Reason for Formwork Design Failure

Reason for Formwork Design Failure

Formwork Design  may  fail  due  to  many  reasons.  The  failure  primarily  occurs  at the time placing of concrete. Some unexpected event may cause one formwork  member  to  fail  causing  overloading  and  misalignment  of  another  formwork  member 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.