FSSS_571.03_for_LRFD.docx

571.03 Design Requirements. For required loadings use the most recent AASHTO “Standard Specifications for Highway Bridges” and Figure 1.

Design approach guardrail (transitions, length, and anchoring at either end) in conformance with AASHTO’s Roadside Design Guide. The approach guardrail must allow a gradual transition from the flexible approach railing to the more rigid bridge railing.

AASHTO’s Roadside Design Guide defines and provides a formula for calculating minimum “length of need” of the approach guardrail length. The minimum “length of need” depends on the variables that are defined and illustrated in chapter 5 of AASHTO’s Roadside Design Guide. For the Sandy Beach Road the following values for these variables may be used:

1. Runout Length (Lr). Lr is the theoretical distance needed for a vehicle that has left the roadway to come to a stop. For a design speed of 30 mph or less, the RL may be taken as 130 feet.

2. Lateral Extent of Area of Concern (La). The La is the distance from the edge of the road to the far side of a fixed object that is a hazard or the outside edge of the clear zone. The hazard at a bridge is the end of the bridge railing. Where the bridge railing is aligned with the edge of the road, the La may be taken as 4 feet.

3. Tangent Length of Barrier Immediately Upstream of Area of Concern (L1). For low-volume and low-speed roads with flared approach railings, the L1 may be assumed to be 10 feet (approximately one-half the length of a typical transition section).

4. Flare Rate (FR). FR is the ratio of the length versus the lateral offset of the approach railing. For a design speed of 30 mph or less, the FR may be taken as 13:1.

Using the above values and a breakaway cable terminal (BCT) end treatment, the minimum length of approach guardrail for very low-volume, low-speed roads is 25 feet, with a lateral offset of 4 feet.

Other appropriate, approved, crash-tested approach guardrail systems are available. Contact the regional bridge engineer to identify other systems meeting these criteria.

When using state or other federal agency bridge railing plans, consider also using the associated approach guardrail plans.

BRIDGE COATING: The bridge coating shall provide protection for an aggressive marine environment. The coating system shall be either hot dipped galvanized or a three coat moisture cured urethane(Paint System 3, table 563-1) applied in a 2-3 mil thickness (dry)primer, intermediate, and top coat for a total dry thickness of 6-9 mils. New steel surfaces shall be prepared to a near white metal according to SSPC-SP10. In addition, a small volume of matching paint shall be shipped with each bridge in order to provide for the event of field touch up.

When design of the structure is required, submit plans and calculations signed by a professional engineer registered in the state where the bridge will initially be located or in the state where the fabricator’s offices are located.

Consider temporary loads due to handling and erection.

Consider Southeast Alaska’s moist climate and high potential for wood decay and steel deterioration.

Use durable materials to allow removal, transportation, and re-installation using typical forest logging or construction equipment. Use design techniques and fabrication methods to minimize field installation difficulties. Fabricate primary components from steel.

Unless components are furnished by the Government, furnish prefabricated, modular bridge superstructure components complete and in place, including deck, and railing when required, to form a bridge superstructure capable of supporting traffic as soon as construction of approaches is complete. Include all incidental materials required to provide a complete structure ready for use.

Rig main superstructure components with permanent lifting devices to facilitate efficient installation and removal of these items using typical forest logging or construction equipment. Place lifting devices so as not to interfere with traffic.

Design continuous spread or sill type footings between points of superstructure bearing. Provide 5 ft depth of suitable excavated material under the footing and do not exceed 5 kips per square foot of footing-soil contact pressure exerted on the base material, other than solid bedrock. Footing material to be pressure treated wood, glulam, or precast concrete. Native log sills are acceptable if allowed in the contract. Place the front edge of the footing three feet (minimum) back from the top edge of the embankment slope on which it bears. Do not locate the riprap bank protection in this three foot setback. Place footings on a 6 inch layer of crushed aggregate which meets the requirements of the State of Alaska, Standard Specifications for Highway Construction 1998, Table 703-2, grading D1. Extend this leveling course 8 inches (minimum) beyond the edge of the footing.

Design backwalls and wingwalls to retain roadway fill material across the full width of the roadway prism at a slope of 1 vertical to 1.5 horizontal. Extend backwalls to the bottom of the footing. Provide pressure treated wood or precast concrete backwalls. Native log backwalls are acceptable if allowed in the contract.

Provide an untreated timber wearing surface for each longitudinal component. Provide wearing surface planks 3 inches to 4 inches in nominal thickness; 12 inches in nominal width. Extend the wearing surface full length and full width from curb to curb. For bridges installed in a permanent location extend the wearing surface over the top of the backwall. Orient the wearing surface planks parallel to the longitudinal axis of the roadway and offset the longitudinal joints of the wearing surface over the longitudinal joint of the two main bridge components. Install at least one plank after connection of the two components to cover the center joint. Do not locate plank attachment hardware within or above the top ¼ inch of the wearing surface plank. Provide plank attachment hardware that does not extend below the bottom of the deck planks.

When a curb only is system is required, top of curb shall be 15 inches above the top of the wearing surface.

If bridge and approach railing are required, design a bridge railing and approach railing system for 50% of AASHTO rail loading (low volume, single lane bridges). Include in the design proper bridge railing, bridge/approach railing transitions, approach railing, and approach railing terminal sections.

The following modular bridge designs (with curb only) are approved for use in Region 10.

If bridge and approach railing are required, the Contractor is responsible for bridge railing and approach railing design for all bridges.

Hamilton Construction Company

www.hamil.com Bridge lengths of 30, 40, 50, 60, 70, and 80 feet have been approved by Region 10, US Forest Service.

Big “R” Manufacturing and Distributing Company

www.bigrmfg.com Bridge lengths of 10, 20, 30, 40, 50, 60, 70, 80, and 90 feet have been approved by Region 10, US Forest Service.