Investigation of the non-linear interaction between a masonry infill wall and a surrounding frame

The masonry infill walls are usually disregarded in the structural design of RC frame buildings. However, the infill walls affect the stiffness and dynamic characteristics of the building, and contribute to its resistance. It is especially evident when extreme loads act on the building; the infill walls interact with the surrounding frames, absorb energy, contribute to load redistributions and may have a key role in the prevention of progressive collapse. Recently, manuals instructions for earthquake design [1] suggest simplified models account for the infill wall effect. These models add an equivalent diagonal strut that is connected to the frame's opposite corners to represent the infill wall. More advanced models consider additional off-diagonal struts [2-5] that are connected at fixed locations, aiming at the representation of the contact zone between the masonry wall and the surrounding frame and yielding the interaction stresses in this zone. While this limited information is known for the case of laterally loaded infill walls, no information is provided for the case of similar walls that are subjected to loss of a supporting column. The latter may result from an extreme earthquake or explosion and lead to extended structural damage including progressive collapse. In an ongoing research, an innovative experimental system has been constructed, aiming at the examination of the interaction between a masonry wall and a surrounding frame. Early experiments indicate non-linear interaction behaviour with a variable contact region depending on the loading level. This finding contradicts the presently common assumption of fixed contact regions. The proposed paper aims at presenting new experimental results that illuminate the complex interaction between the infill wall and the surrounding frame.