Investigation of Damage to a Masonry Condominium Building from the 1994 Northridge Earthquake

This paper presents the findings of a structural engineering evaluation of earthquake damage to an 8-story reinforced masonry residential building in Los Angeles. The load in some of the upper level masonry walls of the building is transitioned at the 2-story subterranean parking garage levels through reinforced concrete transfer beams and columns. On-site damage investigation revealed severe cracking of the concrete transfer beams. The cracks were most significant in the mid-span of the beams as opposed to the termination point of masonry wall above closer to the beam ends where shear and moment transfer and consequent damage would be expected to occur. A staged finite element analysis of the building subjected to gravity loads, to replicate the sequence of construction, revealed that the walls had separated from the transfer beams during construction when the temporary shoring was removed. This is consistent with field observations of separations along the beam-wall interface. This separation was incorporated into a detailed computer model of the building for evaluation of the building's response to the 1994 Northridge Earthquake. The locations and sizes of observed beam cracks correspond well with the location of predicted large moment demands in the beam elements. Predicted regions of overstressed masonry walls also correlated well with locations of observed wall cracks.