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Design Example 1 Cantilevered Overhead Sign Support ...

Design Example 1. Cantilevered Overhead Sign Support - Truss with Post Problem statement: Location: I-85 Atlanta, GA. Design a structure to Support a sign 22 ft. long and 11 ft. high. The distance from the center of the upright to the center of the sign is 24 ft. The distance from the base of the post to the center of the sign is 23 ft. and no walkway is included. Use API-5L-X52 round steel pipe (Fy=52 ksi) for the main structure members and ASTM. A-53 Grade B pipe for the secondary members. Use AASHTO M314-90 Grade 55. anchor bolts. The structure would cross a lifeline travelway should it collapse. Reference:E:\BT\Projects\NCHRP 10-80\Examples\Release\ (R). Several commonly-used functions are stored in a separate include file that is used in multiple Example problems. These include functions to determine Cd and resistance values for flexure, shear, and torsion for common steel shapes.

Truss: htruss:=23ft Height at which the truss frames into the post (centroid). ltruss:=35ft Length of the truss. lpanel:=4ft Length and height of a truss panel. dtruss:=3ft Depth of the truss along the z-axis. The following section properties are from the AISC Steel Design Manual. Assume that the truss

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Transcription of Design Example 1 Cantilevered Overhead Sign Support ...

1 Design Example 1. Cantilevered Overhead Sign Support - Truss with Post Problem statement: Location: I-85 Atlanta, GA. Design a structure to Support a sign 22 ft. long and 11 ft. high. The distance from the center of the upright to the center of the sign is 24 ft. The distance from the base of the post to the center of the sign is 23 ft. and no walkway is included. Use API-5L-X52 round steel pipe (Fy=52 ksi) for the main structure members and ASTM. A-53 Grade B pipe for the secondary members. Use AASHTO M314-90 Grade 55. anchor bolts. The structure would cross a lifeline travelway should it collapse. Reference:E:\BT\Projects\NCHRP 10-80\Examples\Release\ (R). Several commonly-used functions are stored in a separate include file that is used in multiple Example problems. These include functions to determine Cd and resistance values for flexure, shear, and torsion for common steel shapes.

2 You may need to reset the path to this file for your computer by right-clicking on the reference. Contents Definitions and Assumptions Dead Loads Wind Loads Wind Load Combinations Factored Actions Truss Chord Resistance Vertical Web Member Resistance Horizontal Web Member Resistance Second Order Effects Design Checks at the Post Base Anchor Bolt Design Base Plate Design Base Plate Weld Design Contents Definitions And Assumptions Definitions and Assumptions: Back to Contents Materials: lbf lbf steel := 490 ice := 3 3. ft ft Fy_main := 52ksi Fy_sec := 35ksi Es := 29000ksi Fy_bp := 36ksi Resistance Factors: flexure := shear := weld := torsion := axial := bolt_tension := bolt_shear := Sign: bsign := 22ft hsign := 11ft wsign := 7psf Psign := bsign hsign wsign = kip Wind Loads: VE1 := 120mph Figure VS2 := 76mph Figure Post: Assume the main post is 24" diameter, t = 5/16".

3 5. dpost := 24in tpost := in 16. Lpost := 25ft dpost_out := dpost + tpost = in dpost_in := dpost tpost = in d 2 2 . post_out dpost_in 2. Apost := = in 4. d 4 4 . post_out dpost_in 4. Ipost := = 1697 in 64. d 4. dpost_in . 4. Spost := . post_out = 140 in3. 32 d post_out 2 2. dpost_out + dpost_in rpost := = in 4. 3. Zpost := = in From Table dpost Es Es p_post := = 39 r_post_comp := = post := = Fy_main Fy_main tpost Es r_post_flex := = Fy_main Es . Qpost := + = Equation dpost Fy_main .. tpost . Truss: htruss := 23ft Height at which the truss frames into the post (centroid). ltruss := 35ft Length of the truss. lpanel := 4ft Length and height of a truss panel. dtruss := 3ft Depth of the truss along the z-axis. The following section properties are from the AISC Steel Design manual . Assume that the truss chords are HSS X 2. dchord := tchord := Achord := 4 3. Ichord := Schord := rchord := 4 3 3.

4 Jchord := Zchord := Cchord := wchord := dchord Es p_chord := = Qchord := Table chord := = Fy_main tchord Assume the vertical struts and diagonals are 1" Standard Pipe: dvdiag := tvdiag := 2. Avdiag := 4 3. Ivdiag := Svdiag := 4 3. rvdiag := Jvdiag := Zvdiag := wvdiag := Es dvdiag p_vdiag := = Qvdiag := Table vdiag := = Fy_sec tvdiag Assume the horizontal diagonals are " Extra Strong Pipe: 2. dhdiag := thdiag := Ahdiag := 4 3. Ihdiag := Shdiag := rhdiag := 4 3. Jhdiag := Zhdiag := whdiag := Es dhdiag hdiag := = p_hdiag := = Qhdiag := Table Fy_sec thdiag Definitions And Assumptions Dead Loads Dead Loads Back to Contents Psign = kip dx_sign := 24ft Distance from post to sign centroid, lever arm Post weight: Ppost := Apost steel Lpost = kip Truss Weights: Chords for truss: nchords := 4 ltruss = 35 ft wchord = plf Pchords := nchords ltruss wchord = kip Vertical Diagonals (for truss): 2 2.

5 Nverticals := 18 ndiagonals := 16 ldiagonal := lpanel + lpanel = ft lvertical := lpanel = ft Pvert := nverticals lvertical wvdiag + ndiagonals ldiagonal wvdiag = kip Horizontal Diagonals (top and bottom): nhorizontals := 18. Phorz := nhorizontals dtruss whdiag = kip Totals: (. PtoPost := Pchords + Pvert + Phorz + Psign = kip ). Pchords Pvert Phorz . PFrontTruss := + + + Psign = kip 2 2 2 . Pchords + Pvert + Phorz wtruss := = plf ltruss PPostBase := PtoPost + Ppost = kip Moments: Mz_sign := Psign dx_sign = 41 kip ft dtruss Mx_sign := Psign = kip ft dtruss/2 is the eccentricity of the sign. 2. ltruss (. Mz_truss := Pchords + Pvert + Phorz . 2. ). = kip ft Chord Forces: Dead load moment: Mz_truss MinFrontTruss := + Mz_sign = kip ft Assume that the sign load is carried entirely by the 2 front truss. MinFrontTruss Pchord := = kip Maximum chord force in the front truss.

6 Lpanel Vertical Strut Forces: PDC_VStrut := PFrontTruss = kip PDC_VDiag := 2 PDC_VStrut = kip Dead Loads Wind Loads Wind Loads Back to Contents Areas: Conservatively consider wind acting simultaneously on both panels of the truss. Post: 2. Apost_E1 := Lpost dpost_out = ft Truss Chords: ( ). Achords_E1 := dchord + tchord ltruss 4 = ft 2. Truss Diagonals: ( ). Adiag_E1 := dvdiag + tvdiag ldiagonal ndiagonals = ft 2. Truss Verticals: ( ). Avert_E1 := dvdiag + tvdiag lvertical nverticals = ft 2. Truss Horizontals: ( ). Ahorz_E1 := dhdiag + thdiag dtruss 2 = ft 2. Pressures: 2. hr lbf This units factor is needed for consistent units in the wind pressure Factor :=. 4 equations. 27878400 ft ztruss := htruss = 23 ft Lpost zpost := = ft 2. zg := 900ft := Article 2.. ztruss . Kz_truss := = Equation zg . 2.. zpost . Kz_post := = zg . G := Gust effect factor, minimum value.

7 Use MRI = 1700 as failure VE1 = 120 mph Extreme I Wind Speed - Figure , 1700 year mean recurrence interval. Kd_post := Directionality factor, see for a round Support . Kd_truss := Directionality factor, see for an overheard truss. Kd_sign := Directionality factor, see Post: ( ). Cd_post_E1 := Cd_cylindrical VE1 , dpost_out = 2. Pz_post_E1 := Kz_post Kd_post G VE1 Cd_post_E1 Factor = psf Ppost_E1 := Pz_post_E1 Apost_E1 = kip Sign: bsign . CdSign := Cd_sign = hsign . 2. Pz_sign_E1 := Kz_truss Kd_sign G VE1 CdSign Factor = psf Psign_E1 := Pz_post_E1 bsign hsign = kip Truss Diagonals: (. Cd_diag_E1 := Cd_cylindrical VE1 , dvdiag + tvdiag = ). 2. Pz_diag_E1 := Kz_truss Kd_truss G VE1 Cd_diag_E1 Factor = psf Pdiag_E1 := Pz_post_E1 Adiag_E1 = kip Truss Verticals (same size as diagonals): (. Cd_vert_E1 := Cd_cylindrical VE1 , dvdiag + tvdiag = ). 2. Pz_vert_E1 := Kz_truss Kd_truss G VE1 Cd_diag_E1 Factor = psf Pvert_E1 := Pz_vert_E1 Avert_E1 = kip Truss Horizontals: (.)

8 Cd_horz_E1 := Cd_cylindrical VE1 , dhdiag + thdiag = ). 2. Pz_horz_E1 := Kz_truss Kd_truss G VE1 Cd_horz_E1 Factor = psf Phorz_E1 := Pz_horz_E1 Avert_E1 = kip Truss Chords: ( ). Cd_chord_E1 := Cd_cylindrical VE1 , dchord + tchord = . 2. Pz_chord_E1 := Factor Kz_truss Kd_truss G VE1 Cd_chord_E1 = psf Pwchord_E1 := Pz_horz_E1 Avert_E1 = kip Totals: PE1 := Phorz_E1 + Pvert_E1 + Pdiag_E1 + Pwchord_E1 + Psign_E1 = kip PE1. wE1 := = plf ltruss Moments: ltruss ME1 := PE1 + Psign_E1 dx_sign = 166 kip ft 2. Chord Forces: ME1. Pchord_E1 := = kip lpanel Reactions to Post: Rpost_E1 := PE1 = kip Parallel to the z axis Torsion (My): My_E1 := ME1 = kip ft Moment (Mz): Mz_DC := Mz_sign + Mz_truss = kip ft Horizontal Strut Forces: Rpost_E1. PE1_HStrut := = kip 2. 5. PE1_HDiag := P = kip 3 E1_HStrut Wind Loads Wind Load Combinations Wind Load Combinations Back to Contents From Article By engineering judgement, Load Case 1 will control.

9 Wind Load Combinations Factored Actions Factored Actions Back to Contents DC_E1 := W_E1 := Dead Load Actions: Pchord = kip PDC_VStrut = kip PDC_VDiag = kip PPostBase = kip Mz_DC = kip ft Mz_sign = kip ft Mx_sign = kip ft Wind Load Actions: Pchord_E1 = kip PE1_HStrut = kip PE1_HDiag = kip VPostBase_E1 := Rpost_E1 = kip Factored Truss Chord Force: Pu_chord := DC_E1 Pchord + W_E1 Pchord_E1 = 56 kip Factored Web Element Forces: Pu_VStrut := DC_E1 PDC_VStrut = kip Pu_VDiag := DC_E1 PDC_VDiag = kip Pu_HStrut := W_E1 PE1_HStrut = kip Pu_HDiag := W_E1 PE1_HDiag = kip Factored Actions at the Post Base: Pu_PostBase := DC_E1 PPostBase = kip Vu_PostBase := W_E1 VPostBase_E1 = kip Mu_yPostBase := W_E1 My_E1 = 166 kip ft Torsion Mu_zPostBase := DC_E1 Mz_DC = kip ft Mu_xPostBase := DC_E1 Mx_sign = kip ft 2 2. Mu_Total := Mu_zPostBase + Mu_xPostBase = kip ft Factored Actions Truss Chord Resistance Truss Chord Resistance Back to Contents flexure = shear = weld = torsion = axial = bolt_tension = bolt_shear = Lchord := lpanel = 4 ft kchord := rchord = in kchord Lchord kl_over_rchord := = rchord Qchord = ( ).

10 Fcr := Fcr_roundTube_compr Fy_main , Es , kl_over_rchord , Qchord = ksi Pn_chord := axial Fcr Achord = kip Pu_chord = 56 kip Pu_chord DesignRatio := = Pn_chord ( ). ChordResistanceCheck := if Pu_chord Pn_chord , "OK" , "No Good" = "OK". Truss Chord Resistance Vertical Web Member Resistance Vertical Web Member Resistance Back to Contents LVDiag := 2 lpanel = ft kVDiag := rvdiag = in kVDiag LVDiag kl_over_rVDiag := = rvdiag Qvdiag = ( ). Fcr := Fcr_roundTube_compr Fy_sec , Es , kl_over_rVDiag , Qvdiag = ksi Pn_vert := axial Fcr Avdiag = kip Pu_VDiag = kip Pu_VDiag DesignRatio := = Pn_vert (. VWebResistanceCheck := if Pu_VDiag Pn_vert , "OK" , "No Good" = "OK"). Vertical Web Member Resistance Horizontal Web Member Resistance Back to Contents 2 2. LHDiag := dtruss + lpanel = 5 ft kHDiag := rhdiag = in kHDiag LHDiag kl_over_rHDiag := = rhdiag Qhdiag = ( ). Fcr := Fcr_roundTube_compr Fy_sec , Es , kl_over_rHDiag , Qhdiag = ksi ( ).


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