A series of push-out tests of rectangular concrete-filled tubular columns (CFT) was recently conducted. The objective of this research program was to identify the shear transfer mechanisms between the infilled concrete and the steel tube and to determine a method for evaluating the capacity of the steel-concrete interface in a CFT column. The experimental variables investigated were the wall slenderness ratio (b/t) of the steel tube and the use of shear tab connections to apply axial load to the steel tube. The results of this study indicated that three mechanisms are responsible for shear transfer along the steel-concrete interface in a push-out specimen: adhesion of the concrete to the steel surface, friction, and wedging of the concrete core. The role of each mechanism in transferring shear between the concrete and steel in the CFT push-out specimen at various stages of load and slip is discussed. Design guidelines for shear transfer in rectangular CFT columns are presented, including a proposed bond strength equation and a recommended strength reduction factor for bond.

the reinforcing bars and the surrounding concrete within the beam column joint. This paper introduces a new innovative steel-concrete composite frame system with controlled plastic mechanism. This frame system consists of steel tubed reinforced concrete (STRC) columns, and ordinary reinforced concrete beams with relocated plastic hinges. Beam plastic hinges are relocated by the use of straight headed bars. The STRC column is an ordinary reinforced concrete column but, transversely reinforced with light ordinary ties and a thin steel tube. Compared to concrete filled tube column (CFT), the steel tube of STRC column transfers no axial load, provides better confinement, and consequently, increases column ductility. In this paper, experimental investigation of two full scale STRC columns and two beams with and without headed bars are presented. Test results suggest that STRC columns and beams with relocated plastic hinge regions could offer a more ductile structural frame system for medium and high rise buildings in zones of high seismicity.

This book is dedicated to Walter P. Moore, Jr., a leader in composite building design and engineering education. Topics include beam connection detail, advanced composites for waterfront infrastructure, evaluation of high-strength square CFT columns, push-out behavior of rectangular concrete-filled steel tubes, damping factors of composite RCS frames, structural safety of reinforced concrete flexural and compression members, behavior of new steel-concrete hybrid frame system, and hybrid RC frame-steel wall systems. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP196

The behavior of concrete filled steel tube (CFT) columns made from high strength materials was investigated experimentally. The effects of the width-to-thickness (b/t) ratio, steel tube stress-strain characteristics, and axial load on the stiffness, strength, and ductility of CFT beam-columns and stub columns were studied. Twelve experiments, which included four stub tests (monotonic axial load) and eight beam-column tests (constant axial and monotonic flexural load) were conducted. The CFT specimens were 305 mm square tubes, made from either conventional (A500 Grade-B) or high strength (A500 Grade-80) steel with nominal b/t ratios of 32 and 48. The CFT specimens were filled with high strength ( 104 MPa) concrete. Experimental results indicate that the concrete infill delays the local buckling of the steel tube, and that for lower levels of axial load and smaller b/t ratios the steel tube confines the infill concrete, thus increasing its ductility. Comparison of the experimental results with predictions based on current code provisions indicates that the axial load capacity of the high strength CFT stub column specimens can be predicted with reasonable accuracy by superposition of the yield strength of the steel tube and 85% of the compressive strength of the concrete infill. The moment capacity of the high strength CFT beam-column specimens can be conservatively estimated using American Concrete Institute provisions for conventional strength CFT beam-columns. The initial and serviceability-level section flexural stiffness of these specimens was predicted with reasonable accuracy using the uncracked transformed and cracked transformed section properties, respectively. The experimental results indicate that the curvature ductility of a high strength CFT beam-column decreases significantly with an increase in the axial load or the b/t ratio of the steel tube.

Using experimental data from previous tests and detailed analytical studies, the applicability of ACI and AISC standard techniques for concrete-filled tubular columns (CFTs) is evaluated. The test specimens include short and slender CFTs made with normal and high strength steel tubes filled with normal and high strength concrete. The focus of this paper is on rectangular and square tubes. To gauge the success of the code-based methods, the capacities are also computed by the fiber analysis techniques, along with a member level iteration algorithm for analyzing members with significant length. The results indicate that the ACI and AISC methods can yield substantially different capacities. In general, the capacities from the ACI method are reasonably close to those obtained from detailed analytical methods so long as normal strength tubes are used. Both the ACI moment magnifier method and AISC method are appropriate for slender CFTs although the ACI method tends to match the analytically calculated capacities more closely. Neither the ACI nor AISC method is applicable for CFTs made with high strength steel tubes as both techniques substantially underestimate the capacity of such columns. For CFTs with high strength steel tubes, it is more appropriate to assume that the steel tube fully yields when the capacity is developed. A revised version of the ACI standard method was developed by incorporating this assumption. The revised ACI method provides a fairly close estimate of the experimentally obtained capacities and those from detailed analysis.