MCEER RESEARCH TASK STATEMENT

Thrust Area: 2 Budget: Yr 9 Assigned

Project Number: 9.2.2 Task Title: Controlling Response of Structural and Non-Structural Components and Systems in Acute Care Facilities by Passive Displacement-Activated Damping and Isolation Mechanisms 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 investigates the use of metallic displacement-based energy dissipation systems on achieving integrated resilience objectives for structural and non-structural systems. The concepts developed are valid for a broad range of metallic energy dissipation systems, but two systems are considered for the specific implementation studies in the MCEER West Coast Demonstration Hospital, namely Steel Plate Shear Wall Systems (SPSW) and Buckling Restrained Braces (BRB). These passive displacement-activated damping systems provide significant stiffening and strengthening that can effectively help achieve the structural resilience objectives. They are combined with isolation systems for non-structural components and floor systems to achieve the non-structural performance objectives. Research also takes advantage of the work on the structural-fuse concept considered in earlier Year 8. Research efforts are also invested to expand previous findings on SDOF systems to MDOF structures. Note that all work herein is applicable for both the retrofit of existing hospitals, or the design of new ones. Problem Description and Research Approach of Proposed Work for Year 9: (Detailed description of research to be conducted and methodology to be used.) This task focuses on controlling response of structural and non-structural components and systems in acute care facilities by passive displacement-activated damping and isolation mechanisms. Research will proceed by expanding on the results obtained in Year 8 work. On one hand, the design procedure proposed for structural fuses will be verified experimentally using a multi-story frame and a BRB strategy, with proposed connection details intended to ensure the target physical structural resilience objectives and allow to facilitate replacement of the sacrificial energy dissipating element, in compliance with the structural fuse philosophy. The performance of non-structural components and contents will be investigated through experimental study of the floor response. Analytically derived information on floor response indicates that the displacement-based strategies considered here are effective in reducing drift, but velocity and acceleration response could increase or decrease, depending on the period of the non-structural component (see Figure 1). This may result in satisfactory or unsatisfactory performance, for

various types of non-structural components (quantitative limit states remain to be determined through other research tasks for most non-structural component types at this time). Performance of isolated floor systems will be investigated in the perspective of the structural systems of interest here. Much work has been done on isolated floor systems, and various such systems are available today on the market. Qualification testing of many such type of system has been done in the past decades; many suppliers do not provide specific methodologies for the design of such systems, but available code-specified methodologies provide guidance. The objective here is not to develop floor isolation systems, but rather to use existing isolation technologies to integrate the performance of the structural and non-structural systems as part of a comprehensive design approach that can ensure compliance with both resilience objectives. Note that the approach taken here is to isolate an entire floor (area enclosed by partitions) and develop details to achieve this objective if necessary, not to isolate individual pieces of equipment, or only the portion of a floor that support equipment. Simplified design approach will be sought as much as possible. Shake-table test of the isolated floor system will be conducted using the floor time-histories obtained in earlier parts of this project. Work has significantly progressed on SPSWs and analytical investigation of experimental results is underway (Figure 2). Year 9 work on SPSWs will address some remaining gaps in the knowledge on their seismic performance. MCEER Strategic Partners have already inquired about the effectiveness of alternative perforated plate geometries and other base materials. Analytical models developed in Year 8 will be used to investigate such alternative geometries deemed more compliant with the threading of non-structural components through the ductile walls. Other shortcomings include the unclear role of intermediate beams towards satisfactory seismic performance, the challenges of SPSWs in achieving ideal structural fuse performance objectives, and questions regarding the respective benefits of SPSWs versus BRBs both in terms of achieving structural and non-structural resilience objectives. Parametric studies will be conducted such that a range of retrofit situations can be investigated and conclusions developed.

Figure 1: Impact of BRB on floor response spectra (acceleration on vertical axis; period of non-structural component on horizontal axis)

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Figure 2: Finite element analysis of typical SPSW cyclically tested in Year 8

Standardized ground motion definitions and analysis model provided by Assawin and Filiatrault as well as Yang and Whittaker will be used as much as possible in this project. The MCEER West Coast Demonstration Hospital is considered throughout. Assessment of State-of-the-Art: (Describe other relevant work being conducted within and outside of MCEER, and how this project is different.) There is a strong interest from practicing engineers in using buckling restrained braces and steel plate walls for the retrofit of existing structures, as well as for the design of new structures. The impact of such systems on the performance of non-structural components is most important and unknown. There are also other important questions that remain unresolved on how to meet resiliency objectives using these systems. One such question is whether perforations in SPSWs impact the performance of the steel plates. To the best of the investigator’s knowledge, the approach proposed in this Task is not currently being studied in the US. While buckling restrained brace systems and steel plate shear walls have become of much interest in the US, no research is looking at these systems from the MCEER perspective of attempting to address both the structural and non-structural resilience objectives. This 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. 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, 2004, to March 31, 2005.) Substantial education outcomes and publications have been achieved from this project over that period, and are reported in the sub-section “Educational outcomes and deliverables, and intended

audience” below. Research progress is summarized here. A design procedure for the displacement-activated damping systems formulated for single-degree-of-freedom systems has been expanded to multi-degree-of-freedom systems. Constraints under which steel plate walls and buckling restrained braces can be used to meet the resilience objectives have been preliminarily identified. Research investigated how various metallic displacement-based energy dissipation systems can provide the target structural response control objectives in MDOF Systems. BRBs, shear panel systems, triangular added damping and stiffness (TADAS) systems, and steel plate infills were considered as part of this investigation. Preliminary research has been conducted to identify and define the limits and constraints that must be met to provide seismic protection of non-retrofitted secondary systems (also known as non-structural systems). Floor displacement, velocity, and acceleration spectra were generated for various types of metallic displacement-based energy dissipation systems. Based on these results, an investigation of the seismic performance of SDOF systems with metallic and viscous dampers installed in parallel was conducted. The purpose was to analyze the alternative of using hysteretic dampers to mitigate lateral displacements, along with viscous dampers to reduce acceleration demands. Parametric analyses of hysteretic damping and spectral acceleration were developed for short, intermediate, and long period structures. Furthermore, response in the frequency domain was also prepared as graphics of inertial, viscous damper, and hysteretic damper forces represented in the complex plane. Preliminary results indicate that, although viscous dampers are known to decrease both displacements and acceleration demands in structures with elastic behavior, for structural fuse systems where hysteretic dampers are designed to behave inelastically, the floor accelerations are likely to increase if viscous dampers are added in parallel to hysteretic dampers (especially for systems with small strain-hardening ratio). Adding such viscous dampers in parallel is, therefore, not only ineffective but detrimental. Experimental results obtained during testing at NCREE during Year 7 research are being analyzed to verify the effectiveness of ideas developed during Year 6 and 7. A paper that describes part of the results obtained to date is being submitted for possible publication to the ASCE Journal of Structural Engineering, focusing on parametric studies and seismic responses of SDOF systems with structural fuses, and a systematic simple design procedure for MDOF structures using metallic structural fuses. A MCEER technical report is also being prepared for possible publication. This report also includes results on the effect of metallic structural fuses on the response of non-structural components, and the seismic behavior of hybrid systems with metallic and viscous dampers acting in parallel. 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 proposed task strongly supports the MCEER Strategic Plan, particularly with regard to the achievement of the seismic resilience objectives by the control of performance of both primary and secondary systems (in terms of reduction of probability of failure, consequences of failure, and time to recovery). A rigorous implementation of the proposed 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.) The proposed research uses ground motion time histories and building models developed by Assawin and Filiatrault as well as building models by Yang and Whittaker. The proposed research will also provide floor response data to be used by researchers involved in the non-structural tasks (e.g. Whittaker, Filiatrault, Maragakis, etc.). Reciprocally, since a key resilience objective is the performance of secondary systems in structures, the research in this Task will account for the limit states data (expressed as fragility curves or other limits) for various non-structural components to be provided by those investigators. As such, this Year 9 task is compatible with the focus on performance of secondary systems described by the system diagrams for Thrust Area 2. Outcome of this effort are to be integrated into the decision support methodologies developed by by 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: While there are significant advantages in using this combined approach of controlling response of structural and non-structural components and systems in acute care facilities by passive displacement-activated damping and isolation mechanisms, there are important challenges in that the research is moving forward while for the development of clear quantified target limit states for various non-structural contents remain missing. Some assumptions must therefore be made regarding targets (limit states) for inter-story drifts, floor velocities, and accelerations need to be specified, and the developed methodologies and design procedures must be developed with sufficient flexibility to account for a large range of potential limits. Anticipated Outcomes and deliverables: (Also indicate those of particular benefit to IAB members and other end users.) Integrated approach for the seismic retrofit of critical buildings (i.e. acute care facilities) having flexible frames, using the combined approach described here, to meet specific resilience objectives for various secondary systems.

An AISC Design Guide on Steel Plate Shear Walls (co-authored with a reputable practicing engineer from California) – see Education Outcomes below.

Potential end-users beyond academic community: (IAB members and others.) Practicing engineers who will design or retrofit/repair structural and non-structural 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

Both of the above outcomes are deemed to be valuable by MCEER IAB members such as OSHPD, practicing engineers involved in seismic retrofit of hospitals (such as KPFF Engineers or Degenkolb and Associates), and manufacturers of non-structural equipment/content.

capability of their critical facilities 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 FEMA 450 (Recommended NEHRP Seismic Provisions) published in 2004 and adopted in the 2005 AISC Seismic Provisions, itself the reference document for seismic-resistant of steel in the US. These design provisions are now integrated into the course CIE-524 Steel Structures taught at the University at Buffalo by Michel Bruneau. As a follow-up to those efforts, technical presentations to practicing engineers of Steel Plate Shear Wall design concepts and examples, are being given to a number of groups (e.g. short course at 2005 AISC North American Steel Construction Conference, participation to MCEER Seminar at the California Office of State Health, Planning, Development (OSHPD) February 2005, plans to include topic as part of an EERI Short Course, etc.). The PI has also been invited to co-author (with Rafael Sabelli, SE, Senior Associate at DASSE Design, Inc. California) an AISC Design Guide on Steel Plate Shear Walls (publication scheduled for 2006). Education efforts also include a number of presentations to general public (e.g. UB Alumni Association, etc.). The PI is also regularly providing information on steel plate wall design to individual MCEER Strategic Partners (e.g. Chris Tokas of OSHPD, Jay Love of Degenkolb, etc.) 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. Publications produced as a result of this work, and published over the period from January 1, 2004, to March 1, 2005. are listed below: Refereed Journal (since 2004): 1. Berman, J., Celik, O., (2005). Bruneau, M., “Comparing Hysteretic Behavior of Light-gauge Steel Plate Shear

Walls and Braced Frames”, Engineering Structures Journal (in press). 2. Celik, O. C., Berman, J. W., and Bruneau, M. (2005). “Cyclic Testing of Braces Laterally Restrained by Steel

Studs,” ASCE Journal of Structural Engineering (in press). 3. Bruneau, M., Engelhardt, M, Filiatrault, A., Goel, S., Hajjar, J., Itani, A, Leon, R., Stojadinovic, B., Uang,

C.M., (2005).“Selected Recent Research on US Seismic Design And Retrofit Strategies For Steel Structures,”

Journal of Progress in Structural Engineering and Materials, (in press). 4. Berman, J., Bruneau, M., (2005). “Experimental Investigation of Light-Gauge Steel Plate Shear Walls”, ASCE

Journal of Structural Engineering, Vol. 131, No. 2, pp. 259-267. 5. Berman, J., Bruneau, M., (2004). “Steel Plate Shear Walls are not Plate Girders”, AISC Engineering Journal,

Vol.41, No.3, pp.95-106. 6. Warn, G., Berman, J., Whittaker, A., and Bruneau, M. (2004). “Reconnaissance and Preliminary Analysis of a

Damaged Building Near Ground Zero”, Journal of Structural Design of Tall and Special Buildings, Vol.12, No.5, pp.371-391.

Refereed Journal – Submitted for Possible Publication (since 2004) 1. Vargas, R., Bruneau, M., “Seismic Response and Design of Buildings with Metallic Structural Fuses”,

submitted for review and possible publication to the ASCE Journal of Structural Engineering. Technical Reports (since 2004): 1. Celik, O.C.., Berman, J., and Bruneau, M. (2004) “Cyclic Testing of Braces Laterally Restrained by Steel Studs

to Enhance Performance During Earthquakes,” Technical Report MCEER-04-0003, Multidisciplinary Center for Earthquake Engineering Research, Buffalo, NY.

Refereed Conference Publications (since 2004) 1. Bruneau, M., Berman, J., Vian, D., Invited Speaker, “Steel Plate Shear Walls - Design Procedures and

Innovative Concepts”, ASCE 2005 Structures Congress, New York, 2005. 2. Filiatrault, A., Aref, A., Bruneau, M., Constantinou, M., Lee, G., Reinhorn, A., Whittaker, A., Invited Speaker

(Bruneau), “MCEER's Integrated Research to Enhance the Seismic Resilience of Acute Care Facilities”, International Conference in Commemoration of 5th Anniversary of the 1999 Chi-Chi Taiwan Earthquake, Taipei, September 2004 - on CD-ROM - also presented/published in Structural Engineers Association of California 2004 Convention, Monterey, California, August 2004, pp.73-81

3. Bruneau, M., Invited Keynote Speaker, “Seismic Retrofit of Steel Structures”, VIII Mexican Symposium on Earthquake Engineering, Tlaxcala, Mexico, September 2004.

4. Vian, D., Bruneau, M.,“MCEER’s Experimental Research on Steel Plate Walls”, Structural Engineers Association of California 2004 Convention, Monterey, California, August 2004, pp.211-215.

5. Vargas, R., Bruneau, M., “Seismic Response of Single Degree (SDOF) Structural Fuse Systems”, 13th World Conference on Earthquake Engineering, Vancouver, Canada, August 2004 - CD-ROM paper #3277.

6. Berman, J., Bruneau, M., “Plastic Design and Testing of Light-Gauge Steel Plate Shear Walls”, 13th World Conference on Earthquake Engineering, Vancouver, Canada, August 2004 - CD-ROM paper #3323.

7. Vian, D., Bruneau, M., “Testing of Special LYS Steel Plate Shear Walls”, 13th World Conference on Earthquake Engineering, Vancouver, Canada, August 2004 - CD-ROM paper #978.

8. Vargas, R., Bruneau, M., "Investigation of the Structural Fuse Concept", Workshop of the Asian-Pacific Network of Center in Earthquake Engineering Research, Honolulu, July 2004 - CD-ROM.

9. Filiatrault, A., Aref, A., Bruneau, M., Constantinou, M., Lee, G., Reinhorn, A., Whittaker, A., “Recent Progress Towards the Seismic Control of Structural and Non-structural Systems in Hospitals”, US-Japan 36th Technical Meeting of Panel on Wind and Seismic Effects, Washington, D.C., May 2004.

Project Schedule and Expected Milestones for the Project: (Milestones and estimated time of achievement; e.g., Fall, Spring, Summer.) Shake table testing (early Year 9) of specimens to validate the proposed concept, and calibration

of analytical model, considering structural and non-structural response (focusing on control of floor displacements, velocities, and accelerations as resiliency objectives: October 1, 2005 – January 31st, 2006.

Development of design procedure toward implementation of the proposed concept and structural and non-structural control objectives: February 1st – September 31st, 2006:

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 8 research), under supervision of Michel Bruneau, are: Ramiro Vargas (Ph.D. student) Darren Vian (Ph.D. student) Another Ph.D. student is to be hired to work on this project starting in Summer 2005. Dr. Diego Lopez-Garcia, post-doctoral researcher. Dr. Oguz Celik (visiting professor, from Technical University of Istanbul, Turkey, remotedly worked with PI to complete publication of Year 6 and 7 work). Personnel at start of Year 9 may differ substantially from that list. It is also hoped that undergraduate students could provide assistance during the summer (through the MCEER REU programs), as well as during the academic year. 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). Multi-Hazard Statement: a) (Conceptually describe in 200 words or less how some of the work you are conducting as part of your MCEER Year 9 research task can be exported/applied to other natural or man-made hazards including multi-hazard research.) There are some direct multi-hazard applications that are possible as a result of the work proposed in this Task. Some of those immediate possibilities are described in part (b) below. b) If you are seeking supplemental multi-hazard funding, describe the multi-hazard milestones that you plan to complete as part of your Year 9 research. It has been often mentioned and long recognized that, in most States, seismic design and/or retrofit of structures would be best achieved if “bundled” within the framework of a multi-hazard framework. In other words, design solutions that can ensure achievement of the desired objectives for a number of different hazards would be more valuable, and thus more likely to be implemented, that those solutions that address a single hazard. This philosophy has been described and is a logical and promising way to significantly enhance the seismic resilience of communities, while simultaneously enhancing their resilience against other hazards, but to date few (if any) such design solutions have been developed.

Since the tragic events of September 11, 2001, many engineers have recognized that important design synergies might exist between earthquake-resistant design and blast-resistant design for many structures, in spite of the substantial differences that exist in the “loading” regimes relevant to each hazard. A strong linkage exist between the impact of these two fundamentally different hazards in that, in most cases, past practice has evolved to favor collapse-resistant design approaches that rely on the ability of structures to withstand substantial damage without collapsing (i.e. structures pushed into a severe state of non-linear response without developing instability, thus providing life safety at the cost of infrastructure loss). This was indeed one of the fundamental conclusions emphasized as a result of an invitational MCEER Workshop (MCEER 2002). Yet, strategies to achieve this for some types of structures are few (and in some cases non-existent). Past research by others (as presented at the MCEER 2002 Workshop and other conferences) has clearly shown that infill partition walls can be substantially damaged and even fully-projected into the building by blast shockwaves, with wall debris being one of the major causes of casualties and injuries in such cases. Various retrofit strategies have been developed, many consisting of composite reinforcement fabrics epoxied/glued to the walls and surrounding frames. The Year 8 research activities by the PI are investigating the use of infill steel plates as displacement-based energy dissipation systems and structural fuses, functioning in a steel shear-plate wall. One of the advantages of metallic infills systems in the perspective of multi-hazard applications is that they are already ductile in resisting out-of-plane blast pressure forces, and already connected to the surrounding frames. A specific design method to quantify the necessary plate thicknesses and detailing does not exist, and a design approach must also be flexible to consider a wide range of detonation size and standoff distance. The exceptional ductility of the infills might provide them a substantial advantage that more than overcome the disadvantage of low reactive mass (low mass is usually a negative for blast-resistant design, contrary to seismic applications). Impulse-momentum analysis will first be considered, but results are likely to lead to the use for large displacement analysis to accurately capture the ultimate behavior of the system. In another multi-hazard perspective, the very high in-plane strength of steel plate shear walls is advantageous in the perspective of developing tsunami resistant building systems. The design strategy is to align buildings such that the steel walls are perpendicular to the shoreline, and develop a building ground floor with “sacrificial” non-structural component and content (as typically done along the eastern seaboard to protect against high storm surge during hurricanes) and higher floors designed to provide emergency refuge for at-risk populations. The challenge here is that, contrary to hurricane induced storm-surge, the design must consider considerable wave forces and the scour problems they can potentially induce, as well as the sizeable impact forces imparted to the system by large debris carried by the tsunami flow. Again, because (in addition to the large shear-strength of the system) steel plate shear walls require very large boundary columns to meet the seismic design requirements, the system would be well suited to resist these in-plane forces as part of a multi-hazard design strategy.

It is proposed here to investigate this specific potential application, and develop workable design solutions that could be subsequently investigated experimentally starting in Year 10 (along with the work to provide resilience to blast load). The proposed research to develop and experimentally validate the above concepts, is a natural extension of the work proposed as part of this Task Statement. For Year 9, as part of this multi-hazard supplement, a Ph.D. student would analytically investigate the feasibility of this initiative, and propose design procedures for various multi-hazard conditions. Milestones would include: preliminary design of concepts (Dec. 2005); assessment of blast performance using time-history analysis (March 2006); enhanced design concepts (June 2006); development of test specimens (Sept. 2006). Experimental work would follow in Year 10 (or earlier if the schedule can be accelerated and additional funding from other sponsors can be identified). References MCEER (2002). Proceedings from the MCEER Workshop on Lessons from the World Trade Center Terrorist Attack: Management of Complex Civil Emergencies and Terrorism-Resistant Civil Engineering Design, New York City, June 24-25, 2002