CONTINUOUS COMPOSITE BEAMS FOR BRIDGES

COMPOSITE DESIGN FOR BRIDGES IN THE UNITED STATES HAS BEEN LIMITED PRIMARILY TO SIMPLE SPANS OR TO THE POSITIVE MOMENT (SLAB IN COMPRESSION) REGIONS OF CONTINUOUS SPANS. IN THE LATTER CASE, EVEN THOUGH THE STEEL BEAM AND THE CONCRETE DECK ARE CONTINUOUS, CONNECTORS ARE USUALLY OMITTED FROM THE NEGATIVE MOMENT (SLAB IN TENSION) REGIONS OVER INTERIOR SUPPORTS. A PRINCIPAL REASON IS THAT THERE ARE AT PRESENT NO SIMPLE DESIGN RULES FOR SUCH IMPORTANT FACTORS AS CONNECTOR STRENGTH, INFLUENCE OF SLAB CRACKING, OPTIMUM REINFORCEMENT, EFFECTIVE WIDTH, AND TIME EFFECTS. AS A RESULT, MOST DESIGNS IGNORE ANY CONTRIBUTION OF THE SLAB AND REINFORCEMENT IN THE NEGATIVE MOMENT REGIONS. PREVIOUSLY, FULL-SCALE FATIGUE TESTS OF A TWO-SPAN CONTINUOUS COMPOSITE T-BEAM DESIGNED ACCORDING TO THE 1969 AASHO BRIDGE SPECIFICATIONS AND EMPLOYING DISCONTINUOUS SHEAR CONNECTION HAVE REVEALED FATIGUE FAILURES IN THE TOP LAYER OF LONGITU- DINAL REINFORCEMENT OVER THE INTERIOR SUPPORT AT ABOUT HALF THE DESIGN LIFE BASED ON THE FATIGUE REQUIREMENTS OF THE CONNECTORS. IN THE RESEARCH REPORTED HERE, ANALYTIC AND EXPERIMENTAL RESULTS INDICATE THAT SATISFACTORY PERFORMANCE RESULTS IF THE CONTINUOUS LONGITUDINAL REINFORCING STEEL IS AT LEAST 1--1.5% OF THE CROSS-SECTION AREA OF THE FREE SLAB AND SUFFICIENT ANCHORAGE CONNECTORS ARE PLACED NEAR THE POINTS OF CONTRAFLEXURE TO DEVELOP THE LONGITUDINAL REINFORCEMENT. THE MAJOR PARAMETERS EXAMINED WERE THE FREE SLAB LENGTH (LENGTH OF NEGATIVE MOMENT REGION OVER WHICH SHEAR CONNECTORS ARE OMITTED), THE AREA AND PERIMETER OF THE LONGITUDINAL REINFORCEMENT, AND THE INFLUENCE OF CONNECTOR CONCENTRATION AT THE ENDS OF THE FREE SLAB.