Bridge Construction

Overview
This project involved rebuilding a previously deteriorated wooden bridge over a stream to support vehicle traffic. The work included removing the old structure, designing a replacement, sourcing appropriate materials, and carrying out construction.

Figure 1: Wooden Bridge to be Replaced

Figure 6: Laying the Support Beams

Figure 8: Completed Bridge

Figure 2: Isometric View — CAD

Figure 3: Side View — CAD

Figure 4: Front View — CAD

Figure 7: Ice and Water Shield Application

Figure 5: Material Transport

Takeaway
Years later, the bridge remains structurally sound, unaffected by changing river levels and continued vehicle traffic. It was a unique and rewarding project that combined engineering design with hands-on construction.

Design and Structural Challenges
A key challenge was designing a bridge that was both structurally sound and practical to build and transport. Material selection had to ensure longevity against constant exposure to the elements. The final design used two sets of three grouped 8"x12" hemlock beams as the primary supports which were chosen for their high strength and resistance to wet/dry cycles. Cross treads and vehicle planks were then installed over the beams to complete the deck. For the footings, concrete blocks were placed at the river’s edge, backfilled with soil, and capped with pressure-treated lumber to support the beams.

Environmental and Logistical Considerations
Stream behavior presented another challenge. The bridge needed to withstand rising water levels without floating or being swept away. To address this, the bridge deck height was set above the 100-year flood level. In addition, the project required securing environmental approvals from the town, coordinating light machinery for placement, and selecting appropriate tools for assembly.

To streamline installation, the primary support beams were partially assembled prior to transport, reducing complexity on construction day. Each set of three beams were grouped using spacer blocks and long threaded rods.