Seismic Analysis of RC Walls with Unequal Lengths (Analisi Sismica di pareti in CA di diversa lunghezza)

Two reinforced concrete walls of unequal length, coupled together with floor diaphragms are analyzed in this study. The system considered is represented by a 2D model, where both the structure and the loads lie in the same plane.
The main objective of the work is to analyze the consequence of coupling, especially in terms of base shear demand because previous studies (Rutenberg, 2004), (Rutenberg & Nsieri, 2006) have shown that the common design assumptions, based on the repartition of the forces between walls proportionally to the walls capacity, can be unconservative, especially concerning the base shear demand of the shorter wall.
Different modeling approaches (lumped plasticity, distributed plasticity and shell models), and different assumptions concerning the representation of the structure are compared in order to understand if the big coupling forces observed in the floor diaphragms, which cause the base forces redistribution between the walls, are "real" or whether they are a consequence of modeling simplifications.
Static non-linear analyses are performed by means of the software "SeismoStruct" version 5.0.5 (SeismoSoft, 2011), for the beam element models, and by the program "Vector2" version 2.9 (Vecchio & Wong, 2002) for the shell element models.
It is found that the lumped plasticity approach oversimplifies the real behavior of the structure and that it is not able to represent correctly the pushover response of the coupled wall system, while the distributed plasticity and the shell models give very similar results when they are calibrated with the same assumptions.
It is observed that the coupling effect depends on the modeling, but even using a more realistic model, it is still rather significant. A brief parametric study is proposed in order to understand how it is influenced by the geometry of the system, and it is found that it becomes more important for high buildings with large wall length ratios.