Formwork

Formwork is a kind of temporary structure whose purpose is to support its own weight and that of freshly placed concrete as well as the construction live loads including materials, equipment and workmen. Formwork as a temporary structure is desired to safely support the concrete until it gains adequate strength to stand on its own. According to IS: 14687–1999, formwork should be made in such a manner that the finished concrete is in proper position in the space measured with respect to certain predefined reference points.

Types of Formwork based on Orientation

• Vertical – E.g., Columns, Walls
• Horizontal – E.g., Slabs and Beam soffits.

Components of Formworks

The basic idea of the components is that the load from the concrete and construction live should be properly taken without any failure, as if any kind of service failure (deflection) failures occurs then the ultimately the shape and finish of the concrete will not be desirable.

Components of Vertical Formwork

• Sheeting member – direct contact with the concrete.
• Stud member – supporting the sheeting member.
• Tie Rod – for taking the load coming from the studs.

Components of Horizontal Formwork

• Sheeting member – direct contact with the concrete.
• Joists – supporting the sheeting member
• Stringers – supporting the joists
• Props – vertical long bars like columns used to support the stringers and the overall formwork.

Loads of Formwork

1. Dead Loads

Self-Weight of Formwork

• IS 875 PART 1 if proper data is available or 500 N/m² when data is not available
  
• weight of any ancillary temporary work connected or supported by formwork, filling materials
  
• the weight of freshly placed concrete, including reinforcement steel.
  

2. Imposed Loads

• The lateral pressure of concrete
  
• Loads from construction personnel, plant and equipment, vibration and impact of machine-delivered concrete
  
• Unsymmetrical placement of concrete
  
• Concentrated load and storage of construction materials
  

LOAD TRANSFER MECHANISM FOR VERTICAL FORMWORK SYSTEM

Concrete lateral pressure is calculated using various methods (which will be discussed in the later part of this theory section), from the sheeting member to studs to the wales and finally to tie rods.

LOAD TRANSFER MECHANISM FOR HORIZONTAL FORMWORK SYSTEM

The vertical loads coming from the self-weight of concrete and combining all the loads (DL+LL) is firstly taken by the sheeting member to the joist and then to stringer and finally to the shores.

MONOLITHIC FORMWORK

1. Definition and Concept

Monolithic formwork refers to the use of formwork systems that enable the construction of large, continuous concrete structures in one go. This method contrasts with traditional formwork, where structures are built in separate stages and then joined together.

2. Advantages

• Structural Integrity: By eliminating joints between different parts of a structure, monolithic formwork can enhance the overall strength and durability of the building.
  
• Reduced Leakage: Fewer joints mean there are fewer opportunities for leaks and weaknesses, leading to improved waterproofing and resistance to environmental factors.
  
• Faster Construction: Since the entire structure is cast at once, this method can reduce construction time and labor compared to traditional methods involving multiple stages.
  
• Aesthetic Benefits: Monolithic construction can result in a smooth, continuous finish, which can be visually appealing and reduce the need for additional finishing work.
  

3. Challenges

• Complexity of Formwork Design: Designing formwork that can handle the demands of a monolithic pour requires precise planning and engineering, which can be complex and costly.
  
• Construction Risks: If the formwork or the concrete mix isn’t managed correctly, there can be risks such as collapse or defects in the final structure.
  
• Temperature and Curing: The entire structure needs to be cured uniformly to avoid problems like cracking or uneven setting, which can be challenging for large, monolithic pours.
  

4. Applications

Monolithic formwork is particularly useful in constructing:

• High-rise buildings: Provides a seamless vertical load path, enhancing stability and strength.
  
• Bridges and large civil engineering projects: Where continuity and strength are critical.
  
• Complex geometric structures: Allows for innovative and intricate designs that would be difficult to achieve with traditional methods.
  

5. Modern Innovations

• Precast Monolithic Formwork: Innovations include using precast panels that are assembled on-site to form a monolithic structure, speeding up the process and improving quality control.
  
• Self-Compacting Concrete (SCC): Reduces the need for vibration and helps achieve a smooth finish, which is beneficial for monolithic construction.
  
• 3D Printing: Emerging technologies in 3D printing offer new possibilities for creating monolithic structures with complex designs and reduced labor.
  

In summary, monolithic formwork is a powerful technique in modern construction, offering significant advantages in terms of strength, aesthetics, and speed. However, it requires careful planning, sophisticated formwork systems, and effective curing processes to ensure success.