Single-column pier bridge anti-overturning structure with intelligent detection

Abstract

The application relates to a single-column pier bridge anti-overturning structure with intelligent detection, which comprises a prefabricated steel cover beam, a steel pull rod and a foot pier. Ear plates are arranged at the two ends of the prefabricated steel cover beam and located on the two sides of the bridge. Rubber pads are arranged on the ear plates, the rubber pads are located between the ear plates and the bridge and gaps exist between the rubber pads and the bridge. A cushion stone is arranged at the upper end of the prefabricated steel cover beam. Rubber bearings under the box girder which are supported on the lower end of the bridge are arranged on the cushion stone. Force sensors are arranged at the side of the rubber pads close to the bridge and the connection positions of the rubber bearings and the bridge. Distance measuring sensors are arranged at the centers of the two rubber bearings and are attached to the box girder. According to the data of the force sensors and the distance measuring sensors, the total stress is calculated and compared with the compressive strength of the concrete to determine whether the column end of the bridge is damaged. The working mode of the single-column pier bridge single-node support is changed through the prefabricated steel cover beam, and the anti-overturning performance of the bridge is improved. According to the data of the sensors, whether the bridge has a large displacement is detected in real time.

Description

Technical Field

[0001] This invention relates to the field of bridge reinforcement technology, and in particular to an anti-overturning structure for single-column pier bridges with intelligent detection. Background Technology

[0002] Single-column piers were widely used in the past due to their small footprint, large space underneath, and aesthetically pleasing design. However, with societal progress, the hidden dangers they pose have become a growing concern. The rapid increase in the number of vehicles and their load-bearing capacity mean that even with safety margins, significant risks remain, especially when overloading occurs. Uneven loading can easily lead to overturning, causing severe loss of life and property. Therefore, reinforcing single-column pier bridges is of paramount importance.

[0003] Existing reinforcement methods for single-column piers each have their advantages and disadvantages. Most rely solely on the strength of the pier's end to resist unbalanced forces under eccentric loading. Over long-term use, this can damage the pier and lead to beam overturning and collapse. Some reinforcement methods involving adding nodes are also ineffective. While some utilize spring isolators for energy release, these lack restoring capacity and cannot be used long-term. For example, patent CN 110700126 A discloses an anti-overturning device for single-column pier bridges, including viscous spring isolators, hinged supports, and chemical bolts. The hinged supports are first anchored to both sides of the bridge main beam and the pier column. A pair of viscous spring isolators are installed on both sides of the pier column and the main beam, connecting the main beam and the pier column. Although the structure is simple, it still relies on the supporting force of the single-column pier, and long-term use will negatively impact both the pier and the bridge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a single-column pier bridge anti-overturning structure with intelligent detection to improve the existing reinforcement methods, with a short construction period and long service life.

[0005] The technical solution adopted in this invention is: an anti-overturning structure for single-column pier bridges with intelligent detection, including precast steel cap beams, steel tie rods and foot piers. By changing the working mode of single-node support of single-column pier bridges through precast steel cap beams, the anti-overturning performance of bridges is improved.

[0006] The precast steel cap beam adopts an upward-opening "C"-shaped structure. The two ends of the precast steel cap beam are equipped with ear plates located on both sides of the bridge. Rubber pads are provided on the ear plates, and the rubber pads are located between the ear plates and the bridge with gaps between them.

[0007] Furthermore, the precast steel cap beam is uniformly provided with stiffening ribs to improve overall rigidity. A pad stone is provided at the upper end of the precast steel cap beam, and rubber bearings supporting the box girder at the lower end of the bridge are provided on the pad stone. Two rubber bearings are symmetrically arranged on both sides of the main body of the single-column pier.

[0008] Force sensors are installed on the side of the rubber pads closest to the bridge and at the connection between the rubber bearings and the bridge. Distance sensors that fit against the box girder are installed at the center of each of the two rubber bearings.

[0009] The force sensor measures the force at the end of the bridge column, and the distance sensor measures the distance from the rubber bearing to the center of the bridge. Based on the data from the force sensor and the distance sensor, the total stress is calculated and compared with the compressive strength of the concrete to determine whether the end of the bridge column has failed. The calculation is as follows:

[0010] The bridge rotation angle θ = arctan(L1-L2) / L3, where L1 is the fluctuation value of the distance measuring sensor, L2 is the initial value of the distance measuring sensor, and L3 is the distance from the rubber bearing to the center of the bridge.

[0011] At this point, the bending moment at the bridge column end M = θEI / L, where E is the elastic modulus of the bridge, i.e., the elastic modulus of the concrete used (when the reinforcement ratio is a few tenths of a percent, the elastic modulus of the concrete can be equivalent to the elastic modulus of reinforced concrete), I is the moment of inertia of the section, and L is half the width of the bridge.

[0012] The stress σ caused by the bending moment at the end of the bridge column at this time M =My / I Z Where M is the end moment of the column, y is the distance from a point on the cross-section to the neutral axis, and I is the distance from the end moment of the column to the neutral axis. Z —Moment of inertia about the centroidal axis on the cross section;

[0013] The axial force at the end of the bridge pier is the total weight G.

[0014] Therefore, the stress σ caused by the axial force at the end of the bridge column at this time Fn =G / A, where A is the cross-sectional area of ​​the bridge pier.

[0015] The shear force at the bottom of the column is calculated using sensors placed at the column end.

[0016] EW[(ε U1 -ε d1 )-(ε U2 -ε d2 )] / 2=P n *H, where

[0017] W—Net section modulus at the end of the bridge column, P n —Shear force at the column end, H—Distance between the upper and lower strain gauges, ε U1与 εU2 It refers to the values ​​of strain gauges placed on both sides of the bridge pier end, ε d1与 ε d2 The values ​​are those of strain gauges placed at the lower part of the bridge pier ends.

[0018] The horizontal stress at the end of the bridge column is σ V =P n / B, where B is the vertical cross-sectional area of ​​the column pier.

[0019] At this point, the stress σ at the end of the bridge column is determined. 总 =σ V +σ Fn +σ M .

[0020] Assuming the neutral axis remains unchanged during bridge overturning, and if the rubber bearings are not damaged, a basic overturning angle can be determined by comparing the magnitude of the overturning force caused by the bridge's self-weight at different angles with the magnitude of the frictional force between the bridge and the rubber bearings. Then, using the bridge's length and width and this overturning angle, the distance between the side rubber pads and the bridge can be calculated. This determines that the bridge has reached its theoretical maximum overturning angle when the force is recorded. When a certain degree of tilt is reached, the side rubber pads will act as a buffer, and data will be transmitted in real time to a wireless terminal to record the force at that moment. The force on the rubber bearings will also be recorded in real time. Based on the magnitude of the forces on both sides, it is possible to detect whether the bridge has experienced significant displacement in real time.

[0021] The steel tie rods are symmetrically distributed on the left and right sides of the single-column pier body. Spring isolators are installed on the steel tie rods. The steel tie rods are hinged to steel cap beams A and B via lower lugs, and to the foot pier via hinged supports. The steel tie rods and spring isolators transfer lateral forces to the bottom of the single-column pier, reducing the bending moment at the column end. This enhances overturning resistance while preventing easy damage to the column end. The spring isolators, located in the middle of the steel tie rods, can also reduce the stress on the column base through energy release and possess a certain degree of restoring force.

[0022] Preferably, a sensor is installed inside the spring isolator to detect the supporting force of the steel tie rod on the bridge.

[0023] The foot pier is cast outward from the bottom of the main body of the single-column pier, and the foot pier is used to expand the cross-section of the bottom of the single-column pier and reinforce the bottom of the single-column pier.

[0024] The precast steel cap beams include steel cap beam A and steel cap beam B, which are fixed to the main body of the single-column pier by connectors.

[0025] The connecting parts are clamps, which include fitting clamp A and clamp B.

[0026] The clamps A and B are respectively installed at one of the adjacent ends of the steel cap beam A and the steel cap beam B.

[0027] Furthermore, both clamp A and clamp B are fitted to the main body of the single-column pier, with a gap between them for mutual fixation after being tightly fitted onto the outside of the main body of the single-column pier with high-strength bolts B. The main body of the single-column pier is clamped and fixed by the pair of clamps A and clamp B.

[0028] Clamps A and B are fixedly connected to the main body of the single-column pier by high-strength bolts A, which are driven into the main body of the single-column pier for fixation.

[0029] Furthermore, the steel tie rod adopts a two-section structure, and the two sections are connected to the spring isolator by external threads at their adjacent ends.

[0030] Furthermore, the steel tie rods are arranged in pairs on both sides of the main body of the single-column pier, with the two steel tie rods on each side of the main body of the single-column pier symmetrically distributed on the front and rear sides of the main body of the single-column pier.

[0031] Furthermore, the foot pier is constructed from a steel cage and poured concrete.

[0032] Compared with the prior art, the present invention has the following advantages: by changing the working mode of single-node support of single-column pier bridge through prefabricated steel cap beams, the overturning resistance of the bridge is improved; by using steel tie rods and spring isolators to transfer lateral forces to the bottom of the single-column pier, the bending moment at the column end is reduced, which enhances the overturning resistance and avoids the column end being easily damaged. The spring isolators arranged in the middle of the steel tie rods can also reduce the force on the column bottom through energy release and have a certain restoring force; by using sensor data, the bridge can be detected in real time whether there is a large displacement. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the prefabricated steel cap beam of the present invention;

[0035] Figure 3 This is a structural schematic diagram of the steel tie rod of the present invention.

[0036] Numbering in the diagram: 1-Steel cap beam A, 2-Steel cap beam B, 3-Rubber pad, 4-Bridge, 5-Rubber bearing, 6-Stone pad, 7-Stiffening rib, 8-High-strength bolt A, 9-High-strength bolt B, 10-Ear plate, 12-Steel tie rod, 14-Spring vibration isolator, 16-Lower ear, 17-Foot pier, 18-Reinforcing cage, 19-External thread, 20-Clamping hoop A, 21-Clamping hoop B, 22-Hinged support, 23-Single column pier main body, 24-Box girder. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0038] Figures 1-3 The diagram shows a single-column pier bridge anti-overturning structure with intelligent detection, comprising a precast steel cap beam, steel tie rod 12, and foot pier 17.

[0039] The precast steel cap beam adopts an upward-opening "C"-shaped structure. Both ends of the precast steel cap beam are equipped with ear plates 10 located on both sides of the bridge 4. Rubber pads 3 are provided on the ear plates 10. The rubber pads 3 are located between the ear plates 10 and the bridge 4, and there is a gap between the rubber pads 3 and the bridge 4.

[0040] The precast steel cap beams include steel cap beam A1 and steel cap beam B2. Steel cap beam A1 and steel cap beam B2 are fixed to the main body 23 of the single column pier by connectors. Both steel cap beam A1 and steel cap beam B2 are precast in the factory, which can effectively reduce the on-site production time and ensure that their load-bearing capacity meets the requirements.

[0041] Steel tie rods 12 are symmetrically distributed on the left and right sides of the main body 23 of the single-column pier. Spring vibration isolators 14 are installed on the steel tie rods 12. The steel tie rods 12 are hinged to the steel cap beams A1 and B2 through the lower lugs 16. The steel tie rods 12 are hinged to the foot pier 17 through the hinge support 22.

[0042] The foot pier 17 is cast outward from the bottom of the main body 23 of the single-column pier.

[0043] Stiffening ribs 7 are evenly distributed on the precast steel cap beam. A pad stone 6 is provided at the upper end of the precast steel cap beam. Rubber bearings 5 ​​supporting the box girder 24 at the lower end of the bridge 4 are provided on the pad stone 6. Two rubber bearings 5 ​​are symmetrically arranged on both sides of the single-column pier body 23.

[0044] Force sensors are installed on the side of the rubber pad 3 near the bridge 4 and at the connection between the rubber bearing 5 and the box girder 24. Distance sensors that fit against the box girder 24 are installed at the center of both rubber bearings 5. The force sensors on the rubber pad 3 have gaps between them and the sides of the bridge and do not come into contact with them.

[0045] Force sensors measure the force at the ends of bridge columns, while distance sensors measure the distance from the rubber bearings to the center of the bridge. Based on the data from the force and distance sensors, the total stress is calculated and compared with the compressive strength of the concrete to determine whether the bridge column ends have failed. The calculation is as follows:

[0046] The bridge rotation angle θ = arctan(L1-L2) / L3, where L1 is the fluctuation value of the distance measuring sensor, L2 is the initial value of the distance measuring sensor, and L3 is the distance from the rubber bearing to the center of the bridge.

[0047] At this point, the bending moment at the bridge column end M = θEI / L, where E is the elastic modulus of the bridge, i.e., the elastic modulus of the concrete used (when the reinforcement ratio is a few tenths of a percent, the elastic modulus of the concrete can be equivalent to the elastic modulus of reinforced concrete), I is the moment of inertia of the section, and L is half the width of the bridge.

[0048] The stress σ caused by the bending moment at the end of the bridge column at this time M =My / I Z Where M is the end moment of the column, y is the distance from a point on the cross-section to the neutral axis, and I is the distance from the end moment of the column to the neutral axis. Z —Moment of inertia about the centroidal axis on the cross section;

[0049] The axial force at the end of the bridge pier is the total weight G.

[0050] Therefore, the stress σ caused by the axial force at the end of the bridge column at this time Fn =G / A, where A is the cross-sectional area of ​​the bridge pier.

[0051] The shear force at the bottom of the column is calculated using sensors placed at the column end.

[0052] EW[(ε U1 -ε d1 )-(ε U2 -ε d2 )] / 2=P n *H, where

[0053] W—Net section modulus at the end of the bridge column, P n —Shear force at the column end, H—Distance between the upper and lower strain gauges, ε U1与 ε U2 It refers to the values ​​of strain gauges placed on both sides of the bridge pier end, ε d1与 ε d2 The values ​​are those of strain gauges placed at the lower part of the bridge pier ends.

[0054] The horizontal stress at the end of the bridge column is σ V =P n / B, where B is the vertical cross-sectional area of ​​the column pier.

[0055] At this point, the stress σ at the end of the bridge column is determined. 总 =σ V +σ Fn +σ M .

[0056] Taking the design of a single-column pier bridge on Longjiang Road in Changzhou City as an example, the original single-column pier was reinforced. The height of the clamp was selected to be one-tenth of the actual pier height, i.e., h = 1.2m. It was connected to the pier using M22 high-strength bolts of grade 10.9. The first connecting bolt was placed 0.1m from the edge of the pier, followed by four rows every 0.5m, and four rows vertically every 0.3m. The base dimension of the pier was doubled, with a trapezoidal cross-section and the two hypotenuses at a 45° angle to the ground. By selecting a sample similar to this section of the viaduct for comparative analysis, it was found that under the conditions of maximum daily traffic flow, the inclination angle of the reinforced pier support decreased by 20%. Comparison with the initial value showed that the bridge possesses a certain degree of tilt recovery force.

[0057] θ=arctan(13.2-13.09) / 5=1.260°

[0058] M = 1.260 x 3.45 x 10 4 x(1.8 3 x6 / 12)x10 6 / 8 = 1.6 x 10 10 N·m 2

[0059] σ M =My / I Z =1.6x10 10 x6 / 4238 = 2.3x10 7 Pa

[0060] σ Fn =2x10 6 / 23.6=8.5x10 4 Pa

[0061] EW[(ε U1 -ε d1 )-(ε U2 -ε d2 )] / 2=P n *H

[0062] P n =1.7x10 7 N

[0063] σ V =P n / B = 1.7 x 10 7 / 22.9=1.2x10 6 Pa

[0064] Therefore σ 总 =σ M +σ Fn +σ V=2.5x10 7 Pa is much less than 50 MPa, which is the strength of C50 concrete, so it meets the strength requirements and will not cause damage.

[0065] The connectors use clamps, including compatible clamps A20 and clamps B21.

[0066] Clamps A20 and B21 are respectively installed at one adjacent end of steel cap beam A1 and steel cap beam B2.

[0067] Both clamps A20 and B21 are fitted to the main body 23 of the single-column pier. There is a gap between clamps A20 and B21 to allow for mutual fixation after they are tightly fitted onto the outside of the main body 23 of the single-column pier with high-strength bolts B9.

[0068] Clamps A20 and B21 are fixedly connected to the main body 23 of the single column pier by high-strength bolts A8.

[0069] The steel tie rod 12 adopts a two-section structure, and the two sections are connected to the spring vibration isolator 14 by external threads 19 at their adjacent ends.

[0070] The steel tie rods 12 are set in pairs on both sides of the single-column pier body 23. There are four steel tie rods 12 arranged in pairs. The two steel tie rods 12 on each side of the single-column pier body 23 are symmetrically distributed on the front and rear sides of the single-column pier body 23.

[0071] The foot pier 17 is constructed from a steel cage 18 and concrete. By pre-measuring the dimensions of the foot pier 17, arranging the steel cage 18, and completing the concrete pouring, the construction period can be effectively shortened, sufficient curing time can be allowed, and the strength of the foot pier can be improved.

[0072] The specific construction steps are as follows:

[0073] 1) Before fabricating steel cap beams A1 and B2, first determine the style and specific dimensions of the main body 23 of the single-column pier, ensuring that clamps A20 and B21 can fit tightly with the main body 23 of the single-column pier, while leaving a certain gap between clamps A20 and B21 to facilitate reinforcement connection using friction-type high-strength bolts B9; measure the relative position of the main body 23 of the single-column pier and the box girder 24, and then determine the height of the concrete pad 5 on the steel cap beam;

[0074] 2) Before installation, the contact surfaces between the column end of the single column pier and the clamps A20 and B21 need to be cleaned and leveled. During installation, structural adhesive is applied to the contact surfaces between the clamps A20 and B21 and the column end. After that, the steel cap beams A1 and B2 are raised to a suitable height and the column end is wrapped. The column end is then fixed to the steel cap beams A8 with friction-type high-strength bolts. The pad stone 6 is placed at the designated position on the precast steel cap beams A1 and B2. Rubber supports 5 and sensors are placed on the pad stone 6.

[0075] 3) Install the rubber support 3 at the ear plate 10 position. A force sensor is installed at the front end of the rubber support 3, and the measured force can be transmitted to the terminal using a wireless transmission device.

[0076] 4) The foot pier 17 is constructed using a steel cage 18 and concrete casting;

[0077] 5) Calculate the length of the steel tie rod 12, and then connect the upper and lower sections of the steel tie rod 12 to the spring vibration isolator 14 through the external thread 19. Then, the upper section of the steel tie rod 12 is hinged to the steel cap beam A1 and the steel cap beam B2 through the lower ear 16, and the lower section of the steel tie rod 12 is hinged to the foot block 17 through the hinge support 22.

[0078] One side of the steel cap beam is slightly wider than the bridge by 200mm to accommodate rubber pads and force sensors. Theoretically, the higher the clamp height, the better, as it reinforces the column end. However, considering practical use and cost, after comparison, we found that a clamp height of approximately one-tenth of the pier height ensures that the column end will not be damaged when the bridge reaches its ultimate overturning angle.

[0079] Considering the varying heights of the piers and the different widths of the bridge, the angle between the tie rods and the ground should be kept below 60° as much as possible. This places higher demands on the hinge joints at the connection points, so Q420 grade steel is used at the hinge joints.

[0080] At the location of the foot pier, chemical anchoring reinforcement was carried out at the bottom of the pier, and 150mm of steel bars were left out to be riveted to the foot pier steel cage and then cast as a whole.

Claims

1. A monopole pier bridge anti-overturning structure with intelligent detection, characterized in that: The precast steel cover beam, steel pull rod (12) and foot pier (17), The precast steel cover beam adopts an open upward "C" type structure, both ends of the precast steel cover beam adopt the ear plate (10) located on both sides of the bridge (4), the ear plate (10) is provided with rubber pad (3), the rubber pad (3) is located between the ear plate (10) and the bridge (4) and there is a gap between the rubber pad (3) and the bridge (4), The precast steel cover beam includes steel cover beam A (1) and steel cover beam B (2), the steel cover beam A (1) and the steel cover beam B (2) are fixed on the single column pier body (23) through the connecting piece, The precast steel cover beam is uniformly provided with stiffened rib plate (7), the upper end of the precast steel cover beam is provided with cushion stone (6), the cushion stone (6) is provided with rubber support (5) supporting the box girder (24) at the lower end of the bridge (4), the rubber support (5) is symmetrically provided with two rubber supports (5) on both sides of the single column pier body (23), The rubber pad (3) is provided with force sensor near the side of the bridge (4) and the connection between the rubber support (5) and the box girder (24), the center of the two rubber supports (5) is provided with distance measuring sensor adhering to the box girder (24), The steel pull rod (12) is symmetrically distributed on both sides of the single column pier body (23), the steel pull rod (12) is provided with spring vibration isolator (14), the steel pull rod (12) is hinged with the steel cover beam A (1) and the steel cover beam B (2) through the lower ear (16), the steel pull rod (12) is hinged with the foot pier (17) through the hinge support (22), The foot pier (17) is poured along the bottom of the single column pier body (23) to the outer ring; The force sensor measures the stress of the bridge (4) column end, the distance measuring sensor measures the distance between the rubber support (5) and the center of the bridge (4), according to the data of the force sensor and the distance measuring sensor, the total stress is calculated, compared with the compressive strength of concrete, whether the bridge (4) column end is damaged is judged, the calculation is as follows: The bridge rotation angle θ = arctan (L1 - L2) / L3, wherein, L1 is the fluctuation value of the distance measuring sensor, L2 is the initial value of the distance measuring sensor, and L3 is the distance between the rubber support and the center of the bridge, At this time, the bending moment M of the bridge column end is θEI / L, wherein, E is the elastic modulus of the bridge, that is, the elastic modulus of the concrete used (in the case of the reinforcement ratio of zero point several percent, the elastic modulus of the concrete can be equivalent to the elastic modulus of the reinforced concrete), I is the moment of inertia of the section, and L is the half value of the width of the bridge, The stress σ at this time due to the bending moment at the end of the bridge column M = My / I Z where M is the bending moment at the end of the column, y is the distance from the point to the neutral axis on the cross section, and I Z is the moment of inertia about the centroidal axis on the cross section. The axial force of the bridge column end is the overall gravity G, Therefore, the stress σ caused by the axial force of the bridge pier end at this time Fn =G / A, A - the cross-sectional area of the pier The shear force of the column end bottom is calculated by the sensor arranged at the column end, EW[(ε U1 -ε d1 )- (ε U2 -ε d2 ) ] / 2=P n *H, wherein, W—Net section modulus at the end of the bridge column, P n —Shear force at the end of the column, H—Distance between the upper and lower strain gauges, ε U1与 ε U2 It refers to the values ​​of strain gauges placed on both sides of the bridge pier end, ε d1与 ε d2 The values ​​are those of strain gauges placed at the lower part of the bridge pier ends. The horizontal stress on the end of the bridge column is σ V = P n / B, where B is the vertical cross-sectional area of the column. At this time, the stress σ at the end of the bridge column is determined 总 = σ V + σ Fn + σ M .

2. The monopole pier bridge anti-overturning structure according to claim 1, characterized in that: The connecting piece adopts the hoop, the hoop includes the matched hoop A (20) and the hoop B (21), The hoop A (20) and the hoop B (21) are respectively arranged at the adjacent end of the steel cover beam A (1) and the steel cover beam B (2).

3. The anti-overturning structure of a single-column pier bridge according to claim 2, characterized in that: The hoop A (20) and the hoop B (21) are adhered to the single column pier body (23), and there is a gap between the hoop A (20) and the hoop B (21) for being tightly sleeved on the outside of the single column pier body (23) through the high strength bolt B (9) and being fixed with each other, The hoop A (20) and the hoop B (21) are fixedly connected with the single-column pier body (23) through high-strength bolts A (8).

4. The anti-overturning structure for a single-column-pier bridge according to claim 1, characterized by: The steel pull rod (12) adopts a two-section structure, and the two-section structure is integrally connected with the spring vibration isolator (14) through the outer threads (19) at the adjacent ends.

5. The anti-overturning structure for a single-column-pier bridge according to claim 1, characterized by: The steel pull rod (12) is arranged in the form of two groups of two rods on the two sides of the single-column pier body (23), and the two steel pull rods (12) on each side of the single-column pier body (23) are symmetrically distributed on the front and rear sides of the single-column pier body (23).

6. The anti-overturning monolithic pier bridge structure of claim 1, wherein: The foot pier (17) is formed by pouring concrete into a steel reinforcement cage (18).

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