Modeling shear behavior of hybrid RCS beam-column connections

A model to predict the shear strength versus shear distortion response of hybrid connections between reinforced concrete columns and steel (RCS) beams is presented. Based on a preestablished maximum attainable joint shear deformation, design equations were developed for use in both interior and exterior RCS connections in buildings located in high seismic risk zones. The proposed model is based on the definition of the state of plane strain in the joint through the development of a ratio between the principal tensile and compression strains. The strength of the joints is given by contributions from the steel web panel and concrete diagonal struts. The joint model is capable of predicting the shear force, and stirrup and concrete strains at any level of joint shear distortion for exterior joints. In addition, the use of the proposed design equations led to excellent agreement between predicted and measured shear strength for both interior and exterior RCS joints. Hybrid structures with reinforced concrete and steel (RCS) members have gained popularity during the last few years. Steel and reinforced concrete (RC) elements are used in these mixed structures such that the advantages of each material are combined to form efficient structural systems. One of the most common types of composite structures is represented by RCS frames consisting of RC columns and steel beams. Several advantages have been reported regarding the construction and behavior of these structures. From the construction viewpoint, these systems are usually built by first erecting a steel skeleton, which allows the performance of different construction tasks along the height of the building (Griffis 1986). Structurally, the connections between steel beams and RC columns have been reported to possess a good strength and stiffness retention capacity when subjected to large load reversals (Kanno 1993; Parra-Montesinos and Wight 2000a). In 1994 an ASCE task committee published guidelines for the design of connections in RCS frames (ASCE 1994). Al- though these guidelines were primarily based on experimental results obtained from testing of only interior connections under monotonic and cyclic loading, they were intended for use in both interior and exterior joints in buildings located in low to moderate seismic risk zones. Testing of interior RCS beam- column subassemblies under severe earthquake-type loading revealed that these guidelines give conservative estimates of the shear strength in interior joints (Kanno 1993). To evaluate the adequacy of these design provisions for use in exterior joints under seismic loading, a series of tests on exterior con- nections were conducted at the University of Michigan. De- tailed information on this research can be found elsewhere (Parra-Montesinos and Wight 2000b). Test results indicated large discrepancies between predicted and experimental shear strength in exterior RCS joints, when using the ASCE design guidelines. Therefore, a new model to predict the shear force, and stirrup and concrete strains at any level of shear distortion in RCS joints was developed. Based on this model, design equations for evaluating the ultimate shear strength of both exterior and interior RCS connections are presented. 1