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.

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.

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.

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.

Equivalent macromodel-based analytical tools, comprised of flexibility-based element models, are used to accurately represent the non-linear moment-curvature (force-deformation) response characteristics in structural systems using columns of reinforced concrete (RC) or composite steel sections encased in reinforced concrete (SRC), structural steel beams, and composite beam-column joints. To facilitate the modeling of inelastic deformations in joint regions, a panel element capable of representing joint shear distortions and joint bearing deformations was developed and incorporated into an existing computer program, IDARC. The inelastic shear-deformation characteristics of the joint panel were partly established from guidelines published by an ASCE Task Committee (1). Various hysteretic control parameters for members of the subassemblage, such as strength degradation, stiffness deterioration, and pinching (slip), were quantified based on observed experimental response. Potential failure modes in the steel beam, RC or SRC column, and composite joint of the frame subassemblage can be represented in the proposed formulation. Experimental subassemblage testing performed at Cornell University (2) was used to validate the analytical platform. It is shown that the revised IDARC program can be used for seismic evaluation of composite structures and for development of design guidelines to ensure desirable mechanisms in RCBRC structures.