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\SpecificationFunctions.xmcd(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. 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:

Materials:

steel

:=

490

lbf ft3

ice

:=

56.8

lbf ft3

Fy_main := 52ksi Fy_sec := 35ksi

Es := 29000ksi

Fy_bp := 36ksi

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Resistance Factors: flexure := 0.90 shear := 0.90

weld := 0.75 torsion := 0.95 axial := 0.90

bolt_tension := 0.75

bolt_shear := 0.33

Sign: bsign := 22ft

hsign := 11ft

Wind Loads:

VE1 := 120mph VS2 := 76mph

wsign := 7psf Psign := bsignhsignwsign = 1.694kip

Figure 3.8-2a Figure 3.8-4a

Post: Assume the main post is 24" diameter, t = 5/16"

dpost := 24in Lpost := 25ft

tpost

:=

5 in

16

dpost_out := dpost + tpost = 24.3in

dpost_in := dpost - tpost = 23.7in

Apost

:=

dpost_out2 -

4

dpost_in2

=

23.6in2

Ipost

:=

dpost_out4 -

64

dpost_in4

=

1697in4

Spost :=

dpost_out4 - dpost_in4

32dpost_out

=

140in3

rpost :=

dpost_out2 + dpost_in2 = 8.49in 4

Zpost := 1.27Spost = 177.3in3

From Table 5.7.2-1

post :=

dpost tpost

=

76.8

p_post :=

0.07 Es Fy_main

=

39

r_post_comp :=

0.11 Es Fy_main

=

61.3

Qpost

:=

0.67

+

0.038 dpost

Es Fy_main

=

0.946

tpost

r_post_flex :=

0.31 Es Fy_main

=

172.9

Equation 5.10.2.2-1

Truss: htruss := 23ft

ltruss := 35ft lpanel := 4ft dtruss := 3ft

Height at which the truss frames into the post (centroid). Length of the truss.

Length and height of a truss panel.

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 3.5 X 0.188

dchord := 3.5in

Ichord := 2.52in4

Jchord := 5.04in4 wchord := 6.66plf

chord :=

dchord tchord

=

20.1

tchord := 0.174in Schord := 1.44in3 Zchord := 1.93in3

Achord := 1.82in2 rchord := 1.18in Cchord := 2.88in3

p_chord :=

0.07 Es Fy_main

=

39.0

Qchord := 1.0

Table 5.7.2-1

Assume the vertical struts and diagonals are 1" Standard Pipe:

dvdiag := 1.32in Ivdiag := 0.0830in4 Jvdiag := 0.166in4

tvdiag := 0.124in Svdiag := 0.126in3 Zvdiag := 0.177in3

wvdiag := 1.68plf

vdiag :=

dvdiag tvdiag

=

10.6

p_vdiag :=

0.07 Es Fy_sec

=

58.0

Assume the horizontal diagonals are 1.5" Extra Strong Pipe:

dhdiag := 1.90in Ihdiag := 0.372in4 Jhdiag := 0.744in4

thdiag := 0.186in Shdiag := 0.392in3 Zhdiag := 0.549in3

whdiag := 3.63plf

hdiag :=

dhdiag thdiag

=

10.2

p_hdiag :=

0.07 Es Fy_sec

=

58.0

Definitions And Assumptions

Avdiag := 0.460in2 rvdiag := 0.423in

Qvdiag := 1.0 Table 5.7.2-1 Ahdiag := 1.00in2 rhdiag := 0.610in

Qhdiag := 1.0 Table 5.7.2-1

Dead Loads

Dead Loads

Psign = 1.69kip

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dx_sign := 24ft

Distance from post to sign centroid, lever arm

Post weight:

Ppost := ApoststeelLpost = 2.00kip Truss Weights:

Chords for truss: nchords := 4 ltruss = 35 ft wchord = 6.66plf Pchords := nchordsltrusswchord = 0.932kip

Vertical Diagonals (for truss): nverticals := 18 ndiagonals := 16 ldiagonal := lpanel2 + lpanel2 = 5.66 ft

lvertical := lpanel = 4.0 ft Pvert := nverticalslverticalwvdiag + ndiagonalsldiagonalwvdiag = 0.273kip

Horizontal Diagonals (top and bottom): nhorizontals := 18 Phorz := nhorizontalsdtrusswhdiag = 0.196kip

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