heavy timber buckling-restrained braced frames · • an extension of codified aisc 341 steel brbf...

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


Rd Ro Height Limits (m)

R CdΩΩΩΩo Height Limits (ft)

4 Load Slip Relationship of Fasteners


Dowel type fastener

Attributes of Wood in Seismic Systems

5 Hysteresis of Light Wood Framed Shear Walls (Source: FEMA)



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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



Heavy Timber Braced Frame Precedents

Braced Frames – Side Plates & Bolts (Source: Cal Poly)



Braced Frames – Dowel and Flitch Plates (Source: Structurlam)



Braced Frames – Dowel & Flitch Plates (Source: Sweco)



The BRB - 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


R ΩΩΩΩo Cd


The HTBRB

Heavy Timber Buckling-Restrained Brace


HTBRB Construction


BRB Specimen Capacity = 100k

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HTBRB Component Level Test Requirements

β

∆bm

2.2


HTBRBF System Level Evaluation

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HTBRBF System Level Study

Archetype Building Dimensions

X

Y


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Archetype Building Column Sizes


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Archetype Building BRB Sizes

BRB Core Areas

(Fy = 42ksi)BRB Sizes


89kip

65kip

135kip

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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


Analysis 2nd Period

1st Mode = 1.77s

Mass Part. = 73%

2nd Mode = 0.57s

Mass Part. = 18%

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Story Drifts – Wind & Seismic


H/5

00

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HTBRB Forces


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HTBRBF Column Forces

24x24 GL Column

φφφφPn = 2570k

3.75” dia A354 Rod

φφφφTn = 1014k


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Wind Acceleration (Occupant Comfort – ISO 10137)


ISO 10137 Wind Acceleration

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


heavy timber buckling-restrained braced frames · • an extension of codified aisc 341 steel brbf...

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