The following is the content and method analysis of construction control of long-span continuous beam bridge brought by Zhong Da Consulting for your reference.

The research and practice of suspension bridge, arch bridge and continuous rigid frame bridge in China have achieved good results, but the research on construction control technology of long-span prestressed concrete continuous beam bridge is relatively few. Therefore, it is of great practical significance to study and apply the construction control technology of long-span prestressed concrete continuous beam bridge. This paper first analyzes the factors that affect the construction control of long-span bridges, and then expounds the contents and methods of construction control and the basic principles of construction control.

1 preface

The construction of long-span bridges will go through a complicated process, which will be affected by many deterministic and uncertain factors, resulting in the actual state of bridge structure deviating from the theoretical calculation and analysis state. Therefore, the focus of bridge construction control is to analyze and identify the deviation in the construction process, find problems and correct them in time, and predict the subsequent stage of the structure, so that the construction system is always under control.

2 factors affecting construction control [1]

The main purpose of construction control of long-span continuous beam bridge is to make the actual construction state coincide with the ideal design state (linearity and stress) to the maximum extent. In order to achieve the above objectives, we must fully understand all the factors that may make the construction state deviate from the theoretical design state, so as to implement targeted and effective control of the construction.

2. 1 structural parameters [2]

No matter what kind of bridge construction control, structural parameters are important factors that must be considered. Structural parameters are the basic data of controlled structure construction simulation analysis, and their accuracy directly affects the accuracy of analysis results. In fact, the actual bridge structural parameters are generally difficult to completely match the structural parameters used in the design, and there will always be some errors. How to correctly record these errors in construction control and make the structural parameters as close as possible to the real structural parameters of the bridge is the first problem to be solved. Structural parameters mainly include the section size of structural members, elastic modulus of structural materials, bulk density of materials, thermal expansion coefficient of materials, construction load, prestress or cable force, etc.

2.2 Construction technology

Construction control serves the construction, in turn, the construction quality directly affects the realization of control objectives. Construction control requires that the construction technology must meet the control requirements, but also must consider the manufacturing and installation errors of components caused by non-ideal construction conditions, so that the construction state is under control.

2.3 Construction monitoring

Monitoring is one of the most basic means of bridge construction control. Monitoring includes stress monitoring and deformation monitoring. Because there are errors in measuring instruments, instrument installation, measuring methods, data collection and environmental conditions, there are always errors in structural monitoring. In the control process, in addition to trying to reduce the measurement error from the measurement equipment and methods, it must also be included in the control analysis.

2.4 temperature change

The temperature change has a great influence on the stress and deformation of bridge structure, and it changes with the temperature change. The results of measuring the structural state (stress and deformation) at different times are different. If this factor is ignored in the construction control, it will be difficult to obtain the real state data of the structure, thus it is difficult to ensure the effectiveness of the control. Therefore, the influence of temperature change must be considered. Generally, the morning when the temperature changes little in a day is taken as the collection time of the measured data needed for control. But we should pay attention to the influence of seasonal temperature difference and residual temperature in the bridge.

2.5 material shrinkage and creep

For concrete bridge structure, material shrinkage and creep have great influence on the internal force and deformation of the structure, which is mainly caused by the short loading age of concrete in the construction of long-span continuous beam bridge and the great difference in different stages. It should be carefully studied in order to adopt reasonable and practical creep parameters and calculation model. Shrinkage and creep will also affect the structural deformation in the operation stage after the bridge is completed, which is also a factor to be considered in setting the pre-camber.

3. Tasks and work contents of construction control

The task of bridge construction control is to control the bridge construction process [3], to ensure that the internal force and deformation of the bridge structure in the construction process are always within the allowable safety range, and to ensure that the completed bridge state (including the completed bridge alignment and internal force of the completed bridge structure) meets the design requirements. Bridge construction control revolves around the above control tasks, and its construction control work mainly includes the following aspects:

3. 1 geometry (deformation) control

No matter what construction method is adopted, the bridge structure will always be deformed (buckled) during the construction process. The deformation of the structure is influenced by many factors, which easily makes the actual position (elevation and plane position) of the bridge structure deviate from the expected state during the construction process, making it difficult for the bridge to be closed smoothly, or the finished bridge line shape does not meet the design requirements. Therefore, it is necessary to control the bridge so that the error between the actual position and the expected state of the structure during construction is within the allowable range.

3.2 pressure control

Whether the stress of bridge structure is consistent with the design during construction and in the completed state is an important issue that needs to be clarified in construction control. Usually, the actual stress state is known by monitoring the structural stress. If it is found that the difference between the actual stress state and the theoretical (calculated) stress state exceeds the limit, it is necessary to find out the reason and make adjustments to make it change within the allowable range. The quality of structural stress control is not as easy to find as deformation control. If the stress control is not effective, it will do harm to the structure, and in severe cases, it will cause structural damage (the main girder fracture of Zhaobaoshan Bridge in Ningbo, China is an example). Therefore, the structural stress must be strictly controlled.

The items and precision of stress control are not clearly defined and need to be determined according to the actual situation, usually including:

(1) Stress of the structure under self-weight (the difference between actual stress and design should be controlled at 5%).

② Stress of structure under construction load (the difference between actual stress and design should be controlled at 5%).

(3) In addition to the dual control of tensioning (dipstick control and elongation control, the elongation error is allowed within 6%), the influence of pipeline friction (for post-tensioned structures) must also be considered.

(4) temperature stress, especially mass foundation, pier, etc.

⑤ Other stresses, such as structural stress caused by foundation displacement, wind load and snow load.

⑥ The stresses of supports, hanging baskets and cable hoisting systems that have a direct impact on the safety of bridge construction are within the safe range.

3.3 Stability control

The stability of bridge structure is related to the safety of bridge structure, which is of equal or even more important significance to the strength of bridge. There have been many cases in the world in which the whole bridge was damaged due to instability during construction, the most typical one being the Quebec Bridge in Canada. When the south anchor analysis frame was about to be completed, the bridge suddenly collapsed due to the buckling of the lower chord web at the cantilever end. The Zhouhe Bridge in Sichuan, China is also unstable and damaged because the main girder of cantilever system bears excessive axial force in the middle of the main span. Therefore, in the process of bridge construction, it is necessary to strictly control not only the stress and deformation, but also the local and overall stability of structural members at all stages of construction. At present, stability is mainly evaluated and controlled through stability analysis and calculation (stability safety factor) combined with structural stress and deformation.

3.4 Safety control

Safety control in bridge construction is an important part of bridge construction control. Only by ensuring the safety in the construction process can other control and bridge construction be discussed. In fact, the safety control in bridge construction is a comprehensive embodiment of the above-mentioned deformation control, stress control and stability control. By controlling the above items, the safety is also controlled (except for the safety problems caused by bridge construction quality problems). Due to different structural forms, the factors directly affecting construction safety are also different. In construction control, the key points of safety control should be determined according to the actual situation.

4 the method of construction control

Continuous beam bridge is a cyclic process from construction → monitoring → identification → adjustment → prediction → construction, and its essence is to make the construction advance smoothly according to the predetermined ideal state (mainly the construction elevation). In fact, there are errors in both the ideal state obtained by theoretical analysis and the actual construction. Therefore, the core task of construction control is to analyze, identify and adjust all kinds of errors and predict the future of the structure.

4. 1 predictive control method

Predictive control method refers to the prediction before and after the formation of each construction stage (segment) of the structure after comprehensive consideration of various factors affecting the state of the bridge structure and the goals to be achieved in construction, so that the construction can proceed along the predetermined state. Because there are inevitable errors between the predicted state and the actual state, the influence of some errors on the construction target will be considered in the prediction of the subsequent construction state, and so on until the construction is completed, and the structural state that meets the design will be obtained. This method is suitable for all bridges. For those bridges that have become structural state and cannot be adjusted, this method must be adopted for construction control. Predictive control is based on modern cybernetics, and the commonly used predictive methods are Kalman filter method and grey system theory control method.

4.2 Adaptive control method

In view of the uncontrollability of completed segments of continuous beam bridge and the limited corrective measures for alignment errors in construction, it is extremely important to control the occurrence of errors, so it is also very effective to control them by using adaptive control method.

4.3 Linear regression analysis

Linear regression analysis method is to summarize and establish a linear regression mathematical model of deflection through linear regression processing of cantilever box girder deflection, cantilever length and cantilever weight. It can be used to analyze the deflection and deformation law of box girder, and can also be used to predict the deflection of the beam section to be constructed. But it can't correct the errors caused by temperature and construction, and needs more regular data. When the number of beam segments is small, it is difficult to ensure the accuracy of the regression curve.

5 abstract

This paper mainly discusses the factors affecting the construction control of long-span continuous beam bridge, the tasks and work contents of construction control and the methods of construction control. The theory and practice of bridge construction control in China have not yet established a set of perfect construction control technology system and organization management system. Therefore, it is urgent to study the bridge construction control theory, develop more reasonable and practical control software and more convenient and accurate monitoring equipment, and establish a perfect bridge construction control technology system and organization management system.

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