EFFECT OF STAGGERED OPENINGS ON SHEAR RESISTING MECHANISMS OF REINFORCED CONCRETE MULTI-STORY STRUCTURAL WALLS

Abstract

 Multi-story structural walls, which are one of the most important lateral load carrying components in reinforced concrete buildings, often have openings for architectural reasons. Although these openings hamper the formation of diagonal compression strut in wall panels and decrease ultimate shear capacity, the Japanese design standard and guidelines do not consider the effect of location of openings on the assessment of the ultimate shear capacity. The objective of this study is to simulate the effect of staggered openings on shear resisting mechanism of walls and propose analytical methods with line element models.

 Two 2/5-scale reinforced concrete multi-story structural wall specimens, L5 and L6 were tested. Both specimens had one opening on each story and these openings were staggered. The openings of L5 specimen were arranged close to the boundary columns and those of L6 specimens were arranged closer to each other, respectively. Shear failure and tensile yielding of longitudinal bars in the boundary beam resulted in lower ultimate shear capacity than the one calculated by the current design method.

 Nonlinear static analyses were conducted on line element models of the specimens. In these analyses, members around openings were modeled as column elements with a wing wall, wall elements with a boundary column and elements between openings. The restoring force characteristics of axial, shear and flexural springs in these elements were modeled based on the current commentary on structural regulations and other design guidelines. The ultimate shear capacities of column elements and wall elements were increased by from 20% to 40% based on the database of past experiments. The ultimate shear capacities of elements between openings were determined by punching shear capacities of boundary beams with a hanging wall.

 The proposed models simulated the lateral stiffness after cracking, the maximum lateral load and failure mechanisms of L5 specimen in both positive and negative loading directions and L6 specimen only in positive loading direction. However, they overestimated the ultimate shear capacities by approximately 30% and did not simulate shear failure of the wall with a boundary column on the second story in negative loading direction of L6 specimen. The opening of the first story might have caused deterioration of ultimate shear capacity of the wall of the second story. In order to obtain better analytical results, the paper adopted an evaluation method of ultimate shear capacity for wall located above open story proposed by Izumi et al. The modified models agreed well with the experimental results of L6 specimen in negative loading.