MCEER RESEARCH TASK STATEMENT

Transcription

1 MCEER RESEARCH TASK STATEMENT Thrust Area 2 Budget: Yr 8 Assigned Project Number: Task Title: Formulation and Operationalization of the Structural Fuse Concept using Metallic Passive Energy Dissipation Systems Investigator/ Institution: Michel Bruneau, University at Buffalo* Andre Filiatrault, University at Buffalo Michael Constantinou, University at Buffalo * indicates task leader Statement of Project Goals: (Conceptually describe what the work is intended to accomplish, in 100 words or less. Do not provide detailed description here.) This task is the continuation of previous work investigating the use of metallic displacementbased energy dissipation systems and development of the structural fuse concept, by integrating control of the performance of non-structural systems as one main performance objective beyond the control of structural response. Work is conducted to investigate how structural fuses can provide protection of secondary systems in Hospitals, in terms of floor demands (floor displacements, velocities, and accelerations). A particular focus here is to extend previous findings on SDOF systems to MDOF structures. Problem Description and Research Approach of Proposed Work for Year 8: (Detailed description of research to be conducted and methodology to be used.) This task first expands the theoretical framework for the structural fuse concept, already formulated for single-degree-of-freedom systems, to be applied to multi-degree-of-freedom systems, and to identify under which conditions steel plate walls and unbonded braces can be used to meet the resilience objectives. This includes the development of guidelines and methodology to design and retrofit MDOF systems using metallic dampers working as structural fuses. Within the framework of MDOF, research will be conducted to identify metallic displacement-based energy dissipation systems that can provide the target structural response modification, and which types give the designer the flexibility to achieve the structural control objectives (and under which conditions this can be achieved) in MDOF Systems. Unbonded braces, shear panel systems, triangular added damping and stiffness (TADAS) systems, and steel plate infills will continue being considered as part of this investigation. Second, this task will expand its focus on defining the limits and constraints that must be met to provide seismic protection of non-retrofitted secondary systems (also known as non-structural systems). As such, using the standardized ground motion definitions to be provided by Filiatrault, the floor displacement, velocity, and acceleration spectra will be generated for various types of metallic displacement-based energy dissipation systems, and their quantitative

2 impact on the performance of certain types of equipment will be investigated. As this will be conducted in parallel with MCEERfunded tasks that consider other structural control strategies and/or limit states for various non-structural systems, this will allow to establish a compendium of possible solutions (outlining the advantages/disadvantage s of each system and its possible range of applications), that itself could be used to formulate hybrid solutions to deliver all (or most) of the performance objectives. Figure 1: Design Space for Allowable Structural Fuse Design Solutions A third part of this task is to prepare experimental works to validate the structural fuse concept through designed models dynamically tested. This task will be performed using the type of metallic damper shown to provide the most reliable results in the analytical studies. Details and size of specimens will depend on the results of the analytical works with MDOF systems. A fourth component of this task is to continue to formulate improved types of metallic energy dissipating systems that can contribute to achieve the objectives of seismic resilience, while being more adaptable to cope with practical on-site conditions, and more compliant to meeting the practicing engineer design objectives (particularly with respect to the need to avoid unnecessary overstrength in a capacity design perspective). Detailed formulation of the best concepts will depend in large part on the outcomes of Year 7 research, and will expand on the solutions already developed, to enhance the range of ductile response. Experimental results discussed below are being analyzed; allowing researchers to Figure 2: Regularly Perforated Steel Plate Wall Specimen

3 verify the effectiveness of ideas developed during Year 6 and 7. Relations for limit states are being developed using this data and will aid designers in properly implementing various structural systems under consideration. Parametric studies will be conducted using simplified models such that a range of retrofit situations can be investigated and conclusions developed. The effect of such systems on non-structural building components can then be efficiently investigated. Assessment of State-of-the-Art: (Describe other relevant work being conducted within and outside of MCEER, and how this project is different.) The structural fuse concept has not been consistently defined in the past. In some cases, fuses have been defined as elements with well defined plastic yielding locations, but not truly replaceable as a fuse; in other cases, they were defined and used more in the context of reducing inelastic deformations of the existing frame (damage control). In a few cases, for high rise buildings having large structural periods (i.e., T > 4s), fuses were used to achieve elastic response of frames that would otherwise develop limited inelastic deformations. Design procedures were also developed for systems with friction dampers intended to act as structural fuses, but these required design validation by nonlinear time history analyses. In that perspective, knowledge on how to achieve and implement a structural fuse simple design concept that would limit damage to disposable structural elements for any general structure, is lacking. Furthermore, there currently is a strong interest from practicing engineers in using unbonded braces and steel plate walls to retrofit of existing structures. The impact of such systems on the performance of non-structural components, as well as the impact of perforations on the performance of the steel plates, is unknown. To the best of the investigator s knowledge, no similar work is currently being conducted in the US. While research in Japan and Taiwan has focused on the use of many different types of displacement-based energy dissipation systems, few of these systems have found implementation in the US. However, in the last few years, unbonded brace systems and steel plate shear walls have become of much interest in the US. Coupling this interest with MCEER s objectives of seismic resilience provides significant opportunities to achieve solutions of broad appeal that can control both the seismic performance of structural and non-structural systems. The approach followed in the proposed research also makes it possible to consider issues of minimal seismic retrofit disturbance, optimization of energy-dissipation, and quantification of performance objectives. These important issues have not received much attention to date. Progress to date: (If applicable, a short description of achievements in previous years. Clearly distinguish progress achieved in the past year, i.e., accomplishments from April 1, 2003, to March 31, 2004.) Two papers that describe part of the results obtained to date on the development of the structural fuse concepts and design methodologies have been submitted for possible publication to the ASCE Journal of Structural Engineering. These papers document the work accomplished to date, including parametric studies and seismic responses of SDOF systems with structural fuses,

4 and a systematic simple design procedure for SDOF structures using metallic structural fuses. Other papers and report (see below) document the work conducted on Steel Plate Walls. These documents have supported the development of NEHRP (adopted) and AISC (proposed) codified design provisions for steel plate walls. Tests in cooperation with the National Center for Research in Earthquake Engineering (NCREE) in Taipei, Taiwan, were conducted in August and in November Three different types of steel plate shear wall (SPSW) systems were tested. All utilized low yield strength (LYS) steel infill panels, providing the first known tests of such material for SPSW. Two of the tested specimens had accommodations for the penetration of the wall by utilities. One specimen utilized cutout corners of the panel to provide a location for utilities to pass through the wall. This cutout portion was reinforced to allow the wall to still resist the same ultimate load as the corresponding solid panel. A second panel utilized a pattern of perforations placed throughout the panel, to allow pass-through of utilities, as well as to reduce the overall strength and stiffness of the panel. The strength and stiffness reduction aspect of the specimen configuration would be particularly attractive for designers in markets that do not have access to LYS steel, thereby providing an option for effectively lower strength material, when considering the panel versus its solid panel counterpart. As with the tests conducted at UB, these specimens were designed taking in account characteristics of the MCEER Demonstration Hospital, and analytical results that suggested that relatively thin steel plates might provide an adequate seismic retrofit solution. Some experimental results and initial observations of the NCREE testing were presented at the 16th KKCNN Civil Engineering Symposium in Korea. In addition, an abstract about this research was accepted for oral presentation at the 13th World Conference on Earthquake Engineering, to be held in Vancouver, British Columbia in August Role of Proposed Task in Support of Strategic Plan: (Describe how the effort will make a unique, useable contribution to the MCEER strategic plan.) The project plays an important role in support of the definition of seismic resilience, particularly with regards to control of performance of secondary systems (in terms of reduction of probability of failure, consequences of failure, and time to recovery). A rigorous implementation of the structural fuse concept through displacement-based energy dissipation systems (as sacrificial elements) can provide a satisfactory solution at all three levels. Task Integration: (Describe how the work performed interfaces with other tasks and researchers funded by MCEER.) In Year 8, research becomes more integrated through the work conducted by Filiatrault on the normalization of seismic input, and by providing floor response data to the non-structural tasks (Whittaker, Filiatrault). Focus is on the performance of secondary systems in structures, which cross-correlated with the work on seismic protective systems (Constantinou), and with the fragility assessments of nonstructural components in acute care facilities (Reinhorn, Filiatrault, Whittaker). The proposed Year 8 task is therefore designed to be compatible with the focus on performance of secondary systems described by the system diagrams for Thrust Area 2. Year 8 work will also lead to integration into the decision support methodologies developed by by

5 Dargush/Alesch/Petak, and Grigoriu/Winterfelt. Regular meetings (started in Year 7) of researchers working on this topic of Thrust Area 2 are planned throughout Year 8 to further the coordination objectives. Possible Technical Challenges: This research attempts to quantify the concept of structural fuse for MDOF, and consider which types of implementations are needed to achieve the resilience objectives. Other challenges lie in the development of innovative and cost-effective structural response modification systems that can simultaneously control response of secondary systems, using metallic-based devices, something that has again never been attempted. Unbonded braces and steel plate walls are used as case studies for this purpose. Furthermore, targets (limit states) for inter-story drifts, floor velocities, and accelerations need to be specified. Anticipated Outcomes and deliverables: (Also indicate those of particular benefit to IAB members and other end users.) New advanced technologies for the seismic retrofit of critical buildings (i.e. acute care facilities) having flexible frames, and that can provide a determined level of response to secondary systems. A document outlining design concepts with worked examples (see Education outcomes below). Both of the above outcomes are deemed to be valuable by MCEER IAB members such as OSHPD and practicing engineers involved in seismic retrofit of hospitals (such as KPFF Engineers or Degenkolb and Associates). Potential end-users beyond academic community: (IAB members and others.) Practicing engineers who will eventually design retrofit/repair systems using such strategies (many of which are MCEER IAB members). OSHPD (MCEER IAB member) who would use these tools to assist their consultants. Acute care facility owners who will be able to ensure the seismic survival and full operational critical facility following an earthquake. Educational outcomes and deliverables, and intended audience: Knowledge generated as part of this project has been summarized in papers published in referred journals and presented at conferences (see publication list below). Documents prepared as part of this project also include codified provisions for the design of Steel Plate Walls, which have been adopted into the next edition of the Recommended NEHRP Seismic Provisions published by the Building Seismic Safety Council, usually the first step toward implementation into the AISC Seismic Provisions, itself the reference document for seismic-resistant of steel in the US. Indeed, at the time of this writing, the same provisions are being balloted by the AISC Task Committee 9 (Seismic Design) for inclusion into the 2005 AISC Seismic Provisions. Furthermore, these design provisions are now integrated into the graduate course CIE-524 Steel Structures taught at the University at Buffalo by Michel Bruneau. Discussions are now underway as part of Thrust Area 2 to develop professional development courses on the use of

6 energy dissipation systems for seismic retrofit, to be attended by professional engineers, and the above material on the design of such systems would be part of such short courses. As part of such a short course, a document outlining the retrofit design concepts, with a complete example, would be prepared. The California Office of Statewide Health Planning and Development (OSHPD) has already agreed to endorse and distribute such a document when available. The systems studied within this task also hold the promise that they could also be implemented in new constructions, thereby leveraging the technology transfer and outreach activities in a significant way. Publication produced as a result of this work, and published over the period from April 1, 2003, to March 31, are listed below: Refereed Journal (since May 2003): Berman, J., and Bruneau, M. (2003) Plastic Analysis and Design of Steel Plate Shear Walls, Journal of Structural Engineering, ASCE, Vol. 129, No. 11, pp Vian, D., Bruneau, M. (2003) Tests to Collapse of SDOF Frames Subjected to Earthquake Excitations, ASCE Journal of Structural Engineering, Vol. 129, No. 12, pp Berman, J. W., and Bruneau, M. (2003) Steel Plate Shear Walls are Not Plate Girders, Engineering Journal, AISC (in press). Refereed Journal Submitted for Possible Publication (since May 2003) Vargas, R., Bruneau, M., Seismic Response of Single Degree of Freedom Structural Fuse Systems, submitted for review and possible publication to the ASCE Journal of Structural Engineering. Vargas, R., Bruneau, M., Design of SDOF Systems with Metallic Structural Fuses, submitted for review and possible publication to the ASCE Journal of Structural Engineering. Celik, O. C., Berman, J. W., and Bruneau, M. Cyclic Testing of Braces Laterally Restrained by Steel Studs, submitted for review and possible publication to the ASCE Journal of Structural Engineering. Berman, J. W., and Bruneau, M. Experimental Investigation of Light-Gauge Steel Plate Shear Walls, submitted for review and possible publication to the ASCE Journal of Structural Engineering. Other Publications (since May 2003): Berman, J., and Bruneau, M. (2003) Experimental Investigation of Light-Gauge Steel Plate Shear Walls for the Seismic Retrofit of Buildings, Technical Report MCEER , Multidisciplinary Center for Earthquake Engineering Research, Buffalo, NY. Celik, O.C., Berman, J., and Bruneau, M., (2003) Cyclic Testing of Braces Laterally Restrained by Steel Studs to Enhance Performance During Earthquakes, Technical Report MCEER-03-XXXX, Multidisciplinary Center for Earthquake Engineering Research, Buffalo, NY (in press). Berman, J., Bruneau, M., (2003) Cyclic Testing of Special Steel Shear Walls and Modular Infill Panels, Fourth International Conference on Behavior of Steel Structures in Seismic Areas - STESSA 2003, Naples, Italy, June 2003, pp Vian, D., Lin, Y.C., Bruneau, M., and Tsai, K.C., Cyclic Performance Of Low Yield Strength Steel Panel Shear Walls, The 16th KKCNN Symposium on Civil Engineering, Gyeongju, Korea, December Berman, J., Bruneau, M., Plastic Design and Testing of Light-Gauge Steel Plate Shear Walls, accepted for presentation at the 13th World Conference on Earthquake Engineering, Vancouver, Canada, August Vian, D., Bruneau, M., Testing of Special LYS Steel Plate Shear Walls, The 13th World Conference on Earthquake Engineering, Vancouver, B.C. Canada, August Vargas, R., Bruneau, M., Seismic Response of Single Degree (SDOF) Structural Fuse Systems, accepted for presentation at the 13th World Conference on Earthquake Engineering, Vancouver, Canada, August Warn, G., Berman, J., Whittaker, A., and Bruneau, M., (2003). Investigation of a Damaged High-Rise Building Near Ground Zero, Chapter in Beyond September 11th: An Account of Post-disaster Research, Special Publication #39, Natural Hazards Research and Applications Information Center, University of Colorado, Boulder, CO, pp

7 Project Schedule and Expected Milestones for the Project: (Milestones and estimated time of achievement; e.g. Fall, Spring, Summer.) Formulation of Secondary Systems Control Parameters for SDOF Systems Focusing on control of floor displacements, velocities, and accelerations as resiliency objectives: October 1, 2004 January 31 st, Implementation of the Structural Fuse Concept in MDOF Systems Constraints for achievements of Non-Structural Control objectives in SDOF: February 1 st September 31 st, 2004: Shake table testing is planned (late Year 8); details of specimen will largely depends on findings from Year 7 task; scheduling is awaiting Year 7 research findings. Team Members: (If known, provide names of team members associated with project including project leader, other faculty and their departments, undergraduate students, graduate students, postdoctoral students, industrial participants.) Currently working in this project (Year 7 research), under supervision of Michel Bruneau, are: Ramiro Vargas (Ph.D. student) and Darren Vian (Ph.D. student). Dr. Oguz Celik, visiting professor from Technical University of Istanbul, Turkey and involved during Year 6, is still working with Jeffrey Berman on the writing of technical reports and papers summarizing Year 6 work. Vian and Vargas will work on the Year 8 task. It is hoped that an REU student could provide assistance during the summer. Addition of a third graduate student is also planned. Possible Direction of Work in Subsequent Years: Development of fragility information for systems retrofitted with metallic energy dissipation systems and structural fuses, both for structural and non-structural performance. Integration of retrofit strategy into the decision methodologies being developed by other MCEER researchers. Development of design document for use by practicing engineers (see educational outcomes section above).

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