eighteen steel construction: materials & beams Steel Beam Design Steel Materials Steel Materials American Institute of Steel Construction

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1 ARCHITECTURAL STRUCTURES: FOR, BEHAVIOR, AND DESIGN DR. ANNE NICHOLS SPRING 016 lecture eighteen Steel Beam Design American Institute o Steel Construction anual o Steel Construction ASD & LRFD combined in 005 steel construction: materials & beams Steel Beams 1 Architectural Structures F009abn Steel Beams Steel aterials smelt iron ore add alloing elements heat treatments iron, carbon microstructure AISC Steel aterials cast into billets hot rolled cold ormed residual stress corrosion-resistant weathering steels stainless Hot Rolled Cold Formed Steel Beams 3 A36 steel, JO 1998 Steel Beams 4 AISC 1

2 Steel aterials steel grades Steel Beams 5 AST A36 carbon plates, angles F = 36 ksi & F u = 58 ksi AST A57 high strength low-allo some beams F = 60 ksi & F u = 75 ksi AST A99 or building raming most beams F = 50 ksi & F u = 65 ksi Steel Properties high strength to weight ratio elastic limit ield (F ) inelastic plastic ultimate strength (F u ) ductile strength sensitive to temperature can corrode atigue Steel Beams 6 strain hardening Winnepeg DOT Structural Steel standard rolled shapes (W, C, L, T) open web joists plate girders decking Steel Construction welding bolts Steel Beams 7 Steel Beams 8

3 Steel Construction ire prooing cementicious spra encasement in gpsum intumescent expands with heat sprinkler sstem Uniied Steel Design ASD R a R n bending (braced) = 1.67 bending (unbraced * ) = 1.67 shear = 1.5 or 1.67 shear (bolts & welds) =.00 shear (welds) =.00 * langes in compression can buckle Steel Beams 9 Steel Beams 10 Uniied Steel Design braced vs. unbraced LRFD loads on structures are not constant can be more inluential on ailure happen more or less oten UNCERTAINTY R u D R D R L L R n - resistance actor - load actor or (D)ead & (L)ive load Steel Beams 11 Steel Beams 1 3

4 LRFD Steel Beam Design limit state is ielding all across section outside elastic range load actors & resistance actors = 50ksi E 1 = LRFD Load Combinations 1.4(D + F) 1.(D + F + T)+ 1.6(L + H)+ 0.5(L r or S or R) 1.D + 1.6(L r or S or R) + (L or 0.8W) 1.D + 1.6W + L + 0.5(L r or S or R) 1.D + 1.0E + L + 0.S 0.9D + 1.6W + 1.6H 0.9D + 1.0E + 1.6H ASCE-7 (005) Steel Beams 13 Steel Beams 14 Beam Design Criteria (revisited) Steel Beams strength design bending stresses predominate shear stresses occur serviceabilit limit delection stabilit superpositioning use o beam charts elastic range onl! add moment diagrams add delection CURVES (not maximums) = + lateral stabilit - bracing local buckling stien, or bigger I Steel Beams 15 Steel Beams 16 4

5 Local Buckling steel I beams lange buckle in direction o smaller radius o gration web orce crippling Local Buckling lange web Steel Beams 17 Steel Beams 18 Shear in Web panels in plate girders or webs with large shear buckling in compression direction add stieners Shear in Web plate girders and stieners Steel Beams 19 Steel Beams 0 nisee.berkele.edu/godden 5

6 Steel Beams bearing provide adequate area prevent local ield o lange and web LRFD - Flexure R i i u b n 9 u - maximum moment b - resistance actor or bending = 0.9 n - nominal moment (ultimate capacit) F - ield strength o the steel Z - plastic section modulus* 0. F Z Steel Beams 1 Steel Beams Internal oments - at ield material hasn t ailed I c bh 6 Internal oments - ALL at ield all parts reach ield plastic hinge orms ultimate moment A tension = A compression b c 6 bc 3 p bc 3 = 50ksi 1 E = Steel Beams 3 Steel Beams 4 6

7 n.a. o Section at Plastic Hinge cannot guarantee at centroid Plastic Hinge Development A 1 = A moment ound rom ield stress times moment area p A d 1 n. a A d i i Steel Beams 5 Steel Beams 6 Plastic Hinge Examples stabilit can be eected Plastic Section odulus shape actor, k = 3/ or a rectangle k p 1.1 or an I k Z S plastic modulus, Z Z p Steel Beams 7 Steel Beams 8 7

8 LRFD Shear (compact shapes) i R i = V u v V n = 1.0(0.6F w A w ) V u - maximum shear v - resistance actor or shear = 1.0 V n - nominal shear F w - ield strength o the steel in the web A w - area o the web = t w d LRFD - Flexure Design limit states or beam ailure 1. ielding. lateral-torsional buckling* 3. lange local buckling 4. web local buckling minimum n governs R i i u b n Steel Beams 9 Steel Beams 30 Compact Sections plastic moment can orm beore an buckling criteria b t h andc Steel Beams 31 t w E F E F Lateral Torsional Buckling Steel Beams 3 C b n C. 5 moment based on b p max lateral buckling 1. 5 max 3 4 C b = modiication actor max - max moment, unbraced segment A - moment, 1/4 point B = moment, center point C = moment, 3/4 point A B 3 C 8

9 Beam Design Charts Charts & Delections beam charts solid line is most economical dashed indicates there is another more economical section sel weight is NOT included in n delections no actors are applied to the loads oten governs the design Steel Beams 33 Lecture 15 Su011abn Steel Beams 34 Design Procedure (revisited) 1. Know unbraced length, material, design method (, ) Beam Charts b S x (Appendix A). Draw V &, inding max 3. Calculate Z req d ( a n /) ( u b n 4. Choose (economical) section rom section or beam capacit charts ) Steel Beams 35 Lecture 15 Su011abn Steel Beams 36 9

10 Beam Charts b Z x Beam Design (revisited) 4*. Include sel weight or max it s dead load and repeat 3 & 4 i necessar 5. Consider lateral stabilit Unbraced roo trusses were blown down in 1999 at this project in oscow, Idaho. Photo: Ken Carper Steel Beams 37 F011abn Steel Beams 37 Lecture 15 Su011abn Beam Design (revisited) 6. Evaluate shear - horizontal (V a V n /) or ( Vu v Vn rectangles and W s vmax ) 3V A V A web Beam Design (revisited) 7. Provide adequate bearing area at supports (P a P n /) (P u P n ) V n = 0.6 F w A w general vmax VQ Ib Steel Beams 38 Lecture 15 Su011abn Steel Beams 39 10

11 Beam Design (revisited) 8. Evaluate torsion v F v Beam Design (revisited) 9. Evaluate delections NO LOAD FACTORS circular cross section v T J rectangular v T c 1 ab max ( x) actual allowable Steel Beams 40 Steel Beams 41 Load Tables & Equivalent Load uniorml distributed loads equivalent w max w equivalent 8 L Sloped Beams stairs & roos projected live load dead load over length Steel Beams 4 load or live load delection limit in RED, total in BLACK Architectural Structures perpendicular load to beam: equivalent distributed load: w w adj. cos Steel Beams 43 w wcos 11

12 Steel Arches and Frames solid sections or open web Steel Shell and Cable Structures nisee.berkele.edu/godden Steel Beams 44 Steel Beams 45 Approximate Depths Steel Beams 46 1