Based on the investigation and research of old bridges, through technical and economic comparisons, we chose to make full use of the original bridge to fight for width, and use the abutment to change the arched structure into a plate-type structure to meet the requirements of over-limitation transportation.
Baokang has more than half a metre of mountains and mountains. The geographical environment is very poor. There are also many bridges. In addition to the poor economic conditions, there are many bridges built before 2000 and there are many old bridges to be repaired.
The old highway bridge has the characteristics of low load level and long service life. From the analysis of technical data, most of the bridges are three unknown: 1 I do not know the basal geology; 2 I do not know the basic depth; 3 I do not know the shading some standards. From the analysis of bridge technology, because the riverbed is washed by floods, the bottom of the river bed is deepened, and the foundations of bridge piers and abutments are exposed and emptied, resulting in uneven settlement. As a result, additional stress occurs on the abutment and arch, cracking occurs, and some of them even open and close. Phenomenon; Some bridges are due to the high abutment, which is affected by the driving and earth pressure behind the platform, and the abutment is cracked, convex and other diseases; due to the long application time, the concrete deck pavement of bridge deck will cause cracking and falling. Falling diseases. According to the bridge technology, it is determined that most of the three types of bridges are. Following the development of the national economy and the construction of key projects, the load on highway bridges now has three characteristics:
1 The volume of traffic continues to increase; 2 Heavy-duty vehicles have increased and overloaded; 3 Over-limit transport has occurred and increased. According to the current situation of bridges and transportation, the bearing capacity of the bridge and the passing vehicle load is one of the hostile forces of the highway and the transportation. The reinforcement of old bridges and the carrying capacity of the old bridges to ensure the safety of transportation are the missions facing now and in the future. According to the composition of the bridge, this article introduces some methods for strengthening the bridge.
1. Grout Grout Grout Grouting is to inject concrete (sand) pulp and epoxy resin (sand) slurry produced by a certain proportion into the gaps of structures through a spraying machine to fill the cracks and avoid rebars. Rust and advance the role of the structure of the overall strength. Cracks are more widespread in bridge diseases. There are many elements of cracks and they are very messy. Once a crack occurs in a structure, the stress redistribution occurs in the force section, which means that the useful section of the force becomes smaller, the structural stress increases, and the bearing capacity decreases. Plug grouting is to fill the cracks in the structure with cementing materials, so that the effect and transmission of force can be restored to the original conditions as much as possible.
Plug grouting is generally used to deal with cracks in the upper and lower parts of the bridge. Grouting is divided into cement paste, cement mortar, epoxy resin paste, epoxy resin, and mortar. Which one to choose depends on the actual situation. General cement (sand) slurry is used for cracks in stone piers, benches and arches. The size of the cracks is a good choice for grouting. It is not a matter of sand mixing. The use of cement (sand) slurry is cheap and effective. Epoxy resin slurry is generally used for reinforced concrete structures. Due to the small cracks in reinforced concrete components, it is easy to be filled and has good adhesion. Epoxy resin mortar is mostly used for bridge cracks.
The general method of plug grouting is to use a 1:1 cement mortar to make a joint, and to reserve a grouting hole with a diameter of about 6 to 8 mm during the jointing. The distance between the holes depends on the width of the crack, and the gap between the holes is 0.6 to 1.0. m, the gap between the small holes 0.4-0.6m. After the mortar has reached a certain strength, it can be grouted. The cracks of reinforced concrete beams are relatively small, and the joints are filled with epoxy resin. Any hole larger than o.2mm should be filled with grouting. The hole spacing is generally o.25-o.30m. The grouting method is roughly the same as that for cement slurry. In the reinforcement of highway old bridges, plug grouting is one of the methods for induction and treatment. It is widely used, and through trial and application surveys, the role is good.
2. On the basis of investigation and research of old bridges, the upper structure was reconstructed through technical and economic comparisons, and the bridges were selected to make full use of the original bridges, and the abutment structure was changed to a plate-type structure by using abutments to make it meet the limit of transportation. Guiqiu.
2.1 Sham-Kiu Bridge For the old bridges that cannot meet the requirements for exceeding the limit of transportation, after the technical and economic comparisons, the bridges are bridged according to the over-limit transport load scheme adopted in practice to ensure the safety of over-limit transportation.
2.2 The use of the original abutment to change the arch structure to a plate structure For a small span stone arch bridge, due to the thickness of the arch circle can not meet the over-limit transport requirements or uneven settlement due to poor foundation, resulting in cracking of the arch ring, reduce the bearing capacity, can be used This method.
3. Reinforced abutments of the lower part of the old bridge, especially the abutments with higher heights, are affected by driving loads and earth pressure. The most common problems are cracking of abutments, protruding bellows, collapse of the wing walls, cracking, and misalignment. For stone arch bridges with small spans and little water flow, we chose to reinforce the reinforced concrete structures within the bridge spans.
4. The foundation of the old bridge foundation reinforcement bridge is especially the shallow foundation on the natural foundation. Due to the shallow depth of embedment, it is vulnerable to river water flushing and emptying. Diversion of the river to the bridge approached the bridge, causing the foundation of the abutment to empty and the approach road to be destroyed. The foundation of the bridge is somewhat fragile, resulting in uneven settlement of the abutment, resulting in cracking of the abutment. For the above diseases, we use the riverbed with mortar stone paving, paving the upper riverbed, setting up the foundation of the pile to extend the abutment, etc.
For bridges with small spans, due to the diversion of river water, the flood directly erodes the foundation of the abutment, causing the bases to empty or even drop their feet. This can be reinforced by laying slabs of concrete No. 15 in the bridge span scheme, with a paving thickness of 30 cm. Two water intercepting walls are installed on the paving, and the cutoff wall has a depth of 1m and a width of 0.6m. This method was used to reinforce 8 bridges and culverts. For riverbed transitions upstream of bridges, diversion of waterways, floods directly eroded the abutment foundations and abutment approaches, resulting in bridges with abutment emptying and approach roads being damaged, and adopting spur dike and other regulating structures in the correct orientation of the upper reaches of the bridge to transfer river water. Import the main channel.
5. Cracking or peeling of the pavement of the deck of the bridge deck pavement reinforcement. It is easy for the reinforced concrete girder bridge to corrode the steel bar and weaken the bridge's horizontal generality; for the stone arch bridge, due to the rain and water seepage of the bridge deck, The water content of the filler on the arch increases the water seepage phenomenon of the arch ring; due to the damage of the bridge deck pavement, the bridge deck is poor in smoothness, when the vehicle passes, the bridge vibrates, and the helium affects the bridge. It also increased the disease on the bridge deck. According to the specific conditions of the bridge, different reinforcement methods are selected. For the long-term use and serious damage, the removal and correction plan shall be adopted. For diseases that are lighter and have a shorter service life, and the concrete strength is still in line with the program requirements, the disease will be treated first. If the program load standard is not reduced, a program for paving the asphalt and gravel layer can be used.
6. Disposal of old highway bridges The strengthening of the treatment of old highway bridges, and repairs and reinforcements to keep them in normal working conditions and give full play to the role of old bridges is a major mission of the highway handling section. The over-limit transportation and handling of the old bridge has the characteristics of short construction period, high demand, small amount of work, and large amount of pre-work. The highway over-limit transportation is generally for the key construction projects of the state or province. Our experience is:
(1) For road sections that are often oversized, bridges undergo critical inspections and processing, collect initial file information, and grasp their dynamics;
(2) Pay attention to the key and restrict the project during construction;
(3) Pay attention to the collection and collection of initial data in the reinforcement project, and build experience for the reinforcement project in the future;
(4) Fully mobilize the enthusiasm of grass-roots units and correctly handle the liaison between responsibilities, rights and interests.
The repair and reinforcement of the old highway bridge is attributed to the bridge project and it is not possible to rebuild lightly. The reinforcement of the old bridge is harder than the new construction. Due to the repair and reinforcement of the old bridge, there is no ready-made standard, and no standard map is available. The disease of the bridge is Intricate, difficult to determine the factors of the disease, therefore, should pay full attention to the handling of highway bridges, increase capital investment, make it adhere to excellent work conditions, to ensure the safety of road transport.
Currently, the main factor constraining the reinforcement of old bridges is funds. In the case of scarcity of road maintenance funds, the funds invested in the reinforcement of old bridges are more limited. Therefore, the following methods are advocated for gradual processing: (1) The road section should be increased Large and medium-sized bridges will invest in the reinforcement of funds, and the small bridges attributable to the bridges will be assigned to this program, which will be used to bridge the reinforcement of critical bridges for funding; (2) Minor maintenance of bridges should be included in the bid for maintenance of road minor repairs, especially After the implementation of the road maintenance fee system, the bridges for each section of the pipeline can be incorporated into the list of minor maintenance and maintenance quantities. For projects that cannot be contracted for each road class, the construction of the project team can be carried out. The higher levels must strengthen inspection and assessment.
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