(1) the use of steel truss arch, with bracket in situ pouring construction;
(2) the use of section steel or steel pipe concrete strong skeleton, no bracket in situ pouring construction;
(3) the use of tower frame diagonal cable method and diagonal suspension pouring, no bracket in situ pouring construction.
Steel pipe concrete strong skeleton in situ casting construction is arranged in the fourth section of this chapter, steel pipe concrete arch bridge construction. The following are introduced above several commonly used construction methods.
China's top-loading reinforced concrete arch bridge using in situ casting construction is not a large number. The more well-known ones are as follows:
(1) 3006 Bridge in Fukou City, Sichuan Province. Bridge span for a single hole 146m, the deck width of 15m, the cross-section is box-shaped, the arch axis is equal cross-section hanging chain line, the height of the arch ring 2.5m, built in 1972;
(2) Fukou City, Sichuan Province, 3007 Bridge, the bridge span for a single hole 170m, the width of the bridge deck is 12m, the cross-section is box-shaped, the arch axis shape is equal cross-section hanging chain line, the height of the arch ring 2.8m, built in 1979;
(1) Fukou City, Sichuan Province, 3006 Bridge. /p>
(3) Dongguan Bridge, Dongguan City, Guangdong Province, the bridge span of 6 holes 68m, the deck width of 12m, built in 1984.
The above three bridges are constructed with steel truss arches, and the following describes the construction method of the 3006 bridge in Ferry City. The construction process of the arch bridge with braced in-situ casting mainly consists of installation of the arch frame, casting of the arch ring, and casting of the building on the arch.
(A) Arch installation
The arch installation of large-span arch bridge often adopts the cantilever installation method
1.Structure type of arch
The steel truss arch is used, and the structural type of arch is selected as the standing assembly truss type arch. The arch is made up of standard section, arch top section, arch foot section and coupling rods. The arch is made up of the standard section, the arch foot section and the linkage bar connected by steel pins, and then the longitudinal and transverse linkage system connects several pieces of the arch into a whole, which can be used as the bracket for pouring the arch ring or the arch ribs. The curvature of the arch axis curve is obtained by changing the length of the link rods. The height of the truss is 3m, and the length of the upper chord is 1.45m. The structure of the arch is shown in Figure 10-2.
2. Arch installation
(1)Arch lifting installation
Arch installation arrangement is shown in Figure 10-3. Before the installation of the arch need to be composed of a frame form of installation unit, its length can include two to three sections of the arch, a frame maximum lifting weight of 200kN. installation from the foot of the arch to the top of the arch, both sides of the symmetry, the arch **** counting eight pieces, the first to install the middle of the four pieces, sealing the arch unloading lifting, and then install the upstream and downstream of each of the two pieces. The arch is installed with a portal cable tower.
The middle four arches can be lifted directly using the law lifting in place. When the arch transport track is fixed in the middle of the tower door, both sides of the arch can be used to exchange lifting method lifting in place. Exchange lifting method lifting procedures are as follows:
①After the frame is transported to the cantilevered workbench under the tower, the front and rear runners are hung up, as shown in Figure 10-4. Among them, No.2 and No.3 runners are installed axial runners, the transportation ropes of No.1 and No.3 runners shall be exchanged, and the transportation ropes of No.1 and No.2 runners shall be cross-bolted.
②Start No. 1, No. 2 skidding group, raise the frame, No. 3 skidding group to follow the tightening (but not force), the frame lifted to the height that can be detached from the suspension platform and transported out of the suspension platform until the due height.
3) For high altitude exchange, the No.2 and No.3 skidder group will directly pick up the frame and transport it to the installation position.
④Installation in place, drive the steel pin and install the lower chord.
⑤Adjust the axis elevation, install the wind hook, set the wind cable and tighten the diagonal cable.
(2)Arch sealing and unloading
Cantilever installation method is used to install the arch. To use low-temperature arch sealing, high-temperature unloading arch method is more appropriate. Unloading should be carried out from the top of the arch to the foot of the arch in symmetrical cycles. A relaxation can not be too much, the diagonal cable basket bolts a relaxation shall not exceed 5cm.
(3) lifting and sealing the arch and unloading notes
①Lifting should be done before the preparatory work, and should be a test spell.
②Before sealing the arch must adjust the arch axis and the node elevation, tighten all lateral wind cable.
②After sealing the arch together before unloading the crane, all the wind hook bolts tightened once.
(2) box section arch ring pouring and unloading arch frame
1. arch ring section pouring
Large span arch bridge arch ring, in order to reduce the shrinkage stress of the concrete and to avoid cracks due to the deformation of the arch frame should be taken as a general degree of segmentation for 6m to 15m. division of the arch section, the arch must be able to make the top of the two sides of the arch can be maintained evenly and symmetrically. Segmentation point should be reserved interval by. The width of the interval joints to facilitate the construction operation and steel connection is appropriate, generally 50cm to 100cm. interval section of the concrete, in order to prevent the delay of the arch circle together and the arch demolition time, can be used than the arch circle higher than the mark of a cable of semi-dry hard concrete.
2. Box-shaped section arch ring pouring
box-shaped section arch ring generally take ring, segmented pouring both sides of the method. Split ring is generally divided into two or three rings. When divided into two rings, the first section of the bottom plate, and then section of the rib wall, partition wall and the top plate. When the three rings are divided, the bottom slab is poured in sections, then the rib walls and partition walls are poured in sections, and finally the top slab is poured in sections. When pouring in segments, two different methods of closing can be adopted: closing the filling interval joints in segments and closing the filling interval joints for the last time after the completion of the full arch. When filling interval joints together by rings, the closed ring layer can have the effect of arch frame. When pouring the upper ring layer, it can reduce the load of the arch frame, but the construction period is longer than that of the one-time closing method. When the last closing method is adopted. Still must be poured ring by ring, but not after pouring a ring together a ring. Rather, it is left to the last together to fill the ring spacing seam together. At this time, the upper and lower rings of the interval should correspond to each other through, its width is generally about 2m, there are reinforcing steel joints spacing joints for about 4m. Figure 10-5 gives 3006 bridge box arch ring in three rings and 9 sections pouring diagram.
3. Unloading arch
Large-span arch bridge using arch in situ casting construction, the work of unloading the arch is quite critical. Arch dismantling should wait until the arch ring concrete reaches a certain strength before dismantling. In order to make the arch supported by the arch ring gravity can gradually transfer to the arch ring itself to bear, the arch can not be suddenly unloaded, but should be carried out in accordance with certain procedures. In order to ensure that the arch can fall evenly according to the design requirements, must use the specialized unloading equipment. For large-span arch bridge unloading equipment commonly used sandbox and jack.
(1) sand cylinder
Sand Jane is generally made of steel plate, the cylinder is loaded with dried sand, the upper part of the piston inserted (wooden or concrete) composition, as shown in Figure 1O-6.
Unloading is by sand from the lower part of the cylinder in the sand drain hole reserved for outflow, so the sand inside the cylinder is required to dry, uniform, clean. Sand cylinder and the piston between the asphalt filling, so as not to sand moisture and not easy to flow out. By the amount of sand discharge can control the height of the arch unloading, so that the opening and closing of the sand drainage hole, unloading several times, and can make the arch fall evenly without vibration. China's 170m reinforced concrete arch bridge used steel sand cylinder diameter of 86cm, the use of good results.
(2) jack
The use of jacks to remove the arch is often with the arch to adjust the internal force at the same time. Generally in the arch of the notch reserved for the placement of jacks, jacks are used to eliminate the shrinkage of concrete, creep and elastic compression of the internal force and make the arch ring from the arch.
(C) arch building
Large span arch bridge arch building construction, should be symmetrical and balanced. The procedure of pouring and the quantity of coagulation during the construction shall meet the design requirements. In the arch building construction process, false to the internal force and deformation of the arch ring and the displacement of the pier now cut and control.