structural investigation report (sign board)
TRANSCRIPT
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SUMMARY
On 06 July 2008, Royal Commission for Jubail and Yanbu (RC), Madinat Al-
Jubail Al-Sinaiyah, has reported noticeable vertical deflection for the overhead
Road Sign on TS1 at exit 5B South Bound. The mentioned signs structure is a
single post cantilever type Trussed-Column Frame Steel Structure. The cantilever
span of the signs structure is equal to 13.0 m extending across the street. Asprovided by RC (Jubail) Road Department, the estimated vertical deflection of the
cantilever arm, at 7.0 m from its post, is about 200 mm. In addition it has beennoticed that the vertical deflection is started around the first 2.70 m from its post.
Based on the E-Mail provided by RC (Jubail) on 08 July 2008, regarding the
above subject, SAUDCONSULT Structural Engineers reviewed the structuraldesign drawings (provided by RC) and made visual site inspection for the
aforementioned signs structure on 26 July 2008, accompanied with the RC
(Jubail) structural engineer.
The aim of this report is to provide an insight on the existing structural conditionof the mentioned signs structure and to present a preliminary proposal for its
structural design to satisfy the strength/serviceability requirements.
The report describes/discuses (briefly) the designed structural system adopted in
comparison with our finding during site inspection, the possible reasons for theabove mentioned excessive vertical deflection and finally presents a preliminary
structural design proposal for the subject signs structure to keep safety,
enhancing its stiffness/stability and limiting deflection.
1. REVIEW OF THE STRUCTURAL DESIGN DRAWINGS/EXISTING
SIGNS STRUCTURE CONDITIONS
Based on the available data shown on the structural designed drawings, the
structural system of the subject sign is composed of cantilever type Trussed-Column Steel Frame. The cantilever span of the frame is composed of steel truss(N-system configuration) of 13.0 m span extending across the street. Figure (1)
shows the general layout of the designed structural system of the mentioned sign.
However, based on the site visual inspection it has been found out that the verticaland diagonal members of the main trusses have been provided (only) on the first
panel and have not been provided on the remaining panels of the truss, as shown
in Figure 2. Furthermore, it has been noticed that the existing cross section of thetop and bottom chords of the truss member is different from that provided on the
structural drawings. In addition, the dimensions of existing sign board are larger
than that provided by the designed drawings and consequently, the expected
applied wind effect on the signs structure shall be larger than that adopted by thedesign drawings.
Mathematical models using STAAD.Pro software computer program have been
adopted to simulate the subject signs structure/existing conditions of the structureload considering the existing structural system of the signs structure and the
proposed/designed structural system. The cantilever arm of the proposed/designed
structural system (see Figure 1) has been analyzed as a three dimensional truss.
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SIGNAGE (FIGURE-1)3D VIEW
Software licensed to [LZ0 + LND]
Job Title
Client
Job No Sheet No Rev
Part
Ref
By Date Chd
File Date/Time
1
ROYAL COMMISION
PROPOSED DESIGN
AF 03-Aug-08 KF
04-Aug-2008 11:52Str2A.std
Print Time/Date: 04/08/2008 11:53 Print Run 1 ofSTAAD.Pro for Windows Release 2005
Load 1
XY
Z
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EXITING SIGN BOARD (FIGURE-2)
Software licensed to [LZ0 + LND]
Job Title
Client
Job No
Part
Ref
By
FileROYAL COMMISION
EXIS
AF
Str2A
Print Time/Date: 05/08/2008 09:03 STAAD.Pro for Windows Release 2005
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The truss members have been simulated by Frame elements. The torsion/bendingstiffness of the adopted frame elements has been released to simulate the truss
member behavior. The top and bottom connections between the truss and its steel
post have been simulated by Pinned supports. However, based on the structuraldetail of the top connection between the truss and its post, the vertical
displacement of the above mentioned top pinned supports has been released.On the other hand, the existing structural system of the cantilever arm of
mentioned sign may not be appropriate to be simulated as space truss, see Fig. 2.As can be seen from the general layout of the existing structural system of the
signs cantilever arm, the slenderness ratios of the top and bottom chords are
exceeding the acceptable limits and the main loads are acting along its spans.Accordingly, the existing structural system of the cantilever arm of mentioned
sign has been simulated as space Frame considering the same support conditions
as stated above.
The existing post base connection and its (post) connections to the cantilever armstructure have been visually inspected and no defects have been noticed. In
addition structural design review for the mentioned (truss/post) connections has
been carried out.
2. STRUCTURAL MODEL RESULTS, ANALYSIS AND DISCUSSION
Based on the results of the mathematical models analysis, it can deduce the
following:
a) The estimated stresses on the existing steel structure of the cantilever armare exceeding the allowable limits, see Figure 3.
b) The estimated maximum elastic deflection on the existing steel structureof the signs cantilever arm is equal to 247 mm, see Table 1. It can benoticed that the estimated maximum elastic deflection is close to its
corresponding existing deflection. It may be worth mentioning that thevertical steel members provided for supporting the sign board have played
a significant role on reducing the mentioned deflection. As can be seen
from Table 2, the expected deflection without the aforementioned
members may exceed 523 mm.
c) The stiffness of the existing steel structure of the sign cantilever arm hasbeen reduced drastically at the end of the orphan panel provided (about
2.60 m from the post). Accordingly, it seems logic for the existing
deflection to be started at this location as mentioned by RC (Jubail) Road
Department.
d) Figures 4 and 5 show a preliminary structural design proposal for the signcantilever arm of the subject road sign to keep safety, enhancing its
stiffness/stability and limiting deflection. In addition, the stiffness/rigidityof base/posttruss connections shall be enhanced by adopting the
following:
i. The use of H.S.B., type 10.9 for the post-truss connections.
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EXITING SIGN BOARD (FIGURE-3)
Software licensed to [LZ0 + LND]
Job Title
Client
Job No
Part
Ref
By
FileROYAL COMMISION
EXIS
AF
Str2A
Print Time/Date: 05/08/2008 07:57 STAAD.Pro for Windows Release 2005
0.951 1
0.727 1.150.498 1.4
1.370.635
11.4
1.190.342
0.7911.06
0.7990.778 0.563
0.94
0.777 0.789
0
0.837 0.68
0.833
1.32
0.849 0.471
1.06
0.507 1.46
0.4281.67 0.982
1.66 1.370.689
1.87 1.04
0.615
0.387 1.06
1.12
0.93
0.525 2.68
2.311.1
0.395 0.67
2.28
0.51 0.719
1.11
1.1e+003
2.89
0.708
1.4
0.985
3.55
0.394
1.6
1.42e+003
2.01 1.15
1.09
0.586 4.61
1.25
1.030.895
0.924 2.42
1.37e+003
1.52
1.42
1.71 0.804
0.537
1.29 1.2
2.46
2.010.674 1.03
0.802
1.78e+0031.562.38
1.51
0.541
1.42
0.499 0.875
0.564
2.27
2.24
2.71
0.624
2.46e+003
2.17
2.18 1.36
0.553
1.26
1.86 3.122.52e+003
0.76
2.28
0.373
1.372.02
0.532
1.55e+0032.1
0.497
1.681.25
0.977
1.67e+0031.29
1.66
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EXITING SIGN BOARD (TABLE-1)
Software licensed to [LZ0 + LND]
Job Title
Client
Job No Sheet No Rev
Part
Ref
By Date Chd
File Date/Time
1
ROYAL COMMISION
03-Aug-08
04-Aug-2008 10:14Str2A-1.std
Print Time/Date: 04/08/2008 14:54 Print Run 1 ofSTAAD.Pro for Windows Release 2005
Node Displacement SummaryNode L/C X
(mm)
Y
(mm)
Z
(mm)
Resultant
(mm)
rX
(rad)
rY
(rad)
rZ
(rad)
Max X 22 6:0.9DL+WL 4.992 -173.849 -168.805 242.371 -0.041 0.015 -0.007
Min X 57 3:WL -4.670 -27.519 -156.603 159.071 -0.040 0.016 -0.002
Max Y 38 4:DL+LL -0.100 2.795 -0.218 2.806 0.001 0.000 -0.001
Min Y 35 5:DL+LL+WL -1.188 -247.109 -96.548 265.303 -0.042 0.008 0.006
Max Z 10 1:DL -0.116 -191.450 3.663 191.485 -0.003 -0.001 -0.008
Min Z 21 6:0.9DL+WL -4.655 -200.526 -168.809 262.162 -0.044 0.016 -0.006
Max rX 4 4:DL+LL -0.190 -48.518 -0.240 48.519 0.014 -0.000 -0.026
Min rX 59 5:DL+LL+WL -4.556 -229.992 -142.155 270.417 -0.048 0.016 -0.015
Max rY 61 6:0.9DL+WL 4.901 -135.459 -118.667 180.153 -0.041 0.017 -0.017
Min rY 36 4:DL+LL 0.349 -218.220 -0.310 218.221 -0.003 -0.002 0.004Max rZ 30 4:DL+LL -0.181 -52.925 1.775 52.955 0.006 0.000 0.011
Min rZ 67 5:DL+LL+WL -3.924 -95.974 -60.121 113.318 -0.024 0.015 -0.033
Max Rst 21 5:DL+LL+WL -4.558 -247.107 -166.875 298.211 -0.043 0.016 -0.006
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EXITING SIGN BOARD (TABLE-2)
Software licensed to [LZ0 + LND]
Job Title
Client
Job No Sheet No Rev
Part
Ref
By Date Chd
File Date/Time
1
ROYAL COMMISION
EXISTNG SIGNAGE
AF 03-Aug-08 KF
04-Aug-2008 10:56Str2A-2.std
Print Time/Date: 04/08/2008 15:05 Print Run 1 ofSTAAD.Pro for Windows Release 2005
Node Displacement SummaryNode L/C X
(mm)
Y
(mm)
Z
(mm)
Resultant
(mm)
rX
(rad)
rY
(rad)
rZ
(rad)
Max X 22 6:0.9DL+WL 4.856 -384.140 -168.232 419.392 -0.036 0.013 -0.014
Min X 57 3:WL -4.713 -22.154 -159.620 161.219 -0.041 0.016 -0.001
Max Y 74 5:DL+LL+WL 1.486 6.267 -7.361 9.780 -0.005 0.007 -0.000
Min Y 35 5:DL+LL+WL 2.665 -522.510 -99.246 531.858 -0.039 0.001 0.014
Max Z 22 2:LL -0.092 -71.141 3.470 71.226 0.003 -0.001 -0.004
Min Z 21 6:0.9DL+WL -4.563 -409.615 -168.242 442.844 -0.042 0.015 -0.013
Max rX 53 4:DL+LL -0.073 -312.002 -2.240 312.010 0.092 0.001 -0.061
Min rX 36 6:0.9DL+WL 4.392 -384.145 -99.158 396.760 -0.045 0.003 0.005
Max rY 58 6:0.9DL+WL 4.846 -363.717 -152.235 394.321 -0.040 0.016 -0.025
Min rY 36 4:DL+LL -0.262 -501.781 -1.148 501.782 -0.001 -0.010 0.009Max rZ 35 5:DL+LL+WL 2.665 -522.510 -99.246 531.858 -0.039 0.001 0.014
Min rZ 65 5:DL+LL+WL -4.152 -238.453 -76.589 250.486 -0.025 0.015 -0.067
Max Rst 21 5:DL+LL+WL -4.407 -522.500 -164.822 547.898 -0.040 0.015 -0.018
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PROPOSED SIGN BOARD (FIGURE-5)
Software licensed to [LZ0 + LND]
Job Title
Client
Job No
Part
Ref
By
FileROYAL COMMISION
PRO
AF
Str2A
Print Time/Date: 05/08/2008 08:48 STAAD.Pro for Windows Release 2005
0.0746 0
0.125 0.05710.0171 0.0
0.129
0.106
0.1540.103
0.103
0.09940.129
0.0694
0.1830.103
0.0171
0.124
0.0867
0.1290.278 0.0223
0.117
0.0231
0.103
0.141 0.149
0.137
0
0.177
0.058
0.175
0.0676
0.0675
0.319
0.342
0.0284 0.17
0.141
0.233 0.0247
0.0657
0.2080.357 0.177
0.0112
0.292 0.008650.0779
0.124
0.414 0.141
0.233
0.00911 0.241
0.141
0.0506
0.0675
0.201
0.127
0.147
0.292
0.4620.16
0.0598
0.0899 0.233
0.0426
0.288
0.324
0.0926
0.201
0.527
0.0579
0.508
0.18
0.16
0.00911
0.42
0.325
0.135
0.15
0.201
0.527
0.576 0.0223
0.134
0.27
0.0426
0.139 0.362
0.105
0.420.21
0.175
0.0644
0.334
0.527
0.112
0.616
0.154
0.337 0.197
0.139
0.628 0.286
0.0773
0.3640.653 0.175
0.0483
0.787 0.2710.471
0.141
0.139
0.628
0.394
0.066
0.384
0.112
0.604
0.0891
0.787
0.0815
0.562 0.628
0.0978
0.0999
0.4971.1
0.0706
0.751
0.0162
0.8760.629
0.0711
1.10.939
0.0978
0.8760.786
0.0875
1.1
0.946
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ii. Stiffened Rectangular Seat Bracket for the lower post-trussconnection
iii. Vertical stiffeners to the post base connection.However, the structural details of these connections shall be subject to
final design
3. CONCLUSION
i. The estimated stresses on the existing steel structure of the cantilever armof the subject road sign are exceeding the allowable limits.
ii. A preliminary structural design for the aforementioned signs cantileverarm has been proposed.
iii. Recommendations for enhancing the base/column-truss connection havebeen proposed.
iv. Accordingly, the existing cantilever arm structure shall be disconnectedand replaced as soon as possible, as per the proposal/recommendationpresented above.
v. The estimated cost of the proposed cantilever arm structure per sign isprovided on Table-3.
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TA
Contract No. 082-C35
Pay Item # Pay Item Description Cantilever sign
UNIT/ Ea
Unit Quantity Unit Price
Demolition of existing str. LS 1 10,000 Removal of existing board, transportation etc.
Str. Steel
Truss Frame & Bracing members Ton 6.00 16,000
Cladding M 90 450
Misc.LS 1 10,000
Sign Painting with Writing LS 1 10,000
Electrical Works
Ligthting fixtures, Cable, Conduits etc. LS 1 35,000
Add Contractor's profit @ 30%
Say SR. 260,000/- per Ea
COST BREAKUP
Contract Title Tareeg Sarie-1
Description Total Cost S R. Remarks
In case of utilization of existing fixtures this amoumay be reduced.
Unit Cost for One Sign 201,500.00
10,000.00
96,000.00
40,500.00
10,000.00
Strengthening the connections,fixing of existing
walkway structure etc.
60,450.00
261,950.00
10,000.00
35,000.00
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