A method for preventing longitudinal cracking of arch foot of cast-in-situ reinforced concrete slab arch bridge

Abstract

The present application relates to a kind of cast-in-place reinforced concrete slab arch bridge's arch foot longitudinal cracking prevention method, belong to civil engineering design and construction technical field.The cast-in-place reinforced concrete slab arch bridge includes at least one main arch unit, each main arch unit includes main arch and main arch support structure, including the following steps: step 1: the construction of main arch support structure, support and bottom die and the installation of reinforcement are completed;Step 2: the construction of single main arch unit is completed;Wherein, post-cast strip is set between the end of each arch segment near arch foot and corresponding arch foot;Step 3: repeat step 2 until the construction of all main arch unit is completed;Step 4: remove the support of all main arch unit, and the construction of arch building and bridge deck system is completed, to obtain cast-in-place reinforced concrete slab arch bridge.The present application can effectively avoid the arch foot longitudinal cracking of cast-in-place reinforced concrete slab arch bridge, improve the durability of bridge.

Description

Technical Field

[0001] This invention relates to the field of civil engineering design and construction technology, and in particular to a method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge. Background Technology

[0002] Currently, cast-in-place reinforced concrete slab arch bridges are widely used in urban bridges in southwestern my country. Cast-in-place reinforced concrete slab arch bridges have the following advantages: First, the main arch ring of the arch bridge is primarily under compression, fully utilizing the excellent compressive strength of stone and concrete; second, the riverbed geological conditions in southwestern my country are favorable, facilitating the use of full-span scaffolding for construction; third, the distinct dry and flood seasons each year, with low river flow and water levels during the dry season, facilitate construction; and fourth, compared to highway bridges, urban bridges have higher aesthetic requirements, and arch bridges possess a beautiful curved structure.

[0003] In existing technologies, the construction method for cast-in-place reinforced concrete slab arch bridges involves setting up a closure section at the crown of the main arch ring. Concrete is poured in stages, starting from the arch foot and moving towards the crown, until the closure section is reached. After 15-30 days, the closure section is then poured. During the period between the start of main arch ring concrete pouring and the pouring of the closure section, the main arch ring concrete can shrink by 30%-40%. The closure section primarily serves to reduce the longitudinal effects of longitudinal shrinkage on the main arch ring, such as axial force and bending moment. Slab arch bridges are thin, prone to dehydration, and shrink rapidly and significantly, while concrete abutments and piers are relatively large, dehydrate slowly, and shrink less. During the period between the completion of the concrete abutments and piers and the pouring of the main arch ring concrete, the construction of supports and bottom formwork, as well as the installation of reinforcing steel, are required, resulting in an age difference of more than three months between the concrete of the abutments and piers and the concrete of the main arch ring. The concrete for the abutments and piers is partially completed, while the shrinkage of the main arch concrete has just begun. Therefore, after the main arch concrete is poured, its shrinkage is much greater than that of the abutment and pier concrete. This creates a lateral shrinkage constraint on the main arch concrete from the abutments and piers, generating tensile stress at the arch foot and compressive stress at the abutments and piers. The wider the main arch, the stronger the lateral shrinkage constraint from the abutments and piers. When the tensile stress at the arch foot exceeds the tensile strength of the concrete, cracks occur. In existing cast-in-place reinforced concrete slab arch bridges with a relatively large width (≥12 meters), despite the presence of numerous longitudinal and transverse reinforcing bars, longitudinal cracking at the arch foot is still common during bridge inspections. Specifically, the cracks originate at the arch foot, point towards the arch crown, with spacing ranging from 2-3 meters to 8 meters, and can generally extend to 1 / 8 of the span, with a width of 0.2-0.3 mm.

[0004] In recent years, cracking at the arch feet of newly constructed cast-in-place reinforced concrete slab arch bridges in cities has become more severe, mainly due to the following two factors: First, for environmental protection reasons, the mining of natural river sand has been banned in various regions, and manufactured sand is now widely used in concrete. However, manufactured sand has poor shape and high stone powder content, resulting in a much greater shrinkage rate than natural river sand concrete. Second, to meet the needs of urban traffic development and road widening, the width of urban bridges has been continuously increasing, with some urban bridges exceeding 40 meters in width. The wider the bridge, the greater the lateral deformation of the main arch foot caused by concrete shrinkage, and consequently, the greater the lateral tensile stress at the main arch foot.

[0005] To address the issue of arch foot cracking in cast-in-place reinforced concrete slab arch bridges, the conventional method is to construct the bridge in transverse sections, dividing it into two, three, or four sections, each bearing independent loads. Architecturally, this still results in a wide bridge, but structurally, it reduces the transverse width and diminishes the bridge's spatial efficiency. However, dividing the bridge into sections presents two problems: First, the junction between adjacent sections needs to be designated as a green belt or crash barrier, preventing it from functioning as a roadway. This can lead to traffic incoordination between the bridge and the roads on both banks, increasing the risk of accidents. Second, severe water seepage occurs at the junction between adjacent sections, affecting both aesthetics and durability. A survey of urban bridges in a southwestern region revealed that almost 100% of cast-in-place reinforced concrete slab arch bridges with a width exceeding 15 meters constructed using conventional methods exhibited longitudinal cracking at the arch foot.

[0006] Therefore, it is necessary to provide a new method for preventing longitudinal cracking at the arch foot of cast-in-place reinforced concrete slab arch bridges to overcome the shortcomings of existing technologies. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge, so as to overcome the above-mentioned problems.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0009] A method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge, wherein the cast-in-place reinforced concrete slab arch bridge includes at least one main arch ring unit, and each main arch ring unit includes a main arch ring and a main arch ring support structure, comprising the following steps:

[0010] Step 1: Complete the construction of the main arch support structure, brackets, and bottom formwork, as well as the installation of reinforcing steel.

[0011] Complete the construction of the main arch ring support structure, install brackets between the main arch ring support structures, install the bottom formwork on the brackets, and install reinforcing bars on the bottom formwork;

[0012] Step 2: Complete the construction of a single main arch unit.

[0013] Step 2.1: Set up the post-pouring strip

[0014] The area where the main arch ring is located is divided into five parts: a closing section, two arch ring segments, and two post-pouring strips. Removable formwork mesh is installed at both ends of each arch ring segment. The closing section is located at the top of the arch in the area where the main arch ring is located. The two post-pouring strips are respectively located between the end of each arch ring segment near the arch foot and the corresponding arch foot.

[0015] Step 2.2: Install the side formwork along the transverse direction of the bridge, pour concrete for the two arch segments and cure them;

[0016] Step 2.3: Simultaneously pour concrete into the closure section and the two post-cast strips and cure them to obtain the main arch ring;

[0017] Step 3: Repeat step 2 until the construction of all main arch units is completed;

[0018] Step 4: Remove all the supports of the main arch units and complete the construction of the superstructure and bridge deck system to obtain a cast-in-place reinforced concrete slab arch bridge.

[0019] The principle of this invention is:

[0020] In existing technologies, after the main arch ring concrete of a cast-in-place concrete slab arch bridge shrinks, the arch foot is most strongly constrained by the abutments or piers, and is also the first place where cracks appear. There is generally a three-month time lag between pouring the concrete supporting the main arch ring and pouring the concrete for the main arch ring itself. During this time, most of the shrinkage of the abutment and pier concrete has been completed, while the shrinkage of the main arch ring concrete has just begun. The abutments and piers constrain the shrinkage of the main arch ring concrete, generating transverse tensile stress at the arch foot and transverse compressive stress at the abutments and piers. When the transverse tensile stress generated at the arch foot of the main arch ring exceeds the tensile strength of the concrete, cracks will appear at the arch foot. Once cracks appear at the arch foot, it poses a safety hazard to the cast-in-place concrete slab arch bridge.

[0021] In this invention, a post-cast strip is set at the arch foot of the main arch ring in each main arch ring unit. The concrete of the arch ring segment is poured first, and after the concrete of the arch ring segment has shrunk to a certain extent, the post-cast strip and the closure segment concrete are poured. The arch ring segment, closure segment, post-cast strip, abutment and pier are connected into a whole that shares the load, that is, the main arch ring and the main arch ring support structure are connected into a whole that shares the load.

[0022] Before the main arch ring and its supporting structure are integrated into a single, stress-bearing whole, the shrinkage of the arch ring segment concrete is free shrinkage and does not generate stress within the main arch ring concrete. After the main arch ring and its supporting structure are integrated, the shrinkage of the main arch ring concrete is constrained by the supporting structure, and the difference in shrinkage between the main arch ring concrete and the supporting structure concrete will generate tensile stress at the arch foot of the main arch ring. Concrete shrinkage is rapid in the early stages and slows down later, generally stabilizing gradually within 5-6 months. In this invention, the concrete for the arch ring segments is poured first, and after a certain interval, the concrete for the post-cast strip and the closure section is poured simultaneously. At this point, part of the shrinkage of the arch ring segment concrete has been completed, and this initial shrinkage will not generate transverse tensile stress at the arch foot of the main arch ring. Therefore, the technical solution of this invention can significantly reduce the transverse tensile stress at the arch foot of the main arch ring caused by the difference in shrinkage between the main arch ring concrete and the supporting structure concrete, thereby avoiding longitudinal cracking at the arch foot of the main arch ring.

[0023] The beneficial effects of this invention are:

[0024] 1. In this invention, a post-cast strip is set at the arch foot of each main arch unit. The post-cast strip and the closure section are poured with concrete at the same time, which reduces the difference in concrete shrinkage between the main arch and the main arch support structure, reduces the tensile stress of the concrete at the arch foot of the main arch, thereby avoiding the occurrence of longitudinal cracking at the arch foot and improving the durability of the bridge.

[0025] 2. This invention eliminates the need for structural segmentation of the bridge, increases the bridge deck width of the arch bridge, enhances the coordination of traffic organization between the bridge and the roads on both banks, and reduces the incidence of traffic accidents.

[0026] 3. The present invention adds only two post-pouring strips to the main arch ring of each main arch ring unit. The post-pouring strips are poured at the same time as the closure section concrete, which is also set in the prior art, so the impact on the construction period is small.

[0027] Based on the above technical solution, the present invention can be further improved as follows.

[0028] Furthermore, when the cast-in-place reinforced concrete slab arch bridge is a single-span arch bridge, the main arch ring support structure includes two abutments; when the cast-in-place reinforced concrete slab arch bridge is a multi-span arch bridge, the main arch ring support structure includes two abutments and at least one pier located between the two abutments.

[0029] The beneficial effect of adopting the above-mentioned further solutions is that the technical solution of the present invention is applicable to both single-span arch bridges and multi-span arch bridges, and its application is more extensive.

[0030] Furthermore, in step 2.1, the arc length of the closing section and the two post-cast strips are both 1-2 meters.

[0031] The beneficial effects of adopting the above-mentioned further solutions are as follows: Workers need to install the formwork mesh without removing it after installing the reinforcing bars. If the arc length of the post-pouring strip and the closure section is too small, the workers' working space will be small, which is not conducive to the workers' construction operations. The post-pouring strip and the closure section need to be poured with UEA shrinkage-compensating concrete or UHPC concrete. The cost of the above two types of concrete is much higher than that of ordinary concrete, and the curing requirements are also higher than those of ordinary concrete. If the arc length of the post-pouring strip and the closure section is too large, it will increase the material cost and curing cost of construction. In Embodiments 1, 2, and 3 of this invention, it is believed that if the arc length of the post-pouring strip and the closure section is less than 1 meter, it will be difficult for workers to install the formwork mesh without removing it. When the number of reinforcing bars in the main arch ring is large, the arc length of the post-pouring strip and the closure section can be appropriately increased. However, when the arc length of the post-pouring strip and the closure section is greater than 2 meters, further increasing the arc length of the post-pouring strip and the closure section will not have a significant effect on reducing the difficulty of workers installing the formwork mesh without removing it, but will only increase the material cost and curing cost of construction.

[0032] In summary, in step 2.1 of this invention, setting the arc length of the closure section and the two post-pouring strips to 1-2 meters is based on the following considerations: it takes into account the actual operating space for workers, and also controls the material and maintenance costs of construction.

[0033] Furthermore, in step 2.1, both of the arch segments are either solid or hollow at the same time.

[0034] The beneficial effect of adopting the above-mentioned further solution is that the technical solution of the present invention is applicable to both solid and hollow arch segments, and has a wider range of applications.

[0035] Furthermore, when both of the arch segments are hollow, the two ends of each arch segment must be set as solid segments, and the arc length of each solid segment is 2-3 meters.

[0036] The advantages of adopting the above-mentioned further solution are as follows: In the existing technology, when the arch segment is also hollow, an inner formwork needs to be installed in the hollow part of the arch segment during construction. That is, the concrete under the hollow part of the arch segment is poured first, then the inner formwork is installed in the hollow part of the arch segment, and finally the remaining concrete is poured. If a non-removable formwork mesh is also installed, it will lead to complicated procedures, difficult operation for workers, and increased risk of quality problems.

[0037] In this invention, when the arch segment is hollow, the end of the arch segment is first set as a solid segment, and the post-cast strip and the closing segment are both solid. The arc length of the solid segment is 2-3 meters, which is 1 meter longer than the arc length of the post-cast strip, which facilitates the construction operation of workers and ensures the construction quality.

[0038] Furthermore, in step 2.1, the removable template mesh is perpendicular to the arch axis of the arch segment.

[0039] The beneficial effect of adopting the above-mentioned further solution is that: when installing the formwork mesh, workers are accustomed to installing it vertically, that is, perpendicular to the ground, which results in a large difference in the arc length between the bottom and top of the post-pouring strip, which is not conducive to the pouring and curing of the post-pouring strip concrete. In step 2.1 of this invention, each of the formwork meshes is perpendicular to the arch axis of the arch segment, which can ensure that the arc lengths of the bottom and top of the post-pouring strip are similar, which is beneficial to the pouring and curing of the post-pouring strip concrete.

[0040] Furthermore, in step 2.3, the concrete pouring uses UEA shrinkage-compensating concrete or UHPC concrete.

[0041] The beneficial effects of adopting the above-mentioned further scheme are as follows: During the hardening process, UEA shrinkage-compensating concrete will undergo micro-expansion. When encountering constraints, it will generate compressive stress, which will offset the tensile stress caused by shrinkage and prevent cracks from appearing in the post-cast strip and closure section concrete due to their own shrinkage. UHPC concrete itself has extremely small shrinkage and will not crack due to shrinkage. Its strength far exceeds that of ordinary concrete, and it has high early strength. The full-span scaffolding can be removed 7 days after the UHPC concrete is poured, which can be used in situations with tight schedules or when the full-span scaffolding needs to be removed as soon as possible due to the risk of flooding. Specifically, the restricted expansion rate of the UEA shrinkage-compensating concrete is ≥0.025%, the strength grade of the UEA shrinkage-compensating concrete is ≥5MPa higher than that of the main arch ring concrete, and the strength grade of the UHPC concrete is ≤C120.

[0042] Furthermore, in step 2.3, the maintenance period is greater than or equal to 14 days.

[0043] The beneficial effects of adopting the above-mentioned further solutions are: UEA shrinkage-compensating concrete or UHPC concrete is used for pouring the closure section and post-pouring strip. If UEA shrinkage-compensating concrete is used, it contains an expansive agent. The necessary condition for the expansion of this agent is a sufficient supply of water. When the water supply is insufficient, the expansive agent in the UEA shrinkage-compensating concrete stops expanding, causing the concrete to lose water and shrink. This also affects the strength development of the UEA shrinkage-compensating concrete, leading to tensile stress in the closure section and post-pouring strip concrete due to shrinkage, and consequently, cracking. If UHPC concrete is used, the hardening process of UHPC concrete has high environmental requirements and requires enhanced curing. In summary, the curing time of 14 days or more in step 2.3 of this invention is based on the following considerations: it ensures that the concrete in the closure section and post-pouring strip reaches the design strength requirements and does not exhibit shrinkage cracks.

[0044] Furthermore, in step 2.3, the lateral width of the main arch ring is greater than 12 meters.

[0045] The beneficial effects of adopting the above-mentioned further solution are as follows: The inventors of this invention investigated cast-in-place reinforced concrete slab arch bridges built in several urban areas and subordinate counties in the past five years. They found that cast-in-place reinforced concrete slab arch bridges with a main arch ring transverse width greater than 15 meters all exhibited longitudinal cracking at the arch foot. For cast-in-place reinforced concrete slab arch bridges with a main arch ring transverse width less than 12 meters, only a few arches had cracks at the arch foot, and the crack patterns were not regular. Analysis determined that these cracks were not caused by the difference in concrete shrinkage between the piers and the main arch ring, but by other reasons. Using a comparative example as the engineering background, the inventors of this invention established a finite element model using Midas FEA software, varied the transverse width of the main arch ring, and calculated the transverse tensile stress of the main arch ring concrete caused by the difference in concrete shrinkage between the piers and the main arch ring. The results showed that when the transverse width of the main arch ring is greater than or equal to 12 meters, the transverse tensile stress of the main arch ring arch foot concrete reaches 2.2 MPa, close to the tensile strength of concrete, which easily causes longitudinal cracking at the arch foot of the main arch ring. In summary, when the transverse width of the main arch ring of a cast-in-place reinforced concrete slab arch bridge is greater than 12 meters, the technical solution of this invention can effectively avoid longitudinal cracking at the arch foot of the main arch ring.

[0046] Furthermore, the time interval between pouring concrete in step 2.2 and pouring concrete in step 2.3 is greater than or equal to 15 days.

[0047] The beneficial effects of adopting the above-mentioned further scheme are: Concrete shrinkage refers to the volume reduction phenomenon that occurs in the early stage of concrete setting or during the hardening process. It is generally divided into plastic shrinkage (also known as settling shrinkage), chemical shrinkage (also known as self-shrinkage) and drying shrinkage, each with its own advantages and disadvantages, as follows: (1) Plastic shrinkage refers to the volume change that occurs in newly poured concrete before hardening. For ordinary concrete, plastic shrinkage is generally completed within 1 day. (2) Chemical shrinkage refers to the shrinkage phenomenon in macroscopic volume caused by the chemical shrinkage of cementitious materials under constant temperature and humidity conditions. Chemical shrinkage is the drying shrinkage caused by the hydration of cementitious materials in concrete consuming the water in capillary pores, resulting in a decrease in internal humidity. For ordinary concrete, chemical shrinkage is generally completed within 3 days. (3) Drying shrinkage is caused by the drying of concrete due to water loss. Its influencing factors include water-cement ratio, aggregate content, aggregate type, component size and relative humidity. Among the above three shrinkage methods, drying shrinkage accounts for the largest proportion, accounting for 80%-90% of the total shrinkage of ordinary concrete. The drying shrinkage rate of concrete is fast in the early stage and slows down in the later stage, gradually stabilizing after 5-6 months of curing.

[0048] The present invention sets the time interval between pouring concrete in step 2.2 and pouring concrete in step 2.3 to be greater than or equal to 15 days, based on the following considerations: 15 days after pouring concrete for the arch segment, the plastic shrinkage and chemical shrinkage of the arch segment concrete have been completed, and the drying shrinkage completion rate is 30%-40%. Then, pouring the closure section and post-pouring strip concrete can effectively avoid longitudinal cracks at the arch foot.

[0049] Definitions:

[0050] The main arch support structure refers to the supporting structure that supports the main arch and transfers its own weight, vehicle loads applied to it, and temperature effects to the foundation. The main arch support structure includes abutments and piers. Abutments are the foundation structures located at both ends of the bridge, connecting the bridge to the roadbed and supporting the bridge superstructure; piers are the intermediate supports in multi-span bridges. Single-span bridges have only two abutments and no piers. Multi-span bridges have two abutments and at least one pier.

[0051] The main arch ring is a load-bearing structure in an arch bridge that is supported at both ends by abutments and piers, arches upwards in a curved shape, bears the loads on the bridge, and transfers the loads to the supporting structure of the main arch ring.

[0052] A slab arch bridge is an arch bridge whose main arch has a rectangular solid cross-section.

[0053] The arch refers to the highest point of the main arch ring.

[0054] The arch foot refers to the connection point between the two ends of the main arch ring and the abutment or pier.

[0055] The arch axis refers to the centroidal line connecting the transverse sections of the main arch ring.

[0056] The superstructure refers to the components and filling material between the bridge deck and the main arch.

[0057] Bridge deck system refers to the bridge deck paving, expansion joints, and railings. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the structure after construction in step 1 of Embodiment 1 of the present invention;

[0059] Figure 2 This is a schematic diagram of the structure after construction in step 2.1 of Embodiment 1 of the present invention;

[0060] Figure 3 This is a schematic diagram of the structure after construction in step 2.2 of Embodiment 1 of the present invention;

[0061] Figure 4 This is a schematic diagram of the structure after construction in step 2.3 of Embodiment 1 of the present invention;

[0062] Figure 5 This is a schematic diagram of the structure after the support is removed in step 4 of Embodiment 1 of the present invention;

[0063] Figure 6 This is a schematic diagram of the structure after the construction of the superstructure and bridge deck system on the main arch ring is completed in step 4 of Embodiment 1 of the present invention.

[0064] Figure 7 This is a schematic diagram of the bridge structure after construction, provided in Embodiment 2 of the present invention;

[0065] Figure 8 This is a schematic diagram of cracks that occur after bridge construction, as provided in Embodiment 2 of the present invention. Figure 1 ;

[0066] Figure 9 This is a schematic diagram of cracks that occur after bridge construction, as provided in Embodiment 2 of the present invention. Figure 2 ;

[0067] Figure 10 This is a schematic diagram of cracks that occur after bridge construction, as provided in Embodiment 2 of the present invention. Figure 3 ;

[0068] Figure 11 This is a schematic diagram of the bridge structure after construction, provided in Embodiment 3 of the present invention;

[0069] Figure 12 This is a structural diagram of the bridge construction process provided in Embodiment 3 of the present invention;

[0070] Figure 13 This is a schematic diagram of the structure of the middle span of the bridge after construction, provided in Embodiment 3 of the present invention;

[0071] Figure 14 A schematic diagram of the bridge structure after construction, provided as a comparative example of the present invention;

[0072] Figure 15 This is a schematic diagram of cracks that occur after bridge construction, provided as a comparative example of the present invention.

[0073] The attached diagram lists the components represented by each number as follows:

[0074] 1. Main arch ring; 2. Support frame; 3. Bottom formwork; 4. Closing section; 5. Arch ring segment; 6. Post-cast strip; 7. Removable formwork mesh; 8. Arch crown; 9. Arch foot; 10. Superstructure; 11. Bridge deck system; 12. Abutment; 13. Pier; 14. Arch axis. Detailed Implementation

[0075] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0076] Example 1

[0077] like Figures 1 to 6 As shown, a reinforced concrete solid slab arch bridge in a certain location has a single span of 11 meters and a main arch ring width of 15.15 meters. It was constructed using full-span scaffolding, and the main arch ring used C40 grade concrete. The original construction plan was to first complete the abutments, scaffolding, formwork, and reinforcing steel in sequence, then pour concrete from the arch foot to the arch crown in one go, followed by concrete curing. A 1-meter-wide closure section was reserved at the arch crown, and concrete pouring was temporarily postponed. The closure section concrete was poured 14 days later, using UEA shrinkage-compensating concrete with a strength grade of C45. Thirty days after pouring the closure section concrete, the scaffolding and formwork were removed, completing the construction of the superstructure and bridge deck system.

[0078] During the preliminary design review, the inventors of this invention made the following suggestions to the designers: The main arch of the bridge is 15.15 meters wide, classifying it as a wide bridge. After the abutments are completed, at least two months pass before the main arch concrete is poured. During this time, most of the concrete shrinkage in the abutments will have occurred, while the main arch, at only 0.5 meters thick, is relatively thin, resulting in significant and rapid concrete shrinkage. The shrinkage of the main arch concrete is constrained by the abutments and piers, leading to lateral tension in the main arch concrete. This poses a risk of longitudinal cracking at the arch foot of the cast-in-place reinforced concrete slab arch bridge. Therefore, the inventors suggest setting a 1-meter-wide post-cast strip at the arch foot of the main arch and a 1-meter-wide closure section at the arch crown. The arch segments should be poured and cured first. Fifteen days after pouring the arch segment concrete, the post-cast strip and closure section should be poured simultaneously. This will significantly reduce the difference in concrete shrinkage between the abutments and the main arch, decrease the lateral tensile stress on the arch foot concrete, and prevent cracking at the arch foot.

[0079] The bridge designers adopted the above suggestions, and the actual construction process was as follows:

[0080] Step 1: Complete the construction of the main arch support structure, bracket 2 and bottom formwork 3, and install the reinforcing steel.

[0081] In May 2021, the construction of the bridge abutments was completed. In July 2021, after the rainy season ended, the support frame 2 for the bottom formwork 3 was erected between the 12 abutments, and the bottom formwork 3 was installed on top of the support frame 2. In September 2021, the reinforcing steel bars were installed on the bottom formwork 3.

[0082] Step 2: Complete the construction of a single main arch unit.

[0083] Step 2.1: Set the post-pouring strip 6

[0084] The area where the main arch ring 1 is located is divided into five parts: a closing section 4, two arch ring segments 5, and two post-cast strips 6. The arc length of the closing section 4 and the two post-cast strips 6 is 1 meter. A non-removable formwork mesh 7 is installed at both ends of each arch ring segment 5. The non-removable formwork mesh 7 is perpendicular to the arch axis 14 of the arch ring segment 5. The closing section 4 is located at the arch crown 8 of the area where the main arch ring 1 is located. The two post-cast strips 6 are respectively located between the end of each arch ring segment 5 near the arch foot 9 and the corresponding arch foot 9.

[0085] Step 2.2: Install the side formwork along the transverse direction of the bridge. In October 2021, pour concrete for the two arch segments 5, and then cure them normally according to the construction technical specifications.

[0086] Step 2.3: In November 2021, C45 grade UEA shrinkage-compensating concrete was poured simultaneously into the closure section 4 and the two post-cast strips 6, and cured for 15 days to obtain the main arch ring 1.

[0087] Step 3: In May 2022, the support 2 of the main arch ring unit was removed, and the construction of the superstructure 10 and the bridge deck system 11 was completed, resulting in a cast-in-place reinforced concrete slab arch bridge.

[0088] In June 2022, an inspection revealed no longitudinal cracks at the arch foot of the main arch ring. In June 2023, another inspection also revealed no cracks at the arch foot of the main arch ring.

[0089] It should be noted that: in the technical solution of this invention, ... Figure 2 Taking the perspective shown as an example, the side formwork is a plate-like structure set at the front and rear ends of the main arch ring reinforcement, that is, in Figure 2 The two ends of the structure, one away from the reader and the other closer to the reader, are equipped with slab-like structures to block the concrete.

[0090] Concrete shrinkage and its influencing factors exhibit a high degree of randomness and distinct regionality. Therefore, when experimental conditions permit, concrete shrinkage parameters can be determined experimentally, and three-dimensional finite element analysis and experimental data can be used to accurately calculate concrete shrinkage. For manufactured sand concrete, it is advisable to use experiments to determine the parameters of the manufactured sand concrete shrinkage model.

[0091] Removable formwork mesh is an existing component in the field of civil engineering. The bonding and shear strength of the joints in removable formwork mesh is comparable to that of well-treated rough-cut joints. During secondary pouring, it eliminates the need for drilling and roughening processes, shortening the construction cycle and increasing the strength of the poured body. Removable formwork mesh is a permanent formwork bonded to concrete. After concrete is poured, its perforated mesh automatically embeds itself, creating a mechanical bond for the next pour, resulting in strong adhesion and shear resistance at the joints.

[0092] UEA stands for U-type Expansive Agent for Concrete, abbreviated as United Expansing Agent (UEA). UEA-compensating shrinkage concrete refers to concrete with an appropriate amount of expansive agent added or prepared with expansive cement. The expansive agent, through its own chemical reaction or reaction with other components in the cement, generates a certain amount of limited expansion during the concrete hardening process to compensate for the shrinkage. Expansive agents such as aluminum sulfate, alumina, and potassium aluminum sulfate are the main expansion sources. Using UEA-compensating shrinkage concrete, one grade higher than the main arch ring concrete, in the post-cast strip and closure section ensures minimal shrinkage, or even slight expansion, in the post-cast strip itself, preventing cracking due to shrinkage.

[0093] UHPC stands for Ultra High Performance Concrete. UHPC possesses exceptionally high mechanical properties and durability, along with good toughness, bonding properties, impact resistance, and fatigue resistance. Its formulation principle involves increasing the fineness and reactivity of its components, eliminating the use of coarse aggregates, and minimizing internal defects (porosity and microcracks) to achieve ultra-high strength and durability. It boasts a compressive strength exceeding 120 MPa and exhibits ultra-high toughness, long-term durability, rapid hardening, and low shrinkage. Using UHPC offers two main advantages: firstly, its high strength allows for earlier scaffolding removal, especially beneficial during the rainy season to meet flood control requirements; secondly, its low shrinkage prevents cracking at the arch foot due to concrete shrinkage. However, UHPC is significantly more expensive than ordinary concrete and is only used when timelines are tight or in the event of flooding.

[0094] Therefore, in Example 1, a post-cast strip is installed at the arch foot. Concrete is first poured and cured onto the arch segment, allowing partial shrinkage of the arch segment concrete to occur. Then, concrete is simultaneously poured onto the post-cast strip and the closure section to form a complete main arch, connecting the main arch and the abutment into a unified load-bearing structure. Before the main arch and abutment are connected, the shrinkage of the arch segment concrete is free shrinkage and does not generate stress. After the main arch and abutment are connected, the abutment constrains the shrinkage of the main arch concrete, but by this time, partial shrinkage of the arch segment concrete has already occurred. The post-cast strip and closure section use UEA (Underlying Surface Anti-Shrinkage) concrete, whose self-shrinkage will not cause cracking. Therefore, the technical solution of this example reduces the tensile stress on the main arch foot concrete, thereby avoiding longitudinal cracking at the arch foot and improving the bridge's durability.

[0095] Example 2

[0096] like Figures 7 to 10 As shown, a reinforced concrete solid slab arch bridge in a certain area has a span arrangement of 35 meters + 35 meters + 35 meters, constructed in four sections, each with a width of 17.5 meters + 10 meters + 10 meters + 17.5 meters. The main arch ring is made of C40 strength concrete.

[0097] During the construction drawing review, the inventor of this invention suggested to the design and construction units that post-cast strips be installed at the arch feet of each main arch span. However, a stacked arch was required above the intermediate piers, resulting in extremely complex reinforcement structures at the arch feet above the piers. Therefore, the construction unit ultimately only installed post-cast strips at the arch feet of the end abutments, and not at the arch feet of the piers. The post-cast strips delay the pouring of UEA shrinkage-compensating concrete. The specific implementation steps and processes are as follows:

[0098] Step 1: Complete the construction of the main arch support structure, bracket 2 and bottom formwork 3, and install the reinforcing steel.

[0099] In April 2021, the construction of two abutments 12 and two piers 13 was completed. A support frame 2 was erected between abutments 12 and piers 13 to support the formwork, and a bottom formwork 3 was installed on top of the support frame 2. In July 2021, steel bars were installed on the bottom formwork 3.

[0100] Step 2: Complete the construction of a single main arch unit.

[0101] Step 2.1: Set the post-pouring strip 6

[0102] The area where the main arch ring 1 is located is divided into five parts: a closing section 4, two arch ring segments 5, and two post-cast strips 6. The arc length of the closing section 4 and the two post-cast strips 6 is 1 meter. In July 2021, a non-removable formwork mesh 7 was installed at both ends of each arch ring segment 5. The non-removable formwork mesh 7 is perpendicular to the arch axis 14 of the arch ring segment 5. The closing section 4 is located at the arch crown 8 of the area where the main arch ring 1 is located. The two post-cast strips 6 are respectively located between the end of each arch ring segment 5 near the arch foot 9 and the corresponding arch foot 9.

[0103] Step 2.2: Install the side formwork along the transverse direction of the bridge, pour C40 strength concrete for each arch segment 5 and cure it normally according to the construction technical specifications.

[0104] Step 2.3: Simultaneously pour UEA shrinkage-compensating concrete of strength grade C45 into the closure section 4 and the two post-cast strips 6, and cure the concrete of the post-cast strips 6 and the closure section 4 for 16 days to obtain the main arch ring 1.

[0105] Step 3: Repeat step 2 until the construction of all main arch units is completed.

[0106] Step 4: In February 2022, the supports 2 of all main arch ring units were dismantled, and the construction of the superstructure 10 and the bridge deck system 11 was completed, resulting in a cast-in-place reinforced concrete slab arch bridge.

[0107] In March 2022, one week after the scaffolding was removed, cracks were discovered in the 17.5-meter-wide arch bridge. Specifically, no cracks were found at the arch feet of the abutments at both ends where post-cast strips were installed; however, longitudinal cracks pointing towards the arch crown appeared at the arch feet of the middle piers where no post-cast strips were installed. The maximum width of the cracks was 0.25 mm, originating at the arch foot and pointing towards the arch crown, with a length of approximately 3 meters. Meanwhile, no cracks were found in the 10-meter-wide arch bridge.

[0108] The following conclusions can be drawn from this embodiment: (1) Longitudinal cracks at the arch foot of cast-in-place reinforced concrete slab arch bridges only occur on wider bridges, and finite element analysis shows that cracks are more likely to occur when the bridge deck width is greater than 12 meters; (2) Setting a post-cast strip at the arch foot can avoid the generation of longitudinal cracks at the arch foot of cast-in-place reinforced concrete slab arch bridges.

[0109] Example 3

[0110] like Figures 11 to 13 As shown, a certain bridge has 5 spans with a span arrangement of 30m + 47m + 52m + 47m + 30m. The two side spans are reinforced concrete curved beams, and the three middle spans are reinforced concrete slab arch bridges with a hollow interior. The main arch ring is 21.5m wide and is made of C50 strength concrete.

[0111] The inventor of this invention participated in the design of the bridge. The original design only included a closure section at the top of each arch span. Given that longitudinal cracks are prone to occur at the arch feet of other similar bridges, the construction and construction methods of the main arch ring of this bridge were modified during the construction phase according to the method of this invention. The original design used a box-shaped hollow cross-section for the main arch ring; the modified design changed the arch foot to a 3-meter-long solid section, with a 2-meter-wide post-cast strip within this solid section. A 3-meter-long solid section was also installed at the top of the arch, with a 1-meter-wide closure section within it.

[0112] The specific implementation steps are as follows:

[0113] Step 1: Complete the construction of the main arch support structure, bracket 2 and bottom formwork 3, and install the reinforcing steel.

[0114] Complete the construction of 2 abutments 12 and 4 piers 13. Erect a support frame 2 between abutments 12 and piers 13 to support the formwork. Install the bottom formwork 3 on the top of the support frame 2 and install steel bars on the bottom formwork 3.

[0115] Step 2: Complete the construction of a single main arch unit.

[0116] Step 2.1: Set the post-pouring strip 6

[0117] The area where the main arch ring 1 is located is divided into five parts: a closing section 4, two arch ring segments 5, and two post-cast strips 6. The arc length of the closing section 4 is 1 meter, and the arc length of the two post-cast strips 6 is 2 meters. The two arch ring segments 5 are hollow. The two ends of each arch ring segment 5 need to be set as solid segments, and the arc length of each solid segment is 3 meters. The non-removable template mesh 7 is installed at both ends of each arch ring segment 5. The non-removable template mesh 7 is perpendicular to the arch axis 14 of the arch ring segment 5. The closing section 4 is set at the arch crown 8 of the area where the main arch ring 1 is located. The two post-cast strips 6 are respectively set between the end of each arch ring segment 5 near the arch foot 9 and the corresponding arch foot 9.

[0118] Step 2.2: Install the side formwork along the transverse direction of the bridge, pour concrete for the two arch segments 5, and cure them normally according to the construction technical specifications.

[0119] Step 2.3: 20 days after pouring the arch segment concrete, pour UEA shrinkage-compensating concrete of strength grade C55 simultaneously into the closure segment 4 and the two post-pouring strips 6; cure the concrete of the post-pouring strips 6 and the closure segment 4 for 14 days, ensuring that the relative curing humidity of the concrete of the post-pouring strips 6 and the closure segment 4 is higher than 95% during the 14-day curing period, and obtain the main arch 1.

[0120] Step 3: Repeat step 2 until the construction of 5 main arch units is completed.

[0121] Step 4: Remove all the supports 2 of the main arch ring units and complete the construction of the superstructure 10 and the bridge deck system 11 to obtain a cast-in-place reinforced concrete slab arch bridge.

[0122] The scaffolding was removed in February 2019, the bridge was opened to traffic for trial operation in October 2019, and the first full-bridge inspection and load test were conducted in April 2020. No cracks were found at the arch foot of the main arch.

[0123] It should be noted that in Example 3, when the main arch span of the reinforced concrete arch bridge is greater than 50 meters, a box-shaped hollow section is used to reduce the self-weight effect due to the large cross-sectional dimensions. The hollow section requires internal formwork support. If the post-cast strip and closure section are also made hollow, construction will be difficult. Therefore, solid sections are set at the arch foot and arch crown to reduce the difficulty of on-site construction for workers and ensure construction quality.

[0124] As can be seen from Examples 1-3, using the technical solution of the present invention is beneficial to preventing longitudinal cracking at the arch foot of cast-in-place arch bridges.

[0125] Comparative Example

[0126] like Figure 14 and Figure 15As shown, a reinforced concrete solid slab arch bridge in a certain location has a span of 52 meters and a width of 27 meters. The main arch ring adopts a reinforced concrete slab structure and is constructed using the full-span scaffolding method. The construction method for the main arch ring is to start pouring concrete from the arch corners and continue pouring to the arch crown. A 1-meter-wide closure section is set at the arch crown. No post-pouring strip is set at the arch foot of the main arch ring. The main arch ring uses C40 strength grade concrete, and the closure section uses UEA shrinkage-compensating concrete with a strength grade of C45. The construction steps and process are as follows:

[0127] Step 1: In April 2021, the construction of bridge abutment 12 was completed; in July 2021, after the rainy season ended, the main arch support structure and support 2 were erected between the two bridge abutments 12; the bottom formwork 3 was installed on the top of the support 2, and steel bars were installed on the bottom formwork 3.

[0128] Step 2: On October 15, 2021, construction of individual main arch units began.

[0129] Step 2.1: Install two non-removable formwork nets 7 on the arch top 8 of each main arch span. The spacing between the two non-removable formwork nets 7 is 1 meter, and a closing section 4 is formed between the two non-removable formwork nets 7.

[0130] Step 2.2: After the steel reinforcement inspection was completed, on November 5, 2021, the concrete pouring for the main arch ring began. Pouring started from the arch foot and continued in one go up to the arch crown where the non-removable formwork mesh 7 was installed. This included pouring the main arch concrete excluding the closure section 4. After the concrete was poured, it was cured normally according to the construction technical specifications.

[0131] Step 2.3: On November 22, 2021, pour concrete for closure section 4. The concrete for closure section 4 is UEA shrinkage-compensating concrete with strength grade C45, and is cured for 14 days.

[0132] Step 3: Starting on December 22, 2021, the supports 2 of all main arch ring units were dismantled, and the construction of the superstructure 10 and the bridge deck system 11 was completed, resulting in a cast-in-place reinforced concrete slab arch bridge.

[0133] On January 15, 2022, five days after the scaffolding was removed, a small number of cracks were discovered at the base of the main arch, with water seeping from them. Regular observation of the cracks revealed a gradual increase in their number and their extension towards the arch crown. In March 2022, a follow-up inspection showed that the number and length of the cracks had stopped increasing, indicating that the cracks had stabilized. Also in March 2022, an engineering quality testing company was commissioned to inspect the cracks, and their distribution was as follows: Figure 15 As shown.

[0134] In the comparative example, because no post-pouring strip was installed during construction, cracks appeared at the arch foot of the slab arch bridge after construction, posing a safety hazard to the cast-in-place concrete slab arch bridge. This also proves the necessity of installing post-pouring strips in reinforced concrete slab arch bridges with a width greater than 12 meters.

[0135] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0136] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0137] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0138] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0139] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0140] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge, wherein the cast-in-place reinforced concrete slab arch bridge includes at least one main arch ring unit, each of the main arch ring units including a main arch ring (1) and a main arch ring support structure, characterized in that, Includes the following steps: Step 1: Complete the construction of the main arch support structure, bracket (2) and bottom formwork (3), and install the reinforcing steel. Complete the construction of the main arch ring support structure, install a bracket (2) between the main arch ring support structures, install a bottom formwork (3) on the bracket (2), and install reinforcing bars on the bottom formwork (3); Step 2: Complete the construction of a single main arch unit. Step 2.1: Set up the post-pouring strip (6) The area where the main arch ring (1) is located is divided into five parts, namely the closing section (4), two arch ring segments (5) and two post-pouring strips (6), and a non-removable formwork mesh (7) is installed at both ends of each arch ring segment (5); the closing section (4) is located at the arch top (8) of the area where the main arch ring (1) is located; the two post-pouring strips (6) are respectively located between the end of each arch ring segment (5) near the arch foot (9) and the corresponding arch foot (9); Step 2.2: Install the side formwork along the transverse direction of the bridge, pour concrete for the two arch segments (5) and cure them; Step 2.3: Simultaneously pour concrete into the closure section (4) and the two post-cast strips (6) and cure them to obtain the main arch ring (1). The time interval between pouring concrete in step 2.2 and pouring concrete in step 2.3 is greater than or equal to 15 days; Step 3: Repeat step 2 until the construction of all main arch units is completed; Step 4: Remove all the supports (2) of the main arch ring units and complete the construction of the superstructure (10) and the bridge deck system (11) to obtain a cast-in-place reinforced concrete slab arch bridge.

2. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, When the cast-in-place reinforced concrete slab arch bridge is a single-span arch bridge, the main arch ring support structure includes two abutments (12); when the cast-in-place reinforced concrete slab arch bridge is a multi-span arch bridge, the main arch ring support structure includes two abutments (12) and at least one pier (13) located between the two abutments (12).

3. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.1, the arc length of the closing section (4) and the two post-cast strips (6) is 1-2 meters.

4. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.1, both of the arch segments (5) are either solid or hollow at the same time.

5. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 4, characterized in that, When both of the arch segments (5) are hollow, the ends of each arch segment (5) must be set as solid segments, and the arc length of each solid segment is 2-3 meters.

6. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.1, the non-removable template mesh (7) is perpendicular to the arch axis (14) of the arch segment (5).

7. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.3, the concrete pouring uses UEA shrinkage-compensating concrete or UHPC concrete.

8. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.3, the maintenance period is greater than or equal to 14 days.

9. The method for preventing longitudinal cracking at the arch foot of a cast-in-place reinforced concrete slab arch bridge according to claim 1, characterized in that, In step 2.3, the lateral width of the main arch ring (1) is greater than 12 meters.

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