1. Causes of Formwork Failure: Formwork failure can happen due to various reasons such as improper bracing, unanticipated incident, omissions in assembly detail, and workmanship errors. Improper bracing can lead to the collapse of formwork since the weight of fresh concrete is no longer supported by the formwork system. Unexpected incident can also make a member to fail and cause overloading or misalignment of other members, leading to the failure of the entire formwork structure. Omissions in assembly detail can also cause localized weakness and overstress, destabilizing the formwork system. Additionally, workmanship errors due to haste, indifference, or lack of knowledge can also lead to formwork failure.
2. Consequences of Formwork Failure: Formwork failure can have serious consequences such as loss of life, delay in construction, and increase construction cost. That is why it is important to familiarize with causes of failure and consider proper prevention strategies to ensure safety and efficiency.
3. Prevention Strategies for Formwork Failure: Good practice in designing, constructing, and handling formwork is necessary to prevent formwork failure. This includes adequately bracing the formwork, following the assembly details precisely, and ensuring that the formwork is properly aligned. Additionally, proper supervision and training of workers can help ensure that the formwork is constructed properly.
1. Improper Stripping and Shore Removal
Improper Stripping and Shore Removal
Improper stripping and shore removal practices can lead to serious consequences in the construction of multistory buildings. When forms are stripped too early, it can cause the concrete to sag, resulting in cracking and maintenance issues. Additionally, if reshores are not spaced and sized properly, it can lead to formwork collapse during construction, resulting in damage to the concrete structure. Ultimately, this could result in progressive collapse of the structure, which can be catastrophic.
Preventing Formwork Collapse
In order to prevent formwork collapse, proper stripping and shore removal protocols must be followed. Care must be taken to ensure that forms are not stripped too early, and that the reshores are spaced and sized correctly. Furthermore, the use of high-quality formwork materials and proper installation techniques can help to ensure the safety and stability of the structure.
Advantages of Proper Stripping and Shore Removal
Following proper stripping and shore removal protocols has a variety of benefits. It can help to ensure the safety of the structure and the people working on it. Additionally, it can lead to a higher quality end product and fewer maintenance issues down the line. Lastly, it can help to reduce costs associated with repairs and delays in construction.
2. Inadequate Bracing
Impact of Insufficient Cross Bracing on Formwork Failure
Cross bracing and horizontal bracing are essential components of any formwork system. Without adequate bracing, the formwork may be susceptible to lateral forces, causing lateral deformation of the supporting members. If a failure occurs at one point, inadequate bracing can cause the collapse to spread to a large part of the structure, resulting in increased damage. This highlights the importance of proper bracing for effective formwork safety.
Impact of Poor Horizontal Bracing on Formwork Failure
Horizontal bracing is used to provide stability to formwork systems. If the bracing is insufficient, the formwork may be vulnerable to lateral forces, resulting in the lateral deformation of the supporting members. This can lead to a collapse of the formwork when a failure occurs, and if the bracing is inadequate, the collapse may spread to a large portion of the structure, resulting in greater damage. This underscores the importance of proper horizontal bracing for formwork safety.
3. Inadequate Control of Concrete Placement
Control of Concrete Placement: Key Factors for Formwork Stability: The placement of concrete on horizontal formwork can lead to unbalanced loadings and formwork failure if not properly regulated. To prevent this, several factors must be taken into account. These include the concrete temperature, chemistry, rate of vertical placement, and vibration.
Concrete Temperature: Avoiding Pressure Overload: If the concrete temperature drops during construction operations, the rate of concrete placement must be decreased to prevent the buildup of lateral pressure that could overload the formworks. By doing this, the stability of the formwork is preserved and the risk of failure is reduced.
Concrete Chemistry: Maintaining Strength and Durability: The chemical composition of concrete affects its strength and durability. To ensure that the formwork is strong enough to withstand the loads placed upon it, the concrete must be mixed according to the manufacturer’s specifications. This will also help maintain the stability of the formwork for the duration of the construction project.
Rate of Vertical Placement: Minimizing Risk of Failure: The rate of vertical placement of concrete should be regulated to prevent unbalanced loadings that could cause formwork failure. By controlling the rate of placement, the risk of failure is minimized and the formwork remains stable.
Rate of Vertical Placement: Minimizing Risk of Failure: The rate of vertical placement of concrete should be regulated to prevent unbalanced loadings that could cause formwork failure. By controlling the rate of placement, the risk of failure is minimized and the formwork remains stable.
4. Inadequate Concrete Strength Development
Inadequate Concrete Strength Development: A Case Study of Hyperbolic Cooling Tower Failure
The failure of the hyperbolic cooling tower in Ohio, USA during its construction is a compelling example of inadequate concrete strength development leading to formwork system failure. The jump form system was supported by anchors cast in the previous day’s concrete placement. The forms were linked together around the inside and outside of the circular shell structure. Upon raising the forms and during the casting of an additional ring level, the concrete placed the previous day failed at the anchors, causing the scaffolding and forms to collapse.
Cause of Failure: Insufficient Strength Development
The cause of the failure of the hyperbolic cooling tower was identified as insufficient strength development of the concrete. The concrete had not developed the strength necessary to support the formwork system and additional placement of concrete, leading to the collapse of the system. The failure was attributed to a number of factors, including the size of the concrete placement, the design of the formwork, the curing conditions, and the quality of the concrete mix.
Mitigation Measures for Inadequate Strength Development
To reduce the likelihood of inadequate strength development, there are a number of measures that can be taken. It is important to ensure that the concrete mix is designed to meet the requirements of the project, and that the mix contains the right amount of cement, water, and aggregates. The formwork should also be designed to ensure that the placement of the concrete is appropriate and that the curing conditions are conducive to the development of strength in the concrete. Additionally, it is important to ensure that the concrete is tested regularly to ensure that it has reached the required strength levels.
5. Vibration and Impact
Vibration and impact caused by passing traffic, movement of workers and equipment, and concrete consolidation can have a significant effect on the stability of formwork systems. These vibrations can cause the supporting shores or jacks to become displaced, leading to a collapse of the forms. To reduce the risk of this occurring, it is important for workers to be aware of the potential risks and take appropriate steps to mitigate them. Measures such as using adequate formwork bracing and providing adequate space between formwork components can help to reduce the impact of vibration and impact on formwork stability. Additionally, it is important to regularly inspect formwork systems for any signs of wear or damage that could lead to instability.
Unstable Soil under Mudsills and Out of Plumb Shores
Maintaining Stability of Formwork System with Unstable Soil and Out of Plumb Shores: The stability of formwork in construction is essential and the ability of out of plumb shores to properly support loads is reduced when there is unstable soil. This means that verticality of shores and the strength of the soil must be confirmed to ensure the formwork system is stable.
Avoiding Formwork on Frozen Ground: Formwork should never be placed on frozen ground since the concreting operations or air temperature changes may thaw the soil and cause the formwork to shift or be overloaded. To prevent this, the site drainage should be adequate enough to protect the mudsills from washout.
Ensuring Adequate Load Supporting for Formwork System: To ensure the formwork system is stable, the soil must be able to support the weight of the formwork. This is why sufficient load-bearing capacity of soil must be checked and adequate site drainage must be put in place to prevent washout.
Lack of Attention to Formwork Details
The assembly of formwork needs to be carried out with great care and attention, as even the most well-designed formworks can fail due to improper assemblage. This can happen when the formworks are not properly nailed, metal shores are not tightened, provisions are not made to prevent rotation of beam forms, anchorage against uplift for sloping form faces is inadequate, and corners are not braced or tied. All these errors can lead to formwork failure, making it essential to have skilled and trained labor to assemble the formwork system under proper supervision.
Lack ofWhen Formwork Is Not at Fault
Formwork System Failure: Causes That Are Not Formwork-Related: Formwork systems can fail during building construction for reasons that are not related to the formwork itself. These causes include incorrect soil assumptions in the design stage, inadequate shear reinforcement placement, and the placement of ducts in high-stress areas of slabs.
Incorrect Soil Assumptions: Incorrect initial assumptions about the type of soil present can lead to formwork system failure. If the soil does not provide the support needed for the formwork, it will not be able to sustain the load of the structure and the formwork will fail.
Poor Shear Reinforcement Placement: Inadequate placement of shear reinforcement can also contribute to formwork system failure. Shear reinforcement provides additional structural support to the formwork and helps to disperse the load of the structure. If it is not placed properly, it can lead to the formwork failing under the load.
Placement of Ducts in High Stress Areas: The placement of ducts in high stress areas of slabs can also contribute to formwork system failure. If the ducts are not placed correctly, they can cause additional stress on the formwork and lead to it failing.