Design Philosophies
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Transcript of Design Philosophies
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7/25/2019 Design Philosophies
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DESIGN PHILOSOPHIES
Design should address: UNDERSTRENGTHOVERLOAD
Allowable Stress Design (ASD) Plastic Design (Collapse Design) Load and Resistance Factor Design (LRFD)
RequiredStrength
Availa le Strength!No"inal Resistan#e$
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Allowable Stress Design (ASD) - AISCS 192
F max : "a%i"u" stresses due to &or'ing loads
F all : allo&a le stresses F.S. : (a#tor o) Sa)et* + , !understrength$ F lim : Li"it o) Use)ulness ! F y F u F cr et#$
-an e e%.ressed in ter"s o) Strength
//li""a% S F
F F F all =
Philosophy: 0a%i"u" stress "ust not e%#eedallo&a le stress
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Allowable Stress Design (ASD)
Real Sa)et* Against (ailure is Un'no&n -onservative One Load (a#tor )or All Load T*.es
-o""ents
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Plasti! Design (PD) - AISCS 19"
Ta'es Advantage o) Du#tilit* and Ulti"ate Strength
Philosophy: Limit of Structural Usefulness isload P u that #auses a .lasti#"e#hanis" to )or"
uw P P F L
/$/!(ailure Load
Rea#hes )ailure under )a#tored loads ut sa)e under servi#e loads
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Loa# an# $esistan!e %a!tor Design (L$%D) - 19&"
0a'es )ull use o) test in)or"ation1 design e%.erien#e1engineering 2udg"ent
Probabilistic Analysis
Limit State : Des#ri e a #ondition at &hi#h a stru#ture or .art o) it #eases to .er)or" the intended)un#tion
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Loa# an# $esistan!e %a!tor Design (L$%D) - 19&"
Typical Strength Limit States 3lasti# Strengths 4u#'ling
(ra#ture (atigue Overturning
Typical Ser iceability Limit States !under nor"al servi#e loads$
E%#essive De)le#tions Sli..ing Vi rations -ra#'ing
Deterioration
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Loa# an# $esistan!e %a!tor Design (L$%D) - 19&"
nii RQ Rn : no"inal resistan#eQ i : a..lied loads
: resistan#e )a#tor 5 , !understrength$ : load )a#tor + , !overload$
(or Ea#h Li"it State LR(D Satis)ies
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AISC 'an al
A6S- S.e#i)i#ation Design Aids -atalog o) "ost &idel* availa le stru#tural sha.es
Editions ,78 7+ASD Editions ,91 ,,1 , 7+ LR(D Edition ,1 1 ;
-urrent Edition ,; in#or.orates ASD and LR(D
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AISC 'an al
3art , < Di"ensions and 3ro.erties 3art < General Design -onsiderations 3art ; < Design o) (le%ural "e" ers 3art = < Design o) -o".ression 0e" ers 3art > < Design o) Tension 0e" ers 3art ? < Design o) 0e" ers Su 2e#t to -o" ined Loading 3arts @ to ,> < -onne#tions 3art ,? S.e#i)i#ations and -odes
3art ,@ 0is#/ Data and 0athe"ati#al 6n)or"ation
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AISC S e!i*i!ations (PA$+ 1" o* 'an al)
0ain 4od* < Al.ha eti#all* organi ed to #ha.ters A70 < 0a2or Headings la eled &ith #ha.ter designation )ollo&ed * nu" er < (urther su divisions are nu"eri#all* la eled
A..endi#es < A..endi#es ,7@
-o""entar* < 4a#'ground and ela oration on .rovisions o) the S.e#i)i#ation/ < Organi ed in the sa"e &a* as the s.e#i)i#ation
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Design $e, ire entsS e!i*i!ations - C.a ter /
4, General 3rovisions
4 Loads and Load -o" inations !LR(D or ASD$ < A..li#a le uilding #odes
< 6n the a sen#e use SE6BAS-E @
4; Design 4asis < 4;/, Required Strength: Required strength deter"ined * stru#tural anal*sis
ased on load #o" inations
< 4;/ Li"it State: No a..li#a le strength or servi#ea ilit* li"it state shall ee%#eeded &hen stru#ture su 2e#ted to all load #o" inations
< 4;/; Design )or Strength Using LR(D < 4;/= Design )or Strength Using ASD < 4;/> Design )or Sta ilit*
et#
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Design *or Strengt.
n
a R R
nu R R
ASD LRFD
nii RQ //
li""a% S F
F F F all =
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Loa# Co binations - L$%D
0anual < 3art .age 7C )or LR(D
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Loa# Co binations - ASD
0anual < 3art .age 78 )or ASD
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$esistan!e %a!tors (Manual pp. 2-9)
9/8 )or li"it states involving *ielding 9/@> )or li"it states involvingru.ture
LR(D
,/?@ )or li"it states involving *ielding /9 )or li"it states involving ru.ture
ASD
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L$%D 0 Probabilisti! A roa!.
Stru#tural Sa)et*: A##e.ta l* s"all .ro a ilit* o) !de"and$ e%#eeding R !resistan#e$
Load and Resistan#e (a#tors assure that .ro a ilit* is negligi l* s"all
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L$%D - Design Criteria
9ln 1, 9
Q R
Q R
Q R
( )"ean$deviationBstandard!1
ln::
=+
= V V V
Q R
Q R
mm
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L$%D - Design Criteria
: Sa)et* 6nde% or relia ilit* inde%
The larger the sa)er
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L$%D - Design Criteria
RV
n
m
e R
R
>>/9
=
(or E%a".le
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EFA03LES
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E a le I
A )loor s*ste" has =%>> se#tions s.a#ed C )t on #enter su..orting a dead load >9 .s) andlive load C9 .s)/ The se#tions are si".l* su..orted/ Deter"ine no"inal "o"ent #a.a#it*
=
C
=
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E a le II
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