Chapter 1 - Type of Structure and Loads.pdf

Structural Analysis 7th Edition in SI Units
Russell C. Hibbeler
Chapter 1:
Types of Structures and Loads

Introduction
• Structures refer to a system of connected parts
used to support a load
• Factors to consider:
• Safety
• Esthetics
• Serviceability
• Economic & environmental constraints
© 2009 Pearson Education South Asia Pte Ltd
Structural Analysis 7th Edition
Chapter 1: Types of Structure and Loads

Classification of Structures
• Structural elements
• Tie rods
• Beams
• Columns
• Types of structures
• Trusses
• Cables & Arches
• Surface Structures

Loads
Loads
Structural forms
Elements carrying primary loads
Various supporting members
Foundation

• Design loading for a structure is often specified in
codes
• General building codes
• Design codes
Loads

• Types of load
• Dead loads
• Weights of various structural members
• Weights of any objects that are attached to the
structure
Loads

The floor beam is used to support the 1.83m width of lightweight
plain concrete slab having a thickness of 102mm. The slab serves
as a portion of the ceiling for the floor below & its bottom coated
with plaster. A 2.44m high, 305mm thick lightweight solid
concrete block wall is directly over the top flange of the beam.
Determine the loading on the beam measured per m length of the
beam.
Example 1.1

Using the data provided from the table,
Solution
m
kN
Total
m
kN
m
m
m
kN
m
kN
m
m
kN
m
kN
m
mm
mm
m
kN
/
50
.
15
26
.
12
44
.
0
80
.
2
/
26
.
12
)
305
.
0
)(
44
.
2
)(
/
5
.
16
(
:
block wall
/
44
.
0
)
83
.
1
)(
/
24
.
0
(
:
ceiling
plaster
/
80
.
2
)
83
.
1
)(
102
)(
.
/
015
.
0
(
:
slab
concrete
3
2
2








• Live loads
• Varies in magnitude & location
• Building loads
• Depends on the purpose for which the building is
designed
• These loadings are generally tabulated in local, state
or national code
Loads

• Live loads
• Building Loads
• Uniform, concentrated loads
Loads
2
2
2
m
in
area
tributary
4
column
interior
For
factor.
element
load
live
member
by the
supported
area
of
load/m
live
design
unreduced
member
by the
supported
area
of
load/m
live
design
reduced
where
units)
(SI
57
.
4
25
.
0















T
LL
LL
o
T
LL
o
A
K
K
L
L
A
K
L
L

• Live loads
• Building Loads
• Uniform, concentrated loads
Loads
roof.
or
garage
assembly,
public
for
used
structures
for
or
/
79
.
4
loads
for
allowed
is
reduction
No
floor
one
than
more
supporting
members
for
4
.
0
floor
one
supporting
members
for
5
.
0
2
m
kN
L
L
L
L
o
o




A 2-storey office building has interior columns that are spaced
6.71m apart in 2 perpendicular directions. If the (flat) roof loading
is 0.96kN/m2, determine the reduced live load supported by a
typical interior column located at ground level.
Example 1.2

Solution
kN
kN
kN
F
F
F
kN
m
m
kN
F
m
kN
L
m
m
m
A
K
m
kN
L
kN
m
m
kN
FR
m
m
m
A
F
R
F
T
LL
o
T
0
.
107
9
.
63
1
.
43
9
.
63
)
0
.
45
)(
/
42
.
1
(
50%
59.1%
100%
(1.42/2.4)
is
reduction
load
The
/
1.42
180
57
.
4
25
.
0
4
.
2
2
.
37
180
)
0
.
45
(
4
4
,
4
,
/
4
.
2
floor,
second
For
1
.
43
)
0
.
45
)(
/
96
.
0
(
0
.
45
)
71
.
6
)(
71
.
6
(
2
2
2
2
2
2
2
2
2
2




























• Highway Bridge loads
• Primary live loads are those due to traffic
• Specifications for truck loadings are reported in
AASHTO
• For 2-axle truck, these loads are designated with H
followed by the weight of truck in tons and another
no. gives the year of the specifications that the load
was reported
Loads

• Railway Bridge loads
• Loadings are specified in AREA
• A modern train having a 320kN (72k) loading on the
driving axle of the engine is designated as an E-72
loading
Loads

• Impact loads
• Due to moving vehicles
• The % increase of the live loads due to impact is
called the impact factor, I
Loads
load
live
the
to
subjected
is
that
m
in
span
the
of
length
3
.
0
1
.
38
24
.
15




L
L
I

• Wind loads
• Kinetic energy of the wind is converted into potential
energy of pressure when structures block the flow of
wind
• Effects of wind depends on density & flow of air,
angle of incidence, shape & stiffness of the structure
& roughness of surface
• For design, wind loadings can be treated as static or
dynamic approach
Loads

• Wind loads
Loads
1
alone,
acting
For wind
loads.
of
n
combinatio
to
subjected
is
structure
the
only when
used
is
It
wind.
the
of
direction
for the
accounts
t
factor tha
a
1
ground
flat
For
s.
escarpment
%
hills
to
due
increases
speed
for wind
accounts
t
factor tha
a
1.5.
Table
See
terrain.
ground
upon the
depends
and
height
of
function
A
t.
coefficien
exposure
pressure
velocity
the
occupancy.
building
the
of
nature
upon the
depends
t
factor tha
importance
the
map.
wind
a
from
obtained
are
Values
period.
recurrence
50year
a
during
ground
the
above
10m
measured
wind
of
gust
3s
a
of
m/s
in
velocity
where
)
2
/
(
2
613
.
0








d
K
d
K
zt
K
zt
K
z
K
I
V
m
N
I
V
d
K
zt
K
z
K
z
q

• Wind loads
• Once qz is obtained, the design pressure can be
obtained from a list of relevant equations
Loads
)
( pi
h
p GC
q
qGC
p 

18
.
0
building,
enclosed
fully
For
building.
in the
openings
of
type
upon the
depends
t which
coefficien
pressure
internal
the
surface.
the
from
away
acting
pressure
indicate
values
Negative
t
coefficien
pressure
roof
or
wall
0.85
G
structure,
rigid
For
exposure.
on
depending
factor,
effect
gust
-
wind
a
roof
the
of
height
mean
,
h
z
where
wall
leeward
for the
ground
the
above
z
height
at
wall
windward
for the








pi
pi
p
h
z
GC
GC
C
G
q
q
q

The enclosed building is used for agricultural purposes and is
located outside of Chicago, Illinois on flat terrain. When the wind
is directed as shown, determine the design wind pressure acting
on the roof and sides of the building using the ASCE 7-02
Specifications.
Example 1.3

Solution
m
h
h
K
I
V
K
K
K
q z
d
zt
z
z
63
.
9
2
/
03
.
4
62
.
7
03
.
4
10
tan
6
.
22
'
3
.
853
613
.
0
1
K
is
loading
Wind
1
K
in,
flat terra
For
0.87
I
40m/s,
V
speed,
wind
Basic
0
2
d
zt












Solution
152
85
.
0
)
18
.
0
(
845
)
85
.
0
(
)
(
18
.
0
)
(
,
85
.
0
845
990
0
3
853
990
0
63
9
2
12
04
1
1
9
2
12
98
0
04
1
h
z
for
ion
interpolat
linear
by
determined
was
K
of
value
the
Note
below.
table
in the
listed
are
profile
pressure
of
values
calculated
1.5,
Table
in
K
of
values
Using
2
z
z

p
p
pi
h
p
pi
h
h
h
qC
C
q
GC
q
qGC
p
GC
G
N/m
)
.
(
.
, q
.
K
)
.
-
.
)/(
-K
.
(
)
.
-
.
)/(
.
-
.
(















Solution
z (m) Kz Qz (N/m2)
0 – 4.6 0.85 733
6.1 0.90 776
7.6 0.94 814
h = 9.6 0.990 856

Solution
2
2
2
2
6
.
7
2
2
1
.
6
2
2
6
.
4
0
/
211
/
517
5
.
0
1,
5.72
2(22.86)/4
wall
Leeward
/
709
/
400
/
680
/
374
/
651
/
344
8
.
0
,
all
For
z
height
with
varies
Pressure
wall
Windward
m
N
or
m
N
p
C
L/B
m
N
or
m
N
p
m
N
or
m
N
p
m
N
or
m
N
p
C
L/B
p
p













Solution
2
2
2
2
/
356
/
666
and
7
.
0
that
so
,
25
.
0
211
.
0
86
.
22
/
63
.
9
Here
roofs
Windward
/
356
/
666
7
.
0
,
of
values
all
For
walls
Side
m
N
or
m
N
p
q
q
C
h/L
m
N
or
m
N
p
C
L/B
h
p
p















Solution
2
2
/
65
/
356
and
3
.
0
case,
In this
roofs
Leeward
m
N
or
m
N
p
q
q
C h
p







• Wind loads
• If the structure represents an above-ground sign, the
wind will produce a resultant force on the face of the
sign which is determined from:
Loads
f
f
z A
GC
q
F 
wind
the
into
projected
sign
the
of
face
the
of
area
the
1.6
Table
in
listed
are
Values
N.
dimension
small
the
sign to
the
of
M
dimension
large
the
of
ratio
upon the
depends
t which
coefficien
force
a
previously
defined
factor
t
coefficien
gust
-
wind
the
of
centroid
the
of
z
height
at the
evaluated
pressure
velocity
the
where




f
f
f
z
A
C
G
A
q

• Snow loads
• Design loadings depend on building’s general shape
& roof geometry, wind exposure, location and its
importance
• Snow loads are determined from a zone map
reporting 50-year recurrence interval
Loads

• Snow loads
• For flat roof (slope < 5%):
Loads
hospital
for
1.2
and
facilities
storage
&
e
agricultur
for
0.8
e.g,
For
occupancy.
to
relates
it
as
factor
importance
the
1.0.
then
structure,
heated
normally
a
supporting
is
roof
the
if
whereas
1.2,
freezing
below
kept
structure
unheated
For
building.
within the
re
temperatu
average
the
to
refers
ch
factor whi
thermal
a
1.3
city
large
a
of
centre
in the
located
&
sheltered
is
roof
the
If
0.8.
area
ed
unobstruct
an
in
roof
exposed
fully
A
terrain.
upon the
depending
factor
exposure
an
where
1.5
eqn
7
.
0










I
I
I
t
C
t
C
t
C
e
C
e
C
e
C
g
t
e
f Ip
C
C
p

• Snow loads
Loads
)
/
96
.
0
(
use
,
/
96
.
0
If
or
1.5
eqn
from
computed
either
,
for
lue
largest va
the
use
,
/
96
.
0
If
2
2
2
m
kN
I
p
m
kN
p
Ip
p
p
m
kN
p
f
g
g
f
f
g





The unheated storage facility is located on flat open terrain near
Cario, Illinois where the ground snow load is 0.72kN/m2.
Determine the design snow load on the roof.
Example 1.4

Solution
2
2
2
2
2
/
58
.
0
choose
,
comparison
By
/
58
.
0
)
72
.
0
)(
8
.
0
(
/
96
.
0
/
72
.
0
Since
/
39
.
0
)
72
.
0
)(
8
.
0
)(
2
.
1
)(
8
.
0
(
7
.
0
7
.
0
8
.
0
,
2
.
1
,
8
.
0
1.5
eqn
use
flat,
is
roof
the
Since
m
kN
p
m
kN
Ip
p
m
kN
m
kN
p
m
kN
p
Ip
C
C
p
I
C
C
f
g
f
g
f
g
t
e
f
t
e













• Earthquake loads
• Earthquake produce loadings through its interaction
with the ground & its response characteristics
• Their magnitude depends on amount & type of
ground acceleration, mass & stiffness of structure
• Top block is the lumped mass of the roof
• Middle block is the lumped
stiffness of all the building’s columns
• During earthquake, the ground
vibrates both horizontally & vertically
Loads

• Horizontal accel -> shear forces in the column
• If the column is stiff & the block has a small mass,
the period of vibration of the block will be short, the
block will acceleration with the same motion as the
ground & undergo slight relative displacements
• If the column is very flexible & the block has a large
mass, induced motion will cause small accelerations
of the block & large relative displacement
Loads

• The effects of a structure’s response can be
determined & represented as an earthquake
response spectrum
• For small structure, static analysis is satisfactory
Loads
/ I
R
S
C DS
s 
building
the
of
use
on the
depends
t
factor tha
importance
structure
the
of
ductility
upon the
depends
t
factor tha
on
modificati
response
vibration
of
periods
short
for
accel
response
spectral



I
R
SDS

• Hydrostatic & Soil Pressure
• The pressure developed by these loadings when the
structures are used to retain water or soil or granular
materials
• E.g. tanks, dams, ships, bulkheads & retaining walls
• Other natural loads
• Effect of blast
• Temperature changes
• Differential settlement of foundation
Loads

• Material uncertainties occur due to
• variability in material properties
• residual stress in materials
• intended measurements being different from
fabricated sizes
• material corrosion or decay
• Many types of loads can occur simultaneously on a
structure
Structural Design

• In working-stress design, the computed elastic
stress in the material must not exceed the
allowable stress along with the following typical
load combinations as specified by the ASCE 7-02
Standard
• Dead load
• 0.6 (dead load) + wind load
• 0.6 (dead load) + 0.7(earthquake load)
Structural Design

• Ultimate strength design is based on designing the
ultimate strength of critical sections
• This method uses load factors to the loads or
combination of loads
• 1.4 (Dead load)
• 1.2 (dead load) + 1.6 (live load) + 0.5 (snow load)
• 1.2 (dead load) + 1.5(earthquake load)+ 0.5 (live load)
Structural Design

Chapter 1 - Type of Structure and Loads.pdf

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