Design method for non-through post-inserted steel dowel structure of non-touching formwork support

Abstract

The present invention relates to a non-through post-inserted steel dowel structure for a non-touching formwork support and its design method, which includes a pre-embedded steel pipe (2), a crack-proof through-type steel cushion block, a through-type screw rod (3), a non-through through-type steel dowel (6) and a bracket (7). The pre-embedded steel pipe (2) and the crack-proof through-type steel cushion block are pre-embedded and cast in the bridge pier (1). At least two non-through through-type steel dowels (6) are symmetrically sleeved on the through-type screw rod (3), and the non-through through-type steel dowels (6) are symmetrically located on both sides inside the bridge pier (1). The non-through through-type steel dowels (6) and the through-type screw rod (3) are sleeved in the inner cavity of the pre-embedded steel pipe (2), and the bracket (7) is installed at the exposed end of the non-through through-type steel dowel (6). This structure makes full use of the law that the internal force of the steel dowel gradually decays under the anchoring action of the bridge pier (1), determines the non-through length based on the failure criterion, saves the consumption of high-grade steel inside while ensuring its bearing capacity, reduces the initial investment of the non-touching formwork support, and enhances its comprehensive advantages.

Description

Technical Field

[0001] The present invention relates to the field of engineering of an anchoring structure for a non-grounded formwork support, and particularly to a design method for a non-penetrating post-inserted steel dowel structure of a non-grounded formwork support. Background Art

[0002] In recent years, with the continuous improvement of infrastructure construction, the increasingly cramped construction sites in cities and the increasingly common deep valleys and high piers in field projects have posed great challenges to formwork support projects. Non-grounded formwork supports have advantages in terms of high efficiency and economy, such as saving ground space, reducing the amount of foundation treatment, significantly reducing the number of supports and construction time. Among them, the post-inserted steel dowel type of non-grounded formwork support has characteristics such as not affecting the formwork, low difficulty in post-construction appearance treatment, and high material turnover rate, and has gradually been widely used. However, the post-inserted steel dowels bear a large construction load and often require high-grade alloy steel. At present, the steel consumption of the conventional penetrating steel dowels is large, resulting in a high initial cost of the post-inserted steel dowel type of non-grounded formwork support, which hinders its further popularization and application. At the same time, under the action of construction loads, the internal force of the steel dowels gradually decreases with the increase of the anchorage depth under the anchorage clamping restraint conditions of the bridge pier. The currently used full-length equal-diameter penetrating steel dowels are unnecessary and there is great room for structural optimization in order to improve its economy. Summary of the Invention

[0003] In view of the deficiencies in the background art, the technical problem to be solved by the present invention is to provide a non-penetrating post-inserted steel dowel structure for a non-grounded formwork support, which solves the problems of inconsistent structure and mechanical characteristics of the penetrating steel dowel structure in the traditional post-inserted steel dowel type of non-grounded formwork support, excessive steel consumption and high cost.

[0004] The present invention is achieved by adopting the following technical solutions:

[0005] A non-penetrating post-inserted steel dowel structure for a non-grounded formwork support, comprising a pre-embedded steel pipe, a crack-proof steel cushion block, a penetrating screw rod, a non-penetrating through-hole steel dowel and a bracket. The pre-embedded steel pipe and the crack-proof steel cushion block are pre-embedded and cast in the bridge pier. At least two non-penetrating through-hole steel dowels are symmetrically sleeved on the penetrating screw rod, and the non-penetrating through-hole steel dowels are symmetrically located on both sides inside the bridge pier. The non-penetrating through-hole steel dowel and the penetrating screw rod are sleeved in the inner cavity of the pre-embedded steel pipe, and the bracket is installed at the exposed end of the non-penetrating through-hole steel dowel.

[0006] Further, the crack-proof steel cushion block is sleeved at the port of the outer end of the pre-embedded steel pipe, and the crack-proof steel cushion block is in close contact with the outer end face of the pre-embedded steel pipe against the surface of the bridge pier.

[0007] Further, the penetrating screw rod penetrates through the entire bridge pier, and both ends of the non-penetrating through-hole steel dowel are fixed to the penetrating screw rod through steel dowel positioning nuts.

[0008] Furthermore, the corbel has a reserved hole. The corbel is sleeved on the exposed end of the non-through type through-steel pin rod through the reserved hole and is fixedly installed on the non-through type through-steel pin rod by a corbel fixing nut.

[0009] Furthermore, the outer diameter d1 of the embedded steel pipe is the same as the inner diameter d8 of the anti-cracking steel cushion block. The anti-cracking steel cushion block is tightly sleeved on the outer end port of the embedded steel pipe without a gap.

[0010] Furthermore, the outer diameter d3 of the non-through type through-steel pin rod is smaller than the inner diameter d2 of the embedded steel pipe, and the difference between the outer diameter d3 and the inner diameter d2 does not exceed 1 mm.

[0011] Furthermore, the steel pin rod positioning nut includes an inner positioning nut and an outer positioning nut. The inner diameter d6 of the inner positioning nut is larger than the diameter d5 of the through-type screw rod. The difference between the inner diameter d6 of the inner positioning nut and the diameter d5 of the through-type screw rod does not exceed 1 mm. The inner positioning nut is welded and fixed on the through-type screw rod according to the length of the non-through type through-steel pin rod.

[0012] Furthermore, both ends of the through-type screw rod have threads. The inner diameter of the outer positioning nut matches the threads at both ends of the through-type screw rod. The outer positioning nut is tightened on the exposed end of the through-type screw rod and squeezes the non-through type through-steel pin rod.

[0013] Furthermore, the exposed end of the non-through type through-steel pin rod is provided with threads. The inner diameter d7 of the corbel fixing nut matches the threads at the exposed end of the non-through type through-steel pin rod. The diameter d of the corbel reserved hole 10 is larger than the outer diameter d3 of the non-through type through-steel pin rod, and the diameter d of the corbel reserved hole 10 differs from the outer diameter d3 of the non-through type through-steel pin rod by no more than 1 mm.

[0014] A design method for the non-through post-inserted steel pin rod structure of a non-grounded formwork support includes the following steps:

[0015] 1) According to the width b2 of the bridge pier and the structure of the corbel, determine the number N and spacing b1 of the non-through type through-steel pin rods. The number N shall not be less than 2.

[0016] 2) According to the corbel size, the total construction load P0 borne and the number N of the non-through type through-steel pin rods, determine the vertical construction load P1, horizontal secondary tension P2 and secondary moment M borne by each non-through type through-steel pin rod according to the equal division method.

[0017] 3) According to the vertical construction load P1, horizontal secondary tension P2 and secondary bending moment M borne by the non-through core steel dowel bar, estimate the outer diameter d3 and inner diameter d4 of the non-through post-inserted steel dowel bar according to the combined tension-shear-bending cross-section theory. At the same time, estimate the diameter d5 of the through bolt according to the tensile cross-section theory. During design, it is required that d4 = d5 and d2 = d3 = d8 = d 10 , with a positive error not exceeding 1 mm during manufacturing.

[0018] 4) According to the horizontal secondary tension P2 borne by the non-through core steel dowel bar, estimate the required thicknesses l6 and l7 of the inner positioning nut, outer positioning nut and bracket fixing nut of the steel dowel bar according to the shear resistance theory. Among them, the inner positioning nut of the steel dowel bar is calculated according to the shear resistance of the weld, and the outer positioning nut and bracket fixing nut are calculated according to the shear resistance of the thread.

[0019] 5) Determine the exposed length l3 of the non-through core steel dowel bar and the exposed length l4 of the through bolt according to the thickness l8 of the bracket web, the thickness l7 of the bracket fixing nut, the thickness l6 of the outer fixing nut of the steel dowel bar and the surplus;

[0020] Adopt finite element modeling. Assuming the residual depth l1 = 0, calculate the variation law of shear force, bending moment and tension of the through core steel dowel bar with the anchorage length under the construction load without anti-cracking steel pads;

[0021] 6) According to the emergence position of the pure tension cross-section inside the steel dowel bar when the assumed residual depth l1 = 0, draw up the anchorage depth l2 and residual depth l1 of the non-through core steel dowel bar, and determine the thickness l5 and outer diameter d9 of the anti-cracking steel pad according to the concrete pressure area formed by the embedded steel pipe near the pier surface.

[0022] 7) The thickness of the anti-cracking steel pad shall not exceed the concrete cover thickness of the pier. When the thickness l5 of the anti-cracking steel pad exceeds the concrete cover thickness of the pier, the number N of non-through core steel dowel bars shall be increased and recalculated, or two anti-cracking steel pads shall be set respectively on the inner and outer sides of the main bars of the pier;

[0023] 8) According to the anchorage depth l2 and residual depth l1 of the non-through core steel dowel bar, as well as the thickness l5 and outer diameter d9 of the anti-cracking steel pad, adopt finite element modeling to calculate the internal forces of the through bolt, non-through core steel dowel bar and pier under the construction load;

[0024] 9) When the through bolt fails, its diameter d9 shall be increased and steps 4 - 9 shall be repeated;

[0025] When the non-through core steel dowel bar fails, its outer diameter d3 shall be increased and steps 4 - 9 shall be repeated;

[0026] When damage occurs near the surface of the pier of the embedded steel pipe pier, the thickness l5 and outer diameter d9 of the anti-cracking steel pad shall be increased and step 9 shall be repeated;

[0027] When the pier is damaged near the embedded end of the non-through type through-core steel pin rod, the anchoring depth l2 of the non-through type through-core steel pin rod should be increased and steps 7-9 should be repeated.

[0028] In the present invention, the non-through type through-core steel pin rod is combined with the through type screw rod, and the law that the internal force of the steel pin rod gradually decays under the anchoring action of the pier is fully utilized. The large diameter non-through type steel pin rod is used for the combined tension-shear-bending section, and the small diameter through type screw rod is used for the pure tension section, greatly reducing the consumption of high-grade steel. At the same time, according to the law of load transfer between the steel pin rod and the pier, in addition to the bearing capacity of the steel pin rod and the screw rod itself, the stress concentration phenomena at the surface of the embedded steel pipe pier and near the embedded end of the steel pin rod are focused on, and the size of the crack prevention cushion block and the length of the non-through steel pin rod are determined based on the failure criterion to ensure the reliability of the overall bearing capacity of the non-grounded formwork support structure. Generally speaking, considering both performance and economy, the applicability of the post-inserted steel pin rod type non-grounded formwork support structure is improved. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of the longitudinal section of the non-through post-inserted steel pin rod structure of a non-grounded formwork support;

[0030] Figure 2 It is a schematic structural diagram of the partial section of the non-through post-inserted steel pin rod structure of a non-grounded formwork support;

[0031] Figure 3 It is a schematic structural diagram of the cross section of the non-through post-inserted steel pin rod structure of a non-grounded formwork support.

[0032] Figure 4 It is a front view schematic diagram of some components of the non-through post-inserted steel pin rod structure of a non-grounded formwork support;

[0033] Figure 5 It is an estimated finite element calculation model under the condition of the traditional through type steel pin rod;

[0034] Figure 6 It is the internal force distribution of the traditional through type steel pin rod;

[0035] Figure 7 It is the finite element model of the non-through type through-core steel pin rod structure;

[0036] Figure 8 It is the concrete Mises stress distribution;

[0037] Figure 9 It is the optimized concrete Mises stress distribution;

[0038] Figure 10 Optimize the Mises stress distribution of the steel pin rod.

[0039] Marking description in the figure: pier (1), embedded steel pipe (2), through-type screw rod (3), internal positioning nut of steel dowel bar (4), external positioning nut of steel dowel bar (5), non-through type steel dowel bar (6), bracket (7), bracket fixing nut (8), anti-cracking steel cushion block (9); l1 residual length of non-through type steel dowel bar, l2 anchoring length of non-through type steel dowel bar, l3 exposed length of non-through type steel dowel bar, l4 exposed length of through-type screw rod, l5 thickness of anti-cracking steel cushion block, l6 thickness of internal and external positioning nuts of steel dowel bar, l7 thickness of bracket fixing nut, l8 web thickness of bracket. d1 and d2 outer diameter and inner diameter of embedded steel pipe, d3 and d4 outer diameter and inner diameter of non-through type steel dowel bar, d5 diameter of through-type screw rod, d6 inner diameter of internal and external positioning nuts of steel dowel bar, d7 inner diameter of bracket fixing nut, d8 and d9 inner diameter and outer diameter of anti-cracking steel cushion block, d 10 Diameter of reserved hole in the web of the bracket. b2 width of the pier, b1 spacing of non-through type steel dowel bars. Specific implementation mode

[0040] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the drawings and preferred embodiments to describe in detail the specific implementation mode, structure, features and their effects of the present invention as follows.

[0041] Refer to Figure 1-4 As shown, the present invention provides a non-through post-inserted steel dowel bar structure for a non-grounded formwork support, including an embedded steel pipe (2), an anti-cracking steel cushion block (9), a through-type screw rod (3), a non-through type steel dowel bar (6) and a bracket (7).

[0042] The embedded steel pipe (2) and the anti-cracking steel cushion block (9) are embedded and cast in the pier (1). The anti-cracking steel cushion block (9) is sleeved at the port of the outer end of the embedded steel pipe (2), and the anti-cracking steel cushion block (9) is in close contact with the outer end face of the embedded steel pipe (2) against the surface of the pier (1). The outer diameter d1 of the embedded steel pipe (2) is the same as the inner diameter d8 of the anti-cracking steel cushion block (9). The anti-cracking steel cushion block (9) is tightly sleeved at the outer end port of the embedded steel pipe (2) without gaps, and no gaps are allowed between the two to ensure collaborative load bearing.

[0043] At least two non-through steel dowel bars (6) are symmetrically sleeved on the through bolt (3). The non-through steel dowel bars (6) and the through bolt (3) are sleeved in the inner cavity of the embedded steel pipe (2). The non-through steel dowel bars (6) are symmetrically located on both sides inside the pier (1). The through bolt (3) penetrates through the entire pier (1). Both ends of the non-through steel dowel bar (6) are fixed to the through bolt (3) by steel dowel bar positioning nuts. The outer diameter d3 of the non-through steel dowel bar (6) is smaller than the inner diameter d2 of the embedded steel pipe (2), and the difference between the outer diameter d3 and the inner diameter d2 does not exceed 1 mm. The steel dowel bar positioning nut includes an inner positioning nut (4) and an outer positioning nut (5). The inner diameter d6 of the inner positioning nut (4) is larger than the diameter d5 of the through bolt (3), and the difference between the inner diameter d6 of the inner positioning nut (4) and the diameter d5 of the through bolt (3) does not exceed 1 mm. The inner positioning nut (4) is welded and fixed to the through bolt (3) according to the length l2 + l3 of the non-through steel dowel bar (6). Both ends of the through bolt (3) have threads. The inner diameter of the outer positioning nut (5) matches the threads at both ends of the through bolt (3). The outer positioning nut (5) is tightened on the exposed end of the through bolt (3) and squeezes the non-through steel dowel bar (6). The non-through steel dowel bar (6) is limited and fixed between the inner positioning nut (4) and the outer positioning nut (5).

[0044] The corbel (7) is installed at the exposed end of the non-through steel dowel bar (6). The corbel (7) has a reserved hole. The corbel (7) is sleeved on the exposed end of the non-through steel dowel bar (6) through the reserved hole and is fixedly installed on the non-through steel dowel bar (6) by a corbel fixing nut. The exposed end of the non-through steel dowel bar (6) is provided with threads. The inner diameter d7 of the corbel fixing nut (8) matches the threads at the exposed end of the non-through steel dowel bar (6). The diameter d of the reserved hole of the corbel (7) 10 is larger than the outer diameter d3 of the non-through steel dowel bar (6). The diameter d of the reserved hole of the corbel (7) 10 differs from the outer diameter d3 of the non-through steel dowel bar (6) by no more than 1 mm.

[0045] The construction steps of the non-through post-inserted steel dowel bar structure of the above-mentioned non-touch formwork support include: (1) When pouring the pier (1), embed steel pipes (2) and anti-cracking steel cushion blocks (9) in the pier (1); (2) When preparing the formwork for the capping beam, weld the inner positioning nut (4) of the non-through type through-core steel dowel bar (6) at the specified position of the through-type screw rod (3), put the non-through type through-core steel dowel bars (6) on both ends, and tighten the outer positioning nut (5) at the outer end of the through-type screw rod (3); (3) Then insert the structure in step 2 above into the embedded steel pipe (2); (4) Put the bracket (7) on the exposed non-through type through-core steel dowel bar (6), put on and tighten the bracket fixing nut (8), and at the same time re-tighten the outer positioning nut (5).

[0046] By using the cooperation of the non-through type through-core steel dowel bar (6) and the through-type screw rod (3), and making full use of the law that the internal force of the steel dowel bar gradually decays under the anchoring action of the pier (1), the large-diameter non-through type steel dowel bar is used to bear the tension-shear-bending composite section, and the small-diameter through-type screw rod (3) is used to bear the pure tension section, which greatly reduces the consumption of high-grade steel, reduces the initial investment of the non-touch formwork support, and enhances its comprehensive advantages. At the same time, according to the law of load transfer between the steel dowel bar and the pier (1), in addition to the bearing capacity of the steel dowel bar and the screw rod itself, focus on the stress concentration phenomenon at the surface of the embedded steel pipe (2) of the pier (1) and near the embedded end of the steel dowel bar, and determine the size of the anti-cracking cushion block and the length of the non-through steel dowel bar based on the failure criterion to ensure the reliability of the overall bearing capacity of the non-touch formwork support structure.

[0047] Generally speaking, taking into account both performance and economy, the applicability of the post-inserted steel dowel bar type non-touch formwork support structure is improved.

[0048] The design method of the non-through post-inserted steel dowel bar structure of the above-mentioned non-touch formwork support includes the following steps:

[0049] 1) According to the width b2 of the pier (1) and the structure of the bracket (7), determine the number N and spacing b1 of the non-through type through-core steel dowel bars (6), and the number N shall not be less than 2;

[0050] 2) According to the size of the bracket (7), the total construction load P0 borne and the number N of the non-through type through-core steel dowel bars (6), determine the vertical construction load P1, horizontal secondary tension P2 and secondary bending moment M borne by each non-through type through-core steel dowel bar (6) according to the equal division method;

[0051] 3) According to the vertical construction load P1, horizontal secondary tension P2 and secondary bending moment M borne by the non-through type through-core steel dowel bar (6), estimate the outer diameter d3 and inner diameter d4 of the non-through post-inserted steel dowel bar according to the tension-shear-bending composite section theory, and at the same time estimate the diameter d5 of the through-screw rod according to the tensile section theory. During design, it is required that d4 = d5 and d2 = d3 = d8 = d10 , the positive error during manufacturing does not exceed 1mm.

[0052] 4) Based on the horizontal secondary tensile force P2 borne by the non-through-type through-steel rod (6), the required thicknesses l6 and l7 of the inner positioning nut (4), the outer positioning nut (5) and the bracket fixing nut (8) of the steel rod are estimated according to the shear resistance theory, wherein the inner positioning nut (4) of the steel rod is calculated according to the shear resistance of the weld, and the outer positioning nut (5) and the bracket fixing nut (8) are calculated according to the shear resistance of the thread.

[0053] 5) Determine the exposed length l3 of the non-through-type through-type steel tip rod (6) and the exposed length l4 of the through-type screw rod (3) based on the thickness l8 of the web of the corbel (7), the thickness l7 of the corbel fixing nut (8), the thickness l6 of the outer fixing nut of the steel tip rod and the margin;

[0054] Finite element modeling was adopted, assuming that the residual depth l1 = 0, and the variation of shear force, bending moment and tension of the through-type through-type steel tip rod with the anchoring length under the action of construction load was calculated when no anti-cracking steel pad (9) was provided.

[0055] 6) Based on the position of the pure tensile section in the steel tip rod when the residual depth l1 is assumed to be 0, the anchoring depth l2 and the residual depth l1 of the non-through-type through-core steel tip rod (6) are proposed, and the thickness l5 and the outer diameter d9 of the anti-cracking steel pad (9) are determined based on the concrete pressure area formed by the embedded steel pipe (2) near the surface of the pier (1).

[0056] 7) The thickness of the anti-cracking steel pad (9) shall not exceed the thickness of the concrete cover of the pier (1). When the thickness l5 of the anti-cracking steel pad (9) exceeds the thickness of the concrete cover of the pier (1), the number N of non-penetrating through-type steel tip rods (6) shall be increased and recalculated, or two anti-cracking steel pads (9) shall be installed on the inner and outer sides of the main reinforcement of the pier (1).

[0057] 8) Based on the anchoring depth l2 and residual depth l1 of the non-penetrating through-steel tip rod (6), and the thickness l5 and outer diameter d9 of the anti-cracking steel pad (9), finite element modeling is used to calculate the internal forces of the through-steel screw (3), the non-penetrating through-steel tip rod (6) and the pier (1) under the construction load, and Mises stress is used as the failure criterion.

[0058] 9) When the through screw (3) is damaged, its diameter d9 should be increased and steps 4 to 9 should be repeated;

[0059] When the non-penetrating through-core steel tip rod (6) is damaged, its outer diameter d3 should be increased and steps 4 to 9 should be repeated;

[0060] When the pier (1) is damaged near the surface of the embedded steel pipe (2) pier (1), the thickness l5 and the outer diameter d9 of the anti-cracking steel pad (9) should be increased and step 9 should be repeated;

[0061] When the pier (1) is damaged near the embedded end of the non-through type core steel pin rod (6), the anchoring depth l2 of the non-through type core steel pin rod (6) should be increased and steps 7-9 should be repeated.

[0062] The specific embodiments are as follows:

[0063] I. Determine the number of steel pin rods

[0064] For the capping beam of a bridge on an urban expressway, the post-inserted steel pin rod type non-grounded formwork support construction is adopted. The width of the pier (1) is b2 = 1.6 m. Due to the construction restrictions such as the reinforcement of the pier (1), it is decided that each pier (1) will adopt N = 2 alloy steel pin rods made of 30CrMnTi, and the spacing between the steel pin rods is b1 = 0.4 m.

[0065] II. Determine the construction load

[0066] According to the construction drawing, the total vertical load is calculated to be P0 = 998.3 kN. According to the dimensions of the corbel (7), the vertical load, secondary horizontal tensile force and bending moment borne by the steel pin rod are calculated to be P1 = 499.15 kN, P2 = 228.7 kN and M = 19.97 kN·m respectively.

[0067] III. Estimate the diameter of the through-type screw rod (3) and the inner and outer diameters of the non-through type core steel pin rod (6)

[0068] In the embodiment of the present invention, a through-type screw rod (3) made of Q345 steel and a non-through type core steel pin rod (6) made of 30CrMnTi alloy steel are preliminarily determined. The diameter d5 of the through-type screw rod (3) is checked with reference to the pure tension cross-section formula (A1a) and formula (A1b), and at the same time, the inner diameter d4 of the steel pin rod is determined. The outer diameter d3 of the steel pin rod is checked with reference to the strength checking method of the tension-shear composite cross-section in the "Steel Structure Design Manual". The original checking formula (A2a) of the load form is rewritten into the checking formula (A2b) in stress form, and the normal stress term is further decomposed into the contributions of tension and bending moment to obtain formula (A3a) and formula (A3b).

[0069]

[0070]

[0071] In the formula: N, Q, N u , Q u are the normal load, shear force, normal bearing capacity and shear bearing capacity respectively, P1, P2, M are the vertical shear force, horizontal tensile force and bending moment borne by the steel pin rod respectively, σ, τ, σ u , τ u are the normal stress, shear stress, normal strength and shear strength respectively, σ t , σM They are the normal stresses caused by tensile force and bending moment respectively. d3, d4, and d5 are the outer diameter and inner diameter of the steel pin rod and the diameter of the through-type screw rod (3) respectively.

[0072] According to the provisions of the "Code for Design of Steel Structures" (GB50017-2003), for the through-type screw rod (3) made of Q345 steel, the design tensile strength is taken as σ u = 265 MPa. Using Equation (A1b), the limit value of the diameter d5 of the through-type screw rod (3) is calculated to be 33.15 mm. Then, for conservatism, d4 = d5 = 38 mm is taken. On this basis, according to the provisions of the "Alloy Steel Structures" (GB / T3077-2015), for the steel pin rod made of 30CrMnTi alloy steel, the design tensile and shear strengths are taken as σ u = 850 MPa and τ u = 510 MPa respectively. Using Equation (A3b), the limit value of the outer diameter d3 of the steel pin rod is calculated to be 74.68 mm. Then, for conservatism, d3 = 90 mm is taken.

[0073] IV. Calculate the thicknesses of the inner and outer positioning nuts (5) and the bracket fixing nut (8)

[0074] This embodiment mainly explains the calculation process of the residual length and anchorage length of the non-through type through-steel pin rod (6), and omits the calculation process of the thicknesses of structural measures such as the inner and outer positioning nuts (5) and the bracket fixing nut (8), which has no impact on the design results of the non-through type through-steel pin rod (6).

[0075] V. Analyze the variation law of internal forces under the condition of the through-steel pin rod

[0076] As Figure 5 shown, for the finite element model under the condition of the traditional through-steel pin rod, the symmetry principle is used for local modeling to improve the calculation efficiency. The through-steel pin rod 10, the embedded steel pipe (2), and the bridge pier (1) all adopt tetrahedral solid elements. The normal hard contact and tangential smooth contact are directly adopted between the steel pin rod and the embedded steel pipe (2), and the connection between the embedded steel pipe (2) and the bridge pier (1) is simplified to a fixed connection. Other model parameter settings are as Figure 5 shown.

[0077] As Figure 6 shown in the internal force distribution of the traditional through-steel pin rod, it can be seen that under the action of construction load, the internal force of the steel pin rod decreases rapidly with the increase of the anchorage depth and tends to be stable, that is, it quickly changes from a composite section of bending, shear, and tension to a pure tension section, and the shear force and bending moment gradually dissipate due to the clamping restraint of the bridge pier (1). The position where the pure tension section appears is about 15 cm from the anchorage depth. Then, the anchorage length of the non-through type through-steel pin rod (6) is initially determined as l2 = 15 cm. In addition, the size of the crack prevention cushion block will be finally determined together, and the iterative design of drafting and checking is not carried out in this embodiment.

[0078] VI. Checking and Adjusting the Structure of the Non-Penetrating Steel Pin Rod (6)

[0079] The finite element model of the non-penetrating steel pin rod structure under the condition that the anchorage length is l2 = 15 cm is as follows Figure 7 shown, and the parameter settings are the same as those of Figure 5 For the penetrating screw rod (3), the non-penetrating steel pin rod (6), and the inner and outer positioning nuts (5), normal hard contact and tangential smooth contact are adopted.

[0080] The stress concentration on the surface of the pier (1) of the embedded steel pipe (2) and the stress concentration at the embedded end of the steel pin rod are calculated as follows Figure 8 shown. It can be seen that the Mises stress within the range of 6.45 cm in height and 5.91 cm in depth near the surface of the pier (1) of the embedded steel pipe (2) exceeds the strength of the C50 concrete of the pier (1), which is 50 MPa, and this will cause the concrete to spall and expose the steel bars. Therefore, a crack prevention steel cushion block (9) with an outer diameter of d9 = 210 mm and a thickness of l5 = 45 mm needs to be set. On the other hand, the Mises stress of 74.51 MPa is generated in the concrete of the pier (1) at the embedded end of the steel pin rod, which will cause internal damage to the pier (1). Therefore, the anchorage length of the non-penetrating steel pin rod (6) needs to be increased to l2 = 30 cm.

[0081] After optimizing the anchorage depth of the non-penetrating steel pin rod (6) and setting the crack prevention steel cushion block (9), the Mises stress in the concrete pier (1) (as shown in Figure 9 ) can be seen. The Mises stress on the surface of the pier (1) of the embedded steel pipe (2) is significantly reduced, effectively improving the problem of concrete spalling and exposed steel bars; the stress concentration phenomenon at the embedded end of the steel pin rod disappears, avoiding internal damage to the pier (1). The Mises stress distribution in the optimized steel pin rod is as shown in Figure 10 . It can be seen that the Mises stress of the steel pin rod and the penetrating screw rod (3) meets the strength requirements, and the non-penetrating post-inserted steel pin rod structure of the non-grounded formwork support after optimization passes the bearing capacity check.

[0082] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to it as equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A design method for the non-through post-inserted steel dowel structure of a non-touching formwork support, characterized in that: It includes embedded steel pipes (2), anti-cracking steel cushion blocks (9), through bolts (3), non-through type steel dowels (6) and corbels (7). The embedded steel pipes (2) and anti-cracking steel cushion blocks (9) are embedded and cast in the pier (1). At least two non-through type steel dowels (6) are symmetrically sleeved on the through bolts (3). The non-through type steel dowels (6) are symmetrically located on both sides inside the pier (1). The non-through type steel dowels (6) and the through bolts (3) are sleeved in the inner cavity of the embedded steel pipe (2). The corbel (7) is installed at the exposed end of the non-through type steel dowel (6). The design method includes the following steps: 1) According to the width b2 of the pier (1) and the structure of the corbel (7), determine the number N and the spacing b1 of the non-through type steel dowels (6). The number N shall not be less than 2. 2) According to the size of the corbel (7), the total construction load P0 borne and the number N of the non-through type steel dowels (6), determine the vertical construction load P1, the horizontal secondary tension P2 and the secondary moment M borne by each non-through type steel dowel (sic) according to the equal distribution method. 3) According to the vertical construction load P1, horizontal secondary tensile force P2 and secondary bending moment M borne by the non-through core steel dowel bar (6), estimate the outer diameter d3 and inner diameter d4 of the non-through post-inserted steel dowel bar according to the combined tension-shear-bending cross-section theory. At the same time, estimate the diameter d5 of the through bolt according to the tensile cross-section theory. During design, it is required that d4 = d5 and d2 = d3 = d8 = d 10 , and the positive error during manufacturing does not exceed 1 mm; 4) According to the horizontal secondary tension P2 borne by the non-through type steel dowel (6), estimate the required thicknesses l6 and l7 of the inner positioning nut (4), the outer positioning nut (5) and the corbel fixing nut (8) in the steel dowel according to the shear resistance theory. Among them, the inner positioning nut (4) of the steel dowel is calculated according to the shear resistance of the weld, and the outer positioning nut (5) and the corbel fixing nut (8) are calculated according to the shear resistance of the thread. 5) According to the web thickness l8 of the corbel (7), the thickness l7 of the corbel fixing nut (8), the thickness l6 of the outer fixing nut of the steel dowel and the surplus, determine the exposed length l3 of the non-through type steel dowel (6) and the exposed length l4 of the through bolt (3). Adopt finite element modeling. Assume the residual depth l1 = 0, and calculate the variation law of the shear force, bending moment and tension of the through type steel dowel under the construction load with the anchorage length without setting the anti-cracking steel cushion block (9). 6) According to the appearance position of the pure tension section in the steel dowel when the assumed residual depth l1 = 0, draw up the anchorage depth l2 and the residual depth l1 of the non-through type steel dowel (6). Determine the thickness l5 and the outer diameter d9 of the anti-cracking steel cushion block (9) according to the concrete pressure area formed by the embedded steel pipe (2) near the surface of the pier (1). 7) The thickness of the anti-cracking steel cushion block (9) shall not exceed the concrete cover thickness of the pier (1). When the thickness l5 of the anti-cracking steel cushion block (9) exceeds the concrete cover thickness of the pier (1), the number N of the non-through type steel dowels (6) shall be increased and recalculated, or two anti-cracking steel cushion blocks (9) shall be respectively set on the inner and outer sides of the main reinforcement of the pier (1). 8) According to the anchorage depth l2 and the residual depth l1 of the non-through type steel dowel (6), as well as the thickness l5 and the outer diameter d9 of the anti-cracking steel cushion block (9), adopt finite element modeling to calculate the internal forces of the through bolt (3), the non-through type steel dowel (6) and the pier (1) under the construction load. 9) When the through bolt (3) fails, its diameter d9 shall be increased and steps 4 - 9 shall be repeated. When the non-through type steel pin rod (6) is damaged, its outer diameter d3 should be increased and steps 4 to 9 should be repeated; When the pier (1) is damaged near the surface of the pier (1) of the embedded steel pipe (2), the thickness l5 and outer diameter d9 of the crack prevention steel cushion block (9) should be increased and step 9 should be repeated; When the pier (1) is damaged near the embedded end of the non-through type steel pin rod (6), the anchoring depth l2 of the non-through type steel pin rod (6) should be increased and steps 7 to 9 should be repeated.

2. The design method of a non-through post-inserted steel dowel bar structure for a non-touching formwork support according to claim 1, characterized in that: The crack prevention steel cushion block (9) is sleeved at the port of the outer end of the embedded steel pipe (2), and the outer end face of the crack prevention steel cushion block (9) is in close contact with the surface of the pier (1).

3. The design method of a non-through post-inserted steel dowel structure of a non-touching formwork support according to claim 1 or 2, characterized in that: The through type screw rod (3) penetrates through the entire pier (1), and both ends of the non-through type steel pin rod (6) are fixed to the through type screw rod (3) through steel pin rod positioning nuts.

4. The design method of a non-through post-inserted steel pin structure for a non-touching formwork support according to claim 3, characterized in that: The corbel (7) has a reserved hole. The corbel (7) is sleeved on the exposed end of the non-through type steel pin rod (6) through the reserved hole and is fixedly installed on the non-through type steel pin rod (6) through a corbel fixing nut.

5. A design method for a non-through post-inserted steel dowel structure of a non-touching formwork support according to claim 1 or 2 or 4, characterized in that: The outer diameter d1 of the embedded steel pipe (2) is the same as the inner diameter d8 of the crack prevention steel cushion block (9), and the crack prevention steel cushion block (9) is tightly sleeved on the outer end port of the embedded steel pipe (2) without a gap.

6. The design method of a non-through post-inserted steel dowel structure for a non-touch formwork support according to claim 5, characterized in that: The outer diameter d3 of the non-through type steel pin rod (6) is smaller than the inner diameter d2 of the embedded steel pipe (2), and the difference between the outer diameter d3 and the inner diameter d2 does not exceed 1 mm.

7. A design method for a non-through post-inserted steel pin structure of a non-touching formwork support according to claim 3, characterized in that: The steel pin rod positioning nut includes an inner positioning nut (4) and an outer positioning nut (5). The inner diameter d6 of the inner positioning nut (4) is larger than the diameter d5 of the through type screw rod (3), and the difference between the inner diameter d6 of the inner positioning nut (4) and the diameter d5 of the through type screw rod (3) does not exceed 1 mm. The inner positioning nut (4) is welded and fixed to the through type screw rod (3) according to the length of the non-through type steel pin rod (6).

8. A design method for a non-through post-inserted steel dowel bar structure of a non-touching formwork support according to claim 6 or 7, characterized in that: Both ends of the through type screw rod (3) have threads. The inner diameter of the outer positioning nut (5) matches the threads at both ends of the through type screw rod (3). The outer positioning nut (5) is tightened on the exposed end of the through type screw rod (3) and squeezes the non-through type steel pin rod (6).

9. A design method for a non-through post-inserted steel pin structure of a non-touching formwork support according to claim 8, characterized in that: The exposed end of the non-through core steel dowel bar (6) is provided with threads, and the inner diameter d7 of the bracket fixing nut matches the threads at the exposed end of the non-through core steel dowel bar (6). The diameter d of the reserved hole of the bracket (7) 10 is larger than the outer diameter d3 of the non-through core steel dowel bar (6), and the diameter d of the reserved hole of the bracket (7) 10 differs from the outer diameter d3 of the non-through core steel dowel bar (6) by no more than 1 mm.

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