Aluminum structures, since they are not as strong as steel, require additional support to carry the maximum load and to provide added stiffness to the overall structure. So ribs are added every 9, 18, 27,or 54 inches for reinforcement.  Majority of the time the corrugated panels are offset to produce maximum seam strength.

The materials used to erect these small bridge replacements come from the manufacture ready for assembly. The corrugated steel or aluminum panels are different sizes depending on the size of the structure. These panels are bolted together using ¾ inch galvanized bolts and nuts. As stated before with aluminum structures, ribs are used for stability and strength. On large structures movement control hooks are used to measure the movement of the structure during the back-fill. Anchor bolts are used on Super-Span structures for concrete thrust beams located at the maximum points of stress. These steel bars with bolts attached are bolted to the outside of the structure at or near the quarter points. Anchor bolts of another sort are bolted around the perimeter of the end of the structure. These bolts serve as the tie to the concrete headwalls.

The process for constructing a steel or aluminum structure varies slightly. A structure can either be pre-assembled and set into place or built into place. Bolting the plates together are done in almost the same manner, but with aluminum structures the seams contain two bolts per corrugation where-as the steel plates only have one. This is due to the obvious reason that steel is stronger than aluminum. Lapping plates can have an effect on the whole structures strength so the laps must be done in accordance with the plans and specs.  On all structures the plates are offset to produce maximum seam strength. Bolts are torqued to +/- 150 foot pounds.

The erection site depending on the engineer is done in accordance of what type of structure is being built. If the structure is one without a bottom, concrete footings are formed for the side corrugated panels to seat and usually bolt into. Full pipes lay on a bed of whatever the engineer has determined. Bedding preparation is critical to both structure performance and service life. The bed should be constructed to uniform line and grade to avoid distortions that may create undesirable stresses in the structure and/or rapid deterioration of the roadway. The bed should be free of rock formations, protruding stones, frozen lumps, roots, and other foreign matter that may cause unequal settlement. It is recommended that the bedding be a stable, well graded granular material.

Satisfactory backfill material, proper placement, and compaction are key factors in obtaining maximum strength and stability. Backfill must have the same requirements of the bedding but must meet AASHTO M145 for soil classifications A-1, A-2, or A-3. Backfill must be placed symmetrically on each side of the structure in six to eight inch loose lifts. Each lift is to be compacted to a minimum of 90 percent density per AASHTO T99. During backfill, only small tracked vehicles (D-4 or smaller) should be near the structure as fill progresses above the crown and to finish grade. A minimum cover may need to be increased during construction to handle the heavier machinery. A poor backfill can cause a collapse of the structure underneath.

Erecting these small and large structures has been a family business for a number of years. The business was started in 1973 and has been in the family for the past 29 years (3rd Generation operated).  We travel to places near and far to build these small bridge replacements. We build a lot in Oregon, Washington, Nevada, and California (northern and southern). Most of all of the structures built in the 70's are still in place and performing as if they were just newly built.

Sonoma Fabricators, Inc. Sales and Assembles these Small Bridges. (New and Replacements)