Design Example 1 Cantilevered Overhead Sign Support

399 Pages·2014·5.21 MB·English

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 (F =52 ksi) for the main structure members and ASTM
y
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 C and resistance values for flexure, shear, and torsion
d
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
B ase Plate Design
Base Plate Weld Design
Contents
Definitions And Assumptions
Definitions and Assumptions: Back to Contents
Materials:
lbf lbf
γ := 490 γ := 56.8
steel ice
3 3
ft ft
F := 52ksi F := 35ksi E := 29000ksi F := 36ksi
y_main y_sec s y_bp
Resistance Factors:
ϕ := 0.90 ϕ := 0.90 ϕ := 0.75 ϕ := 0.95 ϕ := 0.90
flexure shear weld torsion axial
ϕ := 0.75 ϕ := 0.33
bolt_tension bolt_shear
Sign:
b := 22ft h := 11ft w := 7psf P := b ⋅h ⋅w = 1.694⋅kip
sign sign sign sign sign sign sign
Wind Loads:
V := 120mph Figure 3.8-2a
E1
V := 76mph Figure 3.8-4a
S2
Post:
Assume the main post is 24" diameter, t = 5/16"
5
d := 24in t := in
post post
16
L := 25ft
post
d := d + t = 24.3⋅in
post_out post post
d := d − t = 23.7⋅in
post_in post post
 2 2
d − d
 post_out post_in  2
A := π⋅ = 23.6⋅in
post
4
 4 4
d − d
 post_out post_in  4
I := π⋅ = 1697⋅in
post
64
 4 4
d − d
 post_out post_in  3
S := π⋅ = 140⋅in
post
32⋅d
post_out
2 2
d + d
post_out post_in
r := = 8.49⋅in
post
4
3
Z := 1.27S = 177.3⋅in
post post
From Table 5.7.2-1
E E
d s s
post λ := 0.07⋅ = 39 λ := 0.11⋅ = 61.3
λ := = 76.8 p_post r_post_comp
post F F
t y_main y_main
post
E
s
λ := 0.31⋅ = 172.9
r_post_flex
F
y_main
 E 
0.038 s
Q := 0.67+ ⋅  = 0.946 Equation 5.10.2.2-1
post
d  F
post  y_main
 
t
 post
Truss:
h := 23ft Height at which the truss frames into the post
truss
(centroid).
l := 35ft Length of the truss.
truss
l := 4ft Length and height of a truss panel.
panel
d := 3ft Depth of the truss along the z-axis.
truss
The following section properties are from the AISC Steel Design Manual.
Assume that the truss chords are HSS 3.5 X 0.188
2
d := 3.5in t := 0.174in A := 1.82in
chord chord chord
4 3
I := 2.52in S := 1.44in r := 1.18in
chord chord chord
4 3 3
J := 5.04in Z := 1.93in C := 2.88in
chord chord chord
w := 6.66plf
chord
E
d s
chord λ := 0.07⋅ = 39.0 Q := 1.0 Table 5.7.2-1
λ := = 20.1 p_chord chord
chord F
t y_main
chord
Assume the vertical struts and diagonals are 1" Standard Pipe:
d := 1.32in t := 0.124in
vdiag vdiag 2
A := 0.460in
vdiag
4 3
I := 0.0830in S := 0.126in
vdiag vdiag
r := 0.423in
4 3 vdiag
J := 0.166in Z := 0.177in
vdiag vdiag
w := 1.68plf
vdiag
E
d s
vdiag λ := 0.07⋅ = 58.0 Q := 1.0 Table 5.7.2-1
λ := = 10.6 p_vdiag vdiag
vdiag F
t y_sec
vdiag
Assume the horizontal diagonals are 1.5" Extra Strong Pipe:
2
d := 1.90in t := 0.186in A := 1.00in
hdiag hdiag hdiag
4 3
I := 0.372in S := 0.392in r := 0.610in
hdiag hdiag hdiag
4 3
J := 0.744in Z := 0.549in
hdiag hdiag
w := 3.63plf
hdiag
E
d s
hdiag λ := 0.07⋅ = 58.0 Q := 1.0 Table 5.7.2-1
λ := = 10.2 p_hdiag hdiag
hdiag F
t y_sec
hdiag
Definitions And Assumptions
Dead Loads
Back to Contents
Dead Loads
P = 1.69⋅kip
sign
d := 24ft Distance from post to sign centroid, lever arm
x_sign
Post weight:
P := A ⋅γ ⋅L = 2.00⋅kip
post post steel post
Truss Weights:
Chords for truss:
n := 4 l = 35ft
chords truss
w = 6.66⋅plf
chord
P := n ⋅l ⋅w = 0.932⋅kip
chords chords truss chord
Vertical Diagonals (for truss):
2 2
n := 18 n := 16 l := l + l = 5.66ft
verticals diagonals diagonal panel panel
l := l = 4.0ft
vertical panel
P := n ⋅l ⋅w + n ⋅l ⋅w = 0.273⋅kip
vert verticals vertical vdiag diagonals diagonal vdiag
Horizontal Diagonals (top and bottom):
n := 18
horizontals
P := n ⋅d ⋅w = 0.196⋅kip
horz horizontals truss hdiag
Totals:
( )
P := P + P + P + P = 3.10⋅kip
toPost chords vert horz sign
P P P 
chords vert horz
P :=  + + + P  = 2.39⋅kip
FrontTruss sign
 2 2 2 
P + P + P
chords vert horz
w := = 40.0⋅plf
truss
l
truss
P := P + P = 5.10⋅kip
PostBase toPost post
Moments:
M := P ⋅d = 41⋅kip⋅ft
z_sign sign x_sign
d
truss
M := P ⋅ = 2.54⋅kip⋅ft d /2 is the eccentricity of the sign.
x_sign sign truss
2
l
truss
( )
M := P + P + P ⋅ = 24.5⋅kip⋅ft
z_truss chords vert horz
2
Chord Forces:
Dead load moment:
M
z_truss
M := + M = 52.9⋅kip⋅ft Assume that the sign load is carried entirely by the
inFrontTruss z_sign
2
front truss.
M
inFrontTruss
P := = 13.23⋅kip Maximum chord force in the front truss.
chord
l
panel
Vertical Strut Forces:
P := P = 2.39⋅kip
DC_VStrut FrontTruss
P := 2⋅P = 3.39⋅kip
DC_VDiag DC_VStrut
Dead Loads
Wind Loads
Back to Contents
Wind Loads
Areas:
Conservatively consider wind acting simultaneously on both panels of the truss.
Post:
2
A := L ⋅d = 50.7⋅ft
post_E1 post post_out
Truss Chords:
( ) 2
A := d + t ⋅l ⋅4 = 42.9ft
chords_E1 chord chord truss
Truss Diagonals:
( ) 2
A := d + t ⋅l ⋅n = 10.89ft
diag_E1 vdiag vdiag diagonal diagonals
Truss Verticals:
( ) 2
A := d + t ⋅l ⋅n = 8.66ft
vert_E1 vdiag vdiag vertical verticals
Truss Horizontals:
( ) 2
A := d + t ⋅d ⋅2 = 1.043ft
horz_E1 hdiag hdiag truss