Research Trends and Results

Revision of “Specifications for Highway Bridges”
TAMAKOSHI Takashi, HeadSHIRATO Masahiro, PhD, Senior Researcher
YOKOI Yoshiteru, Researcher
Road Department
Bridge and Structures Division（Key words） Highway bridge, Technical Standards, Specifications for Highway Bridges
INTRODUCTIONNILIM routinely reviews nation-wide bridge
inspection data and also conducts the field survey ofdamaged structures. These are required to feedback thefindings to technical specifications and standards andidentify what should be done by NILIM in research. Oneof the recent good examples is the revision of theJapanese Specifications for Highway Bridges in 2012.
The revision had been the first time in almost ten years.
Following the adoption of durability design in theprevious revision such as chloride ingress in concrete
members for a design service period of 100 years, thepresent revision incorporates the latest knowledge andexperience that have been obtained for the last ten years
in the broader sense of bridge maintenance such as thedeterioration and seismic damage to existing structures.
Lessons learned from recent experience in bridge
maintenance
NILIM routinely reviews nation-wide bridge
inspection data and conducts the field survey of damaged
structures to feedback the findings to the JapaneseSpecifications for Highway Bridges and identify what
NILIM should do in research. One of the recent good
examples is the revision of the Japanese Specificationsfor Highway Bridges in 2012. The revision had been thefirst time in almost ten years. Following the adoption ofdurability design in the previous revision such as chloride
ingress in concrete members for a design service periodof 100 years, the present revision incorporates the latest
knowledge and experience that have been obtained forthe last ten years in the broader sense of bridge
maintenance such as the deterioration and seismic
damage to existing structures.
Firstly, the bridge inspection data has reconfirmed thatfatigue cracks continue to develop in steel members suchas deck plates of bridges carrying a busy / heavy traffic.
However, as it turns out, the design guidance for fatigue
in steel bridges published in 2002 can cover typicaldamage types that were observed in the bridge inspection.
Damage due to chloride ingress to concrete bridges also
shows that the 2002 Specifications for Highway Bridges
is still effective to prevent damage due to chloride ingressduring the design service life.

Secondly, there were several serious damage cases intruss bridges in the U.S and Japan. The I-35W
Mississippi River Bridge, in Minneapolis, Minnesota, theUnited States, suddenly collapsed in 2007. In Japan, thefailure in a truss bar which was embedded through thedeck concrete occurred at two national highway bridges
on major routes and ceased traffic. These bridges wereinspected under their periodic inspection programs but
these accidents were not staved off. NILIM conducted
field surveys for all these events and analyzed the causesof these collapse and failures. We learned the importancein designing more redundant structures against partial
collapse in structural members. For example, theAASHTO design specifications have load modifiers interms of redundancy and a concept of fracture criticalmembers. In addition, the bridge inspection data obtainedin national highway bridges has indicated that the rate ofdeterioration changes with different members as well as
difference portions / zones even within a member. The
visual inspection and present deterioration curves cannot
completely detect all damage and hidden failure such as
corrosion of steel inside concrete. Rapid development ofexisting damage sometimes appears between theevery-five-year inspections unexpectedly.
Thirdly, the Great East Japan Earthquake occurred in2011. The emergency inspection was conducted by
highway administrators and NILIM also backed up themwhen evaluating the condition of bridges damaged
seriously. However, they had difficulty approaching tosome portions of the bridge or bridges thereof to check ifthey were o.k. in such urgent situations. They also haddifficulty conducting emergency repair work at suchinaccessible portions to open the service of the bridge foremergency vehicles.
KEY ITEMS INTRODUCED IN THE REVISIONREGARDING MAINTAINABILITY
The lessons above brought the following majorrevisions in the 2012 Specifications for Highway Bridges
regarding bridge maintenance:
1) The chapter of fatigue design is incorporated into theSpecification which was formerly guided in a different
design guidance book. The chapter shows design
equations and the classification in fatigue strength of

Research Trends and Results
welded joints.
2) The minimum thickness of steel deck plate is increased
to 16 mm based on NILIM's experimental study.
3) The following items must be considered in design andspecifically described in design reports and drawings.
・Details to secure so-called load-path redundancy,
structural redundancy, and internal redundancy
・Installation of bridge inspection facilities from the
beginning of service
・Details to make it easy to replace the identified
structural members that are supposed / planned toreplace during the design service life, such as theinstallation of mounts for jacks and the
pre-reinforcement of associated structural members
for the future jack-up etc.
・Elimination of portions that are not accessible fromthe inside such as a narrow portion of box
cross-section4) Description of expected failure modes or deterioration
prone portions / zones and the associated inspection
and maintenance strategy in design documents anddrawings.
5) Preservation of all drawings such as project drawings,
shop drawings, working drawings, record drawings,
as-build drawing etc. that will be needed inmaintenance.
It is worth mentioning that the design for chloride
ingress in concrete members remained unchanged fromthe 2002 Specifications for Highway Bridges based on
the findings shown above.
REMARKSNILIM has also been working to upgrade theSpecifications for Highway Bridges into a partial design
factor format and develop repair / reinforcement design
specifications particularly for existing structures. The
reliability theory can give more reasonable load andresistance factors for existing structures that can consider
the present traffic condition and structural condition ofthe particular bridge on a particular site. The related
findings can be seen elsewhere soon.
Reference
Bridge and Structures Division HP (Related papers posted)
http://www.nilim.go.jp/lab/gcg/index.htm