Field Testing and Load Rating Procedures for Steel Girder Bridges

摘要

Many of the nation's bridges are posted for restricted truck loading. Analytical211u001ecapacity rating procedures tend to underestimate the true stiffness and 211u001eoverestimate the response of bridges. Research has shown that in most cases, 211u001ebridges exhibit capacities higher than analytical load capacity rating 211u001epredictions. These rating procedures are based on conservative design assumptions 211u001ethat do not always represent the true bridge behavior. Testing bridges in the 211u001efield has demonstrated this additional capacity and bridge field testing has 211u001ebecome an acceptable means to determine a more accurate estimate of a bridge's 211u001esafe capacity. Many factors not considered in the design process contribute to 211u001ethe response of a tested bridge. Several of these, like the actual load 211u001edistribution and additional system stiffness from curbs and railing, are welcome 211u001ebenefits and can be used to increase weight limits on bridges. However, there are 211u001ealso contributions from bearing restraint forces and unintended composite action 211u001ethat may not be reliable during the service life of the structure. Determining 211u001ehow much of the increase in capacity is acceptable is difficult. This report 211u001epresents systematic field test rating procedures that separate and quantify these 211u001econtributing factors so that owners may remove unwanted contributors and retain 211u001ethe reliable benefits. An efficient test plan is applied to a three-span steel 211u001egirder bridge to demonstrate the procedures. The bridge is currently posted for 211u001erestricted lanes and loads using allowable stress rating procedures. Field test 211u001eresults show that the posted capacity can safely be raised near (opening the 211u001ebridge to two lanes of traffic) or above (maintaining a single lane) legal AASHTO 211u001eH20 truck loads.