Research Trends and Results

Research on the application of super high tension
bolts to highway bridges
TAMAKOSHI Takashi, HeadSHIRATO Masahiro, Senior Researcher
ISHIO Mari, Researcher
Bridge and Structures Division, Road Department(Key words) highway bridges, super high tension bolt, high strength bolted friction joint, slip test, slip coefficient

3. Future challenges
Based on past results, test data and numericalanalyses results will be completed and testing done toreflect these in design and execution standards.

Photo 1. Example of a steel
bridge high strength boltedfriction jointPhoto 2. Accelerated
corrosion test

Figure 1.
Standard Slip
Test
120200200
390
55 80 5555 80
120 80 55
ボルト孔 φ24.5ボルト
Bolts
190

255
390
790
1080 55 55 80
390
255

Figure 2 Girder Bending Test
Load荷重(Plane （側面図）(Edge（平面図）
12060 60view)view)
16 25 16

2. Past results
Durability is tested by measuring the hydrogencontent of bolt materials, which is a factor related todelayed failure, accelerated corrosion testing (photo 2)

and surveys of corrosion of high strength bolts inexisting bridges.
Regarding execution methods, precautions to befollowed in design and execution, which can ensure
quality, are organized.
Standard slip tests were done within a range wherehigh strength bolted friction joints have been used inexisting bridges, and with connection surface
treatment, base material plate thickness, base material
quality, hole diameter, number of rows of bolts, andreassembly etc. as parameters, obtaining a slip
coefficient of 0.45 or higher used to evaluate slip
strength of high strength bolted friction joints
stipulated by the present design standards, except incases where organic zinc rich paint is used as to coatthe surface. The girder bending test performed under
different main girder flange thickness and bolt layout
conditions, similarly, obtained a slip coefficient value
equal or higher than the stipulated 0.45, too.

25

1. Introduction
Connecting members to erect a steel bridge isusually done by welding, or using high strength bolted
friction joints (Photo 1). The higher the strength of thebolts used, the smaller the joints and the less workrequired to construct the connections, contributing to
the reduction of costs of construction, repair, andretrofitting of highway bridges. Although bolts (F13T,F11T) stronger than the usual bolts (S10T, F10T)
since 1964 were adopted, the phenomenon—brittlefailure (delayed failure) suddenly occurred in F13T,
then later the same damage occurred in F11T
beginning in 1975, so its adoption was stopped fromthe 1980 design standards. Since 1991, under anadministration circular from the Road Bureau of theformer Ministry of Construction, bolts in danger ofdelayed failure have sequentially been replaced fall
prevention measures have been taken. As this shows,there was concern about the long-term durability ofhigher strength bolts, so since then, no research on theapplicability of higher strength bolts to steel highway
bridges was carried out. But in recent years, superhigh tension bolts (S14T) created by improving
delayed failure resistance performance weredeveloped, and they have been adopted in the building
construction field. Now the NILIM is studying theapplication of super high tension bolts (S14T) to
highway bridges.
When applying these to highway bridges, because
the harshness of the environment when used mainlyoutdoors (influence on delayed failure in particular),execution methods, number of rows of bolts etc.
differ from those in the building construction field,
joint research by industry, academia, and thegovernment is being carried out to set required
standards for quality of long-term durability andexecution methods, including delayed failure. The
NILIM is performing standard slip tests (Fig. 1),
bending tests of connections of a girder (Fig. 2), andnumerical analyses.

Boltボルト

Load荷重Research Trends and Results[Sources]1) Japan Society of Civil Engineers: Steel structure
series, 15: High strength bolt friction connection joint
design, execution and maintenance guidelines(proposed), December 20062) Tamakoshi et al.: Impact of causal factors on theapplication of super high strength bolts to the bridgefield, Civil Engineering Journal, Vol. 55, No. 8, pp 18– 21, May 2013