Common Defects in Concrete Formwork Systems

Common Defects in Concrete Formwork Systems:

Concrete formwork systems have many potential defects due to imperfect design and construction practices. These can include issues with the foundation level of the formwork, vertical supports, and horizontal supports. Each of these areas may present problems which can lead to structural defects in the finished formwork.

Defects in Foundation Level of Formwork Systems:

When the foundation level of the formwork is not level, this can lead to structural defects. Poorly levelled foundations can cause concrete to settle unevenly, resulting in bulging, cracking, and other issues. Improper drainage on the formwork can also lead to issues with the foundation level.

Defects in Vertical Support of Formwork Systems:

Vertical supports are essential for ensuring the formwork remains stable and rigid. If the vertical supports are not properly installed or are of inadequate strength, this can lead to instability and sagging of the formwork. This can cause the formwork to fail, resulting in issues with the finished concrete.

Defects in Horizontal Support of Formwork Systems:

The horizontal support of the formwork is essential for ensuring the formwork is stable and secure. Poorly installed horizontal supports can lead to uneven settling and bulging of the formwork, resulting in deformations in the finished concrete. It is also important to use adequate bracing and other reinforcement to ensure the horizontal support is structurally sound.

Common Defects in Concrete Formwork Systems

1. Formwork Defects due to Imperfect Design and Construction Practice

1. Tolerances in Construction: Construction projects often require precise measurements and alignments in order to ensure a safe and successful outcome. When tolerances are not properly accounted for, it can lead to formwork defects due to imperfect design and construction practice.
2. Control Vertical Rate of Concrete Placement: When attempting to construct formwork, it is important to consider the rate at which concrete is poured. If the rate is too fast, it can cause formwork defects due to imperfect design and construction practice.
3. Check Tightness of Bolts and Wedges: In order to create a secure formwork system, it is important to check the tightness of bolts and wedges before loading the formwork. If these are not checked properly, it can lead to formwork defects due to imperfect design and construction practice.
4. Allowance for Uplift of Concrete: When constructing formwork, there must be an allowance for the uplift of concrete under inclined formwork systems. If this allowance is not provided, it can lead to formwork defects due to imperfect design and construction practice.
5. Load Distribution Between Members: When constructing formwork, it is important to consider the load distribution between two or more members that are expected to support common loads. If this is not properly accounted for, it can lead to formwork defects due to imperfect design and construction practice.
6. Incorrect Computation of Stresses: In order to properly construct formwork, it is important to accurately compute stresses due to design assumptions. If this is not done correctly, it can lead to formwork defects due to imperfect design and construction practice.
7. Vibration Effects on Ties, Struts, Braces, and Wedges: When constructing formwork, it is important to consider the effects of vibration on ties, struts, braces, and wedges. If this is not accounted for properly, it can lead to formwork defects due to imperfect design and construction practice.
8. Account for Wind Loads: When constructing formwork, it is important to properly account for wind loads. If this is not done, it can lead to formwork defects due to imperfect design and construction practice.
9. Allowance for Influence of Stresses: When constructing formwork, it is important to consider the influence of stresses generated by temperature, prestressing, and moisture movement. If this is not provided for, it can lead to formwork defects due to imperfect design and construction practice.

2. Defects in Foundation Level of Formwork Systems

1. Sole Plate Leveling Issues: One of the most common issues with formwork systems is that the sole plates are not leveled. This can lead to the crushing of the sole plates due to an insufficient distribution of loads from horizontal and vertical members. Poor load carrying capacity of the ground under the sole plate, as well as deterioration of the ground due to factors such as weather conditions, can also contribute to this issue.
2. Ground Load Carrying Capacity: The load carrying capacity of the ground beneath the sole plate is a key factor in the stability of formwork. If the ground is not able to properly support the weight of the formwork, it can lead to the crushing of the sole plate. Additionally, if the ground is prone to deterioration due to factors such as weather conditions, it can further reduce the load carrying capacity of the ground.
3. Deterioration of Sole Plates: Over time, the sole plates of formwork systems can also deteriorate due to various factors. This can include exposure to weather conditions, such as humidity and temperature, as well as other environmental factors. It is important to regularly monitor the condition of the sole plates to ensure that they remain stable and safe for use.

3. Defects in Vertical Support of Formwork Systems

1. 1. Lack of Ties Between Standards at Point of Loading: This issue is caused by inadequate ties between the standards at the point of loading. Without these ties, the formwork system can become unstable and can lead to a collapse. It is important to ensure that all supports are properly connected to the standards in order to maintain the stability of the system.
2. 2. Supports are Out of Plumb: When the supports are out of plumb, the formwork system can become unstable and can lead to a collapse. It is essential to ensure that all supports are correctly aligned in order to provide the necessary stability and support.
3. 3. Insufficient Bracing to Scaffold: Inadequate bracing of the scaffold can lead to instability, which can cause a collapse of the formwork system. It is important to ensure that all bracing is correctly installed to provide sufficient support for the formwork.
4. 4. Bearing Plates at the Top and Bottom of Props are Distorted: Distorted bearing plates at the top and bottom of props can cause instability of the formwork system. It is essential to ensure that the bearing plates are correctly aligned and installed to provide the necessary stability and support.
5. 5. Insufficient Lateral Ties, Vertical and Plan Bracing: When there is a lack of lateral ties, vertical and plan bracing, the formwork system can become unstable and can lead to a collapse. It is important to ensure that all ties and bracing are correctly installed to provide the necessary stability and support.
6. 6. Lack of Rigidity of Screw Connection Because of Lack of Bracing or Over Extension: When the screw connection lacks rigidity due to a lack of bracing or over extension, the formwork system can become unstable and can lead to a collapse. It is essential to ensure that all bracing and screw connections are correctly installed to provide the necessary stability and support.
7. 7. Utilizing Adjustable Steel Props with Nails, Mild Steel Bolts and Reinforcing Bars Instead of Correct Pins: When adjustable steel props with nails, mild steel bolts and reinforcing bars are utilized instead of correct pins, the formwork system can become unstable and can lead to a collapse. It is important to ensure that all pins, bolts and reinforcing bars are correctly installed to provide the necessary stability and support.

4. Defects in Horizontal Support of Formwork Systems

1. Poor Forkhead Placement: Forkheads are designed to centrally support horizontal members of formwork systems, however, if these are not placed correctly it can lead to a number of problems. This includes inadequate lateral and tensional bracing, insufficient support to cantilevers, and inadequate bearing area to vertical supports and underside of main members.
2. Inadequate Staggering in Timber Bolted Connections: When connecting formwork members with timber bolts, it is important to ensure that the connection is staggered correctly. If this is not done, it can lead to the split out of the timber bolted connection.
3. Insufficient Support for Deep Principal Elements: When constructing deep principal elements, it is important to provide sufficient support to prevent overturning. However, if forkheads are frequently omitted, this can lead to instability.
4. Folding Wedges Cut Incorrectly: Folding wedges are used to connect formwork members, and it is important that they are cut to the correct taper and cleated correctly. If they are cut from wet material or cut to too coarse a taper, this can lead to instability.