# Study on Load Transfer Mechanism of Local Curved Prestressed Hollow-Core Slab Bridge

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## Abstract

**:**

## 1. Introduction

## 2. Finite Element Analysis Method

#### 2.1. Finite Element Model of Beam with Joint

#### 2.1.1. Concrete Setting

#### 2.1.2. Rebar Setting

#### 2.1.3. Interface Setting of New-to-Old Concrete

#### 2.1.4. Setting of Unbonded Prestressed Tendons

_{tpk}. When dividing prestressed tendon elements, prestressed tendon nodes and concrete nodes will be automatically coupled. However, the prestress technology used in this paper is unbonded prestress, and the arrangement of prestressed tendons is curved. Referring to the setting method in references [36], this paper uses the coupling method of the local coordinate system to simulate the unbonded state of a curved prestressed tendon. First, the other nodes except the outermost grid nodes on the prestressed tendons are disconnected to make them free, and then each node is set as the origin in turn, and the X axis points to the next node, thus establishing the local coordinate system of the node. In the local coordinate system of each node, the displacement in the beam width direction is constrained, and the displacement in the X direction and the beam height direction is released, so that it can move along the prestressed tendons and the beam height direction. For the two outermost nodes of prestressed tendons, the coupling state with concrete is always maintained, to ensure that prestressed tendons and beams have the same movement. The schematic diagram of prestressed reinforcement is shown in Figure 8.

#### 2.1.5. Bearing and Constraint Setting

#### 2.2. Hollow-Core Slab Bridge Model and Loading

## 3. Model Verification and Result Analysis

#### 3.1. Model Verification

#### 3.2. Interface Stress Analysis

#### 3.3. Stress Analysis of Joint and Laminated Layer

## 4. Hollow-Core Slab Bridge Results Analysis

#### 4.1. Failure Process Analysis of Traditional Hollow-Core Slab Bridge

#### 4.2. Failure Process Analysis of Prestressed Hollow-Core Slab Bridge

#### 4.3. Comparative Analysis of Results

#### 4.3.1. Analysis of Rebar Stress

#### 4.3.2. Relative Deflection Analysis

#### 4.3.3. Analysis of Longitudinal Crack Length and Maximum Crack Width

#### 4.4. Force Transmission Mechanism

- (1)
- Uncracked stage: At this stage, no cracks are generated in the hollow-core slab bridge and the force performance of the joints is good. In this stage, with the load increases, the U-bar stress value, the relative deflection values on both sides of the joints, and the maximum crack width values grow slowly, and the load is mainly transferred by the interface unit.
- (2)
- Working stage with cracks: At this stage, cracks are generated in the hollow-core slab bridge. With the increase of load, longitudinal cracks gradually extend to both sides of the hollow-core slab bridge, and the height of cracks gradually rises. With the increase of load, the stress value of the U-bar, the relative deflection value on both sides of the joint, and the maximum crack width increase faster than that in the uncracked stage. In this stage, in the traditional hollow-core slab bridge, the load is mainly transmitted by U-bars and interface units. In the prestressed hollow-core slab bridge, the load is mainly transmitted by U-bars, prestressed tendons, and interface units.
- (3)
- Failure stage: At this stage, the cracks in the hollow-core slab bridge have reached the bottom of the laminated layer. With the increase of load, the stress value of the U-bar, the relative deflection value on both sides of the joint, and the maximum crack width value increase rapidly. In this stage, the interface unit in the hollow-core slab bridge exits to transfer load. In the traditional hollow-core slab bridge, the load is only transmitted by U-bars. In the prestressed hollow-core slab bridge, the U-bars and prestressed tendons jointly transfer the load.

## 5. Conclusions

- (1)
- The interface normal stiffness of the traditional and prestressed hinge joint finite element models is 12,000 MPa and 20,000 MPa, respectively, and the interface tensile strength is 1 MPa and 0.6 MPa, respectively. The error between the finite element analysis results and the static load test results is basically within 15%.
- (2)
- The total failure process of the prestressed hollow-core slab bridge is cracking near the mid-span under 33.3% ultimate load. Under 44.4% ultimate load, the longitudinal crack length reaches 1.6 m. Under 85.2% ultimate load, the longitudinal crack length reaches 3.4 m. Under 100% ultimate load, the longitudinal crack length reaches 3.9 m. With the increase of load, the longitudinal cracks extend to both sides and the width of cracks increases.
- (3)
- Compared with the traditional hollow-core slab bridge, the cracking load, through-joint load, and ultimate load of the prestressed hollow-core slab bridge are increased by 50.0%, 91.7%, and 66.7%, respectively. The durability and bearing capacity of the prestressed hollow-core slab bridge have been improved.
- (4)
- Under the same load, the U-bar stress, the relative deflection on both sides of joint, and the maximum width of joint of the prestressed hollow-core slab bridge are smaller than those of the traditional hollow-core slab bridge. Under the ultimate load, the longitudinal crack span of the traditional hollow-core slab bridge is 0.22–0.7 L, and that of the prestressed hollow-core slab bridge is 0.3–0.7 L. Prestressed tendons can share the transfer load and restrain the deterioration of a hollow-core slab bridge.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Specimen size. Note: ①-Joint; ②-Laminated layer; ③-Precast beam segment [12].

**Figure 2.**Reinforcement drawing. Ⅰ—U-bar; II—Cross rebar; III, IV—Construction rebar; VI—The rebar of the laminated layer; Ⅶ—The rebar of the precast beam segment [12].

**Figure 7.**Interface unit settings, (

**a**) Schematic diagram of new-to-old concrete interface, (

**b**) Schematic diagram of interface unit.

**Figure 13.**Reinforcement of hollow-core slab, (

**a**) Reinforcement of medium plate, (

**b**) Side plate reinforcement.

**Figure 16.**Beam B-C analysis result diagram, (

**a**) Load-reinforcement stress diagram, (

**b**) Load-relative deflection diagram.

**Figure 17.**Beam B-P analysis result diagram, (

**a**) Load-reinforcement stress diagram, (

**b**) Load-relative deflection diagram.

**Figure 20.**Development trend of cracks in traditional hollow-core slab bridge, (

**a**) Crack height development, (

**b**) Crack width development.

**Figure 23.**Development trend of cracks in prestressed hollow-core slab bridge, (

**a**) Crack height development, (

**b**) Crack width development.

**Figure 26.**Nephogram of tensile damage of joint concrete, (

**a**) Hollow-core slab bridge M-C, (

**b**) Hollow-core slab bridge M-P.

Number | Moulded Dimensions | Enhancement Mode | Model Use |
---|---|---|---|

B-C | Scale model | Unreinforced | Finite element model verification |

B-P | Scale model | local prestress | Finite element model verification |

M-C | Hollow-core slab bridge model | Unreinforced | Finite element result analysis |

M-P | Hollow-core slab bridge model | local prestress | Finite element result analysis |

Number | Cracking Load (kN) | Through-Joint Load (kN) | Ultimate Load (kN) | |||
---|---|---|---|---|---|---|

Test Value | Analysis Value | Test Value | Analysis Value | Test Value | Analysis Value | |

B-C | 60 | 70 | 280 | 300 | 340 | 340 |

B-P | 130 | 100 | 180 | 200 | 870 | 860 |

Number | Cracking Load (kN) | Through-Joint Load (kN) | Ultimate Load (kN) |
---|---|---|---|

M-C | 120 | 240 | 360 |

M-P | 180 | 460 | 540 |

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**MDPI and ACS Style**

Chen, J.; Wang, Y.; Zhu, Q.
Study on Load Transfer Mechanism of Local Curved Prestressed Hollow-Core Slab Bridge. *Materials* **2023**, *16*, 4708.
https://doi.org/10.3390/ma16134708

**AMA Style**

Chen J, Wang Y, Zhu Q.
Study on Load Transfer Mechanism of Local Curved Prestressed Hollow-Core Slab Bridge. *Materials*. 2023; 16(13):4708.
https://doi.org/10.3390/ma16134708

**Chicago/Turabian Style**

Chen, Jihao, Yuxin Wang, and Qian Zhu.
2023. "Study on Load Transfer Mechanism of Local Curved Prestressed Hollow-Core Slab Bridge" *Materials* 16, no. 13: 4708.
https://doi.org/10.3390/ma16134708