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7/26/2019 Lecture -3 Design Loads_updated
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N-W.F.P. University ofEngineering and Technology
Peshawar
1
Lecture 03: Design Loads
By: Prof Dr. Akhtar Naeem Khan
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 2
Topics to be Addressed
Type of !oad
"ind #oad
$arth%uake #oad
#oad &om'ination
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan (
Feeling Responsibility
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )
Types of Loads
Determination of !oad for which a *iven tructure
may 'e dei*ned for i a difficu!t pro'!em.
Questions to be Answered:
+ What loads may structure be called upon duringits lifetime?
+ In what combinations these loads occur?
+ The probability that a specific live load beexceeded at some time during lifetime ofstructure?
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Design load should be rational such that considering !"mph
wind load for a tower is reasonable but not the load of a tan# on
top of the tower$
Types of Loads
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan -
Types of LoadsThree 'road cate*orie:
1. Dead !oad
2. #ive !oad
(. $nvironmenta! !oad
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1. Dead !oad
Dead #oad conit of the wei*ht of a!!materia! and fi/ed e%uipmentincorporated into the 'ui!din* or other
tructure. 0B& ection 1-324"ei*ht of tructure
"ei*ht of permanent machinery etc.
Dead !oad can 'e reaona'!y etimated if themem'er dimenion and materia! denitie are
known.
Types of Loads
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2. #ive !oad:
#ive !oad are thoe !oad produced 'y theue and occupancy of the 'ui!din* or othertructure and do not inc!ude dead !oad6
contruction !oad6 or environmenta! !oad. "ei*ht of peop!e6 furniture6 machinery6
*ood in 'ui!din*.
"ei*ht of traffic on 'rid*e
Types of Loads
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% &uildings serve such diverse purposes that it is
extremely difficult to estimate suitable design
loads$
% Different building codes specify live load
re'uirements$
% (niform &uilding )ode *(&)+
% ,outhern ,tandard &uilding )ode
% &-)A .ational &uilding )ode
Types of Loads2. #ive !oad:
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#ive !oad for variou occupancie
8ccupancy #ive !oad6pf
9eidentia! )3#i'rarie0readin* room4 -3
ercanti!e ,;12,
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The /"psf 0$0 specified by code for 1esidential &uildings is too
)onservative to account for the uncertainties in structural actions
,uch as impact2 fatigue2 temp$ effects etc$
Types of Loads2. #ive !oad:
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Types of loads
(. $nvironmenta! #oad
$nvironmenta! !oad inc!ude wind !oad6
now !oad6 rain !oad6 earth%uake !oad6
and f!ood !oad.
12
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The niform 'ui!din* code and B8&A Nationa!
'ui!din* code permit reduction in 'aic dei*n !ive!oad on any mem'er upportin* more than 1,3ft2
R = r(A-150)
-r R = 23.1(1+D/L)
Where 1 3 reduction2 percent
r 3 rate of reduction 3 "$"45 for floors
A 3 area supported by floor or member
D 3 dead load2 psf 0 3 basic live load2psf
Live load reduction
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Bernou!!i= e%uation for tream f!ow i ued todetermine !oca! preure at ta*nation point6
coniderin* air to 'e non;vicou >
incomprei'!e.
q = (v2/2)
+ This pressure is called velocity pressure2 dynamic pressure2
stagnation pressure$
+ This e'uation is based on steady flow$
+ It does not account for dynamic effects of gusts or dynamic
response of body$
q: pressre: !ass "ensit# o$ air
v: velo%it#
Wind load
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9eu!tant wind preure on 'ody depend upon
pattern of f!ow around it.
Preure vary from point to point on urface6
which depend on hape > i?e of 'ody.
9eu!tant wind preure i e/preed a:
&D = 'DA(v2/2) &L= 'LA(v
2/2)
'D : Dra %oe$$i%ient
'L : Li$t %oe$$i%ient
Wind load
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+ 6or buildings bridges and the li#e pressure is
expressed in terms of ,hape 6actor ),*pressurecoefficient+
& = 'q = '(v2/2)
&=0.0025*'2
+Air at !) weighs "$"78!pcf
: !p,
Wind load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1
eaured wind ve!ocitie are avera*e of
f!uctuatin* ve!ocitie encountered durin* a finitetime.
n avera*e of ve!ocitie recorded durin* the
time it take a hori?onta! co!umn of air 1 mi!e !on*to pa a fi/ed point.
atet mi!e i hi*het ve!ocity in 1 day.
Annua! e/treme mi!e i the !ar*et of the dai!yma/imum.
Wind load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 15
"ind preure to 'e ued in dei*n hou!d 'e
'aed on a wind ve!ocity havin* a pecificmean recurrence interva!.
The f!ow of air c!oe to *round i !owed 'y
urface rou*hne6 which depend on denity6i?e and hei*ht of 'ui!din*6 tree6 ve*etationetc.
e!ocity at ((ft 0B&: ec 1-1-4 a'ove *round
i ued a the 'aic va!ue for dei*n purpoe.
Wind load
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Wind load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 23
hape factor varie conidera'!y with proportion oftructure > hori?onta! an*!e of incidence of the wind.
% '$or in"ar" $a%e o$ $lat roo$e" re%tanlar il"in is 0.
% '$or neative pressre on rear $a%e varies $ro! -0.3 to -0.*
% or s%, il"in resltant pressre e "eter!ine" # s,ape
$a%tor 1.2 to 1.5
% 'o!!onl# se" is 1.3
% ' $or i"e alls -0. to 0.
% '$or roo$ 0.5 to 0.
Wind load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 21
4in" $or%es on trsse" str%tres e.. ri"es trans!ission
toers ea! ri"es ir"er ri"es et%. "i$$i%lt to assesse%ase o$ leear" parts o$ str%tre.
Recommended coefficients for walls of buildings,
gabled roofs, arched roofs, roofs over unenclosed
structures(stadium), chimneys, tanks, signs,transmission towers etc. are given in ASCE !"#
$ind %ressures s%ecified by building codes include
allowance for gust and sha%e factors.
Wind load
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 22
% 9ressure acts on the windward face of the building% ,uction acts on the leeward face of the building%
,uction acts on the sides of the building so a personstanding in The window may be thrown outside
+ ,uction acts on the floor so that I sheet floors are
blown away During strong wind storms
Wind load
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The revolving restaurant supported by a concrete column will
;xperience suction which will cause tension in the column and as
)oncrete is wea# in tension so it may crac#$ As a result the lateral
Wind load may collapse the restaurant$
Wind load
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AA,
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Wind Pressure U! "#
Dei*n "ind Preure:
wsqe IqCCP =
'e: combined height2 exposure and gust factor *Table 8=+
'q (or 's):9ressure coefficient for the structure or portion of
structure under consideration *Table 8=>ft *Table 8=6+
6:importance factor *Table 8=#+
(&) *"=+
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Wind Load $%a&ple
$/amp!e:&a!cu!ate the wind preure e/erted 'y a wind'!owin* at 133mph on the civi! en*ineerin* department o!d'ui!din*.
o!: Accordin* the formu!a *iven a'ove:
or windward face: & C .5inward 0B&7 Ta'!e 1-;
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PwindwardC 23.)5 pf
P!eeward C 12.53 pf
Ptota! C ((.25 pf
&=0.0025*'2
Wind Load $%a&ple
Wi d L d $ l
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 25
A!ternate ethod:
&eC 3.- 0 or (3ft hei*ht > $/poure B6 Ta'!e 1-;4
&%C 3.50 or windward wa!!6 Ta'!e 1-;
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 27
PwindwardC 1,.,- pf
P!eeward C 7.( pf
Ptota! C 2,.27 pf
wsqe IqCCP =
Wind Load $%a&ple
Wi d L d $ l
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Wind Load $%a&ple
$ t' ) L d
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$arth%uake !oad are neceary to
conider in earth%uake prone re*ion.
$arth%uake wave are of two type:Body wave
urface wave
$art'(ua)e Load
$arth%uake "ave
$ t' ) L d
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan (2
+&ody waves consists of 9=waves @ ,=waves
+These waves cause the ground beneath the structure tomove bac# and forth and impart accelerations into
the base of structure$
+9eriod and intensity of these acceleration pulseschange rapidly @ their magnitude vary from small
values to more than that of gravity$
$art'(ua)e Load
$arth%uake "ave
$ t' ) L d
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$art'(ua)e Load$arth%uake "ave
$ t' ) L d
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&ody waves reach thebuildings first2 followed by
the more Dangerous
surface waves
A linear increase in magnitudeof ;Q causes approximately cubic
increase in the corresponding
amount of energy released
$art'(ua)e Load$arth%uake "ave
$ t' ) L d
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,hallow ;Q of depth2 say2 !="#m are far more dangerous than
deep ;Q of depth2 say2 !"=""#m$
$art'(ua)e Load$arth%uake "ave
$ t' ) L d
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$art'(ua)e Loadactor effectin* earth%uake repone of tructure
,tructure response to an earth'ua#e primarilydepends upon:
+ass
+stiffness
+natural period of vibration
+damping characteristics of structure
+location from epicenter
+topography @ geological formation$
$ t' ) L d
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$art'(ua)e Loadactor effectin* earth%uake repone of tructure
$ t' ) L d
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$art'(ua)e Load
9epone odification
actor
$art'( a)e Load
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$art'(ua)e Load
9epone odification
actor
$art'(ua)e Load
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;Q generally have short periods which may match the natural
period of the low rise buildings2 say " to " stories which causes
resonan%eresults in serious damages$ The possibility of
resonance for high rise buildings is low due to longer time periods$
$art'(ua)e LoadNatura! Time period of tructure
$art'(ua)e Load U! "#
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$art'(ua)e Load U! "#tatic #atera! force procedure: #imitation
1-27.5.(: The static lateral force procedure ofSection1630 may be used for the following structures
1! "ll structures# regular or irregular# in Seismic $one 1 and
in %ccupancy Categories & and ' in Seismic $one (!(!)egular structures under (&0 feet in height with lateral
force resistance pro*ided by systems listed in Table 16+,#
e-cept where Section 16(.!/! Item applies!
3!Irregular structures not more than fi*e stories or 6' feet
in height
$art'(ua)e Load U! "#
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$art'(ua)e Load U! "#tatic #atera! force procedure: #imitation
1-27.5.(: The static lateral force procedure ofSection1630 may be used for the following structures
&!Structures ha*ing a fle-ible upper portion supported on a
rigid lower portion where both portions of the structureconsidered separately can be classified as being regular# the
a*erage story stiffness of the lower portion is at least 10
times the a*erage story stiffness of the upper portion and the
period of the entire structure is not greater than 1!1 times the
period of the upper portion considered as a separate
structure fi-ed at the base!
$art'(ua)e Load U! "#
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1-(3.2.1 Dei*n 'ae hear. The total design baseshear in a given direction shall be determined from the followingformula:
V = (Cv I/R T) * W 30+&
The total design base shear need not exceed the following:
V = (2.5 Ca I/R) * W 30+'
The total design base shear shall not be less than the following:
V = (0.11 Ca I) W 30+6
In addition2 for ,eismic Bone /2 the total base shear shall also
not be less than the following:V = (0.ZNv I/R) * W 30+2
$art'(ua)e Load U! "#
$art'(ua)e Load U! "#
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1-(3.2.1 Dei*n 'ae hear.For Seismic Zones 1, !, ", an# $%
V = (0.11 Ca I) W & & ' (Cv R *) + $ & V = (2.5 Ca I/R) * W
For Seismic Zone '%
V = (0.11 Ca I) W & & ' (Cv R *) + $ & V = (2.5 Ca I/R) * W
V = (0.ZNv I/R) * W
$art'(ua)e Load U! "#
$art'(ua)e Load U! "#
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1-(3.2.1 Dei*n 'ae hear.
C 3 total base shear
)a@ )C 3 seismic dynamic response spectrum values$
*table 8=Q @ table 8=1+
B 3 seismic Eone factor$ *Table 8$I+
.v@ .a3 near source factors that are applicable in only
seismic Eone /$ *Table 8=T @ Table 8=,+
Depends on ,eismic Eone and soil profile
$art'(ua)e Load U! "#
$art'(ua)e Load U! "#
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$art'(ua)e Load U! "#
oi! profi!e
$art'(ua)e Load U! "#
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$art'(ua)e Load U! "#
eimic Eone B&P 3
$art'(ua)e Load U! "#
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1-(3.2.1 Dei*n 'ae hear.
I 3 Importance factor *Table 8=F+
W 3 Total seismic dead load
1 3 1esponse factor depends on type of structural system
*Table 8=.+T 3;lastic fundamental period of vibration$
$art'(ua)e Load U! "#
7 = 't,n8
)t3 "$">! for steel moment resisting frame
$art'(ua)e Load U! "#
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1-(3.2.1 Dei*n 'ae hear.
*"$ )a I+: this coefficient is also independent of
the period of vibration$ It is a lowerbound value2 #eeping C at some
minimum value$
$art'(ua)e Load U! "#
$art'(ua)e Load U! "#
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$art'(ua)e Load U! "#
1-(3.2.1 Dei*n 'ae hear.
*)v I G 1 T+: acceleration factor *also #nown as a
seismic base shear coefficient+$ This coefficient
will govern C for buildings with medium to longfundamental period of vibrations$ The forces in
these buildings are induced by the velocity
component of the bedroc# motion$
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$art'(ua)e Load U! "#
1-(3.2.1 Dei*n 'ae hear.
*$! )a IG1+: this coefficient is independent of the period
of vibration$ It will govern C for buildings with short
fundamental periods of vibrations2 li#e the buildings
being studied in this class$ The forces in these stiff
buildings are generated by the acceleration
component of the bedroc# motion$
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ,2
$art'(ua)e Load U! "#
1-(3.2.1 Dei*n 'ae hear.
*"$4 . v I G 1+: this lower bound coefficient is only
applicable to structures located in seismic Eone / and
within J$> miles *! #m+ of a #nown seismic fault$
$art'(ua)e Load U! "#
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan ,(
$art'(ua)e Load U! "#Typica! Bae hear coefficient for aonry
Typical base shear coefficient values for a regular2 single=story masonry building not located near a fault$ In addition2
we conservatively assumed that a geotechnical site
investigation was not completed$ &ecause this type of
building is so stiff2 the *$! )a I G 1+ coefficient governs C$Eone &oefficient C 3 $"87W
a C 3 $W
b C 3 $!8W
> C 3 $""W
/ C 3 $//W
$art'(ua)e Load U! "#
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ,)
ertica! ditri'ution: Tota! force ha!! 'e ditri'utedover hei*ht in the fo!!owin* manner:
=t+ 9
+ )oncentrated force tat top shall determined by:
+ 6orce 6xat each level including level n:
$art'(ua)e Load U! "#
$"7TC K $!C6t 3
" if T K $7 sec$
$art'(ua)e Load U! "#
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
The in*!e tory 'ui!din* i a pecia!
cae. n mot cae6 T F . and tthen
i taken a ?ero.
rom e%uation (3;1,:
,,
$art'(ua)e Load U! "#
ertica! ditri'ution:
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple&a!cu!ate and ditri'ute the 'ae hear for a
five tory reidentia! tee! 'ui!din* ,3 ft hi*h6!ocated at Pehawar. Aumin* Doi!
profi!e.
V = (0.11 Ca I) W & ' (Cv R *) + $ V = (#.5 Ca I/R) * W
,-
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ,
B 3 "$ Table 8$I)a 3 "$4 Table 8=Q
)C 3 "$/" Table 8=1
I 3 Table 8=F
1 3 /$! Table 8=.
7 = 't,n8 = (.035)(50)8 = 0.** se%
ase *'ear $%a&ple
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
V = (0.11 Ca I) W & ' (Cv R *) + $ V = (#.5 Ca I/R) * W
(0.11 Ca I) = 0.0308
(Cv R *) ' ".-
(#.5 Ca I/R) = 0.1556
Therefore 'ae hear i e%ua! to:
& ' ".-$
,5
$art'(ua)e Load U! "#
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ,7
Tota! force ha!! 'e ditri'uted over hei*ht in the
fo!!owin* manner:
$art'(ua)e Load U! "#
W!
W>
W
W
W/
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
As T L "$7 therefore 6t 3 "
W?3 W>3 W!3 / #ips
W3 W/3 " #ips
W 3 / x > M " x 3 4 #ips
C 3 "$>/7 x 4 3 $"/ #ips
-3
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
i. tory !eve! 1: 1
"/h
/C 23 / 13 C 233 k;ft
G "ih
iC 23 / 13 H 1) / 23 H 1) / (3 H 23 / )3 H 1) / ,3 C 2)33 k;ft
1C 3.72 kip
-1
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
i. tory !eve! 2: 2
"/h
/C 1) / 23 C 253 k;ft
G "ih
iC 23 / 13 H 1) / 23 H 1) / (3 H 23 / )3 H 1) / ,3 C 2)33 k;ft
2C 1.27 kip
-2
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
i. tory !eve! (: (
"/h
/C 1) / (3 C )23 k;ft
G "ih
iC 23 / 13 H 1) / 23 H 1) / (3 H 23 / )3 H 1) / ,3 C 2)33 k;ft
(C 1.7( kip
-(
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
i. tory !eve! ): )
"/h
/C 23 / )3 C 533 k;ft
G "ih
iC 23 / 13 H 1) / 23 H 1) / (3 H 23 / )3 H 1) / ,3 C 2)33 k;ft
)C (.-5 kip
-)
ase *'ear $%a&ple
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan
ase *'ear $%a&ple
i. tory !eve! ,: ,
"/h
/C 1) / ,3 C .33 k;ft
G "ih
iC 23 / 13 H 1) / 23 H 1) / (3 H 23 / )3 H 1) / ,3 C 2)33 k;ft
,C (.22 kip
-,
+ean Return Period
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan --
The average Time Period (in years) based on
geological and historical records in which there is agood statistical probability that an earthquake of a
certain magnitude or a hurricane will recur is called
Mean Return Period or Recurrence Interval R
9robability that an event will be exceeded at least once in
the n years is
&n= 1-( 1-1/R)n
9robability of ;xceedence of the event in any one year
is the inverse of the ean 1eturn 9eriod 3 G1
+ean Return Period
+ean Return Period
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan -
)onsidering !"mph with a return period of2 say2 ""years
is 1easonable as compared to !""mph with a return period of2
say2 """ years$
+ean Return Period
+ean Return Period
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan -5
&50=1-( 1-1/5)50
=1- 0.5
= 0.1 or 1
;9a!ple:- A str%tre e9pe%te" to ,ave a li$e o$ 50 #ears ilt
in lo%alit# ,ere !ean re%rren%e interval o$ an in"stor! o$150!p, is 5 #rs. 7,e proailit# t,at str%tre ill
en%onter an in"stor! e9%ee"in 150!p, "rin its li$e isni$or! ?il"in 'o"e spe%i$ies t,at t,e eart,qae $or
,i%, a il"in ,as to e "esine" s,ol" %orrespon" to aneart,qae it, a retrn perio" o$ @5 #ears.
Ass!in t,at a il"in ,as servi%e li$e o$ 50 #ears. 7,e
proailit# t,at it ill e9perien%e an" eart,qae o$ !ean
retrn perio" @5 in its "esin li$e ol" e:
/0"' ! ( ! 0)0"
'! ".1"
' "." or "2
+ean Return Period
,&pact Load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1
prin* $/amp!e
t i cutomary to e/pre mpact !oad apercenta*e of tatic force.
$ffect of impact !oad i taken into account inca!cu!ation of !oad.
f impact i 2, I6 #ive !oad i mu!tip!ied 'y 1.2,
Accordin* to A& !ive !oad on han*erupportin* f!oor and 'a!cony contruction hou!d
'e increaed 'y one;third for impact.
,&pact Load
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 2
oad !o&binations
1. 1.3!H 1.3"
2. 3.,!H 3.,"H 3.,#
(. 3.,!H 3.,"H 3.,$! C dead !oad
" C #ive !oad
#C "ind !oad
$ C $arth%uake !oad
AD #oad com'ination
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan (
Jou can ue fo!!owin* !oad com'ination with theparameterA#T9N& 0A!!owa'!e tren*th
ncreae4to account for the 1( a!!owa'!e
increae for the wind and eimic !oad
1. 1.3!H 1.3"
2. 1.3!H 1.3"H 1.3#
(. 1.3!H 1.3"H 1.3$
oad !o&binations
AD #oad com'ination
oad !o&binations
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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )
016D 0oad )ombinations
. .D
#. .#D3 .4L + 0.5(Lror S or R)
-. .#D3 .4(Lror S or R) + (0.5L or 0.8W)
4. 1.2D +1.3W + 0.5L + 0.5(Lror S or R)0. .#D5 ."E3 ".0L + 0.2S
4. ".1D5 (.-Wor ."E
D ' 6ead load L ' 7ive load
7r ' Roof 7ive 7oad W ' $ind load
S ' Snow 7oad E ' Earth8uake load
R ' Rain $ater or ce
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan ,
"hy on!y Dead !oad in e%uation 014 L
There may 'e a i*nificant !ive !oad on atructure durin* contruction.
oreover6 the tructure may have not
reached it fu!! 25 day tren*th a further
contruction i uua!!y carried out .
016D 0oad )ombinations
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan -
;xample: increase in dead load on the ground floor due bric#s
lying on the roof for the construction of the first floor
016D 0oad )ombinations
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan
"hy ne*ative i*n in e%uation 0-4 L
t account for the ta'i!ity of tructure dueto !atera! !oadin*.
016D 0oad )ombinations
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 5
The stabiliEing effect of gravity is reduced and the destabiliEing
effect of lateral load due to wind or earth'ua#e is increased to
have the worse situation
016D 0oad )ombinations
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 7
;xample:1oof beams W8N>2 spaced 7ft="in center=to=center2
support a superimposed dead load of /" psf$ )ode specified roof
loads are >" psf downward *due to roof live load2 snow2 or rain+and " psf upward or downward *due to wind+$ Determine the
critical loading for 016D$
4 31 plf 5 &0 psf 2!0 ft 4 311 plf
7 4 0
*7r or S or ) 4 30 psf 2!0 ft 4 (10 plf
8 4 (0 psf 2!0 ft 4 1&0 plf
9 4 0
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 53
+ $/
$/*> plf+ 3 />! plf
+ $ 5 1!67 5 0!'7r or S or )
$*> plf+ M " M "$!*" plf+ 3 /74 plf
>+ $ 5 1!67r or S or ) 5 0!'7 or 0!/8
$*> plf+ M $8 *" plf+ M"$4*/" plf+ 3 4 plf
/+ $ 5 1!38 5 0!'7 5 0!'7r or S or )
$*> plf+ M $>*/" plf+ M " M"$!*" plf+ 3 88" plf
oad !o&binations
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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 51
!+ $ : 1!09 5 0!'7 5 0!(S$*> plf+ M " M " M "$*" plf+ 3 /! plf
8+ "$J : 1!38 or 1!09
a+ "$J *> plf+ M $> */" plf+ 3 /8 plfb+ "$J*> plf+ = $>*/" plf+ 3 J4 plf
The critical factored load combination for design is the third2 with
a total factored load of 4 plf$
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T'an) -ou.