Question & AnswerQ&A (DPWH DEPARTMENT ORDER NO. 75)
The purpose is to provide an advisory for the seismic design of bridges to ensure their serviceability during earthquakes and other calamities, mitigating damage and preventing collapse.
Bridges must conform to the current AASHTO Standard Specifications for Highway Bridges, Fourteenth Edition, and the Guide Specifications for Seismic Design (1989 or latest edition) or the 1991 AASHTO Standard Specifications adopting the Guide Specifications for Seismic Design (AASHTO Interim Specification-Bridge).
Continuous bridges with monolithic multi-column bents are preferred due to their high degree of redundancy in resisting seismic shaking.
Deck discontinuities should be minimized to reduce the risk of failure during earthquakes and to ensure better structural integrity.
No, these elements are not recommended due to their vulnerability during seismic events.
Restrainers act as horizontal linkage devices between adjacent spans to prevent loss-of-span type failures, and are required at all joints as per AASHTO Guide Specifications.
Transverse reinforcement confines the main longitudinal reinforcement and the concrete core, preventing buckling and enhancing ductility during seismic activity.
Plastic hinging should occur in ductile column regions rather than in foundation units to ensure better seismic performance and avoid foundation failure.
Designing the backwall to shear off under seismic lateral force protects the abutment piles by preventing direct damage during an earthquake.
In irregular structures soil-structure interaction must be included to accurately consider the overall stiffness and seismic response of the bridge.