Heavy Timber Buckling-Restrained Braced Frames

Transcription

1 Heavy Timber Buckling-Restrained Braced Frames A proposed solution for buildings in regions of high seismicity Hans-Erik Blomgren PE SE P.Eng. Struct.Eng. Mass Timber Research Workshop, November 3, 2015 Session 1: Resistance to Lateral Loads Forest Products Laboratory, Madison Wisconsin

2 Outline Heavy Timber Braced Frames - Current code - System attributes - Precedents The Heavy Timber BRBF concept - BRBF primer - Component testing - System level evaluation Conclusion 2

3 Current Code Definitions IBC 2012 (ASCE 7-10) R Ωo Cd Height Limits (ft) BCBC 2012 Rd Ro Height Limits (m) 3 Codes

4 Attributes of Wood in Seismic Systems Dowel type fastener 4 Load Slip Relationship of Fasteners

5 Attributes of Wood in Seismic Systems 5 Hysteresis of Light Wood Framed Shear Walls (Source: FEMA)

6 Attributes of Wood in Seismic Systems 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 6

7 Heavy Timber Braced Frame Precedents

8 Heavy Timber Braced Frame Precedents Braced Frames Side Plates & Bolts (Source: Cal Poly)

9 Heavy Timber Braced Frame Precedents Braced Frames Dowel and Flitch Plates (Source: Structurlam)

10 Heavy Timber Braced Frame Precedents Braced Frames Dowel & Flitch Plates (Source: Sweco)

11 The BRB - Primer

12 Buckling-Restrained Braced Frame Primer 12

13 Buckling-Restrained Braced Frame Primer 13

14 Buckling-Restrained Braced Frame Primer Current Code: AISC Section F4 Design Provisions - Capacity based philosophy - Section K3 Testing Qualifications - Component - Subassembly R Ωo Cd 14

15 The HTBRB

16 Heavy Timber Buckling-Restrained Brace

17 HTBRB Construction BRB Specimen Capacity = 100k

18 HTBRB Component Level Test Requirements 2.2 bm β 18

19 HTBRBF System Level Evaluation

20 HTBRBF System Level Study Y X 20 Archetype Building Dimensions

21 HTBRBF System Level Study 21 Archetype Building Column Sizes

22 HTBRBF System Level Study 65kip 89kip 135kip BRB Sizes BRB Core Areas (Fy = 42ksi) 22 Archetype Building BRB Sizes

23 HTBRBF System Level Study Site Class C Ie 1.0 R 6 W 6,247k Sds 0.66 SDC D Cd 5 Cs S β 5% Ωo 2.5 V 290k Analysis 2 nd Period Code Period Analysis 1 st Period 1 st Mode = 1.77s Mass Part. = 73% 2 nd Mode = 0.57s Mass Part. = 18% 23 Seismic Design Parameters Linear Response Analysis

24 HTBRBF System Level Study H/ Story Drifts Wind & Seismic

25 HTBRBF System Level Study 25 HTBRB Forces

26 HTBRBF System Level Study 3.75 dia A354 Rod φtn = 1014k 24x24 GL Column φpn = 2570k 26 HTBRBF Column Forces

27 HTBRBF System Level Study ISO Wind Acceleration 27 Wind Acceleration (Occupant Comfort ISO 10137)

28 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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