Calibration of AASHTO LRFD Concrete Bridge Design Specifications for Serviceability (2014) / Chapter Skim
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3 OVERVIEW OF CALIBRATION PROCESS 3.1 Introduction The new generation of bridge design codes is based on probabilistic methods. Load and resistance (load carrying capacity)
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The degree of variation is measured in terms of the coefficient of variation, which is the ratio of standard deviation to the mean value. Regardless of the level of probabilistic design used to perform LRFD calibration, the steps needed to conduct a calibration are as follows: • Develop the limit state equation to be evaluated, so that the correct random variables are considered.
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Step 1: Formulate the Limit State Function and Identify Basic Variables. Identify the load and resistance parameters and formulate the limit state function.
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Step 8: Select Potential Load and Resistance Factors. Prepare a recommended set of load and resistance factors.
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Figure 3-1 Basic calibration framework – flowchart. Step 4 above requires the analysis of data describing load and resistance.
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horizontal axis represents the variable for which the cumulative distribution function (CDF) is plotted, e.g.
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3.2.2 Closed-form Solutions The reliability index, β, is defined as ( )
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3.2.3 Using Monte Carlo Simulation in the Calibration Process The typical application of Monte Carlo simulation, referenced in Step 5 above for bridgestructural reliability, as reported in the literature (Allen, et al., 2005; Nowak and Collins, 2013) is well known.
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PFMRR n ⋅⋅⋅= (3-6) The mean value, Rµ , and the coefficient of variation, RV , of resistance, R , may be approximated by the following accepted equations for the range of values that were considered: PFMnR R µµµµ ⋅⋅⋅= (3-7)
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3.2.4.2 Statistics of Loads Other Than Live Load The data presented below were developed in support of strength calibrations but are equally applicable to load calculations related to SLS calibration. The bias factors for DL1 and DL2 were provided by the Ontario Ministry of Transportation based on surveys of actual bridges in conjunction with calibration of the Ontario Highway Bridge Design Code (OHBDC)
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