Offset Diaphragms. Presentation Based On: By: R. Terry Malone, PE, SE.

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2 Presentation Based On: Offset Diaphragms Presentation updated to 2012 IB, ASE SDPWS opyright McGraw-Hill, I Presented by: By: R. Terry Malone, PE, SE Senior Technical Director Architectural & Engineering Solutions terrym@woodworks.org

3 The Wood Products ouncil is a Registered Provider with The American Institute of Architects ontinuing Education Systems (AIA/ES), Provider #G516. redit(s) earned on completion of this course will be reported to AIA ES for AIA members. ertificates of ompletion for both AIA members and non-aia members are available upon request. This course is registered with AIA ES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

4 ourse Description Lateral force resisting systems in today s structures are much more complex than they were several decades ago, incorporating multiple horizontal and vertical offsets in the diaphragms, multiple irregularities, and fewer lateral resisting elements. This two part presentation will provide a brief review of a method used to analyzed these complex structures. In part 1, topics will include code requirements, how to recognize diaphragm irregularities and discontinuities, how shears are distributed through complex diaphragms, a method of analysis used to solve the transfer of forces across areas of discontinuity, and the analysis of flexible wood sheathed or untopped steel decking diaphragms with horizontal offsets.

5 Learning Objectives Basic Information Discuss boundary elements, complete lateral resisting load path requirements and related code sections. Examine ommon Types of Discontinuities Examine common types of discontinuities and irregularities and discuss how to establish complete lateral load paths across areas of discontinuity. Discuss an Analytical Method of Analysis Review an analytical method used for solving complex diaphragms and shear walls (Diekmann Method) using Transfer Diaphragms and the Visual Shear Transfer Method. Offset Diaphragms-Examples Review the analysis of flexible offset diaphragms for loading in the transverse direction.

6 Presentation Assumptions Assumptions: Loads to diaphragms and shear walls Strength level or allowable stress design Wind or seismic forces. The loads are already factored for the appropriate load combination. ode and Standards: ASE 7-10 Minimum Design Loads for Buildings and Other Structures 2012 IB 2008 SDPWS- Special Design Provisions for Wind and Seismic Analysis and Design references: The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls- Malone, Rice Woodworks-The Analysis of Irregular Shaped Diaphragms Design of Wood Structures- Breyer, Fridley, Pollock, obeen SEAO Seismic Design Manual, Volume 2 Wood Engineering and onstruction Handbook-Faherty, Williamson Guide to the Design of Diaphragms, hords and s-nsea

7 Evolution to omplex Buildings Simple structures omplex structures The method of analysis is: Required for all construction types. Straight forward and simple to use. Based on simple statics! Today s presentation focuses on: ontinuous load paths across areas of discontinuities. Flexible wood sheathed or un-topped steel deck diaphragms. Wood diaphragms are well suited for these shapes as they can be easily adapted to the building shape and are cost effective.

8 omplete Example with narrative and calculations

9 Mid-rise Multi-family Marselle ondominiums Structural Engineer engineer: Yu & Trochalakis, PLL Photographer: Matt Todd Photographer 5 stories of wood over 6 stories concrete (podium) 2 above grade

10 Discontinuous chords Transverse Mid-rise Multi-family Lds. Discontinuous struts Longitudinal ant. Lds. No exterior Shear walls Flexible, semi-rigid, or rigid???

11 Vertically offset Diaphragms? Openings in diaphragm Offsets in the diaphragm and walls Harrington Recovery enter Structural engineer: Pujara Wirth Torke, Inc. Photographer: urtis Walz

12 Basic Information Boundary Elements omplete Load Paths Method of Analysis

13 Strut hord/ hord/ Strut W ( plf) hord hord hord T hord hord Diaphragm support Diaphragm support Strut- receives shears from one side only*. - receives shears from both sides. Discontinuous hord-perpendicular to the applied load and diaphragm receives axial tension and compression chord forces. *[ Drag struts and collectors are synonymous in ASE7] hord Struts, s, and hords- (my) Terminology TD1 hord

14 Strut Diaphragm Boundary Elements A B Fundamental Principles: A shear wall is a location where diaphragm forces are resisted (supported), and therefore defines a diaphragm boundary location. Note: All edges of a diaphragm shall be supported by a boundary element. 1 2 Strut Strut Diaphragm 1 Boundary (typical) hord Diaphragm 2 Boundary (typical) Diaphragm 1 Diaphragm 2 hord Diaphragm Boundary Elements: hords, drag struts, collectors, Shear walls, frames Boundary member locations: Diaphragm and shear wall perimeters Interior openings Areas of discontinuities Re-entrant corners. Diaphragm and shear wall sheathing shall not be used to splice boundary elements. elements shall be provided that are capable of transferring forces originating in other portions of the structure to the element providing resistance to those forces. 3 Note: Interior shear walls without a collector or a complete alternate load path are NOT ALLOWED! hord Required for Seismic and wind

15 Strut 1 hord Deflection if tie Diaphragm 2 Boundary hord A Diaphragm 1 Diaphragm 2 Diaph. Boundary (Longitudinal loading) Deflection if no tie hord Strut Strut 4 B 2 Diaphragm 1 boundary 3 Re-entrant corner Tearing will occur if collectors are not installed at re-entrant corner. 3 hord 1 2 Loads Deflected curve if proper tie Deflected curve if no tie Boundary Elements L Shaped Buildings-Transverse Loading

16 Basic Information Boundary Elements omplete Load Paths Method of Analysis

17 Strut (typ.) 1 Strut Strut Strut (typ.) MRF B 1 Strut/chord (typ.) A 6 Strut/chord Open Strut /chord (typ.) (typ.) Strut chord Multiple offset diaphragm What does this mean? E 2 Strut chord Strut/chord F 4 Strut/chord Offset 3 strut 4 omplete ontinuous Lateral Load Paths D Analysis: ASE7-10 Sections: Design shall be based on a rational analysis At diaphragm discontinuities such as openings and re-entrant corners, the design shall assure that the dissipation or transfer of edge (chord) forces combined with other forces in the diaphragm is within shear and tension capacity of the diaphragm.

18 Strut (typ.) 1 Strut Strut Strut (typ.) MRF1 B 1 Strut/chord 2 5 (typ.) Discontinuous diaphragm 5 chord 3 A Open Strut/chord Discont. diaphragm chord Strut /chord Discont. diaph. chord (typ.) 2 Strut chord E Strut/chord F Discont. diaphragm 4 chord Strut/chord 3 (typ.) 4 Strut chord D Discontinuous diaphragm chord/strut ASE7-10 Section 1.4-omplete load paths are required including members and their splice connections omplete ontinuous Lateral Load Paths

19 Strut (typ.) 1 Strut Strut Strut (typ.) MRF1 B 1 Offset shear walls 2 Strut/chord 5 3 (typ.) A Open Strut/chord Strut /chord (typ.) (typ.) Strut chord E 2 Strut chord Strut/chord F Strut/chord 3 4 D 4 Offset shear walls and struts ASE7-10 Section 1.4-omplete load paths are required including member and their splice connections omplete ontinuous Lateral Load Paths

20 Strut (typ.) 1 Strut Strut Strut (typ.) MRF B 1 Strut/chord (typ.) A Open 6 Vertical offset in diaphragm Strut/chord Strut /chord (typ.) Opening in diaph. (typ.) Strut chord E 2 Strut chord Strut/chord F Strut/chord 3 4 D 4 Design: IB Openings in shear panels that materially effect their strength shall be fully detailed on the plans and shall have their edges adequately reinforced to transfer all shear stresses. omplete ontinuous Lateral Load Paths

21 Basic Information Boundary Elements omplete Load Paths Method of Analysis

22 Method of Analysis The Visual Shear Transfer Method + Symbol for 1 ft x 1 ft square piece of sheathing in static equilibrium (typ.) FY Lds. +M + - FX Positive Direction + - Transverse Direction (shown) Shears Applied to Sheathing Elements Unit shear acting on sheathing element (plf) Unit shear transferred from the sheathing element into the boundary element (plf) Shears Transferred Into Boundary Elements

23 A B + - T Resisting wall (+) shears Strut in tension Strut in comp. Strut Forces Resisting wall (+) shears Positive sign convention Positive diaph. shear elements Pos. + Diaphragm.L. w=uniform load 1 2 (-) (-) + Diaphragm shear transferred into boundary element (typ.) + - Maximum moment 1 ft. x 1 ft. square sheathing element symbol at any location in the diaphragm. T Basic Shear Diagram (-) (-) Neg. Shear Distribution Into a Simple Diaphragm The Visual Shear Transfer Method Strut in ompr. Resisting wall shears (+) Strut in tension T Strut Forces Negative diaph. shear elements All edges of a diaphragm shall be supported by a boundary element (chord, strut, collector) or other vertical lateral force resisting element (shear wall, frame).

24 Introduction to Transfer Diaphragms and Transfer Areas Transfer Diaphragm hord (support) sub-diaphragm Transfers local forces out to primary chords/struts of the main diaphragm. TD1 T TD Ratio=4:1 Maximum Framing members, blocking, and connections shall extend into the diaphragm a sufficient distance to develop the force transferred into the diaphragm. What does this mean? hord (support) T

25 Drag strut Diaph..L. W ( plf) 4 A Diaphragm chord Discontinuous diaphragm chord The length of the collector is often determined by dividing the collector force by the diaphragm nailing capacity. (Wrong!) The collector is often checked for tension only. (Wrong!) ompression is rarely checked. B Diaphragm chord Diaphragm support Transfer Area Diaphragm chord Longitudinal Typical callout MST14 tie strap x 10-0 with (xx) 10d nails over 2x flat blocking. Lap 2-8 onto wall. Transfer Diaphragm Members and Elements Diaphragm support

26 Strut Resisting forces Resisting forces hord/ hord/ A Main chord This force must be transferred out to the main chords. A complete load path is required. B Disrupted chord Transfer area 1 2 Rotation of section Transfer area without transverse collectors Transfer Mechanism 3 Disrupted chord Discontinuous diaphragm chord B hord T Transfer Diaphragm ( Beam) 2 3 NOTE: TD1 Full depth must extend the full depth of the transfer diaphragm Main chord Transfer using beam concept

27 Transfer diaphragm length LTD LTD A 1 hord 2 (TD support) 3 Main chord T(a) VA=, Shear = VA LTD DTD -75 plf - B vnet=+300-(75)= +225 plf vnet =+225 (75)= +150 plf The transfer diaph. aspect Ratio should be similar to the main diaphragm. hord force at discontinuity Disrupted chord vnet=+300+(250)= +550 plf No outside force is changing the basic diaphragm shear in this area T +500 plf TD1 vnet =+225 +(250) = +475 plf (TD support) TD depth DTD Main chord +300 plf plf plf Basic Shear Diagram at transfer diaphragm Basic Procedure Method by Edward F. Diekmann T T No outside force is changing the basic diaphragm shear in this area + Subtract from basic shears +250 plf a b Add to basic diaphragm shears T(b), Shear = V V= LTD DTD Transfer Diaphragm Shears Analogous to a beam with a concentrated Load. vnet= (250) = 550 plf Net shear Basic diaph. shear TD shears

28 B Direction of shear transferred into collector plf +150 plf plf +475 plf Net shear Net direction of shears acting on collector Place the net diaphragm shear on each side of the collector Place the transfer shears on each side of the collector Sum shears on collector (based upon direction of shears transferred onto collector). Shear left= = +325 plf 325 plf 325 plf Lcollector Note: The net shears will not always be equal. Dir. of force on collector Shear right= =+325 plf force=area of shear diagram Fcollector=( )(Lcollector) 2 Resulting net shear diagram on collector Shear Distribution Into The

29 L Transfer Diaph. length L Transfer Diaph. length 1 Transfer Diaph. depth hord, strut or shear wall 2 F( a) R A L A RA 1 Transfer Diaph. depth hord, strut or shear wall 2 F( a) R A b A RA F Transfer Diaphragm TD1 Discont. hord / strut B a b F Transfer Diaphragm TD1 hord, strut or shear wall F( L) R B b a b B RB hord, strut or shear wall F( b) R L R Discont. F hord / strut F Simple Span Transfer Diaphragm Analogous to a simple span beam with a concentrated load Propped antilever Transfer Diaphragm Analogous to a propped cantilever beam with a concentrated load Simple Span and Propped antilever Transfer Diaphragms

30 Diaphragms with Horizontal Offsets

31 V2 lb V3 lb 15 TD chords TD chords Example 1-Diaphragm with Horizontal End Offset Transverse Loading w=200 plf A Diaph..L. Diaph. chord 35 1 TD plf A F2A M= M2B ft.-lb F2B lb A/R=2.5:1 B 25 RL lb F2B B Diaph. chord Free body for F2B RL lb Discontinuous diaphragm chord Diaph. chord Sign onvention RR lb

32 15 Pos. Neg. TD shear diagram Transfer Diaphragm and Net Diaphragm Shear A v1 plf v2l plf v2r plf Basic shear diagram v3 plf Diaph..L. VA lb VA v= plf DTD 1 35 V=Basic shear - TD shear plf (Net shear) 35 v4 plf 2 B F2B Vc v= DTD plf F2B 15 RL lb v= Net shear> 2x Basic shear No net change Net change occurs in TD V lb 80 No net change + - Sign onvention RR lb 4 Net TD shears (basic shear +/- transfer diaph. shears)

33 15 A F2A +v2 +F lb x1 x2 -v3 -F lb v1 v2l F3A FL 0 plf 1 2 F2B F2B T FL B F2B F T 0 plf Diaph..L. Longitudinal hord Force Diagrams + - Sign onvention 4

34 15 A Net shear Net shear 1 F=6000 lb T F3B B + - Sign onvention F=6000 lb (this is not an insignificant force.) F3B Transverse Force Diagrams

35 4/6/12 B 6/6/12 B 6/12 UB ase I 6/12 UB ase I 6/12 UB ase I plf 320 plf 285 plf plf 42.9 plf 37.1 plf 70 plf x1 x2 x3 x4 Special nailing along collectors Sum of shears to collector or highest boundary nailinggreater of plf plf 150 plf Basic shear diagram 70 plf Transfer diaphragm Boundary (Typ.) allout all nailing on drawings: Standard diaphragm nailing Boundary nailing nailing Diaphragm boundary heck the shear capacity of the nailing along the collector /6/12 B Transfer area Boundary (High shear area) Boundary locations Diaphragm Nailing allouts

36 Window wall A No calculations No collector Horizontal offset in chord/strut F=20 kips B Strut/chord 1.L. diaphragm Strut/chord 4 Actual Project

37 95 ft. v=304 plf v=504 plf v=328 plf v=997 plf v=244 plf v=588 plf v=390 plf v=997 plf (designed) 45 ft. Steel decking F=25230 lb F=25278 c.l. diaphragm (calc d=22500 lb) F=24905 lb Diaphragm Shears Transfer diaphragms and collectors are required F=7626 lb F=7454 lb 4 ft. offset F=6991 lb F=7512 lb NOTE: v max=1864 plf ritical connections v max=1748 plf Diaphragm designed as a simple rectangular diaphragm, no offset, using only a spreadsheet. hecked only diaphragm shear and chord force (maximum depth, not offset depth). No collectors, connection designs or details at re-entrant corners. Forces on trusses at collectors were not called out on drawing. Actual Project

38 QUESTIONS? This concludes The American Institute of Architects ontinuing Education Systems ourse Part 1- Offset Diaphragms R. Terry Malone, P.E., S.E. Senior Technical Director WoodWorks.org ontact Information: Events/Presentation Archives (slide handouts)-free Paper: