Bridges, box culverts, retaining walls – a few of the structures SEMA builds. Our crews know how to construct them safely and quickly. In fact, we are known for having built some of the more interesting bridges in the industry. On the I-270 flyover project in Denver, for example, we designed an alternate solution to the use of traditional steel girders: curved, precast-concrete U-girders. Each weighing 240,000 – 330,000 lbs., these girders are the largest and heaviest of their kind. Structure meets substance.