chapter 1site.iugaza.edu.ps/marafa/files/chapter-1-2019.pdf · loads codes a) general building...
TRANSCRIPT
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Chapter 1Chapter 1
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Chapter 1
Types of Structures & Loads
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Introduction
• Structure refers to a system of connected parts used
to support load, such as Buildings, Bridges,
towers, Stadiums, ……………. etc.
Chapter 1 Dr. Mohammed Arafa Structural Analysis I
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Introduction
• Structural Analysis involves the prediction of the
performance of a given structure under prescribed
loads and/or other external effects, such as
support movements and temperature changes.
• The fundamental purpose of a structural analysis
is to determine the magnitudes of force and
displacement for each element of a design system
for a given set of design loads.
Chapter 1 Dr. Mohammed Arafa Structural Analysis I
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Structural Elements
• Tie Rods
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Beams
• Type of Beams
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Columns
• Columns
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Type of Structure
• Trusses
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Cables and Arches
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Cables and Arches
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Frames
• Frames members are subjected to axial, shear and moment
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Surface Structures
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Loads
Codesa) General Building Codes Specify the requirement of minimum design load on structures
1. ASCE
2. UBC
3. IBC
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Loads
Codesb) Design CodeUsed to establish the requirement for the actual structural design
1. ACI
2. AISC
3. AASHTO
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EurocodeEN 1990 Eurocode 0: Basis of Structural Design
EN 1991 Eurocode 1: Actions on structures
EN 1992 Eurocode 2: Design of concrete structures
EN 1993 Eurocode 3: Design of steel structures
EN 1994 Eurocode 4: Design of composite steel and concrete structures.
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EuroCode -Continue
EN 1995 Eurocode 5: Design of timber structures
EN 1996 Eurocode 6: Design of masonry structures
EN 1997 Eurocode 7: Geotechnical design
EN 1998 Eurocode 8: Design of structures for earthquake resistance
EN 1999 Eurocode 9: Design of aluminum structures
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Dead Load
Consist of the weight of the various structural members
and weight of any object that permanently attached to the
structure
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Dead Load
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Dead Load
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Dead Load
10cm
20cm
3m
1.0m1.0m
The floor beam used to support the 2 m width of lightweight plain concrete
slab having thickness of 10cm. The slab serve as a portion of the ceiling for
the floor below, and therefore its bottom is coated with plaster. Furthermore,
an 3m high, 20 cm thick lightweight solid concrete is directly over the top
flange of the beam. Determine the loading on the beam measured per one
meter of the length of the beam
SolutionFrom Table 1-3
Lightweight concrete 0.015 kN/m2 per (mm)
15 kN/m3
Plaster on tile or concrete 0.24 kN/m2
From Table 1-2
Masonry, Lightweight solid concrete 16.5kN/m3
Concrete Slab (0.015)(100)(2) = 3kN/m
Plaster Ceiling (0.24)(2) = 0.48 kN/m
Block Wall (16.5)(0.2)(3) = 9.9 kN/m
------------------------------------------------------------
Total load = 13.38 kN/m
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Live Load
• Building Loads
• Highway Bridge Loads
• Railroad Bridge Loads
Can vary both in their magnitude and location
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Live Load
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Where
L Reduced design live load per square meter supported by the member.
L0 Unreduced design live load per or square meter area supported by the member.
KLL Live load element factor. For interior columns KLL=4
AT Tributary area in square meters.
237.2 mLL Ti K Af
Live load Reduction
For some types of buildings having very large floor areas Many codes will allows a reduction in the uniform live load for a
floor, since it is unlikely that the prescribed live load will occur simultaneously throughout the entire structure at any one time
0
4.570.25
LL T
L LK A
In ASCE 7-10
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Live load Reduction
0
0
50% for members supporting one floor
40% for members supporting more than one floor
LL
L
2 2
0 4.8 kN/m (480 kg/m )
The structures used for pu
No re
blic
duction is a
assembly,gar
llow
ages,or ro
ed
ofs
if
if
L
or
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A two-story office building shown in the photo has interior columns that are spaced 8m apart in two perpendicular directions. If the (flat) roof loading is 0.95 kN/m2. Determine the reduced live load supported by a typical interior column located at ground level.
Example
8m
8m
8m8m
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A two-story office building shown in the photo has interior columns that are spaced 8m apart in two perpendicular directions. If the (flat) roof loading is 0.95 kN/m2. Determine the reduced live load supported by a typical interior column located at ground level.
Example
8m
8m
8m8m
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ExampleThe interior column has a tributary area or effective loaded area of AT= 8x8=64m2 > 37.2m2
A ground floor column supports a roof live load ofFR= 0.95x64= 60.8 kNThis load cannot be reduced since it is a roof load.
For the first floor, the LL is taken from table 1-4 L0=2.4 kN/m2.
2
0
4.57 4.570.25 2.4 0.25 2.4 0.536 1.29 kN/m
4 64LL T
L LK A
1.29The load reduction here is 100% 53.8% 40%
2.4
The Floor load 1.29 64 82.6
The Roof load 0.95 64 60.8 (No Reduction in Roof load)
60.8 82.6 143.4
F
R
R F
F kN
F kN
F F F kN
8m
8m
8m8m
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Wind Load
)(N/m 613.0
22IVKKKq
pressureWind
dztzz
Qz Velocity wind pressure at height z above ground level.
V The velocity of the wind measured 10 m above the ground
I Importance factor depends upon nature of the building
Kz The velocity pressure exposure coefficient which is function of height
Kzt A factor that account for wind speed increases due to hills and
Escarpments for flat ground Kzt=1.0 (topographic factor)
Kd A factor account for direction of wind when subjected to load
combination
Chapter 1 Dr. Mohammed Arafa Structural Analysis I
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Wind Load
)(N/m )(
2
pihp GCqqGCp
BuildingEnclosedforpressureWind
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Wind Load
)(N/m )(
2
pihp GCqqGCp
BuildingEnclosedforpressureWind
G Gust factor, which equal 0.85 for rigid structures.
Cp a wall or roof pressure coefficient
(GCpi ) internal pressure coefficient which depends upon the
type of openings in the building. For fully enclosed
buildings GCpi = 0.18
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Wind Load
)(N/m 613.0
22IVKKKq
pressureWind
dztzz
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Wind Load
)(N/m 613.0
22IVKKKq
pressureWind
dztzz
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fph AGCqF
SignsforpressurewindDesign
Wind Load
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Wind Load
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Snow Load
0.7 e t gF C C I p
If a roof is flat, having a slope of less than 5%.
The pressure loading on the roof can be obtained by modifying the
ground snow loading pg, by the following empirical formula
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Snow Load
0.7 e t gF C C I p
Ce = an exposure factor which depends upon the terrain.
Ce = 0.8 for a fully exposed roof in an unobstructed area
Ce = 1.2 for roof located in the center of a large city.
Ct = a thermal factor, refers to the average temperature within the building
Ct = 1.2 for unheated structures kept below freezing,
Ct = 1.0 for normally heated structure.
Is = the importance factor as it relates to occupancy,
Is = 0.80 for agriculture and storage facilities, and
Is = 1.20 for schools and hospitals
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Earthquake Load
The total design base shear in a given direction:
IBC-03WCV s
1
/ /
0.044
DS Ds
E E
DS
S SC
R I R I T
S
R = Response modification coefficient IE = Seismic occupancy importance factorT = Fundamental period of vibration
Equivalent Lateral Force Analysis
V = Total Design Base Shear
Cs = Seismic Response Coefficient
W = Total seismic dead load
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Earthquake Load
Dynamic Force Analysis
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Hydrostatic and Soil Pressure
Other natural LoadsDepending on the structure location or use.
Blast Loading
Temperature changes,
Differential settlement of the foundation.
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Structural Design
• LRFD (Load and resistance factor design)
Load combination example:
1.4( )
1.2( ) 1.6( ) 0.5( )
1.2 1.6( ) (1.0 0.8 )
1.2 1.6 1.0 0.5( )
1.2 1.2 1.0 1.6 1.0 0.2
r
r
r
U D F
U D F T L H L or S or R
U D L or S or R L or W
U D W L L or S or R
U D F E H L S
U
0.9 1.2 1.6 1.6
0.9 1.2 1.0 1.6
D F W H
U D F E H
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Structural DesignWhere:D= Dead load.L = Live load, except roof live load.Lr = Roof live load.E = Earthquake load.W= Load due to windF = Load due to fluidsH= Load due to lateral earth pressuresR = Rain load.S = Snow load.T = Load due to temperature, shrinkage,
creep, differential settlement