Longitudinally segmented steel-concrete composite precast small box girder bridge and construction method

Abstract

The application discloses a longitudinally segmented steel-concrete mixed precast small box girder bridge and a construction method. The bridge is arranged with two or more mixed precast small box girders in the transverse direction of the bridge. Each two adjacent mixed precast small box girders are connected through a small box girder transverse cast-in-situ segment and a transverse field welding seam. Each mixed precast small box girder is formed by a segment method and is divided into six types of segments in the longitudinal direction of the bridge, including a side support point segment, a transverse beam precast segment, a side span variable height segment, a middle support point transverse beam segment, a middle span variable height segment and a steel-concrete composite beam segment, which are tightly connected together after being tensioned by prestressed steel strands arranged along the longitudinal direction of the bridge. During construction, the segments of each mixed precast small box girder are manufactured, spliced and transversely connected in sequence. The application can ensure that the transportation and hoisting of the small box girders can be completed by conventional equipment, reduces the construction difficulty and improves the construction speed.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to longitudinally segmented precast steel-concrete composite small box girder bridges and their construction methods. Background Technology

[0002] In urban bridges, prefabricated small box girder bridges (such as urban viaducts) are designed using standardized prefabricated structures.

[0003] In the existing technology, the standard section has a span of 25 m to 35 m, and from top to bottom, it consists of: precast concrete small box girder, precast cap beam, precast pier, cast-in-place pile cap + precast steel cage, bored pile + precast steel cage, and precast crash barrier precast together with the edge beam.

[0004] The limitations of using small box girders in existing technologies mainly include the following:

[0005] (1) Applicable span is not large. Due to factors such as land transportation and on-site hoisting, the maximum commonly used span of small box girders is 35m. Small box girders with bridge spans of more than 40m are no longer applicable.

[0006] (2) The lower cap beam is large. Small box girders are multi-beam bridge spans, and generally have a cap beam at the bottom. When the bridge width reaches six lanes or more, the cap beam is large and transportation and hoisting are more difficult.

[0007] Therefore, how to solve the application problems of small box girders has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of the above-mentioned deficiencies of the prior art, the present invention provides a longitudinally segmented precast steel-concrete composite small box girder bridge and a construction method thereof. The purpose is to ensure that the transportation and hoisting of the small box girders can be completed by conventional equipment, thereby reducing construction difficulty and increasing construction speed.

[0009] To achieve the above objectives, the present invention discloses a longitudinally segmented steel-concrete composite precast small box girder bridge; the bridge has two or more composite precast small box girders arranged in the transverse direction; each pair of adjacent composite precast small box girders are connected by transverse cast-in-place sections and transverse field welded joints.

[0010] For bridges with only two hybrid precast small box girders in the transverse direction, both hybrid precast small box girders are edge beams;

[0011] For a bridge with three or more of the aforementioned precast mixed box girders in the transverse direction, the two precast mixed box girders located on both sides of the transverse direction are side beams, and each precast mixed box girder located between the two side beams is a middle beam.

[0012] Each of the aforementioned hybrid precast small box girders is manufactured using the segmental method, and in the longitudinal direction of the bridge, it includes, in sequence, the side support segment, the crossbeam precast segment, the side span height-changing segment, the middle support crossbeam segment, the middle span height-changing segment, and the steel-concrete composite beam segment. All of them are tightly connected together after being tensioned by prestressed steel strands set along the longitudinal direction of the bridge.

[0013] Each of the aforementioned side support segments includes a prefabricated portion inside the small box girder box, a prefabricated portion of the top slab outside the small box girder box, and a prefabricated portion of the side support crossbeam.

[0014] Each of the side support segments of the hybrid precast small box girder that serves as the side beam is provided with a precast side support crossbeam.

[0015] Each of the side support segments of the hybrid precast small box girder that serves as the central beam is provided with two precast side support crossbeams.

[0016] Each of the aforementioned precast crossbeam segments includes a precast portion inside the small box girder box, a precast portion of the top slab outside the small box girder box, and a precast portion of the inner crossbeam.

[0017] Each of the prefabricated crossbeams of the hybrid prefabricated small box girder that serves as the side beam is provided with one prefabricated inner crossbeam section.

[0018] Each of the precast crossbeams of the hybrid precast small box girder that serves as the central beam is provided with two precast inner crossbeam sections.

[0019] Each of the aforementioned side span height-changing sections includes the inner part of the small box girder box and the prefabricated outer top slab of the small box girder box;

[0020] Each of the aforementioned mid-support crossbeam segments includes a prefabricated portion inside the small box girder box, a prefabricated portion of the top slab outside the small box girder box, and a prefabricated portion of the mid-support crossbeam.

[0021] Each of the middle support crossbeam segments of the hybrid precast small box girder that serves as the side beam is provided with a precast middle support crossbeam section.

[0022] Each of the mixed precast small box girders that serves as the central beam has two precast central beam sections in the central support crossbeam segment.

[0023] Each of the aforementioned mid-span variable-height sections includes the inner part of the small box girder box and the prefabricated outer top slab of the small box girder box;

[0024] Each of the steel-concrete composite beam segments includes a prefabricated steel structure portion of the composite beam segment, a prefabricated crossbeam portion of the composite beam segment, and a cast-in-place concrete portion of the top slab of the composite beam segment;

[0025] Each of the aforementioned composite beam segments comprises two pre-embedded sections and a post-installation section, which includes a portion cut to allowance and welded to the pre-embedded sections.

[0026] Each of the steel-concrete composite beam segments of the hybrid precast small box girder that serves as the side beam is provided with several precast crossbeam portions of the composite beam segment inwards.

[0027] Each of the steel-concrete composite beam segments of the hybrid precast small box girder that serves as the central beam is provided with several precast crossbeam portions of the composite beam segments in both directions.

[0028] Each of the steel-concrete composite beam segments of the hybrid precast small box girder that serves as the edge beam is provided with a concrete cantilever arm on its outer side.

[0029] Preferably, each of the side support segment, each of the precast beam segment, each of the side span height-changing segment, each of the middle support beam segment and each of the middle span height-changing segment is provided with an internal prestressing system;

[0030] Each of the aforementioned side beams and middle beams, each of the aforementioned middle support crossbeam segments, each of the aforementioned mid-span variable height segments, and each of the aforementioned steel-concrete composite beam segments is provided with an external prestressing system.

[0031] Preferably, each of the side support segments, each of the precast crossbeam segments, each of the side span height-changing segments, each of the middle support crossbeam segments, and each of the middle span height-changing segments has shear keys installed at the longitudinal splice joints of the precast box girder portion.

[0032] Preferably, epoxy resin adhesive is applied to the splice joint along the bridge direction for each of the following: side support segment, each of the following precast crossbeam segments, each of the following side span height-changing segments, each of the following middle support crossbeam segments, and each of the following middle span height-changing segments before splicing.

[0033] Preferably, a steel-concrete composite section is provided at the connection of each mid-span variable-height section and each steel-concrete composite beam section in the longitudinal direction of the bridge.

[0034] Each of the steel-concrete composite sections is divided into several small compartments on its cross-section;

[0035] Each of the small compartments is equipped with stud shear keys in its top and bottom plates;

[0036] Each of the top plates is provided with a pouring hole.

[0037] Preferably, the length of each precast crossbeam segment along the bridge direction is 0.3 m to 0.5 m;

[0038] The longitudinal length of each of the aforementioned transverse span height-changing sections, each of the aforementioned mid-support crossbeam sections, and each of the aforementioned mid-span height-changing sections is 9.6 m to 10 m.

[0039] The height of each of the aforementioned side support segments, each of the aforementioned precast crossbeam segments, and each of the aforementioned steel-concrete composite beam segments is 2.2m;

[0040] The height of the middle crossbeam in each of the aforementioned middle support crossbeam segments within the beam range is 4.0m;

[0041] The height of each of the aforementioned crossbeams along the bridge direction on both sides is 3.3 m to 3.8 m;

[0042] The beam height of each of the aforementioned side span variable height sections and each of the aforementioned middle span variable height sections is 2.2 m to 3.8 m;

[0043] The spacing between the precast beams of each of the aforementioned precast beam segments, each of the aforementioned side span height-changing segments, each of the aforementioned middle support beam segments, and each of the aforementioned middle span height-changing segments is 4.1m, and a 1.1m cast-in-place wet joint is provided between each of the precast beams.

[0044] The spacing between the precast beams in each of the aforementioned central support beam segments is 4.1m, and adhesive joints are provided between the precast beams.

[0045] The spacing between steel beams in each steel-concrete composite beam segment is 4.1m, and the top slab of each steel-concrete composite beam segment is cast in place.

[0046] The width of each of the side support segment, the precast crossbeam segment, the side span variable height segment, the middle span variable height segment, and the middle support crossbeam segment of the hybrid precast small box girder that serves as the middle beam is 3.0m.

[0047] The width of the crossbeam segment at the central support of each of the hybrid precast small box girders, which serves as the central beam, is 4.1m.

[0048] The steel beam width of each steel-concrete composite beam segment of the hybrid precast small box girder that serves as the central beam is 3.0m;

[0049] The width of each of the side support segments, the precast crossbeam segments, the side span variable height segments, the middle support crossbeam segments, and the middle span variable height segments of the hybrid precast small box girder that serves as the side beam is 3.6m.

[0050] The width of the crossbeam segment at the middle support of each of the hybrid precast small box girders that serves as the side beam is 4.15m.

[0051] Each steel-concrete composite beam segment of the hybrid precast small box girder that serves as the edge beam has a steel beam width of 3.0m and a 0.6m concrete cantilever arm on the outside.

[0052] The top plate thickness of the prefabricated portion of the small box girder in each of the following segments—the side support segment, the side span height-changing segment, the middle support beam segment, and the middle span height-changing segment—is 0.2 m to 0.25 m, the web plate thickness is 0.22 m to 0.35 m, and the bottom plate thickness is 0.2 m to 0.35 m.

[0053] The thickness of the prefabricated portion of the outer top slab of each of the small box girders is 0.25m;

[0054] Each of the aforementioned precast beam sections has a thickness of 0.3m;

[0055] The thickness of the top plate of the precast steel beam in each of the steel-concrete composite beam segments is 16mm, the thickness of the web plate is 20mm, and the thickness of the bottom plate is 30mm.

[0056] The thickness of the cast-in-place concrete top slab for each of the steel-concrete composite beam segments is 250 mm.

[0057] The thickness of the precast beam portion of each of the aforementioned composite beam segments is 16mm;

[0058] Each steel-concrete composite beam segment has 16x160mm longitudinal stiffening ribs on the top and bottom plates of the precast steel beam portion, with a spacing of 400mm between the longitudinal stiffening ribs.

[0059] Each steel-concrete composite beam segment has 20x200mm transverse stiffeners on the web of the precast steel beam section, with a longitudinal bridge spacing of 4m for the transverse stiffeners, and 12mm transverse diaphragms with a longitudinal bridge spacing of 4m.

[0060] Each of the transverse stiffening ribs is spaced 2m apart from the adjacent transverse diaphragm;

[0061] Each of the aforementioned diaphragms is provided with a manhole with a diameter of 600 mm;

[0062] Each of the steel-concrete composite sections has a longitudinal length of 3.4m, including a 1.4m variable-height section and a 2.0m constant-height section;

[0063] The beam height of each of the aforementioned variable-height sections is 2.2 m to 2.34 m;

[0064] The beam height of each of the aforementioned equal-elevation sections is 2.2m;

[0065] Each of the steel-concrete composite sections has a 0.5m high steel strand anchorage zone on its top and bottom plates;

[0066] A field splicing joint is set 0.5m from the steel beam side for each of the steel-concrete composite sections.

[0067] The present invention also provides a construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge, comprising the following steps:

[0068] Step 1: Manufacturing of each segment of the aforementioned hybrid precast small box girder;

[0069] Step 2: Splicing of each segment of the aforementioned precast hybrid box girder;

[0070] Step 3: Lateral connection of each of the aforementioned precast hybrid box girders.

[0071] Preferably, step 1 includes the following steps:

[0072] Step 1.1: Manufacture the crossbeam prefabrication segment and the central support crossbeam segment of each of the aforementioned hybrid prefabricated small box girders;

[0073] Each of the aforementioned precast beam segments and each of the aforementioned mid-support beam segments uses a set of steel formwork to manufacture one of them first, and then manufactures the other after demolding and maintenance;

[0074] Each of the aforementioned precast beam segments and each of the aforementioned mid-support beam segments has two splice joints, and each splice joint is provided with several shear keys;

[0075] Each shear key should be manufactured using an end template that perfectly matches its shape to assist in concrete forming, and fixed to the steel shell of the corresponding precast concrete box girder's steel-concrete composite section by welding shear studs.

[0076] Step 1.2: Manufacture the side span height-varying sections of each of the aforementioned hybrid precast small box girders, as well as the mid-span height-varying sections containing the steel-concrete composite sections;

[0077] Both the outer and inner formwork used in the manufacturing process are steel formwork.

[0078] The end formwork used in the manufacturing process includes the inner span splice joint of the corresponding precast beam segment, the inner span splice joint of the corresponding mid-support beam segment, and the splice joint of the steel-concrete composite beam segment.

[0079] Before pouring concrete, a release agent should be applied to the contact surface between the steel formwork and the concrete, the surface of the inner splice joint of the side span with varying height, and the surface of the inner splice joint of the middle span with varying height.

[0080] Step 1.3: Manufacture the side support segments and steel-concrete composite beam segments of each of the aforementioned hybrid precast small box girders;

[0081] For each of the aforementioned side support segments, the outer template, inner template, and cross-outer end template of the template used are all the corresponding steel templates;

[0082] Among them, the inner end template is the outer splice joint of the side support segment;

[0083] The steel beam embedded section in each of the steel-concrete composite beam segments and each of the mid-span height-changing segments are prefabricated and assembled into a whole in the factory, and then transported to the site for installation together with the corresponding mid-span height-changing segments.

[0084] After completion, the corresponding steel beam post-installation section is then welded to the steel beam pre-embedded section using the method of excess material cutting.

[0085] Before pouring concrete, a release agent is applied to the contact surface between the steel formwork and the concrete, and to the surface of the splice joint on the outer side of the side support segment.

[0086] Preferably, step 2 includes the following steps:

[0087] Step 2.1: When splicing each segment of the precast hybrid box girder along the bridge direction, the segments are hoisted and installed on the support in the following order: the corresponding side support segment, the corresponding precast crossbeam segment, the corresponding side span height-changing segment, the corresponding middle support crossbeam segment, the corresponding middle span height-changing segment, and the corresponding steel-concrete composite beam segment. A 1m gap is left between the splice joints. After being glued and tensioned into a single beam, it is then connected laterally to form a whole.

[0088] Step 2.2: Apply epoxy resin adhesive to each of the eight seams. The epoxy resin adhesive applied to each seam should be 1mm to 3mm thick.

[0089] Step 2.3: Temporary supports are set up on both sides of the middle pier of the bridge, and permanent supports are set up on the middle pier. Two pads are placed on the temporary supports. First, the middle support beam segment is lifted up and then lowered to the permanent support on the middle pier. The two ends of the corresponding segment are supported on the pads, so that the top edge of the corresponding middle support beam segment is kept horizontal in the center. The distance from the outer side of each pad to the corresponding splice of the corresponding segment is 0.5m.

[0090] Step 2.4: Each of the aforementioned pads has the following functions:

[0091] Minor adjustments can be made to the vertical elevation of the supported structure from 1 mm to 20 mm.

[0092] Minor adjustments can be made to the rotational slope of the supported structure in the transverse direction of the bridge, ranging from 1 / 2500 to 20 / 2500.

[0093] Minor adjustments were made to the supported structure at the longitudinal bridge position, ranging from 1 mm to 20 mm.

[0094] Step 2.5: Lift each of the side span height-changing sections and each of the middle span height-changing sections respectively and move them to the vicinity of the corresponding middle support beam section;

[0095] The joint of each of the side span height-changing sections and each of the middle span height-changing sections shall be kept 20mm away from the joint of the corresponding middle support beam section;

[0096] The top edge of the splice joint of each of the side span variable height sections and each of the middle span variable height sections is more than 20mm higher than the top edge of the splice joint of the corresponding middle support beam section.

[0097] Two pads are placed directly below each of the aforementioned side span height-changing sections and each of the aforementioned middle span height-changing sections;

[0098] Adjust the support surface of the pad block to be flush with the bottom edge of the splice joint of the segment, and then lower each of the corresponding side span height-changing segments and the corresponding middle span height-changing segments and support them on the corresponding pad blocks;

[0099] The pads are slightly adjusted so that the cross section of the splice joint of each of the side span height-changing segments and each of the middle span height-changing segments is aligned with the cross section of the splice joint of the middle support beam segment in both the longitudinal and transverse directions.

[0100] Step 2.6: Install temporary prestressing tensioning devices on the top and bottom plates of the box body of each of the side span height-changing sections, each of the middle support beam sections, and each of the middle span height-changing sections, and tension the temporary prestress to make the splice joints of the side span height-changing sections, the middle span height-changing sections and the middle support beam sections tightly connected, and extrude the epoxy resin adhesive applied to the splice joints.

[0101] The term "tightly bonded" means that the average pre-compression stress of the corresponding splice joint is not less than 0.5 MPa.

[0102] Step 2.7: Lift each of the aforementioned side support segments and the corresponding precast crossbeam segments, and move them to the vicinity of the corresponding side span height-changing segment. Ensure that the splice joints of the corresponding side support segments and the corresponding precast crossbeam segments are 20mm apart from the splice joints of the corresponding precast crossbeam segments and the corresponding side span height-changing segment, and ensure that the top edge of the splice joints of the corresponding side support segments and the corresponding precast crossbeam segments is more than 20mm higher than the top edge of the splice joints of the corresponding side span height-changing segment.

[0103] Two pads are placed directly below each of the aforementioned side support segments, and one pad is placed directly below the corresponding precast beam segment.

[0104] Adjust the supporting surface of each of the pad blocks to be flush with the bottom edge of the splice joint of the corresponding side span height-changing section;

[0105] Then, place the corresponding side support segment and the corresponding precast beam segment onto the corresponding pad block;

[0106] The pad is slightly adjusted so that the cross section of the splice joint of the corresponding side support segment and the corresponding precast crossbeam segment is aligned with the cross section of the splice joint of the corresponding side span height-changing segment in both the longitudinal and transverse directions.

[0107] The three pads mentioned above are located at both ends of the corresponding side support segment and the center of the corresponding precast beam segment, respectively, with the outer side distance from the corresponding splice joint and the corresponding beam end on both sides being 0.5m.

[0108] Step 2.8: Install temporary prestressing tensioning devices on the top and bottom plates of the box body of each of the side support segments and the corresponding mid-span variable height segments, and tension the temporary prestress.

[0109] Make the splice joints of the corresponding side support segment and the corresponding crossbeam prefabricated segment, and the splice joints of the corresponding crossbeam prefabricated segment and the corresponding side span height-changing segment tightly bonded, and extrude epoxy resin adhesive applied to the splice joints.

[0110] Step 2.9: Lift each of the steel-concrete composite beam segments and move them to the vicinity of the corresponding mid-span height-changing section; make the lower edge of each of the steel-concrete composite beam segments at least 20mm away from the upper edge of the corresponding mid-span height-changing section;

[0111] Two pads are placed directly below each of the steel-concrete composite beam segments;

[0112] Then, the allowance is cut according to the allowance division line of each steel-concrete composite beam segment.

[0113] After the remaining material is cut, each steel-concrete composite beam segment is lowered and supported on the pad block;

[0114] The pads are slightly adjusted so that the cross sections of the splice joints of each steel-concrete composite beam segment and the corresponding mid-span variable height segment are aligned in the longitudinal and transverse directions, and then the splices are welded on site.

[0115] Step 2.10: Install prestressed steel bars, install the anchorages of the prestressed steel bars, tension the prestressed steel bars, install the wedges of the anchorages of the prestressed steel bars, inject cement grout into the prestressed duct until it is dense, seal the anchorages, remove the temporary prestressing tensioning device, and complete the assembly of each of the precast mixed box girders.

[0116] Preferably, step 3 includes the following steps:

[0117] Step 3.1: Install the reinforcing bars of each precast crossbeam segment, the continuous reinforcing bars of each small box girder outer top slab cast-in-place segment, and the continuous reinforcing bars of the concrete top slab of each steel-concrete composite beam segment on site.

[0118] The continuous steel bar refers to a steel bar whose length is basically the same as the total length of a precast mixed box girder. It enters the closed area enclosed by the transverse steel bars of the adjacent precast mixed box girder from the front support point until it reaches the rear support point. It is a whole steel bar, or a steel bar that is extended by welding or by lap splicing.

[0119] Step 3.2: Cast concrete on site for the cast-in-place top slab of each small box girder, the concrete for the corresponding precast crossbeam section, and the concrete for the top slab of the corresponding steel-concrete composite beam section.

[0120] The beneficial effects of this invention are:

[0121] 1. This invention longitudinally segments the hybrid precast small box girder, which ensures that the transportation and hoisting of the small box girder can be completed using conventional equipment, reducing construction difficulty and increasing construction speed.

[0122] 2. The steel beam segment set in the middle of the span can improve the span capacity of the structure and increase the applicable range of the span of the small box girder structure.

[0123] 3. The steel-concrete composite section of this invention ensures a good bond between the concrete section and the steel structure section, and smooth force transmission.

[0124] 4. The adhesive joint in this invention can speed up construction, and by setting key teeth, the shear resistance of the joint is improved.

[0125] 5. The small box girder cross-section of this invention is relatively small, and the combination of internal and external bundles can effectively utilize the limited cross-sectional space to meet the requirements of prestressing.

[0126] 6. The use of slow-bonding steel strands and deep-buried anchors in this invention can accelerate construction speed and improve construction quality.

[0127] 7. The construction sequence of this invention ensures the feasibility of the structure, ensures that the construction process conforms to the stress principle of the structural design, and facilitates construction guidance.

[0128] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0129] Figure 1 A plan view of a hybrid prefabricated small box girder is shown in one embodiment of the present invention.

[0130] Figure 2 An elevation view of a hybrid prefabricated small box girder is shown in one embodiment of the present invention.

[0131] Figure 3 The diagram shows a cross-sectional view of the mid-span of a hybrid precast small box girder according to an embodiment of the present invention.

[0132] Figure 4 The diagram shows a cross-sectional view of the side span of a hybrid precast small box girder in one embodiment of the present invention.

[0133] Figure 5 The diagram shows a cross-sectional view of the support point of a hybrid precast small box girder in one embodiment of the present invention.

[0134] Figure 6 The diagram shows a cross-sectional view of the side span support of a hybrid precast small box girder in one embodiment of the present invention.

[0135] Figure 7 The diagram shows the arrangement of steel strands in the pre-tensioned internal strand method of a hybrid precast small box girder according to an embodiment of the present invention.

[0136] Figure 8 This diagram illustrates the arrangement of post-tensioned steel strands within the body of a hybrid precast small box girder according to an embodiment of the present invention.

[0137] Figure 9 The diagram shows the arrangement of steel strands in the external tensioning method for hybrid precast small box girders according to an embodiment of the present invention.

[0138] Figure 10 An elevation view of a steel-concrete composite beam segment in one embodiment of the present invention is shown.

[0139] Figure 11 This invention is shown Figure 10 Sectional view of AA.

[0140] Figure 12 This invention is shown Figure 10 Structural diagram at point AA.

[0141] Figure 13 The diagram shows a schematic representation of step 1 in one embodiment of the present invention.

[0142] Figure 14 The diagram shows a schematic representation of step 2 in one embodiment of the present invention.

[0143] Figure 15 The diagram illustrates step 3 in one embodiment of the present invention.

[0144] Figure 16 This diagram illustrates the completion of construction in one embodiment of the present invention. Detailed Implementation

[0145] Example

[0146] like Figures 1 to 12 As shown, the bridge is a longitudinally segmented precast steel-concrete composite box girder bridge; the bridge has two or more precast composite box girders arranged in the transverse direction; each pair of adjacent precast composite box girders are connected by transverse cast-in-place sections and transverse on-site welded joints.

[0147] For bridges with only two precast hybrid box girders in the transverse direction, both precast hybrid box girders are edge beams;

[0148] For bridges with three or more precast mixed box girders in the transverse direction, the two precast mixed box girders on both sides in the transverse direction are side beams, and each precast mixed box girder between the two side beams is a middle beam.

[0149] Each precast hybrid box girder is manufactured using the segmental method. In the longitudinal direction of the bridge, there are six types of segments, including side support segments, precast crossbeam segments, side span variable height segments, middle support crossbeam segments, middle span variable height segments, and steel-concrete composite beam segments. All of them are tightly connected together after being tensioned by prestressed steel strands set along the longitudinal direction of the bridge.

[0150] Each side support segment includes the prefabricated part inside the small box girder box, the prefabricated top plate outside the small box girder box, and the prefabricated part of the side support crossbeam.

[0151] Each precast box girder segment serving as a side beam is provided with a precast side beam section.

[0152] Each hybrid precast small box girder segment that serves as the central beam has two precast side support beam sections.

[0153] Each precast crossbeam segment includes the precast part inside the small box girder box, the precast part of the top slab outside the small box girder box, and the precast part of the inner crossbeam.

[0154] Each precast crossbeam section of the hybrid precast small box girder that serves as a side beam is equipped with an inner crossbeam precast section.

[0155] Each precast crossbeam section of the hybrid precast small box girder, which serves as the central beam, is equipped with two inner crossbeam precast sections.

[0156] Each side span with varying height includes the inner part of the small box girder box and the precast part of the outer top slab of the small box girder box;

[0157] Each mid-support crossbeam segment includes the prefabricated part inside the small box girder box, the prefabricated part of the top slab outside the small box girder box, and the prefabricated part of the mid-support crossbeam.

[0158] Each hybrid precast small box girder that serves as a side beam has a precast mid-support crossbeam section.

[0159] Each hybrid precast small box girder that serves as the central beam has two precast central beam sections at its central support.

[0160] Each mid-span variable-height section includes the inner part of the small box girder box and the precast part of the outer top slab of the small box girder box;

[0161] Each steel-concrete composite beam segment includes the prefabricated steel structure of the composite beam segment, the prefabricated crossbeam of the composite beam segment, and the cast-in-place concrete top slab of the composite beam segment;

[0162] Each composite beam segment's top slab concrete cast-in-place portion includes two pre-embedded sections, and a post-installation section consisting of a section that is cut to accommodate excess material and then welded to the pre-embedded sections.

[0163] Each precast box girder segment, which serves as a side beam, has several precast crossbeam sections of the composite beam segment set inwards.

[0164] Each precast box girder segment, which serves as the central beam, has several precast crossbeam sections of the composite beam segment set in both directions.

[0165] Each steel-concrete composite beam segment of the hybrid precast small box girder, which serves as a side beam, is equipped with a concrete cantilever arm on its outer side.

[0166] In practical applications, the longitudinal length of the hybrid precast small box girder is adjusted by adjusting the longitudinal length of the side support segments and the steel-concrete composite beam segments. The longitudinal lengths of the side span height-changing segments, the middle support crossbeam segments, and the middle span height-changing segments are not adjusted.

[0167] The side beams can be adjusted to accommodate changes in the width of the flat bridge by adjusting the cantilever size.

[0168] In some embodiments, an internal prestressing system is provided in each side support segment, each precast crossbeam segment, each side span height variation segment, each mid-support crossbeam segment, and each mid-span height variation segment;

[0169] Each side beam and middle beam, each crossbeam segment at the middle support, each mid-span variable-height segment, and each steel-concrete composite beam segment is equipped with an external prestressing system.

[0170] In practical applications, the internal prestressing system is divided into two parts: pre-tensioning and post-tensioning. The prestressing system includes: steel strands, corrugated pipes, anchorages, etc., all of which are conventional materials and design methods, and will not be described in detail in this patent;

[0171] The external prestressing system includes steel strands, corrugated pipes, anchors, etc., all of which are conventional materials and design methods, and will not be described in detail in this patent.

[0172] In some embodiments, shear keys are provided at the longitudinal splice joints of the precast box girder section of each side support segment, each crossbeam precast section, each side span height variation segment, each mid-support crossbeam segment, and each mid-span height variation segment.

[0173] In practical applications, shear keys are a standard design and will not be described in detail in this patent.

[0174] In some embodiments, epoxy resin adhesive is applied to the longitudinal splice joint of each side support segment, each precast crossbeam segment, each side span height-changing segment, each mid-support crossbeam segment, and each mid-span height-changing segment before splicing.

[0175] In practical applications, epoxy resin adhesives are conventional materials, and this patent will not elaborate on them.

[0176] In some embodiments, a steel-concrete composite section is provided at the joint of each mid-span variable height section and each steel-concrete composite beam segment in the longitudinal direction;

[0177] Each steel-concrete composite section is divided into several small compartments on its cross-section;

[0178] Each small compartment is equipped with stud shear keys in its top and bottom plates;

[0179] Each top slab is equipped with a pouring hole.

[0180] In some embodiments, the length of each precast crossbeam segment along the bridge direction is 0.3 m to 0.5 m;

[0181] The longitudinal length of each transverse span elevation change segment, each mid-support crossbeam segment, and each mid-span elevation change segment is 9.6 m to 10 m.

[0182] The height of each side support segment, each precast crossbeam segment, and each steel-concrete composite beam segment is 2.2m.

[0183] The height of the middle crossbeam in each mid-support crossbeam segment within the beam range is 4.0m;

[0184] Each crossbeam has a longitudinal beam height of 3.3 m to 3.8 m on both sides.

[0185] The beam height of each side span and each middle span with varying elevation is 2.2 m to 3.8 m;

[0186] The spacing between precast beams in each crossbeam precast section, each side span height change section, each mid-support crossbeam section, and each mid-span height change section is 4.1m, and a 1.1m cast-in-place wet joint is provided between each precast beam.

[0187] The spacing between the precast beams in each central support beam segment is 4.1m, and adhesive joints are provided between the precast beams.

[0188] The spacing between steel beams in each steel-concrete composite beam segment is 4.1m, and the top slab of each steel-concrete composite beam segment is cast in place.

[0189] The width of each precast box girder that serves as the middle beam is 3.0m, including the side support segment, the precast crossbeam segment, the side span variable height segment, the middle span variable height segment, and the middle support crossbeam segment.

[0190] The width of the crossbeam segment at the center support of each of the hybrid precast small box girders serving as the central beam is 4.1m.

[0191] The steel beam width of each precast box girder segment serving as the central beam is 3.0m.

[0192] The width of each precast box girder that serves as a side beam is 3.6m, including the side support segment, the precast crossbeam segment, the side span variable height segment, the middle support crossbeam segment, and the middle span variable height segment.

[0193] The width of the crossbeam segment at the middle support of each of the hybrid precast small box girders serving as edge beams is 4.15m.

[0194] Each steel-concrete composite beam segment of the precast small box girder serving as a side beam has a steel beam width of 3.0m and a 0.6m concrete cantilever on the outside.

[0195] The thickness of the top slab of the precast portion of the small box girder in each side support segment, each side span height change segment, each mid-support crossbeam segment, and each mid-span height change segment is 0.2 m to 0.25 m, the thickness of the web plate is 0.22 m to 0.35 m, and the thickness of the bottom slab is 0.2 m to 0.35 m.

[0196] The thickness of the precast top slab of each small box girder is 0.25m.

[0197] Each precast section of the crossbeam is 0.3m thick;

[0198] The thickness of the top plate of the precast steel beam in each steel-concrete composite beam segment is 16mm, the thickness of the web plate is 20mm, and the thickness of the bottom plate is 30mm.

[0199] The thickness of the cast-in-place concrete top slab for each steel-concrete composite beam segment is 250mm.

[0200] The thickness of the precast beam portion of each combined beam segment is 16mm.

[0201] Each steel-concrete composite beam segment has 16x160mm longitudinal stiffening ribs on the top and bottom plates of the precast steel beam section, with a spacing of 400mm between the longitudinal stiffening ribs.

[0202] Each steel-concrete composite beam segment has 20x200mm transverse stiffeners on the web of the precast steel beam section, with a longitudinal spacing of 4m for the transverse stiffeners. 12mm transverse diaphragms are also installed, with a longitudinal spacing of 4m for the transverse diaphragms.

[0203] Each transverse stiffening rib is spaced 2m apart from the adjacent transverse diaphragm;

[0204] Each partition is equipped with a manhole with a diameter of 600mm;

[0205] Each steel-concrete composite section is 3.4m long along the bridge direction, including a 1.4m variable-height section and a 2.0m constant-height section;

[0206] The beam height of each varying section is 2.2 m to 2.34 m;

[0207] The beam height for each elevation segment is 2.2m;

[0208] Each steel-concrete composite section has a 0.5m high steel strand anchorage zone on its top and bottom slabs.

[0209] A field splicing joint is set 0.5m from the steel beam side for each steel-concrete composite section.

[0210] like Figures 13 to 16 As shown, the present invention also provides a construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge, comprising the following steps:

[0211] Step 1: Manufacturing of each segment of the precast mixed box girder;

[0212] Step 2: Splicing of each segment of the precast mixed box girder;

[0213] Step 3: Lateral connection of each precast mixed box girder.

[0214] In some embodiments, step 1 includes the following steps:

[0215] Step 1.1: Manufacture the precast crossbeam segments and the mid-support crossbeam segments for each precast mixed box girder;

[0216] Each precast beam section and each mid-support beam section uses a set of steel formwork to manufacture one section first, and then manufactures the other section after demolding and maintenance.

[0217] Each precast beam segment and each mid-support beam segment has two splice joints, and several shear keys are set on each splice joint.

[0218] Each shear key should be manufactured using an end formwork that perfectly matches its shape to assist in concrete forming, and fixed to the steel shell of the corresponding precast concrete box girder's steel-concrete composite section by welding shear studs.

[0219] Step 1.2: Manufacture the side span height-varying sections of each precast mixed box girder, as well as the mid-span height-varying sections containing the steel-concrete composite sections;

[0220] Both the outer and inner formwork used in the manufacturing process are steel formwork.

[0221] The end formwork used in the manufacturing process includes the inner span splice joints of the corresponding precast beam sections, the inner span splice joints of the corresponding mid-support beam sections, and the splice joints of the steel-concrete composite beam sections.

[0222] Before pouring concrete, release agent should be applied to the contact surface between the steel formwork and the concrete, the surface of the inner splice joint of the side span with varying height, and the surface of the inner splice joint of the middle span with varying height.

[0223] Step 1.3: Manufacture the side support segments and steel structure parts of the steel-concrete composite beam segments for each precast mixed box girder;

[0224] For each side support segment, the outer formwork, inner formwork, and outer end formwork of the template used are all corresponding steel formwork;

[0225] Among them, the inner end template is the outer splice joint of the side support segment;

[0226] The steel beam embedded sections in each steel-concrete composite beam segment are prefabricated and assembled into a whole with each mid-span variable height section in the factory, and then transported to the site for installation together with the corresponding mid-span variable height section.

[0227] After completion, the corresponding steel beam post-installation section is then welded to the steel beam pre-embedded section using the method of cutting off the excess material.

[0228] Before pouring concrete, apply a release agent to the contact surface between the steel formwork and the concrete, as well as the surface of the splice joint on the outer side of the side support segment.

[0229] In practical applications, each precast mixed box girder is made of self-compacting concrete with a strength grade of not less than C50, ordinary steel bars with a yield strength of not less than 400MPa and Q355D steel, all of which are conventional materials.

[0230] In some embodiments, step 2 includes the following steps:

[0231] Step 2.1: When splicing each segment of the precast mixed box girder along the bridge direction, the segments are hoisted and installed on the support in the following order: the corresponding side support segment, the corresponding crossbeam precast segment, the corresponding side span height-changing segment, the corresponding middle support crossbeam segment, the corresponding middle span height-changing segment, and the corresponding steel-concrete composite beam segment. A 1m gap is left between the splice joints. After being glued and tensioned into a single beam, it is then connected laterally to form a whole.

[0232] Step 2.2: Apply epoxy resin adhesive to each of the eight seams. The epoxy resin adhesive applied to each seam should be 1mm to 3mm thick.

[0233] Step 2.3: Temporary supports are set up on both sides of the middle pier of the bridge, and permanent supports are set up on the middle pier. Two pads are placed on the temporary supports. First, the middle support beam segment is lifted up and then lowered to the permanent support on the middle pier. The two ends of the corresponding segment are supported on the pads, so that the top edge of the corresponding middle support beam segment is kept horizontal in the center. The distance from the outer side of each pad to the corresponding splice of the corresponding segment is 0.5m.

[0234] Step 2.4: Each pad has the following functions:

[0235] Minor adjustments can be made to the vertical elevation of the supported structure from 1 mm to 20 mm.

[0236] Minor adjustments can be made to the rotational slope of the supported structure in the transverse direction of the bridge, ranging from 1 / 2500 to 20 / 2500.

[0237] Minor adjustments were made to the supported structure at the longitudinal bridge position, ranging from 1 mm to 20 mm.

[0238] Step 2.5: Lift each side span height-changing section and each middle span height-changing section separately and move them to the vicinity of the corresponding middle support beam section;

[0239] Maintain a 20mm distance between the splice joint of each side span and each middle span and the splice joint of the corresponding middle support beam segment.

[0240] Make the top edge of the splice joint of each side span variable height section and each middle span variable height section more than 20mm higher than the top edge of the splice joint of the corresponding middle support beam section.

[0241] Place two pads directly below each side span and each middle span;

[0242] Adjust the support surface of the pad block to be flush with the bottom edge of the splice joint of the segment, and then lower the corresponding side span height change segment and the corresponding middle span height change segment and support them on the corresponding pad block.

[0243] Micro-adjustment pads are used to align the cross-section of the splice joint of each side span elevation change section and each middle span elevation change section with the cross-section of the splice joint of the middle support beam section in both the longitudinal and transverse directions.

[0244] Step 2.6: Install temporary prestressing tensioning devices on the top and bottom plates of the box body of each side span height change section, each middle support beam section, and each middle span height change section, and tension the temporary prestress to make the splice joints of the side span height change section, the middle span height change section and the middle support beam section tightly connected, and extrude epoxy resin glue applied to the splice joints.

[0245] Tightly bonded means that the average preload stress of the corresponding splice joint is not less than 0.5 MPa;

[0246] Step 2.7: Lift each side support segment and the corresponding precast beam segment, and move them to the vicinity of the corresponding side span height change segment. Keep the splice joint of the corresponding side support segment and the corresponding precast beam segment 20mm away from the splice joint of the corresponding precast beam segment and the corresponding side span height change segment, and make the top edge of the splice joint of the corresponding side support segment and the corresponding precast beam segment more than 20mm higher than the top edge of the splice joint of the corresponding side span height change segment.

[0247] Place two pads directly below each side support segment and one pad directly below the corresponding precast beam segment.

[0248] Adjust the supporting surface of each pad to be flush with the bottom edge of the splice joint of the corresponding side span height-changing section;

[0249] Then lower the corresponding side support segments and the corresponding precast beam segments and support them on the corresponding pads;

[0250] A small adjustment pad is used to align the cross-section of the splice joint of the corresponding side support segment and the corresponding precast crossbeam segment with the cross-section of the splice joint of the corresponding side span height-changing segment in both the longitudinal and transverse directions.

[0251] The three pads are located at both ends of the corresponding side support segment and in the center of the corresponding precast beam segment, with the outer side distance from the corresponding splice joints on both sides and the corresponding beam ends being 0.5m.

[0252] Step 2.8: Install temporary prestressing tensioning devices on the top and bottom plates of the box girder in each side support segment and the corresponding mid-span height-changing segment, and tension the temporary prestress.

[0253] Make the splice joints of the corresponding side support segment and the corresponding crossbeam prefabricated segment, and the splice joints of the corresponding crossbeam prefabricated segment and the corresponding side span height change segment tightly bonded, and extrude epoxy resin glue applied to the splice joint.

[0254] Step 2.9: Lift each steel-concrete composite beam segment and move it to the vicinity of the corresponding mid-span height-changing section; ensure that the lower edge of each steel-concrete composite beam segment is more than 20mm away from the upper edge of the corresponding mid-span height-changing section;

[0255] Place two pads directly beneath each steel-concrete composite beam segment;

[0256] Then, the allowance is cut according to the allowance division line of each steel-concrete composite beam segment;

[0257] After the remaining material is cut, each steel-concrete composite beam segment is lowered and supported on the pad block;

[0258] A small amount of adjusting pads are used to align the cross sections of the splice joints of each steel-concrete composite beam segment and the corresponding mid-span variable height segment in the longitudinal and transverse directions, and then the splice joints are welded on site.

[0259] Step 2.10: Install prestressed steel bars, install the anchorages for the prestressed steel bars, tension the prestressed steel bars, install the wedges of the anchorages for the prestressed steel bars, inject cement grout into the prestressed ducts until they are compacted, seal the anchorages, remove the temporary prestressing tensioning device, and complete the assembly of each precast mixed box girder.

[0260] In practical applications, the time required to splice the six types of segments into a single precast mixed box girder, i.e., steps 2.2 to 2.10 above, should not exceed 12 hours.

[0261] In some embodiments, step 3 includes the following steps:

[0262] Step 3.1: Install the reinforcing bars of each precast crossbeam segment, the continuous reinforcing bars of each small box girder external top slab cast-in-place segment, and the continuous reinforcing bars of each steel-concrete composite beam segment on site.

[0263] Continuous steel bars refer to steel bars whose length is basically the same as the total length of a precast mixed box girder. They are inserted from the front support point into the closed area enclosed by the transverse steel bars of the adjacent precast mixed box girder until they reach the rear support point. They are a single steel bar, or steel bars that are extended by welding or by lap splicing.

[0264] Step 3.2: Cast concrete on site for the cast-in-place top slab of each small box girder, the concrete for the corresponding precast crossbeam section, and the concrete for the top slab of the corresponding steel-concrete composite beam section.

[0265] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A longitudinally segmented precast steel-concrete composite small box girder bridge; characterized in that, The bridge has two or more precast mixed box girders arranged in the transverse direction; each pair of adjacent precast mixed box girders are connected by transverse cast-in-place sections and transverse field welded joints. Each of the aforementioned hybrid precast small box girders is manufactured using the segmental method, and in the longitudinal direction of the bridge, it includes, in sequence, a side support segment, a precast crossbeam segment, a side span height-changing segment, a middle support crossbeam segment, a middle span height-changing segment, and a steel-concrete composite beam segment. All of them are tightly connected together after being tensioned by prestressed steel strands set along the longitudinal direction of the bridge. Each of the aforementioned side support segments includes a prefabricated portion inside the small box girder box, a prefabricated portion of the top slab outside the small box girder box, and a prefabricated portion of the side support crossbeam. Each of the aforementioned precast crossbeam segments includes a precast portion inside the small box girder box, a precast portion of the top slab outside the small box girder box, and a precast portion of the inner crossbeam. Each of the aforementioned side span height-changing sections includes the inner part of the small box girder box and the prefabricated outer top slab of the small box girder box; Each of the aforementioned mid-support crossbeam segments includes a prefabricated portion inside the small box girder box, a prefabricated portion of the top slab outside the small box girder box, and a prefabricated portion of the mid-support crossbeam. Each of the aforementioned mid-span variable-height sections includes the inner part of the small box girder box and the prefabricated outer top slab of the small box girder box; Each of the steel-concrete composite beam segments includes a prefabricated steel structure portion of the composite beam segment, a prefabricated crossbeam portion of the composite beam segment, and a cast-in-place concrete portion of the top slab of the composite beam segment; Each of the aforementioned composite beam segments includes two pre-embedded sections and a post-installation section that includes a portion of the top slab concrete cast-in-place portion, which is then cut to allowance and welded to the pre-embedded sections.

2. The longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 1, characterized in that, For bridges with only two hybrid precast small box girders in the transverse direction, both hybrid precast small box girders are edge beams; Each of the side support segments of the hybrid precast small box girder that serves as the side beam is provided with a precast side support crossbeam. Each of the prefabricated crossbeams of the hybrid prefabricated small box girder that serves as the side beam is provided with one prefabricated inner crossbeam section. Each of the middle support crossbeam segments of the hybrid precast small box girder that serves as the side beam is provided with a precast middle support crossbeam section. Each of the steel-concrete composite beam segments of the hybrid precast small box girder that serves as the side beam is provided with several precast crossbeam portions of the composite beam segment inwards. Each of the steel-concrete composite beam segments of the hybrid precast small box girder that serves as the edge beam is provided with a concrete cantilever arm on its outer side.

3. The longitudinally segmented steel-concrete composite precast small box girder bridge according to claim 2, characterized in that, For a bridge with three or more of the aforementioned precast mixed box girders in the transverse direction, the two precast mixed box girders located on both sides of the transverse direction are side beams, and each precast mixed box girder located between the two side beams is a middle beam. Each of the side support segments of the hybrid precast small box girder that serves as the central beam is provided with two precast side support crossbeams. Each of the precast crossbeams of the hybrid precast small box girder that serves as the central beam is provided with two precast inner crossbeam sections. Each of the mixed precast small box girders that serves as the central beam has two precast central beam sections in the central support crossbeam segment. Each of the steel-concrete composite beam segments of the hybrid precast small box girder, which serves as the central beam, has several precast crossbeam portions of the composite beam segment arranged in both directions.

4. The longitudinally segmented steel-concrete composite precast small box girder bridge according to claim 3, characterized in that, Each of the aforementioned side support segment, each of the aforementioned precast beam segment, each of the aforementioned side span height-changing segment, each of the aforementioned middle support beam segment, and each of the aforementioned middle span height-changing segment is provided with an internal prestressing system; Each of the aforementioned side beams and middle beams, each of the aforementioned middle support crossbeam segments, each of the aforementioned mid-span variable height segments, and each of the aforementioned steel-concrete composite beam segments is provided with an external prestressing system.

5. The longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 1, 2, or 3, characterized in that, Shear keys are provided at the longitudinal splice joints of the precast box girder section of each of the following: each side support segment, each precast crossbeam segment, each side span height-changing segment, each middle support crossbeam segment, and each middle span height-changing segment.

6. The longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 1, 2 or 3, characterized in that, Each of the aforementioned mid-span variable-height sections, and each of the aforementioned steel-concrete composite beam sections, has a steel-concrete composite section provided at the connection point in the longitudinal direction of the bridge. Each of the steel-concrete composite sections is divided into several small compartments on its cross-section; Each of the small compartments is equipped with stud shear keys in its top and bottom plates; Each of the top plates is provided with a pouring hole.

7. The construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 6, characterized in that, Includes the following steps: Step 1: Manufacturing of each segment of the aforementioned hybrid precast small box girder; Step 2: Splicing of each segment of the aforementioned precast hybrid box girder; Step 3: Lateral connection of each of the aforementioned precast hybrid box girders.

8. The construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 7, characterized in that, Step 1 includes the following steps: Step 1.1: Manufacture the crossbeam prefabrication segment and the central support crossbeam segment of each of the aforementioned hybrid prefabricated small box girders; Each of the aforementioned precast beam segments and each of the aforementioned mid-support beam segments uses a set of steel formwork to manufacture one of them first, and then manufactures the other after demolding and maintenance; Each of the aforementioned precast beam segments and each of the aforementioned mid-support beam segments has two splice joints, and each splice joint is provided with several shear keys; Each shear key should be manufactured using an end template that perfectly matches its shape to assist in concrete forming, and fixed to the steel shell of the corresponding precast concrete box girder's steel-concrete composite section by welding shear studs. Step 1.2: Manufacture the side span height-varying sections of each of the aforementioned hybrid precast small box girders, as well as the mid-span height-varying sections containing the steel-concrete composite sections; Both the outer and inner formwork used in the manufacturing process are steel formwork. The end formwork used in the manufacturing process includes the inner span splice joint of the corresponding precast beam segment, the inner span splice joint of the corresponding mid-support beam segment, and the splice joint of the steel-concrete composite beam segment. Before pouring concrete, a release agent should be applied to the contact surface between the steel formwork and the concrete, the surface of the inner splice joint of the side span with varying height, and the surface of the inner splice joint of the middle span with varying height. Step 1.3: Manufacture the side support segments and steel-concrete composite beam segments of each of the aforementioned hybrid precast small box girders; For each of the aforementioned side support segments, the outer template, inner template, and cross-outer end template of the template used are all the corresponding steel templates; Among them, the inner end template is the outer splice joint of the side support segment; The steel beam embedded section in each of the steel-concrete composite beam segments and each of the mid-span height-changing segments are prefabricated and assembled into a whole in the factory, and then transported to the site for installation together with the corresponding mid-span height-changing segments. After completion, the corresponding steel beam post-installation section is then welded to the steel beam pre-embedded section using the method of excess material cutting. Before pouring concrete, a release agent is applied to the contact surface between the steel formwork and the concrete, and to the surface of the splice joint on the outer side of the side support segment.

9. The construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 7, characterized in that, Step 2 includes the following steps: Step 2.1: When splicing each segment of the precast hybrid box girder along the bridge direction, the segments are hoisted and installed on the support in the following order: the corresponding side support segment, the corresponding precast crossbeam segment, the corresponding side span height-changing segment, the corresponding middle support crossbeam segment, the corresponding middle span height-changing segment, and the corresponding steel-concrete composite beam segment. A 1m gap is left between the splice joints. After being glued and tensioned into a single beam, it is then connected laterally to form a whole. Step 2.2: Apply epoxy resin adhesive to each of the eight splicing seams, with each seam having an epoxy resin adhesive thickness of 1mm to 3mm. Step 2.3: Temporary supports are set up on both sides of the middle pier of the bridge, and permanent supports are set up on the middle pier. Two pads are placed on the temporary supports. First, the middle support beam segment is lifted up and then lowered to the permanent support on the middle pier. The two ends of the corresponding segment are supported on the pads, so that the top edge of the corresponding middle support beam segment is kept horizontal in the center. The distance from the outer side of each pad to the corresponding splice of the corresponding segment is 0.5m. Step 2.4: Each of the aforementioned pads has the following functions: Minor adjustments can be made to the vertical elevation of the supported structure from 1 mm to 20 mm. Minor adjustments can be made to the rotational slope of the supported structure in the transverse direction of the bridge, ranging from 1 / 2500 to 20 / 2500. Minor adjustments were made to the supported structure at the longitudinal bridge position, ranging from 1 mm to 20 mm. Step 2.5: Lift each of the side span height-changing sections and each of the middle span height-changing sections respectively and move them to the vicinity of the corresponding middle support beam section; The joint of each of the side span height-changing sections and each of the middle span height-changing sections shall be kept 20mm away from the joint of the corresponding middle support beam section; The top edge of the splice joint of each of the side span variable height sections and each of the middle span variable height sections is more than 20mm higher than the top edge of the splice joint of the corresponding middle support beam section. Two pads are placed directly below each of the aforementioned side span height-changing sections and each of the aforementioned middle span height-changing sections; Adjust the support surface of the pad block to be flush with the bottom edge of the splice joint of the segment, and then lower each of the corresponding side span height-changing segments and the corresponding middle span height-changing segments and support them on the corresponding pad blocks; The pads are slightly adjusted so that the cross section of the splice joint of each of the side span height-changing segments and each of the middle span height-changing segments is aligned with the cross section of the splice joint of the middle support beam segment in both the longitudinal and transverse directions. Step 2.6: Install temporary prestressing tensioning devices on the top and bottom plates of the box body of each of the side span height-changing sections, each of the middle support beam sections, and each of the middle span height-changing sections, and tension the temporary prestress to make the splice joints of the side span height-changing sections, the middle span height-changing sections and the middle support beam sections tightly connected, and extrude the epoxy resin adhesive applied to the splice joints. The term "tightly bonded" means that the average pre-compression stress of the corresponding splice joint is not less than 0.5 MPa. Step 2.7: Lift each of the aforementioned side support segments and the corresponding precast crossbeam segments, and move them to the vicinity of the corresponding side span height-changing segments, so that the splice joints of the corresponding side support segments and the corresponding precast crossbeam segments are 20mm apart from the splice joints of the corresponding precast crossbeam segments and the corresponding side span height-changing segments, and the top edge of the splice joints of the corresponding side support segments and the corresponding precast crossbeam segments is more than 20mm higher than the top edge of the splice joints of the corresponding side span height-changing segments; Two pads are placed directly below each of the aforementioned side support segments, and one pad is placed directly below the corresponding precast beam segment. Adjust the supporting surface of each of the pad blocks to be flush with the bottom edge of the splice joint of the corresponding side span height-changing section; Then, place the corresponding side support segment and the corresponding precast beam segment on the corresponding pad block; The pad is slightly adjusted so that the cross section of the splice joint of the corresponding side support segment and the corresponding precast crossbeam segment is aligned with the cross section of the splice joint of the corresponding side span height-changing segment in both the longitudinal and transverse directions. The three pads mentioned above are located at both ends of the corresponding side support segment and the center of the corresponding precast beam segment, respectively, with the outer side distance from the corresponding splice joint and the corresponding beam end on both sides being 0.5m. Step 2.8: Install temporary prestressing tensioning devices on the top and bottom plates of the box body of each of the side support segments and the corresponding mid-span variable height segments, and tension the temporary prestress. Make the splice joints of the corresponding side support segment and the corresponding crossbeam prefabricated segment, and the splice joints of the corresponding crossbeam prefabricated segment and the corresponding side span height-changing segment tightly bonded, and extrude epoxy resin adhesive applied to the splice joints. Step 2.9: Lift each of the steel-concrete composite beam segments and move them to the vicinity of the corresponding mid-span height-changing section; make the lower edge of each of the steel-concrete composite beam segments at least 20mm away from the upper edge of the corresponding mid-span height-changing section; Two pads are placed directly below each of the steel-concrete composite beam segments; Then, the allowance is cut according to the allowance division line of each steel-concrete composite beam segment. After the remaining material is cut, each steel-concrete composite beam segment is lowered and supported on the pad block; The pads are slightly adjusted so that the cross sections of the splice joints of each steel-concrete composite beam segment and the corresponding mid-span variable height segment are aligned in the longitudinal and transverse directions, and then the splices are welded on site. Step 2.10: Install prestressed steel bars, install the anchorages of the prestressed steel bars, tension the prestressed steel bars, install the wedges of the anchorages of the prestressed steel bars, inject cement grout into the prestressed duct until it is dense, seal the anchorages, remove the temporary prestressing tensioning device, and complete the assembly of each of the precast mixed box girders.

10. The construction method for a longitudinally segmented precast steel-concrete composite small box girder bridge according to claim 7, characterized in that, Step 3 includes the following steps: Step 3.1: Install the reinforcing bars of each precast crossbeam segment, the continuous reinforcing bars of each small box girder outer top slab cast-in-place segment, and the continuous reinforcing bars of the concrete top slab of each steel-concrete composite beam segment on site. The continuous steel bar refers to a steel bar whose length is basically the same as the total length of a precast mixed box girder. It enters the closed area enclosed by the transverse steel bars of the adjacent precast mixed box girder from the front support point until it reaches the rear support point. It is a whole steel bar, or a steel bar that is extended by welding or by lap splicing. Step 3.2: Cast concrete on site for the cast-in-place top slab of each small box girder, the concrete for the corresponding precast crossbeam section, and the concrete for the top slab of the corresponding steel-concrete composite beam section.

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