recent advances in seismic and wind design of wood ... · 6/15/2015 1 seaoa2015 conference and...

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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.

1. NEHRP Seismic Design Tech Brief 10

2. 2015 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

Seminar Outline

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Wood Design

3SEAoA 2015 Conference and Convention –Wood

Wood Design


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Wood Design


Wood Design


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NEHRP Seismic Design Technical Brief 10:

Seismic Design of Wood Light‐Frame Structural Diaphragm Systems

NEHRP Seismic Design Tech Briefs:Serieshttp://www.nehrp.gov/library/techbriefs.htm

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NEHRP Seismic Design Technical Brief No. 1 (NIST GCR 8‐917‐1) Seismic Design of Reinforced Concrete Special Moment Frames: A Guide for Practicing Engineers

NEHRP Seismic Design Technical Brief No. 2 (NIST GCR 9‐917‐3) Seismic Design of Steel Special Moment Frames: A Guide for Practicing Engineers

NEHRP Seismic Design Technical Brief No. 3 (NIST GCR 10‐917‐4) 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 10‐917‐5) Nonlinear Structural Analysis For Seismic Design: A Guide for Practicing Engineers

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NEHRP Seismic Design Technical Brief No. 5 (NIST GCR 11‐917‐10) Seismic Design of Composite Steel Deck and Concrete‐filled Diaphragms: A Guide for Practicing Engineers

NEHRP Seismic Design Technical Brief No. 6 (NIST GCR 11‐917‐11REV‐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 12‐917‐22) Seismic Design of Reinforced Concrete Mat Foundations: A Guide for Practicing Engineers



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NEHRP Seismic Design Technical Brief No. 8 (NIST GCR 13‐917‐24) Seismic Design of Steel Special Concentrically Braced Frame Systems: A Guide for Practicing Engineers

NEHRP Seismic Design Technical Brief No. 9 (NIST GCR 14‐917‐31) Seismic Design of Special Reinforced Masonry Shear Walls: A Guide for Practicing Engineers

NEHRP Seismic Design Technical Brief No. 10 (NIST GCR 14‐917‐32) Seismic Design of Wood Light‐Frame Structural Diaphragm Systems: A Guide for Practicing Engineers


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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

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Chapter 4: Diaphragm Behavior and Design Principles Diaphragm Design Philosophy

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• 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


Chapter 4: Diaphragm Behavior and Design Principles Observed Earthquake Performance Observed Testing Performance

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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

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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

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Chapter 6: Modeling and Analysis Guidance Equivalent Lateral Force Analysis Dynamic Analysis Diaphragm Stiffness Modeling, Deflection Calculations

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Chapter 7: Design GuidanceChapter 8: Detailing and Construction Issues

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2015 SDPWS Design Provisions:

Highlights of Interest

Sec. 4.1.5.1 Anchorage of Concrete and Masonry Walls

Sec. 4.2.5 Horizontal Distribution of Shear

Sec. 4.3.3.4 Shear Walls in a Line & Sec. 4.3.4 Aspect Ratios &Capacity Adjustments

SDPWS Highlights of Interest


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2015 SDPWS Anchorage of Concrete and Masonry Walls

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Photo credit: FEMA P-1026




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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


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2015 SDPWS Anchorage of Concrete and Masonry WallsChanges ASCE 7‐05 to ASCE 7‐10: 12.11 Structural Walls and Their Anchorage 12.11.1 Design for Out‐of‐Plane Forces 12.11.2 Anchorage of Concrete or Masonry Structural Walls

and Transfer of Design Forces into Diaphragms 12.11.2.1 Anchorage of Concrete of Masonry Structural

Walls to Flexible Diaphragms Wall Anchorage Forces

Fp=0.8SDSIWp= 0.4SDSKaIeWp

12.11.2.2 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)


2015 SDPWS Anchorage of Concrete and Masonry WallsASCE 7‐10: 12.11.2.2 Additional Requirements for Diaphragms

Supporting Concrete or Masonry Walls in Structures Assigned to Seismic Design Categories C through F

12.11.2.2.1 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 2.5:1


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2015 SDPWS Anchorage of Concrete and Masonry WallsASCE 7‐10: 12.11.2.2 Additional Requirements for Diaphragms

Supporting Concrete or Masonry Walls in Structures Assigned to Seismic Design Categories C through F

12.11.2.2.3 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


2015 SDPWS Anchorage of Concrete and Masonry WallsSDPWS Sec. 4.1.5.1: 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 12.11.2 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


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2015 SDPWS Anchorage of Concrete and Masonry WallsSDPWS Sec. 4.1.5.1.1: 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. 4.1.5.1.2: The diaphragm sheathing shall not be considered effective as

providing the ties or struts required by this section.


2015 SDPWS Anchorage of Concrete and Masonry WallsSDPWS Sec. 4.1.5.1.1: 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. 4.1.5.1.2: The diaphragm sheathing shall not be considered effective as

providing the ties or struts required by this section.


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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



ASCE 7‐10 Sec. 12.3.1 Diaphragm Flexibility: Sec. 12.3.1.1. 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 dwellingsc. Light‐frame construction with maximum 1‐1/2” topping

slab and meeting story drift limits at each line of vertical elements

Sec. 12.3.1.2 Rigid Diaphragm Condition… Se. 12.3.1.3 Calculated Flexible Diaphragm Condition...


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SDPWS Sec. 4.2.5:– 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 Sec. 4.2.5.1 Torsional Irregularity: Structures with wood‐frame diaphragms modeled as semi‐

rigid 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


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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 Sec. 4.2.5.2 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 4.2.5.2


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2015 SDPWSHorizontal 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


2015 SDPWSHorizontal distribution of shear

Calculating diaphragm deflection at open front


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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


2015 SDPWS Sec. 4.3.3.4Force 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


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2015 SDPWS Sec. 4.3.3.4 & 4.3.4Shear walls with narrow piers Narrow wall pier capacity

adjustment (multiplier) for force distribution to walls in a line:– Wood structural panel>2:1

2bs/h– Fiberboard>1:1

0.1 + 0.9bs/h Narrow wall pier capacity

adjustment (multiplier):– Wood structural panel>2:1

1.25 – 0.125h/bs

– Fiberboard>1:1 1.09 – 0.09h/bs

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Need not be used in addition to force distribution multiplier


2015 SDPWS Sec. 4.3.3.4 & 4.3.4Shear 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

2bs/h = 2*3/9 = 0.67

Narrow wall pier capacity adjustment (multiplier):– Wood structural panel>2:1

1.25 – 0.125h/bs = 1.25 ‐ 0.125*9/3 = 0.88

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Need not be used in addition to force distribution multiplier


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ASCE 7‐16 Chapter 12:

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

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BSSC IT‐06 Committee Solutions:1. New vertical distribution of forces for near‐elastic

behavior2. Specific recognition of the ductility and

deformation capacity of the diaphragm system

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Coefficient (g)

Flo

or L

evel

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4

ASCE 7‐10 Vertical Distribution of Seismic Forces

Fx Fpx

5-Story concrete shear wall buildingSDS = 1R = 5Ie = 1V = 0.2WCs = wh/whFpx/w = Fx/wx

Cs


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Diaphragm Design Force

0 0.4p DS eC S I

2 2

1 0 2 2pn m s m s piC C C C

First mode contribution reduced by R-factor and amplified by 0

Higher mode contribution not reduced by R or amplified by 0

pxpx px

s

CF = w

R



First mode contribution reduced by R-factor and amplified by 0

pxpx px

s

CF = w

R

1 00 9pi m sC . C


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Coefficient (g)

Flo

or L

evel

5-Story concrete shear wall buildingSDS = 1R = 5Ie = 1V = 0.2WCs = wh/whFpx/w = Fx/wx 0

1

2

3

4

5

6

7

0 0.2 0.4 0.6 0.8


Cs Fpx/wx New



0.0

0.2

0.4

0.6

0.8

1.0

0.5 1.0 1.5 2.0

Relative height

Cpx / Cpo

Measured DEN67

Proposed

Figure C12.10-5 Comparison of measured floor accelerations and accelerations predicted by Eq. 12.10.3-1 for a 5-story special MRF building (Chen et al., 2013).


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0.0

0.2

0.4

0.6

0.8

1.0

0.5 1.0 1.5

Relative height

Cpx / Cpo

Measured EQ4

Proposed

Figure C12.10-4 Comparison of measured floor accelerations and accelerations predicted by Eq. 12.10.3-1 for a 7-story bearing wall building (Panagiotou et al., 2011).



BSSC IT‐06 Committee Solutions:2. Specific recognition of the ductility and

deformation capacity of the diaphragm system

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Diaphragm System Shear‐Controlled

Flexure‐Controlled

Cast‐in‐place concretedesigned in accordance with Section 14.2 and ACI 318 ‐ 1.5 2

Precast concrete designed in accordance with Section 14.2.4 and ACI 318

EDO 1 0.7 0.7BDO 2 1.0 1.0RDO 3 1.4 1.4

Wood sheathed designed in accordance with Section 14.5 and AF&PA (now AWC) Special Design Provisions for Wind and Seismic

‐ 3.0 NA

pxpx px

s

CF = w

R


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Coefficient (g)

Flo

or L

evel

5-Story concrete shear wall buildingSDS = 1R = 5Ie = 1V = 0.2WCs = wh/whFpx/w = Fx/wx

0

1

2

3

4

5

6

7

0 0.2 0.4 0.6 0.8


Cs Fpx/wx New New/Rs



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


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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

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Principal Authors:Dominic Kelly, SGHJohn Lawson, Cal Poly SLO


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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


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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

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CurrentTa = 0.26 sec

AlternateTwo-step designTdiaph = 0.80 secTwall = 0.14 sec

Rdiaph, diaph

Cd diaph



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


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Solutions: Create strengthened protected zone at ends of diaphragm to move inelastic behavior away from critical location





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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


Conclusions

NEHRP Seismic Design Technical Brief No. 10 (NIST GCR 14‐917‐32) – 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


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End Parts 1‐4

Questions?

Rigger’s Loft Historic Preservation

and Wind/ Seismic Upgrade

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Riggers Loft RehabilitationRigger’s LoftShipyard No. 3 Richmond CaliforniaProject for: Port of RichmondContractor: Alten ConstructionHistoric Preservation Architect: WJEStructural Engineer: WJEMEP: ACIESGeotechnical Engineer: Langan/ Treadwell & RolloOriginal Design: Kaiser, March 1942

SEAoA 2015 Conference and Convention – Wood 69

Shipyard No. 3, Richmond California


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WJE Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California

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Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California

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Riggers Loft Rehabilitation, Shipyard No. 3, Richmond California

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UPGRADE FOR SEISMIC AND WINDANALYSIS APPROACH


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UPGRADE FOR SEISMIC AND WINDINCREASED DIAPHRAGM STRENGTH AND STIFFNESS


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UPGRADE FOR SEISMIC AND WINDINCREASED DIAPHRAGM STRENGTH AND

STIFFNESS


UPGRADE FOR SEISMIC AND WINDNEW DIAPHRAGM COLLECTORS


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UPGRADE FOR SEISMIC AND WINDNEW DIAPHRAGM COLLECTORS


UPGRADE FOR SEISMIC AND WINDNEW SHEAR WALL


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UPGRADE FOR SEISMIC AND WINDWIND BRACING

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UPGRADE FOR SEISMIC AND WINDTRUSS IMRPOVEMENTS


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END Thank You


Anna Head Alumnae Hall

Historic Preservation and Wind/

Seismic Upgrade

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Anna Head Alumni HallAnna Head Alumnae HallProject for: UC BerkeleyContractor: BHM ConstructionHistoric Preservation Architect: Cody Anderson WasneyStructural Engineer: WJE

Original Architect:W.H. Ratcliff, 1926



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WJE Shipyard No. 3, Richmond California

UPGRADE FOR SEISMIC AND WIND

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94

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WJE


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WJE

EXISTING TRUSS FRAME SYSTEM

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WJE

EXISTING TRUSS FRAME SYSTEM

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WJE

STEEL CANTILEVERED COLUMNS

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101

WJE


102

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103

104

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WJE


105

106

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WJE

COLUMN BASE AND FOUNDATION

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WJE

COLUMN BASE AND FOUNDATION

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WJE

COLLECTOR

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COLLECTOR

110

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ROOF DIAPHRAGM


TRANSVERSE END WALLS

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LONGITUDINAL WALLS


LONGITUDINAL WALLS

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End

Questions?

recent advances in seismic and wind design of wood ... · 6/15/2015 1 seaoa2015 conference and...

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