fourteen ie. joist on beam acts along a line ie. floor on a beam - - PowerPoint PPT Presentation

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ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN

ARCH 331

• DR. ANNE NICHOLS

SPRING 2019

fourteen

system assemblies & load tracing

Load 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

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Concentrated Loads

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Distributed Loads

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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

loading loading L

A dA wdx W   

 

dx y x

el

x

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Area Centroids

• Table 6.1 – pg. 304

b h

3 b

right triangle only Load Tracing 7 Lecture 14 Foundations Structures ARCH 331 F2008abn

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 W x w   w w 2 2 W x w   w 2w

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Distributed Area Loads

• w is also load per unit area

w

3

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Load Tracing

• how loads are

transferred

– usually starts at top – distributed by supports as actions – distributed by tributary areas

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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

 

width tributary area load w        

width

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Load Tracing

Patcenter Rogers 1986

www.columbia.edu F2008abn Load Tracing 14 Lecture 14 Foundations Structures ARCH 331

Load Tracing

Alamillo Bridge Calatrava 1992

http://en.structurae.de Load Tracing 15 Lecture 14 Foundations Structures ARCH 331 F2008abn

Load Paths

• floors and framing

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Load Paths

• wall systems

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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

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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 Lecture 14 Architectural Structures ARCH 331 Load Tracing 23 Lecture 14 Foundations Structures ARCH 331 F2008abn

Slabs

• edge support
• linear and uniform distribution

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Girders and Transfer

• openings

– no load & no half way

• girder actions at beam supports

+ + + +

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Sloped Beams

• stairs & roofs
• projected live load
• dead load over length
• perpendicular load to beam:
• equivalent distributed load:



 cos w w  



 cos w . adj w 

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Framing Diagrams

• beam lines and “dots”
• breaks & ends

Load Tracing 27 Lecture 14 Architectural Structures ARCH 331 Spanning direction of decking or reinforcement Load Tracing 25 Lecture 14 Foundations Structures ARCH 331 F2008abn

• purpose

– retain soil or other material

• basic parts

– wall & base – additional parts

• counterfort
• buttress
• key

Retaining Walls

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Retaining Wall Types

• “gravity” wall

– usually unreinforced – economical & simple

• cantilever retaining wall

– common

Load Tracing 27 Lecture 14 Foundations Structures ARCH 331 F2008abn

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?
• P

R W

2 5 1

g

• verturnin

   . M M SF

resist

2 25 1   



. F F SF

sliding resist horizontal

Fresist

Load Tracing 29 Lecture 14 Foundations Structures ARCH 331 F2008abn

• 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

3 2 3 x x p x W

max

   a W x W pmax 2 3 2  

 

when a is fully stressed

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Load Tracing 30 Lecture 14 Foundations Structures ARCH 331 F2008abn

Wind Pressure

• distributed load
• “collected” into V
• lateral loads

must be resisted

V

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Bracing Configurations