Lateral Load Resistance - Texas A&M Universityfaculty-legacy.arch.tamu.edu/anichols/index_files/courses/arch631/... · needs to resist most wind ... ± elevator cores Lateral Load
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1
F2012abn
fifteen
design for
lateral loadsLateral Load Design 1
Lecture 15
Applied Architectural Structures
ARCH 631
lecture
APPLIED ARCHITECTURAL STRUCTURES:
STRUCTURAL ANALYSIS AND SYSTEMS
ARCH 631
DR. ANNE NICHOLS
FALL 2013
Lateral Load Design 2
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Lateral Load Resistance
• stability important for any height
• basic mechanisms
– shear walls
– diaphragms
– diagonal bracing
– frame action
• resist any direction laterally without excessive movement
Lateral Load Design 3
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Lateral Load Resistance
• deformations
• load transfer &
in-plane forces
Lateral Load Design 4
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Load Direction
• layout
2
Lateral Load Design 5
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Rectangular Buildings
• short side (in red)• needs to resist most wind
• bigger surface area
• shear walls common
• long side• other mechanisms
• long & low• may only need end bracing
• symmetry important
– avoid distortions, ex. twisting
Lateral Load Design 6
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Shear Walls
• resist lateral load in plane with wall
Lateral Load Design 7
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Shear Walls
• lateral
resistance
F2009abn
Shear Walls
• masonry
• concrete
Lateral Load Design 8
Lecture 15
Architectural Structures III
ARCH 631
A
18’
h=15’
H10’ 6’
B C
http:// nisee.berkeley.edu/godden
3
Lateral Load Design 9
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Shear Walls
• timber
– wall studs with sheathing
– vertical trusses
Lateral Load Design 10
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Shear Walls
• steel
Lateral Load Design 11
Lecture 14
Architectural Structures III
ARCH 631
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Shear Walls
• insulated concrete forms (ICF)
Lateral Load Design 12
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Diaphragms– roof and floor framing and decks
– relative stiffness
– necessary in pin connected beam-column frames with no horizontal resisting elements
4
Lateral Load Design 13
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Diaphragms
• connections
critical
• drag struts
F2009abn
Braced Frames
• pin connections
• bracing to prevent lateral movements
Lateral Load Design 14
Lecture 15
Architectural Structures III
ARCH 631
http:// nisee.berkeley.edu/godden
F2009abn
Braced Frames
• types of bracing
– knee-bracing
– diagonal
– X (cross)
– K, V or chevron
– shear walls
Lateral Load Design 15
Lecture 15
Architectural Structures III
ARCH 631
diagonal X
K, V & chevron shear walls
Lateral Load Design 14
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Rigid Framing and Bracing
5
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Rigid Framing and Bracing
Lateral Load Design 15
Lecture 15
Architectural Structures III
ARCH 631
http:// isee.berkeley.edu/godden
Lateral Load Design 16
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Frame Action
• choice influenced by ease of rigid joint
construction by system
– concrete
– steel
– timber braces
• bending moments mean larger
members
Lateral Load Design 17
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Shear Walls & Diagonal Bracing
• use with pin connected members
– steel common
– concrete rare
• solid shear walls
– concrete
– masonry
• wide spaced shear walls or diagonal
bracing requires floor diaphragms
– timber, steel or composite
Lateral Load Design 18
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Member Orientation
• strong axis
– biggest I in a non-doubly-symmetric section
– resists bending better
• frame action & narrow dimension buildings
– deep direction parallel to long is typical
– very narrowparallel to short
6
Lateral Load Design 19
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Member Characteristics
• long span members preclude frame
action
• shear walls can be combined
with bearing walls
– use determines orientation
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Building Height and Resistance
• low-medium rise
– easier to accommodate
– ex. residential
• shear walls
• diagonal bracing
• floor diaphragms (panels)
• high rise
– shear walls & bracing hinder functions
– frames useful or with shear walls
Lateral Load Design 20
Lecture 15
Architectural Structures III
ARCH 631
http://gardenopolis.files.wordpress.com
F2009abn
Multistory Buildings• strength design
– frame action efficient up to ~ 10 stories
– steel systems
– reinforced concrete• flat plate & columns
– lower lateral capacity
– edge moments can’t be resisted
– end walls offer shear resistance
• flat slab
• one-way
• two-way
– higher resistance
– elevator cores
Lateral Load Design 21
Lecture 15
Architectural Structures III
ARCH 631
www.allaboutskyscrapers.com
F2007abn
• overturning, rigidity
Lateral Load Design 22
Lecture 14
Applied Architectural Structures
ARCH 631
Multistory Buildings
7
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Strength Design
• moments like cantileverbeam
• tube action – bigger I
• elements
– rigid at exterior resist lateral loads
– interior can only carry gravity loads
• “stiffen” narrow shaped plans with shape
Lateral Load Design 23
Lecture 15
Architectural Structures III
ARCH 631
http://darkwing.uoregon.edu/~struct/resources/applets/pencil.html
Lateral Load Design 24
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Deflection and Motion Control
• serviceability issues
– vibration
– deflection
– displacement
• mechanisms
– stiffness
– tuned mass dampers
• rule of thumb:
– limit static wind load deflections to h/500
Lateral Load Design 25
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Wind Design
• codes
– based upon minimum wind speed with 90% probability of 50 yr non-exceedance
• loads
– pressure
– drag
– rocking
– harmonic
– uplift
– torsion
Lateral Load Design 25
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Wind Design Loads
• exposure
– non-linear
– equivalent static pressure based on wind speed
AqCF hdW
pA
8
F2012abn
Flood Design• know your risk
– zone A
• 100 year flood, no
data available
– zone AE
• 100 year flood,
detailed analysis
– zone E
• outside 100 year
flood, minimal depths
Lateral Load Design 29
Lecture 15
Applied Architectural Structures
ARCH 631
http://youtu.be/TkfhuvOGbmI - Lake Delton, WI 2008
Lateral Load Design 27
Lecture 14
Architectural Structures III
ARCH 631
F2007abn
Flood Design
• loads
– hydrostatic pressure
• up, down, lateral
– impact velocities
• scour
– impact from debris
• design
– elevation, proper site
– shear walls with caution
– concrete recommended
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