Numerical Simulation of Typical Damage Patterns for Multi-Story RC Frame Structures With Infill Walls Under Explicitly Consideration of Out-Of-Plane Behavior

Abstract eng:
In case of an earthquake a typical unreinforced masonry (URM) infill wall is subjected to a three dimensional acceleration field and undergoes simultaneous in-plane and out-of-plane loading. Depending on the direction of seismic action, the observed damage mechanisms on URM may be classified as in-plane (IP) and out-of-plane (OoP). In-plane damage is caused mainly by inter-story drift. The typical in-plane damage mechanisms can be classified as cracking due to separation from the structural frame, cracking due to horizontal bed joint sliding, cracking due to tension across the diagonals of the panel, and cracking due to crushing of panel corners. Out-of-plane over turning collapse is the most dominated mechanism in perpendicular wall direction. The overturning effects are increased by the damage due to the horizontal in-plane components of seismic action (shear cracking) and the inter-story drift in out-of-plane direction, which causes the separation from the upper beam. After L’Aquila earthquake in 2009, a conducted damage survey showed that the greatest damage is located on the lower stories (up to the second story in taller buildings). On the contrary, collapse due to out-of-plane mechanisms is expected on the upper stories of buildings (due to higher expected accelerations). Therefore, the collapse due to out-of-plane mechanisms has to be ascribed to the early presence of heavy in-plane induced cracking. In fact, in-plane actions can cause disconnection of the infill panels from structural elements, reducing their seismic capacity. Since the mid-1950s, a number of distinct approaches in the field of analysis of in-filled frames lead to different analytical models. The equivalent strut model is the most common one. A main disadvantage of the strut models is the disability to represent the out-of-plane response of an infill masonry panel. A new model was been proposed, which consists of diagonal beam-column members utilizing fiber element cross sections. It is suitable for nonlinear time history analysis. The model considers both the in-plane and out-of-plane response of the infill, as well as the interaction between IP and OoP capacities. Since the building stock is often mostly composed of reinforced concrete frame buildings with URM, collapse simulation of buildings under seismic loads becomes an important issue. In this paper, the failure mechanisms of the URM will be numerically simulated by using the proposed state of the art strut model. A set of reinforced concrete frame with URM walls with different number of stories will be investigated to examine typical damage pattern and to quantify the damage for RC frames representing different story classes. Finally the achieved results will be used to come up with a proposal for the description of damage to primary and secondary structural elements in multistory and high-rise buildings. Results can be implemented into the EMS-98 or its up-date to an International Macro seismic Scale (IMS).

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