Oct 2016, Volume 10 Issue 3

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    Roberto T. LEON,Yu GAO

    This paper is divided into two parts. The first part addresses the resiliency and sustainability of steel and composite structures from a fundamental standpoint, and it is intended as an introduction to the other six papers that form part of this issue related to resiliency of steel structural systems in seismic areas. The paper posits the idea that resiliency is a characteristic that embodies sustainability rather than the traditional opposite point of view. The second part of the paper is divided into two sections, with the first section describing a number of retrofit technologies with recentering characteristics that have been developed for small, seismically deficient buildings in developing countries. The second section describes an innovative connection between circular concrete filled tubes and conventional beams with reduced flange sections consisting of steel and shape memory alloy bars and end plates. The connection has partial restraint behavior and strong recentering properties. This connection is used to demonstrate that some creative thinking can lead to innovative ways of addressing issues related to robustness, resiliency and sustainability of steel structures.

    Baiping DONG, James M. RICLES, Richard SAUSE

    This paper presents an experimental study of the seismic response of a 0.6-scale three-story seismic-resistant building structure consisting of a moment resisting frame (MRF) with reduced beam sections (RBS), and a frame with nonlinear viscous dampers and associated bracing (called the DBF). The emphasis is on assessing the seismic performance for the design basis earthquake (DBE) and maximum considered earthquake (MCE). Three MRF designs were studied, with the MRF designed for 100%, 75%, and 60%, respectively, of the required base shear design strength determined according to ASCE 7-10. The DBF with nonlinear viscous dampers was designed to control the lateral drift demands. Earthquake simulations using ensembles of DBE and MCE ground motions were conducted using the real-time hybrid simulation method. The results show the drift demand and damage that occurs in the MRF under seismic loading. Overall, the results show that a high level of seismic performance can be achieved under DBE and MCE ground motions, even for a building structure designed for as little as 60% of the base shear design strength required by ASCE 7-10 for a structure without dampers.

    Abhilasha MAURYA,Matthew R. EATHERTON

    In the past, several self-centering (SC) seismic systems have been developed. However, examples of self-centering systems used in practice are limited due to unusual field construction practices, high initial cost premiums and deformation incompatibility with the gravity framing. A self centering beam moment frame (SCB-MF) has been developed that mitigates several of these issues while adding to the advantages of a typical SC system. The self-centering beam (SCB) is a shop-fabricated, self-contained structural component that when implemented in a moment resisting frame can bring a building back to plumb after an earthquake. This paper describes the SCB concepts and experimental program on five SCB specimens at two-third scale relative to a prototype building. Experimental results are presented including the global force-deformation behavior. The SCBs are shown to undergo 5%–6% story drift without any observable damage to the SCB body and columns. Strength equations developed for the SCB predict the moment capacity well, with a mean difference of 6% between experimental and predicted capacities. The behavior of the restoring force mechanism is described. The limit states that cause a loss in system's restoring force which lead to a decrease in the self-centering capacity of the SCB-MF, are presented.

    Patricia M. CLAYTON,Daniel M. DOWDEN,Chao-Hsien LI,Jeffrey W. BERMAN,Michel BRUNEAU,Laura N. LOWES,Keh-Chuan TSAI

    As part of a Network for Earthquake Engineering Simulation research project led by researchers at the University of Washington with collaborators at University at Buffalo, and Taiwan National Center for Research on Earthquake Engineering, a self-centering steel plate shear wall (SC-SPSW) system has been developed to achieve enhanced seismic performance objectives, including recentering. The SC-SPSW consists of thin steel infill panels, referred to as web plates that serve as the primary lateral load-resisting and energy dissipating element of the system. Post-tensioned (PT) beam-to-column connections provide system recentering capabilities. A performance-based design procedure has been developed for the SC-SPSW, and a series of nonlinear response history analyses have been conducted to verify intended seismic performance at multiple hazard levels. Quasi-static subassembly tests, quasi-static and shake table tests of scaled three-story specimens, and pseudo-dynamic tests of two full-scale two-story SC-SPSWs have been conducted. As a culmination of this multi-year, multi-institutional project, this paper will present an overview of the SC-SPSW numerical and experimental research programs. This paper will also discuss innovative PT connection and web plate designs that were investigated to improve constructability, resilience, and seismic performance and that can be applied to other self-centering and steel plate shear wall systems.

    Tony T. Y. YANG,Yuanjie LI

    Buckling restrained knee braced truss moment frame (BRKBTMF) is a novel and innovative steel structural system that utilizes the advantages of long-span trusses and dedicated structural fuses for seismic applications. Steel trusses are very economical and effective in spanning large distance. However, conventional steel trusses are typically not suitable for seismic application, due to its lack of ductility and poor energy dissipation capacity. BRKBTMF utilizes buckling restrained braces (BRBs) as the designated structural fuses to dissipate the sudden surge of earthquake energy. This allows the BRKBTMF to economically and efficiently create large span structural systems for seismic applications. In this paper, a prototype BRKBTMF office building located in Berkeley, California, USA, was designed using performance-based plastic design procedure. The seismic performance of the prototype building was assessed using the state-of-the-art finite element software, OpenSees. Detailed BRB hysteresis and advanced element removal technique was implemented. The modeling approach allows the simulation for the force-deformation response of the BRB and the force redistribution within the system after the BRBs fracture. The developed finite element model was analyzed using incremental dynamic analysis approach to quantify the seismic performance of BRKBTMF. The results show BRKBTMF has excellent seismic performance with well controlled structural responses and resistance against collapse. In addition, life cycle repair cost of BRKBTMF was assessed using the next-generation performance-based earthquake engineering framework. The results confirm that BRKBTMF can effectively control the structural and non-structural component damages and minimize the repair costs of the structure under different ranges of earthquake shaking intensities. This studies conclude that BRKBTMF is a viable and effective seismic force resisting system.

    Chung-Che CHOU,Ping-Ting CHUNG,Tsung-Han WU,Alexis Rafael Ovalle BEATO

    A steel dual-core self-centering brace (DC-SCB) is an innovative structural member that provides both energy dissipation and self-centering properties to structures, reducing maximum and residual drifts of structures in earthquakes. The axial deformation capacity of the DC-SCB is doubled by a parallel arrangement of two inner cores, one outer box and two sets of tensioning elements. This paper presents cyclic test results of a DC-SCB component and a full-scale one-story, one-bay steel frame with a DC-SCB. The DC-SCB that was near 8 m-long was tested to evaluate its cyclic behavior and durability. The DC-SCB performed well under a total of three increasing cyclic loading tests and 60 low-cycle fatigue loading tests without failure. The maximum axial load of the DC-SCB was near 1700 kN at an interstory drift of 2.5%. Moreover, a three-story dual-core self-centering braced frame (DC-SCBF) with a single-diagonal DC-SCB was designed and its first-story, one-bay DC-SCBF subassembly specimen was tested in multiple earthquake-type loadings. The one-story, one-bay subassembly frame specimen performed well up to an interstory drift of 2% with yielding at the column base and local buckling in the steel beam; no damage of the DC-SCB was found after all tests. The maximum residual drift of the DC-SCBF caused by beam local buckling was 0.5% in 2.0% drift cycles.


    The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube (CFST) columns made with Rubberized Concrete (RuC), and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite moment-resisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.

    Chunyan QUAN,Wei WANG,Jian ZHOU,Rong WANG

    This paper presented an investigation on a stiffened joint in practical engineering which was between concrete-filled steel tubular column and steel beam with narrow outer diaphragm and partial joint penetration welds. Through the low-frequency cyclic loading test, the cyclic behavior and failure mode of the specimen were investigated. The results of the test indicated the failure mode and bearing capacity of the specimen which were influenced by the axial compression ratio of the concrete-filled tubular column. On the contrary, the inner diaphragm and inner stiffeners had limited impacts on the hysteretic behavior of the joint. There was no hysteresis damage fracture on the narrow outer diaphragm connected to the concrete-filled steel tubular column with partial joint penetration welds. Due to the excellent ductility and energy dissipating capacity, the proposed joint could be applied to the seismic design of high-rise buildings in highly intensive seismic region, but axial compression ratio should be controlled to avoid unfavorable failure modes.

    Bo GU,Xudong QIAN,Aziz AHMED

    This study reports a deformation limit for the initiation of ductile fracture failure in fatigue-cracked circular hollow section (CHS) X- and K-joints subjected to brace axial tension. The proposed approach sets the deformation limit as the numerically computed crack driving force in a fatigue crack at the hot-spot location in the tubular joint reaches the material fracture toughness measured from standard fracture specimens. The calibration of the numerical procedure predicates on reported numerical computations on the crack driving force and previously published verification study against large-scale CHS X-joints with fatigue generated surface cracks. The development of the deformation limit includes a normalization procedure, which covers a wide range of the geometric parameters and material toughness levels. The lower-bound deformation limits thus developed follow a linear relationship with respect to the crack-depth ratio for both X- and K-joints. Comparison of the predicated deformation limit against experimental on cracked tubular X- and K-joints demonstrates the conservative nature of the proposed deformation limit. The proposed deformation limit, when extrapolated to a zero crack depth, provides an estimate on the deformation limits for intact X- and K-joints under brace axial loads.