No. 40 December 2013

STEEL CONSTRUCTIONTODAY & TOMORROW

http://www.jisf.or.jp/en/activity/sctt/index.html【 t a i 】
“耐 (tai)” in Japanese, or withstanding, resistance in English

This issue, No. 40, features the fire resistanceof steel structures and the advanced fire protection
and fire-resistant design applied to these structures in Japan;
it also discusses an improved approach to theon-site welding of steel structures.

In this issue.....
Special Feature: Fire-resistant Technology
1 Buildings and Fire Resistance
4 Fire Protection for Steel
Structures

6 Fire-resistance Redundancy in
Steel Framing

9 Surveys of Fire Damage ofSteel Structures

Published Jointly by

12 Fire-resistant Design of TOKYO SKYTREEThe Japan Iron and Steel Federation
Japanese Society of Steel Construction

15 Fire-resistant Steel

Steel Application Technology
17 On-site Welding of Steel Structures

Fire Resistance

Buildings and Fire Resistance-Development of Fire-resistant Design in Japanby Mamoru Kohno
Professor, Department of Architecture, Tokyo University of Science
Reasons to Impart Fire Resistance to
Buildings
The frequency of building fires is naturally not very high. And, most buildings neverexperience even one fire during their service
life. However, even while the possibility of afire breaking out is low, once one does occur,
it can cause seriously harmful effects to not
only the building interior but the surrounding area as well. In order to keep such effects
within an allowable range, it is necessary forbuildings to provide specified fire resistance.
Currently, buildings must demonstrate thefollowing capabilities during a fire:(f1) Occupants (persons present in the building)can safely evacuate the building.
(f2) If some occupants cannot evacuate thebuilding themselves, firefighters will beable to search for and safely rescue them.
(f3) Even if all or part of a building were tocollapse, the collapse would not harm surrounding buildings.
(f4) Heat radiating from openings or other structural parts of the building will not cause
fires to break out in surrounding buildings.
(f5) Property incorporated within the building
is protected from the fire.
In order to demonstrate these capabilities, diverse measures are taken-fire prevention, confining a fire to a specified area,and preventing the destruction or collapse ofa building due to heat from a fire. Fire resistance is commonly divided into three performance categories: load-bearing capacity (R),insulation (I) and integrity (E). In order toconfine a fire to a specified area, insulationand integrity are important factors, and toprevent the destruction or collapse of a building, load-bearing capacity plays an importantrole. For example, in order to safely evacuate
a building’s occupants, the structural stabilityof the building, including evacuation routes,
should be secured until the evacuation is finished. Further, in order to restrict a fire fromspreading beyond the fire compartment, insulation and integrity are required for the walls
and floors that serve as the boundaries of thefire compartment.

1 Steel Construction Today & Tomorrow December 2013

Development of Fire-resistant Designin JapanThe structural design work that imparts therequired fire resistance to a building is called
fire-resistant design. This work is conducted
so that the aforementioned three types of performance are appropriately secured for therespective structural sections of a building.
In Japan, the Building Standard Law was enacted in 1950 after the end of the World War
II and, with other building regulations, extensively treats how to promote fire-resistant design. Several revisions have been made to the
Building Standard Law, and the provisions of
the law related to fire resistance prior to therevision in 2000 differ greatly from those after revision.
According to the Building Standard Law,in cases when capabilities (f1) through (f5)above cannot be demonstrated due to a fire
and the resulting effect is severe, the building
should be fire-resistant taking into accountthe use, scale and location of the building.
Prior to the 2000 revision, the only available
measure was to specify that the main structural members, such as the columns, beams,
floors and walls, were composed of fire-resistant members employing incombustible
materials. More specifically, pertaining toload-bearing capacity, it was required thatthe main structural members be composed offire-resistant members and that these members must have the fire resistance times prescribed in Table 1 for the various main structural parts (in addition, it was required for
floors, walls and roofs to have appropriate
insulation and integrity). This approach iscalled design by compliance to prescriptive
provisions.
After its revision in 2000, the BuildingStandard Law incorporated performancebased design as well. Specifically, it prescribes that, in an assumed fire, a fire-resistant building structure be composed of main
structural parts for which the fire resistanceis confirmed to last until the fire is extinguished. As a means to ensure confirmation,
the Law prescribes a fire resistance verification method.
Meanwhile, in future cases where newfire resistance technologies and verification
methods have been developed and put into
application but whose fire resistance cannot
be confirmed using the calculation procedure
prescribed in the Law, it is now possible for
the Minister of Land, Infrastructure, Transport and Tourism to approve their adaptability based on the results of fire resistance

Table 1 Required Fire Resistance Time for Load-bearing Capacity
Uppermost story,
and second to
fourth stories
from theuppermost story

Fifth tofourteenth stories
from theuppermost story

Fifteenth story or
more from theuppermost story

Partition walls(Load bearing)

1 hour2 hours

2 hours

Exterior walls(Load bearing)

1 hour2 hours

2 hours

Columns

1 hour2 hours

3 hours

Floors1 hour2 hours

2 hours

Beams

1 hour2 hours

3 hours

Stories of buildings
Parts of buildings
Walls

Roofs

30 minutes

Stairs30 minutes

Fig. 1 Fire Resistance and Building Standard Law

Method to adapt to the fire resistancerequirements in Building Standard Law

Ministerial
approval
specification

Examplespecification

DTS (deemed to satisfy) solutions
Root A

Fire resistanceverification
methodBuilding

Verification route

Advancedverification
methodPerformance solutions
Route B

Route C
Performance
evaluation
Ministerial
approvalConfirmation

evaluation conducted by an examinationcommittee composed of experts.
Before 2000 only design by complianceto prescriptive provisions could be applied,
except for limited exceptions. Currently, it ispossible to apply performance-based designin addition to design by compliance to prescriptive provisions. (Refer to Fig. 1)
Example of a Large-scale Building
Collapse Caused by Insufficient Fireresistant Design
Even in apparently fine buildings, if the fireresistant design is not adequately executed,
the consequences for the building can be catastrophic. An example of adopting insufficient fire-resistant design which we investigated is introduced below.
A fire broke out at midnight on February 12, 2005 (local time) in a 32-story highrise building (Winsor Building) constructedin the AZCA area of downtown Madrid, thecapitol of Spain. The fire rapidly spread both
upwards and downwards, engulfing nearly
every floor. A large-scale framing collapse
occurred in the middle and upper stories that
resulted in great amounts of curtain walls,

framing members and building containments
being scattered around the area surrounding
the building. The fire was not only disastrous
for the Winsor Building, but it also seriously
affected the ability of the Spanish capitol tofunction by causing both the closure of roadsin the area surrounding the business centerand the suspension of subway operations.
Photo 1 shows an overall view of the damage in the latter part of March, one and a halfmonths after the fire. Most of the building’s
columns, beams, floors and bearing walls
were composed of reinforced-concrete structures, while the columns of the building’s
outer periphery, the end sections of the wide
open office spaces, were made of steel. With
two technical floors located in the middle
and lower stories, the building was structurally divided into a low-rise section (up to thethird floor above ground), a medium-rise section (fourth to sixteenth floors) and a highrise section (seventeenth floor and higher).
Fig. 2 shows the framing elevation, and Fig.
3 the floor plan of the seventeenth to twentysixth floors, including the twenty-first floor
where the fire broke out.
The Winsor Building was completed in

1976 in conformance with the fire resistancestandards of the day. However, as shown in
the photo, the outer periphery of the high-rise
section together with the floor slabs causeda large-scale collapse, and at the same time

Photo 1 Fire damage of Winsor Building, one
and a half months after the fire
December 2013 Steel Construction Today & Tomorrow 2

Fig. 2 Framing Elevation of Winsor
Building
Penthouse story
27th story
26th story

Steel beam

25th story
24th story
23rd story

RC wall column

22nd story
21st story
20th story

Steel column

19th story
18th story
17th story

RC wall beam

T-2 story
16th story

fire has been attained. However, in order toimprove the appropriateness of fire-resistantdesign and its application, R&D will have totake into account the following five tasks:• Understanding the high-temperature properties of various steel products• Development of fire protection that considers application efficiency, durability and environmental concerns• Promotion of framing plans rich in fire resistance redundancy• Development of a standardized testing method that can accurately confirm performance• Structuring of social framework to assess thefire resistance of building as a whole (engineers and evaluators)￭

large-scale collapse. Because the fire brokeout at midnight on a Saturday, when only afew persons were in the building, it was fortunate that no one died.
Toward Further Enhancement of theFire Resistance of Buildings
In this article, we briefly described the needto require fire resistance in building construction, the development of fire-resistant designin Japan and an example of a large-scale collapse of a high-rise building that was attributable to the adoption of an inappropriate fireresistant design. In the fire-resistant designthat currently prevails in Japan, the main goalof realizing buildings that are safe against

RC beam

15th story

Fig. 3 Typical Plan (Upper Stories) of Winsor Building

14th story
13th story
12th story

Steel column

Steel column

11th story
10th story
RC wall column

RC wall column

6285

9th story
8th story
7th story
6th story

Steel beam

RC wall beam

3rd story

RC beam12630

4th story
T-1 story

25200

5th story

2nd story
1st story
0 story

the medium-rise section that sandwiched thetechnical floor was totally destroyed by thefire. In current fire-resistant design, even if
a fire were to break out, it would be confined within a fire compartment, it would not
spread to multiple stories and the columns,
floors and other main structural sections
would not easily cause a collapse.
Because the Winsor Building was designed based on the building regulation standards of the time, fire protection was not provided for the steel columns on the building’s
outer periphery. Further, the connections between the floors and the exterior wall panels, important factors in creating fire compartments between floors, adopted a structurethat easily ignited and allowed the fire to penetrate beyond its area of origin (refer to Fig.
4). In this way, an appropriate fire-resistantdesign was not adopted for the building. Consequently, the fire spread throughout entire
sections of the building, thereby leading to a
3 Steel Construction Today & Tomorrow December 2013

Steel beam

6285

(Spanish indication)

5620

5620

5620

5620

5620

5620

5620

39640

Fig. 4 Section of Perimeter Area of Winsor Building
Glass

Varnished plywood
Metallic panel

Wood-grain printed corrugated board louver
Fan coil unit

Layer closing: Wooden plate 10~20 mm thickGap width: 75 mm

Fire Protection

Fire Protection for Steel Structures
by Shigeki Tasaka
Fire Engineering Lab., General Building Research Corporation of Japan
Outline of Fire Protection
Because fire resistance is not directly imparted to the columns and beams of steel structures, it is necessary to provide fire protection in order to protect a building from fire.
Among the fire protections currently in use
are spraying, coating, wrapping fire protection and formed boards, which are commonly
applied in a single layer or a laminated manner.
However, with exterior wall sections, it
is not possible to create distance between
the exterior wall and the columns or beams,
thereby making it impossible to apply fire
protection to the contact points using only
single-layered or laminated materials. In order to solve this problem, it is necessary totreat exterior wall members as part of the fire
protection system for columns and beams
and this has led to the development of composite methods of fire protection.
In Japan, when applying a specified fire
protection method to a fire-resistant structure, the specified fire protection must satisfy the performance prescribed in the BuildingStandard Law. The specified fire protection
method is tested and evaluated by a designated performance evaluation organization, andministerial approval is given when the fire
protection satisfies the required performance.
The fire protections that have obtained
ministerial approval are publicly listed on thewebsite of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). Table
1 shows the approval number. Of the total
approvals, composite fire protection structures account for nearly half. Further, a total of 35 approvals are given for foam intumescent coatings applied to columns, and 19
to beams.

In Japan, sprayed rockwool and calcium
silicate board are frequently applied in practical fire protection work, and sprayed rockwool and precast concrete board or ALC
panels are frequently used in composite fire
protection construction.
Type of Fire Protection Materials
Ministerial approval by MLIT is given toroughly two types of fire protection.
• Fire protection structures that use singlelayer or laminated material to coat the foursides of column members and three sides(excluding the surface facing the floor) of
beam members• Columns-One surface is protected by theexterior wall and the remaining three surfaces with a single-layer or laminated ma-

Kind of Fire Protection Materials
Fire protection materials can roughly be classified into the following four types:• Sprays and coatings
Rockwool, gypsum materials and cement are

Fig. 1 Example ofComposite
Fire Protection Structure of Steel
ColumnWall panel

Backing
memberConnection
Rib

Reinforcing
memberSteel product

Fire protection

Table 1 Ministerial Approval of Fire
Protection for Steel Structures
Structure

Required fire safety
performance

No. of approval

Of which, approval for
intumescent coating

Column1 hour450

19

2 hours313

16

3 hours229

0

1 hour333

13

2 hours262

6

3 hours

139

0

Beam

terial; Beams-One surface is protected by
the exterior wall, and the remaining two surfaces by a single-layer or laminated material (excluding the surface facing the floor)(Refer to Figs. 1 and 2)
The latter type is classified as a composite
fire protection structure, in which the exterior
walls provide part of the fire protection. The
connection of the exterior wall to the fire protection material is reinforced using a backing material, ribs or reinforcing members toeliminate any gaps.

(Horizontal
section)directly sprayed or coated on the steel product. These materials are commonly applied
while wet. Photo 1 shows an application example of sprayed rockwool fire protection.
• Wraps
Rockwool felt, ceramic wool brackets andother inorganic fiber felts are wrapped aroundthe steel product. These materials are commonly applied dry and are fastened using afastening member. Photo 2 shows an application example of inorganic fiber felt fire proDecember 2013 Steel Construction Today & Tomorrow 4

Fig. 2 Example ofComposite
Fire Protection Structure of SteelBeam

Incombustible material filled in connection offloor and wall

Floor

Steel productBacking
memberReinforcing
Rib member
Fire protection

Wall panel

Connection(Vertical section)

tection.
• Formed materials
Board members such as fiber-mixed calcium silicate board, gypsum board and wooden board are attached or pasted to the steel
product. These materials are commonly applied dry and are fastened using a fastening
member or an adhesive agent. Photo 3 shows
an application example of fiber-mixed calcium silicate board.
• Intumescent coatings
The top coat and a base coat of foamed coating material are directly applied in a laminated state to the steel product. Photo 4 shows
an application example of foamed intumescent coating.
♦♦♦♦♦Among other fire protection materials arethermal-expansion sheet members and moisture aluminum packs. In addition, fire protection consisting of multiple materials is available.
￭

Photo 1 Application example of spray rockwool fire protection

Photo 3 Application example of fiber-mixed calcium silicate board fire protection

Photo 2 Application example of inorganic fiber felt fire protection

Photo 4 Application example of foamed intumescent coating

5 Steel Construction Today & Tomorrow December 2013

Fire-resistance Redundancy

Fire-resistance Redundancy in Steel
Framingby Kenichi Ikeda
Professor, Center for Fire Science and Technology, Research Institute for Science and Technology,
Tokyo University of Science
Concept of Redundancy in Steel Framing during a Fire
The assessment of framing redundancy during a fire differs from room-temperature assessments, and thus it is necessary to examine the external forces at work during a fire
and the changes in strength characteristicsof the structural members that these forces
cause.
The first factor to be taken into account inan examination of the working external forces is that a fire breaks out in one part of abuilding. Fig. 1 shows the differences in theexternal forces dealt with in fire-resistant design and seismic design. The Earth’s gravitational load works vertically throughout
an entire building structure; and, during anearthquake, the ground vibrates and the resultant seismic energy also works not only
on the foundation but on the entire building
structure as well. On the other hand, becausea fire generally breaks out in only part of abuilding and is extinguished before spreading
through the entire building structure, temperature loads caused by fires work on only partof a building. Accordingly, the temperatureof structural members located in the space
where a fire breaks out will rise, but members located in sections untouched by the fire
will not be affected.
Another factor to be taken into accountwith regard to the strength characteristics
of structural members during fire is that thetemperature of these members rises due tothe heat, and as the temperature of a member rises, it not only loses strength and rigidity but experiences thermal expansion as well.
Fig. 2 shows a concept rendering of the behaviors of building structures during a fire.
The structural framing undergoes deformation due to the thermal expansion that occurs
in the members in the early stages of the fire.
While the length of columns normally approximates the height of the floor, the lengthof the beams used in steel framing is several
times the column length. Naturally the thermal expansion of the beams is significant
during a fire. The thermal expansion of thebeams occurs in the axial direction, but theFig. 1 Difference of External Force between Fire-resistant Design and Seismic
DesignFire-resistant design:Part of structure is
subjected to fire heat

Seismic design:
Entire structure is
subjected to vibration

Fig. 2 Concept for Behaviors of Building
Structures during FireFire
heating

Rise of steel
membertemperature

Reduction ofmaterial strengthand rigidity

Thermalexpansionof member

Frame condition during fire

Reduction ofmember strengthand rigidity

Change of stressdeformation condition of member
December 2013 Steel Construction Today & Tomorrow 6

resistance of the columns restricts the thermal expansion, thereby providing bending
rigidity that easily causes flexural deformation in the columns. Accordingly, an important factor in examining frame stability during a fire is the total length of the beams usedin one layer. Then, because the beams progressively lose rigidity as the temperature rises, they start to undergo deflection due to thevertical load. At the same time, the columns
suffer strength reduction due to the effect of
the heat from the fire.
At this stage, in common framing structures, even when a group of members located in the section where a fire breaks out
lose their strength, the surrounding members that stand outside the area of the fire retain their strength and thus are able to redistribute the stress and prevent a total framing
collapse. Fig. 3 shows an image of the stressredistribution. In the framing shown in the
figure, even if a fire breaks out on the lower
floor and causes some of the columns to lose
strength, the axial forces previously borneby these columns is borne by the framing of
the upper floor through stress redistribution,
thereby preventing the frame from collapsing. In cases when the columns and beams
are rigidly joined, stress is easily redistributed. Further, in cases when multiple numbersof beams are installed on the upper floor andthere exists an allowance in the sum of thebending strength of these beams, the possibility of frame collapse is further reduced.
Because seismic resistance is required forapproval in building construction in Japan,
rigid joining is commonly adopted for beamcolumn connections. Further, in order totreat the horizontal force caused by an earthquake, columns and beams are provided withstrength exceeding that needed to support thevertical load. Generally there will be somefires after an earthquake, but during an earthquake violent fires that threaten the structural stability of buildings do not occur. On theother hand, when violent fires break out thatthreaten the structural stability of buildings,
it is extremely unlikely that an earthquake
will occur during a fire that is capable ofthreatening the structural stability of a building. Accordingly, the increased strength provided to handle seismic forces serves to enhance the safety factors designed to prevent
framing collapse during a fire. It is generally accepted that buildings constructed with a
specified seismic resistance have higher fire
resistance, and therefore have high framing
redundancy vis-à-vis fires.
Performance-based fire-resistant design
7 Steel Construction Today & Tomorrow December 2013

Fig. 3 Image of Stress Redistribution in Framing

Even when theaxial-direction force of thecolumn at the lower floor
is lost due to fire, thebeam just above the lower
floor transfers the force tothe right- and left-side
frames due to beam’s
shear strength.

Fig. 4 Condition of Framing when Part of Structural Members Lose Their
Strength due to Fire (Indication by increasing deformation magnification)

is practically applied by actively taking into
account the redistribution of stress in framing during fires, as mentioned above. In suchcases, it is necessary to examine fire resistance by taking into account not only the final fire conditions but fire development as
well. In recent building construction, planar and vertical frame composition has become more complex, and in some cases theframing type proper has become complex. In
such cases, it is necessary to prepare a framing plan that considers the stress deformation
conditions during a fire from the perspectiveof secular change as well.
Example of Fire-resistant Design Capitalizing on Redundancy
Fig. 4 shows an example of fire-resistant design that takes full advantage of framing redundancy during a fire. The building is composed of mega-framing that adopts diagonal
columns at the outer periphery of the building. Loss of strength in the horizontal structural members, such as beams, will lead tocollapse and falling of floors; therefore, it isnecessary to provide fire protection to thesemembers so that structural strength during afire can be retained. Even if vertical members such as columns lose strength, the stressborne by these columns can be redistributed to the diagonal columns that compose themega-framing.
This design example allows the elimination of fire protection for some columns byexamining and confirming stress redistribution. The examination, in addition to studying fire development, confirmed two stressconditions: stress in the peripheral frame
caused by thermal expansion in the columns;
and stress in the peripheral frame caused byloss of strength in the columns. Fire-resistant design, as applied in the case of megaframing, is becoming frequent because it iseasy for the corresponding columns to redistribute stress to the diagonal columns having
high strength.

The use of such fire-resistant design guarantees the fire resistance of the framing of common buildings during a fire. However, whilestrength at the member level during a fire
may have been confirmed, there are cases inwhich a building suffers total collapse triggered by thermal expansion in the structural members of neighboring buildings during
a fire-like the collapse of building WTC7 at
the World Trade Center. In the structural design of steel-frame buildings, it will be necessary to work out a structural plan that takes
into account structural redundancy during a
fire.
￭

Toward Enhanced Redundancy during Building Fires
For common buildings, “member-level” fireresistant design is adopted whereby the fire
resistance of the entire frame during a fire issecured through securement of the fire resistance of the building’s structural members.

Full view of Shimizu Institute of Technologyof Shimizu Corporation, where R&D is being
promoted toward further improvement of fire
resistance of buildings (photo courtesy: Shimizu
Corporation)

December 2013 Steel Construction Today & Tomorrow 8

Fire Damage Surveys

Surveys of Fire Damage of Steel
Structures

by Kenichi Ikeda
Professor, Center for Fire Science and Technology, Research Institute for Science and Technology,
Tokyo University of Science
Concept for Fire Damage Surveys
Fire causes localized damage in a building
due to the heat of the fire. Because the damage occurs in only part of a building, buildings subjected to fire damage are frequently
reused. In order to reuse such buildings, it isnecessary to understand the level of fire damage and, further, to confirm whether or not
the damaged building can tolerate reuse.
A fire damage investigator diagnoses thelevel of fire damage and proposes from anengineering aspect what kind of repairs andmeans of reinforcement are required to facilitate the reuse of a damaged building. The
target performance to which a fire-damagedbuilding should be restored is decided by thebuilding owner and/or building administrator, and its users.
If the target building is to be restored toprevious levels of use, the agreed upon performance at the contract stage must stipulate
complete restoration. On the other hand, incases when the service life of the building isin decline and the building is scheduled forreconstruction in the near future, it is feasible
for the structure’s target performance to besettled at a level sufficient to remain in service for only a few months. In most cases,
the settled target performance is functionallyequal to pre-fire levels. With its main focus
on targeted performance, the Architectural
Institute of Japan has prepared “Guidelines
for the Diagnosis of Building Fire Damage
and Repair and Reinforcement Methods andCommentary” (draft).
Flow of Fire Damage Surveys
Fig. 1 shows the workflow from the fire damage survey to the repair/reinforcement work.
A fire damage survey is composed of the following three parts:• Preliminary survey: Collection of information
about the damaged building from drawings andinformation about the fire from newspapers
and other media prior to visiting the fire site
• Primary survey: Visual on-site survey of thefire conditions• Secondary survey: Implementation of tests
on the structural members extracted from the
9 Steel Construction Today & Tomorrow December 2013

damaged building, if necessary
Based on the survey results, the range andlevel of damage due to fire are diagnosed.
Then, plans for repairs and reinforcement
are worked out based on the fire damage diagnosis. At this stage, settlement is reachedFig. 1 Flow from Fire Damage Survey
to Repair/Reinforcement Work
Fire damage survey

Preliminary survey

Primary survey

Secondary survey

Fire damage diagnosis

Repair/reinforcement plan

Settlement of recovery target

Settlement of
repair/reinforcement range

Selection of
repair/reinforcement method

Repair/reinforcement work

regarding the target performance to be recovered, the method of recovering the performance is selected, and the repair and reinforcement works are implemented.
Figs. 2 and 3 show the workflow in judging the level of fire damage in steel-structure buildings. In the case of surveying steelstructure buildings, not only the loweringof material strength due to fire heat but also the deformation of members and frames
due to thermal expansion greatly affect judgments regarding reuse. Accordingly, estimating the heated temperature of the steel-frame
members and measuring the deformation ofthese members compose the main tasks infire damage surveys.
Estimating the heated temperature of thesteel structural members is made in order toassess the changes in the material characteristics of the steel frame members targeted
for reuse. Changes in the mechanical properties of high-strength steel products and highstrength bolts, whose strength is enhanced
during the manufacturing process, occur
at comparatively low temperatures. Evenamong steel structural members that are barely affected by the heat of a fire, some members suffer large deformation due to the thermal expansion of other steel members. For
steel-structure buildings, the heated temperature and member deformation are surveyed
to diagnose the fire damage.
￭Fig. 2 Workflow of Steel-frame Repair and Reinforcement Based on Estimated Heated Temperature

START

Estimated heatedtemperature:
300°C or moreNo

Increased fastening of
high-strength bolt

Estimated heatedtemperature:
500°C or more

No

Yes

Estimatedheated temperatureaccording to survey:
720°C or more

Repair andreinforcementof connection

No

Yes

Replacement ofhigh-strength bolt set
or welding repair

No
Material test for
high-strength
bolt

Whether or notrecovery target issatisfiedYesIncreased
fastening of
high-strength
bolt

Yes

No

Satisfaction ofrecovery target
in the building
condition as it is“Repair/reinforcement or replacementof structural member” and“replacement of bolt set” or “reinforcementof entire framing”

No

Yes
Repair and reinforcement of connection

Yes

Satisfactionof recovery target
in the building
condition as it isNo“Replacement of structural member andhigh-strength bolt set” or“reinforcement of entire framing”

Yes
Repair and reinforcement of connection

END

December 2013 Steel Construction Today & Tomorrow 10

Fig. 3 Workflow of Steel-frame Repair and Reinforcement Based on Deformation

START
Survey of deformation of member and frame
Examination of structural member
Yes

Member deformation
satisfies recovery target
No

Examination of member from aspect of structural design including
resettlement of recovery target (including steel product material test)
The “recovery target for member deformation”
denotes the allowable amount of numericalvalues pertaining to column collapse and beam
deflection, and the “no occurrence”
pertaining to entire buckling, local buckling and torsion.

Examination
result satisfies
recovery target

Yes

No
No

Reinforcement
can be applied from
aspect of structuraldesignYes

Examination of
replacement of member

Examination ofreinforcement method

Examination of framing

Yes

Frame
deformation satisfies
recovery target

The deformation of framing denotes“collapse of entire frame” and“warping of entire frame.”No
Examination of frame from
aspect of structural design including
resettlement of recovery target

Examination
result satisfies
recovery target

Yes

No
No

Reinforcement canbe applied from aspectof structural design
Yes

Examination ofdemolition

Examination ofreinforcement method

Replacement of member and frame, decision of repair/reinforcement method

END
Reference“Guidelines for the Diagnosis of Building
Fire Damage and Repair and Reinforcement
Methods and Commentary” (draft), Architectural Institute of Japan, February 25, 2010

11 Steel Construction Today & Tomorrow December 2013

Fire-resistant Design

Fire-resistant Design of TOKYO SKYTREEby Tomoyuki Someya, Structural Design Dept., Nikken Sekkei Ltd.
The TOKYO SKYTREE® is a freestanding
broadcasting tower that opened in May 2012
in Tokyo. It has a maximum height of 634
m, and serves primarily as both a broadcasting tower and an observatory tower. According to the provisions of the Building Standard
Law, the tower is classified as a building in a
structure (Fig. 1). The building comprises a
low-rise section with commercial zones anda tower section centered on the observatory.
When a fire breaks out in a building, thefirst priority is to see that all visitors are safely evacuated. A subsequent concern is that aflashover might easily lead to total structur-

al collapse, depending on the scale and location of the building. It is the role of fire-resistant design to prevent this type of building
collapse.
In fire-resistant design, it is importantto factor in the possibility of such flashover
events. Fires that affect a building are classified according to whether they occur insideor outside the building. In the design of TOKYO SKYTREE, both internal and externalfire events were assumed, and appropriate
fire protection and other means were provided to prevent structural instability in the tower if a fire were to occur.

Fig. 1 Classification as a Building in a Structure, and Tower and Lowrise Sections of TOKYO SKYTREELegendTower section
Low-risesectionLegendBuilding section
Structure section

Tembo Galleria

Tembo Galleria

Tembo Deck

Tembo Deck

Tower section

Fire-resistant Design peculiar to theTOKYO SKYTREEThe fire-resistant design adopted for the tower is sufficiently safe against all assumed potential fires that require legal considerations.
In addition, because of the tower’s importance and its gigantic size, the fire assumptions included in the fire-resistant design surpass the legally required levels, making thebuilding fully prepare for the worst.
One of the fire assumptions that surpass
conventional levels pertains to urban fires.
An urban fire is assumed to be a conflagration that engulfs the area surrounding a building. As introduced below, the fire-resistantdesign adopted for TOKYO SKYTREE will
not allow structural problems even in such a
critical state.
A unique structural feature peculiar to
TOKYO SKYTREE is the “glass floor” installed on the Tembo (observation) Deck,through which visitors can look directly below them. If the glass floor were to fall out
due to a fire, it could cause serious damage
in the surrounding area. In order to prevent
such an accident, a fire resistance test was
conducted by heating a full-scale glass floor
model in a furnace to probe whether or not it
could withstand the prescribed fire. The test
confirmed that no problem would arise, as introduced below.
Proving the Fire Resistance of theTower Section during an Urban FireThe first thing done when considering an urban fire is to estimate the incombustibilityof the buildings in the target area and then,based on the obtained incombustibility rate,estimate the intensity of fires that might occur in the neighborhood of the building site.
Wind velocity and other factors are used to
calculate the heated temperature of the section of the tower, and the framing stability at
the calculated heated temperature is proven.

Low-risesectionWest yard

Tower yard

Classification as abuilding in a structure

East yard
Classification as tower
section and low-rise section

December 2013 Steel Construction Today & Tomorrow 12

Fig. 2 Model to Calculate Heated Temperature due to Assumed Fire and Analytical Example (Wind velocity: 0.5 m/sec)
Section in which
temperature rises highest

Medium windvelocityWind and fire
spreading direction

Height (m)Weak wind velocity

Strong wind velocity

Distance up to
structure center

Air current temperature at therear side of tower
peripheryAir current temperature justin front of tower periphery

Section in fire spreading(Fire spreading floor depth D)

Fig. 2 shows the model used to calculate the heated temperature caused by the assumed fire and the corresponding analyticalexample. Fig. 3 shows the approach to prove
the structural stability of the tower framing against the assumed fire. Even when assuming an urban fire, the respective structural members remain under their elastic limit,
and the structural stability of the tower is retained.
Outline of the Fire Resistance Test for
the Glass Floor
Fig. 4 shows the location and a cross sectional view of the glass floor. The lower section of the floor is for exterior use, and theupper section for interior use. In an internalfire emergency, the upper section would suffer direct exposure to the fire. The fire resistance test was conducted by inserting a fullscale model of the glass floor for interior use
into a heating furnace. Photo 1 shows the test
specimen. A loaded heating test was adopted in which the specimen was heated with aweight placed upon it. Meanwhile, the five
white cylindrical members shown in Photo 1
are the fire-resistive covering of the deformation measurement jig.
Photo 2 shows the specimen under heating. While the assumed duration of the fire
inside the building is 36 minutes, a standard
one-hour period of heating was applied in thetest. Photos 3 and 4 show the specimen after
heating. Even in a loaded heating test with afire duration longer than that of an assumed
fire inside the building, cracking occurred inonly the two upper layers of the 4-layer laminated test piece, confirming that the glass
floor would show sufficient safety during afire.
￭

Temperature (°C)

Fig. 3 Proving of Structural Stability of Tower Framing against Assumed Fire
(Concept of Thermal Expansion and Image to Calculate Inter-story Drift)from height-direction
temperature distribution
Width

Setting as the representativevalue for widthSide close to urban fire

Side distant from urban fire

Side radiated from fire source
Concept for thermal expansion range in forecasting tower framing deformation

In the case in which only the left
side is heated and undergoes
thermal expansion

Method to calculate horizontal displacement
13 Steel Construction Today & Tomorrow December 2013

Steel temperature just in
front of tower periphery withconsiderations to radiation
heat from urban fireFig. 4 Location of Glass Floor and Assumed Test Specimen

Fire room
Glass floor unit

Photo 2 Test specimen in heating (from observation window of test furnace)Heat-resistant tempered
glass (thickness t: 12)
Heat-resistant tempered
glass laminate (thickness:
12+12+12)

Range for which test
specimen was prepared

Push rod (SUS FB-5x50)
Photo 3 Test specimen after heating

Photo 1 Test specimen

Photo 4 After heating (two upper layers were removed toconfirm no cracking of third layer of glass laminates)

December 2013 Steel Construction Today & Tomorrow 14

FR SteelFire-resistant Steelby Committee on Fire Prevention and Fire Resistance
The Japan Iron and Steel Federation
The Building Standard Law of Japan prescribes that special buildings (apartmentbuildings, hotels and the like) that are usedmainly by many and unspecified persons
and buildings that are located in urban areas
should be of fire-resistant construction. In a
fire-resistant structure, it is obligatory thatthe columns, beams and other major structural sections meet certain fire-resistant specifications or that the fire resistance of thesestructural members be confirmable by meansof calculation.
One of the means to satisfy certain fire
resistance specifications in the first option
above is to provide fire protection so that thetemperature of steel products during a fire
does not rise. Because the temperature of afire is generally around 1,000°C, it has conventionally been necessary to add fire protection to general steel that is heat-insulated towithstand temperatures up to 350°C. However, with fire-resistant (FR) steel, the heat insulation is adequate up to 600°C, which allows for a significant reduction in the use offire protection. In addition, in cases where
the fire conditions and building design conditions during a fire keep the temperature of
the steel products below 600°C, FR steel canbe applied without fire protection. That is,
the application of FR steel lowers construction costs, reduces construction time and allows for more effective use of indoor space.

Excellent High-temperature
Properties of FR SteelThe high-temperature resistanceof FR steel has been greatly enhanced by the addition of appropriate amounts of alloying
elements such as Mo, Nb andCr and by controlling the heattreatment conditions. The hightemperature yield strength of
FR steel has been improved bymeans of the precipitation andstrengthened distribution of carbon nitrides, and by strengthening the solution treatment of thealloying elements. Among thefeatures of FR steel are:• High-temperature strength is excellent, and the yield strength
at 600°C (0.2% offset) is morethan 2/3 that of the specified
room temperature value.
• The room temperature properties conform to the specifications
for numerous kinds of structural steel products.
• Weldability is similar or superior to that of general steel.
Among the related standards
that specify the high-temperature properties of steel products is ASTM A 1077 (Standard

Fig. 1 Temperature Dependency of High-temperature Yield
Strength

Example of application of FR steel in open-type multi-storiedparking garage

Fig. 2 Temperature Dependency of High-temperature
Young’s Modulus

600
TS

General steel

Young’s modulus (N/mm2)

Strength (N/mm2)

500
400

YS

300
200

FR steel

100
0

FR steel

General steel
0

200

400

600

800

Temperature (℃)
Temperature (℃)
15 Steel Construction Today & Tomorrow December 2013

Member Properties of FR SteelA loaded heating test was conducted to confirm that the high-temperature properties of
FR steel remain intact when used as columns,
beams and other structural members, an outline of which is introduced.
The test method adopted was the loaded heating test for columns prescribed in
ISO834. The test was conducted using alarge-scale fire resistance test furnace forcolumns at the Building Research Institute of
the Ministry of Land, Infrastructure, Transport and Tourism. The FR steel test specimen
was H-300×300×10×15 with a length of 3.5m (Fig. 3). Blanket-type fire protection wasused with the specimen. Meanwhile, another specimen using ordinary steel of identicaldimensions was also tested for a comparisonof their properties. Fig. 4 shows the relation
between the heating time and the steel product temperature. The time up to the collapseof the FR steel column is longer than for thegeneral steel column, and the temperature of
the FR steel column at which collapse occurred is higher. It is understood from thefigure that even when used as a structuralmember, FR steel demonstrates better higher-temperature properties than general steel
does.
Joining Materials for FR SteelIn the welding of structural members made of
FR steel, the welding materials are preparedexclusively in order to secure a high-temper-

Fig. 3 Outline of Fire Resistance Test

500
500

3,800

1,400

Measurement position for steel
product temperature

1,400

Thermocouple

H-300x300x10x15

Fig. 4 Relation between Heating Time and Steel
Product Temperature
1000

800
Temperature (℃)

Material Properties of FR Steel
Fig. 1 shows a comparison of the temperature dependency of high-temperature yieldstrength between FR steel and general steel.
While the yield strength of general steel declines around 350°C to 2/3 the specified value at room temperature, that of FR steel remains at 2/3 or more until the temperaturesurpasses 600°C, which demonstrates thesuperior high-temperature properties of FR
steel compared to general steel. Fig. 2 shows
a comparison of the temperature dependencyof the high-temperature Young’s modulus between FR steel and general steel. The declineof the modulus at 550°C~700°C for FR steel
is smaller than for general steel.

ature strength for the weldsthat is similar or superior to that of the base metal. The characteristic properties of weld joints madeusing welding materials for
FR steel are similar or superior to those of general steel, and the high-temperature tensile strength of
the weld joints is also similar or superior to that of thebase metal.
Further, in the highstrength bolt joining ofmajor structural sections
employing FR steel, thehigh-strength bolts used
for FR steel are designed
to secure a high-temperature yield strength for thebolt joints that is similaror superior to that of thestructural members. Torshear-typehigh-strength
bolts, high-strength hexagonal bolts and galvanized bolts, respectively,
are available for use with
FR steel, and are used forbolt joining in the samemanner as for conventional steel. Fig. 5 shows an example of the tension test
results for the base metal
used in high-strength bolts.
Test results show that highstrength bolts for FR steel
are fire resistant at 600°C,
about twice as high as highstrength bolts for conventional steel.
￭

600

400

Average temperatureof FR steel
Average temperatureof general steel
Average temperatureinside test furnace

200

0

0

20

40
60
80
Heating time (min.)

100

120

Fig. 5 Results of Tension Test for High-strength
Bolt Material
1200

TS

1000

YS
Strength (N/mm2)

Specification for Structural Steel with Improved Yield Strength at High Temperature
for Use in Buildings) that was issued in April
2012. This standard requires advance confirmation from the respective steelmakers as towhether or not they can produce steel in conformance with the standard.

800
600
400

FR steel bolt
material

200
0General steelbolt material
0

200

400

600

800

Temperature（℃）

December 2013 Steel Construction Today & Tomorrow 16

Steel Application Technology

by Tadao Nakagomi
Professor, Department of Architecture
Shinshu University
For Japan with its frequent great earthquakes, seismic design isvery important. Further, there are cases in which welds can become the starting point of fractures that lead to the collapse ofsteel structures. In the No. 37 issue (December 2012), basic details about welding and welding control in steel-frame building structures and information regarding the key dynamic performance characteristics of welds were introduced. The current
issue introduces a discussion about on-site welding, mainly the
problems that occur in on-site welding and appropriate countermeasures.
On-site Welding
In the welding of steel-frame structures, two methods—shop
welding (non-scallop method) and on-site welding (scallop method)—are used. In Japan, shop welding is more extensively adopted. Figs. 1 and 2 show examples of both shop and on-site welding. In the scallop method, the inward preparation of the grooves
allows welding to be done both on the construction site and in the
shop; and, the backing metal is attached outside the members. On
the other hand, in the non-scallop method, the grooves are prepared outward, which means that welding can be applied only ina flat position and that this method, therefore, cannot be applied at
Fig. 1 Shop Welding Non-scallop

Measures to Improve Deformation Capacity
As mentioned above, in on-site welding, strength and deformation capacity decrease. Therefore, it is necessary to take appropriate measures to improve the deformation capacity, three methodsof which are introduced below. Tests were conducted to confirm
the effectiveness of these measures. Fig. 3 shows the shape andinstallation position of the test specimens, Table 1 shows the test
results, and Figs. 4, 5 and 6 show the relation between the load
and the displacement of the on-site scallops.
Fig. 3 Test Specimen Configuration and Installation(Distance between jigs)-On-site Welding-the construction site. In addition, in this method the backing metal is attached inward.
In the construction of giant structures where it is difficult toadopt the non-scallop method, which requires that the shop-welded structural members be transported to the construction site, thescallop method is adopted because it does permit on-site welding. However, in cases when a steel-structure building is subjected to large external forces, such as seismic forces, the strengthand deformation capacities of the on-site scallop welding method, which produces sectional defects (scallops) at the web, fallmuch lower than those of the shop-welding non-scallop method
because the stress concentrates at the scallop bottom.

(Distance between column pin supports)

Basic Details about Welding
and Welding Control

Web(Distance to loading point from column face)(Distance between column and beam pin supports)

Diaphragm

FrangeFig. 4 Load-Displacement
Relation of On-site
Welding Scallop

Fig. 5 Load-Displacement
Relation of On-site
Welding Scallop
1500

Fig. 2 On-site Welding

G_S (On-site welding type)
P(kN)

1200
900
600

Web

300
0
-300
-600

Diaphragm

Frange

-900
-1200
-1500
-350 -300 -250 -200 -150 -100 -50 0

17 Steel Construction Today & Tomorrow December 2013(mm)

50 100 150 200 250 300 350

Fig. 6 Load-Displacement Relationof On-site Welding Scallop
200• Method to Provide Reinforcement Bead to Scallop
BottomIn order to improve deformation capacity, this method aims at relaxing the stress concentration by providing a reinforcement beadto the scallop bottom, which would be the starting point of a fracture in the non-scallop method. Fig. 11 shows the reinforcement
bead, and Fig. 12 the relation between the load and the displacement. Meanwhile, the size of the test specimen was similar to thatused in the two methods mentioned above, but the test method
differed from the above two, and a 3-point bending test was adopted.

SW (On-site welding type)

P(t)

150
100
50
0
-50
-100
-150

Fig. 11 Reinforcement
Bead

(mm)

-200
-80

-60

-40

-20

0

20

40

60

80

• Drilled Flange Method
This method aims at distributing the stress in column-beam welds
to holes drilled in the flanges so as to reduce the stress at the beam
end. Fig. 7 shows the configuration of the drilled flange and Fig. 8
shows the relation between the load and the displacement.

Fig. 12 Load-Displacement
Relation of Reinforcement Bead200

SW-100 (Reinforcement bead)

P(t)

150

100

Reinforcement-bead

50

0Fig. 7 Drilled Flange
398

86

92

Fig. 8 Load-Displacement
Relation of Drilled
Flange

98

-50

-100

φ 4 3φ 4 6 φ 4 9 φ 5 2
50 100 50
200

BackingPlate

-150
(mm)

-200

• Flange Width Enlargement Employing a HaunchThis method aims not only at reducing the stress occurring in the
beam end by means of widening the flange sectional area attainedby enlarging the beam connection width but also at transferring
the position of maximum stress to the beam base metal. Fig. 9shows the haunch, and Fig. 10 the relation between the load andthe displacement.
Fig. 9 Haunch

Fig. 13 Calculation of Skeleton Curve

Fig. 10 Load-Displacement Relation of
Haunch

200
75

75

300
22 5

Method to Calculate ηs
Fig. 13 shows the general P-δ relation of a steel structural member subjected to cyclic bending. The skeleton curve corresponds
to a loading sphere that surpasses the maximum strength so far
demonstrated by the steel member. Because it is shown in existing research that the area produced by joining together the skeleton curves is equivalent to the P-δ curve of a member subjected tomonotonous loading, the skeleton curve can serve as an appropriate parameter in assessing the deformation capacity of a member
subjected to random external forces such as seismic loads. The
accumulated plastic deformation magnification ηs is used as theparameter for the deformation capacity and is obtained by dividing the value found by doubling the elastic limit distortion energy (Ws) of the absorbed energy in the skeleton curve by (cPp×cδp).

BackingPlate

200
350

1500

P(kN)

C_HC Horizontal haunch method

1200

75

900

R7

600

5
300
0
-300
-600
-900

Skeleton curve

-1200
-1500
-350 -300 -250 -200 -150 -100 -50 0

Elastic unloading section(mm)

50 100 150 200 250 300 350(Continued overleaf)
December 2013 Steel Construction Today & Tomorrow 18

Improved Deformation Capacity in On-site Welding
As can be seen in Table 1, the test results show that, while the deformation capacity of conventional on-site welding is low: 1~4,
the deformation capacity of an on-site welding method provided with the measures mentioned above is sufficient: 7~12. Further, it can be understood that while the deformation capacity ofthe shop-welding non-scallop method is 6.9, the on-site scallop
method can offer a deformation capacity similar or superior to theshop-welding non-scallop method by providing the measures introduced above.
￭

Table 1 Test Results
Test specimen Loading direction
GAO
KAO
GBS
G_S
G_HC
SW
SW-100e

Pmax kN
435
-455
550
-573
627
-655
-878
889
-1114
1116
118.5
-118.3147.8-149.9emm
36.73-37.2087.96-80.4994.45-94.37-78.5375.98-244.58
162.95
16.0
-16.0
47.8
-47.4
max

s

1.30
1.60
6.90
7.90
12.40
9.40
2.24
2.91
11.16
8.46
3.14
2.04
8.94
9.56

JISF Operations

Recent Operations of the Committee on Overseas Market Promotion

The Committee on Overseas Market Promotion, The Japan Iron and SteelFederation (JISF), promotes diverse operations pertaining to theintroduction of high-performance steel products and their application
technologies as practiced in Japan. Its main aim is to increase the use ofsteel structures overseas. Recent operations are introduced below.

Embassy of Japan in Cambodia. About 200 engineers from governmental,
academic and private sectors participated in the conference, producing
successful results. The conference was highly assessed by the participants,
and according to a questionnaire survey, more than 90% of the participants
hoped to participate in the next conference.

Local Surveys in Cambodia
The committee has visited Cambodia three times to make local surveys
regarding economic conditions, infrastructure construction, tasks remaining
to encourage wider applications of steel structures and tasks that JISF stillneeds to carry out in that country. In 2012, the “Conference on Advanced
Technologies for Steel Construction 2012” was held in Phnom Penh by
JISF jointly with the Ministry of Public Works and Transport of Cambodia
and the Institute of Technology of Cambodia and with support of the

Local Surveys in Myanmar
Subsequent to the visit to Yangon made in 2012, the committee members
visited a total of six related government agencies not only in Yangon but inNaypydaw, too, for exchanges of ideas and information. These agencies
have high expectations for the steel-structure diffusion activities to bepromoted by JISF. The committee plans to continue conducting surveys on
steel-structure diffusion in the future.

“Conference on Advanced Technologies for Steel Construction 2012” held
for the first time in Phnom Penh in December 2012

H.E. TAUCH Chankosal,
Secretary of State of
MPWT (center) and Mr.
Yoshihiro Higuchi,
Minister Deputy Chief ofMission, Embassy ofJapan in Cambodia(back right)

Lecture delivery

Closing remarks by Dr.
OM Romny, Director
General, Institute ofTechnology ofCambodia

STEEL CONSTRUCTION TODAY & TOMORROW
Published jointly by

The Japan Iron and Steel Federation
3-2-10, Nihonbashi Kayabacho, Chuo-ku, Tokyo 103-0025, Japan
Phone: 81-3-3669-4815 Fax: 81-3-3667-0245
URL http://www.jisf.or.jp/en/index.html
Japanese Society of Steel Construction
Yotsuya Mitsubishi Bldg. 9th Fl., 3-2-1 Yotsuya, Shinjuku-ku, Tokyo 160-0004, Japan
Phone: 81-3-5919-1535 Fax: 81-3-5919-1536
URL http://www.jssc.or.jp/english/index.html

Exchange meeting in Myanmar: (from left to right) Meetings at the
Ministry of Construction, the Ministry of Rail Transportation and theMinistry of Transport© 2013 The Japan Iron and Steel Federation
Edited byCommittee on Overseas Market Promotion, The Japan Iron and Steel Federation
Chairman (Editor): Tetsuya Akahoshi
P u b l i s h e d t h r e e t i m e s p e r y e a r, S T E E L C O N S T R U C T I O N TO D AY &TOMORROW is circulated to interested persons, companies and publicorganizations to promote a better understanding of steel products and theirapplication in the construction industry. Any part of this publication may be
reproduced with our permission. To download content (PDF format), please go
our website at: http://www.jisf.or.jp/en/activitity/sctt/index.html. We welcome yourcomments about the publication and ask that you contact us at: sunpou@jisf.or.jp.