Reinforced concrete constructions with Tunnel Formwork Method.

Tunnel Formwork is one of the methods used in executing buildings with bearing walls and concrete ceilings. Since the formwork of the ceiling and wall is done in cellular form simultaneously. Using this method is called tunnel formwork method. In this system, walls and ceilings are formed and concreted simultaneously. Using this method, no only the quality and speed are improved, but also structural and seismic behavior of the construction, in terms of integrity of components and connections is boosted.

Forms are as large as spaced. There is no need for assembling smaller components and the forms are exited entirely from the space. After concreting and initial set, the form is detached by a horizontal movement on wheels or rolls. Main interior structures and some exterior ones are executed using this method.

Structures executed by Tunnel Formwork method are comparably familiar and lack major seismic problems and have shown acceptable seismic behavior in past earthquakes.

In this method, in some cases, in order to increase progress, non-structural part of the construction such as partitions, stairs, façade panels are prefabricated and installed; yet, this process is not good for stairs.

Using state-of-the-art technologies in increasing setting and resistance of concrete, execution speed may be noticeably increased. Using this method, developers can complete a floor only in two days and gigantic apartment buildings are constructed using this method. One of the shortcomings of this method is that interior design in limited. Designing should be done within the limitations, observing the dimensions of forms, on modular basis.

In this method, mechanical and electrical facilities ducts are designed in the walls and openings for facilities, doors and windows are considered. Then, successive forms are put together (with ceiling form or without ceiling form) and walls and ceiling form is completed

Then, ceiling reinforcement is done and necessary ducts are installed in the ceiling. Walls and ceilings are concreted simultaneously at a single stage. With finished surfaces there is no need for finishing works on the surfaces. This method is evaluated at Housing and Construction Research Center and its use is authorized, observing the below obligations.

Obligations related to reinforced concrete constructions in tunnel formwork method.

1.      This system is designed according to reinforced concrete constructions with bearing walls ad its execution method is tunnel formwork method.

2.      Execution of this system is authorized in all seismic areas of Iran (standard 2800), up to 15 floors or 50 m. high from the base.

3.      Seismic and structural design will be according to the latest standard 2800 of Iran and its bylaws (or bylaw ACI 318-05 and its consecutive editions.)

4.      Observing the regulations related to average and high formability in proportion with seismicity of Iranian regions, according to standard 2800, is mandatory.

5.      Plan and height of the construction should be regular.

6.      Using an opening f 5.5 m for ceiling, maximum 3 m. (net, without thickness of the ceiling), and a minimum of 15 cm for walls, is authorized in this system.

7.      Nominal sectional area of structural walls should be at least 3% of the floor area.

8.      Nominal sectional area of structural wall of one side should be at least 80% of the other side.

9.      Minimum compressive strength of cylinder sample for structural concrete should be 25 mega Pascal and minimum yield stress for steel should be 400 mega Pascal.

10. Special considerations for assembling and disassembling tunnel formwork in architectural plan should be done.

11. Removing formwork of structural components should be performed in compliance with the9th chapter of National Construction Regulations.

12. Chemical additives such as lubricants and concrete set facilitators should be according to National Construction Regulations or other valid international standards. Also, type and amount of additives should be based on executive and climatic specifications.

13. Required strategies should be considered in designing and executing buildings in different climates.

14. Components should be designed and executing appropriately t non-structural wall connections in order not to contribute in side hardness of the structure.

15. Paths and places of electrical and mechanical installations should be exactly determined at design and execution stages.

16. Strategies and equipment necessary for integrated concreting of walls ad ceiling of each floor should be considered.

17. Finishing and façade of concrete surfaces should be taken into account at design and execution stags.

18. Het isolation of exterior parts of the building should be done according to chapter 19 of National Construction Regulations.

19. Chapter 3 of National Construction Regulations in terms of fire protection and the provisions of publication No. 434 of Housing and Construction Research Center relate to resistance of surfaces against fire, with regard to the number of floors, dimension of building, use and performance of constructional components should be observed.

20. Sound absorption of vents, exterior face and ceilings should be according to chapter of National Construction Regulations.