Theory and Design of Structures III
Arch 2191
Structure
Dictionary definition
Everything even intangible things as thought,
emotions and social relationships frequently have
definite pattern called Structure.
The dictionary definition of a structure is;
“the organization or interrelation of all
parts of a whole.”
Structure
Engineering Definition
 Structure can be defined as the assemblage of those
parts that exist for the purpose of maintaining shape
and stability.
Structure of a Building
The primary function of a
building structure is to
support and transmit the
loads and forces to the
ground.
Structures is a way of
achieving the most
strength from the least
material through the most
appropriate arrangement of
elements with a form
suitable for its intended use
Loads (Actions)
Loads can be;
Point, uniformly distributed or distributed.
Permanent, variable or accidental.
Static, impact or dynamic.
Loads
Dead Loads (DL) –fixed loads
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building materials/components and the weight of
structural components
Loads (continued)
Live Loads (LL) – transient and moving loads
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Occupancy loads (usage) and furnishing loads
Stored materials
Movable partitions
Movable machinery
Snow loads
Construction loads
Live Load maybe variable during
structures lifetime
Building codes specify these loads
for floor and roof loadings
Loads (continued)
Wind Load (WL) –
wind load generates
 Lateral load on walls
 Downward and upward
pressure on roofs
Loads (continued)
Wind against a building builds
up a positive pressure on the
windward side and a negative
pressure (or suction) on the
leeward side.
Depending upon the shape of
the structure it may also cause
a negative pressure on the side
walls or even the roof.
Loads (continued)
The pressure on the walls and roof
is not uniform, but varies across
the surface.
Winds can apply loads to structures
from unexpected directions. Thus,
a designer must be well aware of
the dangers implied by this lateral
load.
Loads (continued)
Wind pressure on buildings
increases with increasing
velocity, height & exposure.
The magnitude of the pressure
that acts upon the surfaces is
proportional to the square of
the wind speed.
Loads (continued)
Earthquake Loads (EQ)
 Seismic load depends on
building mass, type and
configuration.
 Vertical and lateral forces
(dynamic)
 Building codes can
simplify loading
A “good” design?
 The building dead load is the only known
load. All other forces will vary in
magnitude, duration and location.
 The building is designed for design load
possibilities that may never occur.
 The structural efficiency of a building is
measured as the ratio of dead to live
load.The building designer strives to keep
the ratio low.
Load path
Load path