RC bridge pier structure under shear-torsion composite stress and construction method thereof
By introducing a combination design of longitudinal reinforcement, spiral stirrup, SMA bar and rotating hinge into the RC bridge pier, combined with ECC and ordinary concrete, the problem of insufficient seismic performance of traditional bridge pier under shear-torsion composite stress is solved, and the piers are realized Improved shear and torsional resistance and rapid repair capability after earthquakes.
Patent Information
- Application Number
- CN202411595763.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-11
- Publication Date
- 2024-12-31
AI Technical Summary
The load-bearing capacity and energy consumption capacity of the traditional RC bridge piers under shear-torsion composite stress are reduced, resulting in brittle damage and structural damage. It is difficult to repair and is expensive in irregular bridges and underwater or deep buried conditions.
Using a structural design including longitudinal ribs, spiral stirrups, SMA bars and rotating hinges, the combination of ECC and ordinary concrete forms a swing layer and a cast-in-place layer. The rotating hinge provides a self-resetting function, and the spiral stirrups and oblique ribs suppress cracks. Development, SMA bars absorb seismic energy and improve shear and torsion resistance.
It improves the seismic redundancy of the bridge piers under shear-torsion composite stress, reduces brittle failure, enhances self-resetting performance, reduces the difficulty and cost of post-seismic repair, and is suitable for complex geological conditions and irregular bridges.
Smart Images
Figure CN119221369A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of bridge engineering, and in particular relates to an RC bridge pier structure under shear-torsion combined stress and a construction method thereof. Background Art
[0002] Bridge piers play an important role in supporting and transmitting the load of the superstructure in bridge structures. In irregular bridges such as curved bridges or skew bridges, earthquakes often cause the piers to be subjected to the combined effects of shear and torque. This combined force significantly reduces the bearing capacity, ductility and energy dissipation capacity of the plastic hinge area of the piers, causing brittle failure and even causing serious earthquake damage such as collapse and falling beams.
[0003] In traditional strength or ductility design, plastic hinges usually appear at the bottom of bridge piers. Severe concrete cracking and steel yielding occur near the pier bottom, which can easily destroy the structural integrity of the pier. Once the pier bottom is damaged, large-scale reinforcement or reconstruction of the pier and its surrounding areas is often required, which is not only costly but also difficult to construct, especially in underwater or deep buried situations, where repair is difficult to achieve.
[0004] In order to improve the post-earthquake functional recoverability of bridges, swing piers allow the piers to swing or rotate in a controlled manner during an earthquake, effectively reducing the impact of seismic forces on the pier body and reducing residual deformation. Especially under the action of a large earthquake, the swing mechanism enables the pier body to adapt to larger horizontal displacements, thereby avoiding brittle failure of the rigid structure and improving seismic toughness. However, swing piers reduce structural rigidity to a certain extent. They are only connected by prestressed steel strands, and the shear resistance of the node connection position is insufficient, which is prone to direct shear failure, stress concentration, and slippage at the connection interface.
[0005] Based on the shortcomings of the above traditional connection methods and design methods, it is urgent to propose a RC (reinforced concrete) bridge pier structure and its construction method to cope with shear-torsion combined forces, so as to improve the mechanical properties of the bridge pier under shear-torsion combined forces. This structure combines the high integrity and energy dissipation characteristics of the cast-in-place structure with the self-resetting characteristics of the rocking structure, and improves the shear and torsion resistance of the bridge pier through the joint action of multiple lines of defense. In addition, transferring the plastic hinge from the bottom of the pier to the artificially designed area can effectively reduce the risk of damage at the junction of the abutment and the pier column, improve the seismic performance and post-earthquake repairability of the bridge pier, ensure the continuity of the transportation network, and adapt to the development needs of resilient cities and smart cities. Summary of the invention
[0006] In view of this, an object of the present invention is to provide a RC bridge pier structure under shear-torsion combined stress and a construction method thereof, so as to improve the mechanical properties of the bridge pier under shear-torsion combined stress.
[0007] In order to achieve the above object, the present invention provides the following technical solutions:
[0008] The present invention provides an RC bridge pier structure under shear-torsion composite force, comprising a pier column, wherein a plurality of longitudinal bars are arranged circumferentially in the axial direction of the pier column inside the pier column, wherein at least one group of spiral stirrups is arranged in the axial direction of the pier column inside the pier column, wherein each group of spiral stirrups comprises two symmetrically arranged spiral stirrups, wherein the spiral stirrups are fixedly connected to the longitudinal bars, wherein the pier column comprises a cast-in-place layer cast by ordinary concrete and a swing layer disposed between the two cast-in-place layers and cast by ECC, wherein the longitudinal bars comprise steel bars disposed in the cast-in-place layer and SMA rods disposed in the swing layer, wherein both ends of the SMA rods are fixedly connected to two steel bars respectively disposed on the two cast-in-place layers and on the same axis, wherein a rotary hinge is arranged in the swing layer, wherein the rotary hinge comprises a fixed seat and a rotary ball connected to the fixed seat by a spherical hinge, wherein the fixed seat and the rotary ball are both fixedly connected to a plurality of oblique bars arranged circumferentially outwardly in the center of the rotary hinge at ends away from each other, wherein the oblique bars extend into the cast-in-place layer away from the rotary hinge end.
[0009] Furthermore, a groove is provided in the fixed seat, and a plurality of balls are placed in the groove. The rotating ball is arranged on the balls so that a plurality of balls surround the bottom of the rotating ball. A fixing ring is fixedly installed on the fixed seat, and the fixing ring is used to press the rotating ball to limit the axial displacement of the rotating ball. The bottom of the rotating ball extends above the fixing ring.
[0010] Furthermore, the SMA rod and the steel bar are fixedly connected by a connecting sleeve, both ends of the SMA rod are provided with a first thread segment, and the steel bar is provided with a second thread segment near the end of the SMA rod, the length of the first thread segment is greater than the length of the second thread segment, and the connecting sleeve is threadedly connected to the first thread segment and the second thread segment to fix the SMA rod and the steel bar.
[0011] Furthermore, a plurality of oblique reinforcements located on the same side of the rotary hinge are fixedly connected by an annular positioning stirrup.
[0012] Furthermore, a rocking layer is provided between the positioning stirrups on both sides of the rotating hinge.
[0013] Furthermore, the strength of the ECC is slightly lower than that of ordinary concrete.
[0014] A construction method for an RC bridge pier structure under shear-torsion combined stress comprises the following steps:
[0015] S1: Prefabricate the rotating hinge, and weld a number of oblique reinforcements that are set circumferentially outward at the top of the rotating ball and the bottom of the fixed seat, and fix them by tying and fixing the positioning stirrups with the oblique reinforcements;
[0016] S2: Install the longitudinal reinforcement, firstly, install a plurality of steel bars circumferentially at the lower cast-in-place layer, then connect and fix the first end of the SMA rod to the end of the steel bar through a connecting sleeve thread, and then connect and fix the steel bar at the upper cast-in-place layer to the second end of the SMA rod through a connecting sleeve thread to form the longitudinal reinforcement;
[0017] S3: Install a set of spiral stirrups, and tie and fix two spiral stirrups to the longitudinal reinforcement in a symmetrical manner;
[0018] S4: The prefabricated rotating hinge is arranged at the middle and lower part of the pier column, and the oblique reinforcement and the longitudinal reinforcement are fixed by binding, wherein the rotating hinge is located between a plurality of circumferentially arranged SMA bars, and the SMA bars are located between the positioning stirrups on both sides of the rotating hinge in the longitudinal direction, and the positioning stirrups on both sides and the two ends of the SMA bars are provided with a preset spacing in the longitudinal direction; and the oblique reinforcement located below is ensured to pass through the cast-in-place layer below and extend to the preset length in the cap to ensure the anchoring effect;
[0019] S5: Support the formwork, and then use ordinary concrete to pour to the positioning stirrups below the rotating hinge to form a cast-in-place layer below. After the cast-in-place layer below is initially solidified, pour ECC to the positioning stirrups above the rotating hinge to form a swing layer. After the swing layer is initially solidified, pour ordinary concrete to form a cast-in-place layer above the swing layer.
[0020] The beneficial effects of the present invention are:
[0021] 1. Through the combined design of the first line of defense (the inhibitory effect of spiral stirrups and diagonal bars on crack development, and the deformation energy dissipation of ECC and SMA bars) and the second line of defense (the swing effect of the rotating hinge), the bridge piers have different energy dissipation paths when facing different earthquake actions, thereby improving the seismic redundancy and converting the piers from brittle failure to ductile failure.
[0022] 2. The rotating hinge increases the self-resetting performance of the bridge pier, which to a certain extent avoids the transmission of excessive seismic forces to the rigid structure and reduces the risk of damage to the superstructure and the abutment.
[0023] 3. The rotation hinge is designed to be located in the potential plastic hinge area in the middle and lower part of the pier, close to the bottom of the pier but not in direct contact with the foundation. This makes it difficult for the damaged area to directly have an adverse impact on the pier foundation, reducing concrete cracking and serious damage at the bottom of the pier. The transfer of the damage location is conducive to post-earthquake repair and reinforcement.
[0024] 4. The superelastic properties of SMA rods reduce the residual deformation of bridge piers after earthquakes and increase their self-reset capability. SMA rods are easy to maintain and replace after earthquakes.
[0025] 5. The pier structure is suitable for various complex geological conditions and structural conditions, especially irregular bridges in earthquake-prone areas and soft foundation conditions, and can significantly improve the shear and torsion resistance of the piers.
[0026] 6. The conventional cast-in-place construction technology is integrated with the modular swing device to achieve the optimization of design and construction; the construction is convenient, the construction efficiency is high, and it is easy to implement and promote.
[0027] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:
[0029] Figure 1 A schematic diagram of the pier structure according to an embodiment of the present invention;
[0030] Figure 2 This is a schematic diagram of the connection between the oblique reinforcement and the rotary hinge according to an embodiment of the present invention;
[0031] Figure 3 A cross-sectional view of a rotary hinge structure according to an embodiment of the present invention;
[0032] Figure 4 A schematic diagram of the connection between a steel bar and an SMA bar according to an embodiment of the present invention;
[0033] Figure 5 It is a schematic diagram of the shear-torsion deformation process of the pier column during an earthquake according to an embodiment of the present invention.
[0034] The markings in the attached drawings are as follows: pier 1, cast-in-place layer 101, rocking layer 102, longitudinal reinforcement 2, steel bar 201, SMA rod 202, connecting sleeve 203, first threaded segment 204, second threaded segment 205, spiral stirrup 3, rotating hinge 4, fixed seat 401, rotating ball 402, groove 403, ball 404, fixing ring 405, oblique reinforcement 5, positioning stirrup 6, and base 7. DETAILED DESCRIPTION
[0035] like Figures 1 to 5As shown, the present invention provides an RC bridge pier structure under shear-torsion composite force, comprising: a pier column 1, wherein a plurality of longitudinal bars 2 are arranged circumferentially in the axial direction of the pier column 1, wherein at least one group of spiral stirrups 3 are arranged in the axial direction of the pier column 1, wherein each group of spiral stirrups 3 comprises two symmetrically arranged spiral stirrups 3, wherein the spiral stirrups 3 are fixedly connected to the longitudinal bars 2, wherein the pier column 1 comprises a cast-in-place layer 101 cast by ordinary concrete and a rocking layer 102 cast by ECC (abbreviation of Engineered Cementitious Composites, Chinese meaning: engineering cement-based composite materials), wherein the rocking layer 102 is arranged between the two cast-in-place layers 101, wherein the longitudinal bars 2 comprise steel bars 201 arranged in the cast-in-place layer 101 and SMA bars 202 arranged in the rocking layer 102, wherein the SMA (Shape Memory Composites) The abbreviation of Shape Memory Alloys, Chinese meaning: Shape Memory Alloy) The two ends of the rod 202 are fixedly connected to two steel bars 201 located on the same axis on the two cast-in-place layers 101, and a rotating hinge 4 is arranged in the rocking layer 102. The rotating hinge 4 includes a fixed seat 401 and a rotating ball 402 connected to the fixed seat 401 by a ball joint. The fixed seat 401 and the rotating ball 402 are fixedly connected to the ends away from each other with a plurality of inclined bars 5 arranged to extend outwardly around the center of the rotating hinge 4. The inclined bars 5 extend into the cast-in-place layer 101 away from the ends of the rotating hinge 4, wherein the inclined bars 5 located at the bottom pass through the cast-in-place layer 101 below and extend into the base 7.
[0036] In this scheme, ECC has large deformation characteristics, and the internal fiber bridging effect can improve the shear and torsion resistance. The strength of ECC is slightly lower than that of ordinary concrete, which is conducive to adapting to the rotation of the rotating hinge 4 after deformation, so as to play a swing function; under the action of earthquake, the irregular bridge pier is subjected to the combined action of shear force and torque, and the swing layer 102 where the rotating hinge 4 is located gradually increases and expands due to the microcracks inside the ECC, and the fiber bridging effect inside the ECC further consumes energy. As the deformation increases, the two symmetrically arranged spiral stirrups 3 play a role in suppressing the increase and expansion of cracks, and then the oblique reinforcement 5 intersecting with the cracks further suppresses the development of cracks; at the same time, the SMA rod 202 plays a superelastic role, which can absorb part of the earthquake energy and restore the original state after the load dissipates; through the microcrack energy dissipation mechanism of ECC, the shear and torsion resistance of the spiral stirrups 3 and the oblique reinforcement 5, and the superelastic deformation energy dissipation mechanism of the SMA rod 202 as the first line of defense, they jointly bear and dissipate the earthquake energy, and can give full play to its earthquake resistance under the action of small and medium earthquakes. During the deformation process, the ECC and SMA rod 202 will gradually transfer part of the energy and stress to the hinge 4. The cracks are concentrated near the hinge 4 and the direction of the cracks tends to be horizontal. When the earthquake force exceeds the bearing capacity of the first line of defense, the hinge 4 plays a swinging role as the second line of defense, reducing the concentrated stress of shear and torque and improving the self-resetting performance. The two lines of defense transform the brittle shear failure into ductile bending failure in the plane where the hinge 4 is located. After the earthquake, the hinge 4 is reset and the vertical bearing function is restored. Subsequently, the cracked ECC is removed in time, the damaged SMA rod 202 is replaced, and the formwork is set up to recast the ECC, so that it can be quickly repaired after the earthquake and the bridge piers continue to function.
[0037] In one embodiment of the present invention, a groove 403 is provided in the fixing seat 401, and a plurality of balls 404 are placed in the groove 403. The rotating ball 402 is placed on the balls 404 so that the plurality of balls 404 surround the bottom of the rotating ball 402. A fixing ring 405 is fixedly installed on the fixing seat 401. The fixing ring 405 is used to press the rotating ball 402 to limit the axial displacement of the rotating ball 402. A waterproof film is attached to the interface between the fixing ring 405 and the rotating ball to prevent cement slurry from entering the groove 403 during pouring. The top of the rotating ball 402 extends above the fixing ring 405.
[0038] In this scheme, when the cross section undergoes a large deformation, the rotating ball 402 and the groove 403 rotate relative to each other, so that the failure surface is concentrated near the rotating hinge 4, changing the traditional failure mode that relies on the plastic hinge area at the bottom of the pier to bear most of the deformation. The rotating hinge 4 is arranged in the middle and lower part of the pier. The top of the rotating ball 402 and the bottom of the fixed seat 401 are both arranged with oblique reinforcements 5 evenly distributed outward. The oblique reinforcements 5 are fixedly connected to the rotating hinge 4 by welding. When welding, it should be ensured that the welding part is clean and free of impurities; the oblique reinforcements 5 extend from the rotating hinge 4 to the outer wall of the pier column 1 in a badminton shape, which can inhibit the expansion of cracks and avoid concentrated cracking of cracks, so as to improve the shear and torsion resistance. The rocking layer 102 where the rotating hinge 4 is located also improves the shear and torsion resistance due to the fiber bridging effect of ECC. The longitudinal force-bearing steel bars within the rocking layer are SMA rods 202, whose superelastic properties make the pier self-recovering and improve the seismic toughness of the pier. Furthermore, by providing the ball 404 , the friction between the rotating ball 402 and the inner wall of the groove 403 is reduced, thereby ensuring the flexible swinging ability of the rotating hinge 4 ; and by providing the fixing ring 405 , the rotating ball 402 is easily installed.
[0039] In one embodiment of the present invention, the SMA rod 202 and the steel bar 201 are fixedly connected by a connecting sleeve 203, and the first threaded segment 204 is provided at both ends of the SMA rod 202. The steel bar 201 is provided with a second threaded segment 205 near the end of the SMA rod 202, and the length of the first threaded segment 204 is twice the length of the second threaded segment 205; the connecting sleeve 203 is threadedly connected to the first threaded segment 204 and the second threaded segment 205 to fix the SMA rod 202 and the steel bar 201.
[0040] In this solution, the above structure is designed to facilitate the connection of the SMA rod 202 and the steel bar 201, as well as the replacement of damage caused by vibration. The connecting sleeve 203 should ensure that the SMA rod 202 and the steel bar 201 are well connected to prevent slippage.
[0041] In one embodiment of the present invention, a plurality of diagonal bars 5 located on the same side of the rotary hinge 4 are connected by an annular positioning stirrup 6, which plays the role of positioning the diagonal bars 5 and restraining the deformation of the diagonal bars 5; a rocking layer 102 is set between the positioning stirrups 6 on both sides of the rotary hinge 4 to control the casting height of the rocking layer 102. The height of the rocking layer can be taken as the height of the plastic hinge zone of the pier, and the height of the plastic hinge zone can be calculated according to the specifications.
[0042] A construction method for an RC bridge pier structure under shear-torsion combined stress comprises the following steps:
[0043] S1: prefabricate the rotating hinge 4, and weld a plurality of oblique reinforcements 5 arranged circumferentially outward at the top of the rotating ball 402 and the bottom of the fixed seat 401, and tie and fix the oblique reinforcements 5 with the positioning stirrups 6;
[0044] S2: installing the longitudinal reinforcement 2, firstly, circumferentially fixing a plurality of reinforcement bars 201 at the lower cast-in-place layer 101, then threading and fixing the first end of the SMA rod 202 to the end of the reinforcement bar 201 through the connecting sleeve 203, and then threading and fixing the reinforcement bar 201 at the upper cast-in-place layer 101 to the second end of the SMA rod 202 through the connecting sleeve 203 to form the longitudinal reinforcement 2;
[0045] S3: Install a set of 3 spiral stirrups, and tie and fix two spiral stirrups 3 to the longitudinal reinforcement 2 in a symmetrical manner;
[0046] S4: The prefabricated rotating hinge 4 is arranged at the middle and lower part of the pier 1, and the oblique reinforcement 5 and the longitudinal reinforcement 2 are fixed by binding, wherein the rotating hinge 4 is located between a plurality of circumferentially arranged SMA rods 202, and the SMA rods 202 are longitudinally located between the positioning stirrups 6 on both sides of the rotating hinge 4, and the positioning stirrups 6 on both sides and the two ends of the SMA rods 202 are provided with a preset spacing; and it is ensured that the oblique reinforcement 5 located below extends to a preset length in the cap 7, and the preset length is an anchoring length that meets the requirements of the construction specifications;
[0047] S5: Support the formwork, and then use ordinary concrete to pour to the positioning stirrup 6 located below the rotating hinge 4 to form the cast-in-place layer 101 located below. After the cast-in-place layer below is initially solidified, pour ECC to the positioning stirrup 6 located above the rotating hinge 4 to form the swing layer 102. After the swing layer 102 is initially solidified, pour ordinary concrete to form the cast-in-place layer 101 located above the swing layer 102.
[0048] In this solution, after the pier 1 is subjected to earthquake load, the rocking layer 102 is damaged, the rotating hinge 4 can be reset and its vertical bearing function can be restored, the SMA rod 202 is replaced and reconnected with the steel bar 201, and the support formwork is cast with ECC, so that rapid post-earthquake repair can be achieved.
[0049] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.
Claims
1. A RC bridge pier structure under shear-torsion combined stress, comprising a pier column, characterized in that: A plurality of longitudinal bars are arranged circumferentially in the direction of the axis of the pier column inside the pier column, at least one group of spiral stirrups is arranged in the direction of the axis of the pier column inside the pier column, each group of spiral stirrups includes two symmetrically arranged spiral stirrups, the spiral stirrups are fixedly connected to the longitudinal bars, the pier includes a cast-in-place layer cast by ordinary concrete and a swing layer arranged between the two cast-in-place layers and cast by ECC, the longitudinal bars include steel bars arranged in the cast-in-place layer and SMA rods arranged in the swing layer, both ends of the SMA rods are fixedly connected to two steel bars located on the same axis on the two cast-in-place layers respectively, a rotary hinge is arranged in the swing layer, the rotary hinge includes a fixed seat and a rotary ball connected to the fixed seat ball joint, the fixed seat and the rotating ball are fixedly connected to a plurality of oblique bars arranged circumferentially outwardly with the center of the rotary hinge at the ends away from each other, and the oblique bars extend into the cast-in-place layer away from the rotary hinge end.
2. The RC bridge pier structure under shear-torsion combined stress according to claim 1 is characterized by: A groove is provided in the fixing seat, and a plurality of balls are placed in the groove. The rotating ball is arranged on the balls so that a plurality of balls surround the bottom of the rotating ball. A fixing ring is fixedly installed on the fixing seat, and the fixing ring is used to press the rotating ball to limit the axial displacement of the rotating ball. The bottom of the rotating ball extends above the fixing ring.
3. The RC bridge pier structure under shear-torsion combined stress according to claim 2 is characterized by: The SMA rod and the steel bar are fixedly connected by a connecting sleeve, both ends of the SMA rod are provided with a first thread segment, and the steel bar is provided with a second thread segment near the end of the SMA rod, the length of the first thread segment is greater than the length of the second thread segment, and the connecting sleeve is threadedly connected to the first thread segment and the second thread segment to fix the SMA rod and the steel bar.
4. The RC bridge pier structure under shear-torsion combined stress according to claim 3 is characterized by: A plurality of oblique reinforcements located on the same side of the rotary hinge are fixedly connected by an annular positioning stirrup.
5. The RC bridge pier structure under shear-torsion combined stress according to claim 4 is characterized by: The rocking layer is set between the positioning stirrups on both sides of the rotating hinge.
6. The RC bridge pier structure under shear-torsion combined stress according to claim 5 is characterized by: The strength of the ECC is lower than that of ordinary concrete.
7. A construction method for an RC bridge pier structure under shear-torsion combined stress according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: Prefabricate the rotating hinge, and weld a number of oblique reinforcements that are set circumferentially outward at the top of the rotating ball and the bottom of the fixed seat, and fix them by tying and fixing the positioning stirrups with the oblique reinforcements; S2: Install the longitudinal reinforcement, firstly, install a plurality of steel bars circumferentially at the lower cast-in-place layer, then connect and fix the first end of the SMA rod to the end of the steel bar through a connecting sleeve thread, and then connect and fix the steel bar at the upper cast-in-place layer to the second end of the SMA rod through a connecting sleeve thread to form the longitudinal reinforcement; S3: Install a set of spiral stirrups, and tie and fix two spiral stirrups to the longitudinal reinforcement in a symmetrical manner; S4: Set the prefabricated rotating hinge in the middle and lower part of the pier column, and fix the diagonal reinforcement and longitudinal reinforcement by binding. The hinge is located between a plurality of circumferentially arranged SMA bars, and the SMA bars are located between the positioning stirrups on both sides of the hinge in the longitudinal direction, and the positioning stirrups on both sides and the two ends of the SMA bars are provided with a preset spacing in the longitudinal direction; and the oblique bars located below are ensured to pass through the cast-in-place layer below and extend to the preset length in the cap to ensure the anchoring effect; S5: Support the formwork, and then use ordinary concrete to pour to the positioning stirrups below the rotating hinge to form a cast-in-place layer below. After the cast-in-place layer below is initially solidified, pour ECC to the positioning stirrups above the rotating hinge to form a swing layer. After the swing layer is initially solidified, pour ordinary concrete to form a cast-in-place layer above the swing layer.