Papers in this issue of the journal come from the following subject areas: seismic effects, dynamic effects, analysis and computation, optimization, reliability and performance of structures. The issue begins with an interesting paper by Morin, Leger, and Tinawi titled ''Seismic Behavior of Posttensioned Gravity Dams: Shake Table Experiments and Numerical Simulations.'' The authors describe sliding shear tests on three scaled concrete lift joint specimens reinforced with an unbonded posttensioned cable. Test variables included surface roughness and the posttensioning force. The tests enabled the validation of a joint constitutive model. Further, shaking table tests on a 3.4-m-high plain concrete posttensioned gravity dam, having a cold lift at about midheight, offered additional validation of the joint model and also provided information on dynamic sliding and rocking behavior as well as failure mechanisms of posttensioned dams. It is shown that the posttensioned cable provides additional strength to the joint through axial forces and the shear resistance mobilized by cable dowel action. Both sliding and rocking were amplified by low frequency records than high frequency excitations. Cable failure at stresses below the tensile capacity is possible due to combined shear-tensile action.
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