A pre-tensioning method prestressed HPFRC H-beam bridge and a construction method thereof

Abstract

This invention discloses a prestressed HPFRC (High-Pressure Fiber Reinforced Concrete) I-beam bridge and its construction method, belonging to the field of bridge engineering technology. The bridge includes a foundation and a bridge body. Multiple I-beams are arranged along the span direction. Each I-beam is internally configured with prestressed steel strands and constructed with high-performance fiber-reinforced concrete. Each I-beam comprises a top plate, a web, and a bottom plate. The steel fiber volume fraction in the bottom plate is less than that in the top plate, and the steel fiber volume fraction in the top plate is less than that in the web. The width of the top plate is greater than the width of the bottom plate. A predetermined distance is maintained between the top plates of adjacent I-beams, and a wet joint is formed at this predetermined distance. An asphalt pavement layer is laid on the upper surface of the top plate of the I-beam and the upper surface of the wet joint. This invention can reduce the self-weight of the bridge structure, improve overall crack resistance and durability, and reduce the total life-cycle cost of the bridge.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering technology, specifically to a prestressed HPFRC I-beam bridge constructed using the pre-tensioning method and its construction method. Background Technology

[0002] Conventional concrete bridges are a widely used structural form in highway bridges. The bridge consists of piers and pile foundations in the substructure, ordinary concrete beams in the superstructure, and a concrete deck poured on top of the beams. However, many problems exist in practical use: First, in the construction of bridges in coastal and corrosive environments, ordinary concrete has low strength and poor tensile properties, making it prone to shrinkage cracks and thermal deformation cracks during use. Once these cracks develop, moisture seeps in, causing internal steel reinforcement to rust and expand, and concrete to detach. Second, in the construction of highway bridges in mountainous areas, the insufficient strength of ordinary concrete forces the use of larger beam cross-sections and steel reinforcement, resulting in excessive self-weight of the components. For example, in a bridge with a span of 30-40m, the lifting weight of a single ordinary concrete I-beam can reach 66.6 tons, which restricts the efficiency of transportation and hoisting. In addition, the top of ordinary concrete beams requires the pouring of a thick concrete bridge deck before laying an asphalt layer, further increasing the structural self-weight and the burden on the substructure. The exposed bridge deck is prone to cracking, leading to water seepage and corrosion, and the on-site construction is complex, increasing the maintenance costs throughout the entire life cycle. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a prestressed HPFRC I-beam bridge and its construction method, which can reduce the self-weight of the bridge structure, improve the overall crack resistance and durability, and reduce the total life cycle cost.

[0004] The technical solution of the present invention is as follows: In a first aspect of the invention, a prestressed HPFRC I-beam bridge is provided, comprising a bottom foundation and a bridge body disposed on the upper part of the bottom foundation; The bridge body includes multiple parallel I-beams arranged at intervals along the span direction. The I-beams are equipped with prestressed steel strands and are made of high-performance fiber-reinforced concrete. The I-beam includes a top plate, a web plate, and a bottom plate. The volumetric steel fiber content of the bottom plate is less than that of the top plate, and the volumetric steel fiber content of the top plate is less than that of the web plate. The width of the top plate of the I-beam is greater than the width of the bottom plate. There is a preset distance between the top plates of adjacent I-beams. A wet joint is provided at the preset distance. An asphalt pavement layer is laid on the upper surface of the top plate of the I-beam and the upper surface of the wet joint.

[0005] In some embodiments of the present invention, the steel fiber volume content of the top plate is 0.7% to 1.0%, the steel fiber volume content of the web plate is 1.4% to 1.6%, and the steel fiber volume content of the bottom plate is 0.3% to 0.5%.

[0006] In some embodiments of the present invention, a single layer of prestressed steel strands is provided in the top plate along the length of the I-beam, and multiple layers of prestressed steel strands are provided in the bottom plate along the length of the I-beam. The spacing of the prestressed steel strands in the bottom plate is smaller than the spacing of the prestressed steel strands in the top plate.

[0007] In some embodiments of the present invention, the thickness of the web of the I-beam is set to increase gradually from the mid-span region of the bridge body towards the two end supports along the span direction of the bridge body. The web of the I-beam at both ends of the bridge span direction is provided with double-leg stirrups vertically from the top plate to the bottom plate; The web of the I-beam in the mid-span region along the span direction of the bridge body is vertically provided with single-leg stirrups from the top plate to the bottom plate.

[0008] In some embodiments of the present invention, transverse diaphragms are provided at a predetermined distance between adjacent I-beams along the span direction, and the transverse diaphragms connect multiple I-beams into a whole along the width direction of the bridge body.

[0009] In some embodiments of the present invention, the top plates of adjacent I-beams have connecting bars extending laterally, and the connecting bars on both sides are connected to each other. The connecting bars are used in conjunction with concrete pouring to form wet joints, and the top plates of multiple I-beams are connected through wet joints.

[0010] In some embodiments of the present invention, the upper surface of the top plate of the I-beam is flush with the upper surface of the wet joint, the upper surface of the I-beam and the wet joint is a rough bearing surface that has been roughened, and an asphalt pavement layer of a set thickness is laid on the upper part of the rough bearing surface.

[0011] In some embodiments of the present invention, the bottom foundation includes a plurality of pile foundations disposed in the ground, a bridge pier is disposed on the top of the plurality of pile foundations, a cap beam is disposed on the top of the plurality of bridge piers, and a plurality of I-beams are erected parallel to each other and spaced apart on the top of the cap beams along a direction perpendicular to the span of the bridge body.

[0012] In a second aspect of the invention, a construction method for a prestressed HPFRC I-beam bridge using the pre-tensioned method is provided, comprising: Precast I-beams are produced by prestressing the steel strands during the precasting process. High-performance fiber-reinforced concrete is poured according to the different steel fiber volume ratios of the top plate, web plate, and bottom plate. The precast I-beams are then transported to the bridge site. The substructure of the bridge was constructed on-site, and I-beams were erected. Transverse diaphragms are poured at predetermined intervals between adjacent I-beams along the span of the bridge. Connecting bars are used to connect the top plates of adjacent I-beams and concrete is poured to form wet joints. The top surface of the I-beam and the top surface of the wet joint are roughened before the asphalt pavement layer is laid.

[0013] In some embodiments of the present invention, the precast I-beam specifically refers to: The steel strands are prestressed using the pre-tensioning method, and I-beam formwork is installed around the tensioned steel strands. According to the different steel fiber volume ratios of the top slab, web slab and bottom slab, high-performance fiber-reinforced concrete with different steel fiber volume ratios was mixed separately, and the flowability of the three types of concrete was made consistent by adjusting the water-reducing agent content, sand ratio and water-cement ratio in each ratio. The consistent flow properties refer to the fact that the difference between the slump and spread of the three types of concrete is controlled within a set range. High-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the bottom plate area of ​​the I-beam formwork. After the bottom plate is poured but before its initial setting, high-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the web area of ​​the I-beam formwork. After the web is poured but before its initial setting, high-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the top plate area of ​​the I-beam formwork. After the concrete is poured and cured to the set strength, a steel strand is laid to obtain an I-beam.

[0014] One or more technical solutions of the present invention have the following beneficial effects: To address the issues of shrinkage cracks and thermal deformation cracks caused by the low strength and poor tensile properties of ordinary concrete, the I-beams are made of high-performance fiber-reinforced concrete. This material has an extremely dense matrix, and with the differentiated steel fiber volume content set in the top plate, web plate and bottom plate respectively, the crack resistance performance of each part is precisely matched with the stress requirements. This eliminates the hidden danger of crack development from the material level, while effectively controlling material costs.

[0015] Secondly, to address the issues of prestressing tendon rusting and beam cracking caused by inadequate grouting in post-tensioned prestressed ducts, pre-tensioned prestressed steel strands are installed inside the I-beams. This eliminates the need for traditional corrugated pipe pre-reserved ducts and grouting procedures. After tensioning, the steel strands bond with high-performance fiber-reinforced concrete to form a unified structure, preventing corrosive media from seeping into the channels due to inadequate grouting and significantly improving the durability of the prestressed system.

[0016] Furthermore, addressing the issues of excessive self-weight and easy cracking of bridge decks caused by the traditional requirement of pouring a thick concrete bridge deck on top of the I-beam, the upper surface of the top plate of the I-beam is directly used as the load-bearing surface. The upper surface of the top plate is flush with the upper surface of the wet joint and an asphalt pavement layer is laid on it. This eliminates the intermediate concrete bridge deck layer, significantly reducing the self-weight of the superstructure and eliminating the common source of bridge deck cracking.

[0017] Furthermore, addressing the material waste and increased self-weight issues caused by the uniform distribution of ordinary steel bars across the entire cross-section of traditional I-beams, this invention incorporates a single layer of prestressed steel strands with large spacing along the length of the top slab of the I-beam to meet the longitudinal compression requirements of the top slab; and multiple layers of densely distributed prestressed steel strands along the length of the bottom slab to meet the longitudinal tension requirements of the bottom slab. This fully leverages the advantages of large-diameter, high-strength prestressed steel strands, reducing the number of prestressed steel strands, minimizing the space occupied by the strands, further reducing structural dimensions, and lowering material consumption. Additionally, double-leg stirrups are installed at both ends of the web of the I-beam along the span direction, while single-leg stirrups are installed in the mid-span region. Both double-leg and single-leg stirrups utilize ordinary steel bars, combined with the high strength and high toughness of high-performance fiber-reinforced concrete, ensuring the shear bearing capacity of the I-beam structure while significantly reducing the amount of ordinary steel bars, thus reducing self-weight and construction costs.

[0018] Furthermore, with the reduction in the self-weight of the bridge body, the load-bearing capacity of the pile foundations, piers, and cap beams is correspondingly reduced, which can reduce the size of the pile foundations, piers, and cap beams, thereby reducing the overall bridge height. This facilitates the reduction of approach bridge length and roadbed fill height, improves transportation and hoisting efficiency, significantly reduces the maintenance cost throughout the entire life cycle, and greatly extends the structural life. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of a prestressed HPFRC I-beam bridge provided in an embodiment of the present invention; Figure 2 A schematic cross-sectional view of a prestressed HPFRC I-beam bridge provided in an embodiment of the present invention; Figure 3 This is a structural schematic diagram of the I-beam, wet joint, and asphalt pavement layer provided in an embodiment of the present invention; Figure 4 This is a schematic cross-sectional view of the mid-span region of an I-beam provided in an embodiment of the present invention; Figure 5 This is a schematic cross-sectional view of the support area at both ends of the I-beam provided in an embodiment of the present invention; Figure 6 This is a schematic diagram showing the volumetric steel fiber content in different parts of an I-beam provided in an embodiment of the present invention.

[0020] In the diagram: 1. Pile foundation; 2. Pier; 3. Cap beam; 4. Guardrail; 5. I-beam; 51. Base slab; 52. Web; 53. Top slab; 54. Steel strand; 55. Single-leg stirrup; 56. Double-leg stirrup; 57. Ordinary steel reinforcement; 6. Wet joint; 7. Asphalt pavement layer; 8. Diaphragm. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] First, it should be noted that HPFRC is a high-performance fiber-reinforced concrete, which is a composite material of HPFRC matrix and three-dimensional randomly distributed fibers. It has the advantages of self-compacting, self-leveling, good workability, and excellent precast casting performance.

[0023] Example In a typical embodiment of the present invention, such as Figure 1 As shown, a prestressed HPFRC (High-Pressure Fiber Reinforced Concrete) I-beam bridge includes a bottom foundation and a bridge body situated on top of the bottom foundation. The bottom foundation comprises multiple pile foundations 1 embedded in the ground, with piers 2 atop each of the pile foundations 1, and cap beams 3 atop each of the piers 2. Multiple I-beams 5 are arranged along the span of the bridge body, parallel to each other and spaced apart from the top of the cap beams 3. The I-beams 5 are internally fitted with prestressed steel strands 54 and constructed using high-performance fiber-reinforced concrete.

[0024] This bridge structure is suitable for highway bridges with spans of 30m to 40m. The pile foundation 1, piers 2, and cap beam 3 together constitute the bridge's substructure support system, transferring the loads of the superstructure to the ground. Supports are installed at the top of cap beam 3, and the I-beam 5 is supported on top of cap beam 3 via these supports. The supports can accommodate minor displacements of the beam under temperature changes and vehicle loads.

[0025] The top surface of the top plate 53 of the I-beam 5 is directly paved with asphalt pavement as the bearing surface, eliminating the need for a concrete bridge deck, which significantly reduces the self-weight of the superstructure and the building height.

[0026] Traditional bridges require a thick concrete deck layer poured on top of the I-beams before laying an asphalt layer. During operation, this deck layer is prone to shrinkage cracks and temperature-induced deformation cracks. Once these cracks develop, moisture seeps in, causing the internal steel reinforcement to rust and the concrete to detach. This embodiment eliminates this additional deck layer, removing the root causes of these problems and saving significant on-site pouring work.

[0027] The bridge is also equipped with guardrails on both sides to protect passing vehicles.

[0028] In this embodiment, the I-beam 5 has a height of 125cm and includes a top plate 53, a web 52, and a bottom plate 51. In this embodiment, the top plate 53 has a width of 1.6m, and the bottom plate 51 has a width of 0.66m, with the top plate 53 being wider than the bottom plate 51. The top plate 53 has a thickness of 12cm to 15cm, and the web 52's thickness gradually changes from 12cm in the mid-span region to 14cm at both end supports.

[0029] When the I-beam 5 is under load, the mid-span region is dominated by bending moment, and the web 52 mainly provides shear resistance, with a relatively small shear force value. However, near the two end supports, the shear force reaches its maximum, requiring a thicker web 52 to resist the shear force. The variable thickness design not only meets the large shear force requirements near the two end supports of the I-beam 5, but also reduces the amount of material used in the mid-span region, achieving efficient material utilization.

[0030] The top slab 53, web 52, and bottom slab 51 of the I-beam 5 are made of high-performance fiber-reinforced concrete with different steel fiber volume fractions. The steel fiber volume fraction of the top slab 53 is 0.7% to 1.0%, that of the web 52 is 1.4% to 1.6%, and that of the bottom slab 51 is 0.3% to 0.5%. The steel fiber volume fraction of the bottom slab is less than that of the top slab, and the steel fiber volume fraction of the top slab is less than that of the web.

[0031] High-performance fiber-reinforced concrete is a novel structural material based on the principle of closest packing of multi-component powders. Its matrix possesses extremely high density, resulting in advantages such as high strength, high durability, and high toughness. The incorporated steel fibers effectively improve the tensile strength and crack resistance of the matrix, enabling the material to exhibit significant strain hardening characteristics under tensile stress. The different volumetric steel fiber dosages in different locations are determined based on the stress characteristics of each part.

[0032] When the top plate 53 is under longitudinal stress, it is a compression zone and has a low requirement for the tensile strength contribution of steel fibers. However, when it is under transverse stress as a one-way plate of the bridge deck, a steel fiber content of 0.7% to 1.0% can exert excellent crack resistance and ensure the shear resistance requirements at the root of the bridge deck.

[0033] The web 52 is configured with 1.4% to 1.6% steel fiber content, preferably 1.5% steel fiber content, to provide sufficient shear resistance for the beam structure.

[0034] The base plate 51 is under compression under the action of high-strength steel strands 54. High-performance fiber-reinforced concrete, together with prestressed steel strands 54, achieves flexural load resistance. A steel fiber content of 0.3% to 0.5% is sufficient to meet the requirements for crack resistance and durability in the base plate 51. Excessive steel fiber content has limited effect on improving the load-bearing capacity of the base plate 51, but instead significantly increases material costs.

[0035] Compared with conventional I-beams with a uniform steel fiber content of 1.5% across the entire cross section, the differentiated steel fiber content distribution can reduce the amount of steel fiber used and lower the cost of high-performance fiber-reinforced concrete materials.

[0036] like Figure 3 As shown, a preset distance is maintained between the top plates 53 of adjacent I-beams 5, and a wet joint 6 is provided at this preset distance. The wet joint 6 is made of connecting bars and concrete pouring, and adjacent I-beams 5 are connected through the wet joint 6. The upper surface of the top plate 53 of the I-beam 5 is flush with the upper surface of the wet joint 6, and an asphalt pavement layer 7 is laid on the upper surface of the top plate 53 of the I-beam 5 and the upper surface of the wet joint 6.

[0037] Several connecting bars are provided in the wet joint 6. These connecting bars extend laterally from the top plate 53 of the adjacent I-beam 5 and connect with each other. Then, concrete is poured to form an integral connection. The thickness of the wet joint 6 is equal to the thickness of the top plate 53 of the I-beam 5, so that the upper surface of the wet joint 6 and the upper surface of the top plate 53 are in the same plane, which facilitates the laying of the asphalt pavement layer 7.

[0038] like Figure 4 As shown, a single layer of prestressed steel strands 54 are installed in the top slab 53 of the I-beam 5, and multiple layers of prestressed steel strands 54 are installed in the bottom slab 51. The spacing between the layers of the prestressed steel strands 54 in the bottom slab 51 is smaller than the spacing between the distributed steel strands 54 in the top slab 53.

[0039] Because the reinforcement in the top slab 53, web 52, and bottom slab 51 of a traditional I-beam 5 is uniformly distributed without distinguishing the stress characteristics of each part, the reinforcement configuration of a traditional ordinary concrete I-beam 5 suffers from the problem of uniform distribution across the entire cross section and serious waste. However, in actual stress, the stress state of different parts of the I-beam 5 varies greatly. The top slab 53 bears compressive stress, the web 52 bears shear stress, and the bottom slab 51 bears tensile stress. The uniformly distributed reinforcement means that a large amount of reinforcement is placed in areas where high strength is not required, resulting in serious material waste.

[0040] In order to meet the load-bearing capacity requirements of the tension zone of the bottom plate 51, the traditional beam is equipped with multiple layers of reinforcement in the bottom plate 51. At the same time, the top plate 53 and the web plate 52 are also forced to be equipped with a considerable number of structural steel bars. The accumulation of a large amount of reinforcement directly increases the self-weight of the beam, further aggravating the difficulty of transportation and hoisting and the burden on the substructure.

[0041] Furthermore, in the traditional I-beam 5, the top plate 53 and bottom plate 51 have the same width. Due to the poor tensile strength of ordinary concrete, the bottom plate 51 is still prone to cracking even with a large amount of reinforcement. Neither the reinforcement nor the concrete is used efficiently.

[0042] This embodiment, based on the use of high-performance fiber-reinforced concrete and differentiated steel fiber content, further differentiates the reinforcement arrangement of the I-beam 5 to achieve synergistic effect. The top slab 53 has a width of 1.6m and a thickness of 12cm to 15cm. The top slab 53 is a one-way slab of the bridge deck in the transverse direction. A steel fiber volume content of 0.7% to 1.0% is sufficient to exert its excellent crack resistance performance, while ensuring the shear resistance requirements at the root of the bridge deck. Therefore, only a single layer of prestressed steel strands 54 are arranged transversely in the top slab 53 with a large spacing. Combined with high-performance fiber-reinforced concrete with a steel fiber volume content of 0.7% to 1.0%, the crack resistance and load-bearing requirements can be met.

[0043] The top slab 53 is equipped with double layers of ordinary steel bars 57, which are spaced apart from the prestressed steel strands 54, working together with the steel strands 54 in the top slab 53 to strengthen the overall structural strength. Ordinary steel bars 57 are also provided at the four corners of the bottom slab 51, and at the geometric center of the bottom slab 51 near the web 52, working together with the steel strands 54 in the bottom slab 51 to strengthen the overall structural strength. This differentiated configuration of ordinary steel bars 57 and steel strands 54, along with the differentiated steel fiber content, creates a synergistic effect, achieving efficient material utilization while ensuring the overall structural strength of the I-beam 5.

[0044] In this embodiment, ordinary steel bar 57 refers to non-prestressed steel bar used in reinforced concrete structures.

[0045] In this embodiment, the thickness of the web 52 gradually changes from 0.12m at the mid-span of the bridge to 0.14m at both ends of the support. Specifically, when the bridge span is 30m, the thickness of the web 52 within a 3m range from both ends of the I-beam toward the mid-span is 0.14m. The thickness of the web within the two 3m ranges gradually decreases along the length of the I-beam toward the mid-span region, while the thickness of the web within a 24m length range in the mid-span region is 0.12m.

[0046] The web 52 adopts a variable thickness design that increases from mid-span to the two end supports, precisely matching the shear force distribution law of a simply supported beam. The shear force is minimal at mid-span, and a thickness of 0.12m is sufficient to meet the shear resistance requirements; the shear force is maximum at the two end supports, and a thickness of 0.14m combined with a 3m gradual transition section can effectively resist the maximum shear force. Compared with a web of uniform thickness, each I-beam can reduce the amount of concrete used, thereby reducing the lifting weight of a single beam with a 30m span, significantly improving transportation and lifting efficiency, and reducing the load on the substructure.

[0047] Furthermore, the variable-thickness web 52, together with the double-limb stirrups 56, single-limb stirrups 55, and HPFRC, creates a synergistic effect. The shear force is greatest at the two end support areas, where the web 52 is thick (0.14m) and equipped with double-limb stirrups 56; the shear force is smaller in the mid-span area, where the web 52 is thin (0.12m) and equipped with single-limb stirrups 55, avoiding material waste in the mid-span area with uniform-thickness double-limb stirrups 56. Among them, the single-limb stirrups 55 are vertically positioned at the geometric center line of the web, and the double-limb stirrups 56 are vertically positioned on both sides of the geometric center line of the web.

[0048] High-performance fiber-reinforced concrete, together with double-leg stirrups 56 and single-leg stirrups 55, bears the load, suppresses cracking, and enhances the shear toughness of the web 52, ensuring that the thin web 52 and the area of ​​the single-leg stirrup 55 still have sufficient safety reserves. The synergy of these three elements reduces the weight of a single 30m span during hoisting, while eliminating two major causes of bridge deck cracking and incomplete grouting in the ducts, achieving a balance between load-bearing capacity, lightweight design, and durability.

[0049] The base slab 51 is 0.66m wide and contains multiple layers of large-diameter, high-strength prestressed steel strands 54 with small interlayer spacing and dense strands 54. These strands work together with the high-performance fiber-reinforced concrete to bear the enormous tensile force generated by bending moment. Because the base slab 51 is much narrower than the top slab 53, although multiple layers of prestressed steel strands 54 are used, the total amount used is still much lower than that of traditional beams.

[0050] The differentiated reinforcement significantly reduces the amount of reinforcement compared to the traditional reinforcement. The configuration of single-layer sparse prestressed steel strands 54 in the top slab, single-leg stirrups 55 in the mid-span area of ​​the web 52, and multi-layer dense prestressed steel strands 54 in the bottom slab significantly reduces the total amount of reinforcement while meeting the bearing capacity requirements, compared to the traditional uniform reinforcement throughout the entire cross section.

[0051] By eliminating the bridge deck composite layer design, the lifting weight of each I-beam 5 with a 30m span is reduced compared to the lifting weight of a regular concrete I-beam 5. The bending bearing capacity fully meets the structural design of traditional beams, and the shear resistance and durability are better. It is also easier to transport and construct, and reduces the self-weight of the bridge.

[0052] After tensioning, the prestressed steel strands 54 form a unified whole with the high-performance fiber-reinforced concrete through bond strength, jointly bearing the operational load. The high bond strength of the high-performance fiber-reinforced concrete enables the prestressing of the pre-tensioned method to be effectively transferred to the entire cross-section of the beam, with minimal prestress loss and high force transfer efficiency.

[0053] The prestressed steel strand 54 has a diameter of 17.8 mm and a tensile strength of 1960 MPa, which is greater than the 15.2 mm diameter and 1860 MPa tensile strength of the conventional prestressed steel strand 54. The larger diameter and higher strength of the steel strand 54 allow each strand to withstand greater tensile force, reducing the number of strands required for the same prestressing requirements, simplifying the beam reinforcement structure, and reducing the number of prestressed anchorage systems.

[0054] Transverse diaphragms are installed at predetermined intervals along the span direction between adjacent I-beams 5. The diaphragms are made of C50 cast-in-place concrete. Multiple diaphragms connect multiple I-beams 5 into a whole along the width direction of the bridge body, which can enhance the lateral stiffness of the bridge superstructure, improve the uniformity of lateral load distribution, and avoid the adverse situation of excessive stress on a single beam. In this embodiment, the width of the diaphragm is set to 30cm.

[0055] The upper surface of the top plate 53 of the I-beam 5 and the upper surface of the wet joint 6 are roughened bearing surfaces. The roughening process is carried out after the prefabrication of the I-beam 5 and the pouring of the wet joint 6. The bearing surfaces are roughened or chiseled using mechanical or manual methods to create a rough interface texture. This roughened surface increases the contact area and mechanical interlocking force between the asphalt pavement layer 7 and the bearing surface, effectively preventing slippage or delamination of the asphalt pavement layer 7 under vehicle loads.

[0056] The asphalt pavement layer 7 is 10cm thick and consists of a surface layer and a bonding layer. The surface layer is laid with dense-graded asphalt mixture, which has good anti-rutting and anti-skid properties. The bonding layer is applied to the roughened bearing surface to ensure a firm bond between the pavement layer and the bearing surface. Since the traditional concrete bridge deck is eliminated, the asphalt pavement layer 7 is laid directly on the upper surface of the top plate 53 of the I-beam 5 and the upper surface of the wet joint 6, which significantly reduces the amount of on-site concrete pouring work.

[0057] The construction method for this prestressed HPFRC I-beam bridge includes the following steps: The precast I-beam 5 is prestressed by pre-tensioning the steel strands 54 during the prefabrication process. High-performance fiber-reinforced concrete is poured according to the different steel fiber volume ratios of the top plate 53, web plate 52 and bottom plate 51. The precast I-beam 5 is then transported to the bridge site. Multiple pile foundations 1 are driven into the ground, and bridge piers 2 are set on the top of the multiple pile foundations 1 respectively. Cap beams 3 are installed on the top of the multiple bridge piers 2 respectively. Multiple I-beams 5 are erected parallel to each other along the span direction of the bridge body on the top of the cap beams 3. Transverse diaphragms 8 are cast at predetermined intervals between the webs 52 of adjacent I-beams 5 along the span direction of the bridge body. Connecting bars are used to connect the top plates 53 of adjacent I-beams 5 and concrete is poured to form a wet joint 6; specifically, when constructing the wet joint 6, first tie the connecting bars, then set up the formwork, then pour the concrete and vibrate it to compact it, and finally cure it until it reaches the design strength. The upper surface of the top plate 53 of the I-beam 5 and the upper surface of the wet joint 6 are roughened, and then the asphalt pavement layer 7 is laid.

[0058] The prefabrication process of I-beam 5 is as follows: Steel strands 54 and ordinary reinforcing bars 57 are arranged within the formwork of the I-beam 5. The two ends of the steel strands 54 are anchored to the tensioning platform and prestressed using the pre-tensioning method. The tension control stress is 80% of the standard value of the tensile strength of the steel strands 54. A dual-control method is adopted for tensioning, with the tension force as the main factor and the elongation value as the secondary factor for verification, to ensure that the prestress value of each steel strand 54 meets the design requirements.

[0059] High-performance fiber-reinforced concrete with different steel fiber volume ratios was mixed for the top slab 53, web 52, and bottom slab 51. The flowability of the three types of concrete was made consistent by adjusting the water-reducing agent dosage, sand ratio, and water-cement ratio in each mix design. Specifically, using the web 52 concrete as a benchmark, the mix design parameters were determined through experiments to ensure that the slump and spread values ​​of the three types of concrete were essentially the same.

[0060] Consistent flow properties mean that the difference in slump and spread of the three types of concrete is controlled within a set range. Ensuring that the slump and spread of the three types of concrete are consistent ensures that the concrete in each area fills the formwork evenly and densely during layered pouring, avoiding material cross-contamination due to differences in flowability. Weak interface bonding ensures that there are no connection gaps between the interface of the top slab 53, web 52, and bottom slab 51, and realizes the overall coordinated stress of the I-beam 5.

[0061] High-performance fiber-reinforced concrete with a corresponding steel fiber volume ratio is poured into the bottom slab 51 area of ​​the I-beam 5 formwork. The bottom slab 51 concrete has a low steel fiber volume ratio, which can fully fill the space at the bottom of the formwork and wrap the steel strands 54 and ordinary steel bars 57. During pouring, due to the self-compacting and self-leveling advantages of high-performance fiber-reinforced concrete, vibration is not required to ensure that the bottom slab 51 concrete is dense and free of air bubbles.

[0062] After the base slab 51 is poured and before its initial setting, high-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the web 52 area of ​​the I-beam 5 formwork. The web 52 area has the highest steel fiber volume ratio, resulting in better concrete cohesion. During the pouring process, the concrete pouring height is controlled to avoid segregation, and the single-leg stirrups 55 and double-leg stirrups 56 are wrapped vertically.

[0063] After the web 52 is poured and before its initial setting, high-performance fiber-reinforced concrete with the appropriate steel fiber volume ratio is poured into the top slab 53 area of ​​the I-beam 5 formwork. The steel fiber volume ratio of the top slab 53 concrete is moderate, and the upper surface of the top slab 53 needs to be smoothed after pouring. The top slab 53 is a relatively wide thin slab structure, so care should be taken to control the thickness and surface flatness of the top slab 53 during pouring, and it should be covered and cured in a timely manner after finishing.

[0064] After the concrete pouring in each area is completed, high-temperature steam curing is carried out. The construction of the curing shed and the curing plan are determined according to the specifications, dimensions, and curing requirements of the components. When the curing temperature is kept constant above 90 degrees Celsius, the curing time should not be less than 48 hours; when the curing temperature is kept constant above 80 degrees Celsius, the curing time should not be less than 72 hours. The relative humidity inside the steam curing shed should not be lower than 95%. A movable prestressing tensioning platform is used. After steam curing, the prestress is released, which can eliminate the prestress loss caused by shrinkage and significantly increase the effective prestress. The release should be carried out slowly and evenly, using jacks and wedges to gradually unload the prestress. After the release is completed, the exposed ends of the steel strands 54 are cut to obtain the finished I-beam 5.

[0065] The above construction method controls the pouring sequence of concrete in each area, pouring a layer of concrete before the initial setting of each layer to ensure a good overall bond between the areas. The consistent flow properties of the three types of concrete ensure that the concrete in each area can fill the formwork evenly and densely during the pouring process, avoiding material mixing or incomplete filling due to differences in flowability, thus ensuring the pouring quality and structural integrity of the I-beam 5.

[0066] Through the aforementioned structural design and construction methods, the prestressed HPFRC I-beam bridge, with a span of 30m, has a single I-beam lifting weight of only 41.4 tons, a reduction of approximately 38% compared to the 66.6 tons of a conventional concrete I-beam. The beam height is reduced from 200cm to 125cm, effectively lowering the bridge's overall height, which helps to reduce the length of approach bridges and the height of roadbed fill, thus lowering the overall project cost.

[0067] Traditional post-tensioned prestressed beam construction requires pre-embedding corrugated pipes to form reserved ducts within the beam structure. After the concrete is poured and reaches its strength, prestressed steel strands 54 are inserted for tensioning, and then cement grout is injected into the ducts. However, in actual engineering projects, incomplete grouting of the ducts is a common quality defect. Gaps easily remain between the grout and the steel strands 54, allowing moisture and corrosive media to seep in along these gaps, leading to corrosion or even breakage of the prestressed steel strands 54, seriously threatening structural safety. Simultaneously, the ducts occupy the beam's cross-sectional space, reducing the effective bearing area of ​​the concrete, and positioning deviations in the ducts can cause excessive prestress loss or localized stress concentration in the beam.

[0068] This embodiment adopts the pre-tensioning prestressing process. The steel strand 54 is tensioned and anchored to the platform before the concrete is poured. After pouring, the steel strand 54 directly forms an integral whole with the high-performance fiber-reinforced concrete through bonding force. There is no need to reserve ducts and grouting process, which fundamentally eliminates the risk of prestressing tendon rusting and breakage caused by incomplete grouting of ducts, and avoids the weakening of the cross section by ducts.

[0069] High-performance fiber-reinforced concrete is internally dense, corrosion-resistant, and freeze-thaw resistant, significantly extending the structural lifespan. It eliminates the need for bridge deck composite layers and post-tensioned prestressed ducts, thus eliminating two common causes of bridge defects: incomplete duct grouting and bridge deck cracking. This significantly reduces the workload of inspection and maintenance during bridge operation. It also uses less material and has lower carbon emissions, aligning with the green and low-carbon development trend of bridge engineering.

[0070] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A prestressed HPFRC I-beam bridge using the pre-tensioning method, characterized in that, Includes the bottom foundation and the bridge structure located on top of the bottom foundation; The bridge body includes multiple parallel I-beams arranged at intervals along the span direction. The I-beams are equipped with prestressed steel strands and are made of high-performance fiber-reinforced concrete. The I-beam includes a top plate, a web plate, and a bottom plate. The volumetric steel fiber content of the bottom plate is less than that of the top plate, and the volumetric steel fiber content of the top plate is less than that of the web plate. The width of the top plate of the I-beam is greater than the width of the bottom plate. There is a preset distance between the top plates of adjacent I-beams. A wet joint is provided at the preset distance. An asphalt pavement layer is laid on the upper surface of the top plate of the I-beam and the upper surface of the wet joint.

2. The HPFRC prestressed I-beam bridge as described in claim 1, characterized in that, The steel fiber volume content of the top plate is 0.7% to 1.0%, the steel fiber volume content of the web plate is 1.4% to 1.6%, and the steel fiber volume content of the bottom plate is 0.3% to 0.5%.

3. The HPFRC prestressed I-beam bridge as described in claim 1, characterized in that, A single layer of prestressed steel strands is arranged in the top slab along the length of the I-beam, and multiple layers of prestressed steel strands are arranged in the bottom slab along the length of the I-beam. The spacing of the prestressed steel strands in the bottom slab is smaller than that in the top slab.

4. A prestressed HPFRC I-beam bridge as described in claim 1, characterized in that, The thickness of the web of the I-beam is set to increase gradually from the mid-span region towards the two end supports along the span direction of the bridge body. The web of the I-beam at both ends of the bridge span direction is provided with double-leg stirrups vertically from the top plate to the bottom plate; The web of the I-beam in the mid-span region along the span direction of the bridge body is vertically provided with single-leg stirrups from the top plate to the bottom plate.

5. A prestressed HPFRC I-beam bridge as described in claim 1, characterized in that, A transverse diaphragm is installed between adjacent I-beams at a predetermined distance along the span direction, and the transverse diaphragm connects multiple I-beams into a whole along the width direction of the bridge body.

6. A prestressed HPFRC I-beam bridge as described in claim 1, characterized in that, The top plates of adjacent I-beams have connecting bars extending laterally, and the connecting bars on both sides are connected to each other; The connecting bars are used in conjunction with concrete pouring to form wet joints, and the top plates of multiple I-beams are connected through wet joints.

7. A prestressed HPFRC I-beam bridge as described in claim 6, characterized in that, The top surface of the I-beam is flush with the top surface of the wet joint. The top surfaces of the I-beam and the wet joint are rough bearing surfaces that have been roughened. An asphalt pavement layer of a set thickness is laid on top of the rough bearing surface.

8. A prestressed HPFRC I-beam bridge as described in claim 1, characterized in that, The bottom foundation includes multiple pile foundations set in the ground, with bridge piers set on top of each pile foundation, and cap beams set on top of each of the bridge piers. Multiple I-beams are erected parallel to each other and spaced apart on top of the cap beams along a direction perpendicular to the span of the bridge.

9. A construction method for a prestressed HPFRC I-beam bridge according to any one of claims 1-8, characterized in that, include: Precast I-beams are produced by prestressing the steel strands during the precasting process. High-performance fiber-reinforced concrete is poured according to the different steel fiber volume ratios of the top plate, web plate, and bottom plate. The precast I-beams are then transported to the bridge site. The substructure of the bridge was constructed on-site, and I-beams were erected. Transverse diaphragms are poured at predetermined intervals between adjacent I-beams along the span of the bridge. Connecting bars are used to connect the top plates of adjacent I-beams and concrete is poured to form wet joints. The top surface of the I-beam and the top surface of the wet joint are roughened before the asphalt pavement layer is laid.

10. The construction method of a prestressed HPFRC I-beam bridge as described in claim 9, characterized in that, The precast I-beams are specifically: The steel strands are prestressed using the pre-tensioning method, and I-beam formwork is installed around the tensioned steel strands. According to the different steel fiber volume ratios of the top slab, web slab and bottom slab, high-performance fiber-reinforced concrete with different steel fiber volume ratios was mixed separately, and the flowability of the three types of concrete was made consistent by adjusting the water-reducing agent content, sand ratio and water-cement ratio in each ratio. The consistent flow properties refer to the fact that the difference between the slump and spread of the three types of concrete is controlled within a set range. High-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the bottom plate area of ​​the I-beam formwork. After the bottom plate is poured but before its initial setting, high-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the web area of ​​the I-beam formwork. After the web is poured but before its initial setting, high-performance fiber-reinforced concrete with the corresponding steel fiber volume ratio is poured into the top plate area of ​​the I-beam formwork. After the concrete is poured and cured to the set strength, a steel strand is laid to obtain an I-beam.

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