Structural Behavior of a Concrete Box Girder Bridge RAYMOND E. DA VIS and JOHN J. KOZAK, California Division of Highways, and CHARLES F. SCHEFFEY, University of California, Berkeley •DURING THE past three years the California Division of Highways and the University of California at Berkeley have carried out an extensive program of research pertinent to concrete box girder bridges. Although the program had a number of objectives, its primary goal was the study of the manner in which live loads are distributed trans- versely in a box girder. Secondary objectives involved the determination of: (a) dead load distribution, (b) influence of intermediate diaphragms on live load distribution, and (c) influence of barrier curbs and railings on live load distribution. The University of California, in addition to providing consulting services in connec- tion with the field test, conducted studies of models, including a small plastic model and a ¼-scale concrete model of the prototype. The program also included a study of analytical methods which might accurately describe the empirically determined behavior of thP ~trnC'tnrP . The box girder section is generally conceded to have high torsional rigidity with at- tendant efficient transverse distributional properties. There is, however, a lack of experimental evidence and analytical procedures which can produce quantitative answers to support design specification provisions for load distribution. SCOPE The principal experimental effort comprised the field test of a new structure on the State highway system, the Harrison street Undercrossing, in Oakland, Calif. This structure was instrumented with SR-4 electrical resistance strain gages, Carlson strainmeters, and deflectometers to permit measurements of longitudinal and trans- verse strains and girder deflections resulting from a dynamic loading provided by a heavily loaded R-15 Euclid dump truck. Tests were conducted first without an inter- mediate diaphragm, secondly with a single intermediate diaphragm, and then after the addition of curbs and barrier railings . Strains and deflections produced by the slowly moving test vehicle were recorded by oscillographs housed in an instrumentation trailer parked beneath the structure. Com- panion tests were conducted and supplementary instrumentation was provided to support the principal objectives and investigate secondary objectives, among which were the following: 1. Control tests were accomplished concurrently with the dynamic testing to evalu- ate physical properties of the component materials of the structure. Tests were con- ducted on four concrete control beams, on standard concrete cylinders, and on rein- forcing steel coupons. 2. Laboratory tests were conducted by the Unive rsity of California on a plastic model of %a-scale and a concrete model of ¼-scale. 3. A small amount of dynamic testing was performed, with the test vehicle travers- ing the structure at speeds of 5, 10, 15, and 20 mph and with various patterns of ob- struction on the structure and its approach. In addition to selected strains and deflec- tions, the accelerations of the structure and test vehicle were measured. This phase of the test was not included in original plans for the program and is not discussed here; however, it was considered a worthwhile adjunct to provide valuable information per- Paper sponsored by Committee on Bridges. 32
Structural Behavior of a Concrete Box Girder Bridge
May 20, 2023
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