Presented on [Date] by [Author’s Name] (Edit the Master Slide to change this text)

CLT Diaphragm Research and Design in North America

Scott E. Breneman, PhD, PE, SE Scott.Breneman@woodworks.org Senior Technical Director WoodWorks – Wood Products Council Photo Ema Peter Photography

USDA Forest Products Lab Mass Timber Workshop November 3rd, 2015

Diaphragm Design • Diaphragm: Roof, floor transferring lateral forces to the

vertical resisting elements • Diaphragm loads are generally uniform loads, resisted by

the diaphragm in bending, similar to a horizontal deep beam

• Diaphragm bending results in tension/compression in chords perpendicular to load

Wood Education Institute NIST NEHRP

New Chapter 10 covering Adjustment Factors for CLT

Formatting Similar to Wood Structural Panels

CLT in NDS 2015 – Panel Strength

ANSI/APA PRG 320 Product Reports

Does not include In-plane Panel Shear Strength

ICC-ES Acceptance Criteria AC 455

Defines In-plane Panel Shear Strength Test for use in Floor and Roof Decks

Connectors for CLT in NDS 2015:

Dowel Type Fasteners, e.g. Lag Screws, Bolts and Nails

CLT in NDS 2015 - Connectors

Panel + Connection = Diaphragm ?

• WSP Diaphragms based on system testing • WSP Diaphragms capacities listed in AWC’s

Special Design Provisions for Wind and Seismic

Need for System Level Diaphragm Strength Verification

CLT Diaphragms for Seismic

Seismic behavior is not simple question of force demands and capacity. Seismic design uses force as a proxy for EQ behavior

An European Approach

Yielding Connections

Non Yielding Connections

Designed to Overstrength factor of 1.3 to 1.6 of yielding connection strength

Fragiacomo, Vasallo et al.

Typical Assumption of Rigid Diaphragm Behavior for CLT wall

and floor systems

US CLT Handbook Approach Yielding Connections

Non Yielding Connections (Anchorage to Support)

• NDS Yield Modes III and IV govern. • Strength of other (non-yielding) limit

states at connection designed to nominal yielding connection capacity. 1/ϕ = 1/0.65 = 1.54 overstrength factor

Design Example White Paper

Diaphragm Design Example

Lateral load, w

Shear Wall

CLT Panels

Design Example White Paper

• Shows calculations for simple diaphragm following US CLT Handbook Recommendations with many limit states.

• Presented modification of WSP diaphragm deflection calculation for large Panels

𝜹𝜹𝒅𝒅𝒅𝒅𝒅𝒅 =𝟓𝟓𝒗𝒗𝑳𝑳𝟑𝟑

𝟖𝟖𝑬𝑬𝑬𝑬𝑬𝑬 +𝒗𝒗𝑳𝑳

𝟒𝟒𝑮𝑮𝒗𝒗𝒕𝒕𝒗𝒗+ 𝑪𝑪𝑳𝑳𝒆𝒆𝒏𝒏 +

∑ 𝒙𝒙𝚫𝚫𝒄𝒄𝟐𝟐𝑬𝑬

𝑪𝑪 =𝟏𝟏𝟐𝟐

𝟏𝟏𝑷𝑷𝑳𝑳

+𝟏𝟏𝑷𝑷𝑬𝑬

PL is panel length PW is panel width

FEM Modeling for Design Work

• Semi-Rigid Analysis of Diaphragm in SAP 2000 • Modelled to match design example assumptions • Concentrated Connection Model

• 4 Springs per corner • With No Chord Slip, 4% difference in deflections • With Chord Slip, 11% difference in deflections

Research In Progress

University of British Columbia: • Prof. Thomas Tannert • Afrin Hossain, PhD Candidate

Cyclic Testing Results Available Soon?

Research In Progress

Colorado State University • John van de Lindt • Planning small full-scale

diaphragm test

Research in Progress

Oregon State University: • Rakesh Gupta, Lech Muszinsky, Andre

Barbosa. CLT connections, etc. University of British Columbia, Vancouver • Terje Haukaas, Frank Lam. CLT connections,

CLT Diaphragm Modelling. And More?

• Testing, Testing, Testing: - Continue connection level testing - Cyclical Testing of Proprietary connectors - Diaphragm Testing paired with Analytical Studies - Chord Design and Detailing.

• Refinement of Engineering Design Approach

• Collaboration of researchers, industry, and practitioners

• Standardization of Developed of Design Method - Code referenceable engineered design standards for capacity

design method - Possibly new testing protocols for panel and connection behavior

• Education of designers for proliferation of use.

Ideas for Design Standardization

• Possible routes for near term seismic project designs under Alternative Means and Methods include

1) Elastic Design Method • Based on lower-bound strength of components • Following new ASCE 7-16 alternative diaphragm method to

determine elastic seismic diaphragm force demands

2) Capacity-Based Design Method

• Using designated yielding connections with overstrength design of non-desirable limit states.

• Based on yielding connection technologies of proven cyclic behavior Relatively equivalent to Wood Structural Panel diaphragm

behavior OR Advanced Engineering with supporting testing to justify design

Ideas for Near Term Seismic Projects

CLT Diaphragm Scenarios

CLT Shear Walls

CLT Panel Diaphragm

Large Diaphragm Spans… With multiple panels per span

Chords and Collectors

CLT Diaphragm Scenarios

CLT Shear Walls

CLT Panel Diaphragm

Small Diaphragm Spans… With full diaphragm-width panels

Chords and Collectors

CLT Diaphragm Scenarios

BRB Frames

CLT Panel Diaphragm

Diaphragm spanning between Soft Braces

Chords and Collectors

CLT Diaphragm Scenarios

Concrete Shear Wall

Core

CLT Panel Diaphragm

Diaphragm cantilevering off Stiff Core

Chords and Collectors

CLT Diaphragm Scenarios

Real buildings are not all rectangles