Lecture -3 Design Loads_updated

7/26/2019 Lecture -3 Design Loads_updated

1/82

N-W.F.P. University ofEngineering and Technology

Peshawar

1

Lecture 03: Design Loads

By: Prof Dr. Akhtar Naeem Khan

[email protected]


2/82

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


4/82

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?


5/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan ,

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


6/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan -

Types of LoadsThree 'road cate*orie:

1. Dead !oad

2. #ive !oad

(. $nvironmenta! !oad


7/82CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan

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


8/82CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 5

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


9/82CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 7

% &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:


10/82CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 13

#ive !oad for variou occupancie

8ccupancy #ive !oad6pf

9eidentia! )3#i'rarie0readin* room4 -3

ercanti!e ,;12,


11/82CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 11

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:


12/82CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan

Types of loads

(. $nvironmenta! #oad

$nvironmenta! !oad inc!ude wind !oad6

now !oad6 rain !oad6 earth%uake !oad6

and f!ood !oad.

12


13/82CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1(

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


14/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1)

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


15/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1,

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


16/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 1-

+ 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


17/82


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


18/82


"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


19/82


Wind load


20/82


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


21/82


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


22/82

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


23/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 2(

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


24/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 2)

AA,


25/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan 2,

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=#+

(&) *"=+


26/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan 2-

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-;


27/82


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


28/82


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-;


29/82


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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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan (3

Wind Load $%a&ple

$ t' ) L d


31/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan (1

$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


32/82

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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CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ((

$art'(ua)e Load$arth%uake "ave

$ t' ) L d


34/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan ()

&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


$ t' ) L d


35/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan (,

,hallow ;Q of depth2 say2 !="#m are far more dangerous than

deep ;Q of depth2 say2 !"=""#m$


$ t' ) L d


36/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan (-

$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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CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan (

$art'(ua)e Loadactor effectin* earth%uake repone of tructure

$ t' ) L d


38/82


$art'(ua)e Load

9epone odification

actor

$art'( a)e Load


39/82


$art'(ua)e Load

9epone odification

actor

$art'(ua)e Load


40/82

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan )3

;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! "#


41/82


$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



42/82


$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!



43/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )(

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




44/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ))

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




45/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ),

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




46/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )-


oi! profi!e



47/82



eimic Eone B&P 3



48/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )5


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$


7 = 't,n8

)t3 "$">! for steel moment resisting frame



49/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan )7


*"$ )a I+: this coefficient is also independent of

the period of vibration$ It is a lowerbound value2 #eeping C at some

minimum value$




50/82

CE-409: Lecture 03 Prof. Dr Akhtar Naeem Khan ,3



*)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$


51/82




*$! )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$


52/82




*"$4 . v I G 1+: this lower bound coefficient is only

applicable to structures located in seismic Eone / and

within J$> miles *! #m+ of a #nown seismic fault$



53/82

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



54/82

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:


$"7TC K $!C6t 3

" if T K $7 sec$



55/82

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,:

,,


ertica! ditri'ution:

ase *'ear $%a&ple


56/82


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


57/82

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


58/82


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



59/82


Tota! force ha!! 'e ditri'uted over hei*ht in the

fo!!owin* manner:


W!

W>

W

W

W/

ase *'ear $%a&ple


60/82


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


61/82


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


62/82


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


63/82


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


64/82


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


65/82


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


66/82

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


67/82

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


68/82

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


71/82


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


72/82


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


73/82

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


74/82


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


75/82

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 .


oad !o&binations


76/82

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


oad !o&binations


77/82

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*.


oad !o&binations


78/82


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


oad !o&binations


79/82


;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


80/82


+ $/

$/*> 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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!+ $ : 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.

Lecture -3 Design Loads_updated

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Transcript of Lecture -3 Design Loads_updated