Discrete Element Modeling of Masonry-Infilled Frames

Introduction

Building frames are usually infilled with masonry walls. Infilled frames have high in-plane strength and stiffness compared to the corresponding bare frames (no infill). At low levels of lateral forces, the surrounding frame and infill panel behave as a monolithic composite frame. However, as the levels of lateral load increases, an interaction between the surrounding frame and infill panel occurs. The frame behaves in flexural mode and the infill panel deforms in a shear mode. Also, the provision of the infill increases the later stiffness and strength of the frame. However, in current practice the structural effect of infill walls is not taken into account during the analysis of building frames and leads to inaccurate predictions of the building’s stiffness, strength and ductility.

Over the last 60 years, extensive numerical and experimental studies have been performed on lateral load behavior of masonry-infilled frames. Experimental and analytical investigations on the lateral stiffness and strength of steel frames infilled with masonry panels have been carried out by Stafford-Smith (1962 and 1966), Mallick and Garg (1971), Riddington and Stafford-Smith (1977), Liauw and Kwan (1985) and Moghadam et al (2006). Also, Dawe and Seah (1989), Mosalam et al. (1997), Schneider et al. (1998), Flanagan and Bennett (1999) and El-Dakhakhni et al. (2002) have studied the behavior of masonry-infilled steel frames under lateral in-plane loads. Saneinejad and Hobbs (1995) developed a method for infilled steel frames inelastic analysis and design subjected to in-plane forces. The model was later adopted by Madan et al. (1997) and implemented in software IDARC for dynamic analysis of infilled frames. A smeared-crack finite element model to study the nonlinear behavior of infilled reinforced concrete frames have been proposed by Mehrabi and Shing (1997). Based on minimizing the factor of safety with reference to the failure surfaces in a masonry infill, Moghadam (2004, 2006) proposed a new analytical approach for the evaluation of shear strength and cracking pattern of masonry infill panels.