Building steel bridges in New York,Virginia,Pennsylvania and Maryland: Progressive application of LRFD to steel bridge erection engineering

Abstract

This paper tells the story of how a Bridge Construction Engineer and a Civil/Structural Engineering Professor learned from each other through the observation of bridge erection projects, and concurrent participation with industry organizations during development of the AASHTO LRFD Bridge Design Specifications (3rd–5th editions). Illustrations from several highway bridge projects in four states are used to explain a successful transitional journey from Service Load/Allowable Stress (SLD/ASD) to Load and Resistance Factor Design (LRFD) in steel bridge superstructure erection. Stability analysis and construction practice included the following: evaluation of controlling strength and serviceability criteria, steel bridge erection load (γ_i) factors, reconciliation of state-assigned construction wind loadings to the AASHTO Design Guide for Bridge Temporary Works and ASCE 7 (Minimum Loads for Buildings and other Structures), computation of lateral flange bending stress (f_l) utilized on straight, curved, haunched multi-girder bridges, as well as cross-box girder (straddle bent) piers during erection; member resistance during construction under local flange/web and lateral torsional buckling of single girders, girder slenderness (λ_i), L/b ratio rules of thumb and controlling bracing lengths during critical stages in the construction sequence, bearing point development, bridge system slenderness and the securing of partially constructed bridges (during storm events). Bridge erectors often exercise individual preferences in applying construction means and methods toward achieving specified geometry within alignment tolerances, so the interface between LRFD designed bridge members, ASD rigging components and ASD/Load Factor Design (LFD) temporary foundation components is also discussed.