CFST bridge

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Wushan Bridge over the Yangtze, 460 m span

The term CFST Bridge was the English short form CFST (arch) bridge borrowed a concrete filled steel tube arch bridge ( with concrete filled steel tube arch bridge called) and thus a construction of arch bridges describes where the carrying sheet of two or more with concrete filled steel pipes, whereby the bridge arch is first built from the empty steel pipes, which are only filled with concrete after its completion.

distribution

CFST bridges have been built frequently, especially in China, since 1990. The Wanchang Bridge with a span of 115 m was the first, followed (until March 2005) by well over 229 CFST bridges with spans over 50 m, including 131 bridges with spans over 100 m and 33 bridges with spans over 200 m, including the Wushan Bridge with 460 m and the Bosideng Bridge with 530 m span.

advantages

CFST bridges have various advantages over conventional arch bridges made of steel or concrete: The empty steel tubes, which are comparatively light in relation to the finished bridge, can be used to create a stable load-bearing system without auxiliary structures such as falsework or temporary supporting pillars. The pipes then take on the functions of formwork and reinforcement for the concrete. The composite structure can withstand both high compressive loads and tensile stresses, since the concrete filling largely prevents the steel pipes from buckling or buckling and the steel casing significantly increases the compressive strength of the concrete. The construction time is well below that of comparable concrete or steel bridges.

description

As a rule, CFST bridges have two load-bearing arched ribs, each consisting of one tube or two parallel tubes with concrete-filled cross connections, or three or four, sometimes six parallel tubes that are stiffened by a lattice made of hollow steel tubes. The two arched ribs are connected by cross members at regular intervals. As a rule, the arched ribs formed by several tubes on the abutment have a larger cross section, which tapers continuously towards the apex of the arch. In bridges with an overhead carriageway, the arched profile often corresponds to a slightly modified chain line , whereas in the case of other types of bridges it is mostly a parabola . The arrow ratio is often 1: 5. The bridge deck is usually a reinforced concrete or prestressed concrete slab, which, depending on its height, is suspended from the bridge arch on ropes or raised on the arch with narrow supports.

Types of bridges

CSFT bridges are available in the different variants of conventional arch bridges, i.e. as so-called real arch bridges (in which the arch transfers its loads to the abutment), in which the roadways are arranged above, in the middle or below, or as so-called fake arch bridges, in which the horizontal forces of the arch are absorbed by steel cables that are readjusted according to the degree of completion of the arch. On the other hand, a Langerscher beam is rare in which the tensile forces are absorbed directly by the roadway below, as this construction only takes effect when the roadway slab is completed. Finally, there is one of Chinese as Vogelflug sheet ( fly-bird-type arch ) designated mixed form, wherein the main arc resting on pillars which are outwardly supported by a respective arc segment with a larger radius and in which the running in the middle of the main arc , but the roadway on the outer segments also absorbs horizontal forces. These basic forms naturally occur in different modifications, especially with regard to the number of bridge fields.

At first only road bridges were constructed as CFST bridges until the Beipanjiang Railway Bridge in Liupanshui District in Guizhou Province was completed in November 2001 . The Qian-jiang No. 4 Hang-zhou Bridge was the first double-decker bridge ; With spans of 2 × 85 m + 190 m + 5 × 85 m + 190 m + 2 × 85 m, it is a total of 1145 m long. With the Lianxiang Bridge in Xiangtan , Hunan , a rare combination of a CFST bridge and a cable-stayed bridge was even realized. On the Wanxian Bridge , which was completed in 1997, a CFST arch was first erected, which, based on the Melan construction method, served as a formwork beam for the concrete arch and was concreted in as reinforcement. The same procedure was used on the Qinglong Railway Bridge for a 350 km / h high speed line to build the largest concrete arched railway bridge in the world.

Construction

Danighe Bridge near Wushan, 400 m span

CFST bridges are built in different ways:

  • In cantilever construction , in which initially only the arch halves anchored back with ropes are made from tubular elements, which are lifted to the assembly site with the help of cable cranes until the arch is finally closed. This method is used in particular when deep, difficult-to-access valleys are to be bridged, since only the abutments have to be concreted in the valley slopes and the pylons of the cable cranes and auxiliary anchors have to be erected, the further construction of the bridge is only supplied by the cable cranes and without contact with the valley floor.
  • with vertical pivoting. In bridges in the lowlands, one half of the pipe bend can first be made horizontally on auxiliary supports and then lifted into the final position with ropes that run over auxiliary pylons (the method occasionally used in other countries of first making the bridge halves in a vertical position and then does not seem to be used with Chinese CSFT bridges.)
  • with lateral pivoting. The arch halves are produced on the valley sides and then hydraulically pivoted into their final position.

After the arch is made, concrete is pressed into the pipes from below. Only then is the roadway suspended or elevated.

See also

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