Experimental Cyclic Response of RC Walls With Setback Discontinuities

Abstract eng:
Chile concentrates a high number of earthquakes along its history. One of the strongest in recent years was in the south of the country, specifically in Maule regions in February, 2010 (8.8 Mw). Several buildings of the modern construction presented damage in reinforced concrete (RC) walls (crushing of concrete, buckling and fracture of steel reinforcement); this was due to little or no confinement used in the design. Other characteristics that are common in damage walls was the relatively high axial load, thin walls, as well as, discontinuities in the walls. Slender RC walls are often used in Chile and commonly, due to architectural constrain, the length of walls changes between floors designated for parking space and upper floors, presenting wall extensions in the upper levels and creating a setback. Similar situation are observed in other cases, but as extensions for walls oriented in an opposite direction. These types of elements are commonly called flag walls. The level of discontinuity has not been treated experimentally and therefore it is necessary to observe its impact in RC walls and compare the results obtained with finite element models used in previous works. Also, the plastic hinge length will be estimated from the test program providing important information for design purposes. Four structural wall specimens were designed with thickness of 15cm and height of 2,65m. All specimens have a length of 90cm at the base, increasing the length at a specific height for three of them. Two are increased over a length of 25cm and 50cm at a height of 30cm, whereas other specimen increases its length to 25cm, but a height of 60cm. All of them are tested under constant axial stress (0.1f'cAg) and cyclic lateral loads increasing at specific drift levels. The axial load is applied by means of four post-tensioning bars anchored to the wall pedestal. The specimen is fixed to the strong floor and the lateral load is applied with an actuator at the top of the specimen. Main deformation measurements are registered by strain gages on steel bars, LVDTs at the wall surface and photogrammetry to monitor the global response, as well as, local response close to the discontinuity. The effect of the height and length of the discontinuity will be studied regarding plastic hinge length and maximum compressive and tensile strains in the wall boundary that can lead to damage, and compared with predictive expressions developed in a previous work.

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