The near fault ground motion (NFGM) is characterized by a single long period velocity pulse of large magnitude.(Somerville et. al 1997) Extensive research for the far fault ground motion (FFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. For reinforced concrete (RC) bridge piers constructed before implementing the 1992 seismic design code in Korea, longitudinal reinforcing steels were practically lapspliced in the plastic hinge region between column and footing. This research aims at investigating the seismic behavior of RC bridge piers with lap-spliced longitudinal steels subjected to NFGM in low or moderate seismic region. Five RC pier specimens with a diameter of 400 mm and height of 1400 mm were tested on a shake table, and two identical specimens were tested under a quasi-static load and a pseudo-dynamic load. The effects of lap-spliced longitudinal reinforcing steels are investigated. Shaking test results are compared to those by Quasi-static test and Pseudo-dynamic test. It was concluded that: a) displacement ductility was significantly decreased in RC column specimens with lap-spliced longitudinal reinforcing steels; b) bond failure in the lapped starter bars and buckling of the longitudinal steel bars initiated failure in RC specimens with and without lap-spliced longitudinal steels, respectively; c) more transverse reinforcing steels induced better displacement ductility; and d) a decrease of displacement ductility and energy dissipation was observed in the specimens on a shake table excitation in comparison with the specimens by the quasi-static and the pseudo-dynamic test.

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The 14th World Conference on Earthquake Engineering

Summary
A three-dimensional beam–truss model (BTM) for reinforced concrete (RC) walls that explicitly models flexure–shear interaction and accurately captures diagonal shear failures was presented in the first part of this two-paper series. This paper extends the BTM to simulate RC slabs and coupled RC walls through slabs and beams. The inclination angle of the diagonal elements for coupled RC walls is determined, accounting for the geometry of the walls and the level of coupling. Two case studies validate the model: (1) a two-bay slab–column specimen experimentally tested using cyclic static loading and (2) a five-story coupled T-wall–beam–slab specimen subjected to biaxial shake table excitation. The numerically computed lateral force–lateral displacement and strain contours are compared with the experimentally measured response and observed damage. The five-story specimen is characterized by diagonal shear failure at the bottom story of the walls, which is captured by the BTM. The BTM of the five-story specimen is used to study the effects of coupling on shear demand for lightly reinforced RC coupled walls. The effect of mesh refinement and bar fracture of non-ductile transverse reinforcement is studied. Copyright © 2016 John Wiley & Sons, Ltd.

Three-dimensional beam–truss model for reinforced concrete walls and slabs – part 2: modeling approach and validation for slabs and coupled walls

In high seismic zone regions, slender reinforced concrete structural walls are commonly used in high-rise buildings as a main lateral load resisting element. These walls are very effective in limiting the lateral drift of the building due to their large in-plane stiffness. However, the presence of floor slabs influences the behavior of the shear wall. Also, the current design requirements do not account for the presence of floor slabs. To understand the behavior of wall-slab junctions and address the shortcomings of the current design requirements, the influence of two parameters, namely (a) aspect ratio and (b) longitudinal reinforcement ratio on the behavior is studied numerically. It is observed that the presence of floor slabs at different levels tends to partition the wall into squat wall panels between two consecutive floors. The wall-slab junctions show large stress concentrations arising from the strut action in the squat panels. It is also observed that the floor slabs can get significantly damaged near the wall-slab junction for lower vertical reinforcement ratios in the wall. Thus, the current code-prescribed minimum reinforcement in shear walls is not sufficient and needs to be revisited at for improved performance.

Seismic behavior of slab-structural wall junction of RC building

A finite element analysis is performed on the effective coupling stiffness and bending stress distribution in a cracked slab coupling a pair of laterally loaded shear walls. Particular attention is focused on the effect of a transverse crack situated at the highly stressed inner edges of the walls. The influence of the length of crack on the effective stiffness and longitudinal bending stress distribution is examined for typical slab-wall configurations. It is shown that the presence of a transverse crack results in a substantial reduction in slab-coupling stiffness, especially when the wall-opening ratio is small. The distribution of longitudinal bending moments in the slab is not greatly affected by the presence of a crack, apart from the region close to the crack tip, where bending stress concentrations occur.

R. G. Taylor

Papers

Slab Coupling of Earthquake-Resisting Shearwalls