The Stiffness Change and Dynamic Characteristics of the RC Frame Weak Layer under Strong Earthquakes

In China Wenchuan earthquake, the main characteristic of reinforced concrete frame structure is the weak layer yielding or collapse. Through the analysis of the stiffness change of the reinforced concrete frame weak layer during the whole process form the elasticity, yielding till collapse, the dynamic characteristics of reinforced concrete frame weak layer in the yielding and collapse processes were discussed. The lateral stiffness of the frame weak layer includes two parts: the lateral stiffness and the equivalent negative stiffness of column under the load action. It is shown that when the value of former decrease to the latter, the weak layer is in a collapse critical status. The frame weaker experiences form steady periodic vibration to variable periodic vibration then aperiodic motion. Some obvious chaos characteristics exist in the aperiodic motion in the plastic stage. It deserves further study to avoid weak layer collapse caused by the chaos motion.