A construction method for the closing section of a cast-in-place cantilever box girder with corrugated steel web

Abstract

The present invention belongs to the technical field of bridge closing section construction, and particularly relates to a method for constructing a closing section of a corrugated steel web cast-in-place cantilever box girder. The method comprises the following steps: Step 1: constructing N-1 segment concrete top plates on both sides of the closing section of the bridge; Step 2: constructing the closing section, including sequentially installing N segment steel webs, installing N segment concrete bottom plates, and installing N segment concrete top plates. In the technical scheme of the present invention, through the force analysis of the existing corrugated steel web cast-in-place cantilever box girder rigid frame structure during the construction process, it is found that in the existing construction process, during the construction process of the closing section, the structure's own corrugated steel web can be directly used to replace the function of the stiffness skeleton added by the construction measures. Practice has proved that this construction method greatly reduces the cost investment of the closing section construction on the one hand, and simplifies the construction process on the other hand, further speeding up the construction process of the bridge. It provides a practical basis for the construction of the closing section of the same type of bridge.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge closure section construction, and particularly relates to a closure section construction method of a cast-in-place cantilever box girder with a corrugated steel web. Background Art

[0002] The rigid skeleton of the closure section of the cast-in-place continuous box girder plays an important role in reducing the impact of temperature and ensuring accurate closure. The main construction processes of the rigid skeleton include pre-embedded steel bars, steel plate welding, 14b channel steel welding, and 40b channel steel welding. The installation construction period of the rigid skeleton of the whole bridge is 5-7 days. The overall rigid skeleton cost is about 300,000-500,000 yuan. The rigid skeleton is mainly used for the accurate closure of mid-span bridges.

[0003] In order to further optimize the construction process of the closing section, improve the construction progress and reduce the construction cost without reducing the quality of the bridge, a new construction design scheme for the closing section is proposed based on engineering examples and mechanical analysis. Summary of the invention

[0004] The purpose of the present invention is to provide a method for constructing a closing section of a corrugated steel web cast-in-place cantilever box girder in view of the technical defects of the prior art that the closing section of a bridge has a long construction time and high construction cost.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A construction method for a closed section of a cast-in-place cantilever box girder with a corrugated steel web comprises the following steps:

[0007] Step 1: Carry out the construction of N-1 segment concrete top slabs on both sides of the bridge closure section;

[0008] Step 2: Closure section construction, including the installation of N-segment steel webs, N-segment concrete bottom plates and N-segment concrete top plates in sequence. Specifically, N-segment corrugated steel webs replace the rigid frame directly as the load-bearing unit and permanent structure of the bridge.

[0009] The present invention proposes an improved construction scheme for the closing section of a corrugated steel web cast-in-place cantilever box girder. Through the force analysis of the existing corrugated steel web cast-in-place cantilever box girder rigid frame bridge structure during the construction process, it is found that in the existing construction process, the corrugated steel web can be directly used to replace the rigid frame for force during the construction of the closing section. Practice has proved that this construction method greatly reduces the cost investment of the closing section construction on the one hand, and simplifies the construction process on the other hand, further speeding up the construction process of the bridge. It provides a practical basis for the construction of the closing section of the same type of bridge.

[0010] As a preferred technical solution of the present invention, in step 2, during the construction of the closing section, before the installation of the N-segment steel web, a stress analysis process of replacing the rigid skeleton with the steel web is also included, and the stress analysis is performed according to the following steps:

[0011] Step 201: Establishing a physical model based on data information of two main piers corresponding to the closure section of the bridge;

[0012] Step 202: performing stress analysis calculations on the closing section of the bridge as a working condition 1 in which the bridge is connected by a rigid skeleton and as a working condition 2 in which the bridge is connected by a steel web;

[0013] Step 203: Compare the calculation results of step 202. When the stress value and strain value of the working condition 2 are greater than the stress value and strain value of the working condition 1, the rigid skeleton connection structure is omitted, and the corrugated steel web is used as the load-bearing unit to directly carry out the N-segment steel web installation construction process.

[0014] In the technical solution of the present invention, the connection and installation method of the rigid skeleton is firstly carried out in the construction process of the closing section of the bridge in the prior art to conduct modeling and compare the forces between the two, so as to obtain accurate data analysis to determine the feasibility of using corrugated steel webs to replace the rigid skeleton. According to many years of bridge construction practice, the inventor found that in the prior art, the closing section is first connected by the rigid skeleton, and then the corrugated steel web is connected. The role of the rigid skeleton is to bear or replace the additional force generated during the concrete of the closing section, ensuring the quality of the concrete of the closing section and the reliability and safety of the connection of the two cantilever ends. In this process, after the corrugated steel web is installed, since the rigid skeleton is the main load-bearing unit, the corrugated steel web does not bear the force. Considering the economic efficiency of the construction, the rigid skeleton is only a temporary connection unit between the closing sections, which does not belong to the main part of the bridge and needs to be removed in the later stage. The additional construction-removal process has a large amount of engineering and will further increase the construction cost. If the role of the corrugated steel web can be brought into play and it can replace the role of the rigid skeleton, it can not only further shorten the construction period, but also save the high material cost of the rigid skeleton. Therefore, according to the structure of the folded section, the forces on the rigid frame and the corrugated steel web were compared, and the feasibility of the scheme was supported by the data results.

[0015] As a preferred technical solution of the present invention, in step 202, in working condition 1, the closing section is fixed by a rigid frame, and the rigid frame mainly bears the compressive stress along the longitudinal direction of the bridge. During the force analysis, the compressive stress and compressive strain of the rigid frame under the temperature rise state are calculated;

[0016] In working condition 2, the closing section is first bolted and then welded through the corrugated steel web. The compressive stress borne by the entire corrugated steel web in the longitudinal bridge direction is negligible. Therefore, in the process of force analysis, the compressive stress generated by the corrugated steel web under the heated state is calculated; the compressive stress is borne by the PBL shear key and the bottom plate on the corrugated steel web respectively.

[0017] The bridge under construction is a rigid frame structure. The main pier and the abutment, as well as the main pier and the 0# block are rigidly connected. During the construction process, the rigid skeleton of the middle span closing section mainly resists the tensile and compressive stresses caused by temperature changes in the cantilever section, and the bending and shear stresses can be ignored.

[0018] As a preferred technical solution of the present invention, in step 201, the heights of the two main piers at the closing section are compared, and the main pier with the lower height is selected for modeling analysis; there are two ways to establish a physical model: a. a single pier column is regarded as a rod, and the double-limb pier and the 0# block are regarded as a "door" type steel frame; b. The two piers of a single main pier are regarded as cantilever rods with hollow cross sections. By measuring and calculating respectively by different forms of modeling methods, the final data can be mutually verified to ensure the feasibility of the scheme.

[0019] Combined with static analysis, static loads are applied to the main pier and the closing section to analyze the stress on the main pier and the closing section, and to analyze the deformation, strain and other parameters of the main pier and the closing section.

[0020] After the rigid frame is fixed, it mainly bears the compressive stress along the longitudinal direction of the bridge. The installation time of the rigid frame is set at the time of the day when the temperature is the lowest. Therefore, only the compressive stress and compressive strain of the rigid frame under the warming state are considered, and the tensile stress and tensile strain under the cooling state are not considered.

[0021] Before the rigid frame is closed, the expansion and contraction of the main span due to temperature change is calculated according to the following formula:

[0022] ΔL=a·ΔT·L;where:

[0023] ΔL represents the total expansion and contraction due to temperature change;

[0024] a represents the linear expansion coefficient of the concrete beam, which is 0.00001 (valued according to the appendix of the design specification);

[0025] ΔT represents the maximum temperature difference between day and night during the construction of the closing section, which is determined based on the measured value;

[0026] L represents the maximum length of the cantilever section, which is half of the length of the clear distance between the two main piers minus the length of the closing section;

[0027] Specifically, the calculation of the resistance stress is calculated according to two different modeling methods:

[0028] The calculations are performed according to two modeling methods:

[0029] a. The force required to produce a displacement of 1 mm f1 = (12E·I1) / h 3 ; The force that the rigid skeleton needs to bear is: F1 = f1·ΔL;

[0030] b. The force required to produce a displacement of 1 mm f2 = (3E·I2) / h 3 ; The force that the rigid skeleton needs to bear is: F2 = f2·ΔL;

[0031] Compare F1 and F2, and use the larger value as the reference value for comparison.

[0032] E represents the elastic modulus of concrete (C40).

[0033] I1 represents the moment of inertia of a single span in a double-leg pier relative to the transverse centerline of block 0#.

[0034] h represents the height of the double-limb pier.

[0035] As a preferred embodiment of the present invention, in step 202, the stress analysis process of working condition 2 is as follows: the total longitudinal compressive cross-sectional area A of the corrugated steel webs on both sides of the box girder is calculated, and the stress borne by the corrugated steel webs as a rigid skeleton is:

[0036] σ=f2 / A (2);

[0037] [σ] is the compressive elastic modulus of the steel web, [σ] = 340 MPa;

[0038] Strain calculation of corrugated steel web as stiffening frame: ε=F / (A·E) (3);

[0039] Among them, ε is the strain of the corrugated steel web due to temperature change, F is the internal force that the steel web needs to withstand when the temperature rises, A is the cross-sectional area of ​​the steel web, E is the compressive elastic modulus of the steel, E = 200000 MPa, [ε] is the ultimate deformation of concrete, [ε] = 0.002.

[0040] Preferably, in step 1, the construction of the N-1 segment concrete top slab specifically includes: putting the N-1 segment concrete top slab formwork in place on both sides of the closure section of the bridge, tying the N-1 segment concrete top slab steel bars on both sides of the closure section, and pouring the N-1 segment concrete top slab steel bars concrete on both sides of the closure section and maintaining.

[0041] Specifically, the N-1 segment concrete top slab formwork on both sides of the closure section of the bridge is in place, the N-1 segment concrete top slab steel bars on both sides of the closure section are tied, and the N-1 segment concrete top slab steel bars are poured and maintained; because the cast-in-place cantilever section adopts the staggered asynchronous hanging basket construction method, the top slab concrete and the bottom slab concrete are staggered by one segment. Specifically, the hanging basket trusses are respectively located at the N-1 segment positions on both sides of the closure section of the bridge, and the top slab formwork is moved forward from the N-2 segment to the N-1 segment. When the N-1 segment bottom slab is poured, the top slab of the N-1 segment has not yet been poured and needs to be poured separately. During construction, the hanging basket remains in place and does not move. It only needs to move the top slab formwork from the N-2 segment to the N-1 segment.

[0042] Preferably, in step 2, the installation of the N-segment steel web comprises the following steps:

[0043] Step 2.1: Measure the precise position of the steel webs at the cantilever ends on both sides of the closure section; check the length, height, and bolt hole positions of the steel webs of the closure section; ensure that the geometric dimensions of the steel webs of the closure section correspond and the bolt hole positions are accurate;

[0044] Step 2.2: Use the gantry crane on the hanging basket to hoist it into place on the working surface, lift the steel web at the corresponding position to the docking position, and temporarily fix it with bolts; note that the installation and penetration direction of the bolts of the entire bridge are consistent, and their axes must be perpendicular to the surface of the steel plate.

[0045] Preferably, after the bolt fixation of the large surface of the corrugated steel web is completed in step 2.2, the welding fixation of the steel bottom plate and top plate PBL keys of the corrugated steel web is performed.

[0046] In the technical solution of the present invention, according to the unique design structure and mechanical calculation of the bridge body, the top plate reinforced concrete, steel web and bottom plate reinforced concrete are constructed asynchronously. The steel web is first closed without counterweight, followed by the bottom plate reinforced concrete casting and closing, and finally the top plate reinforced concrete casting and closing are completed. The core technical point of the technical solution of the present invention is to divide the concrete top plate, corrugated steel web and concrete bottom plate of the box girder closing section into three constructions. After the precise closing of the steel web is completed, the beam body force system is basically formed to meet the three-way force. Then the steel web is used as the force basis, and the bottom plate and top plate reinforced concrete are completed in sequence to complete the closing of the entire bridge. By applying the construction technical solution of the present invention, the construction process of the closing section is greatly reduced, the construction steps of the closing section are significantly simplified, the construction period is shortened, and the construction cost is reduced.

[0047] As a preferred solution of the present invention, in step 2, the installation of N-segment concrete bottom plates and N-segment concrete top plates specifically includes the following steps:

[0048] Step 2.3: Put the template of the closing section, i.e. the N-segment concrete bottom slab, in place; tie the N-segment concrete bottom slab reinforcement; pour the N-segment concrete bottom slab reinforcement concrete of the closing section;

[0049] Step 2.4: The N-segment concrete top slab formwork is in place; the prestressed tendons of the N-1-segment concrete top slab are tensioned and grouted; the reinforcement of the closure section concrete top slab is tied; the reinforcement concrete of the closure section concrete top slab is poured; and the closure of the entire bridge is completed.

[0050] As the preferred technical solution of the present invention, in step 2, the friction surface of the bolt connection on the N-segment steel web needs to be polished before lifting, and the burrs and dirt in the bolt holes need to be trimmed; the lap surface of the steel web and the welding parts on both sides are polished within 3 to 5 cm to ensure smoothness.

[0051] A flatbed truck is used to transport the steel web from the temporary stacking point to the bottom of the pier, and then a tower crane is used to lift the steel web from the bottom of the pier to the working surface. Finally, a gantry crane on a hanging basket is used to lift it into place on the working surface; the steel web is lifted to the docking position and temporarily fixed with bolts.

[0052] The welding operation time period of the corrugated steel web at the closing section should be the period of the lowest temperature of the day, and the specific temperature range should be adjusted according to the construction season.

[0053] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0054] 1. The present invention adopts a box girder design steel web to replace the temporary rigid frame, eliminating the design and construction of the temporary rigid frame in the original design. When the main span is closed, the corrugated steel web part is closed first, and then the top and bottom concrete of the closing section are closed. After the steel web of the closing section is firmly welded, the positions of the beams on both sides of the closing section in the XYZ directions are fixed and the deformation is kept consistent.

[0055] 2. In the technical solution of the present invention, according to the unique design structure and mechanical calculation of the bridge body, the top plate reinforced concrete, steel web and bottom plate reinforced concrete are constructed asynchronously. The steel web is closed first, and then the bottom plate reinforced concrete is poured and closed, and finally the top plate reinforced concrete is poured and closed. The core technical point of the technical solution of the present invention is to divide the top plate, web and bottom plate of the box girder closure section into three constructions. After the precise closure of the steel web is completed, the beam body force system is basically formed to meet the three-way force. Then the steel web is used as the force basis, and the bottom plate and top plate reinforced concrete are completed in sequence to complete the closure of the entire bridge.

[0056] 3. By applying the construction technology scheme of the present invention, the construction process of the closing section is greatly reduced, the construction steps of the closing section are significantly simplified, the construction period is shortened, and the construction cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a structural schematic diagram of a rigid frame bridge involved in the present invention;

[0058] Figure 2It is a schematic diagram of the cross-sectional structure of the rigid frame bridge involved in the present invention;

[0059] Figure 3 is a plan view of a single main pier of the present invention;

[0060] Figure 4 is a front view of the rigid skeleton of the present invention;

[0061] Figure 5 is a side view of the rigid skeleton of the present invention;

[0062] Figure 6 It is a construction process flow chart of the present invention;

[0063] Figure 7 It is a schematic diagram of the elevation structure of the corrugated steel web of the present invention;

[0064] Figure 8 It is a schematic diagram of the three-dimensional structure of the corrugated steel web of the present invention;

[0065] Icon: 1-concrete top plate; 2-concrete bottom plate; 3-corrugated steel web; 31-large surface, 32-PBL shear key, 33-steel bottom plate, 4-main pier, 5-capping platform, 6-rigid frame. DETAILED DESCRIPTION

[0066] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0067] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0068] Example 1

[0069] like Figure 1 The figure shows the No. 1 bridge in a certain county of a certain province. It is a single-box single-chamber, corrugated steel web cast-in-place cantilever continuous beam rigid frame bridge. The total length of the bridge is 455m. The approach bridges at both ends are 3×30m prestressed concrete first simply supported and then continuous T-beams, and the middle main bridge is 72m+125m+72m corrugated steel web continuous rigid frame beam. The whole bridge facade is as follows Figure 1 shown.

[0070] Specifically, the concrete top plate 1 and concrete bottom plate 2 of the box beam of the 1 to 10 segments and the closure section are reinforced concrete, and the webs on both sides are corrugated steel webs 3. The top of the steel web is inserted into the top plate reinforced concrete, and the bottom of the steel web is covered with the bottom plate reinforced concrete. The typical cross-sectional structure is as follows Figure 2 As shown;

[0071] The main pier is designed as a thin-walled hollow double-limb pier, with two in total. Each main pier 4 includes two supporting piers 41 on the left and right sides. The plan view of a single main pier is as follows: Figure 3 As shown. The four supporting piers 41 constituting a single main pier 4 are all located on the same cap 5. The pier heights are 78m and 85m respectively, and the 0# block is 7.8m high. The main pier 4 is made of C40 reinforced concrete.

[0072] Among them, in the prior art, the construction plan of the closing section is specifically as follows:

[0073] The first step is to install the rigid frame, followed by the top and bottom plates, and finally the corrugated steel web.

[0074] Specifically, the structure of the rigid skeleton 6 is to embed φ20 steel bars in concrete, connect 600×20mm steel plates to the steel bars, then weld 14b channel steel to the steel plates, weld 600×20mm steel plates to the channel steels, weld 40b channel steel to the steel plates, and finally weld 600×10mm steel plates to the channel steels.

[0075] See Figure 4-5 As shown, further, the number of full bridge rigid frame design projects is shown in Table 1:

[0076]

[0077] The total amount of steel required is 66 tons, and the construction cost is about 420,000 yuan.

[0078] Example 2

[0079] The technical solution of this application:

[0080] The construction process of this technical solution is shown in Figure 6 Specifically, the steps include:

[0081] Step 1: Carry out the construction of N-1 segment concrete top slabs on both sides of the bridge closure section;

[0082] Step 2: Closure section construction, including the installation of N-segment steel webs, N-segment concrete bottom plates and N-segment concrete top plates in sequence.

[0083] In step 1, since the cast-in-place cantilever section adopts the staggered asynchronous hanging basket construction method, the top slab concrete and the bottom slab concrete are staggered by one section. Each time, the N-1 section concrete top slab and the N-1 section concrete bottom slab concrete are poured at the same time. Therefore, when the N-1 section bottom slab is poured, the N-1 section top slab has not been poured and needs to be poured separately. During construction, the hanging basket remains in place and only needs to move the top slab formwork from the N-2 section to the N-1 section.

[0084] Specifically, in step 1, the construction of the N-1 segment concrete top slab includes: putting the N-1 segment concrete top slab formwork in place on both sides of the closure section of the bridge, tying the N-1 segment concrete top slab steel bars on both sides of the closure section, and pouring the N-1 segment concrete top slab steel bars concrete on both sides of the closure section and maintaining it.

[0085] It should be noted that: before tying the top plate reinforcement, ensure that the position of the corrugated pipe is accurate; when performing welding operations near the corrugated pipe, it is necessary to use a template or thin steel plate to block and protect it to prevent welding sparks from burning the prestressed corrugated pipe or causing the corrugated pipe to deform, causing subsequent processes to be unable to proceed normally.

[0086] The top plate steel bars that cross the steel web horizontally play the role of connecting the reinforced concrete and the steel web. They must not be disconnected at will and must be installed accurately. The annular reinforcement steel bars at the anchor position must be set concentrically and coaxially with the anchor.

[0087] During the concrete pouring process, in order to ensure continuity, the concrete is pumped into the warehouse. The tower crane cooperates with manual movement of the discharge pump pipe to evenly distribute the material. Manual insertion vibration is performed, and manual roughening is performed after final setting. After the final setting of the concrete, geotextile or quilt is used to cover the concrete surface, and water is sprinkled to keep it moist. The concrete near the anchor position is mainly maintained.

[0088] Furthermore, the installation of the N-segment steel web includes the following steps:

[0089] Step 2.1: Measure the precise position of the steel webs at the cantilever ends on both sides of the closing section; check the length, height and bolt hole positions of the steel webs of the closing section; ensure that the geometric dimensions of the steel webs of the closing section correspond and the bolt hole positions are accurate; it should be noted that the friction surface of the bolt connection on the steel webs of the N-segment steel webs needs to be polished before hoisting, and the burrs and dirt in the bolt holes need to be trimmed; the lap surface of the steel webs and both sides of the welding parts need to be polished within 3 to 5 cm to ensure smoothness.

[0090] Before installing the steel web, prepare hand winches, supports, temporary brackets, lifting equipment, etc.

[0091] A flatbed truck is used to transport the steel web from the temporary stacking point to the bottom of the pier, and then a tower crane is used to lift the steel web from the bottom of the pier to the working surface. Finally, a gantry crane on a hanging basket is used to lift it into place on the working surface.

[0092] Step 2.2: Use the gantry crane on the hanging basket to hoist it into place on the working surface, lift the steel web at the corresponding position to the docking position, and temporarily fix it with bolts; note that the bolts of the entire bridge should be installed in the same direction, and their axes should be perpendicular to the surface of the steel plate. Preferably, after the bolt fixation of the large surface of the corrugated steel web is completed in step 2.2, the PBL keys of the steel bottom plate and top plate of the corrugated steel web are welded and fixed.

[0093] The bridge forces in the closed section are mainly borne by the PBL shear keys on the top of the corrugated steel web and the steel bottom plate.

[0094] The welding operation time period of the closing section steel web should be the period with the lowest temperature of the day.

[0095] In step 2, the installation of N-segment concrete bottom plate and N-segment concrete top plate specifically includes the following steps:

[0096] Step 2.3: Put the template of the concrete bottom plate of the closing section (N section) in place; tie the steel bars of the concrete bottom plate of the closing section (N section); pour the steel bars of the concrete bottom plate of the closing section (N section);

[0097] Step 2.4: The formwork of the concrete top slab of the closure section (N segment) is in place; the prestressed tendons of the concrete top slab of the N-1 segment are tensioned and grouted; the steel bars of the concrete top slab of the closure section (N segment) are tied; the reinforced concrete of the concrete top slab of the closure section (N segment) is poured; and the closure of the entire bridge is completed.

[0098] The bottom formwork should be flat, clean and polished. The rods of the suspended formwork must meet the force requirements, and the fastening formwork should be closely attached to the concrete bottom plate and the steel web bottom plate. Where there are gaps, wooden strips or foam glue should be used to seal them.

[0099] The two ends of the prestressed steel strand pre-buried corrugated pipe should be connected with the reserved joints of the N-1 segment, concentric, coaxial, and sealed. The pipeline line is a straight line, and the pipelines are parallel to each other. Bending, flattening, and gaps are strictly prohibited.

[0100] The direction of the hook between the two layers of steel bars is perpendicular to the bottom plate surface, and the connection at both ends is tight without looseness. The hook is firmly tied to the longitudinal and transverse steel bars.

[0101] Since the bottom plate of the closing section is 6.4m wide and only 3.2m long, the pouring sequence is from all sides to the middle.

[0102] Move the top formwork of the N-1 segment on one side of the closing section forward to the closing section as the top plate formwork of the closing section.

[0103] Beam flange bottom formwork support method: Pass the high-quality rolled threaded steel bar through the reserved hole of the N-1 segment concrete top plate and connect it firmly with the formwork longitudinal beam to play a load-bearing role.

[0104] The formwork support method for the middle part of the box girder top plate: 20 I-beams can be used as columns, and the N-1 segment bottom plates on both sides are used as the load-bearing foundation to vertically support the formwork longitudinal beams and play a load-bearing role.

[0105] Steel strands should be cut with a grinder, and cutting with oxygen acetylene or electric welding is strictly prohibited.

[0106] The prestressing construction shall be completed when the concrete strength is ≥90% of the design strength and the age is >7 days.

[0107] The difference between the construction process of Example 1 and Example 2 is that during the construction process of the closing section of Example 2, the temporary erection of the rigid frame is omitted.

[0108] Force analysis

[0109] Modeling and analysis were performed on the closing sections of the two construction methods of Example 1 and Example 2 respectively:

[0110] Specifically include:

[0111] 1. Physical Modeling

[0112] The heights of the two main piers are 86m and 93m respectively. When the two 0# blocks produce the same displacement deformation value, the shorter pier requires a greater thrust, so the 86m high pier is more representative for calculation and analysis.

[0113] Since the main pier is rigidly connected to the abutment and block 0#, the first modeling method is to regard a single pier as a rod, and the double pier and block 0# as a "gate-shaped" steel frame. The second modeling method is to regard the two piers of a single main pier as cantilever rods with hollow cross-sections.

[0114] 2. Calculation of expansion and contraction of beam under temperature change

[0115] Since the bridge is a rigid frame bridge, there is no support at block 0#. Taking the rigid frame of the mid-span closing section as an example, during the construction process, it mainly resists the tensile and compressive stresses caused by temperature changes in the cantilever section, and the bending and shear stresses can be ignored.

[0116] The installation time of the rigid frame is set at around 04:00 in the morning, when the temperature is the lowest and the beam body shrinks to the shortest. After the rigid frame is fixed, it mainly bears the compressive stress along the longitudinal direction of the bridge. Therefore, the compressive stress and compressive strain of the rigid frame under the temperature rise state are considered, and the tensile stress and tensile strain under the temperature drop state are not considered.

[0117] Before closing, the expansion and contraction of the main span due to temperature change is:

[0118] ΔL=a·ΔT·L

[0119] =0.00001m / (℃·m)×20℃×56.9m

[0120] =0.01138m

[0121] =11.38mm

[0122] Where: ΔL – total expansion and contraction due to temperature change.

[0123] a——linear expansion coefficient of concrete beam, taken as 0.00001 (valued according to the appendix of design specification);

[0124] ΔT——The maximum temperature difference between day and night during the construction of the closing section, which was measured to be 20°C;

[0125] L——is the maximum length of the cantilever section, which is the net distance between the two main piers minus half of the length of the closing section, which is (125m (main span) - 2×4m (vertical distance from the edge contour line of the main pier to the horizontal center axis of block No. 0) - 3.2m (length of the closing section)) / 2=56.9m.

[0126] 3. Resistance stress calculation

[0127] Calculations are performed according to the two modeling methods mentioned above.

[0128] If we follow the first modeling method, and regard a single pier as a rod, and the double-leg pier and 0# block as a "gate-type" steel frame, the force required to generate a 1mm displacement is:

[0129]

[0130] Where: f1 is the force (KN / mm) required to cause the 0# block of the "gate-type" steel frame to produce a 1mm longitudinal horizontal displacement.

[0131] E——Elastic modulus of C40 concrete: 32.5GPa.

[0132] I1——Double-legged pier single pair

[0133] Moment of inertia of the horizontal center line of block 0#, 6.75m×(2.5m) 3 / 12=8.789m 4 .

[0134] h——Height of double-limb pier: 86m.

[0135] The force that the rigid skeleton needs to bear is:

[0136] F1=f1·ΔL

[0137] =5.39KN / mm×11.38mm

[0138] =61.34KN.

[0139] If we follow the second modeling method, and regard a single pier as a rod, and the two piers of a single span of the main pier as a cantilever rod with a hollow cross-section, the force required to make the 0# block produce a 1mm displacement is:

[0140]

[0141] Where: f2 is the force required to cause the cantilever end of the rod to produce a 1mm longitudinal horizontal displacement (KN / mm).

[0142] E——Elastic modulus of C40 concrete: 32.5GPa.

[0143] I2——moment of inertia of cantilever member, 6.75m×(8 3 -3 3 )m 3 / 12=272.8125m 4 .

[0144] h——Height of double-limb pier: 86m.

[0145] The force that the rigid skeleton needs to bear is:

[0146] F2=f2·ΔL

[0147] =41.82KN / mm×11.38mm

[0148] =475.91KN.

[0149] According to the calculation results of the two methods, F2 is much larger than F1. For the sake of safety and reliability, F2 is used for verification here.

[0150] 4. Stress verification of corrugated steel web

[0151] The façade of the steel web of the closure section is as follows Figure 7 The schematic diagram of the three-dimensional structure of the steel web of the closure section is shown in Figure 8 shown.

[0152] After the steel web is closed and welded, the large surface 31 of the corrugated steel web mainly bears the shear load, and bears less effect on the longitudinal bending load and tensile and compressive load of the bridge. Therefore, the effect of the steel web in the longitudinal compression of the bridge is negligible here, and the compressive stress of the rigid skeleton caused by the temperature increase is mainly borne by the upper flange plate (PBL shear key 32) and the steel bottom plate 33 of the steel web.

[0153] The total longitudinal compressive cross-sectional area of ​​the corrugated steel webs on both sides of the box girder is:

[0154] A=(A 上翼缘板 +A 底板 )×2 sides

[0155] =(42cm×2.5cm+80cm×2.5cm)×2

[0156] =(105+200)×2cm 2

[0157] =610cm 2

[0158] Where: A 上翼缘板 ——compression area of ​​flange plate on steel web;

[0159] A 底板 ——Compression area of ​​steel web bottom plate.

[0160] The stress borne by the corrugated steel web as a rigid skeleton is:

[0161]

[0162] [σ]——Compressive elastic modulus of steel web: 340MPa.

[0163] The calculation results show that the stress of the optimized design, which uses corrugated steel web 3 instead of rigid frame 6, meets the requirements of the specification.

[0164] 5. Strain calculation using corrugated steel web as rigid skeleton

[0165] When the temperature rises by 20℃, the strain of corrugated steel web 3 becomes:

[0166]

[0167] ε——Strain of corrugated steel web due to temperature change.

[0168] F is the internal force that the steel web needs to bear when the temperature rises.

[0169] A——Cross-sectional area of ​​steel web.

[0170] E——compressive elastic modulus of steel: 200000MPa.

[0171] [ε] is the ultimate deformation of concrete.

[0172] The verification results show that the optimized design uses corrugated steel webs instead of rigid frames, and the strain meets the requirements of the specifications.

[0173] Compare the costs of the two methods mentioned above:

[0174] The original design required a total of 66 tons of steel for the rigid frame, with a construction cost of approximately RMB 420,000.

[0175] After the design optimization, the rigid frame of the original design was cancelled, 66 tons of steel were saved, and the cost was reduced by about 420,000 yuan. Since the steel web is a permanent structure of the box girder, the installation process is the work content of the original box girder construction. After the design optimization, there is no increase in work content and no increase in other costs. Therefore, the design optimization directly saves about 420,000 yuan in costs.

[0176] The main construction procedures of the original temporary rigid frame include: pre-embedded steel bars, steel plate welding, 14b channel steel welding, and 40b channel steel welding. The installation construction period of the entire bridge rigid frame is 6 days.

[0177] After the design scheme was optimized, the temporary rigid frame installation construction process in the original design was cancelled to meet the force requirements. The construction process of the closing section was greatly reduced, which significantly simplified the construction steps of the closing section, shortened the construction period by 6 days, and reduced the construction cost.

[0178] The present invention adopts corrugated steel web cast-in-place continuous beam bridge, based on mechanical analysis and through the construction practice of the closing section of No. 1 bridge in a certain province, cancels the rigid frame of the original design and adopts corrugated steel web to replace the rigid frame, optimizes the design, reduces the cost, simplifies the process, speeds up the progress, and the structural stress and strain meet the requirements of the specification, and the quality and function meet the design requirements, which provides reference and reference for the same type of construction.

[0179] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a closed section of a cast-in-place cantilever box girder with a corrugated steel web, characterized in that: The following steps are involved: Step 1: Carry out the construction of N-1 segment concrete top slabs on both sides of the bridge closure section; Step 2: Closing section construction, including the installation of N-segment corrugated steel webs, N-segment concrete bottom plates and N-segment concrete top plates in sequence. Specifically, the N-segment corrugated steel webs replace the rigid skeleton directly as the load-bearing unit and the permanent structure of the bridge. In step 2, during the closing section construction, before the installation of the N-segment corrugated steel webs, a stress analysis process of the corrugated steel web replacing the rigid skeleton is also included, and the stress analysis is performed according to the following steps: Step 201: Establishing a physical model based on data information of two main piers corresponding to the closure section of the bridge; Step 202: The closing section of the bridge is connected by a rigid skeleton as working condition 1; connected by a corrugated steel web as working condition 2; and force analysis and calculation are performed for the two working conditions respectively; Step 203: Compare the calculation results of step 202. When the stress value and strain value of the working condition 2 are greater than the stress value and strain value of the working condition 1, the rigid skeleton connection structure is omitted, and the corrugated steel web is used as the load-bearing unit to directly carry out the N-segment steel web installation construction process.

2. The construction method for the closure section of the cast-in-place cantilever box girder with corrugated steel web according to claim 1 is characterized in that: In step 202, in working condition 1, the closing section is fixed by a rigid frame, and the rigid frame mainly bears the compressive stress along the longitudinal direction of the bridge. During the force analysis, the compressive stress and compressive strain of the rigid frame under the temperature rise state are calculated; In working condition 2, the closing section is first bolted and then welded through the corrugated steel web. The compressive stress borne by the entire corrugated steel web in the longitudinal bridge direction is negligible. During the force analysis, the compressive stress generated by the corrugated steel web under the heated state is calculated; the compressive stress is borne by the PBL shear key and the steel bottom plate on the corrugated steel web respectively.

3. The construction method for the closure section of the cast-in-place cantilever box girder with corrugated steel web according to claim 2 is characterized in that: In step 201, the heights of the two main piers at the closing section are compared, and the main pier with the lower height is selected for modeling and analysis. There are two ways to establish the physical model: a. a single supporting pier column is regarded as a rod, and the double-legged pier and the 0# block are regarded as a "gate" type steel frame as a whole; b. The two supporting piers of a single main pier are regarded as cantilever rods with hollow cross-sections.

4. The construction method for the closure section of the cast-in-place cantilever box girder with corrugated steel web according to claim 3 is characterized in that: In step 202, the stress analysis process of working condition 1 is as follows: before closing, the expansion and contraction of the main span due to temperature change is ΔL=a.ΔT.L(1); Wherein, ΔL: total expansion and contraction due to temperature change; a: Linear expansion coefficient of concrete beam, taken as 0.00001; ΔT: Maximum temperature difference between day and night during the closing section construction; L: is the maximum length of the cantilever section; The calculations are performed according to two modeling methods: a. The force required to produce a displacement of 1 mm f1 = (12E·I1) / h 3 ; The force that the rigid skeleton needs to bear is: F1 = f1·ΔL; b. The force required to produce a displacement of 1 mm f2 = (3E·I2) / h 3 ; The force that the rigid skeleton needs to bear is: F2 = f2·ΔL; Compare F1 and F2, and use the larger value as the reference value for comparison.

5. The method for constructing the closed section of a cast-in-place cantilever box girder with corrugated steel web according to claim 4, characterized in that: In step 202, the stress analysis process of working condition 2 is as follows: Calculate the total longitudinal compressive cross-sectional area A of the corrugated steel webs on both sides of the box girder, and the stress borne by the corrugated steel webs as a rigid skeleton is: σ=f2 / A(2); [σ] is the compressive elastic modulus of the steel web, [σ] = 340 MPa; Strain calculation of corrugated steel web as rigid skeleton: ε = F / (A·E)(3); Among them, ε is the strain of the corrugated steel web due to temperature change, F is the internal force that the steel web needs to withstand when the temperature rises, A is the cross-sectional area of ​​the steel web, E is the compressive elastic modulus of the steel, E = 200000 MPa, [ε] is the ultimate deformation of concrete, [ε] = 0.

002.

6. The construction method for the closure section of the cast-in-place cantilever box girder with corrugated steel web according to claim 1 is characterized in that: In step 1, the construction of the N-1 segment concrete top slab specifically includes: putting the N-1 segment concrete top slab formwork in place on both sides of the bridge closure section, tying the N-1 segment concrete top slab steel bars on both sides of the closure section, and pouring the N-1 segment concrete top slab steel bars concrete on both sides of the closure section and maintaining it.

7. The construction method for the closure section of the cast-in-place cantilever box girder with corrugated steel web according to claim 1 is characterized in that: In step 2, the installation of the N-segment steel web includes the following steps: Step 2.1: Measure the precise position of the steel webs at the cantilever ends on both sides of the closure section; check the length, height, and bolt hole positions of the steel webs of the closure section; ensure that the geometric dimensions of the steel webs of the closure section correspond and the bolt hole positions are accurate; Step 2.2: Use the gantry crane on the hanging basket to hoist it into place on the working surface, lift the steel web at the corresponding position to the docking position, and temporarily fix it with bolts; the bolts of the entire bridge should be installed in the same direction, and their axes should be perpendicular to the surface of the steel plate.

8. The method for constructing the closed section of a cast-in-place cantilever box girder with corrugated steel web according to claim 7, characterized in that: Step 2.2 After completing the bolt fixation of the large surface of the corrugated steel web, weld and fix the steel bottom plate and top plate PBL keys of the corrugated steel web.

9. The method for constructing the closed section of a cast-in-place cantilever box girder with corrugated steel web according to claim 8, characterized in that: In step 2, the installation of N-segment concrete bottom plate and N-segment concrete top plate specifically includes the following steps: Step 2.3: Put the template of the closing section, i.e. the N-segment concrete bottom slab, in place; tie the N-segment concrete bottom slab reinforcement; pour the N-segment concrete bottom slab reinforcement concrete of the closing section; Step 2.4: The N-segment concrete top slab formwork is in place; the prestressed tendons of the N-1-segment concrete top slab are tensioned and grouted; the reinforcement of the closure section concrete top slab is tied; the reinforcement concrete of the closure section concrete top slab is poured; and the closure of the entire bridge is completed.

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