Loads on a structure are ultimately passed on to the soil underneath. Let's assume that the soil or earth beneath the structure is strong enough to absorb the load without failure. In such cases, understanding what goes on above the ground and inside the structure is key.
Any structure is composed of members. If we consider a Reinforced Concrete Structure (RCC) the component structural members are usually slabs, beams, and columns.
In such a case having an understanding of how the loads are transferred from the top of the structure to the bottom of the structure is one of the best skills you can acquire as a structural consultant or engineer.
In a single-story RCC frame structure, the load starts to flow from the slabs onto the supporting beams.
This load on the beams is then transferred onto the columns supporting the beams.
From thereon the load moves down to the supports where it is eventually supported by the soil.
This seems simple enough to understand. But the true understanding comes from realizing how the loads from slabs are distributed to the beams. Usually, the load on a slab is divided by the 45-degree rule. If we have a square slab the load is divided into 04 equal triangles with each beam taking up the triangular load.
If we replace the square slab with a rectangular slab the load distribution changes slightly. Now the shorter beam takes the triangular part of the slab load and the longer side takes a trapezoidal portion of the load (again using the 45-degree distribution pattern).
Beams are relatively straightforward to solve for the transference of loads. The key point here is that each beam is only taking the combination of loads from the adjacent slabs and nothing from the floor above it. The same goes for slabs. Slabs usually resist only the load on themselves. The beams take the load of adjacent slabs.
The tricky part is the column. A column takes up the loads transferred on to it from the beams it supports. However, unlike slabs that support loads on themselves and beams that support loads from adjacent slabs on the same level, a column takes up the CUMULATIVE load from the beams above it and from the columns above it.
Hence, a column at the top floor would be supporting only the loads from the beams at the top floor. However, a column at the bottom-most floor would be supporting not only the loads from the beams at that level but also all the column loads above right from the top floor downwards.