Seismic Failure of Precast Concrete Structures
Seismic design of buildings has been made mandatory in many states in USA. Even in other countries that fall in Region 3 and above, seismic design has become a part of construction jobs. Unidirectional and bi-directional cyclic loads are exerted upon a precast concrete member during an earthquake, and column and beam failures occur. A precast concrete beam has connections, joints, and loops that hurt the most at the time of sudden earthquake loading because they do not allow the structure to behave as a single unit, and hence they fail at columns and joints.
Tensile strain field is produced by earthquake loading and that results in beam rotation inside the precast joints. Once beam rotations are developed, the structural members do not stay in their actual positions and failure occurs. However, if beam rotation can be minimized, structural failure of precast beams would not happen. In beam to column failures, high joint stresses are produced that cause structure failure. Plastic hinge formation near the fixed end of the beam results in concrete crushing and fracture of longitudinal bars, and thus, again, failure of the structure.
Americans have been working in collaboration with the Japanese to develop safe and sound seismic design guidelines for precast concrete beam to column connections, precast concrete beams, and other precast concrete structures. The program started in 1988 and today it has seen two phases of development and improvement. Economic and technically viable design solutions for seismic zones have been put forward by Precast Concrete Seismic Structural System (PRESS) that are being used in the earthquake prone areas in US, Japan, and many more countries.