Earthquake-Resistant Statically Determinate Stairs in Buildings

Two laws of structural mechanics are presented in this paper. (1) If an entire structure consists of a main part and a statically determinate subsidiary part, then the load applied on the subsidiary part always produces internal forces in the main part, but the load applied on the main part generates no internal force in the subsidiary part. (2) If an entire structure consists of a main part and a subsidiary part with statically determinate horizontal forces, then the load applied on the main part produces no horizontal internal force in the subsidiary part. These laws can be applied to the seismic design of buildings. If the stairs are the statically determinate subsidiary part of an entire building structure, then internal forces in the stair structure are always small, because no large loads are applied on the stairs. In this case the stairs do not fail. If the stair structure corresponds to the subsidiary part, in which horizontal forces are statically determinate, then horizontal internal forces in the stair structure are always small. Hence, adopting statically determinate stairs or stairs with statically determinate horizontal forces is a critical measure for preventing stair failure.(C) 2016 American Society of Civil Engineers.