2.Design Requirements. All structures shall be designed in accordance with the requirements given in the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, 2009 Edition, and the requirements given in this Section. Fatigue importance factors shall be as follows: SECTION 718 STRUCTURES FOR TRAFFIC CONTROL DEVICES AND HIGHWAY LIGHTING STRUCTURE FATIGUE IMPORTANCE FACTOR CATEGORY Strain Poles No Fatigue Mast Arm Poles/Lighting Poles/ITS Poles less than 45 ft. in height Category II with 25-year service life High Mast Poles/Sign Structures/Overhead Sign Bridges/Lighting Poles/ITS Poles 45 ft. or greater in height Category I Wind pressures shall be calculated in accordance with “Appendix C: Alternate Method for Wind Pressures”. Minimum design wind speed shall be 100 miles per hour {165 km/hr} for Mobile and Baldwin Counties and 80 miles per hour {130 km/hr} elsewhere in the State. The Combined Stress Ratio (CSR), shall be less than or equal to 0.9, for all load cases.
3.Foundations. Foundations shall be located to avoid damaging existing underground installations and avoid conflicting with known future installations such as pipes, conduits, guardrail posts, lighting standards, etc. The design shall be sufficient to provide a minimum factor of safety of 2.0 against overturning and torsion induced displacement.
c.Drilled Shaft Foundations. Drilled shaft foundations shall be placed only in undisturbed material or in fill made by controlled compaction. Drilled shaft foundations for cantilever structures shall be designed to resist the torsional effects of the wind loads.
d.Concrete Spread Footings. Footings shall be placed only in undisturbed material or in fill areas constructed by controlled compaction. Footings for cantilever structures shall be designed to resist the torsional effects of the wind loads.
e.Direct Embedment of Support. Prestressed concrete poles shall be installed by direct embedment in the ground. GFRP poles may be installed by direct embedment in the ground. The design and details of the direct embedment shall be submitted as Working Drawings for Structures. The required embedment is the responsibility of the contractor, however the minimum depth of embedment shall not be less than L/6, where L is the above ground length of the upright member or pole.
f.Pile Foundations. Pile foundations may be required in areas where the upper soil layers will not support a drilled shaft or spread footing. The foundations may be designed with steel piles or prestressed concrete piles. However, steel piles shall not be used in brackish or salt water locations in Mobile or Baldwin counties, or other locations with corrosive environments. Piles shall meet the requirements of Section 505, Piling. g.Anchor Bolts. Foundation anchor bolts for overhead highway sign structures and high mast lighting assemblies shall be Charpy V-Notch tested in accordance with the requirement provided in Section 891. Anchor bolts shall be a minimum one inch in diameter. Overhead sign structures with single pole uprights shall be anchored with at least eight anchor bolts in each base plate. Overhead sign structures with double pole (truss type) uprights shall be anchored with at least four anchor bolts in each base plate. Traffic signal poles and luminaire poles shall be anchored with at least four anchor bolts. High mast lighting assembly poles shall be anchored with at least eight anchor bolts. SECTION 718 STRUCTURES FOR TRAFFIC CONTROL DEVICES AND HIGHWAY LIGHTING h.Base Plates. All base plates shall be designed by calculating the bending moment about a line that is taken at the edge of the upright and is the shortest diagonal across the plate. The required thickness of the plate shall be based on the section modulus at the diagonal line using 60 % of the width of that line. The allowable stresses for a base plate shall be: 90 % of the yield strength of the base plate for plates that are designed for the yield moment of the upright or; 90 % of the allowable stresses for the Group loading for plates that are designed for the actual upright service load moment.
i.Overhead Roadway Sign Structures. All overhead sign structures shall be supported by a reinforced concrete footing. The overhead portion of the structure shall be attached to the footing by means of base plates and anchor bolts. The vertical dead load deflection of cantilever sign structures shall not exceed L/120, where "L" is the cantilever length in inches {millimeters}. The vertical support for a cantilever structure shall be a round uniform diameter tube which has adequate moment of inertia, without additional reinforcement, to limit the dead load deflection of the arm, including the deflection caused by bending in the vertical support, to L/120 and to a maximum angular deflection of the centerline of the upright, at the top, in relation to the centerline at its base, of 1°40'. Horizontal trusses (span type) shall be limited to a vertical dead plus ice load deflection of L/240, where "L" is the total truss length center to center of supports in inches {millimeters}. A uniform camber, in accordance with the requirements of Section 9 of the AASHTO Sign Specifications , shall be provided for all horizontal portions of a structure. The use of full penetration circumferential welds on upright poles is not allowed. Horizontal trusses of triangular cross-section are not allowed. Flange plates that are used for splicing overhead truss chords and uprights shall be designed using the requirements given for BASE PLATES. Design and basic member shape once selected shall be used throughout the project. The detail drawings shall list all ASTM or AASHTO material specifications to be used for all the structural elements. Brackets shall be provided for the mounting of the required flat panel signs. These brackets shall permit mounting the sign faces at an angle of five (5) degrees from vertical except for louvered panels which shall be mounted vertically. This five degree angle shall be obtained by rotating the front top edge of the sign away from the vertical position. All brackets shall be of lengths sufficient for the heights of the signs being supported. Where required by the contract plans, tubular structures shall have electrical outlets provided on a front chord member and shall have hand holes within twelve inches of the base of vertical supports. If necessary, in order to comply with design requirements, compensation for loss in section shall be accomplished by reinforcement. Maintenance walkways, when required by the plans, shall be provided in front of the lower front chord. No part of the walkway shall be located so as to obstruct normal viewing of the lower portion of the sign.
j.Traffic Signal Poles. The structural analysis of a pole shall be made at the base of the pole, and at every tenth point interval up the pole. The maximum deflection of the centerline at the top of the pole in relation to the centerline at its base, due to the moment load of the signal and support bracket, shall not exceed two and one half percent of the pole height. Calculations shall be submitted to verify this deflection. At intersections involving four traffic signal poles, each pole shall be designed equally for the most severe loading condition at the intersection. The pole base design shall conform to the following table of standard parameters if the maximum bending moment in the pole is less than or equal to 300 kip-ft. SECTION 718 STRUCTURES FOR TRAFFIC CONTROL DEVICES AND HIGHWAY LIGHTING TRAFFIC SIGNAL POLE BASE STANDARD PARAMETERS Pole Type Moment Range (kip-ft.) Bolt Circle (Diameter) (inches) Bolt Diameter (inches) Bolt Quantity Base Plate Thickness (inches) P-120 Up to 120 20 2 4 2 P-170 121 – 170 20 2 6 2 P-225 171 – 225 22 2 6 2 P-300 226 – 300 26 2 8 2 If the bending moment is greater than 300 kip-ft, the bolt circle or bolt quantity, or both, shall be different from that given in the table for the standard parameters. If the proposed difference is in the diameter of the bolt circle, the diameter shall be a minimum of 27 inches.
k.Luminaire Poles. High mast lighting assembly poles shall be supported by a reinforced concrete footing. A luminaire pole shall be analyzed at the base of the pole, at every tenth point interval up the pole, at section changes and at the points above and below each slip joint splice. Design calculations shall be submitted to verify that the maximum allowable deflections will not be exceeded.
l.Intelligent Transportation Systems and Traffic Surveillance Poles. Poles used for mounting Intelligent Transportation Systems, traffic surveillance devices, or other similar devices, shall be designed in accordance with the requirements given for luminaire poles and any additional criteria (i.e., more stringent deflection, vibration damping, etc.) provided on the contract plans.