Bridges need foundations to be fixed to and to spread the weight of the bridge and its users into the ground efficiently
Foundations carry two loads.
The dead load is the weight of the bridge. This is usually spread equally between foundations
The Live Load is the load applied by its users
The Live Load is also spread equally between the foundations
These loads are combined to decide how wide the foundations need to be to spread them safely into the ground
There are very many considerations to be taken into account when making this decision
The Ground Conditions are critically important when making decisions about the foundations
These can be assessed by digging pits or in extreme cases by sinking bore holes, testing samples and calculating their strength
These processes are rarely iused when “Designing” small bridge foundations as the loads are so small.
Modest concrete pads are usually adequate but this is not always the case.
