International Concrete Abstracts Portal

Composite reinforced concrete column-steel beam (RCS) frame systems initiated in high-rise construction in the United States as perimeter moment framing (tnbular construction) due to the speed of erection, material cost savings, and enhanced lateral load resistance and performance. An overview of traditional RCS frame construction, advantages, previous research, and beam-column joint issues are presented. Then, the idea of using this form of construction for three-dimensional space frames is discussed and previous research on the performance of these systems for zones of high seismic risk is summarized. In a collaborative effort with structural engineers, an expenmental and analytical investigation of composite RCS fiame systems is proposed for low- to mid-rise construction in areas prone to high-level wind storms and/or moderate seismic risk. New beam-column joint connection details that are economically feasible and constructable are presented. The preliminary results from the analytical investigation on the proposed experimental specimen tests during lateral loading are also presented.

The new ACI 318-02 provision for minimum shear reinforcement, Equation (11-13), is based on tests of normal weight concrete beams. The evaluation of experimental data supported the code change making minimum shear reinforcement a function of the concrete cylinder strength. However, it also indicated that caution should be exercised when extrapolating current code minimums to beams with concrete cylinder strengths above 13 ksi (90 MPa). Because of the paucity of data on the shear strength of higher strength lightweight concrete beams with stirrups near code minimum values, the performance of this type of member is experimentally evaluated in this paper. The program consisted of four prestressed concrete beams, two specimens contained no stirrups, and two had stirrups near the code minimum. The specimens failed at shear capacities above calculated values. In the beams without stirrups, a 44% increase of the concrete cylinder strength resulted in a 28% increase of the measured shear strength. However, in the specimens with shear reinforcement (PC6S and PC10S), a 56% increase of the concrete cylinder strength only resulted in a 3% increase of the measured shear strength. The findings from the experimental program indicate that the current code minimum stirrups for lightweight concrete beams should he re-examined. The requirement results in a lower amount of minimum stirrups for higher strength lightweight concretes in comparison to the minimum amount required for an otherwise identical normal-weight concrete beam.

Design requirements for composite construction in steel and concrete as practiced in the United States are reviewed. Included are buildings and highway bridges. After a brief account of the origins of composite construction in America, an emphasis is placed on the early rules issued by ACI and AISC for composite columns in buildings, by AASHO - the predecessor of AASHTO-for composite beams in highway bridges and by AISC for composite beams in buildings. All four sections include outlines of subsequent changes that have taken place over the years. The paper is concluded with a discussion of a potential decrease in the strength of a stud shear connector located in the trough of a steel deck.

The use of high-strength concrete in construction industry has expanded in recent years for its superior strength and performance. However, many aspects of structural design for high-strength concrete columns remain to be developed. Of fundamental importance is the development of a rectangular stress block that is applicable to high-strength concrete. The current rectangular stress block parameters, intended for normal-strength concrete, are not suitable for use in high-strength concrete columns. A new rectangular stress block is presented in the paper for the computation of column strength under combined flexure and axial compression. Strength and ductility of concrete are inversely proportional. Therefore, high- strength concrete columns exhibit brittle characteristics, developing sudden and explosive failures under concentric compression. Therefore, the design of high-strength concrete columns becomes a challenge, especially for seismically active regions. While column ductility can be increased through confinement, the ACI 318-02 (1) confinement requirements are intended for normal-strength concrete columns and are not applicable to columns cast from high-strength concrete. A displacement based design procedure has been developed for the confinement of high-strength concrete columns. The procedure is presented in the paper with related design expressions. Summary of experimental findings on inelastic deformability of high-strength concrete columns is also presented with the effects of design parameters highlighted.

This paper presents the research work, experimental and analytical, on precast hybrid concrete beam-to-column connections at the National Institute of Standards and Technology and its contribution to the development of seismic design provisions for precast concrete frame structures.