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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.

Reinforced concrete buildings with shearwalls are very efficient to resist earthquake disturbances. In general, reinforced concrete frames are governed by flexure and shearwalIs are governed by shear. If a structure includes both frames and shearwalIs, it is generalIy governed by shearwalIs. However, the ductility of ordinary reinforced concrete framed shear walls is very limited. To improve the ductility, this paper describes experiments on framed shearwal I s made of corrugated stee I, and the experimental results are compared with ordinary reinforced concrete frames and shearwalls. It is found that the ductility of framed shearwalls can be greatly improved if the thickness of the corrugated steel wall is appropriate to the surrounding reinforced concrete frame. If the thickness of the corrugated steel wall is too large when compared to the surrounding frame, the ductility will be reduced. It is also shown in this paper that the fiber-reinforced plastic composites can be used to strength the critical sections of the reinforced concrete frames, so that the seismic behavior (including ductility and dissipated energy) is improved.

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.

This paper summarizes the assumptions and analyses used for developing the reliability-based design of reinforced concrete flexural and compression members. Based on data on the variability of concrete and reinforcing steel physical and dimensional properties, estimates were made of the variability of strength of reinforced concrete beams and columns. These data, plus statistical descriptions of loadings, were used in a first-order, second-moment probabilistic analysis to compute resistance factors. Two sets of resistance factors for reinforced concrete members subjected to flexure or combined axial load and flexure are discussed: (a) resistance factors compatible with the current American Concrete Institute (ACI) load factors specified in ACI 3 18-95 Section 9.2; and (b) resistance factors compatible with the American Society of Civil Engineers (ASCE) Standard 7-95 (ANSI A58-1) load factors included in ACI 3 18-95 Appendix C. This paper provides a direct comparison between the two sets of load and resistance factors that are now part of the ACI 3 18 safety criteria.

Steel-concrete composite columns may be designed either by requirements of the American Concrete Institute Building Code AC1 3 18-99 or by the American Institute of Steel Construction Specifications for Load and Resistance Factor Design, 2d Edition (1995). Each design standard is described for application to a concrete filled steel tube and to a concrete encased structural shape as each is designed for the same dimensional and service load conditions. These standard type column sections are used for the comparison, as the LRFD specification can be used directly only for such standard sections. The design exercise demonstrates that a) the LRFD specification requires fewer computational steps and is therefore easier to apply, b) the ACI rules tend to exaggerate the influence of slenderness, and c) different but very similar results were obtained for the two methods applied to the same design problem.