●Research Trends and Results

Towards theintroduction of the partial factor design
method to road bridge design standards
TAMAKOSHI Takashi, HeadNAKASU Keita, Senior Researcher
YOKOI Yoshiteru, Researcher
Road Department, Bridge and Structures Division(Key words) road bridge, technical standards, performance-based specifications, partial factor design method
1. Introduction
The Technical Standards for Bridges and Highway
Bridges (below called, “Specifications for HighwayBridges”), which are design standards for road bridges,
consist of a system based on the allowable stressdesign method, which designs member sections so thatthe stress produced in each member by the action ofloads does not exceed the allowable stress of themember. Under technical standards for infrastructureson the other hand, performance-based specifications
are implemented to flexibly design various types ofstructures, and at the same time, the partial factor
design method, which permits the consideration ofbridge-building environmental conditions or thedegree of reliability of the safety allowance ofmaterials in order to clarify the required performance,
is being introduced with rising frequency.
NILIM studies an overall system of technicalstandards, settings of the basic required performances
for bridges, analyses of the safety allowances for theexisting standards, and settings of load factorsbasedon analysis from the perspective of reliability.
2. Setting load factors
Introducing the partial factor design method, it isnecessary to set partial factors considering the safety
allowances which should be ensured for each type offactor. In order to clarify the load coefficients, NILIM
studies the analyses of the safety allowances to secure
reliabilitybased on evidence of load regulations for theconventional standards with regard to dead load, liveload, wind load, temperature, earthquakes, snow load,
earth pressure and other load factors after collecting
the latest available data. Moreover, in order to study
effects of partial factorization, we extracted roadbridges with the proven structure’s types and scales inJapanand conducted numerical simulations
considering the characteristics of loads obtained by ananalysis of their design service lifetime (100 years) toanalyze the bridge performances from a variety ofperspectives such as the safety allowances which has
been ensured by the existing standards.
3. Future research policies
An introduction of the partial factor design

STEP 1: time series simulations (1,000 times)

Focus members

STEP 2: Extract of the maximum
section force force
Focus on N

STEP 3: 100 year maximum value
distribution

1,000
Focus on M
1,000

Distribution formed in 1,000
maximum values

Focus on N
Focus on M

Focus on S

Focus on S
1,000 results
simulations
Extract of maximum section
force of the focus members

Extract of section force equivalent to that for theexisiting standards

Figure 1. Numerical Simulations
methodto the Specifications for Highway Bridges will
makeit possible to reflect designs based on appropriate
evaluations, and to conduct designs rationally andeconomically.
Until now, we have conducted the setting the loadfactors by analyzing against representative structuralforms or focused members. In the future, we willcontinue to increase trial calculation cases and widely
conduct a survey to verify the appropriateness of thefactors at the practical design level, and at the sametime, we will study applicability to repair andreinforcement design. We will perform various kindsof studies in cooperation with various related
institutions to achieve an early introduction of thepartial factor design method to the road bridge design
specifications.
[Reference]
Bridge and Structures Division web site (containsrelated paper)
http://www.nilim.go.jp/lab/gcg/index.htm