Rectanuglar Mudmat with hole

[ScottishGeo]

If we had a 6.5m x 5.2m foundation and we wanted to remove the central section (2m x 2.5m) to reduce weight, how should we consider this for design under VHM loading?

Consider teh longitudial strips and then add the lateral areas to the breadth to give the equivalent area and then add the two large strips togther to create a single footing or do we have to conside rteh footing independantly of each other?

Cheers!

 

[DRMABZ]

The short answer is; use 3D numerical analysis e.g. FE/FDM. This is the only way to get accurate shape factors for complex shapes not addressed in design codes, it also does the HVM load distribution for you. Having said that 3D FE is time consuming, not everyone has access to it, appropriate experience, etc, etc. My feel is that a lot of structures like this are designed without it.

Alternative hand calc, spread sheet, or 2D numerical analysis approaches need a lot of care and conservative assumptions.

If I was using a simple method I would probably treat this as two strip footings in the plane of loading and distribute the HVM loading to these two strips. Note depending on the load application point the two strips will see different loading, you then consider load shedding if one of the strips approaches failure. I would then try and decide how I address the additional area in the sides between the strips, but I would probably do this quite conservatively. Even HVM loading on two separated strips is quite complex and not well addressed in design codes, there are a couple of academic papers that can point you in the right direction with a quick literature review.

This can be quite a complex area, so worth discussing with experienced colleagues, and if necessary involving an appropriate consultant.