Recent Advances in Seismic and Wind Design of Wood Structures &Historic Preservation Examples

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1 SEAoA 2015 Conference and Convention Recent Advances in Seismic and Wind Design of Wood Structures &Historic Preservation Examples Kelly Cobeen Wiss Janney Elstner Associates, Inc. Seminar Outline 1. NEHRP Seismic Design Tech Brief SDPWS Highlights 3. ASCE 7 16 Alternative Diaphragm Force Level 4. NEHRP Rigid Wall Flexible Diaphragm Buildings 5. Rigger s Loft Historic Preservation 6. Anna Head Alumnae Hall Historic Preservation 2 1

2 Wood Design 3 Wood Design 4 2

3 Wood Design 5 Wood Design 6 3

4 NEHRP Seismic Design Technical Brief 10: Seismic Design of Wood Light Frame Structural Diaphragm Systems NEHRP Seismic Design Tech Briefs: Serieshttp:// NEHRP Seismic Design Technical Brief No. 1 (NIST GCR ) Seismic Design of Reinforced Concrete Special Moment Frames: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 2 (NIST GCR ) Seismic Design of Steel Special Moment Frames: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 3 (NIST GCR ) Seismic Design of Cast in Place Concrete Diaphragms, Chords, and Collectors: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 4 (NIST GCR ) Nonlinear Structural Analysis For Seismic Design: A Guide for Practicing Engineers 8 4

5 NEHRP Seismic Design Tech Briefs: Serieshttp:// NEHRP Seismic Design Technical Brief No. 5 (NIST GCR ) Seismic Design of Composite Steel Deck and Concrete filled Diaphragms: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 6 (NIST GCR REV 1) Seismic Design of Cast in Place Concrete Special Structural Walls and Coupling Beams: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 7 (NIST GCR ) Seismic Design of Reinforced Concrete Mat Foundations: A Guide for Practicing Engineers 9 NEHRP Seismic Design Tech Briefs: Serieshttp:// NEHRP Seismic Design Technical Brief No. 8 (NIST GCR ) Seismic Design of Steel Special Concentrically Braced Frame Systems: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 9 (NIST GCR ) Seismic Design of Special Reinforced Masonry Shear Walls: A Guide for Practicing Engineers NEHRP Seismic Design Technical Brief No. 10 (NIST GCR ) Seismic Design of Wood Light Frame Structural Diaphragm Systems: A Guide for Practicing Engineers 10 5

6 NEHRP Seismic Design Tech Brief 10: 11 NEHRP Seismic Design Tech Brief 10: Chapter 2: The Roles of Diaphragms Chapter 3: Diaphragm Components Diaphragm Sheathing Diaphragm Boundary Elements Concrete and Masonry Wall Anchorage and Subdiaphragms

7 NEHRP Seismic Design Tech Brief 10: Chapter 4: Diaphragm Behavior and Design Principles Diaphragm Design Philosophy Primary source of energy dissipation is the fasteners connecting the sheathing to framing Primary sources of deflection are yielding of the fastener, fastener withdrawal, and local crushing of the wood under head and around shank NEHRP Seismic Design Tech Brief 10: Chapter 4: Diaphragm Behavior and Design Principles Observed Earthquake Performance Observed Testing Performance

8 NEHRP Seismic Design Tech Brief 10: Chapter 4: Diaphragm Behavior and Design Principles ASCE 7 10 diaphragm classification for purposes of force distribution to vertical elements Idealized as rigid Calculated as flexible Idealized as flexible Braced with concrete or masonry shear walls, steel braced frames One and two family dwellings Wood structural panel diaphragms with up to 1 1/2 nonstructural topping provided drift limits met at each vertical element NEHRP Seismic Design Tech Brief 10: Chapter 5: Diaphragm Seismic Design Forces Inertial forces generated by the seismic weight tributary to the diaphragm Transfer forces generated by discontinued vertical elements or generated by changes in stiffness of vertical elements over height of structure

9 NEHRP Seismic Design Tech Brief 10: Chapter 6: Modeling and Analysis Guidance Equivalent Lateral Force Analysis Dynamic Analysis Diaphragm Stiffness Modeling, Deflection Calculations NEHRP Seismic Design Tech Brief 10: Chapter 7: Design Guidance Chapter 8: Detailing and Construction Issues

10 2015 SDPWS Design Provisions: Highlights of Interest SDPWS Highlights of Interest Sec Anchorage of Concrete and Masonry Walls Sec Horizontal Distribution of Shear Sec Shear Walls in a Line & Sec Aspect Ratios &Capacity Adjustments 20 10

11 2015 SDPWS Anchorage of Concrete and Masonry Walls Photo credit: FEMA P SDPWS Anchorage of Concrete and Masonry Walls 22 11

12 2015 SDPWS Anchorage of Concrete and Masonry Walls SDPWS Anchorage of Concrete and Masonry Walls The SDPWS Committee Issues: Ensuring that users of SDPWS are aware of ASCE 7 provisions that materially affect diaphragm design and construction Providing commentary to help guide users 24 12

13 2015 SDPWS Anchorage of Concrete and Masonry Walls Changes ASCE 7 05 to ASCE 7 10: Structural Walls and Their Anchorage Design for Out of Plane Forces Anchorage of Concrete or Masonry Structural Walls and Transfer of Design Forces into Diaphragms Anchorage of Concrete of Masonry Structural Walls to Flexible Diaphragms Wall Anchorage Forces F p =0.8S DS IW p = 0.4S DS K a I e W p Additional Requirements for Diaphragms Supporting Concrete or Masonry Walls in Structures Assigned to Seismic Design Categories C through F (green is errata acknowledged by but yet to be published by ASCE) SDPWS Anchorage of Concrete and Masonry Walls ASCE 7 10: Additional Requirements for Diaphragms Supporting Concrete or Masonry Walls in Structures Assigned to Seismic Design Categories C through F Transfer of Anchorage Forces into Diaphragms Continuous ties between diaphragm chords Diaphragm connections positive, mechanical or welded Added chords are permitted to be used to create subdiaphragms Maximum length to width ratio of subdiaphragm is 2.5:

14 2015 SDPWS Anchorage of Concrete and Masonry Walls ASCE 7 10: Additional Requirements for Diaphragms Supporting Concrete or Masonry Walls in Structures Assigned to Seismic Design Categories C through F Wood Diaphragms Ties in addition to diaphragm sheathing No toenails or nails subject to withdrawal No ledgers or framing in cross grain tension or cross grain bending Diaphragm sheathing shall not be used as continuous ties SDPWS Anchorage of Concrete and Masonry Walls SDPWS Sec : Anchorage of Concrete or Masonry Structural Walls to Diaphragms. In Seismic Design Categories C, D, E or F, diaphragms shall be provided with continuous ties or struts between diaphragm chords to distribute concrete or masonry structural wall anchorage forces in accordance with Section of ASCE 7. Subdiaphragms shall be permitted to be used to transmit the anchorage forces to the main continuous cross ties. The maximum length to width ratio of the structural subdiaphragm shall be 2.5:1. Connections and anchorages capable of resisting the prescribed forces shall be provided between the diaphragm and the attached components 28 14

15 2015 SDPWS Anchorage of Concrete and Masonry Walls SDPWS Sec : Anchorage shall not be accomplished by use of nails subject to withdrawal or toe nails nor shall wood ledgers or framing be used in cross grain bending or cross grain tension. SDPWS Sec : The diaphragm sheathing shall not be considered effective as providing the ties or struts required by this section SDPWS Anchorage of Concrete and Masonry Walls SDPWS Sec : Anchorage shall not be accomplished by use of nails subject to withdrawal or toe nails nor shall wood ledgers or framing be used in cross grain bending or cross grain tension. SDPWS Sec : The diaphragm sheathing shall not be considered effective as providing the ties or struts required by this section

16 2015 SDPWS Horizontal Distribution of Shear The SDPWS Committee Issues: Coordinating with ASCE 7 flexible, rigid, and semi rigid diaphragm designations Providing greater clarity to provisions for open front and torsionally irregular buildings and cantilevered diaphragms Requiring more attention to analysis detail at open front and torsionally irregular buildings and cantilevered diaphragms Further consideration of acceptable diaphragm cantilevers given increased use in multi family residential projects SDPWS Horizontal Distribution of Shear ASCE 7 10 Sec Diaphragm Flexibility: Sec Flexible Diaphragm Condition. Diaphragms constructed of untopped steel decking of wood structural panels are permitted to be idealized as flexible is any of the following exist: a. Vertical element are steel braced frames, concrete or masonry shear walls, etc. b. One and two family dwellings c. Light frame construction with maximum 1 1/2 topping slab and meeting story drift limits at each line of vertical elements Sec Rigid Diaphragm Condition Se Calculated Flexible Diaphragm Condition

17 2015 SDPWS Horizontal Distribution of Shear SDPWS Sec : Distribution of shear to vertical elements based on analysis where diaphragm is modeled as semi rigid, idealized as flexible, or idealized as rigid Where idealized as flexible, based on tributary area When idealized as rigid, based on relative stiffness of vertical elements When not idealized as rigid or flexible, distribute based on relative stiffness of diaphragm and vertical elements In lieu of semi rigid, envelope method may be used SDPWS Horizontal Distribution of Shear SDPWS Sec Torsional Irregularity: Structures with wood frame diaphragms modeled as semirigid or idealized as rigid shall be considered as torsionally irregular under seismic load when the maximum story drift, computed from seismic design forces including accidental torsion, at the end of the structure is more than 1.2 items the average of the story drifts at the two ends of the structure. When a torsional irregularity exists in structures assigned to SDC B, C, D, E of F, diaphragm shall meet all of the following requirements: Wood structural panel or diagonal lumber sheathed L/W<=1.5 wood structural panel, <=1 diagonal lumber Maximum story drift checked at each edge of structure 34 17

18 2015 SDPWS Horizontal Distribution of Shear SDPWS Sec. 2.2 Terminology Open Front Structure. A structure in which any diaphragm edge cantilevers beyond vertical elements of the lateral force resisting system SDPWS Horizontal Distribution of Shear SDPWS Sec Open Front Structures: Wood structural panel or diagonal lumber sheathed L/W<=1.5 wood structural panel, <=1 diagonal lumber When open front AND torsionally irregular L /W <= 0.67 for multi story and <=1 for single story Model as semi rigid or rigid for loading parallel to open front Limit maximum story drift at each edge of diaphragm Cantilever length L not to exceed 35 feet Exception: Diaphragms with cantilevers not more than 6 feet need not meet requirements of

19 2015 SDPWS Horizontal distribution of shear Practical Limits: Diaphragm not permitted to be classified as flexible for purposes of force distribution to vertical elements when diaphragm cantilevers greater than six feet Sheathing limits Aspect ratio limits 35 foot maximum diaphragm cantilever SDPWS Horizontal distribution of shear Calculating diaphragm deflection at open front 38 19

20 2015 SDPWS Force distribution to shear walls in a line SDPWS Committee Issues: 2005, 2008 SDPWS method for distributing forces between walls in a line differed from common design practice Need clarity for distribution where wall lines include slender walls SDPWS Sec Force distribution to shear walls in a line 2005, 2008 SDPWS: Distribute seismic/ wind forces to provide same deflection where materials and construction are same 2015 SDPWS: Exception: where materials and construction are same, distribute seismic/ wind forces proportional to shear capacity, adjust for slender piers 40 20

21 2015 SDPWS Sec & Shear walls with narrow piers Narrow wall pier capacity adjustment (multiplier) for force distribution to walls in a line: Wood structural panel>2:1 2b s /h Fiberboard>1: b s /h Narrow wall pier capacity adjustment (multiplier): Wood structural panel>2: h/b s Fiberboard>1: h/b s Need not be used in addition to force distribution multiplier SDPWS Sec & Shear walls with narrow piers Narrow wall pier capacity 3 x9 adjustment (multiplier) for force distribution to walls in a line: Wood structural panel>2:1 2b s /h = 2*3/9 = 0.67 Narrow wall pier capacity adjustment (multiplier): Wood structural panel>2: h/b s = *9/3 = 0.88 Need not be used in addition to force distribution multiplier 42 21

22 ASCE 7 16 Chapter 12: Alternative Provisions for Diaphragms Including Chords and Collectors Alternative Provisions for Diaphragms Including Chords and Collectors BSSC IT 06 Committee Issues: Rodriguez and Restrepo study of diaphragm force levels, vertical distribution of forces Higher forces than current code (when near elastic) Diaphragm forces limited by vertical element overstrength, 0, in first mode, but not necessarily for higher mode behavior Precast concrete industry post Northridge development of seismic design methodology for precast concrete diaphragms 1997 UBC consideration of real demand and capacity for vertical elements, but not for diaphragms 44 22

23 Alternative Provisions for Diaphragms Including Chords and Collectors BSSC IT 06 Committee Solutions: 1. New vertical distribution of forces for near elastic behavior 2. Specific recognition of the ductility and deformation capacity of the diaphragm system Alternative Provisions for Diaphragms Including Chords and Collectors 5-Story concrete shear wall building S DS = 1 R = 5 I e = 1 V = 0.2W C s = wh/ wh F px /w = F x / w x Floor Level ASCE 7 10 Vertical Distribution of Seismic Forces Fx Cs Fpx Coefficient (g) 46 23

24 Diaphragm Design Force First mode contribution reduced by R-factor and amplified by pn m 1 0 s m2 s2 pi C C C C Higher mode contribution not reduced by R or amplified by 0 C S I p DS e C px F px = wpx Rs 47 Diaphragm Design Force First mode contribution reduced by R-factor and amplified by 0 C 09. C pi m1 0 s C px F px = wpx Rs 48 24

25 Alternative Provisions for Diaphragms Including Chords and Collectors 5-Story concrete shear wall 7 building 6 S DS = 1 5 R = 5 4 I e = 1 3 V = 0.2W 2 C s = wh/ wh 1 F px /w = F x / w x 0 Floor Level ASCE 7 10 Vertical Distribution of Seismic Forces Cs Fpx/wx New Coefficient (g) 49 Diaphragm Design Force Relative height Measured DEN67 Proposed C px / C po Figure C Comparison of measured floor accelerations and accelerations predicted by Eq for a 5-story special MRF building (Chen et al., 2013)

26 Diaphragm Design Force Relative height Measured EQ4 Proposed C px / C po Figure C Comparison of measured floor accelerations and accelerations predicted by Eq for a 7-story bearing wall building (Panagiotou et al., 2011). 51 Alternative Provisions for Diaphragms Including Chords and Collectors BSSC IT 06 Committee Solutions: 2. Specific recognition of the ductility and deformation capacity of the diaphragm system Diaphragm System Shear Controlled Flexure Controlled Cast in place concrete designed in accordance with Section 14.2 and ACI Precast concrete designed in accordance with Section and ACI 318 EDO BDO RDO Wood sheathed designed in accordance with Section 14.5 and AF&PA (now AWC) Special Design Provisions for Wind and Seismic C px F px= wpx Rs 3.0 NA 52 26

27 Alternative Provisions for Diaphragms Including Chords and Collectors 5-Story concrete shear wall 7 building 6 S DS = 1 5 R = 5 4 I e = 1 3 V = 0.2W 2 C s = wh/ wh 1 F px /w = F x / w 0 x Floor Level ASCE 7 10 Vertical Distribution of Seismic Forces Cs Fpx/wx New New/Rs Coefficient (g) 53 Alternative Provisions for Diaphragms Including Chords and Collectors What is going into ASCE 7 16 is: Required for precast concrete diaphragms in SDC s C through F Permitted for precast concrete, cast in place concrete and wood diaphragms in any SDC 54 27

28 FEMA P 1026: Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Principal Authors: Dominic Kelly, SGH John Lawson, Cal Poly SLO 56 28

29 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach 57 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach NEHRP Committee Issues: Current design methods are not capturing behavior of this building type Building seismic response is dominated by diaphragm, while our design methods focus on the vertical shear wall elements Analytical studies predict poor performance of diaphragms, suggesting larger than acceptable probability of collapse 58 29

30 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Reformulate seismic design forces in two step process to specifically recognize diaphragm period in combination with mass acting with diaphragm, and vertical element period in combination with mass acting on vertical element Current T a = 0.26 sec Alternate Two-step design T diaph = 0.80 sec T wall = 0.14 sec R diaph, diaph C d diaph 59 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location Reduce nailing away from end to encourage predictable yielding Conceptually equivalent to treatment of moment frame connections 60 30

31 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location 61 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location 62 31

32 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location 63 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location 64 32

33 Seismic Design of Rigid Wall Flexible Diaphragm Buildings: An Alternate Approach Caution Status of Published Document: No formal code adoption exists serves as a guideline only, does not have ASCE 7 or building code recognition Recommendations for strengthening ends of diaphragm could be implemented on a voluntary basis for new design or retrofit right now as an above code measure Reduction of design forces in center of diaphragm would fall below current code and could only be implemented as an alternate design method with case by case approval of the building official Only works for simple diaphragm geometries 65 Conclusions NEHRP Seismic Design Technical Brief No. 10 (NIST GCR ) currently available for free download 2015 SDPWS currently available for download, in print 2015 SDPWS Commentary coming soon ASCE 7 16 Chapter 12 changes ASCE putting out to public ballot FEMA P 1026 Seismic Design of Rigid Wall Flexible Diaphragm Buildings currently available for free download 66 33

34 End Parts 1 4 Questions? Rigger s Loft Historic Preservation and Wind/ Seismic Upgrade 34

35 Riggers Loft Rehabilitation Rigger s Loft Shipyard No. 3 Richmond California Project for: Port of Richmond Contractor: Alten Construction Historic Preservation Architect: WJE Structural Engineer: WJE MEP: ACIES Geotechnical Engineer: Langan/ Treadwell & Rollo Original Design: Kaiser, March Shipyard No. 3, Richmond California 70 35

36 Shipyard No. 3, Richmond California

37 WJE Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California 73 Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California 74 37

38 Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California 75 UPGRADE FOR SEISMIC AND WIND ANALYSIS APPROACH 76 38

39 UPGRADE FOR SEISMIC AND WIND ANALYSIS APPROACH 77 UPGRADE FOR SEISMIC AND WIND ANALYSIS APPROACH Shipyard No. 3, Richmond California 78 39

40 UPGRADE FOR SEISMIC AND WIND ANALYSIS APPROACH 79 UPGRADE FOR SEISMIC AND WIND INCREASED DIAPHRAGM STRENGTH AND STIFFNESS 80 40

41 UPGRADE FOR SEISMIC AND WIND INCREASED DIAPHRAGM STRENGTH AND STIFFNESS 81 UPGRADE FOR SEISMIC AND WIND NEW DIAPHRAGM COLLECTORS 82 41

42 UPGRADE FOR SEISMIC AND WIND NEW DIAPHRAGM COLLECTORS 83 UPGRADE FOR SEISMIC AND WIND NEW SHEAR WALL 84 42

43 UPGRADE FOR SEISMIC AND WIND WIND BRACING 85 UPGRADE FOR SEISMIC AND WIND TRUSS IMRPOVEMENTS 86 43

44 UPGRADE FOR SEISMIC AND WIND TRUSS IMRPOVEMENTS 87 UPGRADE FOR SEISMIC AND WIND TRUSS IMRPOVEMENTS 88 44

45 END Thank You 89 Anna Head Alumnae Hall Historic Preservation and Wind/ Seismic Upgrade 45

46 Anna Head Alumni Hall Anna Head Alumnae Hall Project for: UC Berkeley Contractor: BHM Construction Historic Preservation Architect: Cody Anderson Wasney Structural Engineer: WJE Original Architect: W.H. Ratcliff,

47 UPGRADE FOR SEISMIC AND WIND WJE Shipyard No. 3, Richmond California

48

49 UPGRADE FOR SEISMIC AND WIND WJE 97 EXISTING TRUSS FRAME SYSTEM WJE 98 49

50 EXISTING TRUSS FRAME SYSTEM WJE 99 STEEL CANTILEVERED COLUMNS WJE

51 UPGRADE FOR SEISMIC AND WIND WJE Shipyard No. 3, Richmond California 101 STEEL CANTILEVERED COLUMNS WJE

52 UPGRADE FOR SEISMIC AND WIND WJE Shipyard No. 3, Richmond California

53 STEEL CANTILEVERED COLUMNS WJE

54 COLUMN BASE AND FOUNDATION WJE 107 COLUMN BASE AND FOUNDATION WJE

55 COLLECTOR WJE 109 COLLECTOR

56 ROOF DIAPHRAGM 111 TRANSVERSE END WALLS

57 TRANSVERSE END WALLS 113 TRANSVERSE END WALLS

58 LONGITUDINAL WALLS 115 LONGITUDINAL WALLS

59 117 End Questions? 59