Physical Infrastructure: 

Connections

METALS

Using a complementary approach of experimental 

measurements and detailed finite element analysis, we 

will develop more realistic yet computationally efficient 

global models incorporating bridge connection mechanical 

performance for ordinary, extreme, and degraded conditions. 

Due to years of limited investment and maintenance, the U.S. 

transportation infrastructure network (including approximately 

4 million miles of highway, 700,000 bridges, and 120,000 

miles of urban rail) has been pushed to the breaking point, 

and has received a grade of ‘D’ for condition from the ASCE 

in 2009. An estimated $2.2T will be required for remediation 

over the next 5 years, and guidance is needed on prioritization 

of projects and the efficient use of funds. 

Objective

Impact and Customers

• Critical measurement science will be provided to better assess the 

condition of aging physical infrastructure, and guide cost-effective 

strategies for maintenance, repair, and replacement.

• Validated computational tools and abstractions of degraded 

connections to improve the ability of customers to model aging and 

damaged bridges more realistically, permitting better assessment of 

current bridge health, proper selection and placement of sensors, and 

identification of connection damage. 

• Verification of sub-scale testing methods for structural connections, leading into testing methodologies for extreme 

condition testing (e.g., fire, shock loading, corrosion) for use in the bridge community.

• Incorporate more realistic material models for atypical conditions through the development of more robust, yet 

computationally efficient, global models to enable better bridge assessment. These models will require the new civilian 

testing facilities for high-rate ductile fracture and high-temperature testing of structural materials we are developing.

Approach

Materials Science and Engineering Laboratory

The NIST Physical Infrastructure Program will provide the critical measurement science needed to assess the 

condition of aging physical infrastructure and guide cost-effective strategies for its maintenance, repair, and 

replacement. Infrastructure management challenges in the U.S. have received considerable public attention recently 

due to several major structural failures (e.g., 2007 I-35W bridge collapse, 2009 failure on the San Francisco Bay 

Bridge, 2008 water main break in Bethesda, Maryland, 2007 steam pipe rupture in New York City). These failures 

have been costly, and even catastrophic in some instances. Dramatic improvements in condition assessment are 

necessary to prevent future failures, and to rationally prioritize resources. To enable the necessary improvements 

in infrastructure condition assessment, NIST must provide critical mechanical property data, advanced material 

and component models, new calibration services, reference artifacts, and advanced sensor technologies. The 

Infrastructure Connections Program is designed to addresses the first two items in collaboration with the Material 

Reliability Division, which will focus on the latter three items.

855-12-26b
Materials Science and Engineering Laboratory

In this program, we use an integrated 

multi-prong approach in three key areas: 

experimental investigation of the mechanical 

behavior of connections, measurement of 

material properties at extreme rates and 

elevated temperatures, and numerical 

modeling of connections. These efforts will 

build on one another as we move forward. 

Early connection testing will be the basis for 

more complex connection testing, including 

connections degraded from corrosion or 

exposure to fire or shock loading. The 

experimental work will be guided by the 

numerical modeling results that will use 

the high-rate and elevated-temperature 

properties. Impact requires disseminating the 

results into the bridge community; therefore 

extensive outreach was a strategic goal in the 

project’s first year.

Our outreach effort this year included 

participation in two international conferences 

as well as presentation at AASHTO (which 

sets the national specifications for highway 

bridges), and the Transportation Research 

Board (TRB) annual meetings. Multiple 

visits were made to the Federal Highway 

Administration (FHWA), especially the TurnerFairbank Research Center laboratories to 

develop collaborative efforts. We also hosted 

a one-day workshop including FHWA, TRB, 

NTSB, and the U. of Rome. As a result, FHWA 

invited us to collaborate in their full scale 

gusset plates tests, a program arising from the 

2007 I35W bridge collapse. Dr. Duthinh was 

appointed to NCHRP Project Panel C12-85 

“Roadway Bridges Fire Hazard Assessment.” 

Preliminary research on the topic revealed that 

statistics on this issue are very incomplete. The 

panel has selected a contractor to collect more 

complete data, perform numerical modeling 

of fire effects on the most widespread types of 

bridges, assess risks, and propose standards 

for rehabilitating bridges exposed to fire. 

Our experimental and numerical investigation 

of the behavior of bridge connections (bolted, 

riveted, and welded) in both as-built and 

post-service state under various loading 

conditions will be used to assess effects of 

service conditions and abnormal loads on 

performance of the overall structure. We plan 

to perform laboratory mechanical component 

tests of prototypical and salvaged connections 

to determine baseline metrology, and develop 

a numerical model in commercially available 

software. We will use these results to verify 

and validate the numerical model of the tested 

components, and abstract to a simplified 

numerical implementation for an aged 

connection in a complete structural model. 

We hope to collaborate in field testing and 

compare the resulting bridge performance 

with model predictions.

Our experimental connection work started 

by demonstrating the use of our 3-D digital 

image correlation (DIC) system for a reducedscale double-lap bolted connection, Fig 1. 

This helped diagnose problems and required 

corrections for issues with lighting, camera 

angles, and analysis procedures. In FY10 the 

system will be used for the full-scale gussetplate experiments at the FHWA Structures 

Lab. In the future, this project will require 

dedicated laboratory facilities; therefore, 

we are renovating our expanded laboratory 

space.

In our numerical modeling of connections we 

have developed a finite element model (FEM) of 

gusset plates that can accommodate a variety of 

geometries and member stiffness but is simple 

enough to rapidly test many loading conditions. 

We verified it against existing experimental data. 

These efforts, Fig. 2, showed that the Whitmorelength method recommended by FHWA (as 

emergency guidance for state DOT use) for 

load rating of gusset plates is conservative for 

compression and buckling (rating/ultimate ≈ 

60 %), but is less conservative for large initial 

out-of-plane deformations. Also, the stiffness of 

the members framing into the gusset plate and 

the distribution of loads carried by the bolts or 

rivets in the direction of the load path strongly 

affect the gusset plate strength, but the FHWA 

guidelines do not explicitly consider these 

factors. We shared these results directly with 

FHWA and TRB.

Accomplishments

Dat Duthinh

William Luecke

Tim Foecke

Chiara Crosti

Steve Mates

Li Ma 

Mark Iadicola

Metallurgy Division

(301) 975-5703

mark.iadicola@nist.gov

Learn More Publications

Crosti, C. and Duthinh, D., “Buckling of Steel Gusset Plates,” Fifth International 

Conference on Bridge Maintenance, Safety and Management (IABMAS 2010), 

Philadelphia, Pa. July 11-15, 2009, WERB G2010-0307

Fig. 1 Double-lap bolted connection during 

bending. Top: painted speckle pattern; bottom: 

measured positions of elements.

Fig 2 Finite element model of a gusset-plate 

corner after applied loading that resulted in 

buckling of the plate.