Moment Redistribution Behavior of Steel Fiber Reinforced Concrete Continuous Beams

Abstract

The redistribution of moment has been confirmed in reinforced concrete structure by experimental investigations. It is also a fact that reinforced concrete structures have comparatively lower capacity to rotate than steel structures. Yet, this phenomenon is drawing the attention of the designers. Presently, design codes of most of countries allow the redistribution up to maximum limit. The addition of steel fibers will enhance the redistribution of moment forming ductile section. The study characterized the moment redistribution behavior of a steel fiber reinforced concrete (SFRC) continuous beam subjected to five point bending test modelled in FEA using constitutive material model. The compression behavior was obtained using uniaxial compression strength tests while the tensile behavior was obtained using splitting strength test analysis performed according to flexural test results. These properties were utilized to derive a theoretical moment-curvature relation for each SFRC member which supplied the basis for the characterized moment-rotation behavior and the finite element analyses (FEA) performed on the continuous beam. The laboratory tests for compressive and splitting tensile strength of SFRC were conducted for volume of steel fibers, 0%, 0.5%, 0.75% and 1.5%. From the tests results it was observed that the compressive strength increased by 26.8% for 0.5% SFRC, 30.7% for 0.75% SFRC and reduced by 5.3% for 1.5% SFRC. The splitting tensile strength increased by 11.2% for 0.5%, 5.8% for 0.75% and 2.5% for 1.5% SFRC. Increment of peak strain was also confirmed. The ductility of the member was increased 1.59 times, 2.41 times and 3.25 for 0.5%, 0.75% and 1.5% SFRC member respectively, compared to that of the 0 % SFRC member’s rotation capability. Section moment capacity was also enhanced by Increasing steel fibers volume. The development of the moment redistribution was accompanied by the rotation of the plastic hinges at the critical sections in the beam. The amount of moment redistribution of SFRC reduced as volume of steel fiber increased. So utilizing permissible moment redistribution for SFRC as prescribed by design standards needs further study.