Why is propping required for long structures once the formwork is removed?

Properties of steel reinforcement when not supported will sag especially on long structure. If it happens that the form works are removed including its bottom support and the concrete didn't meets its 70% minimum strength then there is a possibility that the structure will sag, cracks will appears on the bottom & sides so it will be rejected. Mostly contractors remove form works on the sidings first afters 24 hours of concreting for the purpose of curing without disturbing its bottom supports until its reaches the specified days to remove totally its formworks.

Formwork can be removed 24 to 48 hours after casting but here is the trick 

concrete will only be cured after 28 days and only then is it regarded as full strength

therefore propping is necessary to allow for it to cure otherwise you will have sagging.

l agree with specialists answers

The propping shall maintain the load till the concrete get it's final strength, this is one reason, also for preventing of further deflections which can appear specially for long spans.  

Thanks for your invitation

For directing the object need such as (steel wire) to the save port.

thanks for invitation

It can not happen until the building cracked and must phase out by a specialist engineer and not for a long time not to strain concreted

Thanks for invitation

Once the process of concreting is performed the striking of the formworks should be done as soon as possible as delay in this process can lead to the discoloration of the concrete structures. In case of long structures particularly long span structures once the structures have attained enough strength to support themselves it is essential to provide them with propping as creep deflection can take place which can greatly reduce the integrity of the structure. Due to the above mentioned reasons propping should be done after the removal of formwork. Also the props should not be made to stand long as it can lead to overstress for the structures.

Strenght of concrete structure at this point of time is not yet well develop so it require temporary support not to stress the structure at early stage.