Nowadays, with the rapid development of bridge construction in China, how to use existing equipment to meet people's demand for convenient transportation has become the main problem facing bridge construction. It is believed that with the development of construction technology, the accumulation of experience and the popularization of calculation software, there will be more and better highway bridge construction methods.
1 Development Status of Bridges in China
As China is still in the primary stage of socialism, the bridge construction units in China, like some other enterprises, still rely on the direct orders of their superiors, and the scientific research projects and technical improvements to be made can only be followed up by the funds of relevant departments. However, after the completion of bridge construction, it is often shelved, and only a small part can produce considerable benefits. Since China joined WTO, due to the influence of international relations, the bridge construction industry in China is still far from the real international standards. This greatly reduces the sense of urgency and enthusiasm of enterprises in bridge construction technology innovation.
First of all, the technological innovation system is progressing slowly. Although the relevant departments of the state have explicitly requested large-scale bridge construction units to establish a systematic innovation system with technology as the core, only a few enterprises have responded to the call of the state, and most bridge construction units still choose to maintain the old construction technology system, and even some enterprises have only established technology centers on the surface, but they have not actually operated according to the new system.
Secondly, bridge construction units pay insufficient attention to technological innovation. Due to the imperfection of the construction market and the influence of some bad construction atmosphere, many people think that a series of tasks can be completed as long as they can win the bridge construction project, which also causes the problem of attaching importance to management and neglecting technology.
In addition to the above two aspects, the investment in architectural technology innovation is still not enough. This leads to low enthusiasm for technological innovation, insufficient investment in science and technology by most bridge construction units, and the speed of technological progress is affected to varying degrees, resulting in a corresponding lag in industrial upgrading.
2 Bridge construction technology
2. 1 concrete mixing
Construction personnel can mix concrete by force. It should be noted that the mixing time must meet the construction requirements, and the mixing time should not be too long or too short. Because if the mixing time is too short, the mixing of concrete will be uneven, while if the mixing time is too long, the structure of concrete raw materials will be destroyed. At the same time, in the process of concrete mixing, the amount of water and additives must be strictly controlled. Only by scientifically controlling the water-cement ratio can the drying shrinkage of concrete be reduced. Only by mixing the concrete evenly can the design strength of concrete be achieved, thus meeting the needs of bridge construction.
2.2 concrete pouring
Good concrete construction technology can not only reduce the internal temperature of concrete, but also reduce the temperature difference between inside and outside of concrete, which will reduce the probability of cracks caused by temperature. Construction workers can use the vibration of plug-in vibrator to carry out the process of concrete pouring. In this link, it is not allowed to cause the segregation of coarse and fine aggregates on the concrete surface and the concentration of aggregates on the concrete surface near the formwork. We should also pay attention to the quality problems such as pits, honeycombs, holes and cracks on the concrete surface due to vibration leakage. Vibrate the vibrating parts every time until the concrete stops sinking, no bubbles appear, and the surface is smooth and pulpy, and then slowly lift the vibrator. In a word, construction personnel should pay enough attention to the vibration of concrete. Only when the concrete vibrating results meet the requirements can the construction quality of the bridge be guaranteed.
2.3 concrete curing
Cracks are the main diseases in bridge construction, so the key to prevent cracks lies in concrete maintenance. After the completion of concrete pouring and slurry collection, water conservation should be carried out as soon as possible to keep the concrete surface moist. This also requires that concrete is resolutely not allowed to be exposed to high temperature. Because cement generates a lot of heat in the hydration process, concrete hollow slab must be sprayed with water outside the side formwork after pouring to avoid cracks caused by excessive volume expansion and contraction of concrete after cooling at too high temperature.
3 problems that should be paid attention to in bridge construction
3. 1 prestress problem
During the construction of bridge engineering, the test results of prestress are normal. However, during the construction of the cast-in-place beam in the adjacent sections in the later period, it was found that the elevation of the top surface of the beam was abnormal, which was probably caused by the suspension of the internal support at the top of the side pier. In dealing with the problem of bridge prestress, the bridge construction unit is facing great pressure, and all the processes of bridge foundation, pier and cast-in-place beam construction will produce prestress problems. After the bridge is open to traffic, the increase of temperature will cause the bearing cavity at the bent beam of the bridge to varying degrees, which will seriously damage the expansion joints of the bridge deck and make the road surface unable to run normally. The treatment of bearing cavity is very difficult and complicated. It is necessary to jack up the box girder as a whole and move the support. At the same time, the pier cap and pier should be widened, and bored piles should be added on the basis. The ramp was forced to close and the processing time was as long as half a year.
3.2 Local Honeycomb Problem
The local honeycomb problem is mainly due to the strength of concrete structure greatly reducing the compactness of the structure, and the strength of its loose structure almost reaches the lowest point. When the bridge is in use, if there is a local honeycomb problem, its bearing capacity will be greatly reduced, and the probability of serious damage caused by corrosion is greater, which will greatly reduce the bearing capacity and durability of the bridge construction project.
3.3 continuous beam cantilever casting web cracking problem
In the cantilever casting construction of continuous beams, some stretching will produce through cracks along the bending direction of web prestressing tendons; Some will have horizontal and oblique cracks on the web along the joint of two adjacent segments after tensioning. In the event of a bridge accident, it is necessary to check the construction operation process and data records, and at the same time, detect the strength of concrete through core drilling sampling. In the past, construction workers investigated every tiny link that may have problems in the construction process, and found that the main reason for the problems was some irregular behaviors in the construction. Even if the construction process is strictly inspected and monitored, cracks will still appear in the next cantilever pouring construction. The fundamental reason for this phenomenon lies in the unreasonable design of prestressed tendons, which leads to the tensile failure of local concrete. Only after adjusting the reinforcement of prestressed beam and ordinary steel bar can the construction be carried out smoothly. When cantilever casting, the first tensioning value should meet certain requirements, because the shear force of box girder segments is very large under bending, and insufficient tensioning times will cause cracks in box girder. In addition, under the condition of imperfect prestress setting and ordinary steel bar configuration, box girder will also produce cracks.
3.4 Cast-in-place beam construction support problems
Through the analysis of statistical data, it can be seen that in the process of cast-in-place construction of continuous beam brackets in many bridges, the accidents of bridge collapse caused by bracket instability are often staged. At the scene of the collapse of the support, many people suffered different degrees of casualties, which caused serious losses to the country and individuals. The main reason is that people have not paid attention to the construction of cast-in-place beam support for a long time, and even ignored many minor problems in the design and construction of cast-in-place support, which eventually led to a big accident due to small mistakes. Recently, it has been clearly pointed out in many codes and guidelines that all supports must be preloaded, which is actually worth discussing. The use of different bracket designs directly affects the construction quality, construction period and economic benefits of the bridge.
3.5 Problems arising from cracks
Crack is one of the most common diseases in bridge construction. The appearance of cracks will reduce the strength and bearing capacity of concrete. Under the continuous stress, the crack problem will become more and more serious, which will also lead to huge economic losses. But sometimes there will be cracks, but the degree is less than the limit required by the standard. Usually, it will not affect the bearing capacity, use function and durability of engineering structures, but often only affect the appearance of the structures, causing suspicion.
3.6 Problems in Geological Exploration
During the construction of some bridges, bored piles and pile caps are included in the design of deep water foundation, but the position of pile caps is designed below the river bed surface, so the construction preparation takes up precious dry season, which is very unreasonable bidding time. Some projects still build platforms after the steel box sinks in place, ignoring the influence of geological exploration on bridge construction, resulting in serious losses for construction units.
4 conclusion
Nowadays, the bridge construction in China is in full swing, and how to use the existing construction technology to meet people's demand for convenient transportation has become the main problem to be solved in bridge construction. It is believed that with the development of construction technology and the accumulation of experience, there will be more and better bridge construction methods to provide more effective protection for the property safety of the country and people.
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