SP-174 Innovative design applications and advanced research has led to widespread use of steel and concrete composite and hybrid systems in the construction of buildings, bridges, and many other types of civil structures. The state of the art in this field continues to move forward today. Extensive research programs and field testing have yielded efficient, reliable, and safe procedures, incorporating these two dissimilar materials for overall improved construction. This publication presents an overview of the latest developments in behavior and design of composite and hybrid structures. In 1995 ACI Committee 335 sponsored two technical sessions in Montreal, Quebec on the current practice of the composite and hybrid construction and the state of the art in the field. Researchers and practicing engineers from the United States, Europe and Japan gave presentations encompassing topics related to design and construction of composite and hybrid systems and the advancement of research in three continents. The twelve papers appearing in this volume include topics presented in Montreal, along with additional manuscripts. The breadth and depth of the material covered make this publication a useful resource to practicing engineers, educators and researchers.

This paper describes research associated with the seismic behavior of moment connections for concrete filled tube (CFT) column-to-wide flange (WF) steel beam framing systems. The objective of this multiphase research program is to assess the force transfer mechanism in these connections, examining the effect various structural details have on this mechanism, as well as on the connection’s strength, stiffness, and ductility. The first phase of the program was devoted to assessing the shear capacity of the panel zone in a CFT column-to-beam connection under simulated seismic lateral load conditions. The results from tests show that a CFT panel zone possesses exceptional ductility, including connections without interior diaphragms. In addition, a capacity equation based on the superposition of the shear strength contribution of the steel tube and concrete core within the panel zone provides a prediction that agrees reasonably well with specimen strength. The second phase of the research program involves full-scale structural connection subassemblage tests. Results from tests show that specimens in which the beams are designed to dissipate energy can have exceptional cyclic ductility. However, connections’ must be properly detailed to avoid strain concentrations which could lead to fracture. Measured deformations in the column show that a CFT column’s initial stiffness is well estimated by transformed section theory. However, interstory drift deformations beyond 0.5% of the story height tend to reduce the stiffness after concrete cracking and debonding of the concrete from the steel tube.

The earthquake that shook southern Hyogo Prefecture in Japan on January 17, 1995 (also known as the Kobe earthquake) measured 7.2 on the Richter Scale. This event was the most devastating earthquake to strike Japan since the Kanto earthquake of 1923. This paper focuses on the performance of a particular composite system, referred to as Steel Reinforced Concrete (SRC). This type of structural system comprises approximately 10 percent of all square meters of construction in Japan. A major factor contributing to the collapse of many SRC buildings, known to Japanese researchers prior to the earthquake, could be said to be the lack of adequate confining steel and cross ties, especially for large columns. Additionally, the use of 90 degree hooks, even with close tie spacing, was shown to be undesirable.

Composite and Hybrid Structures (CHS) provide many advantages over those employing conventional systems. Since the available design codes in Japan do not cover these systems, the current Japanese Building Standard Law requires detailed experimental and/or analytical studies before the building permit for a structure with CHS can be issued. As part of the U.S.-Japan Cooperative Earthquake Research Program on Composite and Hybrid Structures, three major types of composite and hybrid systems are being studied. These include concrete-filled tubular columns (CFT), reinforced concrete columns with steel beams (RCS), and reinforced concrete cores with steel perimeter frames (HWS). Among other objectives, these studies are expected to lead to design guidelines which can be incorporated in the Building Standard Law. The availability of these guidelines are expected to encourage the Japanese designers to use CHS more frequently. This paper provides an overview of the ongoing studies in Japan. After a brief historical review of each system, the important issues related to each system are summarized. Planned and ongoing studies for each group of composite systems are also described.

Design of composite structures for earthquake loading has to address different problems to static design, as the advantageous greater damping may be offset by the disadvantage of increased mass and stiffness, leading to higher seismic loads. However, since composite construction is used extensively, especially for high-rise construction, the seismic performance of this form of structure requires investigation and the development of specific design guidance. European work over the past ten years or so confirmed that, with minimum design and detailing alterations, composite structures offer a most economical and reliable design alternative to steel and reinforced concrete structures. This paper reviews some of the European work on composite members. Particular emphasis is placed on work at Imperial College, since this was mostly carried out by the writer and his co-researchers. The work on a novel type of composite member is described,with special emphasis on ductility-based design recommendations. This is followed by a discussion of the role of composite beam-column connections and beam members in providing lateral stiffness, resistance and energy dissipation. Hierarchical assessment limit states are defined and are used to arrive at earthquake yield and ultimate response accelerations. These are used to calculate analytical behaviour factors of typical composite frames, which are shown to be more economical than steel frames designed for the criteria. Finally, brief comments regarding current and future work on seismic resistance of composite structures in Europe are given.