Tied-arch bridge

Some tied-arch bridges only tie a segment of the main arch directly and prolong the strengthened chord to tie to the top ends of auxiliary (half-)arches. The latter usually support the deck from below and join their bottom feet to those of the main arch(es). The supporting piers at this point may be slender, because the outward-directed horizontal forces of main and auxiliary arch ends counterbalance. The whole structure is self-anchored. Like the simple case it exclusively places vertical loads on all ground-bound supports.

An example is the Fremont Bridge in Portland, Oregon which is the second-longest tied-arch bridge in the world and also classifies as a through arch bridge. The Chaotianmen Bridge in Chongqing is a tied-arch, through arch and a truss arch bridge.

Contrarily, the Hart Bridge uses a cantilevered trussed arch, it is self-anchored, but its arch is non-tied. In particular the bridge deck is suspended, but does not tie the arch ends.

Tied arch bridges may consist of successively lined up tied arches in places where a single span is not sufficient. An example for this is the Godavari Arch Bridge in Rajahmundry, India. It has four separate supports on each pier and carries the South Central Railway Line of India. It was designed for 250 km/h rail services.

Like for multi-span continuous beam bridges the tying chord continually spans over all piers. The arches feet coincide (fuse) at the bridge piers. A good visual indication are shared supports at the piers. Dynamic loads are distributed between spans.

This type may be combined with the shouldered tied-arch design discussed above. An example for this is Dashengguan Bridge in Nanjing, China. Its two main arches are shouldered by short auxiliary arches. It is both, a (rigid) tied-arch and a cantilevered trussed arch design. Because the traffic runs through the structural envelope, it is also a through arch bridge. Guandu Bridge in New Taipei, Taiwan is a non-trussed example with three main arches augmented by two auxiliary arch segments at the bridge portals.

The Infinity Bridge uses two arches of different height and span length that both bifurcate before their apex. Above its single, middle-displaced river pier the deck lies between the arches. Contrarily each abutment on the riverbanks supports a single arch end only, in the middle of the deck. The tying chord(s) consist of a composite deck structure. Four post tensioned coil steel cables, two to each side of the walking deck, are locked in place by orthogonally run steel beams every 7.5 meters. The hangers are joined to each of these beams between each cable pair. 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. However, for dynamic and non-uniform loads the visually defining arch continuations must not be neglected.[5]

Usually, for a single span, two tied-arches are placed in parallel alongside the deck, so the deck lies in between the arches. Axial tied-arch or single tied-arch bridges have at most one tied-arch per span that is usually centered in the middle of the bridge deck.[6] An example for this is Hoge Brug in Maastricht. Since it has hinged hangers it might also classify as a Nielsen bridge who held a patent on tied-arch bridges with hinged hangers from 1926.

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

In analogy to twin bridges, two tied arch bridges erected side by side to increase traffic capacity, but structurally independent, may be referred to by tied arch twin bridges. Each in return may use a single- or multi-span, discrete or continuous tied-arch design.