| With the rapid development of our country's transportation, many large-span bridges have been constructed. The cable-stayed bridge has been used as one of the most popular types because of its advantages in structural behavior, economy and beautiful facade etc. Partially cable-stayed bridge (short pylon cable-stayed bridge) has been considered as a new type of structure in recent years, which is characteristic of the concentrative layout of short pylons, rigid beams and cables . As for structural properties, partially cable-stayed bridge is between continuous girder bridges and cable-stayed bridges. The cable-stayed bridge is multi-undetermined structure. And during the construction, the adjustment of a certain strayed cable will have an effect on the elevation of the girder and the internal force in the strayed cable nearby. The construction has a great effect on the configuration and the distribution of the internal force. The disharmony of the configuration and furthermore much damage happened because of the construction error, which illustrates that construction control is indispensable in order to ensure the configuration of the cable-stayed large bridge and the internal force to meet the demand of the design.This paper takes the No. 1 Bridge over Zhan River as a real engineering project, which is being constructed now. This bridge is on the Developing Road in Pingding- shan City. The mechanics performance and the construct control technique will be studied in this paper. This bridge is a two-span single-cable-plane cable-stayed bridge with only one bridge pylon. The spans of the main bridge are 88m and 72m respectively. The bridge takes fixed pylon-pier -beam system. The main bridge girders sections are variable cross-section boxes with only a box or three-room box. The girder is a three direction prestressed girder. The main pylon is 22.7m high from the bridge deck. The bridge's pylon is 3.40m width along the bridge direction and 2.0m width perpendicular to the bridge direction with a rectangular section. The pylon sits on the central reserve of the bridge. The cable is sector-shaped and distributed near the 1/3 span of the bridge beam. The distances from the bridge and pylon to the cable are 4m and 0.8m respectively. The cables are nine pairs and symmetry to the tower with two rows. The cables are fixed on the clapboards on the box girders. Based on the site condition of the bridge, span by span method, a way in building the bridge is adopted. And according to the structural characteristics of the bridge, the finite element method is adopted to discrete it. The variable cross-section beam element is used to discrete the main girder. The truss element and the beam element are respectively used to simulate the tensile cable and the main tower, the thin abutment. The finite element model is constructed of the bridge. Then the Midas/Civilprogram is used to make the static, the dynamic and the stability analysis and to check the state of the bridge. In addition, give a detailed analysis of the construction control method etc. At last, combing construction project management for the No.1 Bridge over Zhan River in Pingdingshan city, the numerical simulation of the construct procedure is completed by Midas/Civil. The study fruits have been applied in the practice of the bridge construct control. From the solutions aforementioned, we can get the conclusions as follows:1. As for partially cable-strayed bridge, the moment distribution in the girder is comparatively even. But because of many pretressed bars in the box beam and the tensile force in the strayed cable of the bridge surface, the girder endures rather high axial force. The calculation illustrates that the stress which the girders and the pylons bear is under the design value prescribed in the code for design of bridge structure. And the computing tensile force of the tensile cable is within the permitted value of the code for design of bridge structure. It is shown that the bridge is safe.2. The stiffness of the girder plays an important role in affecting the natural frequency of the whole bridge. The results of dynamic calculation show that the first mode is the vertical vibration of the main span and the second mode is the vertical vibration of the fringe span. The frequency on the surface of the bridge is less than that out of the surface, which is contrary to the dynamic characteristics of the common bridge. It is proved that the girder of the No.l Bridge is rigid while the cable is flexible. This is satisfied with the structural properties of partially cable-strayed bridge.3. The first stability coefficient of the partially cable-strayed bridge is 3.94 during the working, which is satisfied with the demand of the stability. The first 4 instability modes are all in the surface, which conforms to the dynamic analysis of the beam. From the first 4 instability figure, the stiffness of the pylon is high and the instability problem needn't be considered.4. According to the characteristics and the construction procedure of this bridge, the detailed scheme for construct control is made. Firstly, based on the construction method of the bridge, the academic calculation of each construction is developed; the controlled parameters of every construction is abtained and the control paper is formed.Secondly determine the key section of the bridge monitoring. Lastly as to the inconsistent problems between the testing results and calculating results caused by all kinds of factors during the construction, some measure is taken to control and adjust them.5. By forward-analysis method and comparing the testing value with the computing value, the testing results show that the stress of the bridge is reasonable and agrees with the computing results. It is also proved that the members of the bridge having been cast are in thepermitted state of the design. Furthermore estimation and control for the next construction is provided by the computing result.6. The vibration method is used to test the force in the strayed cable of the bridge. The testing results and the computing results have a satisfied agreement. And the errors are less than the precision demanded for the force of the cable during the construction.7. The construction of closure of the main girder is the key part of the main construction for the whole bridge. According to the characteristics of the No.l Bridge over the Zhan River in Pingding Mountain City. Some suggestions of the closure of the main girder are given.The calculating results have been applied to construct control of the No. 1 Bridge over the Zhan River in Pingding Mountain City, and the practical effect is good. From the practical results of the construct control of it, this partially cable-strayed bridge has reached expected purpose. Some of the calculation data and conclusions of this paper can provide the health detection and maintenance of the bridge with the basic data in using phase. Furthermore they can be referred, when similar bridges are designed and constructed. The applicable value of this paper is high. |
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