Workshop on Engineering Resilient Tall CLT Buildings in Seismic Regions January 24, 2014 Seattle WA Seismic Resilient Systems: Concepts and Challenges James D. Dolan Professor Washington State University James M. Ricles Bruce G. Johnston Professor of Structural Engineering Richard Sause Joseph T. Stuart Professor of Structural Engineering Lehigh University Jeffery Berman Associate Professor University of Washington
Presentation Summary Presentation 1: NEES-CLT Project Overview (15min) Presentation 2: CLT for Northwest U.S. (30min) Presentation 3: Development in Canada (30min) Coffee break Presentation 4: Performance requirements and codify efforts(30min) Presentation 5: New Zealand Experiences(30min) Coffee break Presentation 6: Resilient system concepts (35min) Contents Background and Concept of seismically resilient structural systems that can be applied to CLT. Break out discussion Contents of this presentation will be discussed further in Break-out discussion (C): Design considerations, architectural limitations on CLT structures Key words Seismic resilience, rocking walls, higher mode effects
Performance Goals Main Goal: Achieving higher level seismic performance than conventional systems Performance objectives of resilient CLT systems are planned to be : 1. Immediate Occupancy (IO) under Design Basis Earthquake (DBE) Structural and non-structural components are sufficiently undamaged after DBE IO performance can be achieved either by remaining undamaged under typical DBE level drifts (Type 1) or by reducing the drift that the system will undergo under DBE (Type 2) 2. Enhanced Collapse Prevention (CP) under Maximum Considered Earthquake (MCE)
Structural Concepts Development of resilient CLT Systems Self-centering rocking CLT panel systems PT bars for self-centering behavior Replaceable energy-dissipating (ED) devices to provide additional energy dissipation Rocking system configurations: a. Single story configuration b. Segmental (multiple story) configuration Rocking of individual stories Rigid Story Rocking Story Rocking Planes Rocking extends over multiple stories a. Single story configuration b. Segmental configuration
Rocking Structural System Concepts Goal: eliminate structural damage for DBE ground motions. Discrete structural members are post-tensioned (PT) to pre-compress joints. Gap opening at joints provides softening of lateral forcedrift behavior without damage to members. PT forces close joints and permanent lateral drift is avoided (Self Centering). M
Single-story Configuration Potential layout (one of many possible): Rigid stories connected to floor system Rocking story connected via post-tension Post-tensioning anchored to floor systems Cutouts provided for PT anchors in rigid panels above and below Diaphragm loads transferred to rocking system with plates Steel energy dissipation between rocking panels
Potential Detailing of Rocking Panels
Background-Past Experience Previous studies on rocking systems Unbonded Post-tensioned Precast Concrete Walls (Kurama, Sause & Pessiki, 1999) Hybrid Precast Concrete Walls (Restrepo& Rahman, 2000 ; Smith & Kurama, 2009) Multi-Story Post-tensioned Timber Walls (Pampanin et al., 2006) Self-Centering Concentrically Braced Frames (SC-CBFs) (Sause, Ricles & Roke et al., 2006) Structural systems with higher mode mitigation Controlled rocking systems with multiple rocking joints (Wiebe et al., 2012) Dual Wall Systems (Panagiotou& Restrepo, 2008) Construction details- connections Connection of Floor System to Rocking Frame (SC-CBF)(Sause, Ricles & Roke et al., 2006) Connection of Floor System to Rocking Precast Wall (Fleischman, Restrepo& Sause et al., 2011)
Early Work on Rocking Precast Concrete Walls (1994-2004) Rectangular 100 precast concrete wall panels stacked by horizontal 50joints at the floor levels Developed 0 during PRESSS Program: Perez, Sause, Pessiki(2007) ASCE Journal of Structural -50 Engineering Perez, -100 Pessiki, Sause(2004) PCI Journal Base Shear (kips) 200 150 Kurama, -150 Sause, Pessiki, Lu (2002) ACI Structural Journal El-Sheikh, -200 Pessiki, Sause, Lu (2000) ACI Structural Journal Kurama, -4Sause, -3 Pessiki, -2-1 Lu (1999) 0 ACI 1 Structural 2 3 Journal 4 Lateral Drift (%) Gap opening behavior at 3% rad drift Little damage with potential for Immediate Occupancy (IO) under DBE
Hybrid Precast Concrete Walls (Restrepo& Rahman, 2000 ; Smith & Kurama, 2002) Hybrid Precast Concrete Walls are developed to improve seismic performance of precast concrete walls. In studies of Smith & Kurama (2009) on hybrid walls : Rectangular precast concrete wall panels stacked by horizontal joints at the floor levels. A seismic design procedure in accordance with ACI-318 is developed. Experimental tests were performed on six 4-story precast concrete wall structures. Self-centeringbehavior provided by unbonded PT bars. Energy dissipation provided by bonded mild steel bar Test set-up (Smith & Kurama, 2009)
Multi-Story Post-tensioned Timber Buildings (Pampanin et al., 2006) Seismic-resistant Laminated Veneer Lumber (LVL) timber buildings with controlled rocking motion Jointed ductile connections combined with PT tendons and energy dissipaters Quasi-static or pseudo-dynamic tests were performed on 6 story hybrid timber frame buildings. No stiffness degradation or structural damage was observed. All tests self-centered and residual deformations were negligible. Direct Displacement Based Design (DDBD) procedure was used to design structures, New Zealand Standard: NZS3101-2006, Appendix B Beam to Column Wall to Foundation Column to Foundation Paired coupled wall Flag shape hysteresis for Wall to foundation test Test set-ups of different type of rocking subassemblies and structures (Pampanin et al., 2006)
Self Centering Concentrically Braced Frames ( Sause, Ricles & Rokeet al., 2006) To eliminate permanent structural damage and residual driftassociated with conventional Concentrically Braced Frames (CBFs), Self-Centering Concentrically Braced Frames (SC-CBFs) were developed by Sause et al. (2006). Self centering mechanism is provided by PT bars, self weight of the frame, and friction bearings. CBF columns are not attached to foundation. Rocking motion is provided by column uplifting.
Self Centering Concentrically Braced Frames Probabilistic Performance-Based Design (PBD) of SC-CBFs: Criteria (Roke et al., 2010) Limit States IO Performance DBE IO MCE CP CP Performance 2 3 4 Performance Objectives 1. Immediate Occupancy (IO) under Design Basis Earthquake (DBE) with ~ 500 yr.returnperiod 1 2. Collapse Prevention (CP) under Maximum Considered Earthquake (MCE) ~ 2500 yr.returnperiod Column decompression PT bar yielding Member yielding Member failure
Self Centering Concentrically Braced Frames Large-Scale Hybrid Earthquake Simulations on 4-Story SC-CBF Test Specimen 31 Mean intense analytical EQs used response in hybrid for simulations 30 ground motions at each seismic input level For tak90 ground motion, maximum roof drift, θ r,max = 0.0433rads, which is 5.68σ larger than the mean θ r,max = 0.0147rads under the MCE.
Self Centering Concentrically Braced Frames Large-Scale Hybrid Earthquake Simulation under exmce Level GM record: Tak090_01-13-2010
Self Centering Concentrically Braced Frames Collapse Potential of SC-CBFs (Tahmasebi et al., 2012) Results: Incremental Dynamic Analysis 6 story SC-CBF How is the potential for collapse of SC-CBF systems under the MCE (~2500yr) affected by the rocking feature of SC- CBFs? FEMA P695 methodology to assess the collapse performance of SC-CBF Systems using Incremental Dynamic Analysis (IDA) to establish the margin against collapse under the MCE. Preliminary results show collapse potential for SC-CBF is less than that of conventional Special Steel Concentrically- Braced Frames. Collapse Criteria 10% Max Drift 80% slope reduction Median Collapse (g) 4.6 3.4
Self Centering Concentrically Braced Frames Performance-Based Design Methodology for Steel Self-Centering Braced Frame (Chancellor et al., 2012) In SC-CBF design, Base Overturning Moment (OM) response is assumed to be a first mode dominant response; BUT, Research studies have shown that as the aspect ratio increases, contribution of higher modes to response also increases. Contribution of Modes to Total OM Response 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 3 6 9 12 15 18 Total Number of Stories in SC-CBF 2 nd mode contribution gets as large as 1 st mode. First Mode Second Mode 1 st mode response is effectively controlled by rocking motion.
Higher mode mitigation in Self-Centering walls (Wiebe, 2008) Wiebe(2008) proposed providing multiple rocking joints along the height of self-centering walls, to mitigate higher mode response. To examine the effect of multiple rocking joints in controlling the higher mode response, a parametric study is performed on a 20 story structural wall with one, two, and ten rocking joints respectively. (Wiebe, 2008) (Wiebe, 2008) kst: Story stiffness ksp: Stiffness of the rotational spring Base Base + Midheight Every second story Number of rocking joints Single Two Ten Moment at higher stories relative to Base OM in the wall with single rocking joint 38% higher than OM base_single 25% less than OM base_sigle 48% less than OM base_single
Higher mode mitigation in Controlled Rocking Systems (Wiebe et al., 2012) Large scale shake table tests were performed under a set of DBE and MCE level GM records on an 8 story structure with four different mitigation mechanisms. Response of the structure under ENA-1* ground motion record Overturning moment envelope Shear force envelope 2M0V 1M1V 2M1V % reduction in base shear response relative to 1M0V 18% 52% 57% % reduction in story shear response relative to 1M0V 54% >20% >22% % reduction in OM response relative to 1M0V 58% ~58% ~75% *ENA-1 is a short and an impulsive GM record
Self Centering Concentrically Braced Frames Connection of Floor System to Rocking Frame Large-Scale Hybrid Earthquake Simulation- Behavior of Friction Bearings Behavior of friction bearings under MCE level GM record. Relative behavior of CBF columns with rocking columns, % 2 1 2 100
Rocking Precast Concrete Wall - Connection of Floor System to Rocking Frame Test conducted at UCSD as part of Inertial Force-Limiting Floor Anchorage Systems for Seismic Resistant Building Structures Project (Fleischman, Restrepo & Sause, 2011) Precast hybrid walls with JVI PSA connections between wall and floor diaphragm. PSA slotted inserts for precast concrete panel construction developed by Pan & Steenson(1993)
Resilient System Concepts Vertically distributed deformable diaphragms Trench to accommodate Dampers and restoring springs
Numerical simulation on multiple sliding layers Numerical simulation showed that when concentrated in the lower 3-4 stories, there is significant benefits Limit slip to <1.0 inches per slip layer, utilities can be installed in building without expensive special connections Demands on upper stories reduced in MCE reduced to enable damage free performance
Numerical simulation on multiple sliding layers Numerical simulation showed that when concentrated in the lower 3-4 stories, there is significant benefits Limit slip to <1.0 inches per slip layer, utilities can be installed in building without expensive special connections Demands on upper stories reduced in MCE reduced to enable damage free performance
Breakout Session-Items for Discussion 1. Archetype Choices of building height and floor plans for CLT tall structures 2. Architectural and structural constraints in placing elements/ components of rocking systems What architectural constraints on location of PT bars, ED devices, shear keys, etc. exist? What are their damage modes (Energy dissipater yielding, CLT damage, PT yielding ), and what should the expectation be for this damage to happen? 3. Gravity, floor diaphragm, and non-structural systems must be compliant with the rocking system. Connection/anchorage details for maintaining the integrity of the gravity and diaphragm systems, and non-structural components to enable the deformations occurring in the rocking system. Detailing of the load transfer mechanism between floor diaphragm and rocking systems
Breakout Session-Items for Discussion 4. Multiple floor isolation system What architectural constraints must be considered in developing the system? Connection/anchorage details for maintaining the integrity of the gravity and diaphragm systems, and non-structural components to enable the deformations occurring in the isolation system. 5. Other Combining CLT system with different type of structural systems -> hybrid frames, possibility of combining the CLT system with other seismically resilient structural systems What might be the possible restrictions in placement of multiple rocking joints? What restrictions may arise during the construction of structures with multiple rocking joints What are the possible/ alternative connection details? Is there a potential for modular construction with panel assembly prefabricated in factory?
Key issues for CLT implementation 1. Performance based design procedures developed for other seismically resilient structural systems can be reviewed carefully and exploited while developing the design procedure of rocking CLT panel systems. Performance objectives Determining the strength of rocking joints Relative strength of multiple rocking joints with respect to base rocking joint 2. Floor diaphragm to wall connections used in other research studies can be modified to be used in rocking CLT systems. 3. Experience obtained from previous large scale experimental tests on rocking walls can be exploited during Design and construction of tests Implementation of tests
Acknowledgements Many thanks to ARUP Local Office for providing the venue and organizing assistants to this workshop. The workshop is supported by National Science Foundation under George E. Brown Jr. Network for Earthquake Engineering Simulation Research (NEESR) Program. (Awards CMMI: 1344617; 1344646; 1344798; 1344590; 1344621). The financial support is greatly appreciated. The views and conclusions resulted from the workshop does not reflect the view of the sponsors.
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