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The influence of top cantilever length on shoring load of disc-lock formwork

July 16th, 2019 | Categories: news

Rapid Scaffolding (Engineering) Co., Ltd has  established a strategic partnership with Southeast University since 2004 and also established a strong scientific research team to take a deeply system research for the affecting disk lock formwork support safety factor. The length of top cantilever is the distance from the top face of adjustable U head to the topmost layer horizontal ledger of support scaffold, as the cantilever length a in below picture, hereinafter called cantilever length.

Cantilever lengths usually need to be adjusted to meet the formwork height of design requirement. As the distance from standard to the closest octagonlock disc is 250mm or 325mm(base collar upwards), considering the height of adjustable U head, so the length of cantilever is equal to or greater than 300mm in general.

The weakest position of rigidity of disc lock formwork is at the support structure upside, in order to study the influence of the cantilever length a on the stable loading capacity of the scaffold structure, taking 4×4 span 1 step and 4×4 span 4 steps formwork support structure as the research object (standard step h=1500mm), consider separately the length of the cantilever end to be 300~1000mm, and increase the nonlinear stability by 50mm each time for calculating.

With the cantilever length increasing and formwork support insteading, the maximum displacement keeps going up, the support structure changes from bending instability to local instability at the top cantilever end. The instability mode is shown in the following figure:

The calculation results of the ultimate stable loading capacity of the 4×4 span 1 step and the 4×4 span 4 steps disc lock formwork support structure with the length of the cantilever segment are shown in the following table:

From this table, it indicated that the cantilever length has enormous influence to the stable loading capacity of formwork support. For example: for 4X4 span 4 steps support structure, when a=300mm, its stable loading capacity Pcr=77.91KN, or when a=1000mm, its stable loading capacity Pcr=21.97kN, when a=300mm, corresponding loading capacity's 27.9%.

The results show that the cantilever length has a great influence on the stable lodaing capacity of the formwork support structure. Therefore, in engineering design and construction, the length of the cantilever should be strictly controlled to ensure the safety of the formwork support structure. Designers need to be based on the load (vertical, horizontal) size. For larger cantilever lengths, structural measures to reduce horizontal ledger step can be used to improve the safety of the formwork support structure.