Causes of formwork design failure
Failure of formwork design occurs because of various reasons. The failure mostly happens at the time of placing concrete. Owing to some unpredictable situation, if one formwork member fails, problems like overloading and misalignment of another formwork member arise that result in collapsing of the whole formwork system.
The collapsing occurs due to the following reasons :-
a. Extreme Loads
b. Detachment of forms or shores too early
c. Inaccurate Stripping & Shore Extraction
Stripping of forms as well as elimination of shore & inaccurate method in reshoring will create catastrophic results.
Insufficient lateral bracing-wind, the loads of the construction lead to formwork failures which were caused because of lateral force components or disposition of supporting members. Insufficient cross/horizontal bracing of shores also accelerate the scope of collapsing.
High shoring containing heavy load at the top is prone to eccentric or lateral loading. When a failure happens in one segment, insufficient bracing motivates the collapse to expand to bigger section of the structure and enhance the damage significantly.
The main purpose of bracing is to resist any negligible accident or failure so that it can’t become severe in due course of time.
Vibration because of concrete placing equipment
Formwork may often collapse when their supporting shore or jacks are dislocated with the vibration resulting from passing traffic, the movement of the workers and the equipment on the formwork as well as the impact of vibrating concrete to solidity it.
Some failures may occur because of the weight of RMC pouring pipe lines and its jerking vibration at the time of pumping that is completely neglected when design is created for the formwork and shoring.
Unstable soil under Mudsills, Shoring Not Plumb
The formwork may also collapse due to unstable soil under the mudsills. The mudsills function as a base for a shore or post in a formwork. The mudsills may be a timber plank, a frame, a small footing or pedestals.
All loads from formwork are transferred to the earth via vertical members. Shores should be settled for a solid stratum with the intension of dispersing the load axially.
Precautions should be taken to discharge the water shed down throughout rain or concrete process and check that the water should not wash away the under stratum soil that causes settlement of props.