Effect of bidirectional interaction on seismic demand of structures

• Existing seismic codes primarily suggest to consider only unidirectional motion.
• Effect of bidirectional interaction of ground motion is ignored in seismic code.
• Proposed model for bidirectional interaction is validated with experimental ones.
• Considerable effect in inelastic response is observed.
• Such interaction depends on ratio of accelerations, P−Δ effect and overstrength.

Existing practice to estimate inelastic seismic demands does not consider the impact of inelastic bidirectional interaction of load resisting members arising due to bidirectional horizontal ground motions. This paper utilizes a simple yet reasonably accurate bidirectional hysteresis model to study the storey drifts of single as well as multistorey idealized systems under both bidirectional and unidirectional seismic excitations using 20 far fault ground motions. The ratio of the storey drifts under bidirectional and unidirectional excitations is investigated for a feasible range of system parameters. Biaxial interaction is found to cause magnification in drift demand.