concrete slab will be put in tension,

and vice versa. Normal structures are not designed for this loading condition and the structural system will be more susceptible to failure and collapse. When portions of a structure begin

to fail the next step is to minimize the area of failure. If the area

of failed members cannot be controlled then progressive collapse occurs. The damage seen in the Murrah Federal Building

in Oklahoma City was the result of progressive collapse, as the

area of collapse was disproportionate to that of the original area

damaged. Another area of consideration when studying blastloaded structures is the number of openings in the exterior

envelope of the building. Doors and windows are typically

weak points of the structure and can fail rather dramatically

with blast loads. Therefore, many of the DOD standards (as

defined by UFC 4-010-01) are being put into place to minimize casualties and damage for critical facilities, as well as to

define a baseline level of protection that can be easily upgraded

as the level of threat elevates.

Security Engineering Definitions

Controlled Perimeter The controlled perimeter is a physical

boundary to control access of vehicles or personnel. Controlled

perimeters are used on installation boundaries, or around critical facilities. This boundary must be capable of channeling 

all vehicles and personnel to a defined access control point 

(or points), where inspections can occur before entering the

controlled area. 

Standoff Distance Standoff distance is maintained between a

structure or inhabited portion of a structure and the potential

location of an explosive detonation. Standoff distance must be

increased to reduce the blast effects on the structure. The

required standoff distances will vary with building components

used in the construction. Blast pressures near an exploding

vehicle bomb are very high, but they decrease rapidly with

increased standoff distance. Maximizing the standoff distance is

the primary design strategy. Maximizing standoff distance also

ensures that there is opportunity in the future to upgrade buildings to meet increased threats or to accommodate higher levels

of protection.

Level of Protection The level of protection is the degree to

which an asset is protected against injury or damage. This

would include personnel and equipment. We could define

three levels of protection: low, medium, and high. For a low

level of protection, the structure would be near collapse, a

medium level of protection would result in a damaged but

repairable structure, and a high level of protection would cause

superficial damage to the structure. Selecting the level of protection means trading-off an acceptable level of risk.

18 The AMPTIAC Quarterly, Volume 6, Number 4
Exclusionary Zones Once the concepts of a

c o n t rolled perimeter, standoff distance,

and level of protection are understood, the

application of an exclusionary zone is an

easy concept. As shown in Figure 1, a controlled perimeter is established at a distance of de

, where the structural system

can accept a given blast load and provide a

given level of protection. Vehicles that are

authorized to enter these areas would be

limited to those that provide for facility

s e rvice, maintenance, delive ry, disabled

parking, etc. To gain access to this zone an

entry control point would be used and

depending on the mission, it may be

manned or operated with an entry control

device.

Nonexclusive Zones The next perimeter

used in conjunction with an exclusive

zone for a higher explosive threat condition is the nonexclusive zone, depicted in

Fi g u re 2. At the nonexc l u s i ve zo n e

perimeter large trucks could be stopped,

inspected, and turned around if necessary,

prior to entering the exclusive zone. The

intent is to minimize the number and size

of vehicles that can park relatively close to

the facility. Typically only automobiles

would enter the exclusive zone. However,

larger vehicles could enter after being

searched. Therefore, entry to this area is

t h rough a continuously manned entry

control point. The nonexclusive zone is

useful when the primary type of vehicle

entering the exclusive zone of the facility is

an automobile. 

Clear Zones A clear zone is used aro u n d

facilities when a smaller hand delive re d

device can be placed close to the facility

e x t e r i o r. In order to aid in vision detection

of such devices an obstacle free area can be

p rovided around the facility. This allows for

the direct observation of small packages

that are within 30 feet of the exterior walls

of the facility, as depicted in Fi g u re 3. Gr a s s

and landscaping within this area should not

be taller than 6 inches. In this case, there is

at least 50 feet of standoff from the facility

exterior to a seven-foot high fence or wall to

reduce the likelihood of an explosive device

being thrown tow a rd the building. If it

we re to happen, the explosive would land

in the clear zone where its detection would

be made much simpler. This means that an

e n t ry - c o n t rolled opening will need to be

p rovided through the fence or wall for

access to the facility.

Facility Cluste ri n g A useful approach to

p rotecting multiple buildings that are

exposed to a similar threat is to use facility

clustering as shown in Fi g u re 4. The efficiencies of this scenario are apparent in

that they are using common exc l u s i ve and

n o n e xc l u s i ve standoff zones. This scheme

also minimizes the number of entry cont rol points to the area. This can be effective

in a campus arrangement of buildings.

Lines of Sight Controlling lines of sight is

important in a variety of threats, from

visual observation, to ballistics. To protect

the asset these lines of sight need to be

blocked. There are many ways to accomplish this, such as the use of vegetation,

structures, obscuration fencing, or window coverings. Another approach is to

place assets to the interior of the building

to remove them from unwanted lines of

sight. For example, if the threat were from

a ballistic weapon, then the window and

door glazing would need to be designed to

stop the ballistic threat, or hide the asset

with blinds or shades. 

Minimum Measure s While not eve ry

t h reat can be anticipated, there are sets of

minimum measures that can be applied to

g i ve a baseline level of protection. T h e s e

m e a s u res can be applied to the facility

re g a rdless of the threat. Such measure s

could include: the elimination of hiding

places that are near the facility, locating the

facility within sight of other facilities on

that installation, and providing 150-feet of

standoff from the installation boundary.

Other measures include eliminating

straight-line approaches for vehicles driving tow a rd the facility, minimizing ve h i c l e

access points, locating entry and exit doors

on the opposite side of the facility than the

installation perimeter fence, and eliminating under-building parking. Steps which

should be utilized during the design phase

a re to locate the facility away from natural

and man-made vantage points that provide advantageous lines of sight for an

a g g ressor and illuminating the exterior of

the building and parking areas. For a re i nf o rced concrete-framed stru c t u re, use of

m o re robust seismic details at the framing

connections, and top and bottom re i nThe AMPTIAC Quarterly, Volume 6, Number 4 19

Figure1. Exclusive Standoff Zone

with Entry Control Point That Does

Not Need to be Manned.

Figure 2. Nonexclusive Standoff

Zone Requires a Manned Entry

Control Point.

Figure 3. Clear Zone Used with a

50’ Standoff Zone.

Figure 4. Facility Clustering of

Buildings with Similar Threats Using

the Same Exclusive and 

Nonexclusive Zones.

Entry Control Point

Facility de

de=Exclusive Standoff

Zone Distance

de=Exclusive Standoff Zone Distance

dn=Nonexclusive Standoff Zone Distance

Facility

Entry Control Point

de dn

Clear Zone

Fence

50 ft. min.

Standoff

Zone 30 ft.

min.

de= Exclusive

Standoff

Zone Distance

dn= Nonexclusive

Standoff

Zone Distance

Entry Control

Point

de

dn

de

dn

Exclusive Zone

Nonexclusive

Zone
f o rcement in the slabs will improve blast resistance. Another

good idea is to locate protected assets to the interior of the

building when practical, thus allowing the outside offices and

corridors to act as standoff. When using this approach, the center of the building could be used as a court y a rd to allow natural

light to enter the interior located offices.

Entry Control Points

There are several systems used to make the entry control point

function for the required level of protection and traffic flow

rate. The system defined here is for the control of vehicles and

personnel. At the installation perimeter fence this facility is

constantly manned. However, during peak usage many such

entry control points can be in use based on the processing rate

at each gate.

Approach Road The approach road is the main road leading

to the facility or area as shown in Figure 5. Controlling vehicle

speed along this road is critical to the success of the entry control point since the momentum and kinetic energy of a vehicle

is related to its entry velocity and the velocity squared respectively. For example, by reducing the approach velocity by one

half, the kinetic energy would be reduced to a fourth, and a

smaller barrier would be required. The common method used

to reduce the speed of the approaching vehicle is through the

use of massive concrete barriers arranged in a serpentine pattern. These barriers will control traffic flow, and the spacing

between barriers will slow the vehicles’ approaching speed.

Typically, a single lane road would be used when entering an

exclusive zone. Multiple lane roads are used when approaching

a nonexclusive zone and traffic is segregated into lines for automobiles, and trucks. 

Visitor and Truck Access Control Center Visitors wanting to

enter the installation must report to the visitor control facility.

Once there, they will have their ID checked, and if cleared they

will be issued a permit for entry. This area is also separated from

the facility or installation by a vehicle barrier to prevent access

to the installation. The visitor control center will have a parking area and a truck inspection area. While parked in this area,

vehicles can be searched, and if they do not pass this inspection,

they can be rejected without entering the installation.

Entry Control Point The entry control point is that point

whereby all access is allowed onto the installation. The requirements vary depending on whether the area being entered is

used as an exclusive or nonexclusive zone. When entering the

exclusive zone only a single lane of traffic and an active vehicle

barrier is used because of the limited amount of traffic entering

the zone. Even though the exclusive zone Entry Control Point

need not be manned, it should have a means of communicating with the operator who processes clearance information

within the facility. Once approved the vehicle can be cleared to

enter the exclusive zone. When the threat level is low, electronic entry control equipment may be used for access control. The

nonexclusive zone requires the use of a manned guardhouse,

and an active vehicle barrier. The next concern would be the

number of lanes required. This is determined by knowing the

maximum throughput needed for the area or installation. Table

1 shows some typical throughput ranges per lane given various

processing patterns. Last but not least, the entry control point

needs to be illuminated in order to make the appropriate ID

and vehicle inspections.

Gates and Barriers Two types of barriers are commonly used

for the entry control point: passive and active barriers. Active

barriers are operable gates that are designed to stop a moving

vehicle. While the passive gates are not operable, they can also

stop the kinetic energy of a moving vehicle. When designing a

nonexclusive zone, large vehicles need to be directed to a search

area that is provided with a rejection route outside of the

nonexclusive zone. Barriers need to be provided on both

incoming and outgoing traffic lanes to prevent the vehicle from

trying to enter the facility by going the wrong direction.

Figure 5. Entry Control Point.

Table 1. Vehicle Processing Rates.

Rate

Processing Pattern

(Vehicles/Hour/Lane)

Verify driver and vehicle identification 200 to 400

Verify driver and vehicle for all trucks 190 to 380

and perform visual observation of passenger 

and cargo area of random number of trucks

Perform all of the above and perform 150 to 280

basic search of passenger and cargo 

areas of random number of trucks

Perform all of the above and perform 90 to 170

comprehensive search of passenger and 

cargo areas of random number of trucks

Entry Control Point

Concrete Planter

Visitor Control Center

Visitors

and Trucks

Handicap and

Security Police

Parking Visitors Parking

Gate

20 The AMPTIAC Quarterly, Volume 6, Number 4
The AMPTIAC Quarterly, Volume 6, Number 4 21

Site Planning

Site planning integrates operational, logistic, and security

requirements into an overall design package that includes

buildings, exterior equipment, parking areas, road layouts,

perimeter barriers and gates, and site landscaping. The most

cost-effective overall solution for a project to mitigate explosive

effects on the buildings is to keep explosives as far away as possible. The design team can optimize the project cost by balancing the available standoff distance and the appropriate level of

building hardening. Normally that occurs when land is readily

available and conventional construction can be used. The site

layouts shown on Figures 6 and 7 identify the minimum standoff distances, that when achieved, will allow the buildings to be

built with minimal additional construction costs. Where these

standoff distances cannot be achieved because land is unavailable, DOD standards require that buildings be hardened to

maintain the same level of protection as the minimum standoff

distances. Costs and requirements for building hardening will

be addressed in the new DOD Security Engineering Manual.

Vantage Points Vantage points are natural or man-made positions from which an aggressor can observe and target, people or

other assets in and around a building. In many cases this is

known as having the high ground, thus giving the aggressor the

ability to shoot down on the unsuspecting personnel. The

design team needs to identify the vantage points that are outside the control of personnel in the targeted building, and

either eliminate them or shield the asset from a threat that is

posed by that vantage point. There are several means available

to the designer to eliminate this advantage, including the reorientation of the building to shield the personnel or asset, or to

use one of many different screening techniques such as the use

of reflective glazing, solid walls, privacy fencing, or vegetation

with dense foliage.

Minimum Standoff Distances Minimum standoff distances as

shown on Figures 6 and 7 are for a specific explosive weight and

a given level of protection. When the project can use

“Conventional Construction Without Analysis” the controlled

perimeters standoff distances are shown on Figure 6. Should

the project have an uncontrolled perimeter, conventional construction may be used with the minimum standoff distances

shown in Figure 7. If those standoff distances are not available,

the building must be analyzed by a qualified engineer and hardened to mitigate the effects of the explosives at the available

standoff for the appropriate level of protection. 

Figure 6. Standoff Distances and Building Separations – Controlled Perimeter.

45m = 148 ft

25m = 82 ft

10m = 33 ft

150mm = 6 in

Trash

Containers

Parking Roadways

Unobstructed Space

(150mm Height)

Primary Structures

Inhabited

Structures

Uninhabited Building

10m 25m 10m

10m 10m

Note: Standoff 

distances indicated

are for conventional

construction without

computational

analysis

Fence, Earthen Berm, or Similar Barrier
45m = 148 ft

25m = 82 ft

10m = 33 f t

150mm = 6 in

Trash

Containers

Parking Roadways

Unobstructed Space

(150mm Height)

Primary Structures

Inhabited

Structures

Uninhabited

Building

10m 10m

10m 10m

Note: Standoff 

distances indicated

are for conventional

construction without

computational

analysis

Unobstructed Space It is assumed that aggressors will not

attempt to place bombs in areas around buildings where building occupants could visually detect an explosive device.

Therefore, the site plan should use an unobstructed space of 30

feet around the facility. Vegetation within this area should not

be greater than six inches in height. This does not completely

preclude the placement of site furnishings or plantings around

buildings. It only requires that any explosive devices placed in

that space would be obser vable by building occupants. 

Railroad Location Avoid sites for inhabited structures that are

close to railroads. Where railroads are in the vicinity of existing

buildings, standoff distances between the railroad and any

inhabited structure should be provided based on the standoff

distance and the explosive weight associated with the controlled

perimeter. Where those standoff distances are not available,

ensure that there are procedures in place to prohibit trains from

stopping in the vicinity of inhabited structures.

Building Layout

Parking Beneath Buildings When vehicles are allowed to park

under the building the blast load becomes an internal blast condition, and shock and gas loads need to be considered. T h e s e

loads are ve ry large and create a re verse loading condition for the

s t ru c t u re, thus increasing the amount of damage to the facility.

The first parking garage bombing at the World Trade Center

re m oved two levels of support for columns of that stru c t u re. T h e

columns then needed temporary support to stabilize them

against buckling. T h e re f o re, it is best to eliminate park i n g

beneath buildings. In some instances, real estate is limited and

this may make parking beneath the buildings unavo i d a b l e .

When this happens, the following measures must be incorporated into the design: provide access control to ensure that personnel and vehicle access is limited, and ensure that the floors

beneath inhabited areas will not be breached from an explosive

detonation in the parking area. 

Drive-up/Drop Off Locate the drive-up and drop-off zone away

from large glazed areas of the building. This will minimize the

potential for hazardous flying glass fragments in the event of an

explosion. For example, the lane may be located at an outside

corner of the building, or otherwise away from the main

entrance. The drive-up/drop-off point should be coordinated

with the building geometry to minimize the possibility that

explosive blast forces could be increased due to being trapped

or otherwise concentrated. For further discussion of this issue

refer to the DOD Security Engineering Manual.

Superstructure All structural elements within a facility are subject to the progressive collapse provisions. For all structures that

are over three stories in height, progressive collapse analysis is

required. This provision requires that columns perform at twice

the actual length to simulate missing lateral support when floor

beams are lost. Also, beam strength needs to be increased to

Figure 7. Standoff Distances and Building Separations – No Controlled Perimeter.

22 The AMPTIAC Quarterly, Volume 6, Number 4
carry the remaining structure should a column be lost. Either

of these conditions will force beams and columns into plastic

yielding, and will lead to instability of the overall structure.

Therefore, the beams and columns within the structure will

require additional strengthening in order to prevent progressive

collapse. Progressive collapse analysis is performed on loadbearing structures by removing a section of a wall, then analyzing the stability of the residual structure. During the progressive collapse analysis, plastic structural design limits are used in

lieu of normal elastic building design limits. These limits

include support rotations and ductility and are required for

each member in the structure. Also, structural accelerations

from falling debris and the catenary action of the members are

considered. Structural connections need to be evaluated, as

they will take on the characteristics of those used in seismic

detailing.

Building Location Activities with large visitor populations provide opportunities for potential aggressors to get near buildings

with minimal controls, and therefore limit opportunities for

visual detection. Therefore, separation distance between DOD

inhabited buildings and public spaces should be maximized.

Also, buildings should be a minimum of 150 feet from the

installation perimeter. This will provide sufficient space for the

placement of barriers, vegetation screens, lighted perimeters,

and standoffs against moderate sized explosive devices.

Asset Location To minimize the exposure of assets to direct

blast effects and the potential impacts from hazardous glass

fragments and other potential debris, locate critical assets and

mission critical or high-risk personnel away from the building

exterior. Such offices could be placed within interior spaces of

the building and separated from the facility exterior by noncritical spaces such as storage rooms, hallways, utility rooms,

and low use areas. If personnel are placed within an interior

room an interior courtyard could be used to bring natural light

into those office spaces.

E l e c t rical and Mechanical Equipment Equipment located outside can be a security problem. Should a public use area be

close to a critical facility, this equipment could be used to

shield the location of an explosive device. T h e re f o re, the 

p re f e r red location for exterior electrical and mechanical equipment is outside the unobstructed space, or on the ro o f. All

mechanical air intake louvers should be placed on the roof or

at least 10-feet above the ground level. Howe ve r, equipment

such as: transformers, air-cooled condensers, and packaged

chillers, could be placed within the unobstructed space as long

the equipment does not provide the aggressor an opport u n i t y

to conceal explosive devices. If this equipment is placed 

within the unobstructed space, they should be placed in an

equipment enclosure .

Equipment Enclosures If walls or other screening devices with

more than two sides are placed around electrical or mechanical

equipment within the unobstructed space, the equipment is to

be enclosed on all four sides and the top. Openings in the

screening material, and gaps between the ground and the bottom of the screens or walls making up an enclosure are not to

be greater than six-inches. Openings within the enclosure are to

be properly secured to prevent unauthorized access into the

enclosed space.

SUMMARY

This article should provide the reader with a background into

some of the procedures that are used in the security-engineering field. Many of those procedures deal with blast loadings

from explosive events, since blast effects can be devastating to

structures as well as personnel. Also, by considering the blast

event, we can provide a more robust structure that can be used

as an opportunity to defeat other types of threats against the

facility and personnel. 

The main goal of the DOD standards, as summarized in

these pages, is personnel protection by incorporating smart

protective measures into a facility during the engineering and

design process. Many of the minimum measures are low-cost as

we trade-off the value of hardening versus site considerations.

When dealing with standard construction, the lowest cost

alternative is to use more standoff distance. When standoff distance is not available, then the structure must be hardened to

provide the same level of protection. Another key to the process

is the understanding and appropriate use of controlled perimeters and zones. These zones not only provide standoff, but work

as access control perimeters for entry into a controlled space

around the facility.

The key to the security engineering process is to define a

threat in terms of an aggressor, weapons, tools, and explosive,

and then define the appropriate level of protection. Once the

threat and level of protection are defined, the protective measures can be selected through the systematic security engineering

process. Then the facility will have a known baseline level of

protection that can be counted on should the threat level

increase.

GENERAL REFERENCES

Department of Defense, Interim Antiterrorism / Force Protection

Construction Standards, December 16, 1999 (hereby cancelled)

Department of Defense, UFC 4-010-01, DOD Minimum

Antiterrorism Standards for Buildings, July 2002

De p a rtment of Defense, In s t ruction 2000.16, D O D

Antiterrorism Standards, June 14, 2001

Department of the Army, and the Air Force, TM 5-853-1,

AFMAN 32-1071 Vol. 1, Security Engineering Pro j e c t

Development, May 1994

Department of the Army, and the Air Force, TM 5-853-2,

AFMAN 32-1071 Vol. 2 Security Engineering Concept Design,

May 1994

Department of the Army, and the Air Force, TM 5-853-3,

AFMAN 32-1071 Vol. 3 Security Engineering Final Design,

May 1994

Department of the Army, TM 5-853-4, Security Engineering

Electronic Security Systems, May 1994

The AMPTIAC Quarterly, Volume 6, Number 4 23
24 The AMPTIAC Quarterly, Volume 6, Number 4

Patrick Lindsey is the Chief of Hardened Structures Section for the USACE Protective Design Center. This group

performs design and analysis for the Army and other DOD agencies, in the areas of conventional and nuclear

weapons ef fects, chemical/biological/radiological effects, as well as explosive safety design. Much of this

technology is directly applicable to the antiterrorism criteria the Protective Design Center is assembling for

DOD.

Department of the Army, the Navy, and the Air Force: TM 5-

1300, P-397, and AFR 88-22, Structures to Resist the Effects of

Accidental Explosions, November 1990

De p a rtment of the Na v y, MIL-HDBK-1013/1A, De s i g n

Guidelines for Physical Security of Facilities, October 1987

Department of Defense, UFC 3-340-01 (TM 5-855-1), Design

and Analysis of Hardened Structures to Conventional Weapons

Effects (DAHS-CWE), June 2002

Yes, there is absolutely a difference. While both entities serve the greater security interests

of the nation, they are two distinct missions, separated by policy and constitutional limits of

power. The White House defines them as follows:

The distinction is important; defining the separation of civilian and military authority. This is a

result of the Posse Comitatus Act, which specifically limits the use of the military in domestic law

enforcement activities.

By virtue of their constitutional charge, the military’s primary mission is Homeland Defense. In

certain cases, the military may provide direct support to Homeland Security efforts, but in all

such cases, the military units involved report to a civilian lead agency.

Homeland Security is the prevention, preemption, deterrence of, and defense against

aggression targeted at US territory, sovereignty, domestic population, and infrastructure,

as well as the management of consequences of such aggression and other domestic

emergencies. Homeland Security is the responsibility of the civil authorities at the local,

state, and federal levels.

Homeland Defense is the protection of US territory, domestic population, and critical

infrastructure against military attacks emanating from outside the United States. Homeland

Defense is primarily the responsibility of the military (and the various intelligence agencies

as well).

Homeland Security vs. Homeland Defense...

Is there a difference?
Robert J. Odello

Director, Waterfront Structures Division

Naval Facilities Engineering Service Center

Port Hueneme, CA

INTRODUCTION

This article describes Navy efforts to apply composite materials

to pier decking and support columns for the purpose of repairing deteriorating installations and strengthening structures not

designed for current load requirements. The successes of this

program have laid the groundwork for a better understanding

of how composite retrofits work in real-world, reinforced concrete structures serving in harsh environments. These retrofits

have many similarities to some of the solutions proposed to

retrofit buildings to make them more blast resistant. The

approaches, if implemented, will increase load carrying capacity of floor sections, can enable sections designed only for 

gravity loading to withstand negative (upward) loads, and will

reinforce support columns for higher strength and greater

resistance to progressive collapse. Lessons learned in these Navy

projects will help further advance the protection and hardening

of land-based structures.

BACKGROUND

The Navy has many waterfront facilities that are already old

and continuing to degrade as they remain in use. Many of these

facilities are mission critical piers and wharfs that were built

during or soon after World War II. The replacement rate for

these structures has been slow, with the average age continuing

to increase. The cost of current deficiencies is approaching $1B

for piers and wharfs. 

The two primary reasons for these structural deficiencies are

deterioration and mission changes. In some installations saltwater has migrated through cracks or permeated the concrete 

to initiate corrosion of the steel reinforcing bars. As the reinforcing bars corrode, they expand and cause cracking of the

concrete, thus leading to more saltwater intrusion. There is also

speculation that global warming is leading to higher tide levels

and raising the level of the splash zone to further aggravate the

problem. In more recent structures, there is also evidence of

chemically-induced deterioration of the concrete due to curing

processes or aggregate composition. Changes in mission and

operating practices also lead to deficiencies in structural 

capacity of piers. 

In the past, the Navy designed and built piers with railmounted cranes which typically had large beams under the rails

to take the loads. Today, the Navy prefers truck-mounted

mobile cranes. These allow more flexibility in operations, since

they can set-up anywhere on the deck. However, not all areas of

the decks are able to sustain the outrigger loads from such

cranes. These loads are increasing, because more ship maintenance and repair operations are being conducted pier-side

rather than in shipyards.

Conventional methods to reduce deficiencies are costly and

disruptive to operations. Construction of new piers requires

budget approval and subsequent funding. Approvals may take

many years, and actual construction can prevent operations at

the site of the project and at adjacent berths. Conventional

repair practices tend toward brute force methods. A typical

approach is to simply increase the thickness of the deck.

However, the increased mass could lead to seismic problems.

Further, if the corrosion products are not carefully removed and

the areas sealed, the corrosion will continue. This situation has

led to the search for new materials or technologies that the

Navy could use to strengthen and repair these structures.

TECHNOLOGY DEVELOPMENT

The Naval Facilities Engineering Service Center (NFESC),

under sponsorship by the Office of Naval Research began a

project in the early 1990’s to explore the use of composite

materials for repairing or strengthening waterfront structures.

During that time the Navy teamed with the Army Corps of

Engineers and what is now known as the Market Development

Alliance (MDA) of the FRP (Fiber Re i n f o rced Po l y m e r )

Composites In d u s t ry on a project for the Constru c t i o n

Productivity Advancement Research (CPAR) Program. The

program involved testing of fender piles fabricated from FRP

materials. The Navy uses fender piles* along the edges of piers

to protect ships from impacts with the pier or wharf structure.

Some of the piles were completely FRP, while others used an

FRP casing around a concrete core [1][2]. This second type

showed very good stiffness and strength properties under bending loads. The analogy to column wrapping for seismic

upgrades was obvious.

NFESC fabricated a test site in Port Hueneme, CA to evaluate other FRP technologies in a controlled waterfront environment (Figure 1). The Army Corps of Engineers CPAR Program

contributed funding and member companies of the

Composites Institute of the Society of the Plastics Industry

The AMPTIAC Quarterly, Volume 6, Number 4 25
(forerunner of the MDA) contributed fabricated materials for

the test site. Known as the Advanced Waterfront Technology

Test Site (AWTTS), this structure has ten 10-foot test spans

available for a variety of structural and materials specimens and

two 20-foot spans holding an all-composite deck and a concrete deck with carbon fiber reinforced pre-stressing strands

[3]. The South Dakota School of Mining and Technology 

contributed the pre-stressed concrete panel under a related

CPAR project. The shorter spans simulate typical Navy piers 

at approximately one-half scale. Engineers, scientists and 

construction contractors have used the test site to evaluate the

constructability and performance of concepts before taking

them to an operational Navy application.

Numerical analyses, laboratory tests and tests at the AWTTS

helped to validate the concepts for pier strengthening and

repair. Small-scale beam tests showed that unidirectional carbon fibers bonded to the bottom (tensile stress) side of beams

increased flexural strength and fibers bonded to the sides of the

beams increased shear strength [4]. Adding both flexural and

shear strengthening resulted in better load behavior with enhanced ductility and energy absorption.

Tests on small, under-reinforced, two-way concrete slabs

showed that multiple layers of orthogonal carbon fiber sheets

could increase both the flexural strength and punching shear

resistance [5]. The increase in punching shear stre n g t h

appeared to be consistent with the European code design

guidelines. One-fifth scale laboratory tests and one-half scale

tests at the AWTTS further demonstrated the increases in flexural strength, ductility and punching shear resistance with 

carbon fiber reinforcement bonded to the tension face [6]. The

authors concluded that the increase in punching shear was

attributable to the additional lateral constraint provided by the

carbon fiber sheets. 

Engineers also investigated the durability of the repair technique. A major concern was the durability of bonded carbon

fiber strengthening on the topside of pier decks. On protruding or cantilevered sections of decks, or on continuous decks

over pile bents*, the tension reinforcement must be on or near

the top surface. Without proper protection, the carbon fiber

would be damaged by vehicular traffic on the deck. The

strengthening technique for the topside involved cutting a

groove in the concrete surface, placing an epoxy adhesive in the

groove, and embedding a preformed carbon fiber reinforced

polymer rod in the groove (Figure 2). Laboratory tests demonstrated the strength and durability of strengthened members

that depended on the bond between the epoxy, the rod and the

concrete [7].

A similar series of tests also demonstrated the durability

and strength of slabs with carbon fiber sheets bonded to conc rete. Fu rther tests evaluated the bond strength of adhesive s

to concrete under various moisture and temperature conditions [8]. These tests helped to establish the re q u i rements for

a d h e s i ve pro p e rties and surface preparation methods that

would insure good load transfer between fiber sheets and the

c o n c rete substrate.

DEMONSTRATION PROJECTS

The technology development phase removed many of the hurdles to implementing this technology into Navy shore facility

applications. The efforts validated previously postulated design

methodologies, and identified critical areas in the construction

or installation process. The results provided sufficient data to

take the program to the field.

The demonstration projects that follow provided Navy field

activities with the data necessary to specify the use of FRP

materials for repair and upgrade of Navy piers. Although they

were demonstration projects, they all corrected real structural

deficiencies on operational Navy piers. In all cases, the activity

shared costs with the technology demonstration project. 

Typically the work was performed via design-build contracts

which allowed the selection of contractors on the basis of best

qualifications and best value. Except for the first project,

Government specifications we re more perf o r m a n c e - b a s e d

rather than proscriptive. The reinforcement was specified in

force per unit length rather than calling for a specific number

of carbon fiber layers and a given adhesive material. Bidders

Figure 1. Advanced Waterfront Technology Test Site.

Figure 2. Placing Preformed Carbon Fiber

Reinforced Polymer Rods Near the Top Sur face.

26 The AMPTIAC Quarterly, Volume 6, Number 4
had access to the test and development information developed

by the Navy, but they were free to design their own retrofits.

On successive projects, the bidders became more knowledgeable and more numerous. This led to more competition and

lower unit cost for the technology. The engineering field divisions also became more knowledgeable in writing contracts for

the work.

Norfolk Pier 11

The first of the three demonstration projects to apply external

reinforcement to upgrade the strength of existing Navy piers

was completed in December 1996. The project was executed

on a deck span of Pier 11 at Naval Station Norfolk [9]. The

project consisted of a load and condition assessment of the

existing deck slab, the design of a graphite reinforced epoxy

laminate composite overlay for the underside of the deck,

preparation of the concrete surface, installation of the upgrade

overlay, installation of monitoring sensors, and a load assessment of the upgraded deck slab. Contractors completed the

entire project while the pier continued in service.

Pier 11 was designed for 70-ton truck-mounted cranes and

limited use by 90-ton cranes. An engineering study identified

deck slabs in the portable crane operating lanes in the 22-ft

spans to have shortfalls that limited 70-ton crane service. The

goal of the upgrade was to reinforce two crane operating lanes

between bents 50 and 51 so that restrictions on 70-ton crane

service would be removed.

Proof load tests verified the upgrade reinforcement to be

integral with the deck. As a result, there was no need to place

restrictions on operating 70 or 90 ton cranes on the upgraded

span. The laminate overlay had little effect on the stiffness of

the uncracked deck slab. However, in the damaged areas the

retrofits increased the service load stiffness by as much as 5%,

increased the strength by 10% while restricting crack growth,

and added protection from salt water corrosion for the reinforcing steel. The upgrade is expected to have a service life of

a p p roximately 20 years. The project demonstrated that

graphite/epoxy laminate overlays can be used to extend the useful life of existing piers at substantial savings compared to deck

replacement. 

NFESC is continuing to conduct intermittent tests and evaluations of the upgrade. Health and load monitoring sensors are

in place and functioning under the deck for future tests.

San Diego Pier 12

This project strengthened Pier 12 at the Naval Station San

Diego to meet demands of operational changes accompanied

by higher vertical loads [10]. It is a cast-in-place, reinforced

concrete structure 1,458 feet (444 meters) long and 30 feet (9.1

meters) wide. Pier 12 was one of several piers constructed in

1946 to berth the mothball fleet stationed in San Diego after

World War II. It is currently used for berthing large but relatively shallow draft ships such as amphibious ships and landing

craft (Figure 3). Deck operations were limited to 30-ton truck

mounted cranes that could operate only in limited areas. 

The project included concrete repair, surface preparation,

and strength upgrades for 14 spans. The specific project tasks

included:

1.Repaired deteriorated concrete of the deck and replaced 

corroded reinforcing steel.

2. Sealed existing cracks in the deck with polyurethane.

3. Embedded high strength carbon composite reinforcing rods

in the top surface of the deck.

4.Bonded wet lay up, high strength carbon laminate to the 

bottom surface of the 24-inch thick deck section.

5.Bonded pultruded, high strength carbon composite strips to

Figure 3. Pier 12 at San Diego.

Figure 4. Cross Sections of the Reinforced San Diego Pier 12

at the Pilecap* and at Midspan Between Pilecaps.

Pilecap

Midspan

Carbon/Epoxy Laminate

Reinforcement Upgrade

(Both Sides)

Utility

Loop

Utility

Loop

10’

Carbon/Epoxy Laminate

Reinforcement Upgrade

(Both Sides)

5’6” 1’0”

12” I-Sections

13” Wide Strips

4’6”

The AMPTIAC Quarterly, Volume 6, Number 4 27
the bottom surface of the 8-inch

deck section.

6 .Bonded pultruded, fiberglass

composite I-beams to the bottom

s u rface of the 8-inch deck section

and anchored ends to pile caps,

utility loops (as seen in Fi g u re 4),

and bollard platforms.*

7 .Installed pre-formed fiberglass

cylindrical shells around batter

piles* and filled gaps with

s h r i n k - resistant gro u t .

Contractors installed these upgrades at each berthing of Pier 12

( Fi g u re 4). The upgrade methodology allowed pier operations to continue without interruptions. Wi t h

these upgrades the deck is suitable

for 50-ton mobile truck crane operations with 100,000 pounds (450

k i l o n ewtons) maximum outrigger

loads. T h e re would be no re s t r i ctions on the locations for the crane

outriggers. The deck is also capable

of supporting a uniform load up to

750 pounds per square foot (36

kilopascals). (For comparison, the floor in a typical commercial building is rated at a uniform loading of about 150 psf. )

Proof tests after completion of the project demonstrated the

upgraded areas could support these new loads at stress levels in

the re i n f o rcement that remained well within service limits. 

Pearl Harbor Bravo 25

Bravo 25 at Naval Station Pearl Harbor is a cast-in-place, reinforced concrete deck and superstructure supported by precast

concrete piles and is 550 feet (168 meters) long and 37 feet (11

meters) wide. The Bravo wharves are more than 50 years old.

They were originally designed to support 50-ton (45 metric

ton), rail mounted, portal cranes and train cars, as well as a distributed load of 900 pounds per square foot (43 kilopascals). In

recent operations, truck-mounted, mobile cranes have replaced

track-mounted cranes on the Bravo wharves. Mobile crane load

limitations placed on Bravo wharves due to degradation were

very restrictive. They limited crane outrigger loads to the track

slabs and the rail girders. Other areas were restricted to truck

and forklift wheel loads. Maximum uniform live load was limited to 490 pounds per square foot (23 kilopascals).

The objective of this project was to rehabilitate the concrete,

protect existing reinforcement from corrosion, and increase the

load capacity of the areas at each end of the Bravo 25 berthing

[11]. This upgrade provided platforms with the ability to 

support mobile crane outrigger loads up to 125,000 pounds

(560 kilonewtons) and a uniform load up to 750 pounds per

square foot (35 kilopascals). To accomplish this, unsound concrete was removed and replaced, an impressed-current cathodic protection system was installed to protect the existing steel

reinforcement, and carbon/epoxy composite reinforcement was

added to the top and bottom surfaces of the deck and track

slabs (Figure 5). The upgrade was completed with minimal

interruptions to normal pier operations. 

APPLICATION TO THE STRUCTURAL 

PROTECTION COMMUNITY

The applications of composite materials described in this article deal with strength upgrades for primarily static loads. The

objective was to extend the life of structures with a minimal

cost and disruption of activities on the piers. The Navy is doing

follow-on work to consider the use of composite materials in

the construction of new piers. But the work, which is still in

progress, has indicated that the economics for employing composites in new construction are not as favorable as those for

retrofits. The development effort to date indicates that a modular floating double deck pier constructed of high volume fly

ash concrete with conventional post-tensioning strands and

stainless steel secondary reinforcement has the most promise of

providing a long life, low maintenance pier at a minimal

increase in initial cost. In this case, dynamic or blast resistant

design is not a major element.

Designers need to use caution when applying FRP technology to upgrades of slabs or panels for resistance to explosions.

Carbon fiber may not be a good choice because of its cost and

potential for a brittle failure. Also, the wet lay-up method presented here does not provide shear resistance around the

periphery of the slab or panel. This may be a critical design

parameter for some blast loading conditions. However, carbon

fibers bonded to the bottoms and sides of reinforced concrete

beams or girders could improve the overall strength of frame

structures and help in the prevention of progressive collapse.

Figure 5. Applying Carbon Fiber Sheets to Underside of the Deck.

28 The AMPTIAC Quarterly, Volume 6, Number 4
The process is analogous to providing external reinforcement

for bending members. Even in an office building, this upgrade

can be accomplished with minimal disruptions to operations. 

The use of pre-formed FRP shells around existing columns

may help to provide additional ductility under blast loads. This

was the technique used on batter piles in San Diego. In many

cases workers may need to gain access to a column by chipping

away the adjacent walls. The two-piece round cylinder can be

placed around any shape column and the workers fill the gap

with non-shrink grout. This effectively increases the size of the

column and provides confinement for additional strength and

ductility. However, like the slab strengthening, it does not help

transfer shear or moment to girders.

Another application of wet lay-up bonded carbon fibers

might be in providing upgrades to floor slabs that we re originally designed for gravity loads. T h reat situations in which the

blast loading could be coming from below the floor slab provide a unique situation, because the designer places the re i nf o rcement to resist dow n w a rd loads. Ty p i c a l l y, there is little

steel to resist negative (upw a rd) loadings. To resist this type of

loading, workers could bond carbon or other fiber sheets to

the floor surface and place a floor covering over them to protect the fibers. This invo l ves minimal disruption to the

s t rengthened are a .

All of these potential applications of FRP upgrades for blast

resistant design have proven very effective for upgrading piers

for new loadings. We have demonstrated and proven the technology in the re l a t i vely seve re marine enviro n m e n t .

Furthermore, by implementing the process through the people

who design and specify upgrades to docks and piers, the

methodology has transitioned to practical use. In addition to

producing more test data for reducing risks of applying the

same technology to blast design upgrades, we need to develop

a similar strategy for the implementation process. This will

insure the greatest number of qualified designers, suppliers and

contractors and will help reduce the costs.

REFERENCES

[1] D. Hoy, G.E. Warren, and D.A. Davis. Environmentally

Acceptable Piling for Use in Navy Pier Fender Systems.

Materials for the New Millennium, 4th ASCE Materials

Conference, Washington, DC, November (1996)

[2] D.E. Hoy. Plastics for Piles. The Military Engineer, Vol. 88,

No. 576, February-March (1996)

[3] G.E. Wa r ren, L.J. Ma l va r, C. Inaba and D. Hoy.

Rehabilitating the Navy’s Waterfront Infrastructure. Ports 95,

7th Conference on Port Engineering and Development for the

21st Century, Tampa, FL, March (1995)

[4] L.J. Malvar, G.E. Warren and C. Inaba. Rehabilitation of

Navy Pier Beams with Composite Sheets. Second FRP

International Symposium, No n - Metallic (FRP) Re i n f o rc ements for Concrete Structures, Ghent, Belgium, pp.533-540,

August (1995) 

[5] C.M. Inaba, G.E. Warren and L.J. Malvar. Rehabilitation of

Navy Pier Decks with Composite Sheets. First International

Conference on Composites in the Infrastructure, ICC 96,

Tucson, AZ, January (1996)

[6] L.J. Malvar, G.E. Warren and C.M. Inaba. Large Scale Tests

on Navy Reinforced Concrete Pier Decks Strengthened with

CFRP Sheets. Second International Conference on Advanced

Composite Materials for Bridges and Structures, ACMBS-2,

Montreal, Quebec, Canada, August (1996)

[7] G. Warren, D. Burke, S. Harwell, C. Inaba and D. Hoy. A

Limited Marine Durability Analysis of CFRP Adhered to

Concrete. Second International Conference on Concrete under

Severe Conditions, Environment and Loading, CONSEC ’98,

Tromsø, Norway, June (1998)

[8] N.R. Joshi. “Effect of Moisture and Temperature of Cement

Mortar Surfaces on Quality of Adhesive Bond.” NFESC

Contract Report CR-98.18-SHR, September (1998)

[9] G.E. Warren. Demonstration Program for Waterfront

Structures Repair and Upgrade: Site No. 1 Pier 11 NAVSTA

Norfolk. Site Specific Report SSR-2295-SHR, Naval Facilities

Engineering Se rvice Center, Po rt Hueneme, CA, Ja n u a ry

(1997)

[10] G.E. Warren. Waterfront Repair and Upgrade, Advanced

Technology Demonstration Site No. 2: Pier 12 San Diego. Site

Specific Report SSR-2419-SHR, Naval Facilities Engineering

Service Center, Port Hueneme, CA, November (1998)

[11] G.E. Warren. Pier Upgrade – Demonstration Site No. 3 –

Bravo 25, Naval Station, Pearl Harbor, Hawaii. Site Specific

Report SSR-2567-SHR, Naval Facilities Engineering Service

Center, Port Hueneme, CA, July (2000)

ENDNOTE

* The following description of terms used in the construction

of piers might be helpful to the reader. Piles are usually timber

or reinforced concrete poles driven into the ground. Groups 

of piles (bents) are typically capped, and a flat deck is built

across the pile bents. Batter piles are driven diagonally to help

stabilize the structure from side loads. Fender piles line the

edges of the pier to help protect both the pier and docked 

vessels from damage. Bollards (bulbous posts usually made of

steel and concrete on Navy piers) and cleats (horizontal bars

supported in the middle) are attached along the edge of the pier

to tie off vessels at rest.

Robert J. Odello has been with the Naval Facilities Engineering Service Center since its inception in 1993 and

with its forerunner, the Naval Civil Engineering Laboratory since, 1968. He holds a B.S. in Civil Engineering

and M.S. in Structural Engineering from the University of California, Berkeley. His technical work has involved

concrete structures, ground shock and structural response from explosions and facility specialized inspection 

systems. He has been a program manager and technical supervisor since 1980. He is a registered Civil

Engineer in California.

The AMPTIAC Quarterly, Volume 6, Number 4 29
30 The AMPTIAC Quarterly, Volume 6, Number 4

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n a m i s . a l i o n s c i e n c e . c o m
INTRODUCTION

C o n ventional building components are highly vulnerable to

t e r rorist vehicle bomb attack. Common annealed glass wind ows break at ve ry low blast pre s s u res and the resulting flying

glass fragments are a major cause of injuries in many bombing incidents (Fi g u re 1). Ma s o n ry in-fill walls are also we a k

elements and another source of hazardous debris (Fi g u re 2). 

T h rough the combined re s e a rch and development efforts of

the Army Corps of Engineers, the Defense T h reat Re d u c t i o n

A g e n c y, the Technical Su p p o rt Wo rking Gro u p, the Air Fo rc e

Re s e a rch Laboratory, and the Bu reau of Diplomatic Se c u r i t y

of the State De p a rtment, significant advances have been made

since 1996 in improving methods for protection of conve ntional military and government facilities. Unique and innovat i ve methods for re t rofitting windows and walls have been

d e veloped that increase the blast capacity of these vulnerable

components five- to ten-fold resulting in decreased standoff

re q u i rements and improved protection for personnel. 

RETROFIT MEASURES

Fabric Coverings

Among the earliest of the innovative techniques for wall retrofit was the use of anchored high strength fabrics to catch wall

debris. The fabrics used are typically woven polypropylene 

similar to those used for sandbags and often generally referred

to as “geotextiles.” This technique does not entail increasing the

strength of the wall itself (as was the typical approach taken

previously) but is based on catching the wall debris to prevent

it from entering the building and posing a hazard to the 

occupants. This technique was developed and validated with

full-scale tests in 1998, then transitioned to the Corps of

Engineers’ Protective Design Center for incorporation into

design guidance. As later shown, anchored geotextile fabric was

one of the components used to retrofit the exterior walls in the

original Pentagon Renovation Project. 

Fi g u re 3 shows a full-scale five - s t o ry re i n f o rced concre t e

frame stru c t u re with infill masonry walls constructed to 

Figure 3. Pre- and Post-test Photos of Test Structure.

David Coltharp

and

Robert L. Hall

Geotechnical and Structures Laboratory

US Army Corps of Engineers

Engineer Research and Development Center 

(formerly Waterways Experiment Station)

Vicksburg, MS 

Figure 1. High-speed Photos Depicting

Glass Fragment Hazard.

Figure 2. High-speed Photo Showing

Masonry Wall Debris Hazard.

1CW 1CW

The AMPTIAC Quarterly, Volume 6, Number 4 31
e valuate the effectiveness of various re t rofitted infill

wall types designed to protect building occupants

f rom blast loading from a simulated vehicle bomb detonation near the building. Included in the eva l u a t i o n

we re several geotextile, aramid, and E-glass fabrics. 

Figure 4 shows pre- and post-test photos of the

interior of the sample wall labeled 1CW in Figure 3.

The wall consisted of an 8 in.-thick hollow concrete

masonry unit (CMU) infill wall with no windows.

This wall was retrofitted by anchoring a geotextile to

the floor and ceiling on the inside of the wall. The

geotextile performed as expected, preventing wall

debris from entering the room.

Fabric Coverings with Windows

The geotextile retrofit proved to be a very practical

and successful retrofit when applied to solid walls, so

the concept was adapted to be applied to infill walls

with window openings. Figure 5 shows an interior

view of a 20' x 10' (nominal) infill masonry wall constructed using two wythes of clay bricks, and containing two “punch” windows. (Two wythes of brick refer

to two vertical, parallel planes of stacked brick often

separated by an air gap or some sort of fill.) The wall

was retrofitted by applying a geotextile material, glued

to the interior of the wall using a contact adhesive,

and anchored at the floor and ceiling using concrete

anchors. Gypsum board was glued to the geotextilecovered wall to achieve a finished interior wall surface.

Each of the windows was retrofitted differently.

Window 1 (Figure 5 on left, viewed from inside) was

retrofitted by constructing a steel frame that attached

Figure 4. Pre- and Post-test Photos of Anchored Geotextile.

Figure 5. An Infill Masonry Wall

Retrofitted with Geotextile.

Figure 6. Pre- and Post-test Photos of Interior View of Laminated Glass

Window in Steel Frame, Anchored Around Perimeter to Geotextile.

Figure 7. Pre- and Post-test Photos of Interior View of 3/4”

Polycarbonate Window, Secured Using Steel Straps, Anchored 

at Floor and Ceiling Using 3” x 1/4” Steel Straps.

32 The AMPTIAC Quarterly, Volume 6, Number 4
to the geofabric around the perimeter of the frame, and provided sufficient bite to hold a 1" thick laminated glass window

when exposed to the blast pressures. The frame successfully

held the glazing, and became detached from the geotextile very

late in the blast response, preventing any debris or blast pressures from entering the room. The gypsum board became

detached from the geotextile during the large deformation

response of the wall, but with very low velocity, thus not presenting a hazard to occupants. The geotextile remained completely attached at the floor and ceiling, preventing any wall

debris from entering the room. Figure 6 shows a pre-test and

post-test photo of this window/wall retrofit.

The window 2 retrofit (on right as viewed from inside) consisted of a steel frame containing a 3/4" polycarbonate glazing,

anchored to the floor and ceiling using 3" x 1/4" steel straps on

each side of the frame. Figure 7 shows a pre- and post-test

photo of this window retrofit. The window remained securely

in the frame, and the straps remained securely attached to the

floor and ceiling, but allowed the window system to deflect into

the room approximately 42". 

Muntin Window System

Another innovative window retrofit concept involves the installation of a blast-resistant glazing in a rigid steel frame that

incorporates a structural steel muntin made from steel tubes.

This system is designed to transfer the load from the glazing to

the structural muntin and frame, which absorbs the blast energy and effectively reduces the span of the glazing and prevents

the glazing from pulling out of the frame bite. This concept was

successfully tested with a 5' x 7' window opening (Figure 8).

Sheet Steel Wall Retrofit System

Some wall retrofit systems have used sheet steel anchored to the

floor and ceiling to prevent exterior walls from blowing into

rooms. Sheet steel offers advantages of high strength to weight

ratio, ductile performance, ease of fabrication, and familiarity

to construction personnel.

Sheet steel was used as a wall retrofit during the experiment

as shown in Figure 9. The exterior wall was two wythes of

masonry with 4' x 6' (nominal) punch windows. The retrofit

consisted of a custom made commercial product using 20

gauge steel sheets glued to 1/4" gypsum board. The gypsum

board gave the wall a finished appearance. Six-inch legs were

Figure 8. Pre- and Post-test Photos 

of the Structural Muntin F rame System

Installed as a Retrofit.

Figure 9. Pre-test Photos of the Sheet Steel Wall Retrofit.

Figure 10. Post-test Photos of the of the Sheet Steel Wall Retrofit.

The AMPTIAC Quarterly, Volume 6, Number 4 33
bent on the top and bottom of the

steel sheet. The sheet was then glued

to the masonry wall, and anchored

through the legs to the floor and ceiling. The windows consisted of a version of the muntin system described

e a r l i e r. Results of the experiment

(Figure 10) showed the retrofit performed as desired preventing debris

from entering the room. 

Another example of a steel sheet

retrofit for a severe blast environment is shown in Figure 11. The

exterior infill wall was one wythe of

CMU. The retrofit was designed for

a close-in detonation exposing the

wall to very large blast pressures and

consisted of 1/4" thick mild steel

sheets spanning from floor to ceiling,

and securely anchored to reinforced steel anchors that

were attached to the ceiling and floor slab using concrete anchors. One of the keys to the success of this

concept was detailed design of the concrete anchorage

system. 

Steel Stud Wall

Another retrofit concept involves the use of conventional steel studs to construct an interior wall inside

the existing wall. The studs are not attached in the

conventional manner at the top and bottom. Instead,

each stud is anchored to the concrete slabs at the top

and bottom using concrete anchors. Retrofit blast

resistant windows can be installed in a framed opening

in the steel stud wall. Figure 12 shows photos of a

retrofit steel stud wall prior to blast testing. Gypsum

board was installed to the interior surface of the steel

studs using adhesives and screws with bearing strips to

prevent the gypsum board from pulling over the screw

heads during blast loading.

Figure 13 shows the post-test photos of the steel

stud wall, especially the windows. The window s

remained intact, and the steel stud wall successfully

prevented the exterior wall and debris from blowing

into the room. 

Spray-on Elasto-Polymer Coating

The fabric, sheet steel, and steel stud re t rofits all re q u i re

high strength bolted connections to the floor slabs to be

e f f e c t i ve. A less labor intensive method is the use of a

spray-on elasto-polymer coating similar to that used in

the industrial coating industry and in spray-on tru c k

bedliners. The material is sprayed to the interior of the

wall and overlapped onto the floor and ceiling slabs by

a few inches to form a bond. Fi g u re 14 shows an

u n re t rofitted single wythe CMU wall (Wall 3A) and a

single wythe CMU wall with 1/4" thick elasto-polymer

applied to the interior of the wall (Wall 3B). Fi g u re 15

Figure 11. Pre- and Post-test Photos

of Sheet Steel Retrofit Experiment.

Figure 12. Pre-test Photos of Steel Stud Retrofit Walls Before and After

Installation of Interior Gypsum Board.

Figure 13. Post-test Photos of Steel Stud Retrofit Wall with Windows.

34 The AMPTIAC Quarterly, Volume 6, Number 4
s h ows photos of the inside of Wall 3B before and after the experiment. The control wall was breached. While the re t rofitted wall

was damaged significantly, no wall debris or blast entered the

room, thus the hazard was eliminated. 

Elasto-Polymer Wall Covering with Window

The success of the experiments using spray-on elastopolymer

applied to the interior surface of solid infill masonry led to

attempts to apply this retrofit technique to walls with windows.

Figure 16 shows a pre- and post-test photo of a reinforced concrete wall with a 40" x 40" window opening. This wall and

window were retrofitted by developing a steel frame with a 3/4"

polycarbonate sheet in a 3" bite. The steel frame also overlaps

the concrete 3" around the perimeter. Elasto-polymer was

applied to the entire wall and extended 6" over the steel frame,

but was not applied to the window. The retrofit performed 

successfully. The elasto-polymer remained securely attached to

the steel frame, but detached from the wall at least 24" in all

directions around the window as indicated in Figure 16. 

APPLICATION OF BLAST RETROFITS TO THE PENTAGON

At the time of the September 11 attack, the Pentagon was

undergoing a renovation that included retrofit measures to

increase the resistance of the structural envelope to terrorist

attack, particularly for blast effects. These retrofits (Figure 17)

included thermally tempered, laminated glass window s

designed for blast resistance supported by horizontal steel tubes

that framed into vertical tubes that ran from floor slab to floor

slab. In addition, a geotextile membrane was used over the interior surface of the masonry wall to prevent the masonry from

becoming a debris hazard during a blast event. 

The effectiveness of these re t rofits in mitigating blast damage

Figure 14. Pre- and Post-test Photos of Cubicle Three, the Right Half of Which Was Retrofitted with Spray-on

Elasto-polymer.

Figure 15. Pre- and Post-test Photos of Cubicle Three,

Wall 3B.

Figure 16. Pre- and Post-test Photos of the Interior of a Reinforced

Concrete Wall Containing a Window Retrofit Using Spray-on

Elasto-polymer to Catch the Window During Blast Loading.

Figure 17. Schematic of Pentagon Retrofit.

Typical Support Plate

Header Tube

Typical

Vertical Tube 

Sill Tube

Typical

Existing

Concrete

Column

Existing Brick

Infill Covered

w/Geotextile

Fabric

The AMPTIAC Quarterly, Volume 6, Number 4 35
and hazard to personnel is indicated in

Fi g u re 18 which compares the standoffs

re q u i red for pre venting high hazard conditions between the original exterior wall

design and the re t rofitted exterior wall design

for two generic vehicle bomb sizes. High performance computing simulations (Fi g u re 19)

f u rther indicate the effectiveness of the re t rofits under a seve re blast enviro n m e n t .

Fortunately, the section of the Pentagon

that was hit on September 11 was the first

and only section where the renovation had

been completed. Although the retrofits were

not designed for an airplane impact, their

presence was credited with saving lives. In

particular, many of the laminated windows

remained intact, even when appare n t l y

engulfed in the fireball of burning fuel; thus

preventing fire from entering offices on the

upper floors (Figure 20). In addition, it was

conjectured that the steel tubular supports

for the windows added to the resilience of

the building.

CONCLUSION

Conventional buildings come in a wide

variety of structural types, component

materials and construction details. No one

retrofit technique is generally applicable to

all conditions. As a result, engineers need a

“catalog” of cost-effective techniques and design methodologies

to apply and adapt to the particular situation. As discussed here

concerning the attack on the Pentagon, application of some of

these techniques has resulted in lives saved. Continued research

on blast retrofits is needed to provide additional solutions to

this problem with the ultimate goal of protecting building

occupants from the hazards associated with the blast-induced

failure of building components. 

Figure 19. Blast Response Simulation of Original and

Retrofitted Pentagon Wall.

Figure 20. Window Damage from September 11 Attack on the Pentagon. The

Aircraft Impact Area Was Approximately 135 ft. to the Right.

Figure 18. Comparison of Small Bomb Standoffs for

Original (red) and Retrofitted (yellow) Pentagon.

(Satellite Photo of the Pentagon Cour tesy and Copyright

GlobeXplorer, LLC and Its Content Partners.)

No Retrofit Retrofit Complete

36 The AMPTIAC Quarterly, Volume 6, Number 4
David R. Coltharp is a senior research associate with Mississippi State University on an Intergovernment

Personnel Assignment to the Geotechnical and Structures Laboratory (GSL) of the US Army Corps of

Engineers, Engineer Research and Development Center in Vicksburg, MS. He is currently serving as the

technical director for the Joint Antiterrorist/Force Protection research program. Previously he served as a

research physicist with the GSL executing major research programs dealing with protection of military and

government facilities from effects of terrorist weapons. Mr. Coltharp holds a B.S. and M.S. degree in

Physics from Mississippi State University and has published over 50 technical papers related to weapons

effects and blast response of structures.

Dr. Robert L. Hall is the Chief of the Geosciences and Structures Division, Geotechnical and Structures

Laboratory (GSL) of the US Army Corps of Engineers, Engineer Research and Development Center in

Vicksburg, MS. As such, he oversees research in numerous disciplines: antiterrorism/force protection; engineering geology and geophysics; geotechnical and earthquake engineering; structural mechanics; structural engineering; and survivability engineering. Currently, Dr. Hall is responsible for directing and developing analysis techniques for predicting the response and damage of structures to the effects of conventional weapons and terrorist attacks; most recently, chairing an after-action study on the 11 September

Pentagon event. Dr. Hall holds degrees in Civil Engineering from Auburn University (B.S.), Mississippi State

University (M.S.) and Oklahoma University (Ph.D.) and has more than 100 technical publications in various journals and refereed papers in proceedings, international conferences, and symposiums.

The AMPTIAC Quarterly, Volume 6, Number 4 37

answers materials engineering questions

C A L L : 3 1 5 - 3 3 9 - 7 1 1 3

E M A I L : a mp t i a c _ i n qu i ri e s @ a l i o n s c i e n c e . c o m

O R

V I S I T : ht tp : / / a mp t i a c . a l i o n s c i e n c e . c o m / H e l p / i n qu i r y. h t m l

AMPTIAC
132nd TMS Annual Meeting 

& Exhibition

03/02/03 - 03/06/03

San Diego, CA

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Warrendale, PA 15086 

Phone: (412) 776-9000 x 253

Fax: (412) 776-3770

Email: csc@tms.org

Web Link: cms.tms.org

NDIA Science & Technology

Conference/DOD Tech Exposition

03/04/03 - 03/06/03

Charleston, SC

Contact: Simone L. Baldwin

NDIA

2111 Wilson Blvd., Suite 400

Arlington, VA 22201 

Phone: (703) 247-2596

Fax: (703) 522-1885

Email: sbaldwin@ndia.org

Web Link: register.ndia.org/interview/ 

register.ndia?PID=Brochure&SID

National Hydrogen Association's 14th

Annual – U.S. Hydrogen Meeting 

and Hydrogen USA

03/04/03 - 03/06/03

Washington, DC

Contact: Lara Neer

National Hydrogen Association

1800 M St. NW, Suite 300

Washington, DC 20036-5802 

Phone: (202) 223-5547

Fax: (202) 223-5537

Email: nha@ttcorp.com

Web Link: www.HydrogenConference.org

Structural Integrity of New and Aging

Metallic Aircraft

03/17/03 - 03/21/03

Los Angeles, CA

UCLA Extension, Short Course Program

10995 Le Conte Avenue

Los Angeles, CA 90024-2883 

Phone: (310) 825-3344

Fax: (310) 206-2815

Web Link: www.unex.ucla.edu/shortcourses

AIChE 2003 Spring National Mtg.

Safety and Sustainability: Core Issues

Shaping Tomorrow

03/30/03 - 04/03/03

New Orleans, LA

Meetings Departments

American Institute of Chemical Engineers

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Phone: (212) 591-7338

Fax: (212) 591-8894

Email: meetmail@aiche.org

Web Link: www.aiche.org/spring

Fuel Cells 2003: Fuel Cells 

& Hydrogen Infrastructure. 

The 3rd Annual BCC Conference

03/31/03 - 04/01/03

Stamford, CT

Contact: Sharon Faus, Conf. Coordinator

Business Communications Company, Inc.

25 Van Zant Street

Norwalk, CT 06855-1781 

Phone: (203) 853-4266 x 304

Fax: (203) 853-0348

Email: conference@bccresearch.com

Web Link:

www.bccresearch.com/fuel_cells2003

MSS Specialty Group 

on Infrared Countermeasures

04/01/03 - 04/03/03

Laurel, MD

IRCM Program Committee

c/o Infrared Information Analysis (IRIA)

Ctr.

Veridian Systems Division, Inc

P.O. Box 134008

Ann Arbor, MI 48113-4008 

Phone: (734) 994-1200

Fax: (734) 994-5550

Email: mss@veridian.com

Web Link: www.iriacenter.org

Materials Research Society (MRS) 

Spring Meeting 

04/21/03 - 04/25/03 

San Francisco, CA 

MRS Member Services 

506 Keystone Drive

Warrendale, PA 15086-7573 

Phone: (724) 779-3003 

Fax: (724) 779-8313 

Web Link: www.mrs.org 

Window & Dome Tech. 

& Materials VIII

04/21/03 - 04/25/03

Orlando, FL

The Intl Society for Optical Engineering

P.O. Box 10

Bellingham, WA 98225 

Phone: (360) 676-3290

Fax: (360) 647-1445

Email: membership@spie.org

14th International Symp. 

Space TeraHertz

04/22/03 - 04/22/03

Tucson, AZ

DARPA

Web Link: www.darpa.mil/mto/terahertz/ 

thzmeeting.pdf

105th Annual Meeting & Exposition of

The American Ceramic Society

04/27/03 - 04/30/03

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P.O. Box 6136

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Hydrogen & Fuel Cells 2003 Conf. &

Trade Show

06/08/03 - 06/11/03

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Inc.

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National Space & Missile Materials

Symposium

06/23/03 - 06/27/03

San Diego, CA

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Ste. 509

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2003 Electronic Materials Conference

06/25/03 - 06/27/03

Salt Lake City, UT

TMS

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Mark Your Calendar

38 The AMPTIAC Quarterly, Volume 6, Number 4
M a t e r i a l 20

E A S E

AMPTIAC

MATERIALS FOR BLAST AND PENETRATION RESISTANCE

INTRODUCTION TO BLAST AND PENETRATION RESISTANT 

MATERIALS (BPRM)

While only one part of the entire spectrum of structural protection technologies, materials is certainly one of its cornerstones. The focus of this article is

on materials instrumental to providing protection against explosive blasts

and projectile or fragment penetration of critical structures.

Armors, or penetration resistant materials, are the largest classification of

BPRMs, but the term doesn’t do justice to what materials and materials 

systems are available for today’s protective shielding. Traditionally, when we

think of armor, heavy military tanks on a battlefield roll into our imagination. Armor connotes a thick layer, typically steel, employed as a shield from

projectiles fired from various weaponry. While such images accurately depict

traditional armor systems, they are severely dated and do not reflect the

advanced protective materials and systems available today. Protection against

blast and penetrating fragments is accomplished with a plethora of materials

and material combinations; sophisticated systems engineered to mitigate

equally sophisticated projectiles and explosives.

The demand for well-engineered structures has dictated drastic improvements in ductility, fracture toughness, corrosion resistance and machinability of constituent materials. This in turn has driven materials engineers to

conquer new problems. The threat of terrorist attack has heightened awareness of the need for better buildings. These improved structures will protect

occupants from the shock pressure of a blast, and the biggest dangers to personnel in a building: fragmenting structural materials, breaking glass, and

building collapse.

For buildings, weight plays some role, but cost is typically the driving

force. Another key consideration in structural protection of buildings is that

in most cases, blast and penetration protection schemes are installed as retrofits. Beyond the limitations of cost, the occupied volume of the installed

materials and its impact on building form, fit and function is also critical

and a major materials selection concern.

Barring building collapse, fragmenting wall structures and flying window glass would be the main cause of occupant casualties. Primary structural support in most buildings is provided by regularly spaced, reinforced concrete support columns, connecting rigid concrete and steel floor sections. The

interior and exterior walls are typically not load bearing and are usually

made of hollow concrete blocks, or metal or wood frames, covered by metal,

wood, or gypsum board panels. All of these materials will deform, displace,

and/or completely disintegrate when exposed to significant overpressures

associated with bomb blasts, posing the greatest threat to loss of life.

There is ongoing research to replace or cover many of these materials

with polymer, fabric, steel, or laminate sheeting that would maintain the 

aesthetic appearance of the building, while standing up to the shock pressure

and not fragmenting or containing fragments. Combinations of these materials with foam cores may even help to mitigate the shock loading and 

further protect occupants from blast overpressures. For existing buildings,

some researchers have proposed spray-on coatings that could achieve many

of these goals without drastic remodeling.

In the Defense community, recent routine exposure of military personnel

to operations in urban settings has raised the question of how to mitigate acts

of terrorism in close proximity. The issue becomes one of retrofitting existing

buildings quickly without serious degradation of mobility or performance.

This is especially critical, as most domestic American civilian and government buildings currently offer little in the way of protection from explosions.

As we discuss the materials herein, you will begin to see how they may be

incorporated into a facility for protection, based on the individual needs of

each structure. Those protection needs are dictated by the desired level of 

protection the building must provide to its occupants or its ability to function.

The three levels of enhanced protection described in Table 1 outline in broad

strokes what the needs of a building might be. These levels give a general view

of the danger occupants might face, but they also relate to what types of 

solutions would have to be employed to make them blast resistant. For

instance, the Level 1 building will have to employ expensive structural 

hardening measures to make up for its lack of standoff. The Level 2 building

is less likely to be targeted because of active security measures, but if it were

hit damage would be extensive.

M ATERIALS THAT MITIGATE SHOCK AND FRAG M E N TATION EFFECTS

Delving into the nature, mechanisms, and applications of blast and penetration-resistant materials, it is important to develop the necessary context to

The following MaterialEASE is an abridgement of an AMPTIAC report published in 2001. It describes materials and novel combinations of materials used for

blast and penetration resistance and describes their application to structural protection. The field is far too broad to provide a comprehensive treatment within

these pages, but this summary, in conjunction with the accompanying articles in this issue, present a thorough introduction to the materials and current DOD

activities.

We suggest anyone interested in the most complete look at materials and structures for blast mitigation to consider obtaining the State of the Art Review

(SOAR) this MaterialEASE is based on, “Blast and Penetration Resistant Materials” (AMPT-26), as well as a sister AMPTIAC SOAR focused on structures,

“Applications of Structural Materials for Protection from Explosions” (AMPT-21).

The AMPTIAC Quarterly, Volume 6, Number 4 39

Richard Lane, Benjamin Craig, 

and Wade Babcock

AMPTIAC, Rome, NY
M a t e r i a l E A S E

examine this topic. This MaterialEASE addresses five main classes of

materials that apply to the structural protection community. In general,

the materials get more expensive as you proceed through the classes, just

as the cost of protection increases with the level of safety. While most of

the materials presented were developed and studied for strictly military

purposes (for the defeat of battlefield shock pressure and projectiles like

metal fragments and bullets) research has recently been focused on

employing such materials for the mitigation of blast and shock effects in

buildings and other structures.

Geo-Materials

Concrete and soil may not typically be thought of as BPRMs, but they are

the two most widely used materials for protection from blast overpressures and fragments. Obviously they are also widely used in construction

and site planning. Earthen berms are often used as a mitigating barrier

around a facility’s perimeter to reduce access, deflect blast pressure, and

absorb bomb fragments. Concrete is the most widely used construction

material for blast resistance, mostly due to its availability and status as a

relatively inexpensive commodity. Concrete and soil provide mass and

fragment absorption at a very low price when compared to any other

material or material system.

Earthen barriers have been used in many applications for blast and

penetration resistance since soil or sand is readily available and abundant in most locations. The typical use of soil in most structural protection applications is to create berms around the perimeter of a facility.

Berms blend with the environment much more than a large wall or

fence, and provide both fragment absorption and blast deflection, as well

as helping to limit vehicle access. A number of commercial manufacturers produce lightweight fencing or wall structures which can be filled

with soil to construct earth walls. These structures are designed for ease

of installation, reinforcement of the soil, and decreasing the volume of

soil required for the wall.

Concrete is used extensively as a construction material. It ranks second to steel as a stand-alone material in its ability to withstand blast

overpressures, mostly due to its mass. The most important property of

concrete when designing impact resistant structures is compressive

strength. Spalling and fragmentation are however, problems that crop up

as concrete is exposed to blast or fragmentation effects. Fragmentation

may be reduced with fiber reinforcements, but can only be contained by

adding surface layers of additional materials. Internal reinforcements

can be added to increase strength or fracture toughness of the concrete.

Typical reinforcements include steel bars or wires, fiberglass, carbon, and

other polymer materials.

While concrete is one of the oldest and most common materials used

in construction, that does not mean it is a stagnant technology. Please

consult the article by Cargile et al in this issue for more information concerning advanced concretes.

Polymers and Glasses

Polymers are inexpensive materials that can be used to protect building

occupants from potentially dangerous, fractured or splintered walls and

shards of glass from shattered windows during an explosion. Simple

cloths or fabrics (e.g. nylon) can be applied to walls inside the structure

to capture or hinder debris from a fragmented wall. Recently, polymers

Table 1. Levels of Structural Protection.

Level 1

This building utilizes a small standoff perimeter and operational measures to keep unknown personnel away from the structure. The structure itself

may have only minimal hardening features such as laminated exterior windows. The occupants would have a reasonable chance for survival,

depending on their proximity to the blast, but there is a high probability that the facility could suffer severe damage and possibly collapse.

Level 2

This protected structure utilizes an adequate standoff, perimeter controls, some hardening features, and structural modifications to withstand

shock and negative loads from an assumed level of bomb blast. This building and its site provide the occupants a significant level of protection

and very good chance of survival. The building may not be able to continue its functioning without repair, but the damage will probably be

superficial or limited.

Level 3

This level of protection is typically only seen on military installations. The facility provides all the exterior security measures discussed above, but

also calls for a structure that is hardened to blast standards. This structure can take a direct blast of some specified size and not only protect its

occupants, but continue to serve its intended function.

40 The AMPTIAC Quarterly, Volume 6, Number 4
AMPTIAC A D VA N C E D M A T E R I A L S A N D P R O C E S S E S T E C H N O L O G Y

that can be sprayed onto a wide variety of surfaces have been shown to reduce

fragmentation from blast pressures.[1] An elastomeric polymer has been tested on an eight foot by eight foot concrete wall, which was sprayed inside and

out with the polymer and then subjected to 80+ psi blast pressures. The wall

experienced severe fracturing but remained in place with no fragmentation. A

follow-on activity identified additional polymers (e.g. polyurea) that may have

better qualities to decrease wall deflections. The testing continued to show

promising results with stand-off distances reduced over non-sprayed lightweight structures by as much as 50%. Furthermore, polymer foams can be

inserted inside walls to act as an energy absorber, thus reducing the severity of

a blast inside a structure. A further discussion of this technology is covered by

Porter, et al in this issue.

Typical plate glass windows are extremely dangerous to occupants because

they shatter when exposed to even a small overpressure, and the blast

pressure can then carry the shards into the building at high velocity.

Glass laminates or glass replacements, however, can be used to reduce or

prevent this from happening. Thin films of polycarbonate laminated on

glass, for example, will keep the shattered glass in one cohesive (though

shattered) piece. An alternative is thermally tempered glass (TTG),

which can protect against pressures up to about 40 psi.[2] TTG, also used

in automobile windows, fractures into rock-salt size pieces which are not

as dangerous to building occupants. In addition, thick polycarbonate

can be used in place of glass, since it will not shatter upon impact or

when exposed to a relatively high pressure. Advanced-technology transparent armor consisting of ceramic/polycarbonate laminates are also

available, but are prohibitively expensive for the majority of structural

protection applications.

Metals

Many metals make great BPRMs, and the most common include steels

(ferrous alloys), aluminum alloys and titanium. The purpose of metals

in structural protection is often two-fold: protection against fragments

and secondly, maintaining structural integrity. Metals are highly useful

in protecting structures against explosions because of their inherent

strength and toughness and energy absorption capability. Additionally,

metal poles, connectors, and plates can be used to reinforce masonry

structures from negative loads and contain fragments, as well as adding

structural support in the event of masonry failure. They are also useful

in designs due to their relatively low cost and flexibility in modifying

moduli and ductilities. The article by Coltharp in this issue provides an

in-depth look at various reinforcement mechanisms, including metals.

Ductility provides an indication of a material’s resistance to penetration of a projectile, such as a fragment, and its ability to absorb energy from a blast. A higher ductility allows greater deformation of the

metal thus permitting the penetrating object to proceed farther through

it. The converse is true for metals with low ductility where the object may

damage the face of the metal, but would not penetrate far. In addition,

the inherent strength and ductility of metals allows them to absorb blast

energy while possibly maintaining structural integrity.

Some metals have high impact strengths, which are indicators of

their toughness and resilience to fracture when hit by a projectile and also

their ability to sustain multiple hits. Conversely, other metals are unable to

survive these collisions, failing due to their low impact strengths.

Fracture toughness determines how resistant a metal is to crack propagation, which is an important factor when considering sustained loads. There is

a strong correlation of hardness to ballistic performance in metals. High hardness metals perform well against ballistic projectiles, but are more susceptible

to brittle fracture, and thus are poor structural materials. Lower hardness metals have good structural qualities, but are not as effective in resisting fragment

penetration.

Steel exhibits many of the properties that are important for protecting

against the effects of a blast, which is clearly important since steel is a common material in structures. The protection it offers against fragments is largeFigure 1. Hardness vs. Ballistic Per formance for Various Steels[3].

Figure 2. Resistance to Projectile Penetration for

Ti-6Al-4V and RHA[5].

High Hardness

Dual Hardness

Rolled Homogeneous

ARMOR HARDNESS

Cast

ARMOR THICKNESS

1: 7” - 12” (17.78 - 30.48 cm)

2: 2 1/4” - 3 1/4” (5.72 - 8.25 cm)

3: 1/4” - 1 1/4” (0.64 - 3.18 cm)

4: 9” - 12” (22.85 - 30.48 cm)

5: 2” - 4” (5.08 - 10.15 cm)

6: 1/4” - 1/2” (0.64 - 1.27 cm)

7: 1/8” - 1” (0.32 - 2.54 cm)

8: 1/4” - 5/8” (0.64 - 1.59 cm)

1

2

3

4

5

6

7

8

Titanium

RHA

PENETRATOR VELOCITY

The AMPTIAC Quarterly, Volume 6, Number 4 41
M a t e r i a l E A S E

ly attributed to its hardness. As described above however, there is typically a trade-off between hardness and structural integrity. Many existing

research programs have focused on improving the structural capability of

the steel by providing a higher hardness to resist projectiles. Other steel

research is focused on maximizing the hardness for the best protection

against fragments in non-structural applications. Figure 1 shows the correlation between hardness and ballistic performance

as well as the evolution of steel armors, 1 being the

oldest, up to 1990.

The only armor grade steel that is currently in use

for structural applications is rolled homogeneous

armor (RHA). Weight has been a crucial factor in having all other integral armor steels replaced by alternative, better-designed materials. Rolled homogeneous

armor has a density on the higher end of the metals

spectrum and a hardness on the lower end.[4] When

a ballistic projectile impacts RHA, it can be deformed

relatively easily because of its ductility.

Although steel in general is highly resistant to

penetration, it is quite dense; therefore, lighter metals

must be considered in applications where weight is a

factor. Titanium alloys have some advantageous properties (including good high temperature performance

and a significantly lower density than steel) but have

not been extensively used because of their high cost

and difficulties in machining and welding.

Since its development in the 1950’s, the Ti-6Al-4V

alloy has become the only titanium alloy in use for

armor applications (as defined in MIL-A-46077).

Compared to RHA, Ti-6Al-4V has similar hardness and

strength properties, but has outstanding mass efficiency resulting in a weight savings of about 25%.[3]

Moreover, Ti-6Al-4V has a high impact resistance and

fracture toughness, and is capable of sustaining 

multiple hits. It can however, be susceptible to stress

corrosion cracking (SCC). This particular alloy 

provides exceptional protection against ballistic 

fragments, while no other titanium alloys have 

performed better against ballistic projectiles. Ti-6Al-4V

performs almost as well as RHA in ballistic protection,

and the two are very comparable. Figure 2 is a comparison of the ballistic protection performance

between RHA and Ti-6Al-4V.

There are several aluminum alloys that are used

in blast mitigation and penetration resistance applications. Aluminum alloys have a significantly lower

density than steel, although they are only slightly less dense than titanium alloys. Although aluminum alloys typically have low hardness (making them less resistant than steel to ballistic projectiles), some have good

resistance to projectile puncture and fragments. Beyond weight advantages, some aluminum alloys are less susceptible to SCC and have good

machining and welding capabilities.

Figure 3. Ballistic Per formance Comparison of Steel, Titanium and Aluminum.

Figure 4. Cost-Weight Correlation of Ceramic Armor[6].

Titanium

Aluminum

THICKNESS

Steel

Projectile B

Weight/Sq. Ft.

B4C

SiC

Al2O3

Projectile A

B4C

SiC

Al2O3

42 The AMPTIAC Quarterly, Volume 6, Number 4
AMPTIAC A D VA N C E D M A T E R I A L S A N D P R O C E S S E S T E C H N O L O G Y

The selection of blast resistant materials for the protection of structures

requires an understanding of explosion effects and the way shock interacts with structures. This sidebar discusses shock characteristics and the

effects they have on structures.

The Explosion

An explosion is the rapid release of stored energy. This energy is

released in part as thermal radiation; the rest manifesting as shock

waves that are combinations of air blast and ground shock.

The air blast is the main damage mechanism. Air blast has a primary

effect, which is the ambient over-pressure or incident pressure, and a

secondary effect, which is the dynamic pressure or drag load. The first

effect is caused by the air blast (due to shock waves) that propagates

at supersonic velocity, and compresses air molecules in its path. As the

shock wave encounters a wall, it is reflected thus amplifying the overpressure, often by some significant factor greater than two. The air

blast enters the building through wall-openings and failed windows,

affecting floor slabs, partitions, and contents within the building. The

shock waves undergo diffraction as they interact with various surfaces,

thus increasing or decreasing in pressure. Eventually, the air blast subjects the entire building to over-pressure. The pressure decays exponentially in time and with radial distance from the epicenter and eventually becomes negative (negative loading phase), creating suction

forces.

Dynamic pressure or drag loading manifests as a high velocity wind

that propels debris generated by the blast. Another secondary effect

is the ground shock that produces motions similar to high-intensity, short

duration earthquakes. Figure 1 illustrates the various blast loads on a

building.

The following effects are characterized from a blast wave:

• Magnitude of the overpressure or the peak pressure during the overpressure phase of the blast wave.

• Impulse or duration of the overpressure. Impulse is the area under

the overpressure-time curve. Duration measures how long the overpressure phase of the blast wave lasts.

• Shape and rise-time of the overpressure pulse. A shock (or near-zero

rise-time) is usually the worst case. Well-engineered high-explosives will

typically have a very high shock value with close-to-zero rise-time,

which then decays rather rapidly. Figure 2 illustrates the parameters of

a typical blast wave.

Figure 2. Blast Wave Parameters.

Figure 1. Blast Loads on a Building.

Overpressure

Overpressure

Overpressure

Stand Off

Spherical

Shock Wave

Center of Burst

Ground Shock

Reflected

Pressure

Drag

Perimeter Protection 

(Fence - Guards - Barriers)

Overpressure Phase 

(away from explosive)

Suction Phase 

(negative pressure)

(toward explosive)

Po = Peak Overpressure

tp = Rise Time of Overpressure

ti’ = Overpressure Duration Used in Approximations

ti= Overpressure Duration or Length of Impulse

ts - ti = Length of Suction Phase

Red = Impulse (area under positive portion 

of pressure-time curve)

Blue = Negative Pressure

Po

tp ti’ ti ts

The AMPTIAC Quarterly, Volume 6, Number 4 43

EXPLOSION EFFECTS

Type of Curves Often Used in Approximations
M a t e r i a l E A S E

Comparison of Steel, Titanium and Aluminum

Steel has the greatest resistance to penetration of all of the metals considered, but at the expense of added weight to the application. Ti-6Al-4V

provides very good ballistic protection at a much lower density than steel,

and aluminum alloys are comparable to steel in penetration resistance,

but require a much greater thickness. Figure 3 shows a comparison of the

ballistic performance for typical alloy compositions of steel, titanium and

aluminum.

Polymer Matrix Composites

Polymer matrix composites (PMCs) are used for personal protection for

the defeat of small arms projectiles and as backplates, usually with

ceramics, against larger projectiles and blast fragments. PMCs combine

the beneficial properties of both polymer resins (ability to absorb and

mitigate kinetic energy) and high performance fibers (high to ultrahigh

elastic modulus). High performance composites possess higher specific

strengths (ultimate tensile strength divided by density) than their metal

counterparts. That is, they are capable of providing equivalent ballistic

protection at reduced areal weights. Polymer matrix composites utilized

for armor applications include fiberglass, aramid fiber, and polyethylene

fiber composites. 

S-2 Glass®fibers, developed by Owens-Corning Fiberglass

Corporation, have been widely used due to their lower cost. Kevlar®is a

man-made aramid fiber which was first introduced by the DuPont

Corporation in the early 1970’s. It is best known for its use in personal

body armor (bullet-proof vests). Kevlar has exceptional impact resistance

and small caliber ballistic resistance capabilities. Spectra®is a highly 

oriented polyethylene fiber originally developed by Allied Signal

Corporation.[3] Spectra is a tough, low density fiber with excellent

impact resistance and ultrahigh tensile strength. Spectra has been shown

to outperform equivalent composite armors made with Kevlar fiber

because of its high strength to weight ratio (Spectra has a density only

2/3 that of Kevlar).

Matrix resins used in conjunction with these fiber materials are usually thermosets. Thermosets are easier to process, have higher operating

temperatures, are more chemically resistant, and are significantly less

expensive than thermoplastics, but are more susceptible to cracking and

are toxic in their uncured state. Epoxy resins are generally used for the

best energy absorption properties while phenolic resins are used for fire,

smoke and toxicity resistance. Layered composite backplates utilizing

epoxy and phenolic materials are used in some cases to combine the 

beneficial properties of both resins. Such composite laminates are 

generally stitched together for multihit applications as delamination

problems may occur especially after low velocity impacts.

Many laminates and laminate systems can be expensive to apply in

structural protection. However, with judicious selection and design, these

materials may be applied in a very cost effective manner in select, 

critical areas where performance criteria demand them. The article by

Odello in this issue describes various composite structural modifications

in detail. Also, consult the article by Coltharp for a look at how laminates

perform in explosive events.

Ceramics

Ceramic armor materials are used for the containment of blast fragments and bullet penetrators. They were developed strictly for projectile

resistance with a high hardness and compressive strength causing most

Figure 5. How Ceramic/Composite Armors Work.

Impact and

Mitigation

Projectile impacts

ceramic faceplate,

partially shattering

and dispersing

fragment through

the ceramic into

the composite

backplate.

Ceramic is 

penetrated and

spalled locally.

Projectile

Approaching

Armor

Impact 

Imminent

Aftermath

Shockwave

propagates 

in a ‘conoid’,

reflecting off

the composite

backplate and

redistributing

the impact 

energy over a

wider area of

the ceramic.

Ceramic has

suffered only

local spalling,

some cracking

present in the

faceplate, 

but able to

withstand

another strike.

44 The AMPTIAC Quarterly, Volume 6, Number 4
penetrators to break up upon impact. The need for lighter protection materials for use in military aircraft brought about the use of ceramic armor materials. Ceramics offer an advantage over steel in weight reduction, and over all

metals in impact energy absorption. The densities of ceramics are typically

2.5 – 4 grams per cubic centimeter (g/cc), while steels are roughly 7.8 g/cc.

There are considerable differences between the way ceramics and metals

function when used for penetration resistance. Metals absorb the penetrator’s

kinetic energy through plastic deformation, while ceramics absorb the energy through fracture of the ceramic. Any protection scheme utilizing ceramics

must also employ backing plates of metal, polymer, or composite. Backing

plates are required to provide the structural support to the ceramic during the

impact event.

To improve upon the multihit capability of ceramics, ceramic tiles are

used to limit the fracture area. A thin covering over the ceramic tiles also helps

to keep fractured pieces in place providing some additional protection while

also preventing flying ceramic shards. Encapsulated ceramic armors have

been found to further increase protection as the fractured ceramic cannot 

easily move out of the projectile’s path. The penetrator must essentially 

pulverize the ceramic into powder which then moves around the path of the

projectile.

The most common ceramic materials used for armor applications are 

alumina (Al2O3), boron carbide (B4C), silicon carbide (SiC), and titanium

diboride (TiB2). Alumina (85% pure) is the most widely used due to its lower

cost, while B4C offers the best combination of performance and low weight.

Figure 4 shows the cost to areal weight correlation required for three of 

the ceramics to defeat two different projectiles (Projectile B is larger than

Projectile A). Titanium diboride is used to a lesser extent because of its higher

density as well as price.

Ceramics are used in conjunction with a backplate material, a metal 

or polymer matrix composite (PMC), which catch penetrator and ceramic

fragments after impact and absorb impact shock waves, as depicted in 

Figure 5.

EVOLUTION OF BPRM SCIENCE

In buildings where the threat of bomb blast or projectiles are greatest and

standoff is not available, variations of those materials with larger energy

absorbing capabilities will enable designers to lower overall shock overpressures transmitted through building walls, thus reducing fragments. In 

l e s s e r-threatened buildings where standoff is available and blast overpressure

is the main concern, combinations of concrete walls, steels, polymers, and

less sophisticated laminates can lessen shock and fragment propagation at

more reasonable costs. Engineers will continue to improve material 

properties, while at the same time improving their ability to control properties precisely. Processing enhancements will lead to lower costs in the 

long term, which could lead to greater adoption of sophisticated materials 

to mitigate threats.

Current work in BPRM seeks to further optimize the properties of 

combinations of materials. Laminate structures will take center-stage as the

protection systems of the future. They employ diverse materials arranged 

to make the most of breaking up incoming fragments, allowing them to

diverge, absorbing the energy of the fragments and eventually dissipating

that energy.

SUMMARY/CONCLUSIONS

Defending personnel and structures from the effects of explosions is one of the

most important aspects of military technology, and it is becoming all the more

important in the civilian world due to the increased threat of random terrorist

violence. Materials engineers will have to provide many of the solutions to

these problems, with full consideration given to issues such as weight, formability, cost and the ability of the BPRM solution to not intrude on the human

environment within the structure.

The appropriate selection of materials for specific applications is one of 

the most important roles that materials engineers and design professionals

perform. The field of materials engineering is an applied science, and a

highly qualitative one at that. More so than many of the other design and

engineering disciplines, the materials field is application-driven. That is,

engineers must develop an appreciation for the context of the problem before

offering a potential solution.

Integrating materials knowledge into the design process at the inception of

a project will foster superior solutions to complex blast and penetration issues.

Materials support available from DOD agencies can provide some of the fundamental principles of this emerging science – bridging the knowledge gap –

thus giving engineers the appropriate context to conduct their work. In that

light, the potential material choices for blast and penetration protection in any

given scenario are numerous. Like any other material selection process, generating appropriate BPRM solutions requires balanced management of all

design requirements, both BPRM and other more traditional requirements.

REFERENCES

[1] K.J. Knox, M.I. Hammons, T.T. Lewis, and J.R. Porter, Polymer Materials

for Structural Retrofit , 2000

[2] M. Ettouney, R. Smilowitz and T. Rittenhouse, Blast Resistant Design of

Commercial Buildings , Practice Periodical on Structural Design and

Construction, Vol. 1, No. 1, February 1996

[3] D.J. Viechnicki, A.A. Anctil, D.J. Papetti, and J.J. Prifti, Lightweight Armor

– A Status report , MTL-TR-89-8, January 1989; DTIC Doc AD-B130 590

[4] M.G.H Wells, J.S. Montgomery and E.B. Kula, High Strength Steels: 

Army Research and Applications , Speich Symp. Proc., 1992; DTIC Doc 

AD-D150 327

[5] N.L. Rupert and F.I. Grace, Penetration of Semi-Infinite, Bi-Element

Targets by Long Rod Penetrators, ARL-TR-666, January 1995; DTIC Doc 

AD-A291 176

[6] S.L. Blum and J.J. Burke, Technology Assessment of Ceramics for

Lightweight Improved Ballistic Performance Armor , ARL-CR-112,

December 1993, DTIC Doc AD-B179 876

The AMPTIAC Quarterly, Volume 6, Number 4 45
46 The AMPTIAC Quarterly, Volume 6, Number 4

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INTRODUCTION AND BACKGROUND

One of the greatest threats during a bombing attack comes fro m

fragmentation – pieces of walls, windows, equipment, and ve h icle debris flying at high speeds can result in extensive injury and

death. (See Fi g u re 1) A key tactic to defeating this threat is to

e n s u re that the exterior wall of a building can surv i ve the bomb

blast without contributing to the fragmentation problem. W h i l e

this is typically accomplished in existing buildings by adding

s t rength and mass to the wall (usually with concrete and steel),

this is often difficult to implement, time-consuming, heavy, and

e x p e n s i ve. The Materials and Manufacturing Di rectorate of the

Air Fo rce Re s e a rch Laboratory (AFRL/ML) at Tyndall Air Fo rc e

Base Florida is pioneering simpler, lighter, and more expedient

polymer re t rofit solutions to introduce ductility and re s i l i e n c e

into walls. The premise of the re t rofit technique is to apply an

elastomeric coating that bonds to the wall forming a tough elastic membrane. Although fracture of the wall may occur, the

polymer membrane will not ru p t u re and can effectively contain

the debris.

Expedient Retrofit Techniques

The Force Protection Branch of AFRL at Tyndall Air Force

Base has been developing expedient retrofit methods for unreinforced infill concrete masonry unit (CMU) walls in existing

buildings, and for lightweight temporary structures. (CMUs

are commonly referred to as “concrete blocks,” the hollow-core,

pre-cast blocks used for construction.) In many parts of the

world, the most common exterior construction technique for

buildings is to use steel or concrete frames (vertical columns

and horizontal beams) to carry the gravity loads, and fill the

open areas with stacked CMUs to form walls. (Hence the term

“CMU infill” walls.) Unreinforced construction is composed of

CMUs with no embedded steel. When overloaded by airblast,

unreinforced CMU walls typically fracture into pieces that are

propelled at high velocity into the interior of the structure, 

possibly causing severe injury or death. As a result of the threat

posed, this wall type has been prohibited for new military construction in the recently released DOD Minimum Antiterrorism

Standards for Buildings. Many buildings utilizing this type of

construction, however, are still occupied and

in use, resulting in the need for effective retrofit solutions.

Fiber-Epoxy Composite Initial research efforts

to develop expedient re t rofits produced a

field-made composite of high-strength fabric

(aramid or glass) in an epoxy matrix that is

bonded to the entire interior face of the CMU

wall as shown in Figure 2. The composite is

extended beyond the edges of the CMU wall

and overlapping the concrete frame, which

helps it to resist the applied blast pressure. To

enhance shear strength at the connections,

Figure 1. Debris Hazard.

The AMPTIAC Quarterly, Volume 6, Number 4 47

Dr. Jonathan R. Porter

and

Mr. Robert J. Dinan

Materials and Manufacturing Directorate,

Air Force Research Laboratory

Tyndall Air Force Base, FL

Dr. Michael I. Hammons

and

Dr. Kenneth J. Knox

Applied Research Associates, Inc.
additional layers of composite can be used to reinforce the connection points. In the event of an explosion, the composite

enhances the bending strength of the wall and prevents broken

pieces of the wall from entering the protected space and causing injury to the occupants. While this method of increasing

wall ductility and strength is an option, the application method

is time consuming and difficult.

In order to improve upon the composite re t rofit, a search for

an easier and faster re t rofit technique was undertaken. Coupled

with trying to reduce the difficulty and time re q u i red for installation, was a desire to introduce significant resiliency into the

s t ru c t u re - even at the expense of strength and stiffness. T h i s

shift in philosophy was founded on the premise of containing

the fragmentation and eliminating the debris hazard to occupants, rather than pre s e rving the structural integrity of the wall

i t s e l f. Fi g u re 3 shows some engineering stress-strain curves for

typical building materials and re t rofit materials and demonstrates the shift from stiffer, stronger materials like steel and glass

fibers to those with more ductility like polymers. Although the

x-axis is truncated at 0.5% strain, many polymers can undergo

up to 100% elongation without rupturing. As a result, elastomers we re investigated as potential re t rofit materials because

they are easy to apply, cure ve ry quickly, and could intro d u c e

significant ductility and resilience into the wall system.

Po ly m e rs In the fall of 1999, AFRL began evaluating sprayon polymer coatings as an expedient re t rofit technique for

non-load bearing CMU walls. The material that was used is

an elastomer that is ductile, tough, and has modest stre n g t h .

The material is sprayed directly onto the interior surface of

the wall and cures almost instantly, as shown in Fi g u re 4. T h e

thickness of application is re l a t i vely easy to control, and the

polymer bonds to a wide variety of surfaces. This re t ro f i t

technique takes advantage of the toughness and resiliency of

modern elastomers to effectively deform and dissipate the

blast energy, while containing shattered wall fragments.

Although the re t rofitted walls may shatter in a blast eve n t ,

the elastomer does not ru p t u re and effectively contains the

d e b r i s .

ELASTOMERIC MATERIALS

The resilience and large strain capacity of elastomers can be

exploited to absorb blast energy and contain building debris.

Elastomers are composed of long polymer chains, usually

c ross-linked or connected by chemical bonds. Cro s s - l i n k i n g

makes elastomers re versibly stretchable within a significant

range of deformations. In the unstretched state, the polymer

chains are oriented in random directions. When stretched, the

polymer chains become elongated and ord e red along the

Figure 3. Typical Stress-Strain Curves.

Figure 2. Composite Retrofit.

Figure 4. Application of Elastomeric Retrofit.

Table 1. Polymer Characteristics.

Property Value Test Standard

Secant Modulus1 24,000 psi ASTM D638

Elongation at Rupture 90% ASTM D638

Maximum Tensile Strength 2000 psi ASTM D638

Flammability Flame resistant; ASTM E119

2-hr fire rating ASTM E84

Toxicity Nontoxic after curing Review MSDS

1

The slope of a straight line drawn from the stress-strain diagram’s origin to a point

on the curve at 60% of maximum tensile strength.

Polyurethane

Polyurea

Concrete

CFRP

E-Glass

Steel

0.000 0.001 0.002 0.003 0.004 0.005

6000

5000

4000

3000

2000

1000

0

Strain

48 The AMPTIAC Quarterly, Volume 6, Number 4
deformation direction. When no longer stretched, the cro s s -

links guide the elastomer back to its original shape as the

chains once again randomize .

The elastomer used in this study was a two-component

sprayed-on polyurea. Polyurea elastomers do not require a catalyst to accelerate the chemical reaction when the two components are mixed. The polyurea material must be applied at high

p re s s u re and temperature, with 1:1 mixing of the hardener and

resin occurring just beyond the spray gun to minimize clogging.

Te m p e r a t u re does not affect curing of polyurea. With pro p e r

training and equipment, the polymer material can be safely

applied to wall surf a c e s .

Material Properties

Polyureas are characterized by high elongation, high tear

strength, and superior modulus of elasticity. Typical physical

and mechanical properties of the polyurea used in this study are

indicated in Table 1.

Emissions and Fire Performance The polyurea material was

evaluated to determine the type and amount of volatile organic emissions off-gassing from polymer-coated aluminum plates

at room temperature (70°F) and at 95°F to simulate a warm

condition. The rate of emission for each compound identified

decreased as a function of time and most of the emissions were

undetectable one week after application. With adequate ventilation provided, the levels of emitted compounds will be below

National Institute for Occupational Safety and He a l t h

(NIOSH) time weighted averages (TWA) for continuous 10-

hour exposures one day after application.

Two performance tests were conducted to evaluate the hazard resulting from a fire in a retrofitted structure. The first test

was performed on a CMU wall in accordance with ASTM

E119-00, “Standard Test Methods for Fire Tests of Building

Construction and Materials.” The second test was performed

on a polymer specimen in accordance with ASTM E84-00,

“Standard Test Method for Surface Burning Characteristics of

Building Materials” (NFPA 255, ANSI/UL 723 and UBC 8-1).

The wall assembly coated with the polymer met the temperature and structural requirements of ASTM E119-00 for a period of 120 minutes, and did not have a significant negative

impact on the assembly’s fire rating. The polymer specimen was

determined to be a Class III material according to the 1997

Uniform Fire Code with relatively large smoke generation

potential. In practical applications, the smoke hazard can be

mitigated by alternate material formulations or by using an

additional intumescent (swells and chars when exposed to

flame) coating on the retrofit.

Engineering Properties The polyurea was much stiffer than

many other candidate materials. This initial stiffness helps to

reduce wall deflections in response to a lateral load such as airblast. The high elongation at rupture provides the toughness

and ductility to contain the debris and fragmentation, even if

large deformations occur. Based on the engineering properties

determined from uniaxial tensile tests, dynamic models of the

wall system can be used to predict response to airblast loads.

While simple single-degre e - o f - f reedom models have been

developed, higher fidelity models are required to fully understand the effect that varying the retrofit material properties will

have on dynamic performance of the wall system. Current

practice, therefore, relies on laboratory and full-scale explosive

experiments to validate retrofit performance.

LIGHTWEIGHT TEMPORARY STRUCTURES

Because of the promise shown by the elastomeric retrofit concept and the common use of lightweight temporary structures,

AFRL developed methods for increasing the survivability of

these facilities, which are characterized by timber stud walls,

exterior aluminum siding and interior veneer-plywood paneling. Since these walls are load bearing and provide support for

the roofing system, the elastomeric retrofit technique was combined with additional lightweight framing to prevent collapse

of the structure once the load bearing capacity of the walls is

diminished. A series of full-scale tests was conducted at Tyndall

Air Force Base Florida and, as part of an international cooperative research and development program, in Israel to validate

the performance of the retrofit method. Figure 5 shows a typical test result, where the unretrofitted half of the trailer was

destroyed and the retrofitted half is intact. This test article was

coated on the interior and exterior to evaluate where the retrofit material was most effective. While the exterior coating may

provide some load distribution benefits, the interior coating is

critical because it forms the tensile membrane that contains the

wall fragments.

Based on this series of tests and analytical results from singledegree-of-freedom models, retrofit design criteria were established that can reduce standoff distances required for protection

by up to 50 percent. The recommended retrofit consists of a

1/2-in thick coating on interior wall surfaces, or both interior

and exterior coatings each 1/8-in thick.

CONCRETE MASONRY UNIT (CMU) WALLS

A series of explosive performance tests of full-scale unreinforced

CMU walls were conducted at Tyndall Air Force Base and in

Israel. The wall aspect ratios and boundary conditions were varied, as were the blast loadings. Some walls were retrofitted on

the interior only, while others were retrofitted on the interior

and exterior. Three unretrofitted control walls were also included in the test series. In each test, peak displacement was measured using an active displacement gauge or a passive indicator

(scratch gauge).

Figure 5. Retrofitted Lightweight Temporary Structure.

The AMPTIAC Quarterly, Volume 6, Number 4 49
50 The AMPTIAC Quarterly, Volume 6, Number 4

Typical pre-test and post-test photographs are shown in

Figure 6. In general, post-test observations indicated that the

exterior faces of the CMU were shattered at least half way

through the CMU, with the interior faces of the CMU remaining adhered to the polymer liner. However, in all but a one case,

the polymer liner remained intact and effectively contained 

the fragmentation from the fractured CMU. In several cases,

particularly in the tests in Israel, peak dynamic deflections were

near two feet, which are likely unacceptable in a real world 

situation. These deflections can be controlled by material formulations with greater initial stiffness or by increasing the

thickness of the membrane.

The data from the blast performance tests and analytical

results from single-degre e - o f - f reedom models we re used to

d e velop design criteria for buildings consisting of a concrete or

steel frame with non-load bearing CMU infill walls. The 

criteria we re developed assuming an 8-inch nominal CMU

thickness and a wall height of 12 feet and connected on only

two opposing edges (one-way action). These criteria will be

c o n s e rva t i ve for walls connected on all four edges (two-way

action), shorter walls, and for walls with thicker CMU. As

described earlier for temporary stru c t u res, the re c o m m e n d e d

CMU wall re t rofit consists of a 1/2-in thick coating on interior wall surfaces, or both interior and exterior coatings each

1/8-in thick.

SUMMARY AND CONCLUSIONS

Un re i n f o rced CMU in-fill construction and lightweight 

t e m p o r a ry stru c t u res are particularly vulnerable to ove r l o a d i n g

f rom bomb-induced airblast. Many such buildings are 

c u r rently in use with inadequate standoff from ro a d w a y s ,

p a rking lots, or protected perimeters. The spray-on polymer

re t rofit technique offers one solution that decreases the vulnerability of occupants of these common building types. T h i s

i n n ova t i ve re t rofit technique takes advantage of the toughness

and resiliency of modern polymer materials to deform and

e f f e c t i vely dissipate the blast energy while containing the 

s h a t t e red wall fragments.

Blast load capacities for unre i n f o rced non-load bearing

CMU walls retrofitted with polyurea are presented in terms of

charge weight versus standoff distance in Figure 7. In the chart,

charge weight is the equivalent weight of TNT and the standoff distance is the distance from the center of the charge to the

outside face of the wall. The curves represent the threshold of

failure, defined as collapsed walls with objects thrown into the

interior space, such that serious injury and/or death would be

Figure 6. Unretrofitted and Retrofitted CMU Walls.
expected. These curves show that the polymer retrofit technique for CMU walls can reduce standoff distances required to

limit serious injury and death by as much as 80 percent. Similar

charts for lightweight temporary structures show that the technique can reduce standoff distances by as much as 50 percent.

Ongoing efforts are focused on extending the philosophy of

introducing resilience to other building components such as

door and window frames, with the goal of providing a retrofitted building system with balanced resistance to airblast loads.

Figure 8 shows the results of a test in which a blast resistant

window was connected to the wall system with the polymer

retrofit. By connecting the window frame to the retrofit rather

than only to the structural wall components, the tolerance for

deformation is greatly enhanced. Conventional retrofits that

increase mass and strength result in limited deflection of the

wall, which makes adequate connections for windows and

doors even more problematic. By exploiting the resilience

afforded by the polymer retrofit technique, the entire wall system can be held together, providing an expedient retrofit that

greatly reduces the probability of casualties in the event of a terrorist bomb attack.

GENERAL REFERENCES

Air Force Civil Engineer Support Agency (2000). “Airblast

Protection Retrofit for Unreinforced Concrete Masonry Walls”,

Air Force Engineer Technical Letter ETL00-09

Air Force Civil Engineer Support Agency (2002) “Airblast

Protection Polymer Re t rofit of Un re i n f o rced Concre t e

Masonry Walls” Air Force Engineer Technical Letter ETL02-04

Figure 7. Charge Weight versus Standoff

for Unreinforced CMU Walls.

Figure 8. Retrofitted CMU Wall with Window Retrofit.

Nonretrofitted 

CMU Wall

Polymer-Coated 

CMU Wall

10 100 1000 10000 100000

10000

1000

100

10

Yield (lb TNT)

The AMPTIAC Quarterly, Volume 6, Number 4 51
Dr. Jonathan Porter is a Senior Research Engineer with the Air Force Research Laboratory’s Materials and

Manufacturing Directorate (AFRL/ML). He is currently detailed to the Deputy Assistant Secretary of the Air Force

(Science, Technology & Engineering) as the Program Element Monitor for the Air Force’s Materials Science

and Technology Program. Prior to this assignment, Dr. Porter led the Engineering Mechanics Group of

AFRL/ML’s Force Protection Branch located at Tyndall AFB FL. The group develops technologies based on

advanced materials to mitigate the effects of terrorist weapons on the occupants of buildings and to characterize the effects of terrorist improvised explosive devices on deployed personnel and structures.

Jon earned a B.S., M.S., and Ph.D. in Civil Engineering from Vi rginia Po ly te chnic Inst i t u te and Sta te

Un i ve rs i t y. He has auth o red numerous pre s e n tations, te chnical re p o rts and papers on blast mitigation, th e

application of novel mate rials for antite rro rism and fo rce protection, and the ch a ra c te rization of ge ote ch n i c a l

m a te ri a l s .

Mr. Robert Dinan is a Senior Research Engineer with Air Force Research Laboratory at Tyndall AFB, FL, and

Group Leader for the Engineering Mechanics Group of the Force Protection Branch, Airbase Technologies

Division. Before joining AFRL, Mr. Dinan was a research engineer with the US Army Corps of Engineers for 19

years. He leads research efforts in explosive characterization, blast response of structures, force protection, and

physical security. During his 20 year career, Mr. Dinan has conducted numerous experimental and analytical

studies to determine the behavior of a variety of structural types and components subjected to blast loading. 

Dr. Mike Hammons is a Principal Engineer with Applied Research Associates (ARA) and Group Leader for the

Applied Mechanics Group of the Engineering Science Division. He supports the Air Force Research Laboratory

at Tyndall AFB, FL, where he leads research efforts in force protection, physical security, robotics, and explosive

characterization. He has conducted experimental and analytical studies to develop engineering criteria for

expedient retrofit systems for structures subjected to blast loading. Dr. Hammons supports the DOD’s Security

Engineering Working Group in developing force protection construction criteria. He served as structural engineer on Vulnerability Assessment Teams for the US Air Force and the Defense Threat Reduction Agency and as

instructor for workshops to train Combatant Commands, Services, and Major Command staffs charged with

direct planning and programming responsibilities for security engineering aspects of military construction. Before

joining ARA, Dr. Hammons was a research engineer with the US Army Corps of Engineers for 17 years.

Dr. Kenneth J. Knox, P.E. joined Applied Research Associates (ARA) in 1998 following his retirement as an Air

Force civil engineering officer. During his 20-year USAF career, he directed civil engineering research; managed design and construction of airbase facilities; taught engineering at the Air Force Academy; and helped

develop the force protection program for the Defense Special Weapons Agency (now the Defense Threat

Reduction Agency). A recognized expert in force protection and antiterrorism, Dr. Knox is currently conducting

Air Force Research Laboratory research in protective construction and retrofits, weapons effects, and blast mitigation. He also continues to advise military installations on ways to improve their protection from terrorist attack.

52 The AMPTIAC Quarterly, Volume 6, Number 4

Air Force Civil Engineer Support Agency (2002). “Airblast

Protection Retrofit of Lightweight Manufactured Structures”

Air Force Engineer Technical Letter ETL02-10

Department of Defense (2002). “Department of Defense

Minimum Antiterrorism Standards for Buildings” Unified

Facilities Criteria UFC 4-010-01

Hammons, M.I., Knox, K.J., and Porter, J.R. (2002) “Polymer

Materials for Blast Retrofit of Masonry Construction” 30th

DOD Ex p l o s i ve Safety Se m i n a r, De p a rtment of De f e n s e

Explosive Safety Board

Knox, K.J., Hammons, M.I., Lewis, T.T., and Porter, J.R.

(2000) “Polymer Materials for Structural Retrofit” 29th DOD

Explosive Safety Seminar, Department of Defense Explosive

Safety Board
INTRODUCTION

Protective structures over the years have relied on distance and

mass for protection. For thousands of years, people have used

caves and massive stone or wood structures to protect assets.

Exterior walls had few openings because doors and windows are

difficult to harden and defend. Defenders have used guards,

fences, walls, ditches, hills, moats and other barriers to keep

potential threats at a safe distance. Like ancient protective

structures, most hardened structures today use massive construction of wood, rock, soil, or reinforced concrete with few

windows or doors. Contemporary threats are kept at a safe

standoff by operational and physical means similar to those

used over the millennia. This article provides a broad, overall

perspective on the problem of designing a hardened structure.

A hardened facility design example is presented to demonstrate

the procedure.

DEFINITIONS

The terms “hardened structure” and “protective structure”

mean different things in different contexts, and lately with the

increase in the terrorist threat, the common definitions have

changed again. Antiterrorism Protection, Physical Security, and

Hardened Structures are terms being used by many. The following definitions will hold for the bounds of this article:

Physical Security

Physical Security consists of measures taken to address criminal

and vandal threats. Physical Security uses defensive measures

that provide layers of detection and delay around an asset. The

defensive layer must provide enough delay time to allow a

response force to halt the attack. For the DOD, Physical

Security is addressed primarily by policy that defines operational procedures, electronic security systems, and structural

security measures to provide the required delay time. The

assumption is that some minimal level of protection is required

and risk is evaluated on an organization-wide basis with the

assumption that there is always a criminal threat.

Antiterrorism Protection

Antiterrorism Protection addresses the design of both the building and the site to minimize the blast loads and weapon effects

from terrorist threats to assets - usually people. This may mean

the building is destroyed, but damage to assets is minimized.

The actual threat to a specific asset is seldom known and it is

unlikely that a specific asset will ever have a terrorist attack. The

price people are willing to pay for protection from an unlikely

threat of unknown magnitude has historically been very little in

this country, but it is changing. As part of Antiterrorism

Protection, blast hardening is sometimes done, but does not

commonly meet the level of protection in the following definition of a hardened structure.

Hardened Structure

A Hardened Structure is usually designed to perform its primary

mission after a wartime attack making hardening one of its primary requirements and a significant part of its cost. The facility is protected against a wide range of threats including forced

e n t ry, Chemical/Biological/Radiological (CBR), airblast,

ground shock, penetration, fragmentation, and damage to the

structure and equipment due to explosive loading. Designs

must consider how camouflage, concealment and deception,

active defense, and manned response can reduce or limit the

effectiveness of the threat. The design assumptions are that during a war, the facility will be attacked and that it must survive

and function after the attack. Almost all hardened structures

inherently satisfy the requirements for both Physical Security

and Antiterrorism Protection.

Likelihood of Protection

The conceptual differences between the three types of protective measures defined above are the likelihood of the protection

actually being needed, the consequences of it not working, and

the willingness of the user to pay for the protection. The government is willing to pay a limited price for physical security

for all facilities and a high price for hardened structures for specific assets. In the past we funded antiterrorism protection at a

low level because the likelihood was low, but in light of recent

events, our population is reevaluating this stance.

DESIGNING FOR WARTIME THREATS

Designing facilities hardened for wartime threats is sometimes

politically easier than designing normal facilities for the terrorThe AMPTIAC Quarterly, Volume 6, Number 4 53

Bruce Walton, PE

Protective Design Center

US Army Corps of Engineers

Omaha, NE 
ist threat; because the users of the wartime hardened facilities

understand the importance of hardening and are willing to give

up things like large doors and windows, fancy interior finishes,

and easy access. Some of the key aspects in design include:

Conventional Weapons

A wartime conventional weapon threat can range from airblast

only to direct hits from precision-guided bombs and penetrators. Fully hardened facilities are designed to withstand a direct

hit and detonation of a penetrating weapon. Semi-hardened

facilities are designed to withstand small area weapons and near

miss detonations of larger bombs. Other protected facilities are

only designed to withstand airblast and fragments from bombs

detonating at a distance.

Balanced Survivability

Whatever the threat, the designer tries to incorporate balanced

survivability into the building. Balanced survivability is a condition wherein no significant facility failure mode has been

overlooked or its importance underestimated, thus the facility

has no “Achilles Heel.” Balanced survivability exists for a facility when all critical subsystems and resources required for

accomplishing the facility’s mission are equally survivable at a

specified threat level. 

A balanced survivability assessment (BSA) determines the

capability of a facility to survive against a specified threat spectrum and still perform its mission. The BSA is a systems

approach to survivability, yielding recommendations that facility designers can use to make prudent investment decisions in

light of what they consider to be the most critical systems and

most worrisome threats. A BSA can be performed on a facility

design or an operational facility, and it is ideal if a team trained

in BSA techniques examines design drawings early to identify

potential survivability flaws.

Balanced surv i vability ensures that no threat is neglected,

and that all threats are addressed consistently. Ad d i t i o n a l

design considerations are re l i a b i l i t y, maintainability and logistics. Incorporating post-attack expedient measures for a facilit y’s systems that could help it re c over quickly after an attack

(or pre vent further damage) should be considered. Such measu res may include incorporating utility cutoffs, additional fire

p rotection, adequate utility backup connections, and stru c t u ral repair kits. 

Site Planning

Key elements in planning the site include:

D i s p e rs i o n Placing re s o u rces in irregular patterns, and using

physical separation, orientation, staggering, and system component distribution will increase surv i va b i l i t y. Di s p e r s i o n

g reatly increases an attacker’s targeting difficulties, and re d u c e s

the chance of simultaneous or collateral damage from any 

single strike. 

Orientation Hardened facilities should be oriented so their

most vulnerable sides face away from nearby critical structures.

Aircraft shelter entrances should not face each other or nearby

critical facilities. This decreases the potential for damage to 

vulnerable sides of the structure if a nearby structure is hit. A

critical review of the site, its surroundings, and the building’s

orientation and location on the site should be performed. If

this siting analysis shows an explosive threat is more probable

from one direction, the facility should be oriented and/or the

entrances located to minimize blast and fragment loads on the

blast door.

Separation From a survivability standpoint, there is an optimum distance between hardened facilities, such that no two

facilities can be attacked by a single weapon or be acquired by

an airborne target acquisition system on a single pass. Siting

facilities too far apart however, may degrade their operational

performance.

Building Layout

Re d u n d a n c y The surv i vability and overall operability of the

p rotected system can be improved by incorporating re d u n d a n t

facilities, components, paths, and circuits into the system. 

In this manner, damage to one part of the system will not 

necessarily shut down the entire system, but instead shift the

operation to a redundant part .

Footprint and Floor Plan The footprint of a hardened structure

should be a rectangle, square, or other regular geometric shape

that attenuates the effect of an explosive blast. Designers should

avoid reentrant corners that tend to amplify blast pressure and

enhance a structure’s radar image. (Areas such as recessed entryways contain reentrant corners.) Activities of a less critical

nature should be located on the exterior of the building.

Hallways should be located along the exterior wall.

Compartmentalized functional areas (isolation zones) should

be considered to prevent fire or internal bomb blasts from

p ropagating from one area or zone to another. Compartmentalization can be accomplished both by careful functional zoning and by proper design of walls, internal blast

doors, and other separations.

Exterior Openings Exterior openings include personnel and

equipment access, fresh air ventilation, cooling, and combustion equipment intake and exhaust portals. Designers should

anticipate the possibility of blast pressure, heat, dust, fragments, and toxic gases entering the facility through exterior

openings, and take appropriate preventive measures. Entrance

openings should be kept as small and few in number as possible

to minimize shielding problems, but still satisfy operational

and emergency ingress and egress requirements.

Proportioning components The structural design process has

two major, interdependent phases: (1) selecting a trial structural configuration (arrangement, shape, and material), and (2)

proportioning components to prevent failure under prescribed

influences. The proportioning phase is calculational in nature,

and therefore requires a numerical response threshold (performance criterion) for each failure mode (failure modes are

established during design). Typical failure modes are those 

54 The AMPTIAC Quarterly, Volume 6, Number 4
associated with airblast, fragmentation, spall, weapon penetration or perforation, shock motion, cratering, fire, suffocation,

and CBR agents. For the various failure modes, the performance criteria quantify the survivability requirements of the 

protected system elements and functional spaces in terms of

personnel tolerances, equipment tolerances, endurance periods,

and post failure capabilities.

TERRORIST THREATS

Once a defined threat is specified, standard design procedures

for hardened structures are applied. Even if no threat is defined,

the DOD has determined that a minimum level of protection

is warranted for all inhabited buildings, and Unified Facilities

Criteria (UFC) 4-010-01 “DOD Minimum An t i t e r ro r i s m

Standards for Buildings” is applied. This standard establishes criteria for DOD-inhabited buildings to minimize the potential

for mass casualties and progressive collapse from a terrorist

attack. The overarching antiterrorism philosophy is that an

appropriate level of protection can be provided for all DOD

personnel at a reasonable cost, and reduces the risk of mass

casualties. Full implementation of the standards provides a level

of protection against all threats and significantly reduces

injuries and fatalities for the threats upon which these standards

are based. The costs for these protective measures are not significant for most projects. The primary methods used to

achieve this outcome are to maximize the standoff distance, to

construct superstructures resistant to progressive collapse, and

to reduce flying debris hazards from glazing.

Maximize Standoff Distance

Maximizing the standoff distance keeps the threat as far away

from critical buildings as possible. It is the easiest and least costly method for achieving the appropriate level of protection to a

facility. When standoff distance is not available, the structure

needs to be hardened to give the same level of protection that

it would have with a greater standoff. While sufficient space

around a structure is not always available to provide the minimum standoff distances required for conventional construction, maximizing the available standoff distance will always

result in the most cost-effective structural solution. Maximizing

standoff distance also ensures that there is opportunity in the

future to upgrade buildings to meet increased threats or to

accommodate higher levels of protection. If minimum standoff

distances are achieved, conventional construction should minimize the risk of mass casualties from a terrorist attack, with

only a marginal impact on the total project cost.

Progressive Collapse Avoidance

Progressive collapse is a chain reaction of failures following

damage to a relatively small portion of a structure. The resulting damage from a progressive collapse failure is out of proportion to the damage of the initial failed area. Consequences of

progressive collapse are unnecessary loss of life and the entrapment of survivors in the collapsed structure. 

The UFC has provisions that minimize the ability of the

structure to go into a progressive collapse mode of failure.

Designing those provisions into the buildings before construction begins, or during a major renovation project is the most

cost effective solution. All inhabited structures of three stories

or more, are to have a progressive analysis performed. This

analysis assures that the structure will remain stable when key

members are removed and is accomplished by providing structural continuity, redundancy, or energy dissipating capacity

(ductility) in the remaining members of the structure. There

are two approaches to perform a progressive collapse analysis -

the direct and the indirect methods.

Direct Design Approach Direct design explicitly considers

structural resistance through the alternate path method or

through the specific local resistance method. When a local failure occurs, such as the removal of a structural member, the

alternate path method seeks to find a load path that will absorb

the loads created. The specific local resistance method applies

loads to the structure that must be accounted for in the design.

Indirect Design Approach Indirect design implicitly considers

a structure’s resistance to progressive collapse by defining a

minimum level of strength, continuity, and ductility for structural members. Typical guidance recommends using highly

redundant structural systems such as moment resisting frames,

continuity across joints so the member can develop the full

structural capacity of the connected members, and design

members that accommodate large displacements without complete loss of strength. Other design details that minimize the

possibility that collapse of one part of the building will affect

the stability of the remainder of the building should be incorporated. Examples include designing floor systems with top

and bottom steel to accommodate load reversal, and designing

building additions to be structurally independent from the protected portions of the existing building.

Minimize Hazardous Flying Debris

A high number of injuries result from flying glass fragments

and debris from walls, ceilings, and fixtures (non-structural features). Flying debris is minimized through the proper design

and selection of appropriate building materials. The glazing

used in most windows will break at very low blast pressures,

creating hazardous, dagger-like shards. The simplest protection

from flying debris is to minimize the number and sizes of windows used in the building design. Additional protection can be

garnered by using enhanced window units. Blast-resistant window and door units must be purchased as complete, tested

assemblies that include the glazing unit, door or window frame,

and frame connections to the structure. When installed, these

elements become an integrated structural system. The UFC

requires that all glazing units use a 1/4-inch laminated glass in

all new construction and major renovations.

OBSERVATIONS OF CONVENTIONAL STRUCTURES

Re v i ew of typical stru c t u res often re veals that structural 

members have different capacities during the positive and 

negative phases of the blast load. Also, these members can have

significant blast load capacity, but the connections may not.

Special provisions of the concrete and steel design codes need

The AMPTIAC Quarterly, Volume 6, Number 4 55
to be followed to make a structure perform well, even when a

reasonable amount of standoff is provided.

Conventional design of buildings results in balanced design

for normal loads and usually a very unbalanced survivability for

blast loads. Most buildings are initially designed for easy access

and natural lighting, which results in numerous lightweight

doors, and larger windows. Hardening doors and windows for

blast and fragment loadings is difficult and very expensive, typically 2 to 10 times that of normal construction. This results in

a significant increase in building cost. Typical roof construction

is kept lightweight especially in high seismic areas and the lack

of mass in these elements makes it difficult to design them for

blast loads.

GENERAL REFERENCES

Department of Defense, Interim Antiterrorism / Force Protection

Construction Standards, December 16, 1999 (hereby cancelled)

Department of Defense, UFC 4-010-01, DOD Minimum

Antiterrorism Standards for Buildings, July 2002

De p a rtment of Defense, In s t ruction 2000.16, D O D

Antiterrorism Standards, June 14, 2001

Department of the Army, and the Air Force, TM 5-853-1,

AFMAN 32-1071 Vol. 1, Security Engineering Pro j e c t

Development, May 1994

Department of the Army, and the Air Force, TM 5-853-2,

AFMAN 32-1071 Vol. 2 Security Engineering Concept Design,

May 1994

Department of the Army, and the Air Force, TM 5-853-3,

AFMAN 32-1071 Vol. 3 Security Engineering Final Design,

May 1994

Department of the Army, TM 5-853-4, Security Engineering

Electronic Security Systems, May 1994 

Department of the Army, the Navy, and the Air Force: TM 5-

1300, P-397, and AFR 88-22, Structures to Resist the Effects of

Accidental Explosions, November 1990

De p a rtment of the Na v y, MIL-HDBK-1013/1A, De s i g n

Guidelines for Physical Security of Facilities, October 1987

Department of Defense, UFC 3-340-01 (TM 5-855-1), Design

and Analysis of Hardened Structures to Conventional Weapons

Effects (DAHS-CWE), June 2002

ENDNOTE

* “Bare charge” refers to an unconfined explosive mass where

the energetic material is not contained in a rigid vessel. When

an energetic material is confined in a rigid container (for

instance a thick, tightly-wound paper or metal casing) its explosive effect is enhanced.

Figure 1. Schematic Floor Plan of

Example Building.

Project Description 

Review of an ongoing structural design (new construction), and incorporation of blast resistant components. The scope of the review was to examine

structural components and cladding, and then upgrade them for various blast

loading events.

Facility Description

The structure being analyzed was designed for standard seismic, gravity,

wind, and live loads, but not blast effects. The facility consists of an administrative and operations area, and a shipping-and-receiving area that houses

the mechanical and electrical rooms. (See Figure 1) The administration area

is a two-story steel braced-frame structure with a composite steel and concrete

roof deck, and a square floor plan that is 135-feet by 135-feet. The mechanical area is a one-story attached structure measuring about 59-feet by 122-

feet. It is constructed as a mixed system of braced steel frames, and load-bearing cast-in-place concrete walls. The roof is a steel joist with metal decking.

The back and sides are cast-in-place concrete walls, while the front (west) wall

is made of precast concrete panels. Windows are located on the west and

south walls of the administration area.

Blast Events

Two bomb weights were considered in this review. Bare explosives were used

in the analysis, and fragments were not considered. The first threat was 50

pounds of TNT located 100ft from the nearest point on the building exterior. The second was 1000 pounds of TNT, located 200-ft from the building

perimeter. The mechanical area was closer than the administration area, and

needed to be analyzed for the 1000 pound detonation.

Administration

Area

Windows

N

56 The AMPTIAC Quarterly, Volume 6, Number 4

Design Example–

Exterior Blast Upgrade

The following design example will help to illustrate

the use of hardening techniques to strengthen civilian type stru c t u res. The example invo l ves modifying the in-process design of a building to prov i d e

resistance against an exterior terrorist bombing

attack. Blast loads from the example’s standoff

t h reats will cause damage, but the desired level of

p rotection may be achieved with implementation of

re l a t i vely minor modifications.
The AMPTIAC Quarterly, Volume 6, Number 4 57

Figure 2. Blast Pressure for 50 lbs TNT at 100 ft

and 1000 lbs TNT at 200 ft.

50 lbs TNT @ 100 ft

1000 lbs TNT @ 200 f t

Blast X Output

Incident Overpressure Plots

50 75 100 125 150 175 200 225 250 275 300

Time after Detonation (milliseconds)

6

4.5

3

1.5

0

-1.5

-3

Design Standards Used

Many structural design standards and Army manuals are used in preparing

this structural analysis and design. They are the American Concrete Institute

(ACI) 318 - Building Code Requirements for Structural Concrete, the American

Institute of Steel Construction (AISC) - Manual of Steel Construction

(LRFD-Load and Resistance Factor Design), and Army Technical Manuals:

TM 5-853-3, TM 5-855-1 and TM 5-1300 for designing building systems

to resist explosives effects. This design primarily uses TM 5-855-1 (the

Design and Analysis of Hardened Structures to Conventional Weapons

Effects {DAHS CWE} Manual), and its associated computer codes to determine the blast loads and structural responses. Response limits were taken

from TM 5-1300, which has a greater margin of safety, and is more consistent with the protection of civilian personnel during peacetime.

Airblast Prediction

Airblast calculations were made using the BLASTX computer code, which

accurately computes both the positive and negative phases of the shock wave.

The negative phase of the blast wave is often neglected in structural analyses,

but is of particular importance when reviewing unhardened, or normal 

s t ru c t u res. The shockwaves used in the design analysis are shown in Fi g u re 2.

This is a plot of the incident (unreflected) shockwaves obtained for both 

50-lb TNT at 100 ft, and 1000-lb TNT at 200 ft. It is presented to illustrate

the relative size of the two threats, and it is apparent the 1000-pound explosion creates a higher pressure and impulse, even at twice the distance. These

pressures are what the roof structure would experience, while the walls

receive reflected pressures that are about twice these magnitudes.

Dynamic Analysis

Structural elements subjected to blast loads were analyzed individually using

the SPAN computer code. SPAN applies the BLASTX output, and performs

a Single degree-of freedom Plastic ANalysis of wall panels, and beams. It

then performs a numerical integration of the dynamic response to that blast

load. The SPAN analysis for one precast wall panel showed that the panel

was fully plastic for both the inward and outward (rebound) response. This

relatively large rebound was due to the fact that negative pressure (suction)

coincides with the structural elements’ rebound response. Rebound loads

were significant in this design review, and need to be treated as rigorously as

the blast load response during the positive phase loading.

Structural Response Criteria

Two limits were addressed in this design review for blast loadings: (1) the 

structure needed to be repairable and the operation of the facility not severely impacted, and (2) operating personnel should be protected. Therefore, 

dynamic response limits of structural elements in flexure are defined to 

prevent excessive element damage but are within the limits allowed by TM

5-1300 for personnel safety.

Structural Analysis of 50-pound Threat

Damage to the structure was assessed at the worst case bomb location for

each individual structural element. The analysis results showed that the roof,

and the precast wall system of the main area would not be damaged.

However, the mechanical area would receive damage to the roof joists and

beams during the upward rebound because the bottom flanges of the joists

were not adequately braced. This would occur because the roof deck did not

have a concrete topping. As seen in Figure 3, the entire roof of the mechanical area was damaged as were a few of the precast panels. In all roof areas

however, roof decking, steel columns, and roof beam connections were

adequate for this loading condition.

Figure 3. Structural Damage from 50-lb Threat.

Administration

Area

Rebound Instability

Partial Precast Panel Damage

Unacceptable Damage Types:

50 lb TNT

@ 100’

100’
Figure 4. Structural Damage from

1000-lb Threat.

Structural Analysis of 1000-lb Threat

When this facility was analyzed for the 1000-pound event, the damage

was much more significant. It can be seen in Figure 4 that the area of

damage covers the entire facility, as unacceptable damage occurs to

about 60% of the admin area roof, 100% of the mechanical area roof,

and 100% of the precast wall panels in both areas. In each event all roof

joists, except the long span joists in the main area, experience a lateral

instability failure during roof rebound, as do many of the roof beams.

There were considerable beam connection failures in the admin area

roof. Also, in all areas the roof decking and the steel columns were found

to be adequate.

Structural Upgrades for the 50-lb Threat 

The following structural upgrades were required to harden this facility.

(1) Main Area - No changes required.

(2) Mechanical Area

- Modify all open web roof joists to increase the uplift capacity

for rebound resistance, and increase joist shear strength to

exceed flexural strength by at least 10%.

- Provide lateral bracing to bottom flange of all wide flange

roof beams at midspan.

- Provide vertical supports for precast panels on each side of

door and louver openings on the west side walls.

Structural Upgrades for the 1000-lb Threat

The following structural upgrade was required to harden this facility.

(1) Main Area

- Modify all open web roof joists to have full uplift capacity

(equal to downward load capacity), and increase shear

strength to exceed flexural strength by at least 10%.

- Provide lateral bracing to the bottom flange of all main roof

beams at midspan, and at midspan and third points for the

remaining roof beams.

- All beam connections need to carry at least 60% of the beam

web shear capacity.

- All column base plate anchorages need to develop the ultimate strength of the anchor bolts in tension.

- Increase reinforcement in the 5" thick precast walls panels,

and increase the size of the embedded plates for the increased

vertical and horizontal loads.

- Increase reinforcement in the 5" thick south and west precast 

panels by 25%, and increase the steel support capacity by

20%.

(2) Mechanical Area

- Add a 4.5" thick composite steel and concrete roof deck.

- Use revised joists and beams to support new roof deck.

- Modify all open web roof joists to have full uplift capacity

(equal to downward load capacity), and increase shear

strength to exceed flexural strength by at least 10%.

- Provide lateral bracing to the bottom flange of the roof beam

at midspan, and bottom-flange bracing at midspan and third

points on the other roof beams.

- All beam connections need to carry at least 60% of the beam

web shear capacity.

- Replace west side exterior precast wall panels with a 10" thick 

cast-in-place reinforced concrete wall.

Roof Downward Damage and Rebound Instability

95% Roof Beam Connection Failure

25% Roof Beam Rebound Instability

Roof Joist Rebound Instability

Precast Wall Damage

Unacceptable Damage Types:

1000 lb TNT

@ boundary

200’

47’

35’

58 The AMPTIAC Quarterly, Volume 6, Number 4
The AMPTIAC Quarterly, Volume 6, Number 4 59

Bruce A. Walton is a registered structural engineer with the US Army Corps of Engineers’ Protective Design

Center in Omaha, Nebraska. He is a member of the US Army Corps of Engineers’ Urban Search and Rescue

Team as a structural specialist. Mr. Walton is a retired Air Force Lieutenant Colonel, who has worked for the

Protective Design Center since 1989. He has many years of experience in research and design with both the

Air Force and Army. His background consists mainly of research in the areas of weapon effects, rapid repair of

wartime facility damage, and the design of facilities to resist the effects of nuclear weapons, conventional

weapons, and accidental explosions. He has developed computer programs in the areas of weapon effects

prediction and computational dynamics. He was also a major author of UFC 3-340-01, Design & Analysis 

of Hardened Structures to Conventional Weapons Effects. Mr. Walton was also the primary DOD structural

investigator for the World Trade Center, Oklahoma Federal Building, and Khobar Towers – Saudi Arabia 

bombings.

Window Recommendations

The analysis of the building’s window systems for both threats requires a

design layup of an Insulated Glass (IG) unit using two l/4" laminated

heat strengthened glass panels separated by a 1/2" air space. This layup

will fracture, but remain in the frame for the worst-case event (1000 lb

at 200 ft). The minimum glazing bite was 1/2" for all panels and applied

a static frame design load (applied to the glazing surface) of between

3.12 lb/in and 8.85 lb/in of frame length depending on the window size.

The specifications were modified to require the contractor to design the

frames, mullions, and connections to resist the load without reaching the

yield strength of the materials.

Hardening Costs

The cost of this building was around $9 million, not including the cost

of installed equipment. The structural upgrades necessary to blast-harden the building added $150,000 to the price of the project, or just 1.7%.
While the theme of this issue of the AMPTIAC Quarterly is 

protecting people and buildings, our staff informally refers to it as

“The Homeland Security Issue”, as the two topics are inexorably

linked. AMPTIAC and its twelve sister organizations within the

Defense Information Analysis Center (IAC) Program are already

a c t i vely joined in the campaign to support and improve

Homeland Security (HLS) and Homeland Defense (HLD) (see

sidebar page 24).

The IAC Pro g r a m’s sponsoring organization, the De f e n s e

Technical Information Center (DTIC), recently hosted the 2002

I AC Aw a reness Conference held November 12, 2002 at the

C h e yenne Mountain Re s o rt in Colorado Sp r i n g s ,

C o l o r a d o. The theme of the conference was

“DOD IACs: The Homeland Se c u r i t y

C o m m u n i t y’s Information Ed g e . ”

The conference was open to the

De p a rtment of Defense (DOD),

Federal Government Agencies,

State and Local Governments, and

associated industry re p re s e n t a t i ve s .

The conference served as a forum

for this diverse collection of professionals to explore strategic directions in

Homeland Security and to identify some of the 

scientific and technical needs of the community. The conference

objectives were:

1. To introduce the IACs’ subject matter expertise to NORTHCOM and the HLS community

2. Promote awareness of IAC resources and information within

the HLD/HLS community

3. Reinforce relationships between NORTHCOM, the other

unified commands, the HLD/HLS community, and the

IACs

4. Identify ways in which the IAC Program and IAC resources

can support NORTHCOM and the HLD/HLS community.

The agenda featured a slate of speakers that was a virtual “who’s

who” of senior principals from the DOD and HLD/HLS communities. The outstanding speakers shared their own insights on

the information needs and support requirements of their respective organizations. 

The intro d u c t o ry speaker was Dr. Ronald M. Sega, the

Director of Defense Research and Engineering (DDR&E). Dr.

Sega set the tone for the morning session by discussing the overarching issues of information analysis and dissemination, and

identifying areas of criticality in the support of HLD/HLS initiatives. In his position as the head of DDR&E, he is the chief technical advisor to the Secretary of Defense.

Two keynote addresses we re delive red, the first of which was

p resented by US Army Lieutenant General Ed w a rd G. Anderson

III. General Anderson is the Deputy Commander of the Un i t e d

States No rthern Command (NORTHCOM), which was re c e n tly stood up at Peterson Air Fo rce Base in Colorado Sp r i n g s ,

C o l o r a d o. During his presentation, he outlined the mission of

N O RTHCOM, and specifically discussed the unified comm a n d’s role in Homeland Defense. General Anderson also serve s

as the Vice Commander of the No rth American Ae ro s p a c e

Defense Command (NORAD).

The second keynote address was pre s e n ted by the Honorable James S. Gi l m o re III,

former Governor of Virginia (1998-

2002). The Governor spoke about the

continuing threat of terrorism within

the United States and the nation’s ability to respond to such threats, both in

terms of after an attack and in anticipation of such attacks. Governor Gi l m o re

also provided the most sobering thought of

the conference: he cautioned the part i c i p a n t s

that the zeal for domestic security, if allowed to ru n

unchecked, posed a serious risk to our constitutional libert i e s ,

which in long run would constitute a greater threat than any act

of terrorism. Since 1999, Governor Gi l m o re has served as

Chairman of the Congressional Ad v i s o ry Panel to Assess

Domestic Response Capabilities for Te r rorism In vo l v i n g

Weapons of Mass De s t ruction. Also known as “The Gi l m o re

C o m m i s s i o n”, the panel’s findings we re influential in deve l o ping the Office of Homeland Se c u r i t y.

There were also presentations from the Joint Task Force for

Civil Support Initiatives, the Defense Threat Reduction Agency

(DTRA), the DOD Chem/Bio Defense Initiative, the Federal

Emergency Management Administration (FEMA), and the State

of Colorado’s Office of Emergency Preparedness. 

The thirteen DTIC-sponsored IACs (as well as several other

technical organizations) exhibited their information analysis

capabilities at the conference. Mr. Ron Hale, the manager of the

DTIC IAC Program, gave a presentation on how the IACs can

respond to HLD/HLS needs, both presently and in the future. In

addition, two of the IACs, CBIAC (chem/bio), and SURVIAC

(survivability), gave overviews of their current HLD/HLS support

efforts for both military and civilian authorities.

The IAC Program Rises to Meet the Challenges of Homeland Security and Homeland Defense

In need of vital technical information or analyses? Chances are that one of the IACs can help you! 

For more information on individual IACs, log onto http://www.dtic.mil.

AMPTIAC

CBIAC

CPIA

DACS

HSIAC

IATAC

IRIA

Advanced Materials & Processes

Chemical/Biological Warfare

Chemical Propulsion

Software

Human Systems

Information Assurance

Sensors & Detection

MSIAC

MTIAC

NTIAC

RAC

SURVIAC

WSTIAC

Modeling & Simulation

Manufacturing

Non-Destructive Testing

Reliability

Survivability

Weapons Systems

60 The AMPTIAC Quarterly, Volume 6, Number 4
INTRODUCTION

Most fixed protective structures employ concrete in some way.

The US Army Engineer Research and Development Center

(ERDC) is conducting research to provide force protection in

everything from foxholes to fixed facilities and against threats

ranging from small arms to advanced conventional, and even

terrorist weapons. Concrete is a highly economical material, it

can be cast into many shapes, and can be formulated for varying degrees of strength and durability. It is primarily used for its

compressive strength, as concrete is much stronger in compression than it is in tension. With the proper use of tensile reinforcement, concrete can be used in many tensile-loaded

applications, such as flexural members, eccentrically loaded

compression members, and direct tension members.

Because of the wide use and availability of concrete, it is useful to elaborate on its fundamentals. Ad d i t i o n a l l y, a better

understanding of the complex creation of concrete variants will

assist engineers and architects in choosing the best materials that

a d d ress aesthetic, engineering, and pro t e c t i ve considerations.

ADVANTAGES OF HIGHER STRENGTH CONCRETE AND

ITS APPLICATION TO STRUCTURAL PROTECTION

The variability of concrete’s strength and mass make it a useful

material in structural protection. The mass of a concrete member can be varied by altering its component materials and

geometry. For applications where ample mass is needed, a large

section of normal-density concrete or a smaller section of highdensity concrete can be used. For applications where mass or

size is detrimental, yet strength is necessary, concrete structures

can be designed with thin sections of higher-strength concrete.

Engineers are constantly looking for new materials to provide

answers to complex problems. As construction and material

costs escalate, demand has increased for stronger materials that

occupy less space. Research has been examining high-performance concrete materials for use in protective structures [1-4].

Developments in very-high-strength concrete (VHSC) [5-8], a

material made using conventional constituents combined in

critical proportions, have further expanded these capabilities.

Limitations of Conventional Concrete

Unreinforced concrete is inherently brittle, having very little

capacity for inelastic deformation before failure. It is also very

weak in tension. Under compressive loading, it exhibits linear

elastic behavior until initiation of first cracking of its matrix. As

loading continues above this point, concrete exhibits increased

non-linear plastic deformation for a short time before ultimately failing in a brittle manner.

The unconfined (concrete with no exterior covering such as

a steel sleeve) compressive strength of conventional concrete is

generally less than 41 MPa. Concretes with design strength in

compression greater than 41 MPa are called “high-strength”.

High-strength concrete having design compressive strength of

100 to 125 MPa is available in many areas. The tensile strength

of most concrete generally does not exceed 10% of the compressive strength (i.e. approximately 4 to 10 MPa). VHSC 

does not follow this proportional relationship however, as its

tensile strength is often no higher than 10 MPa. For use as a

protective material, both tensile and compressive strength are

important properties. From a ballistic point of view, they are

important in resisting the cratering and break-up of the 

structure caused by projectile penetration and, in many cases,

detonation of a weapon.

VHSC Principles

VHSC is made from the same general constituents as conventional concrete (cementitious material, water, aggregate, and

additional compounds for removing air and water from the mix

{admixtures}). Yet, the careful selection of constituents and

their proportions, as well as proper mixing, results in significantly improved tensile and compressive strength, toughness

The AMPTIAC Quarterly, Volume 6, Number 4 61

Dr. J. Donald Cargile,

Impact and Explosion Effects Branch;

and

Ed F. O’Neil and Billy D. Neeley,

Concrete and Materials Division;

Geotechnical and Structures Laboratory

US Army Corps of Engineers

Engineer Research and Development Center 

(formerly Waterways Experiment Station)

Vicksburg, MS 
and durability, as well as reduced water permeability. The physical and mechanical properties can be further improved by the

application of heat and pressure during the casting and curing

stages of hydration. The principles used in producing VHSC

are listed in Table 1. Some significant differences from conventional and high-strength concrete are:

• size and composition of constituents

• ratio (by weight) of water-to-cementitious material (w/cm)

• the use of steel fibers (sometimes micro-fibers) to improve

ductility and toughness

• the amount of mixing energy employed

• curing procedures used

Conventional concrete is a very heterogeneous material with

components from fine cement to coarse aggregates, each

exhibiting different strengths and modulii of elasticity. Under a

system of forces, all these component materials deform at different rates. The differential movement of these components

produces strains between the component materials that begin

the process of tensile fracture when the strains exceed the tensile strain capacity of the concrete. Concrete such as VHSC is

composed of particles of similar modulii and size, which helps

increase the homogeneity of the composite material thereby

reducing the differential tensile strain in the concrete and

increasing the ultimate load-carrying capacity of the material.

High density* is the second principle employed to increase

strength and decrease permeability. In choosing the volumes 

of component materials, particle-packing techniques can be

used to maximize the amount of solids per unit volume of concrete. As with conventional concrete, the material having the

largest particle size in VHSC is the aggregate. In VHSC that

aggregate is sand whose particle size is limited to a maximum of

4.75 mm. The material having the next largest particle size is

the cement, which is on the order of 10 to 100 μm. The smallest particles are silica fume, which are on the order of 0.1 μm

in diameter. The component volumes of all these particles are

chosen to achieve the greatest particle packing, and hence the

greatest density of the paste. The higher the density, the greater

the strength of the paste and the lower the permeability because

there are fewer and smaller voids. 

Strength of VHSC is further improved by increasing the volume of pozzolanic components (fine siliceous or aluminous

powders) that can react to form hydration products. In VHSC,

materials with a high silica content are necessary for optimum

performance. Cements that are high in silica content (such as

low-carbon silica fume [6]) produce higher strengths. These

materials provide chemically active silica that helps to produce

larger volumes of calcium-silicate-hydrate (CSH), bonding the

other component materials together. High amounts of CSH

increase the strength of the binder and improve the bond

between the cement and the aggregate.

To optimize performance, the w/cm ratio in VHSC must be

carefully controlled. Excess water in the mixture is detrimental

to the strength of concrete. The quantity of water required to

hydrate all of a given amount of Portland cement is about that

present at a w/cm ratio of 0.4. Water that is not chemically or

physically combined in the hydration or pozzolanic reaction,

weakens the paste and thus the compressive and tensile strength

of the concrete. The volume of water used in VHSC is kept low

to insure that there is no excess. This volume is less than that

needed to hydrate all the cement so as to insure that all water is

consumed in the hyd r a t i o n / p o z zolanic reaction pro c e s s .

However, this small quantity of water usually does not provide

sufficient workability to the mixture. High-range-water-reducing admixtures (HRWRA) are used to make the otherwise very

stiff concrete flowable.

All these mixture principles combine to produce concrete

with an ultimate compressive strength up to approximately 175

M Pa, when mixed and cured at ambient temperature s .

Strengths greater than 200 MPa can be achieved when the concrete is cured at 90°C for a few days. The processes of adding

pressure sufficient to expel any excess liquids and air from the

fresh mixture during the casting operations, and providing a

curing environment of up to 400°C, can produce concrete with

a compressive strength greater than 800 MPa.

Figure 1. Flexural-toughness Comparison for VHSC Concrete vs.

Plain and Fiber-reinforced Concrete.

Table 1. Principles of Very-High-Strength Concrete.

• Improved homogeneity through particle size and

material selection.

• Increased density by optimization of particle size

and mixing technology.

• Improved strength by maximizing reactive materials

and minimizing water content.

• Increased microstructure by application of pressure

before setting and post-set heat treatment.

• Increased tensile strength, toughness, and ductility by

incorporation of steel fibers or steel micro-fibers.

3 Point Bending Test

Plain Concrete

Fiber Reinforced Concrete

VHSC

Loading data based on 150- x 150- x 450-mm beams

280

210

140

70

0

0 0.25 0.50 0.75 1.00 1.25

Deflection, mm

62 The AMPTIAC Quarterly, Volume 6, Number 4
Tensile Properties

The tensile strengths of VHSCs can be higher than those of

c o n ventional concretes. As mentioned pre v i o u s l y, tensile

strength of VHSC may nominally be only 10 MPa, while its

compressive strength is on the order of 180 MPa. The addition

of steel fibers increases the first-crack load, increases the ultimate load-bearing capacity, and dramatically increases the flexural toughness.

Very-high-strength concretes exhibit near-linear stress-strain

characteristics up to failure when fabricated without the addition of fibers. Their fracture energy, defined as the area beneath

the load-deflection curve, is somewhat less than 140 J/m2. The

addition of fibers to the matrix improves the behavior of the

concrete in the post-first-crack region of the load-to-failure

cycle. In VHSC, various percentages and types of steel fibers

have been used but the best overall results (incorporating cost

considerations) have been obtained with hooked-ended, steel

fibers 30 mm in length and 0.5 mm in diameter.

The large number of small fibers which cross the path of

potential cracks, coupled with the good bond between fiber

and matrix, provide high resistance to fiber pullout during tensile-cracking, and greatly increase the toughness of the material. Figure 1 shows the load-deflection curve of a typical VHSC

beam. By comparison, a load-deflection curve for a conventional concrete and a conventional fiber-reinforced concrete are

added. Comparison of the areas under the curves gives a relative relationship for the increase in toughness afforded by the

very-high-strength concrete. The greatest effect is in the area of

the curve beyond the first-crack load, where the sample’s loaddeflection behavior transitions from linear to non-linear. Up

until this load, the tensile-carrying-capacity of the concrete has

been responsible for the shape of the curve. In the unreinforced

concrete, the magnitude of the first-crack load is about onetenth that of the VHSC and the load and deflection of the

post-first-crack portion of the curve is very small. Likewise,

even with conventional fiber-reinforced concrete the first-crack

strength is lower than VHSC and the post-first-crack portion

of the curve is also smaller.

Toughness is a measure of the amount of energy that must be

expended to open cracks in the matrix under tensile loading.

An example of toughness would be the resistance to a projectile

passing through a material. This toughness is important in the

performance of protective structures. The amount of energy

required to penetrate the VHSC concrete will be greater than

that required to penetrate conventional concrete. This means

that some projectiles will be less effective at penetrating the

structure, and perhaps will even be stopped by the VHSC. If

the projectile completely passes through the VHSC, the exit

velocity will be lower than that through the same mass of conventional concrete. Also, the amount of material fragmented

from the back of a protective-structure member as the projectile passes through (also called spall) will be reduced by the 

steel fibers in the VHSC matrix.

Penetration Experiments

Normal impact experiments studying depth-of-penetration

versus striking velocity we re conducted with VHSC concre t e

targets. The experiments evaluated the resistance of VHSC to

penetration by a robust projectile (one that should not

deform significantly). The VHSC mixture pro p o rtions, as

well as those for conve n t i o n a l - s t rength portland cement

(CSPC) concrete, high-strength portland cement (HSPC)

c o n c rete, and high-strength, steel-fiber re i n f o rced (HSFR)

c o n c rete, are given in Table 2. (The mixture pro p o rtions in

Table 2 provide the re q u i red masses of constituents in ord e r

to produce roughly one cubic meter of finished concre t e . )

Table 2. Concrete Mixture Proportions (kg/m3).

Material CSPC HSPC HSFR VHSC*

Type I Portland Cement 328 546 459 24

Silica Fume 0 71 59 13**

Class F Fly Ash 0 119 59 0

Coarse Aggregate 1034 817 520 0

Sand 806 0 451 0

Limestone Fine Aggregate 0 657 469 40

Water 187 166 171 17

Water Reducing Admixture 1.7† 0 0 0

High Range Water 0 12 6 3

Reducing Admixture

Air Detraining Admixture 0. 3 1 0.6 0

w/cm 0.57 0.22 0.3 0.18

Fibers 0 0 158 3

* Mixture proportions for VHSC are given in % by volume.

** In VHSC, 8% is silica fume and 5% is silica flour (crushed quartz)

† Water reducing admixture given in l/m3

Figure 2. Drawing of Armor-Piercing Projectile.

Case Material: 4340 Steel

Mass: 0.906 kg

CG Location: 128.5 mm from nose

242.4 mm

206.8 mm

R = 53.6 mm 26.9 mm

35.6 mm

The AMPTIAC Quarterly, Volume 6, Number 4 63

Table 3. Hardened Material Properties.

CSPC HSPC HSFR VHSC

28-day Compressive 35 104 85 157

Strength, (MPa)

Compressive Modulus 34.5 45.2 45.2 46

of Elasticity, (GPa)

56-day Tensile 3.5 4.8 4.5 9.0

Strength, (MPa)

Tensile Modulus 44 39.5 39.6 –

of Elasticity, (GPa)
The concrete for the targets was placed into corrugated, galva n i zed-steel culve rts measuring approximately 762 mm in

diameter by 914 mm in length. The culve rts we re wrapped in

insulation to maintain heat during curing. Curing of the targets consisted of ponding water on the top of the targets for

7 days and then continuing the curing in ambient conditions

until the time of the penetration experiments. The penetration experiments and at least two unconfined-compre s s i o n

tests on samples of the concrete we re conducted on approx imately the same day. The age of the concrete at the time of

the penetration experiments ranged from 30 to 60 days. 

The 0.906-kg projectiles were machined from 4340-steel

rods and heat treated to a hardness of 43-45 on the Rockwell C

scale. Each projectile had an ogive nose, a shank diameter 

of 26.9 mm and an overall length of 242.4 mm as shown in

Figure 2. At the time of the penetration experiments, the 

targets were placed on their sides, still in the metal-culvert

forms, and centered on the longitudinal axis of the gun. The

projectiles were launched into the targets using the ERDC 

(formally WES) 83-mm, smooth-bore powder gun [9] at striking velocities (Vs) ranging from 229 m/s to 754 m/s.

Depth of penetration (P) in calibers (penetration depth/projectile diameter) for the experiments into VHSC are compare d

to results from penetration experiments into a CSPC concre t e

[10], HSPC concrete [10], and HSFR concrete [11], as show n

in Fi g u re 3. The experiments into the CSPC, HSPC, and HSFR

c o n c retes used projectiles with the same mass and dimensions as

the projectile used for the experiments into the VHSC concre t e .

Target fabrication for the CSPC, HSPC, and HSFR experiments was similar to that for the VHSC concrete except that the

targets we re approximately 1.37 m in diameter. The ave r a g e

unconfined compre s s i ve strengths of the VHSC, CSPC, HSPC,

and HSFR concretes used to fabricate targets in these tests we re

159, 35, 104, and 90 MPa, re s p e c t i ve l y. Typical compre s s i ve

s t rength values for VHSC can be higher, on the order of 185

M Pa, depending on the materials and processing used.

Additional material pro p e rty data are presented in Table 3.

Also in Figure 3, results from the penetration experiments are

compared to depth of penetration which was calculated using a

spherical-cavity expansion model developed by Forrestal and

Tzou [12]. The model separates the target response into elastic,

cracked, and plastic (EKP) regions, with the plastic region

being closest to the projectile. The target is described by

density, yield strength, slope of the yield surface, tensile

strength, and linear bulk modulus. The tensile strength of the

material determines the influence of the cracked region on the

depth of penetration. Values for these model parameters were

determined for each concrete based on referenced data [2, 4,

13]. The results from the cavity-expansion calculations agree

well with the experiment results (see Figure 3).

Another model presented by Forrestal and Tzou separates the

target response into elastic and plastic (EP) regions only. This

model was used to illustrate the influence of the cracked region

on the depth of penetration[12]. Results from the two models

are compared in Figure 4. Use of the EP model results in less

depth of penetration than the results from the EKP model. The

influence of the cracked region is greatest for the higherstrength concretes. Results from the calculation using the EP

model represent a limit to the depth of penetration that could

be expected as the tensile-yield strength approaches the compressive-yield strength.

The depth of penetration from experiments into the HSPC

and HSFR concretes was about 30% less than that from experiments into the CSPC concrete, while the penetration depth

observed in VHSC is about 50% less. So, one could expect

approximately a 50% reduction in penetration by using the

VHSC concrete versus conventional concrete. Post-test photographs of the target faces in Figure 5 show the visible damage

to the targets for experiments at a striking velocity of about 800

m/s. The amount of visible damage to the HSPC concrete 

target is about the same as that for the CSPC concrete target,

even though the depth of penetration is about 30% less. The

Figure 4. Comparison of Calculations Using the Elastic-CrackedPlastic (EKP) and Elastic-Plastic (EP) Versions of the Spherical-cavity

Expansion Model.

Figure 3. Comparison of Penetration Experiment Results and

Spherical-cavity Expansion Model Calculations for CSPC, HSPC,

HSFR, and VHSC Concretes.

Data Model

CSPC

HSPC

HSFR

VHSC

100 200 300 400 500 600 700 800 900

Striking Velocity, m/s

40

30

20

10

0

64 The AMPTIAC Quarterly, Volume 6, Number 4

CSPC

HSPC

HSFR

VHSC

100 200 300 400 500 600 700 800 900

Striking Velocity, m/s

40

30

20

10

0

EKP

EP

EKP

EP

EKP

EP
addition of steel fibers in the HSFR concrete resulted in a 

significant decrease in visible damage, and still resulted in a

depth of penetration about 30% less than the CSPC concrete.

The visible damage to the VHSC concrete target is comparable

to the damage to the HSFR concrete target.

CONCLUSIONS

These new VHSCs are useful for force protection and infrastructures in need of blast and penetration resistance. Their

p e rformance, especially in spall resistance and increased 

deflection without failure, mesh well with design requirements

calling for reduced flying debris in buildings and prevention of

progressive collapse. 

De velopment of this new class of ve ry - h i g h - s t rength conc retes, based on use of small-particle component materials and

p a rticle-packing theories, has led to materials with improve d

penetration resistance. Although the direct-tensile stre n g t h s

remain low at approximately 10 MPa, the compre s s i ve stre n g t h s

of these concretes are ve ry high, near 200 MPa. Ad d i t i o n a l l y, 

the flexural toughness of the concrete is greater than 250 times

that of conventional, non-fiber-re i n f o rced concre t e .

Penetration-resistance experiments conducted on the VHSC

indicated approximately 50% less penetration than into CSPC

concrete, and 30% less penetration than into HSPC and HSFR

concrete. Inclusion of fibers into these concretes does not 

significantly improve the penetration resistance of a given

strength of concrete, but does provide for greater resistance to

visible damage surrounding the penetration crater. Results 

from calculations using the spherical-cavity expansion model

with elastic-cracked-plastic regions agreed well with the 

experimental results.

REFERENCES

[1] J.D. Cargile, and L.E. Tidwell, “Penetration of a Subscale

Semi-Armor-Piercing Projectile into Conventional-Strength and

High-Strength Concrete Targets,” Technical Report SL-93-2, US

Army Engineer Waterways Experiment Station, Vicksburg,

MS. 1993

[2] M.I. Hammons, B.D. Ne e l e y, and D.M. Sm i t h ,

“Development and Characterization of Fiber-Reinforced and SlagBinder Concrete Mixtures for Projectile-Penetration Studies,”

Technical Report SL-92-16, US Army Engineer Waterways

a. CSPC concrete b. HSPC concrete

c. HSFR concrete d. VHSC concrete

Figure 5. Front-face Damage to Targets Impacted at Approximately 800 m/s.

The AMPTIAC Quarterly, Volume 6, Number 4 65
Experiment Station, Vicksburg, MS. 1992

[3] B.D. Ne e l e y, and D.J. Frew, “ De velopment and

C h a racterization of a Hi g h - St rength, Hi g h - Density Nylon Fi b e r

Re i n f o rced and Sl u r ry - In f i l t ra t e d - Mat Concrete for Pro j e c t i l e

Pe n e t ration St u d i e s ,” Technical Re p o rt SL-95-17, US Army

Engineer Wa t e rways Experiment Station, Vicksburg, MS.

1 9 9 5

[4] B.D. Ne e l e y, M.I. Hammons, and D.M Sm i t h ,

“Development and Characterization of Conventional Strength

and Hi g h - St rength Po rtland Cement Concrete Mi x t u res for

Projectile Penetration Studies,” Technical Report SL-91-15, US

Army Engineer Waterways Experiment Station, Vicksburg,

MS. 1991

[5] W.M. Dowd, and E.F. O’Neil, “De velopment of Re a c t i ve

Powder Concrete (RPC) Precast Products for the USA

Ma rket,” in: Proceedings, Fo u rth In t e rnational Symposium on

the Utilization of Hi g h - St re n g t h / Hi g h - Pe rf o rmance Concre t e, F.

de Larrard, and R. Lacroix, eds. Presses de l’École Na t i o n a l e

des Ponts et Chaussées, Paris, FRANCE, 29-31 May 1996, pp

1 3 9 1 - 1 3 9 8

[6] B.D. Neeley, and D.M. Walley, “VHS Concrete,” The

Military Engineer, vol. 87, (572), (1995) 36-37

[7] E.F. O’Neil, “Reactive Powder Concrete: A Very-HighPerformance Concrete Material,” in: Proceedings, Corps of

Engineers Structural Engineering Conference, H.W. Jones, and

B.D. Fehl, eds. US Army Corps of Engineers Engineering and

Construction Directorate, San Antonio, TX. 28-30 August

1995, pp 1195-1204

[8] E.F. O’Neil, and W.M. Dowd, “Reactive Powder Concrete:

A New Material for the Construction Industry,” in: Proceedings,

Third National Concrete and Masonry Engineering Conference,

S.K. Ghosh, ed., National Concrete and Masonry Engineering

Conference, San Francisco, CA. June 15-17 1995, pp 43-50

[9] D.J. Frew, J.D. Cargile, and J.Q. Ehrgott, “W E S

Geodynamics and Projectile Penetration Re s e a rch Fa c i l i t i e s , ”

in: Proceedings, Ad vances in Numerical simulation Te c h n i q u e s

for Pe n e t ration and Pe rf o ration of Solids, E.P. Chen, and V. K .

Luk, eds. American Society of Mechanical Engineers, New

Orleans, LA, ASME Winter Annual Meeting, 28 Nov.-3 De c .

1993, pp 1-8

[10] M.J. Fo r restal, B.S. Altman, J.D. Cargile, and S.J.

Hanchak, “An Empirical Equation for Penetration Depth of

Ogive-Nose Projectiles into Concrete Targets,” International

Journal of Impact Engineering, vol. 15, (4) (1994), 395-405

[11] J.D. Cargile, unpublished experimental results, US Army

Engineer Waterways Experiment Station, Geomechanics and

Explosion Effects Division, Structures Laboratory, 1998

[12] M.J Forrestal, and D.Y. Tzou, “A Spherical CavityExpansion Penetration Model for Concrete Ta r g e t s , ”

International Journal of Solids and Structures, vol. 34, (31-32),

(1997) 4127-4146

[13] S.A. Akers, M.L. Green, and P.A. Reed, “Laboratory

C h a racterization of Ve ry Hi g h - St rength Fi b e r - Re i n f o rc e d

Concrete,” Technical Report SL-98-10, US Army Engineer

Waterways Experiment Station, Vicksburg, MS. 1998

ENDNOTE

* In this discussion, density (or in some contexts “denseness”)

means the relative amount of volume in the freshly mixed 

product occupied by solid particles and not the mass per unit

volume of the product.

Dr. J. Donald Cargile is a senior research civil engineer for the Impact and Explosion Effects Branch of the

Geotechnical and Structures Laboratory at the US Army Engineer Research and Development Center (ERDC).

He has worked at ERDC for over 21 years. He currently conducts research studying the response of geomaterials to the high intensity loadings associated with projectile penetration and explosive blasts. The research

involves both experiments and numerical simulation. Dr. Cargile received B.S. and M.S. Degrees in Civil

Engineering from Mississippi State University and a Ph.D. in Civil Engineering from Purdue University.

Mr. Ed F. O’Neil is currently a research civil engineer for the Concrete and Materials Branch of the

Geotechnical and Structures Laboratory at the US Army Engineer Research and Development Center. His areas

of expertise are in material and structural properties of high-performance concrete and corrosion of metals in

concrete. His recent work has been involved with high-performance concretes comprised of ternary and quartenary mixtures of cementitious materials. Mr. O’Neil received a B.S. Degree in Civil Engineering from

Northeastern University and M.S. Degree in Civil Engineering from Purdue University. He is currently pursuing

a Ph.D. in Civil Engineering from Northwestern University.

Mr. Billy D. Neeley is a research civil engineer for the Concrete and Materials Branch of the Geotechnical and

Structures Laboratory at the US Army Engineer Research and Development Center. He has over 20 years of

experience in applied research on concrete and concrete materials. His areas of expertise include the development and placement of high-performance and specialized concretes. Mr. Neeley received a B.S. Degree

in Agricultural Engineering from Mississippi State University and M.S. Degree in Civil Engineering from Purdue

University.

66 The AMPTIAC Quarterly, Volume 6, Number 4
AMPTIAC Directory

G ove rnment Pe rs o n n e l

TE CH N I CA L MA NAG E R/ COT R

Dr. Lewis E. Sloter II

Staff Specialist, Materials & Structures

ODUSD(S&T)/Weapons Systems

1777 North Kent St., Suite 9030

Arlington, VA 22209-2110

(703) 588-7418, Fax: (703) 588-7560

Email: lewis.sloter@osd.mil

DEFENSE TECHNICAL INFORMATION CENTER

(DTIC) POC

Melinda Rozga, DTIC-AI

8725 John J. Kingman Road, STE 0944

Ft. Belvoir, VA 22060-6218

(703) 767-9120, Fax: (703) 767-9119

Email: mrozga@dtic.mil

AS S O C I AT E COT RS

ORGANIC STRUCTURAL MATERIALS &

ORGANIC MATRIX COMPOSITES

Roger Griswold

Division Chief

US Air Force

AFRL/MLS

2179 Twelfth St., Bldg. 652

Wright-Patterson AFB, OH 45433-7702

(937) 656-6052, Fax: (937) 255-2945

Email: roger.griswold@wpafb.af.mil

ENVIRONMENTAL PROTECTION

& SPECIAL FUNCTION MATERIALS

Dr. James Murday

Naval Research Laboratory

4555 Overlook Ave., S.W. Code 6100

Washington, DC 20375-5320

(202) 767-3026, Fax: (202) 404-7139

Email: murday@ccsalpha3.nrl.navy.mil

DI R E C TO R, AMPTIAC

David Rose

201 Mill Street

Rome, NY 13440-6916

(315) 339-7023, Fax: (315) 339-7107

Email: drose@alionscience.com

DE P U TY DI R E C TO R, AMPTIAC

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201 Mill Street

Rome, NY 13440-6916

(315)-339-7009, Fax: (315) 339-7107

Email: cgrethlein@alionscience.com

TE CH N I CA L IN Q U I RY SE RV I C E S MA NAG E R

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Email: dbrumbaugh@alionscience.com

Alion Science and Te chnology Pe rs o n n e l

AMPTIAC Celebrates Its 6th Birthday

On November 1st, AMPTIAC’s staff took a few minutes out of their busy day to mark the IAC’s

sixth birthday. The six years have flown by, but are replete with accomplishments. We are proud

of our success serving the DOD materials and processes community and look forward to continued service in the future. 

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