CN115478481A - A construction method for the closure section of cast-in-place cantilever box girder with corrugated steel web - Google Patents

Abstract

The invention belongs to the technical field of bridge closure segment construction, and particularly relates to a construction method for a corrugated steel web cast-in-place cantilever box girder closure segment. The method comprises the following steps: step 1: constructing N-1 sections of concrete top plates on two sides of the bridge closure segment; step 2: and (3) constructing a closure section, which comprises the steps of installing N-section steel web plates, installing N-section concrete bottom plates and installing N-section concrete top plates in sequence. According to the technical scheme, through stress analysis of the existing rigid frame bridge structure of the corrugated steel web cast-in-place cantilever box girder in the construction process, the function that the structural corrugated steel web can be directly adopted to replace a stiff framework added by construction measures in the construction process of a closure section in the existing construction process is found, and practices prove that the construction method greatly reduces the construction cost investment of the closure section on one hand, simplifies the construction process on the other hand, and further accelerates the construction process of the bridge. And practical basis is provided for the construction of the closure segments of the bridges of the same type.

Description

A Construction Method for Closing Section of Cast-in-situ Cantilever Box Girder with Corrugated Steel Web

technical field

The invention belongs to the technical field of bridge closure section construction, and in particular relates to a construction method for a corrugated steel web cast-in-place cantilever box girder closure section.

Background technique

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

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. By taking the engineering example as the carrier and the mechanical analysis as the basis, a new construction design scheme for the closure section is proposed.

Contents of the invention

The purpose of the present invention is to provide a construction method for the closing section of the cantilever box girder cast-in-place with corrugated steel webs, aiming at the technical defects of long construction time and high construction cost of the closing section of the bridge existing in the prior art.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A construction method for the closure section of a cast-in-place cantilever box girder with a corrugated steel web, comprising the following steps:

Step 1: Carry out the construction of the concrete roof of the N-1 segment on both sides of the bridge closing section;

Step 2: Construction of closing section, including N-segment steel web installation, N-segment concrete bottom plate installation and N-segment concrete roof installation in sequence, specifically, N-segment corrugated steel web replaces stiff skeleton directly as bearing Force elements and bridge permanent structures.

The present invention proposes an improved construction scheme for the closing section of the cast-in-place cantilever box girder with corrugated steel webs. Through the force analysis of the existing rigid-frame bridge structure of cast-in-place cantilever box girders with corrugated steel webs during the construction process, It is found that in the construction process of the closure section in the existing construction process, corrugated steel webs can be directly used instead of the stiff skeleton for stress. It has been proved by practice that this construction method greatly reduces the construction cost of the closure section on the one hand. The investment, on the other hand, simplifies the construction process and further speeds up the construction process of the bridge. It provides a practical basis for the construction of the same type of bridge closing section.

As a preferred technical solution of the present invention, in step 2, in the construction process of the closing section, before the installation of the N-segment steel web, it also includes a force analysis process in which the steel web replaces the stiff skeleton, and the force analysis is carried out according to Follow the steps below:

Step 201: Establish a physical model according to the data information of the two main piers corresponding to the closing section of the bridge;

Step 202: Carry out force analysis and calculation for the position of the closing section of the bridge connected by a stiff skeleton as working condition 1 and connected by a steel web as working condition 2;

Step 203: Comparing 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 stiff skeleton connection structure is omitted, and the corrugated steel web is adopted As a load-bearing unit, the installation and construction process of N-segment steel webs is directly carried out.

In the technical solution of the present invention, during the construction process of the bridge closing section of the prior art, the connection and installation of the stiff skeleton is firstly carried out to model and compare the force between the two, so as to obtain accurate data analysis and use waveforms Feasibility of steel webs replacing stiffeners. Based on many years of bridge construction practice, the inventor found that in the prior art, the closing sections are first connected through the stiff skeleton, and then the corrugated steel web is connected during the construction process. The role of the stiff skeleton is to undertake or replace The additional force generated during the closing of the concrete section ensures the quality of the closing section concrete and the reliability and safety of the connection of the two cantilever ends. During this process, after the corrugated steel web is installed, since the stiff skeleton is the main load-bearing unit, the corrugated steel web does not bear the force. Considering the economy of construction, the stiff skeleton is only a temporary connection between the closed sections Units, which do not belong to the main part of the bridge, need to be demolished later. The additional construction-demolition process requires a large amount of work and will further increase the construction cost. If the corrugated steel web can be used to replace the role of the rigid frame, it will not only further shorten the construction period, but also save High material costs for rigid frames. Therefore, according to the structure of the closed section, the stress of the stiff skeleton and the corrugated steel web are compared respectively. Support the feasibility of the program through data results.

As a preferred technical solution of the present invention, in step 202, in working condition 1, the closing section is fixed by a stiff skeleton, and the stiff skeleton mainly bears the compressive stress along the longitudinal direction of the bridge. During the stress analysis process, the calculation of the The compressive stress and compressive strain of the stiff skeleton at elevated temperature;

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

The construction bridge is a rigid frame bridge structure, the main pier and cap, and the main pier and No. 0# block are all rigidly connected. During the construction process, the rigid skeleton of the mid-span closing section mainly resists the tension and compression of the cantilever section due to temperature changes. Stresses, bending-tensile and shear stresses are negligible.

As a preferred technical solution of the present invention, in step 201, compare the heights of the two main piers at the position of the closing section, and select the lower main pier for modeling analysis; the mode of establishing a physical model includes two kinds: a. The pier column is regarded as a bar, and the double-leg pier and the 0# block are regarded as a "door" steel frame as a whole; b. The two buttresses of a single-width main pier are regarded as a cantilever member with a hollow cross section . Different forms of modeling methods are used to measure and calculate separately, and the final data can be mutually verified to ensure the feasibility of the scheme.

Combined with the static analysis, the static load is applied to the main pier and the closing section, the stress on the main pier and the closing section is analyzed, and the deformation, strain and other parameters of the main pier and the closing section are analyzed.

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 framework 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 framework under the heating state are considered, and the tensile stress and tensile strain under the cooling condition are not considered.

Before the stiff frame is closed, the expansion and contraction of the main span due to temperature changes is calculated according to the following formula:

ΔL=a·ΔT·L; where:

ΔL represents the total expansion and contraction of temperature changes;

a represents the linear expansion coefficient of the concrete beam body, which is taken as 0.00001 (according to the appendix of the design specification);

ΔT represents the maximum temperature difference between day and night during the construction period of the closing section, which is determined according to the measured value;

L represents the maximum length of the cantilever section, half of the length after deducting the closing section from the net distance between the two main piers;

Specifically, the calculation of resistive stress is calculated according to two different modeling methods:

The calculations are carried out according to the two modeling methods respectively:

a. The force f ₁ =(12E·I ₁ )/h ³ required to produce a displacement of 1 mm; the force that the stiff skeleton needs to bear is: F ₁ =f ₁ ·ΔL;

b. The force f ₂ =(3E·I ₂ )/h ³ required to produce a displacement of 1 mm; the force that the stiff skeleton needs to bear is: F ₂ =f ₂ ·ΔL;

Compare F ₁ and F ₂ , and use the larger value as a comparison reference value.

E represents the modulus of elasticity of concrete (C40).

I ₁ represents the moment of inertia of the single frame in the double-leg pier with respect to the transverse centerline of block 0#.

h represents the height of the pier of both limbs.

As a preferred solution of the present invention, in step 202, the stress analysis process steps of working condition 2 are as follows: calculate the total area A of the longitudinal compressive cross-sectional area of the corrugated steel web on both sides of the box girder, then when the corrugated steel web is used as the rigid skeleton The stress to bear is:

σ = f ₂ /A (2);

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

Strain calculation of corrugated steel web as stiff 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 bear when the temperature rises, A is the cross-sectional area of the steel web, E is the compressive elastic modulus of the steel, E=200000MPa, [ε] is the limit deformation of concrete, [ε]=0.002.

Preferably, in step 1, the construction of the N-1 section concrete roof specifically includes: placing the N-1 section concrete roof formwork on both sides of the bridge closing section, binding the N-1 section concrete roof reinforcement on both sides of the closing section, and pouring Reinforced concrete and maintenance for the concrete roof of the N-1 section on both sides of the closing section.

Specifically, the N-1 section concrete roof formwork on both sides of the closing section of the bridge is in place, the N-1 section concrete roof reinforcement bars on both sides of the closing section are bound, and the N-1 section concrete roof reinforcement concrete on both sides of the closing section is poured, cured ; Since the cast-in-place cantilever section adopts the dislocation asynchronous hanging basket construction method, that is, the top slab concrete and the bottom slab concrete are staggered for one section construction. Specifically, the hanging basket trusses are located at the N-1 section on both sides of the bridge closing section, and the roof formwork is moved forward from the N-2 section to the N-1 section. When the N-1 section bottom plate is poured, The roof of section N-1 has not yet been poured and needs to be poured separately. During construction, the hanging basket stays in place, and only needs to move the roof formwork forward from the N-2 section to the N-1 section;

Preferably, 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 closing section; double check the length, height, and bolt hole positions of the steel webs in the closing section; ensure that the geometric dimensions of the steel webs in the closing section correspond to each other, and the positions of the bolt holes are accurate ;

Step 2.2: Lift the gantry crane on the hanging basket 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 whole bridge are installed in the same direction, and their axes must be perpendicular to the surface of the steel plate .

Preferably, in step 2.2, after completing the bolt fixing of the large surface of the corrugated steel web, the welding and fixing of the steel bottom plate and the top plate PBL key of the corrugated steel web are carried out.

In the technical solution of the present invention, according to the unique design structure of the bridge body and mechanical checking calculation, the reinforced concrete of the roof, the steel web and the reinforced concrete of the bottom plate are asynchronously constructed. In the case of basically no counterweight, the steel web is firstly closed, followed by the bottom plate reinforced concrete pouring and closing, and finally the roof reinforced concrete pouring is completed. The core technical point of the technical scheme of the present invention is to divide the concrete roof, the corrugated steel web and the concrete bottom of the box girder closing section into three constructions. After the precise closing of the steel webs is completed, the beam-body stress system is basically formed, which satisfies the three-way stress. Then use the steel web as the force-bearing foundation, complete the bottom plate and roof reinforced concrete in sequence, and complete the closure of the whole bridge. By applying the construction technical 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.

As a preferred solution of the present invention, in step 2, the installation of the N-segment concrete bottom plate and the installation of the N-segment concrete roof specifically include the following steps:

Step 2.3: The closing section, that is, the N-segment concrete floor formwork is in place; the N-segment concrete bottom slab reinforcement is bound; the N-segment concrete bottom slab reinforcement concrete is poured;

Step 2.4: N-section concrete roof formwork is in place; N-1 section concrete roof prestressed tendons are stretched and grouted; the concrete roof reinforcement of the closing section is bound; the concrete roof reinforcement concrete of the closing section is poured;

As a preferred technical solution of the present invention, in step 2, before hoisting, the N-segment steel web needs to complete the work of grinding the bolt connection friction surface on the steel web, and repair the burrs and dirt in the bolt holes; Grinding within 3-5cm on both sides of the joint and welding parts to ensure smoothness.

Use a flatbed truck to transport the steel web from the temporary stacking point to the bottom of the pier, then use a tower crane to lift the steel web from the bottom of the pier to the working face, and finally use the gantry crane on the hanging basket to hoist it in place on the working face; lift the steel web to the docking point The position is temporarily fixed with bolts.

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

In summary, owing to adopting above-mentioned technical scheme, the beneficial effect of the present invention is:

1. The present invention adopts the steel web of box girder design to replace the temporary rigid skeleton, and cancels the design and construction of the temporary rigid skeleton originally designed. When the main span is closed, the corrugated steel web part is closed first, and then the top plate and bottom plate concrete of the closed section are closed. After the steel web of the closing section is welded firmly, the positions of the beams on both sides of the closing section in the XYZ three directions are fixed and the deformation is kept consistent.

2. In the technical solution of the present invention, according to the unique design structure and mechanical calculation of the bridge body, the reinforced concrete of the roof, the steel web and the reinforced concrete of the bottom plate are asynchronously constructed. In the case of basically no counterweight, the steel web is firstly closed, followed by the bottom plate reinforced concrete pouring and closing, and finally the roof reinforced concrete pouring is completed. The core technical point of the technical scheme of the present invention is to divide the roof, web and bottom plate of the closing section of the box girder into three constructions. After the precise closing of the steel webs is completed, the beam-body stress system is basically formed, which satisfies the three-way stress. Then use the steel web as the force-bearing foundation, complete the bottom plate and roof reinforced concrete in sequence, and complete the closure of the whole bridge.

3. By applying the construction technical 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.

Description of drawings

Fig. 1 is the rigid frame bridge structure schematic diagram that the present invention relates to;

Fig. 2 is the cross-sectional structure schematic diagram of the rigid frame bridge that the present invention relates to;

Fig. 3 is the plan view of single main pier of the present invention;

Fig. 4 is the front view of rigid framework of the present invention;

Fig. 5 is a side view of the rigid framework of the present invention;

Fig. 6 is a construction process flow chart of the present invention;

Fig. 7 is the elevation structure schematic diagram of corrugated steel web of the present invention;

Fig. 8 is a three-dimensional structural schematic diagram of a corrugated steel web of the present invention;

Icons: 1-concrete top plate; 2-concrete bottom plate; 3-corrugated steel web; 31-big surface, 32-PBL shear key, 33-steel bottom plate, 4-main pier, 5-cap, 6-stiffness skeleton.

detailed description

Below in conjunction with accompanying drawing, the present invention is described in detail.

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example 1

As shown in Figure 1, the 1# bridge in a certain county in a certain province is a rigid frame bridge with single box and single room, cast-in-place cantilever continuous beam with corrugated steel web. 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 continuous rigid-frame beams with corrugated steel webs. The elevation of the whole bridge is shown in Figure 1.

Specifically, the concrete top plate 1 and the concrete bottom plate 2 of the box girder of sections 1 to 10 and the closing 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 reinforced concrete of the roof, and the bottom of the steel web is surrounded by the reinforced concrete of the bottom plate. The typical cross-sectional structure is shown in Figure 2;

Its main pier is designed as a thin-walled hollow double-limb pier, and there are two in total. Each main pier 4 includes two support piers 41 on the left and right sides respectively. The plan view of a single main pier is shown in Figure 3. The four support piers 41 forming a single main pier 4 all sit on the same platform 5 . The pier heights are 78m and 85m respectively, and block 0# is 7.8m high. The main pier 4 is made of C40 reinforced concrete.

Wherein, in the prior art, the construction scheme of the closing section is specifically:

The first is the installation of the rigid frame, followed by the installation of the top and bottom plates, and finally the installation of the corrugated steel web.

Specifically, the structure of the rigid frame 6 is to pre-embed φ20 steel bars in concrete, connect 600×20mm steel plates to the steel bars, then weld 14b channel steel on the steel plates, weld 600×20mm steel plates on the channel steel, and weld 40b channel steel on the steel plates , and finally weld a 600×10mm steel plate on the channel steel.

See Figure 4-5 for details. Further, the number of engineering works for the stiff frame design of the full bridge is shown in Table 1:

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

Example 2

The technical scheme of this application:

The construction process of this technical solution is shown in Figure 6, specifically, it includes the following steps:

Step 1: Carry out the construction of the concrete roof of the N-1 segment on both sides of the bridge closing section;

Step 2: Construction of closing section, including installation of N-segment steel web, N-segment concrete floor and N-segment concrete roof in sequence.

In step 1, since the cast-in-place cantilever section adopts the dislocation asynchronous hanging basket construction method, the top slab concrete and the bottom slab concrete are constructed in a staggered section. Concrete for the top slab of the N-1 section and the bottom slab of the N-th section are poured at the same time each time. Therefore, when the bottom slab of the N-1 section is poured, the top slab of the N-1 section has not yet been poured and needs to be poured separately. During construction, the hanging basket stays in place, and it is only necessary to move the roof formwork forward from the N-2 section to the N-1 section.

Specifically, in step 1, the construction of the N-1 section concrete roof includes: placing the N-1 section concrete roof formwork on both sides of the bridge closing section, binding the N-1 section concrete roof reinforcement on both sides of the closing section, and pouring the closing Reinforced concrete and maintenance for N-1 section concrete roof on both sides of the section.

It should be noted that before tying the steel bars on the top plate, ensure that the position of the bellows is accurate; when welding near the bellows, it is necessary to use a template or a thin steel plate for protection to prevent welding sparks from burning the prestressed bellows or causing the bellows to deform. Cause subsequent processes can not be carried out normally.

The top plate reinforcement crossing through the steel web plays the role of connecting the reinforced concrete and the steel web, and shall not be disconnected at will, and the installation position is accurate. The annular reinforcing steel bar at the anchorage position shall be set concentrically and coaxially with the anchorage.

In the process of concrete pouring, in order to ensure continuity, the concrete is put into the warehouse by pumping into the warehouse. The tower crane cooperates with the manual movement of the discharge pump pipe to distribute the material evenly. Artificial insertion vibration, artificial napping after final coagulation. After the concrete is finally set, it is covered with geotextiles or quilts on the concrete surface, and sprinkled with water for moisturizing and curing. The concrete near the anchor position should be mainly maintained.

Further, the installation of 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 closing section; double check the length, height, and bolt hole positions of the steel webs in the closing section; ensure that the geometric dimensions of the steel webs in the closing section correspond to each other, and the positions of the bolt holes are accurate ; It should be noted that: before the hoisting of the steel web of the N segment, the friction surface of the bolt connection on the steel web needs to be polished, and the burrs and dirt in the bolt holes should be trimmed; Grinding within 3-5cm from the side to ensure smoothness.

Prepare hand chain hoists, supports, temporary brackets, hoisting equipment, etc. before steel web installation.

Use a flatbed truck to transport the steel web from the temporary stacking point to the bottom of the pier, then use a tower crane to lift the steel web from the bottom of the pier to the working face, and finally use the gantry crane on the hanging basket to hoist it in place on the working face.

Step 2.2: Use the gantry crane on the hanging basket to hoist in place on the working face, lift the steel web at the corresponding position to the docking position, and temporarily fix it with bolts; note that the bolts of the whole bridge are installed in the same direction, and their axes must be perpendicular to the surface of the steel plate . Preferably, in step 2.2, after completing the bolt fixing of the large surface of the corrugated steel web, the welding and fixing of the PBL key of the steel bottom plate and the top plate of the corrugated steel web are carried out.

The force of the bridge in the closed section is mainly borne by the PBL shear key on the top of the corrugated steel web and the steel bottom plate.

The welding operation period of the steel web in the closing section shall be the period of the lowest temperature throughout the day.

In step 2, the installation of the N-segment concrete bottom plate and the N-segment concrete roof installation specifically include the following steps:

Step 2.3: Put the formwork of the concrete floor of the closing section (N section) in place; bind the reinforcement of the concrete floor of the closing section (N section); pour the reinforced concrete of the concrete floor of the closing section (N section);

Step 2.4: The concrete roof template of the closing section (N section) is in place; the prestressed tendons of the concrete roof of the N-1 section are stretched and grouted; the concrete roof reinforcement of the closing section (N section) is bound; the closing section (N section) is poured ) Concrete roof reinforced concrete; that is, the whole bridge is closed.

The bottom template 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 steel web bottom plate, and wooden strips or foam glue should be used to seal the gaps.

The two ends of the pre-stressed steel strand pre-embedded corrugated pipe should be connected to the reserved joint of N-1 section, concentric, coaxial, and sealed. The line type of the pipe is a straight line, and the pipes are parallel to each other. Bending, flattening and gaps are strictly prohibited.

The direction of the hook between the two layers of steel bars is perpendicular to the bottom surface, and the joints at both ends are fastened without looseness. The pull hook is bound firmly with the vertical and horizontal steel bars.

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

Move the top template of the N-1 segment on one side of the closing section forward to the closing section as the top plate template of the closing section.

The support method of the formwork at the bottom of the flange plate of the beam body: the fine-rolled rebar is passed through the reserved hole of the concrete roof of the N-1 section, and it is firmly connected with the longitudinal beam of the formwork to play a load-bearing role.

Formwork support method for the middle part of the box girder roof: 20 I-beams can be used as columns, and the N-1 section bottom plates on both sides are used as the force-bearing foundation to vertically support the formwork longitudinal beams to play a load-bearing role.

Steel strands should be cut with a grinder, and oxyacetylene or electric welding is strictly prohibited.

The tensioning construction is completed when the concrete strength is ≥90% of the design strength and the age is >7 days.

Wherein the difference between the construction process of embodiment 1 and embodiment 2 is only that in the construction process of the closing section of embodiment 2, the temporary erection of the rigid skeleton is omitted.

Force analysis

Carry out modeling analysis respectively to the closure section of two kinds of construction modes of embodiment 1 and embodiment 2 respectively:

Specifically include:

1. Physical modeling

The heights of the two main piers are 86m and 93m respectively. When the two 0# blocks produce the same displacement and deformation value, the shorter pier needs more thrust, so it is more representative to choose the 86m high pier for calculation and analysis here.

Since the main pier is rigidly connected to the cap and the 0# block, the first modeling method: treat a single support pier as a bar, and regard the double-leg pier and the 0# block as a "door type" steel frame. The second modeling method: treat the two supporting piers of a single main pier as a cantilever member with a hollow cross section.

2. Calculation of the expansion and contraction of the beam body under the state of temperature change

Since the bridge is a rigid frame bridge, there is no support at block 0#. Taking the stiff skeleton of the mid-span closing section as an example, during the construction process, it mainly resists the tension and compression stress of the cantilever section due to temperature changes, bending tension and shear stress. Shear stress can be ignored.

The installation time of the rigid frame is determined at around 04:00 in the morning, when the temperature is the lowest and the beam 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 stiff skeleton at elevated temperature are considered, and the tensile stress and tensile strain at low temperature are not considered.

Before closing, the expansion and contraction of the main span due to temperature changes is:

ΔL=a·ΔT·L

＝0.00001m/(℃·m)×20℃×56.9m

=0.01138m

=11.38mm

Among them: ΔL——the total expansion and contraction of temperature change.

a——Concrete beam body linear expansion coefficient, take 0.00001 (take the value according to the appendix of the design specification);

ΔT——The maximum temperature difference between day and night during the construction period of the closing section, the actual measurement is 20°C;

L——Maximum length of the cantilever section, half of the length after deducting the closing section from the clear distance between the two main piers, is (125m (main span) - 2×4m (edge contour line of the main pier to the transverse central axis of block 0#) Vertical distance)-3.2m (length of closing section))/2=56.9m.

3. Calculation of resistance stress

The calculations are carried out according to the above two modeling methods.

If according to the first modeling method, a single pier is regarded as a rod, and the double-leg pier and the 0# block are regarded as a "door-shaped" steel frame, the force required to generate a displacement of 1mm is:

In the formula: f ₁ ——the force (KN/mm) required to cause the 0# block of the “door-shaped” steel frame to produce a 1mm longitudinal and horizontal displacement.

E——C40 concrete elastic modulus: 32.5GPa.

I ₁ ——Single pair of two-leg piers

The moment of inertia of the horizontal centerline of block 0# is 6.75m×(2.5m) ³ /12=8.789m ⁴ .

h - the height of the pier with both limbs: 86m.

Then the force that the stiff skeleton needs to bear is:

F ₁ =f ₁ ·ΔL

＝5.39KN/mm×11.38mm

=61.34KN.

If according to the second modeling method, a single support pier is regarded as a member, and the two supports of a single main pier are regarded as a cantilever member with a hollow cross section, then the 0# block produces 1mm The force required for displacement is:

In the formula: f ₂ ——the force (KN/mm) required to cause the cantilever end of the rod to produce 1mm longitudinal and horizontal displacement.

E——C40 concrete elastic modulus: 32.5GPa.

I ₂ ——the moment of inertia of the cantilever member, 6.75m×(8 ³ -3 ³ )m ³ /12=272.8125m ⁴ .

h - the height of the pier with both limbs: 86m.

Then the force that the stiff skeleton needs to bear is:

F ₂ =f ₂ ·ΔL

＝41.82KN/mm×11.38mm

=475.91KN.

According to the calculation results of the two methods, it can be seen that F ₂ is much larger than F ₁ . To be safe and reliable, take F2 _here for checking calculation.

4. Check calculation of corrugated steel web stress

The elevation of the closed steel web is shown in Figure 7. The schematic diagram of the three-dimensional structure of the closed steel web is shown in Figure 8.

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 tension load of the bridge. Negligible, the compressive stress of the stiff skeleton caused by temperature rise is mainly borne by the upper flange plate of the steel web (PBL shear key 32) and the steel bottom plate 33.

The total area of the longitudinal compressive cross-section of the corrugated steel web on both sides of the box girder is:

A = (A _{upper flange plate} + A _{bottom plate} ) × 2 sides

＝(42cm×2.5cm+80cm×2.5cm)×2

＝(105+200)×2cm ²

=610cm ²

In the formula: A _{upper flange plate} —the compressive area of the flange plate on the steel web;

A _{bottom plate} —the compression area of the steel web bottom plate.

Then the stress borne by the corrugated steel web as the stiff skeleton is:

[σ]——The compressive modulus of elasticity of the steel web: 340MPa.

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

5. Using corrugated steel webs as the rigid skeleton strain checking calculation

When the temperature rises by 20°C, the strain of the corrugated steel web 3 becomes:

ε——strain of corrugated steel web due to temperature change.

F——The internal force that the steel web needs to withstand when the temperature rises.

A—the cross-sectional area of the steel web.

E——Steel compressive modulus of elasticity: 200000MPa.

[ε] is the ultimate deformation of concrete.

The calculation results show that the optimal design, using corrugated steel webs instead of the stiff frame, the strain meets the requirements of the code.

Compare the cost of the above two methods:

The original design of the rigid frame requires a total of 66 tons of steel, and the cost is about 420,000 yuan.

After the optimization of the design, the rigid skeleton of the original design was canceled, 66 tons of steel materials 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 content of the original design of the box girder construction work. After the design optimization, there is no increase in work content or other costs. Therefore, the design optimization directly saves about 420,000 yuan in cost.

The main construction process of the original design temporary rigid frame includes: pre-embedding of steel bars, welding of steel plates, welding of 14b channel steel, and welding of 40b channel steel. The construction period for the installation of the stiff frame of the whole bridge is 6 days.

After the optimization of the design scheme, the installation and construction process of the temporary rigid frame in the original design was canceled to meet the force requirements, the construction process of the closing section was greatly reduced, the construction steps of the closing section were significantly simplified, the construction period was shortened by 6 days, and the construction cost was reduced.

According to mechanical analysis, the present invention cancels the originally designed rigid frame and uses corrugated steel web instead of the rigid frame through the construction engineering practice in the closing section of the 1# bridge in a certain province based on mechanical analysis. The design reduces the cost, simplifies the process, and speeds up the progress. The structural stress and strain meet the specification requirements, and the quality and function meet the design requirements, providing reference and reference for similar types of construction.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A construction method for a corrugated steel web cast-in-place cantilever box girder closure section is characterized by comprising the following steps:

step 1: constructing N-1 sections of concrete top plates on two sides of the bridge closure section;

step 2: and (3) constructing a closure section, which comprises the steps of sequentially installing N-section corrugated steel webs, installing N-section concrete bottom plates and installing N-section concrete top plates, wherein the N-section corrugated steel webs are directly used as a bearing unit and a permanent bridge structure instead of a stiff framework.

2. The method for constructing the closing section of the corrugated steel web cast-in-place cantilever box girder according to claim 1, wherein in the step 2, before installing the N-section corrugated steel web in the closing section construction process, a stress analysis process of the corrugated steel web instead of a stiffened framework is further included, and the stress analysis is performed according to the following steps:

step 201: establishing a physical model according to data information of two main piers corresponding to a bridge closure section;

step 202: the folding sections of the bridge are connected through a stiff framework to serve as a working condition 1; connecting through a corrugated steel web as a working condition 2; respectively carrying out stress analysis calculation on the two working conditions;

step 203: comparing the calculation results in the step 202, and when the stress value and the strain value of the working condition 2 are both greater than those of the working condition 1, directly performing the installation construction process of the N-section steel web by adopting a mode of omitting a stiff skeleton connecting structure and taking a corrugated steel web as a bearing unit.

3. The construction method of the folding section of the corrugated steel web cast-in-place cantilever box girder of claim 2, wherein in step 202, in the working condition 1, the folding section is fixed by a stiff skeleton, the stiff skeleton mainly bears compressive stress along the longitudinal direction of the bridge, and in the process of stress analysis, compressive stress and compressive strain of the stiff skeleton in the heating state are calculated;

in the working condition 2, the closure section is firstly connected by bolts through the corrugated steel web plate and then connected by welding, the compressive stress borne by the whole corrugated steel web plate in the longitudinal bridge direction is ignored, and the compressive stress generated by the corrugated steel web plate in the temperature rise state is calculated in the stress analysis process; the compressive stress is respectively borne by the PBL shear key on the corrugated steel web plate and the steel bottom plate.

4. The construction method of the folding section of the corrugated steel web cast-in-place cantilever box girder according to claim 3, wherein in step 201, the heights of two main piers at the folding section are compared, and the main pier with the lower height is selected for modeling analysis; the physical model is established in two ways: a. one single pier column is regarded as a rod piece, and the double-limb pier and the No. 0 block are integrally regarded as a door-shaped steel frame; b. two buttresses of a single main pier are regarded as cantilever rods with hollow cross sections.

5. The method for constructing the folding section of the corrugated steel web cast-in-place cantilever box girder according to claim 4, wherein in the step 202, the stress analysis process of the working condition 1 is as follows: before closing, the expansion and contraction quantity of the main span caused by temperature change is delta L = a.delta T.L (1);

wherein, Δ L: total expansion and contraction of temperature change;

a: taking the linear expansion coefficient of the concrete beam body to be 0.00001;

Δ T: day and night maximum temperature difference during construction of a closure section;

l: the maximum length of the cantilever section;

respectively calculating according to two modeling methods:

a. force f required to generate a 1mm displacement ₁ ＝(12E·I ₁ )/h ³ (ii) a The force that the strength skeleton needs to bear is: f ₁ ＝f ₁ ·ΔL；

b. Force f required to generate a 1mm displacement ₂ ＝(3E·I ₂ )/h ³ (ii) a The stiff skeleton needs to bearThe force of (A) is: f ₂ ＝f ₂ ·ΔL；

Comparison F ₁ And F ₂ The larger value is used as the comparison reference value.

6. The method for constructing the folding section of the corrugated steel web cast-in-place cantilever box girder according to claim 5, wherein in the step 202, the stress analysis process of the working condition 2 comprises the following steps: calculating the total area A of the longitudinal compression-resistant cross section of the corrugated steel webs at the two sides of the box girder, wherein the stress borne by the corrugated steel webs as a stiff skeleton is as follows:

σ＝f ₂ /A (2)；

[ sigma ] is the compression elastic modulus of the steel web plate, [ sigma ] =340MPa;

and (3) carrying out strain checking calculation on the corrugated steel web as a stiff framework: ε = F/(A · E) (3);

wherein epsilon is the strain of the corrugated steel web plate caused by temperature change, F is the internal force which the steel web plate needs to bear when the temperature rises, A is the cross-sectional area of the steel web plate, E is the compression elastic modulus of steel, E =200000MPa, [ epsilon ] is the concrete limit deformation, and [ epsilon ] =0.002.

7. The construction method for the folding section of the corrugated steel web cast-in-place cantilever box girder according to claim 1, wherein in the step 1, the construction of the N-1 section concrete top plate specifically comprises the following steps: and (3) placing the N-1 sections of concrete top plate templates on two sides of the bridge closure segment in place, binding the N-1 sections of concrete top plate reinforcing steel bars on two sides of the closure segment, pouring the N-1 sections of concrete top plate reinforcing steel bars on two sides of the closure segment, and maintaining.

8. The construction method of the corrugated steel web cast-in-place cantilever box Liang Gelong section staggered hanging basket according to claim 1, wherein in the step 2, the installation of the N-section steel web comprises the following steps:

step 2.1: measuring the accurate positions of the steel webs of the cantilever ends at the two sides of the folding section; rechecking the length size, the height size and the bolt hole position of the steel web plate of the folding section; ensuring that the geometrical sizes of the steel webs of the folding sections are corresponding and the positions of the bolt holes are accurate;

step 2.2: hoisting the steel web plate at the corresponding position to a butt joint position by a gantry crane on the hanging basket in place on a working surface, and realizing temporary fixation by bolts; the installation and penetration directions of the full-bridge bolts are consistent, and the axes of the full-bridge bolts need to be vertical to the surface of the steel plate.

9. The construction method of the corrugated steel web cast-in-place cantilever box Liang Gelong section dislocation hanging basket according to claim 8, wherein after the bolt fixing of the large face of the corrugated steel web is completed in step 2.2, the PBL keys of the steel bottom plate and the top plate of the corrugated steel web are welded and fixed.

10. The construction method for the staggered hanging basket of the Liang Gelong sections of the corrugated steel web cast-in-place cantilever box according to claim 8, wherein in the step 2, the installation of the N-section concrete bottom plate and the installation of the N-section concrete top plate specifically comprise the following steps:

step 2.3: the closure section, namely the N-section concrete bottom plate template is in place; binding N sections of concrete bottom plate reinforcing steel bars; pouring the N-section concrete bottom plate reinforced concrete of the closure section;

step 2.4: positioning the N sections of concrete top plate templates; tensioning and grouting the prestressed tendons of the N-1 section concrete top plate; binding the concrete top plate steel bars of the closure segment; pouring closure section concrete roof reinforced concrete; namely, the full-bridge closure is completed.

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