Laboratory Tests of Multiple-Span Reinforced Concrete Arch Bridges

The multiple-span arch bridge differs from a single-span arch in that, tor the latter, the ends are fixed, whereas, for the former, the fixed points of the structure are the outer ends of the two end spans and the bases of the intermediate piers. As a live load crosses a multiple-span arch bridge the uneven loading of the two spans adjacent to a pier produces a horizontal thrust and moment at the top of the pie r which move the top even if the pier bases and abutments are fixed. This movement of the pier top produces reactions at the end of the span differing materially from those that would be produced by a fixed abutment supporting a similar single- span arch carrying the same load.

The structures tested in this investigation include: (1) A three-span structure consisting of a rib without deck; (2) two three-span structures each consisting of a rib, spandrel columns, and deck, the deck being a considerable distance above the rib of the crown; and (3) two three-span structures consisting of a rib, spandrel columns, and deck, the deck being so low as to be integral with the rib at the crown. Of the two structures constituting each of the latter two groups, one had expansion joints in the deck over the piers only, and the other had expansion joints over the piers and at intermediate joints near the one-third point of each spa n. These structures were tested at pier heights of 20 ft, 15 ft, and 10 ft, except the structures having a low deck, which were tested at a pier height of 20 ft only.