Research on One-Time Pouring Construction Technology of Side-Span Cast-In-Situ Section and Closed Section

Abstract

In recent years, in the construction process of closed-bridge side spans, construction has often been carried out in accordance with the construction sequence of, first, pouring the cast-in-place section, then preburying strong bone and pouring the closed section, and finally tensioning the closure steel bundle. However, the temperature change during the construction process of the conventional hinges leads to a large deformation of the hinges’ strong bone, which disturbs the concrete of the hinged section, and, at the same time, its high stiffness means that the concrete of the hinged section will not be sufficiently precompressed, thus resulting in the loss of prestressing force. Therefore, it is necessary to study the one-time casting construction technology of the side-span’s cast-in-place and closed sections. In this study, on the basis of introducing the conventional side-span joint-construction technology, the one-time pouring joint-construction technology was adjusted. In order to eliminate the sunlight temperature factor, which has a great influence on the process of joining, finite element analysis was used to further compare and analyze the changes in the internal force and the linearity of the structure under different joining methods. The results of this study show that, by adjusting the counterweight, the adverse effect of the disturbance of the main girder on the concrete at the joint end under the effect of sunshine temperature can be effectively controlled. Also, one-time joint construction is more reasonable for the internal force and deflection deformation of the structure compared with the conventional side-span joining method of a continuous rigid bridge, which is more favorable to the structure. The research methods and conclusions of this paper can provide a reference for the improvement of closed side-span one-time casting construction technology.

1. Introduction

In recent years, continuous rigid-frame bridges have been widely deployed because of their advantages of convenient construction, the bending resistance of the main girders, their large torsional stiffness, etc. In the construction of continuous rigid-frame bridges, closed side-span construction is a key construction process. The selection of construction technology is informed by the side piers located in the terrain and the structural stress characteristics. The construction cycle has a greater impact. Therefore, it is necessary to carry out an in-depth study of side-span closed-construction technology. In the existing literature on side-span closed-construction technology, Gong Yuhua [1], Wang Zhongnan [2], and Qin Huibin [3] proposed adapting to the influence of unfavorable terrain in mountainous areas by changing the side-span closed measures of continuous rigid bridges. Chen Cheng [4], Zhang Changxuan [5], and Zhao Jianxiang et al. [6] proposed to change the force characteristics of the main girder and side-pier structure by setting counterweights in the side-span closed-construction process, so as to shorten the construction period and reduce the construction difficulty. In the process of constructing the cast-in-place section of side spans and the one-time casting of the closed section, the method of adjusting the counterweight has been proposed to eliminate the unfavorable influence of closed temperatures on structures [7,8,9]. In view of the long side-span cast-in-place section of high-pier continuous rigid bridges, ensuring reasonable structural force and deformation by changing the order of the closed sections has been discussed. In the above study, the construction measures, counterweight, and order of closed sections were mainly investigated via the conventional side-span closed process. However, there are fewer studies focusing on the unconventional construction technology of cast-in-place side-span sections and one-time casting joint construction of the joint sections. Using the one-time closing construction technology of in situ casting of the edge span section and the closing section has the advantages of saving construction time and reducing construction costs. For a continuous rigid-frame bridge with a high pier and long span, stopping the construction of the cast-in-place section of the side span can effectively reduce the construction difficulty and increase the construction safety; this has important engineering value in relation to updating construction technology.

In this paper, based on the analysis of the advantages and disadvantages of various construction techniques, the method of coordinating the construction of hanging baskets, brackets, and hangers with multiple joining methods is proposed given the characteristics of one-time cast-in-span joining construction technology. When there is a bias condition in the cantilever end of the joining side of the one-time joining technology, the structural stress can be improved by changing the joining measures and joining sequences, and the angular displacement of the cantilever end generated by the action of the temperature gradient load in the process of joining can be improved by changing the joining measures and joining sequences. Meanwhile, as regards the angular displacement of the cantilever end produced by the temperature gradient load during the process of joining, the size of the deflection of the cantilever end can be controlled by adjusting the counterweight.

2. Side-Span Closed Method

Designers of continuous rigid bridges often use the cantilever method for construction after completing the cantilever end of the side-span jointing. It is necessary to take reasonable construction measures to reduce the impact of side-span construction on the strength and stiffness of the main beam. The existing side-span joining methods and problems are as follows:

• Hanger (Guide Beam) closed [10,11].

This is illustrated in Figure 1. The hanger cast-in-place construction method involves setting up hangers at the end of cover girders and cantilevers on the approach abutments, after which cast-in-place sections are first poured on the hangers, and then the joined sections are completed on the hangers. The guide girder method is divided into the upper guide girder method and the lower guide girder method, i.e., the upper bearing type and the lower bearing type structural form;

2.

Bracket closed [12,13].

This is shown in Figure 2. Here, one sets up the bull-leg bracket on the approach abutment and implements the counterweight on the other side of the approach abutment by setting up the bracket and then finally pours the in situ casting section and the joint section onto the construction platform. In the construction of a side-span cast-in section, one applies the side-pier pre-embedded bracket prepressure treatment to eliminate the bracket’s inelastic deformation, and at the same time the elastic deformation of the bracket can be offset by setting the prelift value;

3.

Hanging basket closed [14,15].

This is shown in Figure 3. After the cantilever casting section’s construction is completed, the hanging basket continues to move forward to the side-pier cover beam position, and the closed section formwork and part of the cast-in section formwork are directly erected on the hanging basket. When using hanging baskets and hangers, the cantilever T-structure will be subjected to a larger side-span cast-in section, and the centralized load will be transferred from the joint section. Whether the deflection and stress of the side-span T-member itself meet the requirements under this load will determine the applicability of this method.

4.

Floor stand closed [16].

This is shown in Figure 4. This employs the floor-support method, followed by pouring cast-in-place segmental closed sections on erected floor supports to complete the side span;

5.

Multimodal coordination of construction.

Regarding the construction of the cast-in-place section of the side span, due to the large volume of the cast-in-place section, a floor frame is often set up or a bracket is installed on the junction pier abutment to assist in the construction of the hanging basket and hanging bracket. By reducing the maximum stress on the members by applying various construction measures that ensure the safety of construction, in the side-span cast-in-place section, the joint section of a one-time casting process, the cantilever end in the direction of the side-span joint will be subjected to greater vertical load compared with a conventional joint.

In relation to the above issues, several side-span closed methods have been analyzed. With reference to the construction experience gained in the actual project, different side-span cast-in-place methods show the following characteristics (

Table 1. Comparative analysis of advantages and disadvantages of different closing methods.

Closed Method	Advantages	Disadvantages	Scope of Application
Hanger (guide beam) closed	The use of Berle type rod manufacturing equipment and fine rolled rebar to make the boom, by which the processing cost is reduced. The side-pier bias is small.	The truss at the top of the side pier of the hanger needs to bear a lot of shear force and pressure, which is not conducive to the stress of the truss.	The edge across the straight-line segment must not be too long or too heavy.
Bracket closed	Widely used in construction, mature technology, less abutment bias pressure.	The bracket needs to be welded at high altitude, and the preprocessing of the bracket is cumbersome. The eccentric force of the junction pier requires the counterweight to be set at the approach bridge side.	It is not suitable for continuous rigid-frame bridges with large edge spans and long straight segments.
Hanging-basket closed	The use of hanging baskets after the completion of the cantilever end construction greatly shortens the construction cycle and reduces the cost of the project.	Under the action of the hanging basket and the weight of the concrete across the side of the T structure, there will be a large deflection, which is not conducive to the stress of the structure.	A continuous rigid-frame bridge with a small edge–middle span and a short straight-edge span.
Floor-stand closed	The construction method is relatively simple, and the requirements for construction machinery and lifting equipment are low.	The construction period is long, and the risk coefficient of setting up the landing support is higher for the high pier or the water side terrain.	It is more suitable for the continuous rigid frame bridge with a short pier, large edge span, and long asymmetric beam section.
Multimodal coordination of construction (floor rack + hanging basket, bracket + hanging basket, etc.)	A variety of closure methods that facilitate construction and reduce the impact of adverse load on the structure to ensure the construction quality. For the unconventional closure mode, we can ensure the safety of construction.	The amount of construction equipment required is greater, increasing the construction cost.	A continuous rigid-frame bridge with a small edge–middle span and a short straight-edge span. The side-span cast-in-place section and the closure section are poured all together.

):

3. One-Time Closed Study

The side-to-mid-span ratio of existing high-pier multispan continuous rigid bridges in China is generally between 0.5 and 0.6. The selection of side-and-center-span ratio in the cantilever construction of continuous rigid bridges is related to the method of construction of the side-span cast-in-place section. When the transition pier is high, the cast-in-situ section adopts the construction method of guide beam or hanger, and the length is generally 4–5 m, so the side-to-mid-span ratio is smaller [17]. When the transition pier is high, the construction method of using a guide beam or hanger is adopted, and the length is generally 4~5 m, so the ratio of the side center span is smaller.

For high-pier continuous rigid-frame bridges with small side and center spans, construction of the side spans is performed via the one-time casting and closed method, which is more beneficial than the conventional construction process in terms of construction period and economy [18].

The conventional process of construction of continuous rigid-frame bridge side spans and one-time joining construction are shown in Figure 5 and Figure 6 below.

For the two different construction processes, this paper analyzes the effects of the strong skeleton and structural system conversion on the structural stress, optimizes the structural stress during the construction process by adjusting the construction sequence of the structure or the counterweights, and also considers the effects of the temperature of the closed section on the construction process.

In the process of conventional joint construction, in order to avoid the influence of shrinkage creep in the joint section and the change in deflection of the girder end during the casting process, the influence of the girder-end force is usually optimized by setting up a strong skeleton; at the same time, a negative influence of the strong skeleton persists on the joint section.

3.1. Research on Closing Process

3.1.1. Rigid-Skeleton Effect

In the conventional closure construction process, in order to preclude the impacts of shrinkage and creep on the closure section and the deflection change in the beam end in the process of pouring, the rigid skeleton is usually set to optimize the influence of the beam end force. At the same time, the rigid skeleton still has adverse effects on the closure segment.

1.

Stiffness of the skeleton used for structural optimization:

• Resistance to disturbance before the initial consolidation of the joint section: The concrete used in the joint section has low strength during the curing period, and its ability to resist external forces and deformation is very poor. By installing a strong skeleton, one can prevent the strain caused by tension, pressure, bending moment, shear force, and torque at the location of the jointed section of the concrete and at the same time increase the stiffness and the strength at the jointed section, which is helpful for ensuring the quality of the jointed section and increasing the integrity of the bridge;
• Enhance the reliability of the connection between the two cantilever ends: The strong skeleton and the two cantilever ends are fixed in advance, so that the single T-structure at the end of the joint can act as a super-static structure, ensuring that the cantilever end of the beam will not be deformed significantly in the process of joining.

2.

Limitations of the use of a strong skeleton in the structure:

The hinging of the strong skeleton involves strict requirements regarding temperature. When the change in temperature in the joint is large, it will cause the concrete around the built-in strong skeleton to be crushed under repeated actions, which will affect the quality of the joint section.

3.1.2. Structural System Transformation

In the process of conventional closed construction, according to calculations performed via the closed counterweight method, the weight of the side-span closed counterweight is generally half that of the closed section. As shown in Figure 7, when the one-time closed method is used for construction, it will lead to a large, centralized load at the cantilever end of the T-structure, and the value of the centralized load will be much greater than that of the conventional closed counterweight F₁. Now, the following measures are considered to reduce the unfavorable effects of one-time closed construction on the structure [19,20].

1.

Changing the measures of the closure:

As shown in Figure 8, in order to balance the weight of the side-span cast-in-place section, some designers install cantilever bracket structures on both sides of the side piers, and at the same time take into account the influences of the side piers’ bias loads. The counterweight is then balanced by tensioning the equal-weight stranded wire loads on the sides of the side piers.

2.

Changing the tensioning mode of prestressed steel bars:

This method considers that the approach portion of the bridge to be constructed with the box girders is already in place, as shown in Figure 9 (there may be a case for changing the prestressing strands to single-end tensioning).

3.

Changing the order of the closure:

As shown in Figure 10, the sub-side spans are first combined to form a “π”-shaped super-static structure, and then the side spans are combined so as to eliminate the structural damage caused in the girder body by deformation.

3.2. Technical Control Points

3.2.1. Effect of Temperature

1.

Changes in sunlight temperature (system temperature action):

The bridge-joining process is affected by the temperature of sunshine. In the field of concrete sunshine temperature analysis, usually, in pre-existing air temperature, various places will show maximum and minimum values, and the emergence of the moment used as the basis of the whole-day air temperature change can be simulated as a sinusoidal function. Assuming that the daily maximum and minimum air temperatures are T1 and T2, t0 represents the maximum air temperature, and the minimum air temperature occurs in the middle of the moment, according to the following formula, which is used to calculate the atmospheric temperature at any time T$a$(τ) [21].

$$Ta\left(\tau \right)=0.5(T1+T2)+0.5(T1-T2)\mathit{sin}[(\tau -t0)\pi /12]$$

(1)

2.

Temperature gradient:

A concrete box girder is not uniformly heated under the action of sunlight, and its cross-section will show a temperature gradient. China’s “General Specification for the Design of Highway Bridges and Culverts” (JTGD60-2004) [22] stipulates a vertical temperature gradient pattern, as shown in the

Table 2. Vertical sunshine positive temperature difference calculation of the temperature base.

Concrete Paving		Lay a 50 mm Asphalt Layer		Lay a 100 mm Asphalt Layer
T1 (°C)	T2 (°C)	T1 (°C)	T2 (°C)	T1 (°C)	T2 (°C)
25	6.7	20	6.7	14	5.5

, whereby the temperature gradient pattern T1 is taken to be 25 °C, and T2 is taken to be 6.7 °C.

3.2.2. Research on Temperature Control Measures

According to the relevant research, the longitudinal displacement of the cantilever end of the T-structure under the action of insolation temperature can be divided into two parts; one is the longitudinal lineal displacement produced by the top and bottom plates of the main girder in the longitudinal direction under the action of temperature, and the other is the longitudinal angular displacement produced by the cantilever end cross-section due to the inhomogeneous longitudinal deformation of the top and bottom plates of the main girder.

The longitudinal line displacement results in axial tensile and compressive stresses along the longitudinal direction of the main beam, and the change in longitudinal stress mainly depends on the change in daily temperature during the time period during which the concrete reaches its corresponding design strength. Therefore, contrary to the conventional side-span joining construction process, one-time joining construction should be carried out in the time interval of small daily temperature changes due to the lack of a strong skeleton and the restraining effect of the partial prestressing on concrete that has been tensioned in advance. Longitudinal angular displacement will lead to the main girder producing a certain degree of angular displacement at the end of the cantilever, and this part of the angular displacement can be adjusted by the counterweight to limit its deformation. Before construction, this can be achieved through measurements of the actual temperature gradient trend in the region, through the use of finite element analysis software (MIDAS Civil 2023v1.1) to analyze the change in the vertical deflection of the coupling mouth and the cantilever end under the action of sunshine-induced temperature and then through the adjustment of the counterweight to formulate control measures.

4. Engineering Cases

4.1. Establishment of Finite Element Calculation Model

4.1.1. Overview of Engineering Project

In this paper, a special bridge is analyzed as a case study. The span arrangement of the main bridge is (65 + 6 × 120 + 65) m; it is a single-box, single-compartment box section fully prestressed continuous concrete rigid bridge. The height of the box girder and the thickness of the bottom plate vary according to a 1.8 parabolic. The height of the root girder at the centerline of the box girder is 780 cm, the height of the girder placed in the span is 330 cm, the width of the top plate is 1256 cm, the width of the bottom plate is 650 cm, the length of the cantilever is 303 cm, the thickness of the top plate is 30 cm, the thickness of the bottom plate is 32–95 cm, and the thickness of the web plate is 50–70 cm. The length of the 0 section of the box girder is 1200 cm, and the box girder is divided into 15 cantilevered segments. The single “T” girder is divided into 15 cantilevered segments, the lengths of the segments are 4 × 3.0 m + 6 × 3.5 m + 5 × 4.0 m, the length of the side-span casting section is 3.7 m, and the middle- and side-span closed sections are both 2.0 m. The structural arrangement of the main bridge is shown in Figure 11, Figure 12 and Figure 13. The main bridge is constructed from seven “T”-shaped symmetrical cantilever cast-in-situ piers placed from 26 to 32, which will be gradually merged from the side span to the middle span in the order of closed operation. According to the on-site construction condition, hanging-basket construction was applied at the side span of Pier #26, and one-time pouring was completed; the rest of the closed section was poured via the hanging-basket method, with a preburied strong skeleton and the application of a balancing weight. After many system conversions, the multispan prestressed concrete continuous rigid bridge was finally completed.

4.1.2. Computational Parameters for Structural Analysis

1.

Material and cross-section properties:

The concrete of the main beam is C55, the elastic modulus of concrete is 3.45 × 10⁴ MPa, the longitudinal prestress of the main bridge is 15Фs15.2 with a 19Фs15.2 steel hinge harness, and the control stress under the tension anchor of the steel harness is 1395 MPa. In the calculation of prestress loss, the deviation coefficient of the passage is K = 0.002, the friction coefficient of the pipeline is μ = 0.25, and the retraction of the anchor at one end is Δ = 6 mm.

2.

Bridge deck pavement and load value setting:

The weight of the load hanging basket is 80 t. The concrete bulk density is 26 KN/m³. The second phase of the pavement structure contains an 8 cm concrete leveling layer + 10 cm asphalt concrete surface layer, and the second phase’s dead load is 65 KN/m. The loading age of each cantilever cast-in-place beam segment is 10 days. Concrete shrinkage and creep coefficients are adopted according to the standard, and their calculation considers the effects of local temperature differences in the structure, considering the actual loading age of the concrete, according to the standard.

4.1.3. Finite Element Model

Using MIDAS/Civil, according to the design requirements and combined with the actual construction process undertaken on site, the construction process of suspension casting at each section of the main beam is simulated in three construction stages: concrete pouring → prestressed reinforcement tension → basket forward movement for calculation and analysis. The division of calculation conditions is detailed in

Table 3. Bridge construction phase division.

Construction Phase	Construction Project	Construction Phase	Construction Project
1	Construction of bridge piers	52	Tensioned 32# edge-span segmental steel bundle
2	0# section cast-in-place	53	Remove the 32# side-span section cast-in-place support
3	Tensioned 0# segmental prestressed steel bar	54	Cast-in-place construction for 26# side-pier section
4	Install 1# segment hanging basket	55	26# side-pier segmental closure counterweight
5	Construction of section 1#	56	26# edge cross segment closure
6	Tensioned 1# segmental prestressed steel bar	57	Remove the 26# side-span section cast-in-place support
…	…	58	Secondary edge cross closure counterweight
…	…	59	Secondary edge cross closure incremental launching
…	…	60	Secondary edge spanning closure
47	Install 15# segment hanging basket	61	Tensioned secondary edge cross closed steel bundle
48	Construction of section 15#	62	Middle-span closure
49	Tensioned 15# segmental prestressed steel bar	63	Tensioned middle-span closed steel bundle
50	32# side-pier segmental closure counterweight	64	Secondary constant load
51	32# edge span one-time closure	65	Ten years of concrete shrinkage and creep

, and the finite element of the final bridge is shown in Figure 14 below.

4.2. Comparative Analysis of One-Off Joining and Conventional Joining Methods

4.2.1. Construction Program for a One-Time Joint

In the conventional side-span closed-construction process, the cast-in section of the side span is usually constructed first, and then the side-span closure is carried out. According to the organizational arrangement of the construction site, the 26# side piers will be merged according to the conventional closed method, and the 32# side-span cast-in section and closed section will be merged via one-time casting.

In the process of one-time pouring and closed construction, a longitudinal distribution beam is set up at the location of the 32# side pier and its hanging basket, and the weight of the concrete in the side-span cast-in-place section and closed section is transferred to the side pier and the bearing beam of the hanging basket through the longitudinal distribution beam, as shown in Figure 15.

Now, the cast-in-place section of the side span and the closed section are cast at the same time, using hanging-basket construction. As shown in Figure 16, the cast-in-place section and the closed section are equivalent to the line load that is applied. Points A–C are the solid section of the pier top, A–D are the cast-in sections of the side span, D–B constitute the closed section of the side span, and point E is the vertical support load of the hanging basket. Calculation and analysis show that point E can endure about 42 t of load. Now, the equal displacement weight method is used for weight calculation; according to the finite element simulation results, the cantilever end of the cast-in-place section bears the concrete wet weight of the action of the high-mileage side, and shows downward deflection of about 9.7 mm. The side of the cantilever end needs to be able to endure the weight of the water tank, about 50 t. At the same time, one should consider taking measures to reduce the effects of sunlight temperature on the closed section.

4.2.2. Control Measures for Joint Construction

During the construction of the new closed side span, the stiffening skeleton was not set up, while the prestressed steel bundles were not tensioned in advance. Under this method, the influences of the angular displacement of the cantilever end and the longitudinal displacement on the structure at the closed position are mainly considered. The vertical displacement of the cantilever end of the side-span T-structure is firstly considered to ensure the quality of the concrete casting of the joint. The Midas/Civil structural model of the bridge is shown in Figure 17:

1.

Longitudinal angular displacement control measures

Based on the monitoring of ambient temperature variations in the area, the difference between the daily minimum temperature and the daily maximum temperature reaches 15 °C during this time period in the HCL. This is greatly influenced by insolation, and since the action of insolation temperature occurs within a transient temperature field, a fixed temperature gradient cannot be applied to represent different time distributions within a single day. According to the relevant literature, under the action of sunshine gradient temperature, the deflection of the cantilever end linearly changes between moments with the highest temperature and the lowest temperature in a day. Here, the deflection of the cantilever end is calculated using finite element software at the time of the highest temperature (15:00) and the time of the lowest temperature (5:00), taking into account the action of the temperature gradient. Secondly, after completing side-span jointing, it is proposed to set counterweights to offset the effects of the deflection of the cantilever end on the jointed concrete under the action of sunshine. Since the change in the ambient temperature of the girder body decreases between 0:00 and the moment before sunrise, the changes taking place in the girder body during sunlight hours are studied first. The change in the vertical deflection of the cantilever end and the change in the counterweight are shown in Figure 18.

Under the action of sunshine, the cantilever end of the side-span T-structure adopts the state of downward deflection as a whole, and its vertical maximum deflection is about 17 mm, taking into account the influence of the side-span closed basket and the weight of the closed section; we then set the construction prearching value to 12 mm in order to adjust the girder line shape through the counterweight. In the moments from 6:00 to 10:00 and from 20:00 to 24:00, both sides of the cantilever end present upward deflection relative to the bridge alignment as a whole; in the moments from 11:00 to 19:00, both sides of the cantilever end present downward deflection. Therefore, the line shape of the cantilever end of the main girder is obviously improved after the setting of the dynamic counterweight.

2.

Longitudinal line displacement control measures

The longitudinal displacement of the cantilever end mainly occurs due to the overall rise and fall of the temperature of the system under the action of sunshine, and the pouring of concrete in the new joining process is generally carried out at night when the temperature is low. According to the meteorological data from the region, the average daily maximum temperature difference reaches 15 °C, and the longitudinal displacement of the cantilever end structure can reach 9.5 mm under the action of the overall temperature. As such, the bottom mold of the side-pier support is filled with sand to ensure that the longitudinal displacement of the structure is more effectively released. This reduces the one-time casting process as the cast-in section is too long for the stress release structure to have an adverse effect.

4.2.3. Comparison of Internal Forces and Linear Structures

Through the method of the dynamic adjustment of counterweights shown in Section 3.2.2, the adverse effect of the cantilever end on the closed section at the helicoidal end can be effectively controlled. Now, we compare the effects of the conventional joining construction and the one-time casting joining construction processes on the structural forces. The changes in the bending moment at the bottom of the pier, the stresses at the top and bottom edges of the main girder, and the deflection under different construction stages of the two conditions are considered, as follows:

• Working condition 1—Conventional closed construction of side spans;
• Work condition 2—Unconventional closed construction.

1.

Side-span closed-construction stage

We here select the side-pier support section, closed mouth section, side-span 1/4 section, side-span 1/2 section, side-span 3/4 section, and pier top section under stress to perform comparative analyses of the internal force in different sections under the two working conditions, and the differences between linear effects.

As shown in Figure 19, the trend in stress change at the upper edge of the main girder tends to be the same under one-time joining compared with conventional joining, and the stress value at the lower edge of the main girder is smaller than that at the upper edge, while one-time joining will not produce a tensile stress value. As shown in Figure 20, the trend of the change in the vertical deflection of the main girder is the same in one-time joining as in conventional joining near the mid-span side, and the value of the vertical deflection of the main girder after joining on the side of the side span is a little smaller, which indicates that the method shown in Section 3.2.2 of adjusting the deflection of the cantilever end using weights has an obvious effect.

2.

Bridge Formation Phase

Usually, in the construction and operation process, the main pier has a tendency to tilt inward towards the center span due to the downward deflection of the main girder. The large inward displacement of the main pier may lead to tensile stress at the bottom of the pier, and the size of the displacement of the main pier between the one-time casting and the conventional joining process is analyzed in different construction stages. As shown in Figure 21, in the bridge stage, the horizontal displacement of the side piers will be larger under the action of thrust force produced by one-time cast-in-link construction than by conventional lining construction; at the same time, after ten years of operation, its tendency to undergo inward inclination towards the side of the center span is lower. This shows that the one-time cast-in construction is more favorable for the structure than the conventional cast-in construction process.

5. Conclusions

In this study, the one-time joining construction process was studied via the stress characteristics of the structure, the joining construction sequence, and temperature control measures, and the main results are as follows:

1.

In the one-time casting closed-construction process, the adoption of hanging baskets, brackets, hangers and other closed measures can effectively improve the bias pressure on the side piers produced by the cast-in section and the closed section. At the same time, by applying counterweights or adjusting the order of closure on the side of the side-span main girder, the bias pressure on the end of the cantilever on the closed side can be changed;

2.

The cantilever end of one side of the side-span joint will show a large deflection as an effect of sunshine when the main beam is subjected to a temperature gradient, and the whole section shows a downward deflection trend. On the basis of adjusting the construction pre-arch, the dynamic adjustment of the counterweight according to changes in the environmental temperature during the pouring period can effectively prevent the concrete in the joint section being disturbed by the cantilever end;

3.

The internal force and line shape of the main girder after the performance of side-span joining via the two joining methods, as well as the inward inclination trend of the piers under the action of shrinkage creep at the bridge completion stage and after ten years of operation, were analyzed with numerical simulation, and the results show that the one-time joining construction was more favorable to the structure than the conventional joining construction process.