Back propping refers to the addition of propping support to reinforce an existing suspended floor system. It provides an alternative load path through the superstructure to ensure the existing or as built permanent elements are not overloaded given the imposed load. When we look into back propping there are two common applications that may require this technique or work to be considered and or adopted.
Firstly, back propping is a common application with new builds where multiple stories are being constructed. In this instance back propping is provided to safely distribute formwork and construction loads through the superstructure. These loads typically exceed a permanent floors-imposed design capacity that typically ranges from 2-3kPa; thus, the load will need to transfer through a number of newly constructed floors below to prevent overloading, excessive deflections or worst case collapse. The number of floors and the capacity of propping are predominantly a function of the magnitude of imposed loads, the strength and type of floor systems at the relative age and the stiffness of suspended slabs or support.
The second common application is within projects where structural alterations or demolition works are to be undertaken. These projects require heavy plant and machinery to transverse suspended floor systems or require permanent elements to be removed or altered. With these applications back propping can consider the imposed loadings of the plant when it exceeds the design capacity of the floor. It can also allow for alternative load paths to reinforce compromised connections of the pre-existing permanent structural elements in their temporary state. This can often result in a more safe and flexible construction program as once designed fewer constraints to the demolition scope exist.
When considering any work on a suspended structure the first question you need to ask is; Am I going to exceed the design capacity of this floor or roof system? And the second question is; Am I compromising the structure in a way that will limit its ability to perform as designed? When in doubt you should always engage a structural engineer to review.
Cassaform’s service includes an in-house engineering team who are happy to provide design layouts, support and site inspections before a job commences, as well as support throughout projects 24/7. If you have any questions or want to discuss you back propping options – get in touch below.