9-17 Pay Item Pay Unit
Sign Erection, Type ____ (Overhead) Each Sign Erection, Type ____ (Ground Mounted) Each Sign Erection, Type ____ Each Sign Erection, Milemarkers Each Sign Erection, Overlay (Overhead) Each Sign Erection, Overlay (Ground Mounted) Each Sign Erection, Reposition Overhead Each Sign Erection, Logo to Panel Each Sign Erection, Logo Trailblazer Each Sign Erection, Logo Mileage Panel to Sign Each Sign Erection, Relocate Type (Ground Mounted) Each SECTION 906 1 OVERHEAD SIGN STRUCTURE 2
906-1 Description 3
Design, fabricate, furnish and erect various types of overhead sign assemblies. Fabricate 4 supporting structures using tubular members of either aluminum or steel. The types of overhead 5 sign assemblies included in this specification are span structures, cantilever structures and sign 6 structures attached to bridges. 7
906-2 Materials 8
Refer to Division 10. 9 Item Section Structural Steel 1072 Overhead Sign Structures 1096 Signing Materials 1092 Organic -Zinc Repair Paint 1080 -7 Direct Tension Indicators 440 and 1072 -5
906-3 Construction Methods 10
A.General 11 Fabricate overhead sign assemblies in accordance with the details shown in the approved 12 working drawings and the requirements of these specifications. 13 No welding, cutting or drilling will be permitted in the field, unless approved by the 14 Engineer. 15 Drill bolt holes and slots to finished size. Holes may also be punched to finish size, 16 provided the diameter of the punched holes is at least twice the thick ness of the metal being 17 punched. Flam e cutting of bolt holes and slots is not permitted. 18 Erect sign panels in accordance with the requirement for Type A or B signs as indicated in 19 the plans. Field drill two holes per connection in the Z bars for attaching signs to overhead 20 structures. Provide two U -bolts at each U -bolt connection such as each truss chord to sign 21 hanger and each truss chord to walkway support or light support. Provide two U -bolts at 22 each U -bolt connection where ends of truss chords are s upported. The minimum diameter 23 of all U -bolts is 1/2 inch. 24 For all U -bolt connections of hanger beams to overhead assembly truss chords, provide all 25 U-bolts with a flat washer and double nuts at each end of the U -bolts. All double nuts that 26 are on any U -bolt shall be the same thickness and weight. When assembled, the double 27 nuts shall be brought tight against each other by the use of two wrenches. 28
9-18 Use two coats of a n approved non-aerosol organic -zinc repair paint to touch up minor scars 1
on all galvanized materials. 2 For high strength bolted connections, use direct tension indicators in accordance with 3
Article 440 — 8. When galvanized high strength bolts are required, use bolts, nuts and 4
washers meeting Subarticle 1072 -5(F). 5
B.Shop Drawings 6 Design the overhead sign supports, including foundations, prior to fabrication. Submit 7 design calculations and working drawings of the designs to the Engineer for review and 8 acceptance. 9 Have a professional engineer registered in the State of North Carolina, perform the 10 computations and render a set of sealed, signed and dated drawings detailing the 11 construction of each structure. 12 Submit to the Engineer for review and acceptance complete design and fabrication details 13 for each overhead sign assembly, including foundat ions and brackets for supporting the 14 signs and maintenance walkways, if applicable, electrical control boxes, and lighting 15 luminaires. Base design upon the revised structure line drawings, wind load area and the 16 winds speed shown in the plans, and in accordance with the AASHTO Standard 17 Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals , 18 and the Interim Specifications as shown on the plans . 19 Submit electronic (.pdf) copies of completely detailed working drawings and the design 20 calculations including all design assumptions for each overhead sign assembly to the 21 Engineer for approval prior to fabrication. Working drawings shall include complete 22 design and fabrication details, including foundations, provisions for attaching signs, 23 maintenance walkways , when applicable, lighting luminaires to supporting structures, 24 applicable material specifications, and any other information necessary for procuring and 25 replacing any part of the complete overhead sign assembly. 26 Allow 40 days for initial working drawing review after the Engineer receives them. If 27 revisions to working drawings are required, an additional 40 days shall be required for 28 review and approval of the final working drawings. 29 Approval of working drawings by the Engineer shall not relieve the Contractor of 30 responsibility for the correctness of the drawings, or for the fit of all shop and field 31 connections and anchors. 32
C.Design and Fabrication 33
1.The following criteria govern the design of overhead sign assemblies: 34 Design shal l be in accordance with the AASHTO Standard Specifications for 35 Structural Supports for Highway Signs, Luminaires and Traffic Signals , and the 36 Interim Specifications as shown on the plans . 37 There are several design criteria that are specified. They include: 38
a.Overhead cantilever sign structures shall include galloping loads (exclude four - 39 chord horizontal trusses) 40
b.The Yearly Mean Velocity, V mean, in North Carolina shall be assumed to be 11.6 41 mph. 42
c.The Fatigue Importance Category used in the design, for each type of structure, 43 shall be for: 44
i.Cantilevered structures with span greater than 50 feet – Fatigue Importance 45 Category I. 46
9-19 (ii) Cantilevered structures with span less than or equal to 50 feet – Fatigue 1
Importance Category II. 2 (iii) Non-Cantilevered str uctures – Fatigue Importance Category II . 3
2.The following interpretations or criteria shall be used in the design of overhead sign 4 assemblies: 5
a.For design of supporting upright posts or columns, the effective length factor for 6 columns “K”, as provided for in Appendix B, Section B.5 of the AASHTO 7 Standard Specifications for Structural S upports for Highway Signs, Luminaires 8 and Traffic Signals , and the Interim Specifications as shown on the plans , shall be 9 taken as the following, unless otherwise approved by the Engineer: 10
i.Case 1: For a single upright post of cantilever or span type overhead sign 11 structure , the effective column length factor, “K”, shall be taken as 2.0. 12 (ii) Case 2: For twin post truss- type upright post with the post connected to one chord 13 of a horizontal truss, the effective column length factor for that column shall be 14 taken as 2.0. 15 (iii) Case 3: For twin post truss -type upright post with the post connected to two truss 16 chords of a horizontal tri -chord or box truss, the effective column length factor 17 for that column shall be taken as 1.65. 18
b.For twin post truss -type uprights, the unbraced length of the post shall be from the 19 chord to post connection to the top of base plate. 20
c.For twin post truss -type uprights, when the post is subject to axial compression, 21 bending moment, shear, and torsion, the post shall satisfy the AASHTO Standard 22 Specifications for Structural Supports for Highway Signs, Luminaires and Traffic 23 Signals , and the Interim Specifications as shown on the plans . Apply axial 24 compression, bending, and shear equations: Equations 5.12.2.1- 1, 5.12.2.1- 2 and 25 5.12.2.1-5 as found in the sixth edition. To reduce the effects of secondary bending, 26 in lieu of Eq uation 5.12.2.1- 2, the following equation may be used: 27 𝑓𝑓𝑎𝑎 𝐹𝐹𝑎𝑎+𝑓𝑓𝑏𝑏 �1−0.6𝑓𝑓𝑎𝑎 𝐹𝐹é�𝐹𝐹𝑏𝑏+�𝑓𝑓𝑣𝑣 𝐹𝐹𝑣𝑣�2 ≤1.0 28 Where 𝑓𝑓𝑎𝑎 = Computed axial compression stress at base of post 29
d.The base plate thickness for all uprights and poles shall be a minimum of 2 inches but 30 not less than that determined by the following criteria and design : 31
i.Case 1: Circular or rectangular solid base plates with the upright pole welded to 32 the top surface of the base plate with full penetration butt weld, and where no 33 stiffeners are pr ovided. A base plate with a small center hole, which is less than 34 1/5 of the upright diameter, and located concentrically with the upright pole, may 35 be considered as a solid base plate. 36 The magnitude of bending moment in the base plate, induced by the anchoring 37 force of each anchor bolt shall be calculated as 38 M = (PxD 1)/2. 39 (ii) Case 2: Circular or rectangular base plate with the upright pole socketed into and 40 attached to the base plate with two lines of fillet weld, and where no stiffeners are 41 provided, or any base plate with a center hole that is larger in diameter than 1/5 42 of the upright diameter. The magnitude of bending moment induced by the 43 anchoring force of each anchor bolt shall be calculated as 44 M = P x D 2
9-20 Where:
M = Bending moment at the critical section of the base plate induced by one anchor bolt P = Anchoring force of each bolt D1 = Horizontal distance between the center of the anchor bolt and the outer face of the upright, or the difference between the radius of the bolt circle and the radius of the upright D2 = Horizontal distance between the face of the upright and the face of the anchor bolt nut
e.The critical section shall be located at the face of the anchor bolt and perpendicular to 1 the radius of the bolt circle. The overlapped part of two adjacent critical sections shall 2 be considered ineffective. 3
f.The thickness of Case 1 base plate shall not be less than the calculated based on 4 formula for Case 2. 5
g.Uprights, foundations, and trusses that support overhead signs shall be designed in 6 accordance with the contract for the effects of torsion. Torsion shall be considered 7 from dead load eccentricity of these attachments, as well as for the attachments such 8 as supporting brackets, lights, etc., that add to the torsion in the assembly. Truss 9 vertical and horizontal truss diagonals in par ticular and any other assembly members 10 shall be appropriately sized for these loads . 11
h.Uprights, foundations, and trusses that support overhead mounted signs shall be 12 designed for the proposed sign wind area as noted in the contract drawings. Truss 13 vertical and horizontal truss diagonals in particular and any other assembly members 14 shall be appropriately sized for these loads. 15 For non- cantilevered monotube sign support structures, Table 906 -1 and Figure 906 -1 are 16 considered as a required addition to the AASHTO Standard Specifications for Structural 17 Supports for Highway Signs, Luminaires and Traffic Signals , and the Interim Specifications 18 and shown on the plans : 19 TABLE 906 -1 NON -CANTILEVERED MONOTUBE SIGN SUPPOR T STRUCTURES Construction Detail Stress Category Application Example Mechanically Fastened Connections 25. Bolts in tension D Beam column connection for monotube structures 16 Fillet- Welded Connections 26. Fillet weld with one side normal to the applied stress E’ Beam column connection for monotube structures 16 Mechanically Fastened Connections 27. High -Strength bolts in tension D Monotube or truss - chord splice 17 Fillet- Welded Connections 28. Fillet weld with one side normal to the applied stress E’ Monotube or truss - chord splice 17 Mechanically Fastened Connections 29. U -bolts tied to the transverse truss column to keep the chords in place D Horizon tal truss connection with the vertical truss 18 Mechanically Fastened Connections 30. Net section of full - tightened, high- tension bolts in shear B Truss -bolted joint 18 9-21 From NCHRP Report 494 dated 2003 Figure 906- 1. Details shown in Table 906- 1. Fabricate all overhead sign assemblies, including but not limited to foundations, in accordance 1 with the details shown on the approved shop drawings and with the requirements of these 2 Specifications. 3 Fabricate the span and cantilever supporting structures using tubular members of either 4 aluminum or steel, using only one type of material throughout the project. Sign support 5 structures that are to be attached to bridges shall be fabricated using other structural shapes. 6 Horizontal components of the supporting structures for overhead signs may be of a truss design 7 or a design using singular (monotube) horizontal members to support the sign panels. 8 Truss or singular member centerline must coincide with the centerline of sign design area shown 9 on the structure line drawing. 10 Provide permanent camber in addition to dead load camber in accordance with the AASHTO 11 Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic 12 Signals , and the Interim Specifications as shown on the plans . Indicate on the shop drawings 13 the amount of camber provided and the method employed in the fabrication of the support to 14 obtain the camber. 15
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 409–413 of 857.