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The article discusses a study which examined the seismic behavior of H-beam to circular tubular column connections constrained by a ring diaphragm. It cites the use of a three-dimensional (3D) connection sub-assembly testing system. Particular focus is given to testing of materials to failure under unidirectional or bidirectional cyclic loads. Results of the study showed different failure models for two-dimensional (2D) and 3D weak panel connections. Findings also revealed final structure exhibited by weak beam connections at the junction between diaphragm and beam flange. It mentions the feasibility of small diaphragm width and simplified fillet welding.

Results from an investigation aimed at assessing seismic behavior of transfer story connections for high-rise building consisting of steel-reinforced concrete (SRC) frame and reinforced concrete (RC) core tube are presented. Two types of transfer story connections were experimentally evaluated for adequate strength, ductility and energy dissipation. For each type of connection, two large-scale subassembly tests were carried out under monotonic and cyclic lateral displacement, respectively. Detailed observations and behavior responses were obtained to contrast the differences between monotonic and cyclic performance of the connections. Test results showed that the SRC column failed before connection collapse and that loading types have little effect on the strength but greatly affect the failure modes and the ductility of the connections. All specimens exhibited good properties for earthquake resistance since they all kept a stable inelastic behavior up to the interstory drift demand suggested by the AISC Seismic Provisions. Based on test observations, support stiffeners with appropriate width-to-thickness ratio and mechanical connectors connecting bars with the steel plate are recommended for design purposes in order to achieve more ductile and reliable seismic behavior of transfer story connections. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article summarizes the background information for composite columns and beam-columns relevant to new provisions in the 2005 American Institute of Steel Construction Inc. (AISC) Specification (AISC, 2005b). The columns include steel reinforced concrete (SRC) and concrete-filled steel tube (CFT) members. According to the authors, AISC, 2005b include provisions for composite column axial compressive strength, local buckling strength of concrete-filled tubes, and shear strength of composite members.

A full-scale two-story unreinforced masonry (URM) building was tested in a quasistatic fashion to investigate the nonlinear properties of existing URM structures and to assess the efficiency of several common retrofit techniques. This paper presents the main experimental findings associated with the nonlinear properties of the original URM structure. The test structure exhibited large initial stiffness and its damage was characterized by large, discrete cracks that developed in masonry walls. Significant global behavior such as global rocking of an entire wall, and local responses such as rocking and sliding of each individual pier were observed in the masonry walls with different configurations. In addition, formation of flanges in perpendicular walls and overturning moments had significant effects on the behavior of the test structure. A comparison between the experimental observations and the predictions of FEMA 356 provisions shows that major improvements are needed for this latter methodology. [ABSTRACT FROM AUTHOR]

A variety of elastic and inelastic analytical approaches were used to investigate the response of a full-scale unreinforced masonry (URM) structure tested in the laboratory. Elastic analyses, employing a three-dimensional finite element model, revealed little coupling between parallel walls, and pointed to the appropriateness of two-dimensional analytical tools for further simulation of the test structure. The nonlinear analytical methods employed included, in order of increasing complexity, a rigid body analysis, a two-dimensional nonlinear pushover analysis, and a three-dimensional nonlinear finite element analysis. All methods considered important structural characteristics such as failure modes of perforated walls, flange effects, and global overturning moment effect. All methods predicted the experimental behavior fairly well. Strengths and weaknesses of these analytical approaches are discussed, and recommendations for analyzing old URM buildings are presented. [ABSTRACT FROM AUTHOR]

This study evaluates the feasibility of a new class of partially restrained connections using shape memory alloys. In the martensitic form, shape memory alloys (SMAs) have the ability to recover large residual deformations by heating the alloy above its transformation temperature. The proposed connection consists of four large diameter NiTi SMA bars connecting the beam flange to the column flange and serve as the primary moment transfer mechanism. Two full-scale connections were tested using the SAC loading protocol. The connections exhibited a high level of energy dissipation, large ductility capacity, and no strength degradation after being subjected to cycles up to 4% drift. Following the initial testing series, the tendons were heated to recover the residual beam tip displacement. After initiating the shape memory effect within the tendons, the connections were retested, displaying repeatable and stable hysteretic behavior. An additional test was performed under dynamic loading to examine the strain rate effects on the performance of the connection. The dynamic tests showed similar behavior, except for a decrease in energy dissipation capacity when compared to the quasi-static tests. [ABSTRACT FROM AUTHOR]

Partially restrained connections and their interaction with the floor slab have received recent attention due to numerous failures of welded steel moment frames during the 1994 Northridge and 1995 Kobe earthquakes. After the earthquakes, it was apparent that the “simple” connections, including the slab, served as a “backup” structural system after the full moment connections failed. These connections significantly influenced the behavior of the lateral load resisting system. This paper reports on the results of a unique, full-scale bidirectional test on a composite connection. The connection behaved very well up to a uniaxial drift of about 2%. After that drift level, composite action began to deteriorate and the connection strength and stiffness declined. The results indicate that two previously unreported failure modes may need to be considered in the design of composite buildings if large cyclic bidirectional forces are present. One is a “punch through” of the column web due to the force transfer from the “pinned” side of the connection. The other is the formation of a concrete wedge as a result of the large bearing forces between the slab and steel column flange. As a result of this observation, a suggestion that the full depth of the slab be maintained for a region 150 mm (6 in.) around the joint has been incorporated in the commentary to Part II of the 2002 AISC Seismic Specification. [ABSTRACT FROM AUTHOR]

Presents information on a study which focused on the results of tests on T-stub specimens of bolted steel connections. Behavior of bolted connections; Tension bolt and flange strength; Conclusions.

The Borax corporate headquarters building, a low-rise steel moment frame, was less than one year old when it sustained significant structural damage during the 1994 Northridge earthquake. Seventy-five percent of its steel moment-resisting connections suffered severe brittle fractures. This paper presents a detailed documentation of the forensic investigation performed on this structure immediately following the earthquake. A companion paper presents the findings from a subsequent computational investigation performed on the structure. The two primary failure modes at the Borax building were column flange fracture and pull-out of the girder flange from the column. The failures are primarily attributed to a fundamental flaw in the standard code-prescribed welded-flange bolted-web connection and the extreme ground motion at the site. The paper also describes the repairs made to the structure. These repairs were completed before the SAC research that now guides repair and retrofit of these structures was available. [ABSTRACT FROM AUTHOR]

This paper presents the findings from a computational investigation performed on the Borax corporate headquarters building, a four-story steel frame structure in which 75% of the steel moment-resisting connections suffered brittle fractures during the 1994 Northridge earthquake. A companion paper provides detailed documentation of the forensic investigation and repair design performed immediately following the earthquake on this structure, which was less than one year old when the earthquake struck. This paper describes a series of preliminary analyses conducted shortly after the forensic investigation and repair were completed. The main objectives were to investigate the behavior of the structure during the earthquake, and to determine whether different levels of established, advanced analysis techniques could estimate the distribution and extent of the damage. The results showed that a three-dimensional nonlinear dynamic analysis using a site-specific accelerogram provides strong correlation with the observed damage, while elastic static and dynamic analyses, two-dimensional nonlinear static and dynamic analyses, and three-dimensional nonlinear static analyses show less correlation. In addition, the results indicate that substantial redistribution of forces may have occurred, and that force distribution most likely had a noticeable effect on the pattern of failures observed in the structure. [ABSTRACT FROM AUTHOR]