Seismic Resilient Systems: Concepts and Challengesneesclt.mines.edu/content/ppt6.pdf · Seismic Resilient Systems: Concepts and Challenges ... less than that of conventional Special

Seismic Resilient Systems: Concepts and Challenges

James M. Ricles

Bruce G. Johnston Professor of Structural Engineering

Richard Sause

Joseph T. Stuart Professor of Structural Engineering

Lehigh University

Workshop on Engineering Resilient Tall CLT Buildings in Seismic Regions

January 24, 2014

Seattle WA

James D. Dolan

Professor

Washington State University

Jeffery Berman

Associate Professor

University of Washington

© 2014 Lehigh University

Presentation Summary

• 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

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)


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

a. Single story configuration b. Segmental configuration

Rocking extends over

multiple stories

Rocking Planes Rocking Story

Rigid Story

Rocking of individual

stories

• 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 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 force-drift 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)


Gap opening behavior at 3% rad drift

Little damage with potential for Immediate Occupancy (IO) under DBE

Rectangular precast concrete wall panels stacked by

horizontal joints at the floor levels

Developed during PRESSS Program:

Perez, Sause, Pessiki (2007) ASCE Journal of Structural

Engineering

Perez, Pessiki, Sause (2004) PCI Journal

Kurama, Sause, Pessiki, Lu (2002) ACI Structural Journal

El-Sheikh, Pessiki, Sause, Lu (2000) ACI Structural Journal

Kurama, Sause, Pessiki, Lu (1999) ACI Structural Journal

Early Work on Rocking Precast Concrete Walls (1994-2004)

-200

-150

-100

-50

0

50

100

150

200

-4 -3 -2 -1 0 1 2 3 4

Lateral Drift (%)

Bas

e S

hea

r (k

ips)


• 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.

Hybrid Precast Concrete Walls (Restrepo & Rahman, 2000 ; Smith & Kurama, 2002)

Test set-up(Smith & Kurama, 2009)

Self-centering behavior provided by

unbonded PT bars.

Energy dissipation provided by bonded

mild steel bar


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

Flag shape hysteresis for

“Wall to foundation” test Paired coupled wallColumn to FoundationWall to FoundationBeam to Column

Test set-ups of different type of rocking subassemblies and structures (Pampanin 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 ( Sause, Ricles & Roke et al., 2006)

• To eliminate permanent structural damage and residual drift associated with conventional Concentrically Braced Frames (CBFs),

Self-Centering Concentrically Braced Frames (SC-CBFs) were developed by Sause et al. (2006).


Self Centering Concentrically Braced FramesProbabilistic Performance-Based Design (PBD) of SC-CBFs: Criteria (Roke et al., 2010)

CPPerformance Objectives

1. Immediate Occupancy (IO) under Design Basis Earthquake (DBE)

with ~ 500 yr. return period

2. Collapse Prevention (CP) under Maximum Considered Earthquake

(MCE) ~ 2500 yr. return period

DBE

IO Performance

CP Performance

MCEIO

1

2 3 4

∆��∆��

PT bar yieldingColumn decompression

∆��

Member yielding

∆��

Member failure

Limit States

For tak90 ground motion, maximum roof drift, θr,max = 0.0433rads, whichis 5.68σ larger than the mean θr,max = 0.0147rads under the MCE.

Mean analytical response for 30 ground motions at each seismic input level31 intense EQs used in hybrid simulations

Self Centering Concentrically Braced FramesLarge-Scale Hybrid Earthquake Simulations on 4-Story SC-CBF Test Specimen



Self Centering Concentrically Braced FramesLarge-Scale Hybrid Earthquake Simulation under exMCE Level GM record: Tak090_01-13-2010


Collapse Criteria

10% Max Drift 80% slope reduction

Median Collapse (g) 4.6 3.4

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.

Self Centering Concentrically Braced FramesCollapse Potential of SC-CBFs (Tahmasebi et al., 2012)


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 3 6 9 12 15 18

Total Number of Stories in SC-CBF

First Mode

Second Mode

Co

ntr

ibu

tio

n o

f M

od

es

to T

ota

l

OM

Re

spo

nse

• 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.

• 2nd mode contribution gets as large

as 1st mode.

• 1st mode response is effectively controlled

by rocking motion.

Self Centering Concentrically Braced FramesPerformance-Based Design Methodology for Steel Self-Centering Braced Frame (Chancellor et al., 2012)


Higher mode mitigation in Self-Centering walls (Wiebe, 2008)

Number of rocking jointsMoment at higher stories relative to Base

OM in the wall with single rocking joint

Single 38% higher than OMbase_single

Two ≈25% less than OMbase_sigle

Ten 48% less than OMbase_single

• 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.

Every second storyBase + MidheightBase

(Wiebe, 2008)

kst: Story stiffness

ksp: Stiffness of the rotational spring

(Wiebe, 2008)


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%

• 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.

Overturning moment envelope Shear force envelope

• Response of the structure under ENA-1* ground motion record

*ENA-1 is a short and an impulsive GM record

Higher mode mitigation in Controlled Rocking Systems (Wiebe et al., 2012)


• Behavior of friction bearings under MCE level GM record.

• Relative behavior of CBF columns with rocking columns

�� , �� % �2 ∗ �� 1

��2�∗ 100

Self Centering Concentrically Braced Frames – Connection of Floor System to Rocking Frame

Large-Scale Hybrid Earthquake Simulation- Behavior of Friction Bearings


Rocking Precast Concrete Wall - Connection of Floor System to Rocking Frame

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)

Test conducted at UCSD as part of “Inertial Force-Limiting Floor Anchorage Systems for Seismic

Resistant Building Structures “ Project (Fleischman, Restrepo & Sause, 2011)

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.


Questions

Documents

Seismic Resilient Systems: Concepts and Challengesneesclt.mines.edu/content/ppt6.pdf · Seismic Resilient Systems: Concepts and Challenges ... less than that of conventional Special