Steel Beams Lecture 16: Materials, Properties, & Design in Architectural Structures - Prof, Study notes of Architecture

Download Steel Beams Lecture 16: Materials, Properties, & Design in Architectural Structures - Prof and more Study notes Architecture in PDF only on Docsity! Steel Beams 1 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn ELEMENTS OF ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN ARCH 614 DR. ANNE NICHOLS SPRING 2009 lecture sixteen steel construction: materials & beams Steel Beams 2 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Steel Beam Design • American Institute of Steel Construction – Manual of Steel Construction – ASD & LRFD – now combined in 13th ed. (2005) Steel Beams 5 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Structural Steel • standard rolled shapes (W, C, L, T) • open web joists • plate girders • decking Steel Beams 6 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Steel Construction • welding • bolts Steel Beams 7 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn ASD Steel Design • bending (braced) Fb = 0.66Fy • bending (unbraced*) Fb = 0.60Fy • shear Fv = 0.40Fy • shear (bolts) tabulated • shear (welds) Fv = 0.30Fweld * flanges in compression can buckle Steel Beams 10 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn LRFD Steel Beam Design • limit state is yielding all across section • outside elastic range • load factors & resistance factors E 1 fy = 50ksi εy = 0.001724 f ε Steel Beams 11 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn LRFD Load Combinations • 1.4(D + F) • 1.2(D + F + T)+ 1.6(L + H)+ 0.5(Lr or S or R) • 1.2D + 1.6(Lr or S or R) + (L or 0.8W) • 1.2D + 1.6W + L + 0.5(Lr or S or R) • 1.2D + 1.0E + L + 0.2S) • 0.9D + 1.6W + 1.6H • 0.9D + 1.0E + 1.6H ASCE-7 (2005) Steel Beams 12 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Beam Design Criteria (revisited) • strength design – bending stresses predominate – shear stresses occur • serviceability – limit deflection – stability • superpositioning – use of beam charts – elastic range only! – “add” moment diagrams – “add” deflection CURVES (not maximums) + = Steel Beams 15 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Local Buckling • flange • web Steel Beams 16 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Shear in Web • panels in plate girders or webs with large shear • buckling in compression direction • add stiffeners Steel Beams 17 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Steel Beams • bearing – provide adequate area – prevent local yield of flange and web Steel Beams 20 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Internal Moments - ALL at yield • all parts reach yield • plastic hinge forms • ultimate moment • Atension = Acompression yyp MfbcM 2 32 == E 1 σy = 50ksi εy = 0.001724 σ ε Steel Beams 21 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn n.a. of Section at Plastic Hinge • cannot guarantee at centroid • fy·A1= fy·A2 • moment found from yield stress times moment area iianyyp dAfdAfM .1 Σ== Steel Beams 22 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Plastic Hinge Development Steel Beams 25 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn LRFD - Shear Vu - maximum shear φv - resistance factor for shear = 0.9 Vn - nominal shear Fyw - yield strength of the steel in the web Aw - area of the web = twd )6.0(9.0 wywnvuii AFVVR =≤=Σ φγ Steel Beams 26 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn LRFD - Flexure Design • limit states for beam failure 1. yielding 2. lateral-torsional buckling* 3. flange local buckling 4. web local buckling • minimum Mn governs nbuii MMR φγ ≤=Σ y y p F r L × = 300 Steel Beams 27 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Compact Sections • plastic moment can form before any buckling • criteria – – and yf f Ft b 65 2 ≤ yw c Ft h 640 ≤ Steel Beams 30 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Charts & Deflections • beam charts – solid line is most economical – dashed indicates there is another more economical section – self weight is NOT included in Mn • deflections – no factors are applied to the loads – often governs the design Steel Beams 31 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Design Procedure (revisited) 1. Know Fall for the material or FU for LRFD 2. Draw V & M, finding Mmax 3. Calculate Sreq’d or Z 4. Choose (economical) section from section or beam capacity charts ( )bb Ff ≤ )MM( nbu φ≤ Steel Beams 32 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Beam Design (revisited) Unbraced roof trusses were blown down in 1999 at this project in Moscow, Idaho. Photo: Ken Carper • 4*. Include self weight for Mmax – and repeat 3 & 4 if necessary • Consider lateral stability Steel Beams 35 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Beam Design (revisited) 8. Evaluate torsion • circular cross section • rectangular J Tfv ρ = 2 1abc Tfv = ( )vv Ff ≤ Steel Beams 36 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Beam Design (revisited) 9. Evaluate deflections – NO LOAD FACTORS allowableactualxy Δ≤Δ=)(max Steel Beams 37 Lecture 16 Elements of Architectural Structures ARCH 614 S2009abn Load Tables & Equivalent Load load for live load deflection limit in RED, total in BLACK • uniformly distributed loads • equivalent “w” 8 2 max Lw M equivalent=