SEISMIC LOADS

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SEISMIC LOADS LATERAL LOAD FLOW FRAMES and SHEAR
WALLS
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SEISMIC LOAD
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(No Transcript)
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Determine Spectral Response Parameters at design
location
At 37.80 N , -122.37 W Ss 1.50 S1 0.60
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Determine Site Coefficients
Site Class D Ss gt 1.25 Fa 1.0 S1 gt 0.5 Fv
1.5
Determine Design Spectral Acceleration Parameters
SMS (1.0)(1.5) 1.5 SDS (2/3)(1.5) 1.0
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• Cs SDS /(R/I)
• 1.0/(R/I)
• Class II I 1.0
• Ordinary Moment Resisting Frame
• R 3.5
• V 1.0/3.5 W
• 0.3 W

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Seismic Load is generated by the inertia of the
mass of the structure VBASE
Redistributed (based on relative height and
weight) to each level as a Point Load at the
center of mass of the structure or element in
question FX VBASE Wx hx S(w
h)
(Cs)(W)
VBASE
( VBASE )
Fx
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Total Seismic Loading VBASE 0.3 W
W Wroof Wsecond
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Wroof
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Wsecond flr
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W Wroof Wsecond flr
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VBASE
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Redistribute Total Seismic Load to each level
based on relative height and weight
Froof
Fsecond flr
VBASE (wx)(hx) S (w h)
Fx
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VBASE (wx)(hx) S (w h)
Fx
In order to solve the equivalent lateral force
distribution equation, we suggest you break it
up into a spreadsheet layout Floor w
h (w)(h) (w)(h)/S(w)(h) Vbase Fx Roof 166.67k
30ft 5000k-ft 0.625 110k 68.75k 2nd 200k
15ft 3000k-ft 0.375 110k 41.25k
S (366.67k) S(8000k-ft)
S (110k) Vbase 0.3W 0.3(166.67k200k)
0.3(366.67k) 110k
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Load Flow to Lateral Resisting System
Distribution based on Relative Rigidity
Assume Relative Rigidity
Single Bay MF Rel Rigidity 1
2 - Bay MF Rel Rigidity 2
3 - Bay MF Rel Rigidity 3
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Distribution based on Relative Rigidity SR
1111 4 Px ( Rx / SR ) (Ptotal) PMF1 1/4
Ptotal
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Lateral Load Flow diaphragm gt collectors/drags gt
frames
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STRUCTURAL DIAPHRAGM
A structural diaphragm is a horizontal structural
system used to transfer lateral loads to shear
walls or frames primarily through in-plane shear
stress Basically, combined with vertical shear
walls or frames IT ACTS LIKE A LARGE I-BEAM
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STRUCTURAL DIAPHRAGM
Flexible or Semi-flexible Type Plywood Metal
Decking
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STRUCTURAL DIAPHRAGM
Rigid Diaphragm Type Reinforced Concrete
Slab Concrete-filled Metal Deck composite
Slab Braced/horizontal truss
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STRUCTURAL DIAPHRAGM
Rigid Diaphragm Almost no deflection Can
transmit loads through torsion
Flexible Diaphragm Deflects horizontally Cannot
transmit loads through torsion
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COLLECTORS and DRAGS
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COLLECTORS and DRAG STRUTS
A beam element or line of reinforcement that
carries or collects loads from a diaphragm and
carries them axially to shear walls or frames. A
drag strut or collector behaves like a column.
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COLLECTOR
FRAME
DIAPHRAGM
COLLECTOR
FRAME
Lateral Load Flow diaphragm gt collectors/drags gt
frames
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COLLECTOR
FRAME
LATERAL LOAD
DIAPHRAGM
COLLECTOR
FRAME
Lateral Load Flow diaphragm gt collectors/drags gt
frames
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COLLECTOR
FRAME
LATERAL LOAD
DIAPHRAGM
COLLECTOR
FRAME
Lateral Load Flow diaphragm gt collectors/drags gt
frames
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LATERAL LOAD
COLLECTOR
FRAME
FRAME
COLLECTOR
DIAPHRAGM
COLLECTOR
COLLECTOR
FRAME
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LATERAL FORCE RESISTING SYSTEMS MOMENT
Resisting frames Diagonally BRACED frames SHEAR
walls
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INSTABILITY OF THE FRAME
Pinned connectionscannot resist rotation.This
is not a structurebut rather a mechanism.
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STABILIZE THE FRAME
FIX ONE OR MORE OF THE BASES
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STABILIZE THE FRAME
FIX ONE OR MORE OF THE CORNERS
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STABILIZE THE FRAME
ADD A DIAGONAL BRACE
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RELATIVE STIFFNESS OF FRAMES AND WALLS
LOW DEFLECTION HIGH STIFFNESS ATTRACTS MORE
LOAD
HIGH DEFLECTION LOW STIFFNESS ATTRACTS LESS
LOAD
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BRACED FRAMES
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BRACED FRAMES
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SHEAR WALLS
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SHEAR WALLS
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SHEAR WALLS
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SHEAR WALLS
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SHEAR WALLS
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MOMENT FRAMES
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MOMENT FRAMES
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MOMENT FRAMES
INDETERMINATE STRUCTURES SOLVE BY PORTAL FRAME
METHOD
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MOMENT FRAMES
PINNED BASE 4 UNKNOWNS, 3 EQUATIONS, STATICALLY
INDETERMINATE TO FIRST DEGREE
SOLVE BY PORTAL FRAME METHOD
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MOMENT FRAMES
FIXED BASE 6 UNKNOWNS, 3 AVAILABLE EQUATIONS OF
EQUILIBRIUM STATICALLY INDETERMINATE TO THE 3RD
DEGREE
SOLVE BY PORTAL FRAME METHOD