Steel Diaphragm Innovation Initiative AISI COS/COFS Webinar B.W. Schafer 30 June 2020 COLD-FORMED STEEL RESEARCH CONSORTIUM SDII
SDII Team and Partners: • Management: COLD-FORMED STEEL RESEARCH CONSORTIUM • Industry Sponsors: • Government Sponsors: • Researchers: Currently in its final year of primary research. SDII 2
steeli.org SDII 3
Codes and Standards Efforts of SDII Background ASCE 7 • ASCE7-16 introduces alt. diaphragm design with R s , but no steel provisions are included ASCE 41 AISC 341 • FEMA P-1026 (2015) introduces alt. RWFD design methods, but does not include steel deck in recommendations due to concerns • ASCE41-17 does not allow ductility to be considered in bare or concrete-filled AISC 342 AISI S310 steel deck diaphragms • AISC 341-16 does not link to AISI S310 for capacity AISI S400 • AISI S310-16 provides a grossly conservative prediction for strength of concrete-filled steel deck SDII 4
Codes and Standards Efforts of SDII • Bare steel deck ASCE 7 • seismic detailing for AISI S400 • With PBD methods • R s for ASCE 7 AISC 360 ASCE 41 • R diaph for RWFD in ASCE 7 AISC 341 • m for AISC 342/ASCE 41 • modeling for AISC 342/ASCE 41 Example of links Created by SDII Standards work • Concrete-filled steel deck • strength for AISI S310 • strength callout for AISC 360&341 AISC 342 AISI S310 • R s for ASCE 7 • m for AISC 342/ASCE 41 • modeling for AISC 342/ASCE 41 AISI S400 • more coming… (shear studs, reinforced concrete-filled) SDII 5
Update on latest research • CFSRC Dspace provides public reports: https://jscholarship.library.jhu.edu/handle/1774.2/40428 SelectedTopics • Concrete-filled steel deck cantilever diaphragm testing and connection to final full-scale bay testing • 3D building modeling and assessment of diaphragm design methodologies SDII 6
Concrete-filled steel deck cantilever testing in the lab: schematic: 17 ft. 15 ft. W 24x84 (2 studs at 12 in.) Slave Master Actuator W 24x84 (Studs at 12 in.) Actuator in W 24x84 (Studs at 12 in.) in Force Displacement Control Control 13.3 ft. Deck 12 ft. Direction Stud spacing equal to approximately 36 in. for specimens designed to fail the perimeter fasteners W 24x84 (2 studs at 12 in.) SDII 7
Test matrix Predicted Total Concrete Steel Deck Shear Thickness Test Specimen Objective Failure Mode Status Type Height Strength (in) (k/ft) 3/6.25-4-L-NF-DT LW 3 6.25 9.1 Typical 2 Hr Fire Rating for LW Diagonal Tension Completed 3/7.5-4-N-NF-DT NW 3 7.5 14.6 Typical 2 Hr Fire Rating for NW Diagonal Tension Completed Thin assembly using LW 2/4-4-L-NF-DT LW 2 4 5.5 Diagonal Tension Completed (Fills LW gap in past testing) 3/6.25-4-L-NF-P LW 3 6.25 6.5 Fail Studs with LW Perimeter Fastener Completed Include Reinforcing Steel 2/4.5-4-L-RS-DT LW 2 4.5 19 Diagonal Tension Completed #4@12 each way 3/7.5-4-N-NF-P NW 3 7.5 6.6 Fail Studs with NW Perimeter Fastener In Progress* Include Reinforcing Steel 3/6.25-4-L-RS-DT LW 3 6.25 17.2 Diagonal Tension Future #4@18 each way Include Welded wire fabric 3/7.5-4-N-RS-DT NW 3 7.5 23.2 Diagonal Tension Future 6x6 W4.5xW4.5** SDII *prior to March COVID shutdowns completion of last 3 specimens expected by December 2020, now ~ March 2021 8
Unreinforced Concrete-filled steel deck (3/6.25-4-L-NF-DT) • Hysteresis • Cracking at peak load peak matches well with AISI S310-22 Stiffness is challenging to measure, a little low vs. AISI S310-22 Observed hysteresis part of the justification for R s proposals in ASCE 7, and used in modeling of buildings SDII 9
Test matrix Predicted Total Concrete Steel Deck Shear Thickness Test Specimen Objective Failure Mode Status Type Height Strength (in) (k/ft) 3/6.25-4-L-NF-DT LW 3 6.25 9.1 Typical 2 Hr Fire Rating for LW Diagonal Tension Completed 3/7.5-4-N-NF-DT NW 3 7.5 14.6 Typical 2 Hr Fire Rating for NW Diagonal Tension Completed Thin assembly using LW 2/4-4-L-NF-DT LW 2 4 5.5 Diagonal Tension Completed (Fills LW gap in past testing) 3/6.25-4-L-NF-P LW 3 6.25 6.5 Fail Studs with LW Perimeter Fastener Completed Include Reinforcing Steel 2/4.5-4-L-RS-DT LW 2 4.5 19 Diagonal Tension Completed #4@12 each way 3/7.5-4-N-NF-P NW 3 7.5 6.6 Fail Studs with NW Perimeter Fastener In Progress* Include Reinforcing Steel 3/6.25-4-L-RS-DT LW 3 6.25 17.2 Diagonal Tension Future #4@18 each way Include Welded wire fabric 3/7.5-4-N-RS-DT NW 3 7.5 23.2 Diagonal Tension Future 6x6 W4.5xW4.5** SDII *prior to March COVID shutdowns completion of last 3 specimens expected by December 2020, now ~ March 2021 10
Reinforced Concrete-filled steel deck (2/4.5-4-L-RS-DT) • Hysteresis • Reinforcing SDII 11
Reinforced Concrete-filled steel deck (2/4.5-4-L-RS-DT) • Hysteresis • Cracking at peak load peak matches reasonably with additive strength Including reinforcing. High strength, excellent distributed cracking, essentially ideal concrete response for the load, but… SDII 12
Reinforced Concrete-filled steel deck (2/4.5-4-L-RS-DT) • Hysteresis • Cracking at peak load peak matches reasonably rib shear with additive strength failure Including reinforcing. Geometric and/or reinforcing details exist to avoid this limit state, but are not currently in AISC 360/341 or AISI S310 or ACI SDII 13
Full Building Bay Diaphragm Testing Quick Facts: Stroke: +/- 10” Force: 724 kip each direction combined total Steel framing: 20’ x 28’ Concrete: Lightweight, 6.25” thick total, 3” deck Concrete edge dims: 32’ x 24’ Concrete Reinforcement: wwf only Important realistic building features • floor framing stiffness included • deck fill can bear into columns • To be tested at STRESS lab at Northeastern • Parallel cantilever diaphragm specimen test at VT • SDII
Update on latest research • CFSRC Dspace provides public reports: https://jscholarship.library.jhu.edu/handle/1774.2/40428 SelectedTopics • Concrete-filled steel deck cantilever diaphragm testing and connection to final full-scale bay testing • 3D building modeling and assessment of diaphragm design methodologies SDII 15
BRB Building Study (a) 1-story building (b) 4-story building Seismic Behavior of Steel BRBF Buildings Including Consideration of Diaphragm Inelasticity Gengrui Wei, Matthew R. Eatherton, Hamid Foroughi, Shahab Torabian, Benjamin W. Schafer March 2020 COLD-FORMED STEEL RESEARCH CONSORTIUM REPORT SERIES CFSRC R-2020-04 (c) 8-story building (d) 12-story building Figure 4 3D OpenSees models of archetype buildings Perimeter BRB Vibration - Period • • 1,4,8 and 12 stories Pushover - Ductility • • Diaphragm designs NL time history – Collapse • • Traditional ASCE 7 Across models • • Alt. R s (1, 2/2.5) Across EQ and EQ levels • • SDII https://jscholarship.library.jhu.edu/handle/1774.2/62366 16
Example Building Response (1 EQ, MCE level) 12 100 Δ(𝑢) 𝑄 − 𝜀 10 response at peak drift Typical Floor Diaphragm Truss Force (kip) 50 8 Story Drift (SRSS) (%) 6 0 4 floor -50 2 building drift in time concrete-filled steel deck 0 -100 0 10 20 30 40 50 -0.15 -0.1 -0.05 0 0.05 0.1 Time (sec) Typical Floor Diaphragm Truss Deformation (in) 600 𝑄 − 𝜀 400 20 𝑄 − 𝜀 200 Vertical and horizontal LFRS contribute • Roof Diaphragm Truss Force (kip) 10 BRB Force (kip) to the inelastic response 0 0 BRB dominates inelastic response, and • -200 story drift is the limiting demand -10 roof -400 BRB Drift is 3D Δ ! and Δ " separately do not • bare steel deck -20 -600 effectively capture the actual response -4 -2 0 2 4 BRB Deformation (in) -1 -0.5 0 0.5 1 Roof Diaphragm Truss Deformation (in) SDII 17
Collapse probability across models (ACMR level) 8 story 1 story 1 story 4 story predicted collapse (%) (bare deck roof) (conc.-filled deck roof) (conc.-filled deck floors bare deck roof) 𝑈𝑠𝑏𝑒. 𝐹𝑀𝐺 𝑈𝑠𝑏𝑒. 𝐹𝑀𝐺 𝑈𝑠𝑏𝑒. 𝐹𝑀𝐺 𝑈𝑠𝑏𝑒. 𝐹𝑀𝐺 𝑈𝑠𝑏𝑒. 𝐹𝑀𝐺 diaphragm design: 𝑆 ! = 1 𝑆 ! = 1 𝑆 ! = 1 𝑆 ! = 1 𝑆 ! = 1 𝑆 ! = 2.5 𝑆 ! = 2 𝑆 ! = 2/2.5 𝑆 ! = 2/2.5 𝑆 ! = 2/2.5 Traditional ASCE 7 diaphragm design and the alternative diaphragm design method with R s =2 for • concrete-filled steel deck and 2.5 for bare steel deck result in the same diaphragm designs Performance of the buildings is dominated by story drift and response of the BRB. Collapse • probabilities are acceptable or nearly so for R s =2/2.5 designed diaphragms Increasing this diaphragm demand forces with an Rs=1 design does not typically result in • improved collapse probabilities for this building system. SDII 18
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