Determination of Brace Forces Caused by Construction Loads and Wind Loads During Bridge Construction.

摘要

The first objective of this study was to develop procedures for determining bracing forces during bridge construction. Numerical finite element models and analysis techniques were developed for evaluating brace forces induced by construction loads acting on precast concrete girders (Florida-I Beams) in systems of multiple girders braced together. A large-scale parametric study was performed with both un-factored (service) and factored (strength) construction loads (in total, more than 600,000 separate three-dimensional (3-D) structural analyses were conducted). The parametric study included consideration of different Florida-I Beam cross-sections, span lengths, girder spacing, deck overhang widths, skew angles, number of girders, number of braces, and bracing configurations (K-brace and Xbrace). Additionally, partial coverage of wet (non-structural) concrete load and variable placement of deck finishing machine loads were considered. A MathCad calculation program was developed for quantifying brace forces using a database approach that employs multipledimensional linear interpolation. The accuracy of the database program was assessed by using it to predict end-span and intermediate-span brace forces for parameter selections not directly contained within the database, and then comparing the interpolated predictions to results obtained from finite element analyses of corresponding verification models. In a majority of cases, the database-predicted brace forces were found to be less than ten percent (10%) in error. The second objective of this study was to experimentally determine wind load coefficients (drag, torque, and lift) for common bridge girder shapes with stay-in-place (SIP) formwork and overhang formwork in place, and then to develop recommended global (system) pressure coefficients (e.g., for strength design of substructures). Wind tunnel tests were performed on reduced-scale models of Florida-I Beam (FIB), plate girder, and box girder cross-sectional shapes to measure aerodynamic forces acting on individual girders in the bridge cross-section. Tests were conducted at multiple wind angles, and corresponding tests with and without overhang formwork were conducted. Data from the wind tunnel tests were used to develop conservative procedures for calculating global pressure coefficients suitable for use in bridge design.