Framed shear walls under cyclic loading.

摘要

Framed shear walls, if properly designed, can supply high shear resistance and sufficient ductility to effectively absorb energy during an earthquake. Serving as sacrificial elements to protect the frame elements, the in-filled panels in the structural frames can be easily repaired afterwards. The philosophy used in designing a framed shear wall is to promote a "ductile panel failure" in the panel while suppressing tension flexural (or compression-flexural) failure in the frame elements, particularly in the columns. The validity of this design philosophy is strongly supported by this research.;Thirteen framed shear walls and one pure frame have been systematically tested under reversed cyclic loading using the universal panel tester. Three principal variables were considered: (1) axial load ratio R in the columns, (2) steel ratio rhow in the panels, and (3) hoop reinforcement in the frame elements. The shear drift angles and flexural drift angles were measured directly from LVDTs (Linear Voltage Differential Transformers) on the frames.;Experimental results show that: (1) Panel failure with sufficient ductility can be achieved when the axial load ratio (R) is less than 0.2 and the panel steel ratio (rhow) is greater than the minimum steel ratio of 0.5%. The minimum steel ratio of 0.12--0.25% specified in ACI 318-95 code for the walls is not sufficient for the in-filled panels. (2) The general guidelines for the proportioning of framed shear walls are: (a) The maximum shear strength ratio of the framed shear wall to the pure frame should be in the range of 6.0 to 8.0, and (b) The lateral stiffness ratio of the framed shear wall to the pure frame should be in the range of 14 to 20.;The load-deformation relationship of a framed shear wall can be analyzed as an equivalent membrane element model with the uniform shear stress tau ℓt and the normal stresses sigmaℓ and sigma t on the edges. The longitudinal stress sigmaℓ is a function of the confinement stress due to the frame and the vertical stress due to the axial load. The transverse stress sigmat is caused only by the confinement stress.