This paper mainly studies the problems existing in the construction quality of bridge engineering, firstly outlines the quality evaluation standards, then analyzes the common quality problems of bridge engineering, and finally discusses the quality control measures of key projects of bridge engineering.
Paper Keywords: bridge engineering; Architecture; Quality; analyse
1 summary of bridge quality evaluation
1. 1 quality evaluation standard
Bridge construction has the characteristics of large investment, high cost, complex technology and high degree of mechanization, so engineering inspection and evaluation are more complicated. Therefore, the state has formulated corresponding norms to strengthen the management of quality evaluation. At present, there are two sets of standards, municipal standards and standards of the Ministry of Communications. Municipal standards set inspection items for each working procedure, and all inspection items are divided into main inspection items and non-main inspection items. Specifically, it can be divided into formwork, reinforcement, prestressed reinforcement, cement concrete, pile foundation and other processes. A, every working procedure should be visual inspection, visual inspection qualified before quality inspection and evaluation. The ratio of the qualified points of the same process to the inspection points of this project multiplied by 100% is the qualified rate of this process, and the qualified rate of main inspection items reaches 100%. When the pass rate of non-major inspection items reaches more than 70%, the item can be assessed as qualified. The evaluation of bridge construction quality in the standards of Ministry of Communications adopts 100. Full marks of basic requirements and measured items are 100. If the appearance appraisal and quality assurance materials are defective, the points will be deducted on the previous basis. The final score is less than 70 points, which is unqualified; If it is between 70 and 85, it is qualified; If it is above 85, it will be excellent.
1.2 Significance of quality evaluation
Strengthening quality evaluation is helpful for construction units to complete bridge construction tasks in strict accordance with construction specifications. The quality of bridge engineering not only affects the success or failure of project investment, but also affects the national property and people's life safety. Therefore, the quality evaluation of construction projects can provide the most effective guarantee for the project quality and reduce the possibility of serious consequences.
2 Analysis of common quality problems in bridge engineering
2. 1 Quality problems of bored piles
The quality problem of bored pile is mainly reflected in broken pile, which is a serious quality accident and must be prevented in construction. Generally speaking, the following construction problems may lead to pile breakage: (1) too long pouring time or too deep buried conduit in concrete will lead to the initial setting of concrete on the inner and outer walls of conduit, resulting in excessive friction between concrete and conduit, and the concrete cannot be filled in time after the conduit is pulled out, resulting in mud pouring. (2) Due to the concrete itself, uneven mixing of concrete or segregation during transportation will lead to the concentration of coarse aggregate during grouting, which will lead to pipe plugging and pile breakage; (3) If water leaks around the bottom of the casing during grouting or due to lack of construction experience, hole collapse and pile breakage may occur; (4) In the process of construction, due to various reasons, such as conduit water inflow, mechanical failure, power failure, etc., continuous construction cannot be guaranteed. , it will also lead to broken piles.
2.2 abutment quality problems
When the settlement of abutment is different from that of abutment, it is possible to form steps at abutment, which not only affects driving safety, but also causes great impact on bridge by automobile tires. This quality problem can be avoided through standardized construction: (1) Selection of backfill materials, selection of backfill materials with good compactness and water permeability, and strict compaction during construction can reduce the settlement of embankment fill; (2) Pile-column abutment should be filled first, and abutment should be built after the filled soil has completely settled, so as to minimize the settlement difference between the structure and the filled soil; (3) According to the requirements of technical specifications, corresponding measures should be taken to reduce the cracks in bridge deck pavement, in addition, good expansion joint materials should be selected to ensure the smoothness of bridge deck expansion joints. 2.3 Quality problems of steel bar construction
The quality problems of steel bar processing exist in many aspects. In terms of material selection, if the specification, shape and size of steel bars do not meet the requirements, or the steel bars have serious corrosion problems, it will affect the engineering quality. In steel processing, poor accuracy of blanking and forming dimensions of steel bars, and deformation of steel skeleton or steel mesh will all cause the performance of structural members to decline; In the aspect of steel bar installation, excessive deviation of installation position, less or missing steel bars, improper fixing method of cushion block position and incorrect steel bar binding joint will all cause serious dislocation of steel bars; In steel bar welding, the mechanical properties of welded joints of steel bars can't meet the requirements of construction specifications, and covered electrode varieties have quality problems, and their properties don't meet the requirements. In the welding process, if the weld size deviation is too large, there is a gap between the undercut weld and the steel bar, and there is a gap between the undercut weld and the steel bar, and the steel bar surface is burned by electric arc, the steel bar section will be weakened locally, or the steel bar will be brittle, which will affect the service performance of the steel bar.
3 quality control measures for key projects of bridge engineering
3. 1 cap and tie beam
First of all, we should focus on monitoring the piles that may break, and also focus on monitoring the piles that have been treated with faults, and carry out nondestructive testing on all piles, so that all piles can finally achieve no fault and no interlayer, and the strength can meet the design requirements. The pile head concrete shall be chiseled into dense layer and leveled, so that there is no residual concrete and other sundries, and the elevation must meet the construction design requirements. The length of the pile head and anchoring reinforcement buried in the pile cap or tie beam shall meet the design requirements. Pay attention to the welding quality of reinforcement skeleton and pile reinforcement when accepting reinforcement. The anchoring reinforcement at the top of the pile should be consistent with the design angle, and it should be fixed by spiral reinforcement winding. Mortar cushion should meet the requirements of flatness and elevation, and its size must meet the requirements of supporting pile caps and tie beam templates. There should be no slurry leakage between formwork surfaces, with tight joints and firm support. Its position, geometric size, protective layer thickness and other indicators should meet the design requirements. Before pouring concrete, the formwork should be coated with release agent, and the release agent of exposed concrete formwork should be of the same variety, and the construction joints of steel bars and concrete should not be polluted during the coating process to ensure the beautiful exposed surface and smooth lines.
3.2 Piers and caps
The quality control of pier column should focus on the following tasks: First, check the construction lofting of column center, and check the reinforcement cage of pier column to make it meet the design standards; Then chisel away the loose concrete on the front contact surface of the formwork support, and if there are other sundries, rinse them off; Next, the quality inspection of column formwork is carried out, and the joints must be smooth and tight. The positioning accuracy, verticality and protective layer thickness of the formwork must meet the quality requirements. The release agent must be painted evenly, and the positioning wire rope should be tightened to meet the requirements of consistent stress; The basic requirements of concrete construction are the same as those of pile caps or tie beams. It is required to use a string tube for blanking, and the bottom of the string tube is no more than 2 meters away from the concrete surface to be poured. After pouring, the concrete surface at the top of the column will become rough. There are two key points in the quality control of pile caps, namely, the quality control of formwork supporting process and the quality control of concrete pouring process. When checking the template, we should focus on the flatness, stiffness, size and angle of the template, and at the same time, we should see whether the support of the template meets the requirements, and also observe the treatment of the template joints. Concrete pouring requires controlling the production quality of concrete, mainly including the quality of raw materials, concrete mixture ratio, etc. , and control the vibrating construction technology. If the vibrating time is too long, the concrete may delaminate and dismantle, while if the vibrating time is insufficient, the concrete bubbles cannot be completely discharged, leading to the formation of diseases such as honeycomb and pits.
3.3 capping beam and box girder
The capping beam should check the center of the column top and the axis of the capping beam, as well as the lofting of the steel skeleton. After the capping beam reinforcement skeleton is formed, it shall be accepted. During acceptance, special attention should be paid to checking the welding quality and the position of bending steel bars. After installing the capping beam reinforcement, check the positioning of the skeleton, adjust the anchorage reinforcement at the top of the column according to the design angle, and the stirrup should be good. In addition, check the thickness of steel protective layer, whether the position of embedded parts and embedded steel bars is correct, whether the formwork is reinforced firmly, whether the bottom plate of box girder is cleaned, and whether the joints are leveled with putty. When using plastic plates, it is required to stick them tightly without holes, bulges and folds. Pay attention to setting wedge-shaped blocks at the beam ends of expansion joints, embed load-bearing steel plates, and focus on positioning the positive bending bellows of the web and floor reinforcement to ensure that the concrete will not shift when pouring. Steel strand must