Seismic assessment of RC structures considering vertical ground motion

Civil engineering structures are generally subjected to three-dimensional earthquake ground motion. In the past several decades, horizontal earthquake excitation has been studied extensively and considered in the design process whereas the vertical component of earthquake excitation has generally been neglected in design, and rarely studied from the hazard viewpoint. However, recent studies, supported with increasing numbers of near-field records, indicate that the ratio of peak vertical-to-horizontal ground acceleration can exceed the usually adopted two thirds. Furthermore, field observations from recent earthquakes have confirmed the possible destructive effect of vertical ground motion. Therefore, the significance of vertical ground motion has gradually become of concern in the structural earthquake engineering community. Vertical motion has also been attracting increasing interest from the engineering seismology community.;This dissertation presents an investigation of the effect of vertical ground motion on RC structures studied through a combined analytical-experimental research approach. The analytical study investigated the effect of vertical ground motion on RC bridges and buildings considering various geometric configurations. For the experimental investigation, sub-structured pseudo-dynamic (SPSD) tests and cyclic static tests with different constant axial loads were employed using the Multi-Axial Full-Scale Sub-Structured Testing and Simulation (MUST-SIM) Facility. In the analytical investigation for bridges, a parametric study on a two-span bridge was conducted to probe the effect of geometric bridge configuration including span length, span ratio and column height. Moreover, a bridge structure damaged during the Northridge Earthquake and a Federal Highway (FHWA) bridge design example were also analyzed. In the latter two cases, the effect of various vertical and horizontal peak ground acceleration ratios were presented and the results were compared with the case of horizontal-only excitation. The effect of arrival time interval between horizontal and vertical acceleration peaks were also studied and compared to the case of coincident motion. In the analytical investigation on buildings, a set of RC buildings was studied considering the hazard from recent devastating earthquakes. An ensemble of buildings consisting of 3 non-seismically detailed and 12 code-conforming buildings with various levels of irregularity in plan and elevation, design intensity and ductility were studied. Analysis results from both structural systems (buildings and bridges) show that there is no significant change in global horizontal measurements such as lateral displacement or interstorey drift. However, notable increases in axial force variation within vertical members are observed resulting in significant reduction of shear capacity.;In the experimental investigation, two SPSD tests were conducted in order to experimentally investigate the effect of vertical ground motion. FHWA Bridge systems selected from the previously completed analysis was used during full hybrid simulations designed to realistically represent the loading experienced by bridge columns during earthquakes. The horizontal ground motion was used as the only input for the first specimen while the second specimen was subjected to combined horizontal and vertical components of ground motion. Inclusion of vertical ground motion significantly increased the axial force variation and at several times induced an axial tension force. Moreover, more severe cracking and damage were observed with significant increase in spiral strains when vertical ground motion was included as an input. Based on the observed axial force levels obtained during the second SPSD test, two cyclic static tests with constant axial tension and compression were performed to study the effect of the axial load level. A brittle shear failure including rupture of the spiral was observed for the test specimen subjected to constant axial compression, while the specimen subjected to moderate tension showed less brittle behavior. Therefore, it has been experimentally and analytically confirmed that the deterioration of shear capacity and failure mode are linked to the axial load level and the vertical component of earthquake motion.