Bing Qu

Capacity Design of Intermediate Horizontal Boundary Elements of Steel Plate Shear Walls

Consistent with capacity design principles and requirements of ductile behavior, the 2005 AISC and 2001 CSA seismic design codes require that the intermediate horizontal boundary elements HBEs of steel plate shear walls SPSWs be designed to remain essentially elastic with the exception of plastic hinges at their ends when the infill plates fully yield under seismic loading. However, the unexpected failure observed during the tests on a full-scale two-story SPSW suggested that the current design approach does not necessarily lead to an intermediate HBE with the expected performance. This paper presents analytical models for estimating the design forces for intermediate HBEs to reliably achieve capacity design. Those models combine the assumed plastic mechanism with a linear beam model of intermediate HBE considering fully yielded infill panels and are able to prevent in-span plastic hinges. Design forces predicted using the proposed models are compared with those from nonlinear finite element analysis. Good agreement is observed. Finally, the proposed models are also used to explain the observed premature failure of intermediate HBE. DOI: 10.1061/ASCEST.1943-541X.0000167 CE Database subject headings: Shear walls; Steel plates; Earthquake engineering; Seismic design. Author keywords: Shear walls; Steel plates; Capacity; Design; Earthquake engineering; Seismic design.

Design of Steel Plate Shear Walls Considering Boundary Frame Moment Resisting Action

Conventional design of steel plate shear walls (SPSWs) assumes that 100% of the story shear is resisted by each infill panel. Following this approach, strength provided by the boundary frame moment resisting action, which provides the SPSW with overstrength, is neglected. While this design assumption has a positive impact on seismic performance of SPSWs, no analytical work has been done to quantify the magnitude of this overstrength in general terms. Such preliminary work is conducted in this paper. Based on plastic analysis of SPSWs, this paper investigates the relative and respective contributions of boundary frame moment resisting action and infill panel tension field action to the overall plastic strength of SPSWs, followed by a proposed procedure to make use of the strength provided by the boundary frame moment resisting action. Procedures for design of SPSWs having weak infill panels are also developed in this paper. Then, results from a series of time history analyses using validated models are presented to compare the seismic performances of SPSWs designed using different design assumptions. Future work needed to provide greater insight on SPSW designs is also identified.

Transforming Seismic Performance of Deficient Steel Concentrically Braced Frames through Implementation of Rocking Cores

AbstractThe use of steel concentrically braced frames (CBFs) has substantially increased recently. However, investigations and observations from past earthquakes suggest that some existing CBFs, particularly the older ones that are still in service but were designed without ductile detailing and compliance with state-of-the-art seismic provisions, may exhibit unfavorable performance during strong earthquake events. This research numerically examines the adequacy of a seismic rehabilitation technology for deficient multistory CBFs. The technology consists of one or multiple rocking cores (RCs) added to an existing CBF to redistribute the seismic forces applied to the frame and reduce the system seismic response. For demonstration purposes, one three-story and one six-story CBF buildings are selected and rehabilitated using the RC technology. Finite-element (FE) models of the considered systems, which explicitly take into account the effect of gusset plates, member yielding, brace buckling, brace rupture, a...

Seismic Rehabilitation of Concentrically Braced Frames Using Stiff Rocking Cores

AbstractExisting steel concentrically braced frame (CBF) buildings subjected to seismic hazards can exhibit an undesirable soft-story response, in which drift and damage are concentrated in a singl...

Testing of Buckling-Restrained Braces with Replaceable Steel Angle Fuses

AbstractThis research focuses on a new type of buckling-restrained brace (BRB) with replaceable steel angle fuses. The proposed BRB offers ease of postearthquake examination of fuse damage, conveni...

Rehabilitation of steel concentrically braced frames with rocking cores for improved performance under near-fault ground motions

This article focuses on evaluating the adequacy of a seismic rehabilitation technology which adds rocking cores to deficient steel concentrically braced frames in near-fault regions. Two demonstration buildings were rehabilitated with the technology. Seismic performance of the rehabilitated buildings was evaluated through numerical simulations. Analysis results suggest that the code-compliant concentrically braced frames may be vulnerable to collapse under the fault-normal components of the near-fault ground motions, approximately having a probability of exceedance of 10% in 50u2009years. It is found that the Rocking Core technology is effective in reducing the inter-story drift responses of the demonstration buildings under near-fault earthquakes. The rehabilitated systems can further benefit from the use of hysteretic energy dissipating links between the rocking cores and existing concentrically braced frames. This article also addresses the influence of the rocking cores on modal properties of the rehabilitated buildings. It is found that the rocking core with moderate stiffness does not significantly alter the modal properties of a rehabilitated concentrically braced frame.

Hybrid Testing of the Stiff Rocking Core Seismic Rehabilitation Technique

AbstractThe use of a stiff rocking core (SRC) has been proposed as a seismic rehabilitation technique to mitigate soft-story response in low-rise to midrise steel concentrically braced frame (CBF) ...

Structural Behavior of Thin-Walled Concrete-Filled Steel Tube Used in Cable Tunnel: An Experimental and Numerical Investigation

One steel grid and five thin-walled concrete-filled steel tubes (CTST) used as the supports of tunnel were tested in site for investigating the mechanical behavior. The mechanical influences of thickness, node form, and concrete on CTST were gained and compared with the impacts on steel grid. It is indicated that high antideformation capacity of CTST improved the stability of surrounding rock in short time. The cementitious grouted sleeve connection exhibited superior flexibility when CTST was erected and built. Although the deformation of rock and soil in the tunnel was increasing, good compression resistance was observed by CTST with the new connection type. It was also seen that vault, tube foot, and connections were with larger absolute strain values. The finite element analysis (FEA) was carried out using ABAQUS program. The results were validated by comparison with experimental results. The FE model could be referred by similar projects.

Mitigation of Soft-Story Failures in Multi-Story Steel Concentrically Braced Frames through Implementation of Stiff Rocking Cores

This paper focuses on investigation of a new seismic rehabilitation method to mitigate soft-story failures in deficient multi-story Steel Concentrically Braced Frames (CBFs). The considered method consists of a sufficiently stiff Rocking Core (RC) that is pinned to the foundation and connected to an existing deficient CBF building to re-distribute seismic forces along its height creating more uniform interstory drift and ductility demand distributions. Two benchmark steel CBF buildings including one three-story and one six-story, designed for Los Angeles, California, were selected and retrofitted using the considered method. Nonlinear static pushover analyses were conducted to demonstrate the beneficial contribution of RC in mitigating non-uniform inter-story drift distribution. It is shown that the RC is effective in reducing inter-story drift concentration in both buildings when they reach the maximum inter-story drift limits associated with collapse prevention, lift safety and immediate occupancy recommended in FEMA 356 for performance-based seismic design.

Behavior and Design of Intermediate HBE in Steel Plate Shear Walls

Steel Plate Shear Walls (SPSW) consist of unstiffened infill steel panels surrounded by columns, called Vertical Boundary Elements (VBE), on both sides, and beams, called Horizontal Boundary Elements (HBE), above and below. These infill steel panels are allowed to buckle in shear and subsequently form a diagonal tension field. SPSW are progressively being used as the primary lateral force resisting systems in buildings. Past monotonic, cyclic and shaking table tests on SPSW in the United States, Canada, Japan, Taiwan and other countries have shown that this type of structural system can exhibit high initial stiffness, behave in a ductile manner and dissipate significant amounts of hysteretic energy, which make it a suitable option for the design of new buildings as well as for the retrofit of existing constructions. Analytical research on SPSW has also validated useful models for design and analysis of this lateral load resisting system. Recent design procedures for SPSW are provided by the CSA Limit States Design of Steel Structures and the AISC Seismic Provision for Structural Steel Buildings. Innovative SPSW designs have also been proposed and experimentally validated to expand the range of applicability of SPSW. However, some impediments still exist that may limit the widespread acceptance of SPSW. For example, little experimental information exists on the behavior of intermediate HBE in SPSW as well as the performance of such HBE having reduced beam section (RBS) connections and composite behavior. Note that intermediate HBE are those to which are welded infill steel panels above and below, by opposition to anchor HBE that have steel panels only below or above. To further address the pressing concerns regarding behavior and design of intermediate HBE, a two-phase experimental program was developed to test a two-story SPSW specimen having an intermediate composite beam with RBS connections under the collaboration of the Multidisciplinary Center for Earthquake Engineering Research (MCEER) in the U.S. and the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan. In this paper, following a brief review of the experimental observations from the MCEER/NCREE testing, the design recommendations will be presented, followed by examinations and explanations on the observed failure of the intermediate HBE.