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.

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.

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.

Adequate performance of coupled walls depends on sufficient stiffness, strength, and energy dissipation of coupling beams. To meet these goals, reinforced concrete coupling beams are often deep On the other hand, shallower steel beams can be used instead, and steel/composite coupling beams may be designed as shear-yielding members which have a more desirable energy dissipation characteristics. Such an option is not feasible for reinforced concrete beams. Well-established guidelines for links in eccentrically braced frames can be extrapolated to steel coupling beams. However, these provisions ignore the effects of concrete encasement which often surround the steel coupling beam. The reported research was conducted in an effort to till this void. Four one-third scale subassemblages of a wall segment and a coupling beam were extracted from a prototype structure, and were tested. The main test variables were the presence or lack of concrete encasement, and the number of web stiffeners. The encasement around the steel coupling beam increased the beam stiffness by 25%, and the shear strength by 18%. The additional stiffness enhances the level of coupling action which could lead into significantly larger wall axial loads, and would increase the demands on the foundation system. The increased stiffness needs to be incorporated in design. Although all the specimens could develop and exceed the expected capacities, the specimens failed due to less than desirable performance of the connection. Participation of the connection region towards energy dissipation became more substantial for the encased specimens, which is not desirable in view of post-earthquake repair. Connection design has to account for the increased capacity due to encasement, and details need to be improved to delay connection failure until plastic hinges in the coupling beam are fully mobilized. The encased specimens without any stiffeners performed as well as the specimens with stiffeners equal to or less than those required for steel link beams. No significant differences between the strength and stiffness characteristics of the encased specimens could be found. The experimental data suggest that nominal encasement is an effective means for preventing web buckling, and stiffeners are not needed. Current design codes need to be reevaluated for the cases where the steel coupling beam is encased.

This paper describes a large research project which was conducted to develop experimental data on composite structural elements consisting of a steel-concrete- steel (S-C-S) sandwich using headed studs to transfer shear within the composite element. This form of construction may be used as an alternative to either stained steel plate construction or reinforced concrete construction. The principal focus of the work was on marine structures such as arctic offshore drilling structures, tidal barrages, floating structures and submerged tube tunnels. Three distinct categories of structural elements were evaluated: cylinders, flat panels and curved panek’junctions. A total of 59 tests were conducted on large structural elements. The tests included composite cylinders under static axial, static radial and impact loads, flat panels under static in-plane axial, static out-of-plane bending fatigue out-of-plane bend, and static in-plane shear loads, and curved and junction panels under combined axial and bending loads. A 1: 10 scale was chosen for the cylinder tests and a 1:4 scale was used for all other flat and curved panels. To aid researchers and designers doing work on similar types of elements, descriptions of the test specimens, method of specimen preparation and test procedures are given in the paper. The experimental results will be available for release in 1998.