Case Study: Transverse Analysis of PSC Box Girder in Cable-Stayed Bridge

March 24, 2020
BLOG CASE STUDY

In this webinar, we will introduce the midas Civil application of the transverse analysis of prestressed concrete box girder in the cable-stayed bridge. 

 


 

This case study highlights

 

1. Modeling Concept

 

2. Considered Load Case with Functions in midas Civil

 

3. Considered Boundary Conditions with Functions in midas Civil

 

4. Post-processing and Other Modeling Applications

 


 

The example structure below is the Saemangeum bridge in South Korea. This project is a preliminary design. The structure is a cable-stayed bridge with concrete superstructures, pylons, and piers. The superstructure is composed of pre-stressed concrete girders. The transverse analysis was carried out in midas Civil.

Cable-Stayed Bridge in the Elevation View

Fig 1. Cable-Stayed Bridge in the elevation view
 
 

02.거더 현황

Fig 2.PSC girder detail in the plan & cross-sectional view

 

 

 

1. Modeling Concept 

 

- 3D Plate elements model.

- 3 types of sections were considered in the same element shape.

- Lateral tendon prestressed loads using tendon profiles were considered. 

- Related functions of midas Civil : Import > Auto CAD dxf, Extrude, Translate, Thickness Property with Offset option.

 

Longitudinal view of Target ModelFig 3. Longitudinal View of Target Model
 
 

 

3D plate elements model for the PSC girderFig 4. 3D plate elements model for the PSC girder
 
 
 

Overview of Cross-Sections

Fig 5. Overview of Cross-Sections
 
 
 

Plan view for mesh generation in the cross-section

Fig 6. Plan view for mesh generation in the cross-section
 
 
 
Plate elements with offset optionsFig 7. Plate elements with offset options

 

 

 

2. Load Cases with Functions in midas Civil

 

- This model tried to have all conditions around the structure to get better results.

- Considered conditions are shown below. 

- Functions in midas Civil are shown in bold letters

 

Load conditions

Fig 8. Load conditions

 

 

2.1. Self-weight load of the girder & Superimposed load

 

- Self Weight function was used.

- Plane Loads function was used for superimposed loads.

 

Self Weight & Superimposed Loads
Fig 9. Self weight & Superimposed loads

 

 

 

2.2. Wind load

 

- Nodal Load function was used for the wind force on the barriers which are not modeled as elements.

- Pressure Load function was used for the wind force on the side of the girder.

 

Wind LoadsFig 10. Wind loads
 

 

2.3. Temperature load

 

- Element Temperature function was used for cooling and heating cases of the uniform temperature.

 

Temperature Loads
Fig 11. Temperature loads
 

 

 

2.4. Prestressed load

 

- Tendon Prestressed Load function was used.

- Tendon Profile function was used to check the effect of the profile.

 

Prestress Loads
Fig 12. Prestress loads
 

 

 

2.5. Vehicle load

 

- Plane Load function was used.

- A vehicle is a truck. Wheel Loads of a truck is used.

- The concentrated load of wheels is replaced with the distributed load.

 

Vehicle Type & Wheel Loads
Fig 13. Vehicle type & Wheel loads
 

 

- In order to get critical positions of the vehicle, the influence diagrams were considered in the longitudinal and transverse directions.

 

Influence diagram and critical position in the longitudinal direction
Fig 14. Influence diagram and critical position in the longitudinal direction

 

 


Influence diagram and critical position in the transverse direction

Fig 15. Influence diagram and critical position in the transverse direction
 
 
 
Applied plane load for vehicle loads
Fig 16. Applied plane load for vehicle loads
 
 

 

2.6. Cable force

 

- Pretension Loads function was used.

- Truss elements were used for cables to consider the cable force only.

- In another approach, Point Spring boundary condition with its stiffness can be used instead of modeling cables.

 

Cable Force: Pretension LoadsFig 17. Cable Force: Pretension loads
 
 
 
Cable Force: Point Spring
Fig 18. Cable Force: Point spring

 

 

 

 

3. Boundary Conditions with Functions in midas Civil

 

- Define Supports function was used.

- Rigid Link function was used for the rigid zone of the girder section.

- It would be necessary to consider proper boundary conditions depending on model cases.

 Boundary conditions: Simple support type and Rigid Link type

Fig 19. Boundary conditions: Simple support type and Rigid Link type
 
 

 

 

4. Post-processing and Other Modeling Applications

 

- Load Combination function was used to combine load cases.

- Results function was used to get stresses & forces results.

- Results data can be used to optimize components in the structure. Checkpoints could be the section shape, reinforcements, tendons and etc.

 

Load Combination function
Fig 20. Load Combination function
 
 
 
Analysis results
Fig 21. Analysis results
 
 
 
Modification works
Fig 22. Modification works
 

 

 

- In the detail design step, various ways can be used to get more detailed results.

- There are other options for the detailed analysis in Midas SW family.

 

Transverse analysis with midas FEA
Fig 23. Transverse analysis with midas FEA
 
 
 
24.midasCivil
Fig 24. Transverse Analysis with midas Civil

 


 

Conclusion

 

1. This application was carried out to check the capability of prestressed concrete box girders in the transverse direction under preliminary design.

2. The girder can be modeled as a frame, plate, and solid element.

In this case, plate elements were used.

3. For more detailed results and other design details, detailed analysis was carried out. 

 


 

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TaeYong Yu | Technical Engineer | MIDASIT

Tae Yong is a bridge engineer within MIDASIT Technical Planning Team in South Korea. He has over 3 years of experience in the design of bridges and civil structures in Korea. He is familiar with international codes of practice including AASHTO, Eurocode and BS code. He has experience in discussing technical issues with engineers in Singapore, Malaysia, and Romania. From this webinar, he will share one of his experiences in Cable-stayed bridge design.

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midas Civil Case Study of the transverse analysis of prestressed
concrete box girder in the cable stayed bridge.

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