Bridge System Safety and Redundancy (2014) / Chapter Skim
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Pages 31-38
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From page 31... ...
31 3.1 Behavior of Bridge Systems under Distributed Lateral Load When a bridge system is subjected to an increasing distributed lateral load, its response is often represented in terms of the maximum lateral displacement at a critical point as a function of the applied lateral load's intensity. A typical bridge behavior can be represented using the green plot shown in Figure 3.1.
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From page 32... ...
32 response capacity duc. Alternatively, for bridges in low seismic regions, the AASHTO seismic guide provides equations that give the maximum displacement capacity of bridge columns in function of the column height, cross-section size, end constraints, and lateral confinement reinforcement ratio.
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From page 33... ...
33 columns and the superstructure is compared to the effects of pinned connections. For all bridge configurations, the effect of changes in column height and size, lateral confinement and longitudinal reinforcement ratios, reduction in member curvatures due to deficiencies in column/connection detailing and changes in foundation stiffness are investigated.
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From page 34... ...
34 columns through bearing supports. Changes in the abutment bearing stiffnesses also are considered, including the case where the bearings have negligible stiffness.
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From page 35... ...
35 typical, they are used in order to study the effect of large changes in bridge configurations. Different longitudinal reinforcement ratios for the 6-ft diameter columns varying between 1.66% (original design with steel area As = 67.5 in2)
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From page 36... ...
36 columns that take into consideration the columns' structural properties in addition to their dimensions. 3.3 Calibration of System Factors for Displacement-Based Approach Procedure The evaluation of the safety of a bridge under lateral load can be expressed in terms of the probability of failure, which for the displacement-based approach can be presented in terms of the probability that the ultimate system displacement capacity, duc, is smaller than the displacement demand dd: Pr 1 (3.5)
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From page 37... ...
37 As explained in Chapter 2, a probabilistic measure of system redundancy can be expressed in terms of the additional reliability provided by the system compared to that of the member defined by the reliability index margin as (3.9) u system column∆β = β − β Substituting Equations 3.7 and 3.8 into Equation 3.9, the reliability index margin is ln ln ln (3.10)
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From page 38... ...
38 Sensitivity Analysis and Recommendation A sensitivity analysis is presented to study the effect of the dispersion coefficient and the target reliability index margin on the system factor for the displacement-based approach as calculated from Equation 3.13. The results are presented in Table 3.3 and in Figure 3.5, which show that the system factor is sensitive to the target reliability index margin and the dispersion coefficient.
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