Keith Palmer
Seismic Behavior of Steel Concentrically Braced Frame SystemsConcentrically Braced Frame Systems
St t Of Th P ti CBF D iState‐Of‐The‐Practice CBF Design
• AISC Seismic ProvisionsAISC St l C t M l• AISC Steel Const. Manual
d h• Based on component research• Not based on system behavior
Points C & D – brace fracturePoints G & H – column fracture
(Uriz and Mahin 2008)
NEES CBF R h PNEES CBF Research ProgramNEESR‐SG – International Hybrid Simulation of y
Tomorrow’s Braced Frame Systems
• C. Roeder, D. Lehman, University of Washington
• S. Mahin, University of California Berkeley
• K.C. Tsai, National Taiwan University
• C. Shield, University of Minnesota
• T. Okazaki, Hokkaido University
NEES CBF R h O tNEES CBF Research Outcome
(a) 2t linear offset - Current practice (b) 8t elliptical offset - Proposed
Elliptical offset – thinner, more compact gusset plate design
C t & F t W kCurrent & Future WorkMotivation
• 3D effects not completely understood
• Loading and deformation perpendicular to CBF
• Effect of concrete floor systemffect of concrete floor system
• Limited studies of center connection for Single‐story X configurationstory X‐configuration• System behavior of pin‐ended, collar‐type BRB with typical detailing not clearwith typical detailing not clear
3D CBF System Tests
1st Test Frame:• SCBF• HSS buckling braces• Single-story X-configSingle story X config.
3D CBF System Tests
2nd Test Frame:• BRBF• Star Seismic BRBs• Single diagonalSingle diagonal config.• Pinned ends
MAST Laboratory
3D CBF System Tests
Loading protocolLoading protocol
• Bi-directional• Cyclic• Displacement controlled
3D CBF System Tests
Cyclic Loading ProtocolCyclic Loading Protocol) Drift at initial brace b ckling (SCBF) 0 3%
Rat
io (r
ads) y – Drift at initial brace buckling (SCBF) ~ 0.3%
y – Drift at initial BRB yielding (BRBF) ~ 0.33%
ory
Drif
t RSt
o
[email protected] [email protected]
[email protected] [email protected]
Note: complete protocol not shown (continued in increments of y after 3.0y
3D CBF System Tests
InstrumentationInstrumentation
• Strain gauges (~220)
LVDT ( 74)• LVDTs (~74)
• String potentiometers (~41)• String potentiometers ( 41)
•Metris Kryptonyp
SCBF Test Highlights
First brace to buckle (~0.3% ISDR)
SCBF Test Highlights
Mode 2 brace UnsymmetricalMode 2 brace buckling
1.3% ISDR
Unsymmetrical brace buckling
2.1% ISDR
SCBF Test Highlights
3D CBF System TestsGusset yield lines (+2% ISDR)
3D CBF System Tests
C t W kCurrent Work
Brace Fracture2.0% ISDR
Second StoryY di St Sh (kN) SDR ( d 100)
SCBF Test HighlightsY-dir Story Shear (kN) vs. SDR (rads x 100)
YY
X
First StoryY-dir Story Shear (kN) vs. SDR (rads x 100)
2nd story brace yielding (~0.3% ISDR)
3D CBF System Tests
BRBF Test Highlights
Gusset plateweld tear Columnweld tear
3.1% ISDRColumn flange
Beam flange
3D CBF System Tests
Column flange
BRBF Test Highlightsg
local buckling3.2% ISDR
3D CBF System Tests
Column web and
BRBF Test Highlights
flange tearing4% ISDR
Beam web yielding and tearing, flange
tearing3 6% ISDR3.6% ISDR
Gusset plate
Beam web yielding and tearing, flange
tearing3 6% ISDR3.6% ISDR
Second Story
BRBF Test Highlights
Y-dir Story Shear (kN) vs. SDR (rads x 100)
X
Y
Second StoryX-dir Story Shear (kN) vs. SDR (rads x 100)
S (SCBF)Summary (SCBF)• Out-of-plane frame deformation appears to have had little to no effect on SCBF frame deformation capacity and strength
• XBF deformation capacities the same as those achieved in l t t t UW ith i il fplanar tests at UW with similar frame
• 8t elliptical offset method accommodated large inelastic rotations after brace bucklingafter brace buckling
• Gusset edge deformation caused by frame action – no apparent effect on global performanceeffect on global performance
S (BRBF)Summary (BRBF)• Out-of-plane frame deformation appears to have had little to no p ppeffect on frame deformation capacity and strength
• Frame action had dominating effect on gusset interface weld demands
• Considerable damage to frame occurred before and after brace f tfracture
• The BRB cores fractured at 3.5 and 4% story drift
• No instabilities occurred in the BRB prior to fracture
• Different behavior than BRBF tests at UW and UCB
• UW, UCB drifts prior to BRB instability ~ 2 to 2.5%
A k l d tAcknowledgements
• National Science Foundation (NSF)• Network for Earthquake
Engineering Simulation (NEES)
• American Institute of Steel Construction (AISC)
A k l d tAcknowledgements
MAST LaboratoryMAST Laboratory
• Professor Carol Shield, Director• Paul Bergson, Operations Manager
• Drew J Daugherty IT• Drew J. Daugherty, IT• Rachel Gaulke, Instrumentation Engineer
• Angela Kingsley, Floor Manager
•Mitch Reierson ITMitch Reierson, IT
Questions?
B kli R t i d B d FBuckling‐Restrained Braced Frames
B kli R t i d BBuckling‐Restrained Braces
AA
A
Steel CoreCasing Steel Core
Gap and
CasingSteel jacket
Mortar
Section A-A
Gap and Debonding material
H t ti C iHysteretic Comparison
Conventional Buckling Brace Buckling Restrained BraceConventional Buckling Brace Buckling‐Restrained BraceBlack et. al (2002)Black et. al (1980)
NEES CBF R h O tNEES CBF Research OutcomeBalanced Design ProcedureBalanced Design Procedure
Brace Brace Connection Beam/Column BraceBuckling Yielding Yielding Yielding Fracture
• Ensure that adequate ductility capacity is provided• Unwanted failure limit states are suppressed
SCBF Test Highlights
3D CBF System TestsGusset plate tear1.7% ISDR
3D CBF System Tests
BRBF Test Highlights
Initial Gusset Yielding
~ 1.6% ISDR 1.6% ISDR
SCBF Test Highlights
3D CBF System TestsBase gusset yield pattern