Generally, RC squat shear walls are defined as walls with a height-to-length (aspect) ratio of less than or equal to 2.0. Because of their low aspect ratio, squat shear walls tend to show a shear-dominant behavior with diagonal or sliding shear failure modes and low deformability. A shear-dominated inelastic mechanism is undesirable as it results in low ductility response typically with severe strength degradation and a low energy dissipation capacity. RC squat shear walls were widely used as vertical and horizontal load-resistant elements of multi-story apartment buildings in Korea. Because seismic design for building in Korea had not been stipulated prior to 1988, RC shear walls in the pre-1988 buildings constructed in Korea were not designed and detailed according to seismic design code. In order that existing buildings were satisfied with the current seismic design code, main lateral load-resistant elements in the existing buildings should be seismically strengthened.
Current seismic retrofit or seismic rehabilitation strategies generally focus on increasing the strength, stiffness or upgrading the mechanical properties of a structure. A typical drawback of conventional retrofit or seismic rehabilitation technologies is that an upgraded behavior might result in an increased demand on the structural and sub-structural elements. Recently proposed by Kam is a counter-intuitive but rational seismic retrofit strategy consisting of selectively weakening a structural systems and components such as walls, beams and columns.
This study investigates experimentally the applicability of selectively weakening retrofit for existing and non-ductile squat shear walls. To evaluate the effect of vertical seams on the wall panel on the hysteretic behavior and failure mode of RC squat shear walls, two 1/3 scale shear walls with vertical seams as a variable were made and tested under reversed cyclic loadings.
All specimens had the same rectangular cross-section 1,100mm x 50mm, with wall panel height 600mm. The vertical seam is 40mm wide and 260mm high and 460mm high. Concrete and SHCC for wall specimens was supplied by a local ready mix company with a specified strength of 50MPa.
The specimen was placed into strong rectangular frame structure with four pin joints to simulate the specimen under pure shear. The strong frame for loading comprised two steel frame columns pin-connected with a lateral loading beam and bottom beam fixed to reaction floor. lateral load reversals were applied to the top loading beam connected to a servo actuator that was supported by the strong reaction wall in the laboratory and has the capacity of 1,000kN. 6 displacement transducers and two dial gauges were installed on the wall panel to measure the drift and shear deformation of the wall specimens.
Based on the results of test conducted to investigate the shear behavior of reinforced concrete squat shear walls with and without vertical seams on the wall panel under cyclic loading, the following conclusions are drawn;
1. The selective weakening for structural elements may be an effective alternative to seismic retrofit of existing buildings.
2. The installation of vertical seams or slits on the wall panel improves the ductility of RC rectangular squat shear wall with non-ductile reinforcement details. However, making seams on the wall panel decreases the load-carrying capacity and stiffness of the walls.
3. In future research, it is required to investigate how for shear walls with vertical seams to retain the structural performance such as strength and stiffness of solid shear walls.