Pounding along expansion joints in steel moment resisting frames

Abstract In steel framed structures having large footprints or variable heights, expansion/ settlement joints are usually introduced by structural designers to minimize the straining actions developed within buildings structural elements. These joints separate the buildings into parts which are self-standing. During severe earthquake events, these parts vibrate differently causing pounding which result in damage to buildings structural elements. To overcome such problem, design codes suggested widening these expansion joints to avoid collision between building parts. However, such wide joints pose as challenge to architects since they affect buildings architectural appearance and internal use. This study examines the impact of minimizing the width of the expansion joints on the level of damage experienced by steel framed buildings during earthquakes. For such purpose, hypothetical porotype building having expansion joint between its parts were developed. The main lateral load resisting system for this building was characterized as limited ductile steel moment resisting frame according to Egyptian seismic code which is corresponding to Intermediate moment resisting frames in International codes. The parts of the building were having different number of floors and spans, so they can vibrate differently during earthquake. The building was subjected to seven different time histories with different a/v ratio (ground acceleration to ground velocity ratios). Non-linear inelastic analyses were performed to this building utilizing different expansion joint widths. The recurrence of pounding between buildings' parts in terms of locations and magnitude of pounding forces was identified for each analysis case and evaluated. In addition, the variation in beams & columns straining actions and the spread of plastic hinges within them was recorded and examined. From the obtained results it was concluded that the effect of pounding can be mitigated in this case if expansion joint width set equal to 0.5 the square root of the sum of the squares of the building parts inelastic displacements at collided floors provided the concept of strong column-weak beam is applied to the building.