Section 2429. Pre-Engineered Steel Truss Recreational Trail Bridge
A. These specifications are for an engineered truss bridge of welded steel construction and are minimum standards for design and construction.
B. Install an engineered truss bridge of welded steel construction manufactured by a company on the approved manufacturer’s list in Materials I.M. 557, Appendix D.
1. Designer Qualifications.
a. No less than 5 years experience in design and fabrication of engineered bridge trusses. In addition, provide information regarding similar projects that were previously completed, including references.
b. Professional Engineer licensed in the State of Iowa.
2. Design Loads and Related Requirements.
a. Design shall comply with “LRFD Bridge Design Specifications” and “LRFD Guide Specifications for the Design of Pedestrian Bridges” as adopted by AASHTO.
b. Loads and Load Combinations:
· Pedestrian load: 90 pounds per square foot applied to the complete width of the deck area shown in the contract documents.
· Vehicle load: apply an H5 design vehicle when clear deck width is 7 feet to 10 feet, apply an H10 design vehicle when clear deck width exceeds 10 feet. Vehicle load need not be placed in combinations with pedestrian load.
· Buoyancy and stream pressure due to submergence when indicated in the drawings.
· Wind loads.
· Fatigue shall be considered. Fracture critical requirements may be waived if indicated in the drawings.
· Other AASHTO loads, including seismic, as appropriate.
· Load combinations as designated by AASHTO.
c. Bridge camber to offset full dead load deflections. For flat, single span bridges, camber at center of bridge span should ordinarily be 1% of the total bridge span.
d. Bridge designed for expansion and contraction with a temperature range of -25°F to 125°F.
e. Teflon or other approved slip pads placed between the bearing and setting plates provided by the bridge manufacturer. At least 1 inch clearance provided between the bridges and the abutments.
f. Welded Tubular Connection Design: according to the Structural Welding Code from ANSI/AWS D1.1, Chapter 10 Tubular Structures.
g. Shop Drawings (Manufacturer’s standard schematic drawings and diagrams):
1) Unique drawings prepared to illustrate the specific portion of the project.
2) All relative design information such as member sizes, bridge reactions, and general notes clearly specified.
3) Accurately prepared to be complete in every respect. Include cross referenced details and sheet numbers. Signed and sealed by a Professional Engineer licensed in the State of Iowa.
4) Submit shop drawings according to Article 1105.03.
h. Maximum deflection due to pedestrian load not to exceed that specified in AASHTO.
i. Vibration not to exceed that specified in AASHTO.
j. If intermediate piers are required for the bridge over a railroad, a minimum 25 foot horizontal and vertical clearance, or a distance as specified elsewhere in the contract documents, from the track is required.
3. Geometry.
a. Low profile (pony truss) half through truss design.
b. Provide one diagonal per panel. Chords, diagonals, verticals, and bracing shall be tube steel.
4. Railings and Accessories.
a. All railings:
· Located on the inside surface of the trusses.
· Smooth inside surface with no protrusions or depressions.
b. Top railings: a minimum of 48 inches above the floor for bicycle applications (AASHTO requires a minimum of 42 inches).
c. Safety railings: a maximum railing opening size shall not allow passage of a 4 inch sphere. All ends of angles and HSS welded and ground smooth.
d. Custom railings may be permitted as shown in the plans.
5. Curbs and Toe Plates.
a. A curb, barrier or toe plate shall be provided that prevents the passage of a 4 inch sphere, where any portion of the sphere is within 4 inches of the walking surface.
b. Trail bridges over roadways shall prevent water runoff over the side of the bridge. Minimum curb height shall be by analysis, but no less than 3 inches.
c. Toe plates, when required, shall be located 2 inches above the floor decks and shall ordinarily have a minimum 4 inch vertical projection.
1. Structural Thickness.
· Structural tubing: minimum material thickness of 1/4 inch.
· All other structural members: minimum material thickness of at least 5/16 inch except the web thickness of rolled beams or channel shall not be less than 1/4 inch. Railing members are not subject to minimum thickness requirements.
2. Unpainted Bridges.
· Unpainted and fabricated from high strength weathering steel.
· All fabrications produced from high strength, low alloy, atmospheric corrosion resistant ASTM A 606 or ASTM A 242 plate and structural shapes.
· Minimum yield (Fy) greater than 50,000 psi.
3. Field Splices.
· Bolted with high strength bolts according to ASTM A 325.
· Type 3 bolts are required for Weathering Steel bridges, according to ASTM A 325 or A 490.
· Field connection bolts tightened by the “turn-of-nut method” to obtain proper torque. See Articles 2408.03, S, 5, b and 2408.03, S, 5, c.
4. Welding.
· Materials: according to AWS.
· Welders: certified according to AWS D1.1.
5. Railings and Accessories.
· Railings (except rub rail): fabricated from steel.
· Rub rail: shall have 5.5 inch vertical projection and be fabricated from treated wood, naturally durable wood, or steel.
6. Toe Plates.
Toe plates, when required, shall be fabricated from plate or channel.
7. Anchor Bolts.
Provided by the manufacturer.
Ensure quality, fabrication, and shop connections comply with AASHTO Specifications for Highway Bridges noted in this specification.
1. Welding.
· Comply with Article 2408.03, B.
· Use E70 or E80 series electrodes that have the same weathering characteristics as corrosion-resistance steel, or the gas metal arc welding process (Short Circuiting Transfer) with Carbon Dioxide/Argon shielding gas with ER80-D2 filler material conforming to AWS A5.28.
2. Welding Operators.
Properly accredited experienced operators, each of whom must:
· Submit satisfactory evidence of experience and skill in welding structural steel with the kind of welding to be used in the project, and
· Have demonstrated the ability to make uniform good welds meeting the size and type of weld required.
The Manufacturer pays all costs associated with the following inspection requirements for fabrication and finishes:
1. Welded tubular connections qualified per AWS D1.1-94 using short circuited gas metal arc process.
2. All welds to be visually inspected.
3. Base material certifications to be supplied by the material suppliers.
Have nondestructive weld testing performed by an independent agency. The Manufacturer pays for nondestructive weld testing.
1. Ten percent of all welds are to be magnetic particle tested.
2. Ultrasonic testing is to be performed on all top and bottom chord, full penetration welds.
Sandblast unpainted weathering steel bridges according to SSPC Surface Preparation Specification No. 6.
1. Manufacturer’s Responsibilities.
· Deliver the bridge by truck to a location nearest to the site accessible by roadways.
· Notify the Contractor in advance of the expected arrival time.
· Provide the Contractor information regarding delays after the truck departs the plant, such as inclement weather, delays in permits, rerouting by public agencies, or other circumstances, as soon as possible.
· Advise the Contractor of the actual lifting weights, attachment points, and all other pertinent information needed to install the bridge.
2. Contractor’s Responsibilities.
· Provide proper lifting equipment.
· Unload the bridge from the truck at the time of arrival.
· Splice and bolt the components.
2429.04 METHOD OF MEASUREMENT.
Measurement will be by count for each Pre-engineered Steel Truss Recreational Trail Bridge installed.
A. Payment for each Pre-engineered Steel Truss Recreational Trail Bridge furnished and erected will be the contract unit price.
B. Payment is full compensation for:
· Designing, manufacturing, delivering, erecting, and assembling the unit complete as shown in the contract documents, and
· Bearing plates, pads, bolts, anchor bolts, grouting, decking, railing, and any other materials, labor, and equipment necessary to complete the bridge in place. Foundations, footings, abutments, piers, and pier caps will be paid for separately.