A modular, rapid-deployment steel girder bridge designed to restore access over a storm-ravaged creek despite severe weight restrictions on the approach route.
The Challenge
- The Problem: Heavy storm events washed out the road at Toro Creek. However, the only access route contained another bridge with a reduced load rating, preventing the contractor from hauling in heavy equipment or long-span pre-fabricated girders.
- The Goal: Design a temporary crossing that could be built using only the equipment already on-site, while meeting HS20 vehicle loading requirements.
The Solution
- Approach: We developed a modular 68′ single-span steel girder bridge designed for “on-site assembly.” By using shorter, 20′ W-beams connected with bolted splices, the contractor could transport materials past the restricted access bridge and assemble the spans in place.
- Key Features: * Modular Splices: Bolted connections for ease of assembly/disassembly.
- Foundation & Decking: Utilized “swamp mats” for the foundation and “crane mats” for the decking to simplify construction.
- Rapid Retrieval: The design allows for quick removal if high waters return before the permanent bridge is completed.
- Sustainability: All materials are fully reusable for future projects.
- Tech/Tools Used: Structural Steel Design (AISC/AASHTO standards), HS20 Load Rating Analysis.
The Impact
- Results: Successfully load-tested with a 38,000 lb grade-all. The bridge showed only 3/4″ of deflection, significantly better than the allowable limits.
- The “So What”: This project showcases the ability to design around logistical “bottlenecks.” By tailoring the design to the contractor’s available equipment and the site’s physical constraints, we restored a vital traffic link that is currently serving the county during the permanent bridge’s design phase.
Lessons Learned
- Logistics-Driven Design: This project reinforced that the best engineering solution isn’t just about structural integrity, but also about the “buildability” of the components within the specific logistical constraints of the site.
