Reason for Formwork Design Failure
Formwork Design . the time placing of concrete. Some unexpected event may cause one ultimately leading to the collapse of the entire formwork system.
Many such disasters have revealed the root cause of such failure as
1.Excessive loads
2.Premature removal of forms or shores
3.Inadequate lateral support for the shoring members
Improper Stripping And Shore Removal
Premature stripping of forms,premature removal of shore and careless practices in reshoring can produce catastrophic results. In a case study of a MSB failure, it revealed that a portion of the fourteenth floor of the MSB tower collapsed due to the collapse of the shoring provided to support the concrete. It appears that the shoring was weak and the reshores were missing. The collapse of this floor resulted into impact landing of the floor directly below it which also failed and collapsed to the lower floor. This has a domino effect and by the impact load from the weight of upper floor debris, lower floors also collapsed subsequently all in a short span of less than an hour.
Inadequate Lateral Bracing-Wind, Construction Loads Very often news flasher about formwork failures which were induced due to lateral force components or due to displacement of supporting members. Inadequate cross/ horizontal bracing of shores have played a key role in triggering the accidents.
High shoring with heavy load at the top is vulnerable to eccentric or lateral loading. When a failure occurs in one part, inadequate bracing may induce the collapse to extend to a large portion of the structure and multiply the damage. One major objective of bracing is to prevent any minor accident or failure from becoming a disaster.
Ebook to read Site Engineers Manual
Vibration Due To Concrete Placing Equipment
Form worksome times collapse when their supporting shore or jacks are displaced by the vibration caused by passing traffic, the movement of the workers and the equipment on the formwork and the effect of vibrating concrete to consolidate it. Some failures have taken place due to the weight of RMC pouring pipe lines and its jerking vi-bration while pumping which has totally been ignored while designing the formwork and shoring.
See More Site Inspection of Concrete formwork
Unstable Soil Under Mudsills, Shoring Not Plumb
Unstable soil under the mudsills can also cause the formwork to fail. The mudsills act as a base for a shore or post in a formwork. The mudsills could be a timber plank, a frame, a small footing or pedestals. All loads from formwork are transmitted to the solid ground through vertical members. Shores must be set for plumb on a solid stratum so as to transmit the load axially. Proper care should be taken to drain out the water shed down during rain or during concrete processand shall not allow water to wash away the under stratum soil which may lead to settlement of props.
