heavy timber buckling-restrained braced frames · • an extension of codified aisc 341 steel brbf...
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Heavy Timber Buckling-Restrained Braced FramesA proposed solution for buildings in regions of high seismicity
Hans-Erik Blomgren PE SE P.Eng. Struct.Eng.Mass Timber Research Workshop, November 3, 2015Session 1: Resistance to Lateral LoadsForest Products Laboratory, Madison Wisconsin
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Heavy Timber Braced Frames
- Current code
- System attributes
- Precedents
The Heavy Timber BRBF concept
- BRBF primer
- Component testing
- System level evaluation
Conclusion
Outline
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IBC 2012 (ASCE 7-10)
BCBC 2012
Current Code Definitions
Codes
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Rd Ro Height Limits (m)
R CdΩΩΩΩo Height Limits (ft)
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4 Load Slip Relationship of Fasteners
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Dowel type fastener
Attributes of Wood in Seismic Systems
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5 Hysteresis of Light Wood Framed Shear Walls (Source: FEMA)
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Attributes of Wood in Seismic Systems
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Advantages
- High strength/weight ratio (low mass)
- High short term load strength
Disadvantages
- Brittle failure modes exist
- Localized damage at post-yield (pinched hysteresis)
- Concentrated locations of limited ductility (fasteners)
- Ductile connections = low stiffness
Attributes of Wood in Seismic Systems
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Heavy Timber Braced Frame Precedents
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Braced Frames – Side Plates & Bolts (Source: Cal Poly)
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Heavy Timber Braced Frame Precedents
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Braced Frames – Dowel and Flitch Plates (Source: Structurlam)
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Heavy Timber Braced Frame Precedents
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Braced Frames – Dowel & Flitch Plates (Source: Sweco)
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Heavy Timber Braced Frame Precedents
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The BRB - Primer
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Buckling-Restrained Braced Frame Primer
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Buckling-Restrained Braced Frame Primer
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Current Code:
• AISC 341-10
- Section F4 – Design Provisions- Capacity based philosophy
- Section K3 – Testing Qualifications- Component
- Subassembly
Buckling-Restrained Braced Frame Primer
R ΩΩΩΩo Cd
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The HTBRB
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Heavy Timber Buckling-Restrained Brace
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HTBRB Construction
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BRB Specimen Capacity = 100k
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HTBRB Component Level Test Requirements
β
∆bm
2.2
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HTBRBF System Level Evaluation
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HTBRBF System Level Study
Archetype Building Dimensions
X
Y
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HTBRBF System Level Study
Archetype Building Column Sizes
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HTBRBF System Level Study
Archetype Building BRB Sizes
BRB Core Areas
(Fy = 42ksi)BRB Sizes
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89kip
65kip
135kip
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HTBRBF System Level Study
Seismic Design Parameters – Linear Response Analysis
Site Class C Ie 1.0 R 6 W 6,247k
Sds 0.66 SDC D Cd 5 Cs 0.055
S1 0.39 ββββ 5% ΩΩΩΩo 2.5 V 290k
Code Period
Analysis 1st Period
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Analysis 2nd Period
1st Mode = 1.77s
Mass Part. = 73%
2nd Mode = 0.57s
Mass Part. = 18%
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HTBRBF System Level Study
Story Drifts – Wind & Seismic
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H/5
00
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HTBRBF System Level Study
HTBRB Forces
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HTBRBF System Level Study
HTBRBF Column Forces
24x24 GL Column
φφφφPn = 2570k
3.75” dia A354 Rod
φφφφTn = 1014k
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HTBRBF System Level Study
Wind Acceleration (Occupant Comfort – ISO 10137)
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ISO 10137 Wind Acceleration
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Conclusion
• There is a need for code-defined heavy timber seismic systems
• The HTBRBF is a possible solution b/c:• An extension of codified AISC 341 steel BRBF system
• Easy to analyze
• High strength, stiffness, & ductility (win-win-win)
• Limited irrecoverable timber damage
• Potential for rapid application near-term (PBD – ASCE 41-13)
• Sub-assembly test needed
• Economic/constructible frame details needed
• Start USA code definition• P-695
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