Post on 27-Feb-2018
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7.3 StressDavid Che
Geneva College
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How to describe thestrength of a
particular type ofmaterial?
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Class demoPush and pull on the arm
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Assumptions & denitionhe material is continuous
!o voids
he material is cohesive
!o crac"s# brea"s# or separations
AFstress
A =
0lim
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!ormal stress$ntensity of force%orce per unit areaActing normal to the
unit area
Pull tensilePush
compressive
A
FzA
z
= 0lim
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earstress
$ntensity of force# orforce per unit area#
acting tangent to area
A
FxA
zx
= lim0
A
FyAzy
=0
lim
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stress
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A
FyA
zy
=0
lim
A
Fz
Az
=0
lim
A
FxA
zx
= lim0
'ubscript
notation
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General state ofstress
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(nits for stress'$ units)
!*m+,# or pascal -. Pa / . !*m+,0
"Pa# 1Pa# GPa# are used more often. !*mm+,/ .1!*m+,/.1pa
(' Customary or %oot2Pound2'econd -%P'0
system)pounds per s3uare inch -psi0"si 2 "ilo2pounds -"ip0 per s3uare inch
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. verageNormal Stress in
an Axially LoadedBar
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he section denes
the cross2sectionalarea of the bar
'ince all such cross
sections are thesame# the bar isreferred to as beingprismatic
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nshe bar remains straight both
before and after the load isapplied
he cross section remains 4at
or plane during the deformationhe hori5ontal and vertical grid
lines inscribed on the bar willdeform uniformly when the bar
is sub6ected to the load
Here we will not considerregions of the bar near its ends#
where application of the
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Assumptions -continued0Homogeneous material)
'ame physical and mechanical propertiesthroughout its volume
$sotropic material)
'ame physical and mechanical properties in alldirections
1any engineering materials t this bill'teel contains thousands of randomly oriented
crystals in each cubic millimeter of its volumeCold2rolled steel and wood are both anisotropic
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AdAdFP
===
A
P=
bartheofareasectional-crossA
mequilibriuofequationstheandsectionsofmethod
theusingdeterminedisParea.sectional-crosstheofcentroid
hethrough tappliediswhichforce,normalresultantinternalP
areasectional-crosson thepointanyatstressnormalaverage
=
=
=
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83uilibrium) 0= ZF
0)()( = AA
=(nia7ial stress) two normal stresscomponents on the element mustbe e3ual in magnitude but opposi
$n direction
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a7imum average normal stress
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87ample 9:;
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87ample 9:;
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'olution)
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Condoor 8ngineering 'tatics Page ,egency al"way
Courtesy Dr: @ee @owery# r:# P:8:
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Condoor 8ngineering 'tatics Page B
he Collapse of the =ansas CityHyatt >egency al"way
he wal"way that collapsed connected thesecond and the fourth 4oors across a multi2storied atrium:
A ma6or design change was introducedduring construction:
n uly .9# .
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Condoor 8ngineering 'tatics Page B.
Collapse of =ansas City Hyatt>egency al"way
riginal design 1odied design
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Homewor"Problems %929F 92,F 92B9
Due) %riday# .*B.*,.