If a building foundation sits on soft or filled-in soil, the whole building may fail in an earthquake regardless of the advanced engineering techniques employed. Assuming, however that the soil beneath a structure is firm and solid, engineers can greatly improve how the building foundation system will respond to seismic waves.

Another solution refers to base isolation which involves floating a building above its foundation on a system of bearings, springs or padded cylinders.

Here, positive and negative reinforcement directly relates to positive and negative bending in the member. So wherever we anticipate postive bending or sagging in a member, we provide postive reinforcement and wherever we anticipate negative bending or hogging, we provide negative reinforcement. Most of the times these two may be the same bar.