Tied-arch bridge

However, in a tied-arch or bowstring bridge, these movements are restrained not by the abutments but by the strengthened chord, which ties these tips together, taking the thrusts as tension, rather like the string of a bow that is being flattened.

[1][2] The elimination of horizontal forces at the abutments allows tied-arch bridges to be constructed with less robust foundations; thus they can be situated atop elevated piers or in areas of unstable soil.

[3] In addition, since they do not depend on horizontal compression forces for their integrity, tied-arch bridges can be prefabricated offsite, and subsequently floated, hauled or lifted into place.

The supporting piers at this point may be slender, because the outward-directed horizontal forces of main and auxiliary arch ends counterbalance.

Contrarily each abutment on the riverbanks supports a single arch end only, in the middle of the deck.

Since the beams extend the width of the post-tensioned concrete deck, the tensing cable pairs remain visible.

A close-up of the river pier shows that the structural dead load is tied per span: The larger arch span uses thicker tensing cables and the reflex segments are not suspended from, but supported by steel beams, essentially completing the arches at the river pier.

Some designs tilt the arches outward or inward with respect to the axis running along the bridge deck.

In a 1978 advisory issued by the Federal Highway Administration (FHWA), the FHWA noted that tied-arch bridges are susceptible to problems caused by poor welds at the connection between the arch rib and the tie girders, and at the connection between the arch and vertical ties.

In addition, problems with electroslag welds, while not isolated to tied-arch bridges, resulted in costly, time-consuming and inconveniencing repairs.