Designing Timber Highway Bridge Superstructures Using AASHTO–LRFD Specifications

摘要

The allowable-stress design methodology that has been used for decades to design timber bridge superstructures is being replaced in the near future. Beginning in October 2007, bridge designers will be required by the Federal Highway Administration (FHWA) to utilize the Load and Resistance Factor Design (LRFD) design specifications published by the American Association of State Transportation and Highway Officials (AASHTO). Until recently, significant discrepancies existed between the two design methodologies as they pertain to the design of timber bridges. However, several modifications and improvements to the LRFD bridge design specifications were recently incorporated into the latest edition of the LRFD bridge design standards in an effort to mimic allowable-stress design techniques using current timber design standards. Timber bridge supstructures designed using the latest LRFD design requirements will still not be identical to those designed with allowable-stress design procedures, primarily due to new requirements for higher design vehicle live-loads and modified live-load distribution equations within AASHTO–LRFD design specifications. In addition, timber bridges designed using allowable-stress design methods prior to 2007 will be not be required to use AASHTO– LRFD methods for load rating purposes.