Abolhassan Astaneh-Asl

Hysteresis model of bolted-angle connections

Abstract This paper presents a hysteretic model of bolted-angle connections for seismic analysis of semi-rigid steel frames with bolted connections. A semi-rigid beam-to-column connection is divided into a finite number of fiber elements. Hysteretic behavior of the fiber elements under repeated tension and compression has been established using the combined experimental and analytical results. The model has been implemented into a general purpose computer program and agrees well with experimental results. The main features of the model include: (1) Parameters of the model are directly related to a connection design; (2) Hysteresis rules are developed directly from comprehensive experiments specifically designed for modeling.

Hysteretic behavior of bolted-angle connections

Abstract This paper presents an experimental investigation on the hysteretic behavior of bolted-angle beam-to-column connections. The investigation focused on: (1) the inelastic behavior under large cyclic deformation, (2) the failure modes under cyclic loading, and (3) the energy-dissipation capacity of the bolted-angle connections. Two deformation patterns, distinguished by the relative strength of angles and bolts, had a significant influence on the hysteretic behavior of the connections. Based on the experimental results, hysteresis rules were established to lay a foundation for the development of a behavioral hysteresis model of bolted-angle connections.

Behavior and design of single plate shear connections

Abstract Steel shear connections are primarily used to transfer the reaction of a simply supported beam to its support, normally a column or a beam. Currently, the most common shear connection in North America is a single plate connection consisting of a plate fillet welded to a supporting column or girder and bolted to the web of a simply supported beam. A shear connection should be strong enough to be able to transfer the shear force, yet, it should be sufficiently flexible and ductile to allow the end of simply supported beam to rotate with ease and accommodate the rotation demand of the beam. This paper summarizes a number of research and development projects conducted at the University of California, Berkeley to study behavior of single plate shear (shear tab) connections and to develop design procedures and guidelines, both for gravity and lateral load (seismic and wind) effects. The connections were sufficiently ductile to accommodate end rotation demands of simply supported beams under gravity load and drift rotations under lateral load effects. Design procedures developed and proposed and currently used in design of single plate connections are strength-based procedures that ensure occurrence of ductile and more desirable failure modes, such as yielding of the steel plate prior to occurrence of brittle and less desirable failure modes such as fracture of bolts and welds.

Fire Protection of Steel Bridges and the Case of the MacArthur Maze Fire Collapse

Both steel and reinforced concrete bridges are vulnerable to fire caused by a multitude of events such as tanker truck accidents, wildfires, arson or terrorism. This paper addresses bridges with steel super-structure and steel reinforced concrete or composite piers. After a brief summary of fire effects on bridges, the paper discusses the fire-induced collapse of two spans of the MacArthur Maze, a steel elevated freeway in Oakland, California. The two spans collapsed on April 29th, 2007 due to a fire caused by a tanker truck that overturned on the bridge. This paper discusses solutions and technologies that can mitigate the fire hazard in steel bridges. Based on the field investigation and analysis of collected data as well as fire analysis results, the following conclusions were reached: (1) the collapse could be prevented if the bridge was studies for the fire risk which would have led to recognition of high fire hazard at this intersection and vulnerability of the exposed steel girders,(2) the steel bridges and overpasses can be fire-protected using a variety of technologies and products successfully used in buildings; and (3) the current analytical tools could predict the time of the collapse accurately.

Stability of damaged steel moment frames in Los Angeles

During the 17 January, 1994 Northridge earthquake a number of welded moment resisting frames (WMRF) developed cracks in their beam-column connections. In this work, the seismic performance of a four-story, a 14-story and a 27-story moment resisting frame damaged during the Northridge earthquake is analyzed in order to assess the seismic vulnerability of damaged WMRFs. Analytical models of planar frames with damaged and undamaged connections are developed, and nonlinear analyses are conducted by subjecting the models to various intensities of the Northridge-Newhall, Miyagi-ken-Oki, El Centro and Taft records. Analysis results show that the damaged frames behave somewhat like a semi-rigid steel structure and that, at least in the cases covered by this investigation, it does not appear that the damaged structures were susceptible to collapse as a result of the earthquakes used in this study.

Post-earthquake stability of steel moment frames with damaged connections

Publisher Summary This chapter investigates seismic safety of welded steel moment frames damaged during the 1994 Northridge earthquake. A 4-story, a 14-story and a 27-story building in Los Angeles were examined. Inelastic 2-D models of the undamaged and damaged frames representing the three buildings were subjected to various intensities of several past earthquake records. The results indicated that seismic behavior of the damaged frames is somewhat similar to the behavior of steel semi-rigid frames. The cracks in the bottom flange welds did not cause the study-frames to be more susceptible to collapse than the same frames before the damage. No tendency to collapse due to P-Δ effects was detected in the three study-frames subjected to various intensities of the earthquake records that were used.

The Response of Long-Span Bridges to Low Frequency, Near-Fault Earthquake Ground Motions

Historical seismic hazard characterizations did not include earthquake ground motion waveforms at frequencies below approximately 0.2 Hz (5 seconds period). This resulted from limitations in early strong motion instrumentation and signal processing techniques, a lack of measurements in the near-field of major earthquakes and therefore no observational awareness, and a delayed understanding in the engineering community of the potential significance of these types of motions. In recent years, there is a growing recognition of the relevance of near-fault, low frequency motions, particularly for long-period structures such as large bridges. This paper describes a computationally based study of the effects of low frequency (long-period) near-fault motions on long-span bridge response. The importance of inclusion of these types of motions for long span cable supported bridges is demonstrated using actual measured broad-band, near-fault motions from large earthquakes.

Lateral Stiffness of Steel Shear Wall Systems

Lateral stiffness is an essential design parameter for steel shear wall systems. The research presented in this paper consisted of conducting nonlinear finite element analyses of steel shear wall systems to investigate lateral load resisting strength as well as lateral stiffness of this type of structural systems. Detailed parametric studies were carried out to provide a better understanding of initial buckling behavior, lateral stiffness during the pre- and post-buckling region as well as during the post-yielding region. The studies indicated that initial buckling generally occurs under relatively small drift in the order of 0.0002 radians and after buckling the stiffness of the wall is reduced to less than 70% of its initial stiffness. When the steel shear wall yields, the stiffness rapidly decreases to the level of stiffness provided by the frame alone, which in general was about 20% of the total stiffness. In the parametric studies, the effects of wall thickness, strength and stiffness of the boundary elements as well as aspect ratio of the wall were varied and their effects on the lateral stiffness studied.

Experimental and Analytical Studies of a Steel Plate Shear Wall System

This paper concentrates on the experimental studies of an innovative steel shear wall system used in buildings in USA, presents a summary of test results and discussion on post-test data-analyses, and compares the experimental results to FEA analyses. The innovative steel plate shear wall system, originally developed by the Magnusson Klemencic Associates of Seattle, consists of steel plate shear walls welded inside a steel boundary moment frame in two bays. The two bays are connected through wide flange (WF) coupling beams. The steel moment frame consists of exterior concrete filled steel tubes (CFT), interior WF columns, and horizontal WF beams. Cyclic quasi-static tests were conducted on two half-scale specimens representing this system with two different wall span-to-height ratios of one-to-one and one-to-one and half. Both specimens showed high ductility and stable inelastic behavior with inter-story drift values exceeding 0.03 radians. Data analyses were conducted after the test to validate test observations and summarize general seismic behavior of the system. FEM model of the test specimen were constructed and the analytical results were compared with test results.

STEEL SHEAR WALLS, BEHAVIOR, MODELING AND DESIGN

In recent years steel shear walls have become one of the more efficient lateral load resisting systems in tall buildings. The basic steel shear wall system consists of a steel plate welded to boundary steel columns and boundary steel beams. In some cases the boundary columns have been concrete‐filled steel tubes. Seismic behavior of steel shear wall systems during actual earthquakes and based on laboratory cyclic tests indicates that the systems are quite ductile and can be designed in an economical way to have sufficient stiffness, strength, ductility and energy dissipation capacity to resist seismic effects of strong earthquakes. This paper, after summarizing the past research, presents the results of two tests of an innovative steel shear wall system where the boundary elements are concrete‐filled tubes. Then, a review of currently available analytical models of steel shear walls is provided with a discussion of capabilities and limitations of each model. We have observed that the tension only “strip m...