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1 ! The Most Common Source of AISC Live Webinars Thank you for joining our live webinar today. We will begin shortly. Please standby. Thank you. Need Help? Call ReadyTalk Support: AISC Live Webinars Today s audio will be broadcast through the internet. Alternatively, to hear the audio through the phone, dial For additional support, please press *0 and you will be connected to a live operator. American Institute of Steel Construction 1

2 ! The Most Common Source of AISC Live Webinars Today s live webinar will begin shortly. Please standby. As a reminder, all lines have been muted. Please type any questions or comments through the Chat feature on the left portion of your screen. Today s audio will be broadcast through the internet. Alternatively, to hear the audio through the phone, dial For additional support, please press *0 and you will be connected to a live operator. AISC Live Webinars AISC is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-aia members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation American Institute of Steel Construction 2

3 ! The Most Common Source of AISC Live Webinars Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of AISC is prohibited. The American Institute of Steel Construction 2013 Course Description! The Most Common Source of Presented by Carol Drucker, S.E., P.E. April 10, 2014 Load paths are essential to understand in structural analysis as well as connection design. Learn from an expert in the industry the most common mistakes made in assuming load paths and how they can be avoided. The session pertains to all levels of engineering experience. American Institute of Steel Construction 3

4 ! The Most Common Source of Learning Objectives Gain an understanding of the gravity and lateral systems for steel framed buildings. Learn and understand the load path through trusses and truss connections. Become familiar with solutions to common framing and connection issues in steel framed structures. Gain an understanding of transfer forces. AISC Live Webinars! The Most Common Source of Carol Drucker, S.E., P.E., P. Eng Principal Drucker Zajdel Structural Engineers, Naperville, IL American Institute of Steel Construction 4

5 ! The Most Common Source of By: Carol Drucker, SE, PE, P.Eng 9 Topics Fundamentals Gravity and Lateral Systems Connections Problematic s Good s 10 American Institute of Steel Construction 5

6 ! The Most Common Source of Fundaments Load applied to structure is transferred through the structure to the foundations and ultimately to the ground Loads need a continuous complete load path between elements in a structure Each element along the path must have sufficient strength and stiffness 11 WL WL DL, LL, SL Fundamentals DL, LL WL WL Loads on Structure Dead Live Roof Live/Snow Wind/Earthquake Thermal Soil Ponding/Ice DL, LL Soil DL, LL Soil 12 American Institute of Steel Construction 6

7 ! The Most Common Source of Gravity Slab to Beams Beams to Girders Girders to Columns Columns to Foundation 13 Gravity Slab to Beams Beams to Girders Girders to Columns Columns to Foundation 14 American Institute of Steel Construction 7

8 ! The Most Common Source of Gravity Slab to Beams Beams to Girders Girders to Columns Columns to Foundation 15 Gravity Slab to Beams Beams to Girders Girders to Columns Columns to Foundation 16 American Institute of Steel Construction 8

9 ! The Most Common Source of Fundamentals Shortest is typically best Fundamentals 5 Consider element stiffness Stiffness attacks load 18 American Institute of Steel Construction 9

10 ! The Most Common Source of Fundamentals Higher loaded members have shorter spans More efficient Less efficient 19 Close the Loop and Watch Erection Stub Column in Truss T3 The problem: -T5 supported by T9 -T9 supported by T8 -T8 supported by T3 -T3 supported by T5 Stub Column in Truss T5 20 American Institute of Steel Construction 10

11 ! The Most Common Source of Close the Loop and Watch Erection T3 T5 T8 T9 21 Gravity Remember Statics Missing Moment Connection Missing moment connection for stability at overhang 22 American Institute of Steel Construction 11

12 ! The Most Common Source of Framing TENSION SPLICE Typically larger member with greater load should be continuous 23 Gravity Discontinuous Element Follow 24 American Institute of Steel Construction 12

13 ! The Most Common Source of Gravity Discontinuous Element Overhang produces thrust Thrust resisted by lateral system Must have sufficient continuous load path for applied thrust load to lateral force resisting system 25 Gravity Discontinuous Element Overhang produces thrust Thrust resisted by lateral system Must have sufficient continuous load path for applied thrust load to lateral force resisting system 26 American Institute of Steel Construction 13

14 ! The Most Common Source of Gravity Discontinuous Element Need a complete load path (i.e. load needs to pass through column) Plan view at Column 27 Remember Joint Equilibrium - Sloping Column Equilibrium of sloped column produces thrust Floor beams resist axial load at sloping column From beam to diaphragm From diaphragm to lateral force resisting system From LFRS to foundations 28 American Institute of Steel Construction 14

15 ! The Most Common Source of Remember Joint Equilibrium - Sloping Column Alternate Joint Details 29 Remember Joint Equilibrium Kickers induce tension in floor beams Put axial load on drawings Complete load path 30 American Institute of Steel Construction 15

16 ! The Most Common Source of Continuous Trusses Consider load transfer when sizing members Continuous Trusses Chord may not have sufficient strength at connection 32 American Institute of Steel Construction 16

17 ! The Most Common Source of Continuous Trusses Chord may not have sufficient strength at connection 33 Truss Chords Consider load transfer when sizing members SPLICE 34 American Institute of Steel Construction 17

18 ! The Most Common Source of Truss Chords Consider load transfer when sizing members SPLICE 35 Lateral - Wind Wind on Façade Façade to structure (e.g. beams or diaphragms) Diaphragms to LFRS LFRS to Foundations 36 American Institute of Steel Construction 18

19 ! The Most Common Source of Getting the Load to the Lateral System 37 Getting the Load to the Lateral System +/- 20 k +/- 40 k 38 American Institute of Steel Construction 19

20 ! The Most Common Source of Getting the Load to the Lateral System No transfer force Different beam depths W12x19 W21x73 W10x12 No studs 39 Getting the Load to the Lateral System +/- 30 k +/- 30 k W21x44 (10) W21x73 W21x44 (10) 40 American Institute of Steel Construction 20

21 ! The Most Common Source of Getting the Load to the Lateral System 41 Getting the Load to the Lateral System Drag forces on opposite sides of the column should be equal TF = 14k Horizontal component of brace force is internal to the braced frame and the beam-to-column connection does not need to resist the entire horizontal force component 42 American Institute of Steel Construction 21

22 ! The Most Common Source of Discontinuous Braced Bays Lateral force in a discontinuous bay needs to be transferred to the lateral system below 43 Transfer Loads Team Effort 1. Dependant on diaphragm strength (special attention needed at roof deck) 2. Dependant on actual load combinations 3. Dependant on special project requirements 4. Need a complete load path 44 American Institute of Steel Construction 22

23 ! The Most Common Source of Connections Connections are critical for complete load path A continuous load path is as strong as its weakest link Fine line between load path and equilibrium for connections 45 Critical to Understand the 46 American Institute of Steel Construction 23

24 ! The Most Common Source of Ridge Connections Check for Global Stability 47 Connections - Trusses 48 American Institute of Steel Construction 24

25 ! The Most Common Source of Connections - Trusses Consider work points when designing connections. Work Point Moment due to Beam Shear Connections should not induce moments on supporting members Beam Shear 49 Connections - Trusses Truss End Connections Slot at one chord connection to allow for movement due to truss rotation Alternately, consider some moment in column 50 American Institute of Steel Construction 25

26 ! The Most Common Source of Connections - Trusses Vertical component of diagonal transferred into vertical Welded Truss understand load path Joint must be in equilibrium Check for stiffeners and doublers at relevant sections Check for stiffeners and doublers in chord Pick a load path and stick with it See Blodgett 51 Connections - Trusses Welded Truss understand load path Joint must be in equilibrium Check for stiffeners and doublers at relevant sections Pick a load path and stick with it 52 American Institute of Steel Construction 26

27 ! The Most Common Source of Connections - Trusses Stiffener Welded Truss understand load path Stiffener added to transfer load across joint and avoid stiffeners and doublers in right diagonal 53 Connections - Trusses End Connections 54 American Institute of Steel Construction 27

28 ! The Most Common Source of Connections - Trusses 55 Connections-Bracing TT UFM= TT KISS= 56 American Institute of Steel Construction 28

29 ! The Most Common Source of V c H c M b Connections-Bracing UFM P e b V b P V b r H b P r Vb H b e b M b P( ') V b ' r TT UFM= e c Vc P V b Hc P r r 57 e c Connections-Bracing KISS H b Pcos( ) V c M b H b( e b) M c M b P Vc Psin( ) Mc Vc( ec) H b e b TT KISS 58 American Institute of Steel Construction 29

30 ! The Most Common Source of Connections-Bracing UFM P Hc from gusset-to-column to column-to-beam V c Vb from gusset-to-beam to beam-to-column H c M b Add gravity to Vb Vb H b Consider transfer forces and Hc A H c V b V g Hc A Allows for force redistribution TT UFM= 59 Connections-Bracing KISS e c P NoHc V c M c M b H b e b No Vb Does not impact beam-tocolumn connection Need to consider moment at column TT KISS 60 American Institute of Steel Construction 30

31 ! The Most Common Source of Connections-Bracing KISS BOLT TENSION M c rt n' b dm See Manual Fig. 7-7 CG (tension group) 2r t d m NA CG (compression group) T KISS Method Moment at Column 61 Connections-Bracing UFM Advantage= Possible KISS Advantage= 62 American Institute of Steel Construction 31

32 ! The Most Common Source of Connections-Bracing UFM Special Case II = KISS at Column Webs 63 UFM Special Case II to Column Flange e c P Vc Psin e b V c H c M b H b e c Hc Vc ( eb ) H b Pcos H c M b H b ( e b ) T UFM Special Case II= V b 0 64 American Institute of Steel Construction 32

33 ! The Most Common Source of Vertical Bracing 65 Vertical Bracing Indicate if both top and bottom braces in compression 66 American Institute of Steel Construction 33

34 ! The Most Common Source of Brace to Beam Centers Check for doublers example (bottom brace only) L = Gusset Length 67 Check for doublers Brace to Beam Centers 68 American Institute of Steel Construction 34

35 ! The Most Common Source of Horizontal Bracing Can use horizontal gussets to transfer loads Opening Edge 69 Horizontal Bracing Check Example for doublers Horizontal truss example (bottom brace only) 70 American Institute of Steel Construction 35

36 ! The Most Common Source of Horizontal Bracing Bo Dowswell, MS July Horizontal Bracing Slot Beam Web Can slot beams for horizontal bracing connections to allow for a direct transfer of forces 72 American Institute of Steel Construction 36

37 ! The Most Common Source of Horizontal Bracing Alternately provide a continuous brace or horizontal gussets 73 Horizontal Bracing Consider load path and equilibrium A M=Axe e A 74 American Institute of Steel Construction 37

38 ! The Most Common Source of Moment Connections Consider load path and equilibrium Panel Zone Shear 75 Deflected Shape Joint moments Typ. Lateral Gravity 76 American Institute of Steel Construction 38

39 ! The Most Common Source of Deflected Shape Joint moments Typ. Lateral Gravity 77 Inflection point assumed at h/2 Moment Connections Lateral FBD Vc = (M b )/h Stiffeners if required Vc Pf 1 +Pf 2 Pf 2 = M b2 /d 2 Pf 1 = M b1 /d 1 Vp Mc Mc h Panel Zone, Doublers if Required Vc Vc Vp = Panel Zone Shear = Pf 1 + Pf 2 -Vc Shear Moment 78 American Institute of Steel Construction 39

40 ! The Most Common Source of Moment Connections Doublers M = 0 (M b ) < ( M c ) Sum of beam moments can not exceed sum of column moment strengths Vp max = Panel Zone Shear = 2( Mc)/d b - 2( Mc)/h 79 Moment Connections Doublers Top of Column M = 0 (M b ) < M c At top for column, sum of beam moments can not exceed column moment strengths Vc max = Panel Zone Shear = Mc/d b 80 American Institute of Steel Construction 40

41 ! The Most Common Source of Moment Connections Doublers Add dead load on both sides and live load on one side M D1 M L1 M W1 M D2 M W2 Vp max = Panel Zone Shear = 2( Mc)/d b - 2( Mc)/h 81 Connections Moments to Column Webs Doublers not required Stiffeners Size Stiffeners and Stiffener welds Can be 1-sided or 2- sided Back-up Stiffeners 82 American Institute of Steel Construction 41

42 ! The Most Common Source of Connections Stiffener Beam 1 Beam 2 Dead Load = D 1 Live Load = L 1 Wind Load = W 1 D 1 L 1 W 1 D 2 W 2 Dead Load = D 2 Wind Load = W 2 83 Flange force Connections Stiffener 25K 25K Extend ¾ 10K 10K D 1 +L 1 = 100K 50K 50K 20K 20K D 2 = 40K Reaction due to force W 1 = 20K 25K 5K 25K 5K Gravity Loads Opposite side force transfer 10K 5K 10K 5K Stiffener plate 3-sided weld groups W 2 = 20K 10K 10K 10K 10K 5K 5K Lateral Loads 5K 5K *All welds in the group are to be the same size 84 American Institute of Steel Construction 42

43 ! The Most Common Source of Connections Stiffener Total Flange Weld D 1 +L 1 -D 2 +W 1 +W 2 Web Weld (D 1 +L 1 )/2+(D 2 +L 2 )/2+(W 1 -W 2 )/2 25K 25K 70K 25K 70K 25K Also check D 1 +L 1 +W 1 for total weld 1-side of column 85 Connections Stiffener Beam 1 only Dead Load = D 1 Live Load = L 1 Wind Load = W 1 D 1 L 1 W 1 Back-up Stiffeners Total Flange Weld D 1 +L 1 +W 1 Web Weld (D 1 +L 1 +W 1 )/2 *All welds in the group are to be the same size 30K 60K 30K 30K 60K 30K 86 American Institute of Steel Construction 43

44 ! The Most Common Source of Connections Stiffener Beam 1 only Dead Load = D 1 Live Load = L 1 Wind Load = W 1 D 1 L 1 W 1 No Back-up Stiffeners 87 Connections Stiffener *No Back-up Stiffener Flanges Resist Load Total Flange Weld D 1 +L 1 +W 1 *No Back-up Stiffener Web Resist Load Total Flange Weld - Web Weld - Web Weld D 1 +L 1 +W 1 100K/2 + 20K/2 = 60K 100K+20K=120K 60K *See AISC Design Guide American Institute of Steel Construction 44

45 ! The Most Common Source of Davits 89 Davits Moments at base Moments typically in any direction 90 American Institute of Steel Construction 45

46 ! The Most Common Source of Davit Support Beam FBD Perpendicular beam typically resists the moment applied about the davit support beam s longitudinal axis Typically requires 2, 3, or 4 stiffeners 91 Davits - Alternate Framing Examples 92 American Institute of Steel Construction 46

47 ! The Most Common Source of Davits - Alternate Framing Examples Can transfer load to support through flexure 93 Thermal Expansion Entire frame can expand/ contract Allow for movement Alternately, resist restraining forces Consider thermal loads or allow or movement Less of a concern if entire frame can expand Exterior Frames 94 American Institute of Steel Construction 47

48 ! The Most Common Source of Thermal Expansion Can use single column with slide bearing connection Consider appropriate eccentricity in supporting member 95 Thermal Expansion If possible, avoid connections with slotted holes to accommodate slip Slots need to be long enough to accommodate slip both directions Finger tighten burr threads Bolt threads should be excluded from the shear plane. Bolts should not be over tensioned. Do not over weld 96 American Institute of Steel Construction 48

49 ! The Most Common Source of Thermal Expansion David L. Lawrence Convention Center collapse in February 2007 blamed on expansion joint failure Welded/Bolted Double- Angles should not be used at expansion joints Axial load induces moment through the throat of the fillet weld 97 Framing Hyatt collapse was in part due to revised continuous member 98 American Institute of Steel Construction 49

50 ! The Most Common Source of Simple Connections Beam end connections need to allow for end rotation of simply supported beams (see AISC Spec J1.2) Avoid welded-welded shear plate connections 99 Good - Lateral Axial connection used to transfer chord forces Horizontal bracing used to reinforce diaphragm Axial Connection Moment Connection Plan View 100 American Institute of Steel Construction 50

51 ! The Most Common Source of Good - Lateral Column Above A A A Section A-A Braced Frame 101 Good - Lateral Continuous load path from upper vertical bracing to horizontal bracing to lower vertical bracing Upper Vertical Bracing Gusset for Horizontal Bracing 102 American Institute of Steel Construction 51

52 ! The Most Common Source of Good - Bracing Sway Frames Truss +/- Axial Load 75k 540k 470k 400k 328k 257k 615k 615k 20k 20k 10k 103 Good Transfer Force 104 American Institute of Steel Construction 52

53 ! The Most Common Source of By: Carol Drucker, SE, PE, P.Eng 105 CEU Certificates Within 1 business day You will receive an on how to report attendance from: steel@wyndhamjade.com Be on the lookout: Check your spam filter! Check your junk folder! Completely fill out online form. Don t forget to check the boxes next to each attendee s name! OR American Institute of Steel Construction 53

54 ! The Most Common Source of CEU Certificates Access available in 24 hours Go to: Username: Your Attendee ID (found on your reg. receipt) Password: Your Last Name Completely fill out online form. Don t forget to check the boxes next to each attendee s name! Questions? Please us at webinars@aisc.org. AISC Webinars May 8, 2014: So you want to use K-factors, do you? Effective Length Method vs. Direct Analysis Method Presented by Louis F. Geschwindner American Institute of Steel Construction 54

55 ! The Most Common Source of AISC Seminars Seismic Design Manual and Application of the 2010 Seismic Provisions 24 cities this spring Thank You Please fill out a brief survey at the conclusion of the webinar. Your feedback is greatly appreciated. American Institute of Steel Construction 55