Use of Slurry Infiltrated Fiber Concrete (SIFCON) in Hinge Regions for Earthquake Resistant Structures

Abstract

This dissertation reports on an experimental and analytical study of the use of precast slurry infiltrated fiber concrete (SIFCON) flexural hinges to improve the seismic resistance of reinforced concrete moment frames. The main thrust of the research was to investigate how different variables effect the nonlinear, cyclic, flexural behavior of reinforced SIFCON hinges, and to determine how to optimize hinge performance. In addition, a conceptual analysis was performed to evaluate the improvement in seismic resistance from using SIFCON hinges in concrete structures. Seven 10" wide, 16" deep, and 26" long reinforced SIFCON hinges were designedand fabricated, then tested under quasi-static loading. All specimens were fabricated using between 9 and 11%, by volume, Dramix 30/50 fibers, made by the Bekaert Corporation. Grade 60, Grade 75, and ASTM A722 (Dywidag) bars were used, in combination with three different SIFCON compression strengths. Additionally, various end connection details were used in testing three different reinforcing arrangements. It was shown that precast SIFCON hinges can exhibit better performance than reinforced concrete hinges. The maximum curvature ductility achieved was 26.4 over a 4" inch long interior region of a specimen. The curvature ductility of this hinge specimen, when taken over the full 26 inch hinge length, was 10.5. SIFCON hinges absorb approximately 30% more energy than fiber-reinforced concrete hinges. SIFCON hinge ductility is limited by the ultimate tensile strain of the reinforcing steel. Grade 60 reinforcing resulted in the best hinge behavior seen in testing. Transverse ties may be required to prevent buckling of compression reinforcing. SIFCON flexural stiffness is approximately half that of comparable strength reinforced concrete beams.It was found that SIFCON material behavior is highly variable. Fiber orientation and size effects are the main variables that affect SIFCON behavior. Fabrication technique and skill of workmanship greatly affects fiber orientation, while size effects make it difficult to predict insitu SIFCON properties. State-of-the-art models are not accurate enough to facilitate using SIFCON hinges to build more earthquake resistant structures. With present models, the weakest region of a beam may actually be the strongest region.