3. Design Method of a Low-Cost Steel-Framed Reinforced Concrete Slab Truss Bridge

      Steel truss bridges are frequently used where a comparatively long span is required, and in recent years reinforced concrete (RC) has been increasingly used as the track-supporting slab for reasons of noise reduction. If a steel-framed reinforced concrete (SRC) structure is adopted for the slab, the beam can be made lower (Fig. 1). Track raising can be omitted for bridges adopting this structure before/after the bridge, and weight of steel used can be reduced by about 40% over the conventional type, representing a substantial reduction in construction costs (Fig. 2).
      Since slab joints cannot be created in this structure, harmful cracks can be detected more easily. To control crack occurrence, it is necessary to mix steel fiber with the concrete and conduct verification experimentally. A design method using relatively easy analysis was developed for this purpose. The method incorporates the load assignment effect in the tensile area of the concrete (an area commonly ignored) into the analysis model, and is effective in simulating crack development and changes in the steel-assigned force when cracks appear (Fig. 3). This allows large-scale experimental verification to be omitted in the future.
      The design method developed is described in the Steel Fiber-Reinforced SRC Slab Design Manual, and wide use by design businesses is expected in the future.

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