A UHPC steel truss hollow composite beam and its construction method

Abstract

This invention provides a UHPC (Ultra-High-Pressure Polymer) steel truss hollow composite beam and its construction method. By employing the upper and lower flanges as the main components bearing axial compressive and tensile forces, respectively, this invention fully utilizes the ultra-high compressive strength and excellent durability of UHPC. Simultaneously, steel web members, composed of gusset plates and web members, are set between the upper and lower flanges, with the upper and lower gusset plates staggered in horizontal projection. Adjacent gusset plates are connected obliquely by web members, forming a hollow steel truss system. The complex shear force borne by the web is effectively converted into axial tensile and compressive forces in the web members of the steel web members, thereby releasing the tensile and compressive strength of the steel and achieving precise matching and efficient synergy of material properties. This invention significantly reduces the self-weight of the main beam, lowers the load on the substructure and foundation costs, eliminates the risk of web cracking, and improves structural durability. Moreover, each component can be prefabricated in the factory and assembled on-site, resulting in fast construction speed and controllable quality, making it suitable for bridges in large-span, high-intensity seismic zones.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering technology, and in particular to a UHPC steel truss hollow composite beam and its construction method. Background Technology

[0002] In the field of bridge engineering, the main girder structure is a key component that directly bears the load of the bridge deck and transfers it to the substructure. Its performance directly determines the bridge's span capacity, safety and durability, construction efficiency and life-cycle economic cost. In pursuit of greater span capacity, higher construction efficiency and better economy, the form of the main girder structure continues to evolve.

[0003] Early, widely used traditional structures such as prestressed concrete T-beams and small box girders suffered from inherent defects due to the low tensile strength of concrete, including heavy self-weight, susceptibility to web cracking, and long construction periods. To overcome these defects, improved forms such as steel-concrete composite beams and corrugated steel web composite beams emerged, effectively reducing the structure's self-weight by using steel. In recent years, with the maturation of ultra-high performance concrete (UHPC) materials, prestressed UHPC I-beams without web reinforcement have appeared.

[0004] However, reinforced concrete I-beams have a large self-weight, corrugated steel webs use thick concrete, the amount of steel reinforcement is huge, the substructure is often large in size, and the overall cost is high. UHPC I-beam structures without web reinforcement are heavy, expensive, and have high transportation costs. The webs of the above bridges still mainly serve as shear-bearing components, resulting in low overall structural efficiency and excessively high costs.

[0005] In view of this, the inventor has specifically designed a UHPC steel truss hollow composite beam and its construction method, which leads to this invention. Summary of the Invention

[0006] To solve the above problems, the technical solution of the present invention is as follows: A UHPC steel truss hollow composite beam includes at least two hollow steel trusses arranged laterally side by side. Each steel truss includes an upper flange for bearing axial pressure, a lower flange for bearing axial tension, and a steel web member unit disposed between the upper and lower flanges. The steel web member unit is used to transmit shear force and includes several upper node plates located at the bottom of the upper flange, a lower node plate located at the lower flange, and several web members. The upper node plates and lower node plates are staggered in the horizontal projection, and adjacent upper node plates and lower node plates are inclinedly connected by web members.

[0007] Preferably, the bottom surface of the upper flange is provided with an exposed shear connector and is connected to the upper node plate through the shear connector; the top surface of the lower flange is pre-embedded with an opening plate connector, and the lower node plate is embedded in the opening plate connector and filled with grouting material.

[0008] Preferably, the shear connector is a group of shear studs, the upper end of which extends into and is anchored in the concrete of the upper flange, and the lower end is fixed to the upper node plate.

[0009] Preferably, it also includes a plurality of transverse node members and a transverse connecting system, wherein both ends of the plurality of transverse node members are respectively connected to the upper flange of the adjacent steel truss. The lateral connection system is a K-shaped or X-shaped support structure made of steel profiles, with its ends connected to the lateral node members.

[0010] Preferably, the edges of the upper and lower node plates are rounded.

[0011] Preferably, both the upper flange and the lower flange include several prefabricated segments, and prestressed ducts are arranged within the several prefabricated segments.

[0012] Preferably, the upper and lower flanges of several adjacent prefabricated segments are connected by adhesive joints and shear keyways provided on the end faces, respectively.

[0013] Preferably, the area at the end of the web member located on the upper flange is filled with micro-expansion concrete.

[0014] Preferably, the inclined web members located in the girder web are H-beams, and the vertical web members located at the ends of the precast segments are square steel.

[0015] This invention also provides a construction method for a UHPC steel truss hollow composite beam, comprising the following steps: The upper and lower flanges are prefabricated in the factory, and the web members, upper node plates, and lower node plates are machined. At the bridge site, multiple web members are connected to multiple upper node plates and lower node plates to form a hollow steel truss for each composite beam unit. The open-web steel trusses of the multi-beam composite unit are installed in a horizontal, side-by-side configuration. The prefabricated upper and lower flanges are hoisted to the design positions of the corresponding open-web steel truss and connected to the corresponding upper and lower node plates respectively. Post-tensioning and joint treatment are carried out to make the composite beam a whole.

[0016] The technical solution provided by this invention has the following beneficial effects: This invention fully utilizes the ultra-high compressive strength and excellent durability of UHPC by employing the upper and lower flanges as the main components bearing axial compressive and tensile forces, respectively. Simultaneously, steel web members, consisting of gusset plates and web members, are set between the upper and lower flanges, with the upper and lower gusset plates staggered in horizontal projection. Adjacent gusset plates are connected obliquely by web members, forming a hollow steel truss system. The complex shear force borne by the web is effectively converted into axial tensile and compressive forces in the web members of the steel web members, thereby releasing the tensile and compressive strength of the steel and achieving precise matching and efficient synergy of material properties. Compared with existing technologies, this invention significantly reduces the self-weight of the main beam, lowers the load on the substructure and foundation costs; eliminates the risk of web cracking, and improves structural durability; reduces the amount of steel and concrete used through the hollow truss design, significantly reducing costs; moreover, each component can be prefabricated in the factory and assembled on-site, resulting in fast construction speed and controllable quality; the overall structure has high efficiency and is particularly suitable for bridges with long spans and in high-intensity seismic zones. Attached Figure Description

[0017] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0018] in: Figure 1 This is a schematic diagram of a partial structure of the present invention; Figure 2 This is a schematic diagram of a partial structure of the upper flange section in this invention; Figure 3 This is a schematic diagram of a partial structure of the lower flange section in this invention; Figure 4 This is a schematic diagram of a partial structure of the shear keyway cross section in this invention; Figure 5 This is a schematic diagram of the beam bridge simulation experiment in this invention.

[0019] Label Explanation: 1. Hollow steel truss; 2. Upper flange; 21. Shear connector; 3. Lower flange; 31. Perforated plate connector; 4. Upper node plate; 5. Lower node plate; 6. Web member; 7. Transverse node member; 8. Prestressed duct; 9. Adhesive joint; 10. Shear keyway. Detailed Implementation

[0020] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0021] Please see Figures 1-5This is a UHPC steel truss hollow composite beam, a preferred embodiment of the present invention, comprising at least two hollow steel trusses 1 arranged side-by-side along the transverse direction of the bridge. Each steel truss includes an upper flange 2 for bearing axial compressive force, a lower flange 3 for bearing axial tensile force, and steel web members 6 connecting the two. The upper flange 2 and lower flange 3 are both made of UHPC material. The steel web members 6 are used to transmit shear force and are specifically composed of several upper node plates 4 located at the bottom of the upper flange 2, lower node plates 5 located at the top of the lower flange 3, and several web members 6. The upper node plates 4 and lower node plates 5 are staggered in horizontal projection, and adjacent upper node plates 4 and lower node plates 5 are inclinedly connected by web members 6, thereby forming a spatial triangular truss force-bearing system. Through the above construction, this invention transforms the complex shear force borne by the traditional solid web into the axial tensile and compressive forces of the web members 6 in the steel web member 6 unit. This fully utilizes the excellent compressive strength of UHPC material while maximizing the tensile and compressive strength of steel, achieving efficient synergy between the two materials. Compared with the prior art, this specific implementation effectively solves the problems of heavy self-weight of traditional bridge main beams, easy cracking of webs, low material utilization efficiency, and high cost in the background art, achieving the following beneficial effects: First, it significantly reduces the self-weight of the structure and reduces the load on the substructure; second, it eliminates the hidden danger of web cracking and improves durability; third, the hollow truss design reduces the amount of steel and concrete used, reducing the overall cost; fourth, each component can be prefabricated in the factory and assembled on site, resulting in fast construction speed and controllable quality; fifth, the overall structure has high efficiency and is particularly suitable for bridges with large spans and in high-intensity earthquake zones.

[0022] Please see Figures 1-5The bottom surface of the upper flange 2 is provided with an exposed shear connector 21 (in this embodiment, a group of shear nails). The lower end of the shear connector 21 is fixedly connected to the upper node plate 4, and the upper end extends into and is anchored in the concrete of the upper flange 2. The top surface of the lower flange 3 is pre-embedded with a perforated plate connector 31. The lower node plate 5 is embedded in the hole of the perforated plate and filled with C50 micro-expansion concrete. The C50 micro-expansion concrete contains UEA expansion agent, and its limited expansion rate is controlled at 0.02%-0.04%. It can generate micro-expansion in volume during the hydration and hardening process, thereby eliminating the gap between the lower node plate 5 and the hole wall of the perforated plate, ensuring that the two are tightly connected and share the load. Through the above construction, this invention achieves reliable and efficient shear force transfer between the upper flange 2 and the steel web member 6. The shear connector 21 converts the vertical load borne by the upper flange 2 into the axial force of the node plate and the web member 6. The lower flange 3 is embedded in the lower node plate 5 through the perforated plate connector 31, and with the filling and anchoring of micro-expansion concrete, a strong mechanical interlocking and pin-like effect is formed, effectively anchoring the huge axial tensile force borne by the lower flange 3. This specific embodiment directly solves the problems of low shear resistance and easy cracking of traditional concrete beam webs in the background art. Its beneficial effects are: on the one hand, the combined application of the shear connector 21 and the perforated plate connector 31 greatly improves the bond strength of the steel-UHPC interface, ensuring that the two materials are subjected to force in concert and avoiding interface damage; on the other hand, the filling of C50 micro-expansion concrete eliminates the connection gap, enhancing the overall structure and durability.

[0023] Please see Figures 1-4 The UHPC steel truss hollow composite beam also includes several transverse node members 7 and a transverse connection system. The two ends of the transverse node members 7 are fixedly connected to the upper flanges 2 (or upper node plates 4) of two adjacent steel trusses, thus connecting multiple independent main trusses into a whole in the transverse direction. The transverse connection system consists of K-shaped or X-shaped support structures made of steel profiles, with their ends connected to the transverse node members 7. Specifically, the transverse node members 7 act as connecting bases, rigidly connecting the upper flanges 2 of adjacent trusses, while the K-shaped or X-shaped supports provide spatial bracing, together forming a spatial transverse stability system. Its beneficial effects include significantly improving the transverse stiffness and torsional resistance of the bridge, resisting wind loads, seismic forces, and vehicle eccentric loads.

[0024] Please see Figures 1-4The edges of the upper node plate 4 and the lower node plate 5 are rounded. Specifically, the radius of curvature R of this rounded transition is set to 20mm to 30mm. The surface of the transition area is ground to remove all burrs, sharp corners, and welding spatter, and the rounded edges are lightly hammered after welding to eliminate residual tensile stress. Under the combined action of welding residual stress and operational live load, the right-angled edges of traditional node plates are prone to forming high-stress zones at the sharp corners, leading to fatigue cracking or even brittle fracture. This invention significantly reduces the stress concentration factor in this area (by approximately 30% to 40%) by processing the node plate edges into rounded transitions. Simultaneously, combined with post-weld grinding and hammering, residual welding tensile stress is eliminated, greatly improving the fatigue life of the node plate. This improves the fatigue resistance of the composite beam under long-term alternating loads, extending the service life of the bridge; secondly, it enhances the safety reserve of the node area, avoiding the risk of sudden brittle fracture.

[0025] Please see Figures 1-4 Both the upper flange 2 and the lower flange 3 of the UHPC are assembled from several precast segments along the longitudinal direction of the bridge. Each precast segment contains pre-tensioned prestressed ducts 8 and post-tensioned prestressed ducts 8 arranged along its length. Specifically, during factory prefabrication, the pre-tensioned prestressed ducts 8 are tensioned and temporarily anchored to the abutment before the UHPC is poured. After the UHPC reaches 90% of its design strength, the tension is released, allowing the prestress to be transferred to the segment and providing initial prestress for the flange. The post-tensioned prestressed ducts 8 are pre-reserved within the segment. After the segment is assembled on site, they are threaded through and tensioned, connecting the flanges of the entire bridge into a whole. Its beneficial effects are as follows: First, the pre-tensioning method imparts independent prestress to each precast segment, significantly improving the segment's crack resistance during transportation and hoisting, and avoiding damage during construction. Second, the post-tensioning method connects the segments into a continuous whole, eliminating weak links at the joints, and ensuring that the rear flange of the completed bridge is under compression throughout its entire length, completely preventing the generation of cracks during operation. Third, the combination of segment precasting and double prestressing enables rapid, template-free construction of the bridge, significantly shortening on-site operation time, while reducing material consumption and substructure load, resulting in excellent overall economy and durability.

[0026] Please see Figures 1-4Several adjacent precast segments are joined at their ends via adhesive joints 9 and shear keyways 10, respectively, through the upper flange 2 and lower flange 3 of the UHPC. Specifically, on the end face of each precast segment, a matching shear key (convex key and groove) is pre-formed along the circumferential or periphery. The key tooth height is typically 20mm to 30mm, and the keyway depth matches it. Simultaneously, a layer of epoxy resin structural adhesive with a thickness of approximately 2mm to 3mm is applied to the end face. During assembly, the end faces of adjacent segments are aligned, the convex key is precisely embedded in the groove, and a temporary clamping force is applied to uniformly extrude and cure the adhesive layer, forming the adhesive joint 9. Through this structure, the interlocking of the shear keyways 10 directly resists the enormous shear force at the joint, enabling the shear strength of the joint to reach or even exceed that of the segment's concrete body.

[0027] Please see Figures 1-4 The space formed at the end of the web member 6 (i.e., around the connection between the web member 6 and the upper node plate 4) in the beam end region is filled with C50 micro-expansion concrete. Specifically, UEA expansion agent is added to this micro-expansion concrete, and its restricted expansion rate is controlled at 0.02% to 0.04%. A pressurized grouting process is used to ensure that the concrete is tightly bonded to the inner wall of the steel web member 6 and the node plate without shrinkage gaps. The filling range is the internal cavity of the web member 6 in the last 1 to 2 sections of the beam end region. Before grouting, the inner wall of the steel component should be cleaned and derusted, and vent holes should be set to ensure that the grouting is dense.

[0028] Please see Figures 1-4 The inclined web members 6 located in the truss web are H-beams, while the vertical web members 6 located at the ends of the precast segments are square steel. In the open-web steel truss 1, the inclined web members 6 located in the mid-span region are H-beams, while the vertical web members 6 located at the ends of the precast segments (i.e., the beam end region) are square steel. Specifically, the cross-sectional specifications of the H-beams gradually decrease from the support point to the mid-span according to the stress requirements; for example, HW250×255 is used near the support point, and HW200×200 is used at the mid-span. The side length and wall thickness of the vertical square steel at the ends are determined by calculation and are usually 200mm×200mm×16mm. Through the above structure, the present invention effectively solves the technical problems of the traditional steel truss web member 6 having a single type selection, complex end node stress, and insufficient buckling resistance in the prior art.

[0029] Please see Figures 1-4 A construction method for a UHPC steel truss hollow composite beam includes the following steps: Factory prefabrication stage: Separately process and manufacture each web member 6, upper node plate 4, lower node plate 5 of the steel truss, as well as prefabricate the upper flange 2 and lower flange 3; when prefabricating the UHPC flange, accurately position and pre-embed shear stud group, pre-tensioned prestressed duct 8, and post-tensioned prestressed duct 8; after the UHPC strength reaches more than 90% of the design strength, release the pre-tensioned prestressed duct 8; Segment assembly and transportation stage: In the factory, prefabricated steel truss members are welded to the node plates to form the open-web steel truss 1 web plate system, and it is assembled with the prefabricated UHPC upper and lower flanges 3 through connectors to form composite beam segments; multiple segments are transported to the bridge site; On-site installation and integration stage: Multiple composite beam segments are assembled at the bridge site, and the segments are connected in series and tensioned through post-tensioned prestressed ducts 8 to form an integral load-bearing structure for the entire beam; Install crash barriers and related facilities.

[0030] This embodiment conducts a load simulation experiment on the bridge in this invention, such as... Figure 5 As shown, looking at the strain gauges at the reinforcing bars, the curves change smoothly and almost linearly in the early stages of loading, indicating good coordination between the reinforcing bars and the UHPC, with the structure primarily functioning elastically. As the load continues to increase, the curves begin to differentiate significantly: a few gauges show faster strain growth accompanied by minor fluctuations, reflecting the increasing proportion of tensile force borne by the reinforcing bars as cracks gradually develop, and strain "jitter" caused by localized bond slippage and repeated crack opening and closing. In the later stages, one curve exhibits an abnormal pattern of sudden drop and rebound, more like gauge point debonding or signal instability, possibly corresponding to instantaneous redistribution caused by sudden local damage. The strain curves at the strain gauges in the web members show a clear division between tension and compression: some gauges show a continuous positive increase with the load, indicating that the web member is mainly under tension; more gauges show a negative trend, indicating that these web members are mainly under compression, and the compressive strain gradually accumulates with the load. In the early and middle stages, the curves remain largely linear, indicating a stable force transmission path and a relatively clear axial force distribution in the truss. During the high-load stage, the descent rate of the compression measuring points accelerates, and some curves show broken lines or slight abrupt changes, indicating that the stiffness change or force flow adjustment in the nodal area begins to be significant, and the compression web member may be entering a more sensitive nonlinear stage. The main pattern in this figure is "stable axial force distribution, with enhanced nonlinearity on the compression side in the later stage".

[0031] In summary, this invention fully utilizes the ultra-high compressive strength and good durability of UHPC by employing the upper flange 2 and lower flange 3 as the main components bearing axial compressive and tensile forces, respectively. Simultaneously, a steel web member 6 unit, composed of node plates and web members 6, is set between the upper and lower flanges 3, with the upper and lower node plates 5 staggered in horizontal projection. Adjacent node plates are connected obliquely by the web members 6, forming a hollow steel truss system 1. The complex shear force borne by the web plate is effectively converted into axial tensile and compressive forces in the web members 6 of the steel web member 6 unit, thereby releasing the tensile and compressive strength of the steel and achieving precise matching and efficient synergy of material properties. Compared with existing technologies, this invention significantly reduces the self-weight of the main beam, lowers the load on the substructure and foundation costs; eliminates the risk of web plate cracking, and improves structural durability; reduces the amount of steel and concrete used through the hollow truss design, significantly reducing costs; moreover, each component can be prefabricated in the factory and assembled on-site, resulting in fast construction speed and controllable quality; the overall structure has high efficiency and is particularly suitable for bridges with long spans and in high-intensity seismic zones.

[0032] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A UHPC steel truss hollow composite beam, characterized in that, The system comprises at least two horizontally arranged open-web steel trusses. Each steel truss includes an upper flange for bearing axial pressure, a lower flange for bearing axial tension, and a steel web member unit disposed between the upper and lower flanges. The steel web member unit is used to transmit shear force and includes several upper node plates located at the bottom of the upper flange, a lower node plate located at the lower flange, and several web members. The upper and lower node plates are staggered in the horizontal projection, and adjacent upper and lower node plates are connected obliquely by web members.

2. The UHPC steel truss hollow composite beam according to claim 1, characterized in that, The bottom surface of the upper flange is provided with an exposed shear connector and is connected to the upper node plate through the shear connector; the top surface of the lower flange is pre-embedded with an opening plate connector, and the lower node plate is embedded in the opening plate connector and filled with grouting material.

3. A UHPC steel truss hollow composite beam according to claim 2, characterized in that, The shear connector is a group of shear studs, with the upper end of the group of shear studs extending into and anchoring in the concrete of the upper flange, and the lower end fixed to the upper node plate.

4. A UHPC steel truss hollow composite beam according to claim 1, characterized in that, It also includes several transverse node components and transverse connecting systems, with both ends of the transverse node components respectively connected to the upper flange of the adjacent steel truss. The lateral connection system is a K-shaped or X-shaped support structure made of steel profiles, with its ends connected to the lateral node members.

5. A UHPC steel truss hollow composite beam according to claim 1, characterized in that, The edges of the upper and lower node plates are rounded.

6. A UHPC steel truss hollow composite beam according to claim 1, characterized in that, Both the upper and lower flanges include several prefabricated segments, and prestressed ducts are arranged within several of the prefabricated segments.

7. A UHPC steel truss hollow composite beam according to claim 6, characterized in that, The upper and lower flanges of several adjacent prefabricated segments are connected by adhesive joints and shear keyways provided on the end faces, respectively.

8. A UHPC steel truss hollow composite beam according to claim 1, characterized in that, The area at the end of the web member located on the upper flange is filled with micro-expansion concrete.

9. A UHPC steel truss hollow composite beam according to claim 1, characterized in that, The inclined web members located on the girder are H-shaped steel, and the vertical web members located at the ends of the precast segments are square steel.

10. A construction method for a UHPC steel truss hollow composite beam as described in any one of claims 1-9, characterized in that, Includes the following steps: The upper and lower flanges are prefabricated in the factory, and the web members, upper node plates, and lower node plates are machined. At the bridge site, multiple web members are connected to multiple upper node plates and lower node plates to form a hollow steel truss for each composite beam unit. The open-web steel trusses of the multi-beam composite unit are installed in a horizontal, side-by-side configuration. The prefabricated upper and lower flanges are hoisted to the design positions of the corresponding open-web steel truss and connected to the corresponding upper and lower node plates respectively. Post-tensioning and joint treatment are carried out to make the composite beam a whole.

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