Comparative study of NCHRP Report 472 with the current AASHTO seismic specifications

Recently published NCHRP Report 472 has recommended major changes, which appear to have an economic impact on the cost of bridges. This paper is presented in two steps, review of the current (mandatory) and review of the future (proposed) specifications. It firstly reviews differences in currently used AASHTO Load Factor Design (LFD) and Load Resistance Factor Design (LR-FD) specifications as applied to actual straight, skew and curved bridges. The paper discusses the proposed changes recommended by Report 472 from the current AASHTO seismic specifications. In future, the classification of bridge categories will be performance based. Emphasis will be rightly placed on pushover analysis, ductility, use of new soil site factors, liquefaction effects and loss of bearing capacity during seismic event. Certain difficulties need to be overcome to implement the new recommendations. The structural engineer needs training in structural dynamics, geotechnical engineering, computer softwares and seismic detailing. This may require developing, new courses at university level, continuing education courses and holding suitable examinations for licensure.