Transcript Loads & Supports - Architecture, Design and Planning

Peter Smith & Mike Rosenman
General Structural Concerns

Functionality / Stiffness
deformations

Stability
equilibrium

Strength
material behaviour
University of Sydney – DESA 1102 Structures
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Peter Smith & Mike Rosenman
Stability

Loads
● act on structure
● tend to destabilise structure
● also tend to break elements

Supports
● provide reactions
● must be such as to
provide equilibrium
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Peter Smith & Mike Rosenman
Loads
Loads
Static
Forces
due to
Settlements,
Thermal effects,
...
Self-Weight
of
Structure
Dynamic
Dead Loads
(fixed)
Fixed
Building
Elements
Live Loads
(movable)
Continuous
Impact
Earthquakes
Occupancy
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Environmental
(snow, ...)
Wind
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Peter Smith & Mike Rosenman
Loads

Two main types

dead loads - self-weight,
fixed elements

live loads - occupancy, contents, wind
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Peter Smith & Mike Rosenman
Loads (cont.)

The building materials impose dead loads
(fixed, vertical)

The occupants and contents impose live
loads (variable, mostly vertical)

Wind and earthquake impose live loads
(variable, mostly horizontal)
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Dead Loads

Permanent weight of structure
● non-moveable partitions
● built-ins, heavy equipment
Roof
Walls
Floors
Equipment
Cowan, Gunaratnam and Wilson (1995). Structural Systems, Department of Architectural and Design Science
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Peter Smith & Mike Rosenman
Dead Loads (cont.)

How much does the stuff weigh?

How much of each material is there?
Dead loads
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Peter Smith & Mike Rosenman
Dead Loads - Typical Values
Bulk Material
Weight/unit
volume
Sheet Material Weight/unit
area
Concrete, dense
23.5 kN/m3
Gypsum plaster
13mm
0.22 kN/m2
Hardwood
11.0 kN/m3
Fibre cement
6mm
0.11 kN/m2
Steel
76.9 kN/m3
Brick
19.0 kN/m3
Appendix A of SA loading code AS1170.1
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Peter Smith & Mike Rosenman
Live Loads

Furniture, Equipment, People, Snow
 Moveable Partitions
 May or may not be acting all the time
Cowan, Gunaratnam and Wilson (1995). Structural Systems, Department of Architectural and Design Science
University of Sydney – DESA 1102 Structures
LOADS & SUPPORTS
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Peter Smith & Mike Rosenman
Live Loads (cont1.)
people move around
may get heavy concentrations
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Peter Smith & Mike Rosenman
Live Loads (cont2.)

Could calculate - but tedious

Codes specify loads for various types of
occupancies

AS 1170.1 specifies minimum floor live loads

Uniformly Distributed (kPa)

Concentrated (kN) - e.g. tall bookshelves
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Peter Smith & Mike Rosenman
Live Loads (cont3.)

Building Codes give minimum values
 Domestic live loads range from 1.5 kPa
 Corridors and balconies are generally 4kPa, to
allow for crowding
 Most stores and workshops are >= 5 kPa
Live loads
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Peter Smith & Mike Rosenman
Wind Loads

Both Pressure and Suction
 Always important for tall buildings
 But also important for low buildings bracing
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Peter Smith & Mike Rosenman
Wind loads on Buildings

Pressure on the windward face

Suction on other faces

Suction on lowpitched roofs - < 300

Buildings need bracing and tying-down

Wind can come from any direction
wind
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Peter Smith & Mike Rosenman
Wind Loads on Buildings (cont1.)
may need to hold
roof down
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Peter Smith & Mike Rosenman
Wind Loads on Buildings (cont2.)

Wind tends to overturn a tall building
 Acts as a vertical cantilever
Overturning
Moment
Pressure
Suction
Reaction
Resisting Moment
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Reaction
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Peter Smith & Mike Rosenman
Factors in Wind Speeds

General wind speed in the region
● (pressure varies with square of the
speed)
 Local topography affects wind patterns
 Wind speed increases with altitude
 Wind speed decreases with terrain
roughness
Very exposed
More sheltered
Wind
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Peter Smith & Mike Rosenman
Factors in Wind Loads (cont.)

Shelter from anything permanent will
reduce loads
 Shape of building affects loads
● Boxy vs streamlined
Pinchgut is
exposed
Curved
shapes
would
need
special
analysis
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Sheltered
by buildings
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Peter Smith & Mike Rosenman
Wind Loads on Elements

Timber Framing Code has a procedure for
finding maximum wind speeds
 Timber Framing Code also has simplified
rules for bracing single-storey houses

In non-cyclone areas, wind loads in the
1kPa range

Multiply by the area exposed to wind
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Seismic Loads

Earthquakes cause damage by horizontal
acceleration - may swing
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Settlement, Temperature Loads

Stresses caused by temperature changes

Uneven settlement of
foundations creates stresses
- Gothic Cathedrals
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Peter Smith & Mike Rosenman
Loads on Elements

So far we have looked at the effect of loads
on the building overall

Now let’s consider individual elements
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Peter Smith & Mike Rosenman
Distributed Loads and Point Loads

Floors, walls and roofs are generally
distributed loads (kN per m or kPa)
 Other beams are point loads (kN)
Distributed
Load
Point Loads
Reactions
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Effect of one Member on Another

The forces at the supports are the
reactions
 For equilibrium, the reactions just balance
the loads
Point Load on beam
Point Loads
from beam to beam
Reaction
from beam
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Point Load
on column
and reaction
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Peter Smith & Mike Rosenman
Types of Reactions
Simple Support

Beam sitting on supports

Provides vertical support only

No horizontal reaction
Rv

Allows rotation
no moment developed
Rv
V
V
HH
simple beam
Rv
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Rv
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Types of Reactions
Roller Support

Provides vertical support only

deliberately avoids
horizontal restraint
(allows expansion)
Rv
Rv
a true roller support
(only needed on
very large structures)
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Peter Smith & Mike Rosenman
Types of Reactions
Hinged (pin) Support

Provides vertical and
horizontal support,
 Allows rotation - no
moment developed
RH
RV
RH
RV
a definite ‘hinged’ support
(most simple supports just involve
a beam sitting on something)
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Peter Smith & Mike Rosenman
Types of Reactions — Rigid Support
RH
Welded steel frame
M

RV
Provides V, H, and
moment restraint, M

Cantilever beams or
posts, and rigid
frames

Make sure you can
physically achieve it!
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