Cracking and Shear Effects on Structural Walls

Abstract

A mathematical model taking into account flexural and shear deformation, rotary moment of inertia, and axial loads is developed to calculate the natural frequencies of isolated walls. Results of free vibration tests of nine 1/3‐scale reinforced concrete isolated walls are evaluated using the mathematical model. The measured “uncracked” fundamental frequency varied from 90%‐100% of the calculated value. Results of the free vibration tests are also compared with calculated frequencies using simplified formulas available in standard textbooks. It is shown that damping increases with the amplitude of the free vibration and with structural damage. It is concluded that shear deformations have a significant effect in the calculation of natural frequencies, particularly for walls with large boundary elements, and linear analyses based on “uncracked” properties may give unreasonably conservative values for earthquake design because of rapid reduction in natural frequencies caused by cracking.