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.

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 amount of tension reinforcing steel bars plays a major role in determining the flexural ductility of reinforced concrete beams. The addition of Carbon Fiber Reinforced Polymer (CFRP) composites, which is another form of tension reinforcement, affects the ductility of concrete beams strengthened with CFRP sheets. Several researches have'investigated the use of CFRP for increasing the flexural strength of concrete beams. However, the flexural ductility of beams with respect to the amount and yield strength of existing ordinary steel bars has not been investigated in depth. In addition, delamination of CFRP sheets dominates the ultimate mode of failure of flexural members strengthened with CFRP sheets, which limits the ductility of strengthened members. There is a need to investigate the effect of CFRP anchorage system on the overall ductility of strengthened girders. This paper presents the results of an experimental investigation of nine large-scale reinforced concrete beams strengthened with CFRP composite sheets. The main variables are the amount of the existing reinforcing steel bars, yield strength of steel bars, and the type of CFRP anchorage. The amount (size and type) of the longitudinal CFRP sheets was maintained constant. Test results showed that the lower the amount of existing ordinary steel bars the lower the flexural ductility of the CFRP strengthened beams. Test results have also shown that CFRP anchorage could significantly increase the flexural ductility of CFRP strengthened beams. Such important findings should be reflected on the design equations of CFRP sheets required for strengthening existing reinforced concrete beams to ensure an acceptable level of flexural ductility.

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.

This Symposium Publication is a compilation of 13 papers presented at a sympsoium held at the 2002 ACI Spring Convention in Detroit honoring Richard W. Furlong. Topics include high-strength high-performance concrete columns and biaxial bending, the rold of FRP reinforcement and strut-and-tie models, the use of precast prestressed concrete in building and highway pavements, composite steel-concrete construction, and the teaching of structural concrete design. 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. SP213