Abstract
Inelastic dynamic analyses were carried out using 3D and 2D models to predict the mean seismic response of four-span reinforced concrete (RC) bridges considering directionality effects. Two averaging methods, including an advanced method considering displacement direction, were used for the prediction of the mean responses to account for different incident angles of ground motion records. A method was developed to predict the variability of the mean displacement predictions due to variability in the incident angles of the records for different averaging methods. When the concepts of averaging in different directions were used, significantly different predictions were obtained for the directionality effects. The accuracy of the results obtained using 2D and 3D analyses with and without the application of the combination rules for the prediction of the mean seismic demands considering the incident angle of the records was investigated. The predictions from different methods to account for the records incident angles were evaluated probabilistically. Recommendations were made for the use of the combination rules to account for the directivity effects of the records and to predict the actual maximum displacement, referred to as the maximum radial displacement.
Highlights
Conclusions from this study are summarized as follows: (1) The use of the 30% rule using 2D analyses resulted in good predictions of the maximum radial displacement of columns for the case of the straight bridges studied in this research, when the average displacements were computed using the maximum absolute displacements for each ground motion record
(2) When the averaging procedure involving the prediction of the mean displacements in different radial directions was adopted for the bridges in this study, the maximum radial displacements obtained using 3D analyses were smaller than the maximum displacements obtained in the longitudinal and transverse directions using 2D analysis
When the averaging procedure based on the maximum absolute values was adopted to determine the mean displacements, the displacements in the transverse and longitudinal directions needed to be combined using the 30% rule resulting in predictions similar to those obtained using 3D analyses
Summary
Some issues are not very well addressed in seismic codes, including the effects of directivity of records in 2D and 3D analysis, the use of different combination rules for prediction of inelastic displacements and the methods for predicting the mean response of structures subjected to a number of records at different incident angles. Maleki and Bisadi [11] in 2006 investigated the orthogonal effects in linear seismic analyses of skewed bridges using three ground motion records and compared the predictions of different combination rules They concluded that the use of 100–40% rule was satisfactory only for the response spectrum analysis, while for the linear time history analyses none of the combination rules were able to predict the maximum response obtained using three records.
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