Question

if you're given a number of dead loads on a 4 story building and a floor plan with beams. how do you find the total dead load and live load on each beam? the goal is setting up a shear stress and moment diagrams for each beam.

say I was given a number of dead loads in psf and I'm supposed to find the total dead load and the live load.

Answer 1

Dead loads are computed by the geometry of the section.

Any buliding is constructed according to the function and following the code.

Those codes will suggest what is the loading the element needs to be designed.

The total structure is load is combination of dead loads and live loads.

1. For now, consider the top slab, the dead weight of the slab and other dead weights and live loads make the slab to deflect slightly (Not visible to a naked eye) (deflection depends on the type of slab one-way slab or a two-way slab).

2. The load will transfer to the beams that are supporting the slab due to the deflection of the slab, and these loads are approximated as UDL (Uniformly distributed loads). (We can obtain shear force and bending moment diagrams by knowing the support conditions and loading conditions (UDL)).

3. Now, beams will also deform/deflect due to these loads. Due to the deflection of beams, the load will transfer to the columns as axial loads. (A column can absorb loads from the beams which it is supporting). If the loads absorbed by the column are not eccentric, such loads are buckling loads; as a result, the column will buckle (In the design stage itself, the loads are computed, and columns and beams are designed such that loads will act at a low eccentricity).

4. Now we shall check for the slab, which is just below the top slab.

Again loads will act on the slab. Slabs will deflect and transfers the load to beams. Beams will deform and transfer the load to the columns.

But the total axial load taken by this penultimate columns (the columns just below top columns) is the sum of the loads generated by slab and beams and the axial load of the top columns.

This process of transfer of load from slab to beam and from beam to column and column to column takes place till the ground floor where the total load of the structure (Including live loads and dead loads) is in the form of axial load in the columns.

Ultimately all the axial loads are transferred to the foundation and from the foundation to the soil/ground.

(Note: If you are not clear with the load transfers please do this experiment

Place a book on two supports, now the book deflects due to the self weight and then load will trasfer to the supports. If you slowly push the book up with your palm the supports wont observe any weight of the book because there is no deflection).

I hope you have understood.

All the best.!

Please do mention your questions in the comments section.