The reinforcement scheme of long-span arch bridge usually contains complicated construction contents and steps. In the whole process of bridge reinforcement, it is often necessary to reinforce the main arch ring, reinforce the buildings on the arch frame, and remove and replace the bridge deck system by increasing the section or pasting. Hingeless arch is a cubic statically indeterminate structure. In the process of complex reinforcement construction, the change of stiffness distribution, the change of loading and unloading sequence on arch and the different combination of these two aspects, that is, adopting different construction sequence for reinforcement, will have a great impact on the internal force distribution of the structure during and after reinforcement. More importantly, in the process of demolishing the buildings on the arch, the deviation between the axis of the main arch ring and the load pressure line is getting bigger and bigger. If the reinforcement sequence is not designed properly, it will easily lead to arch ring cracking and other diseases. Therefore, the design of reinforcement sequence and loading scheme is the key problem in the reinforcement process of long-span arch bridge, which has an important influence on the safety of reinforcement and the bearing capacity and state of the structure. Regarding the design of arch bridge reinforcement sequence, taking the reinforcement of a stone arch bridge as an example, the internal forces in different construction processes are analyzed and compared, and the reasonable reinforcement technology is put forward. By adjusting the position of the building load on the arch, the deviation between the dead load pressure line and the arch axis is controlled to reduce the internal force of the bare arch ring, and the reasonable load adjustment process of the building on the arch is obtained by using the influence line.
First, the theoretical basis of rational reinforcement sequence design
In order to make the arch bridge in a safe state during reinforcement and in an ideal stress state after reinforcement, it is necessary to ensure that the main stress component, the main arch ring, has sufficient strength, stiffness and stability, and at the same time design the reinforcement sequence. For reinforced arch bridges and reinforced arch bridges, except for some special States, the structural stability problem is not prominent; Structural stiffness is reflected by the deflection of the strengthened bridge under live load, so it is not considered in the reinforcement process. In a word, the design of arch bridge reinforcement sequence should take the strength of the main arch ring, that is, the bearing capacity, as the main index. Of course, after the reinforcement sequence is determined, the strength, stiffness and stability of the structure in each stage of the reinforcement process must be comprehensively and thoroughly calculated to ensure the safety of the bridge.
Eccentricity is the key parameter of 1. 1 arch bridge structure, and it is also the main stress component of arch bridge. Usually, there are bending moments and axial forces on each section at the same time. Press the bending member for analysis. The eccentricity of the resultant force on the section is a key parameter in the calculation of the bearing capacity of compression-bending members. For masonry arch bridges, different methods and formulas must be used to calculate the bearing capacity according to the eccentricity in different ranges. According to the Code for Design of Highway Masonry Bridges and Culverts, when the eccentricity e ≤ [E0] (e = m/n, where m and n are the bending moment and axial force on the section respectively), the bearing capacity is calculated according to the formula (1):
( 1)
When e > [E0], the section resistance is calculated according to formula (2): one-way eccentricity: (2a)
Bidirectional eccentricity: (2b)
Theoretical analysis and a large number of bridge calculation results show that the resistance calculated by formula (2) on the right side is usually less than the load effect, while the bearing capacity calculated by formula (1) on the right side often meets the requirements, that is, when the composite eccentricity e≤[e0] on the section, the bearing capacity of the section is sufficient, and vice versa. Accordingly, the author reflects whether the bearing capacity of the structure is satisfied by the relative relationship between eccentricity e and [e0]. When designing the reinforcement sequence, calculate the eccentricity e of each section and ensure that e is always within the envelope of its allowable value [e0]; If e≤[e0] is not met at a certain stage, the reinforcement sequence will be adjusted until E does not exceed the limit. After the order of arch bridge reinforcement construction is determined, the bearing capacity of each construction stage must be checked to ensure that the bearing capacity of each segment always meets the requirements and the structure is always safe and reliable. Therefore, it is reasonable and effective to describe whether the bearing capacity can be met by the relative relationship between eccentricity and its allowable value.
1.2 eccentric influence line
In order to make full use of eccentricity e to assist the design of reinforcement sequence, the concept of eccentricity influence line is introduced. Eccentricity influence line refers to the variation law (curve) of composite eccentricity of section when moving unit load acts on structure; According to the calculation method of e, the influence line of eccentricity can be calculated from the influence line of bending moment m and axial force n, that is, the influence value of the influence line of section m divided by the influence value of the corresponding position on the influence line of n. Eccentric influence line comprehensively reflects the changing law of M influence line and N influence line. The important function of eccentricity influence line is that it can be used to directly, conveniently and accurately point out which section of the arch can increase or decrease the composite eccentricity when loading or unloading, even if the variation of the composite eccentricity is controlled.
1.3 Main measures and technical means for rational reinforcement sequence design of arch bridge
In the sequential design of arch bridge reinforcement, the reinforcement of arch ring, the demolition and reconstruction of buildings on arch and the loading and unloading of other dead loads should be considered comprehensively. The stiffness and strength distribution of the main arch ring change due to the change of reinforcement sequence, which leads to the change of the internal force distribution law of the system. From the point of view of reinforcement sequence design, although this structural change with construction increases the complexity of design, it can also become a means of regulation after reasonable utilization-to achieve better reinforcement effect by controlling structural change. Therefore, when designing the reasonable reinforcement sequence of arch bridge, the main measures and technical means that can be taken are as follows: ① adjustment of the reinforcement sequence of each section of the main arch ring; ② Loading (unloading) program design; (3) Adjust the counterweight when necessary. In a word, in principle, the reasonable reinforcement sequence design of arch bridge is realized by controlling the eccentricity e not to exceed its allowable value [e0] during construction; The concrete realization means include adjusting the arch ring reinforcement sequence, loading (unloading) sequence and counterweight. In the above adjustment process, the structure is in a safe state during the reinforcement process and in an ideal stress state after reinforcement.
Second, the reinforcement sequence design method-step line method
2.65438+
The general idea of step line method is: select the control section and draw the influence of eccentricity in the corresponding state, and establish the step line diagram of eccentric section; In the initial state (n = 0), the corresponding points of the actual value of eccentricity and its allowable value on the upper and lower edges of the section (i.e. the upper and lower line points) are pointed out on the step diagram, and the distances between the upper line point and the horizontal axis and the lower line point and the horizontal axis are divided into m sections (m = 4 in this paper) to form the subsequent control steps, and * * corresponds to m+ 1 step. N(≤m+ 1) step line is selected as the control (step) line for subsequent design; In the reinforcement sequence design of each stage, according to the relative relationship between the actual eccentricity value and the control step line in the current stage, after selecting the appropriate reinforcement/loading content on the eccentricity influence line, calculate the eccentricity and control step line points in the next stage and ensure that the actual eccentricity is within the control value range; Complete the sequence arrangement of all reinforcement stages in the same way. In the process of adopting the step-by-step design method, it is suggested that:
2. 1. 1 Classify all reinforcement structures according to their effects on the section, for example, by increasing or decreasing the eccentricity of the section after adopting this reinforcement measure, divide all reinforcement contents into two categories; In this way, in the design process, we can quickly choose the right one from the two categories as needed.
2. 1.2 In order to stabilize the deformation and stress of the structure during the reinforcement process, the eccentricity of the adjacent two stages should be avoided from the overall situation of the whole reinforcement process.
2. 1.3 in the reinforcement project, the construction of the main arch ring section with enlarged section will directly change the important parameters of the section, and these stages should be arranged before the maximum or minimum eccentricity.
2. 1.4 Speed up according to the actual engineering experience. It should be pointed out that the step-by-step method can only provide an available reinforcement sequence for a concrete masonry arch bridge, and this reinforcement procedure is not optimal. However, the existing reinforcement sequence can be optimized step by step according to constraints or indicators through iterative process using similar methods.
2.2 Checking calculation and monitoring after the reinforcement sequence is determined
In order to ensure the safe and smooth implementation of reinforcement, after determining the reinforcement sequence, it is necessary to check (calculate): ① Whether the strength of load-bearing structures in each stage meets the requirements; (2) If there is a bare arch, whether its longitudinal and lateral stability under self-weight and load meets the requirements; ③ Deflection values of deflection control points of main arch ring in each stage. In the whole reinforcement construction process, the deflection of each deflection control point must be carefully monitored and compared with the above calculation results. When the measured deflection is too large or there are abnormal phenomena such as asymmetric deformation, the reasons should be analyzed immediately, and measures should be taken in time or the reinforcement order should be adjusted.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd