load tracing 1 architectural structures f2012abn lecture
TRANSCRIPT
1
F2012abn
ARCHITECTURAL STRUCTURES:
FORM, BEHAVIOR, AND DESIGN
ARCH 331
DR. ANNE NICHOLS
FALL 2013
fourteen
system assemblies
& load tracingLoad Tracing 1
Lecture 14
Architectural Structures
ARCH 331
lecture
reed.tamu.edu
Load Tracing 2
Lecture 14
Foundations Structures
ARCH 331
F2008abn
Structural Loads
• gravity acts on mass (F=m*g)
• force of mass
– acts at a point
• ie. joist on beam
– acts along a “line”
• ie. floor on a beam
– acts over an area
• ie. people, books,
snow on roof or floor
Load Tracing 3
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Concentrated Loads
Load Tracing 4
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Distributed Loads
2
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Equivalent Force Systems
• replace forces by resultant
• place resultant where M = 0
• using calculus and area centroids
dx
w(x)
x
L
loadingloading
L
0AdAwdxW
dx
y
x
elx
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Area Centroids
• Table 7.1 – pg. 242
b
h
3
b
right triangle only
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Equivalent Load Areas
• area is width x “height” of load
• w is load per unit length
• W is total load
x
x/2
W
x/2
x
2x/3
W/2
x/3
x
x/2
W
x/6 x/3
W/2
0
Wxw w w 22
Wxw
w
2w
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Distributed Area Loads
• w is also load per unit areaw
3
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Load Tracing
• how loads are
transferred
– usually starts at top
– distributed by
supports as actions
– distributed by
tributary areas
Load Tracing 10
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Load Tracing
• areas see distributed
area load
• beams or trusses
see distributed line
loads
• “collectors” see
forces
– columns
– supports
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Load Tracing
tributary area
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Load Tracing
• tributary load
– think of water flow
– “concentrates” load of
area into center
widthtributaryarea
loadw
width
4
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Load Tracing
Patcenter
Rogers 1986
www.columbia.edu
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Load Tracing
Alamillo Bridge
Calatrava 1992
http://en.structurae.de
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Load Paths
• floors and framing
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Load Paths
• wall systems
5
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Load Paths
• openings & pilasters
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Load Paths
• foundations
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Load Paths
• deep foundations
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Spans
• direction
• depth
6
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Levels
• determine span at top level
• find half way to next element
• *include self weight
• look for “collectors”
• repeat
• one:
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Levels
• two:
• three:
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Irregular Configurations
• tracing still ½ each side
Load Tracing 23
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Architectural Structures
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Slabs
• edge support
• linear and uniform distribution
7
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Girders and Transfer
• openings
– no load & no half way
• girder actions at beam supports
+
+ +
+
F2008abnLoad Tracing 58
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Sloped Beams
• stairs & roofs
• projected live load
• dead load over length
• perpendicular load to beam:
• equivalent distributed load:
cosww
cos
w.adj
w
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Framing Diagrams
• beam lines and “dots”
• breaks & ends
Load Tracing 27
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Spanning direction of decking or reinforcement
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• purpose
– retain soil or other material
• basic parts
– wall & base
– additional parts
• counterfort
• buttress
• key
Retaining Walls
8
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Retaining Wall Types
• “gravity” wall
– usually unreinforced
– economical & simple
• cantilever retaining wall
– common
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Retaining Wall Loads
• gravity
W = V
• fluid pressure
p = ’ h
P = ½ p h at h/3
• friction
F = N
• soil bearing pressure, q
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Retaining Wall Equilibrium
• sliding - overcome friction?
• overturning at toe (o) - overcome mass?
o
P
R
W251
goverturnin
.M
MSF resist
2251 .F
FSF
sliding
resisthorizontal
Fresist
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• want resultant of load from pressure inside
the middle third of base (kern)
• triangular stress block with pmax
• x = 1/3 x width of stress
• equivalent force location:
Pressure Distribution
32
3 xxpxW max
a
W
x
Wpmax
2
3
2
when a is
fully stressed
9
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Wind Pressure
• distributed load
• “collected” into V
• lateral loads
must be
resisted
V
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Bracing Configurations