Design Philosophies

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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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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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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: Sa)et* 6nde% or relia ilit* inde%

The larger the sa)er


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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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Design Philosophies