twenty one Steel Construction 1 and design APPLIED ARCHITECTURAL STRUCTURES: DR. ANNE NICHOLS SPRING 2018 lecture STRUCTURAL ANALYSIS AND SYSTEMS

Transcription

1 APPLIED ARCHITECTURAL STRUCTURES: STRUCTURAL ANALYSIS AND SYSTEMS DR. ANNE NICHOLS SPRING 2018 lecture twenty one steel construction and design Steel Construction 1

2 Steel cast iron wrought iron - steel cables columns beams trusses frames Steel Construction 2

3 Steel Construction standard rolled shapes open web joists plate girders decking Steel Construction 3

4 Steel Construction welding bolts Steel Construction 4 AISC Education

5 Steel Construction fire proofing cementitious spray encasement in gypsum intumescent expands with heat sprinkler system Steel Construction 5

6 Steel Materials high strength to weight ratio ductile beam size often limited by deflection column size limited by slenderness Steel Construction 6

7 Steel Beams types manufactured shapes castellated Steel Construction 7

8 Steel Beams types wide flange Steel Construction 8

9 Steel Beams types open web joists (manufactured trusses) Steel Construction 9

10 Steel Beams types (more) plate girder decking Steel Construction 10

11 Steel Beams Steel Construction 11

12 Steel Beams lateral stability - bracing local buckling - stiffen Steel Construction 12

13 Local Buckling steel I beams flange buckle in direction of smaller radius of gyration web force crippling Steel Construction 13

14 Local Buckling flange web Steel Construction 14

15 Shear in Web panels in plate girders or webs with large shear buckling in compression direction add stiffeners Steel Construction 15

16 Steel Beams end conditions a) away from connection - full section effective b) high shear only web effective Steel Construction 16

17 Steel Beams end conditions c) bolt holes less material d) local web buckling Steel Construction 17

18 Steel Beams bearing provide adequate area prevent local yield of flange and web Steel Construction 18

19 Steel Beams connections welds bolts Steel Construction 19

20 Steel Design Open Web Joists SJI: Vulcraft: K Series (Standard) 8-30 deep, spans 8-50 ft LH Series (Long span) deep, spans ft DLH (Deep Long Spans) deep, spans ft SLH (Long spans with high strength steel) pitched top chord deep, spans ft Steel Construction 20

21 Steel Design Open Web Joists ASD load for live load deflection limit in RED total in BLACK Steel Construction 21

22 Steel Design Open Web Joists load for live load deflection limit (L/360) in RED total in BLACK Steel Construction 22

23 Steel Beam Design American Institute of Steel Construction steel grades ASTM A36 carbon plates, angles F y = 36 ksi & F u = 58 ksi ASTM A572 high strength low-alloy some beams F y = 60 ksi & F u = 75 ksi ASTM A992 for building framing most beams F y = 50 ksi & F u = 65 ksi Steel Construction 23

24 Steel Beam Design AISC: 14 th ed. combined ASD & LRFD in one volume in 2005 Steel Construction 24

25 Unified Steel Design ASD R a bending (braced) = 1.67 bending (unbraced * ) = 1.67 shear = 1.5 or 1.67 shear (bolts & welds) = 2.00 shear (welds) = 2.00 R n Ω * flanges in compression can buckle Steel Construction 25

26 Unified Steel Design braced vs. unbraced Steel Construction 26

27 LRFD Steel Beam Design limit state is yielding all across section outside elastic range load factors & resistance factors f y = 50ksi f 1 E y Steel Construction 27

28 Load Types D = dead load L = live load L r = live roof load W = wind load S = snow load E = earthquake load R = rainwater load or ice water load T = effect of material & temperature Steel Construction 28

29 LRFD Load Combinations 1.4D 1.2D + 1.6L + 0.5(L r or S or R) ASCE-7 (2010) 1.2D + 1.6(L r or S or R) + (L or 0.5W) 1.2D + 1.0W + L + 0.5(L r or S or R) 1.2D + 1.0E + L + 0.2S 0.9D + 1.0W 0.9D + 1.0E F has same factor as D in 1-5 and 7 H adds with 1.6 and resists with 0.9 (permanent) Steel Construction 29

30 Pure Flexure R M M 0.9F Z i i u b n y M u - maximum moment b - resistance factor for bending = 0.9 M n - nominal moment (ultimate capacity) F y - yield strength of the steel Z - plastic section modulus* Steel Construction 30

31 Internal Moments - at yield material hasn t failed I bh M f f c 6 y y y b(2 c) 2bc f y 6 3 f y Steel Construction 31

32 Internal Moments - ALL at yield all parts reach yield plastic hinge forms ultimate moment A tension = A compression M bc 2 f 3 M p y 2 y y = 50ksi 1 E y = Steel Construction 32

33 n.a. of Section at Plastic Hinge cannot guarantee at centroid f y A 1 = f y A 2 moment found from yield stress times moment area M f A d f A d p y 1 y i i na. Steel Construction 33

34 Plastic Hinge Development Steel Construction 34

35 Plastic Hinge Examples stability can be effected Steel Construction 35

36 Plastic Section Modulus shape factor, k = 3/2 for a rectangle k M p M y 1.1 for an I k Z S plastic modulus, Z Z M f y p Steel Construction 36

37 LRFD Shear (compact shapes) R V V 1.0(0.6 F A ) i i u v n yw w V u - maximum shear v - resistance factor for shear = 1.0 V n - nominal shear F yw - yield strength of the steel in the web A w - area of the web = t w d Steel Construction 37

38 Flexure Design limit states for beam failure 1. yielding L 2. lateral-torsional buckling* 3. flange local buckling 4. web local buckling minimum M n governs p 1.76r y F y E R M M i i u b n Steel Construction 38

39 Compact Sections plastic moment can form before any buckling criteria b f 2t f 0.38 E F y and h t c w 3.76 E F y Steel Construction 39

40 Lateral Torsional Buckling moment based on lateral buckling M C M n b p C Steel Construction 40 b max 12.5M C b = modification factor M max - max moment, unbraced segment M A - moment, 1/4 point M B = moment, center point M C = moment, 3/4 point max 2.5M 2M 4M 3M A B C

41 Beam Design Charts Steel Construction 41

42 Deflection Limits based on service condition no impairment to serviceability avoid ponding L/360 due to live load for beams & girders supporting plaster (service) Steel Construction 42

43 Steel Arches and Frames solid sections or open web Steel Construction 43

44 Steel Shell and Cable Structures Steel Construction 44

45 Approximate Depths Steel Construction 45

46 Unified Column Design limit states for failure 0.90 P F A c n cr g P P n a P P u c n 1. yielding 2. buckling Kl E 4.71 or F e 0.44 F r F y Kl E 4.71 or F e 0.44 F r F y y y F e elastic buckling stress (Euler) Steel Construction 46

47 Unified Column Design P n = F cr A g for for Kl r Kl r where 4.71 E F F cr y 4.71 E F 0.877F F cr F e y 2 E KL r 2 F F e y e F y Steel Construction 47

48 Procedure for Analysis 1. calculate KL/r biggest of KL/r with respect to x axes and y axis 2. find F cr from appropriate equation tables are available 3. compute P n = F cr A g or find f c = P a /A or P u /A 4. is P a P n / or P u P n? yes: ok no: insufficient capacity and no good Steel Construction 48

49 Procedure for Design 1. guess a size (pick a section) 2. calculate KL/r biggest of KL/r with respect to x axes and y axis 3. find F cr from appropriate equations or find a table 4. compute P n = F cr A g or find f c = P a /A or P u /A Steel Construction 49

50 Procedure for Design (cont d) 5. is P a P n / or P u P n? yes: ok no: pick a bigger section and go back to step check design efficiency percentage of stress = if between %: good Pr 100% P if < 90%: pick a smaller section and go back to step 2. c Steel Construction 50

51 Column Tables Steel Construction 51

52 Beam-Column Design moment magnification (P-) M B M u 1 max factored B 1 C m 1 ( P / P ) u e1 C m modification factor for end conditions = (M 1 /M 2 ) or 0.85 restrained, 1.00 unrestrained P e1 Euler buckling strength P 2 EA e1 2 Kl r Steel Construction 52

53 Beam-Column Design LRFD (Unified) Steel for for P r P c P r P c 0.2 : 0.2 : P 8 u M M ux uy 1.0 cpn 9 bm nx bm ny P u M M ux uy 1.0 2c P n bm nx bm ny P r is required, P c is capacity c - resistance factor for compression = 0.9 b - resistance factor for bending = 0.9 Steel Construction 53

54 Construction Supervision proper grade material high strength bolts quality welds proper bolted conditions (ex. sc) fabrication and erection of steel frame connection details Steel Construction 54