Question

The first system of forces consist of _____________

(a) Difference between actual column loads

(b) Varying distributed load acting downwards

(c) Column support reaction acting downwards

(d) All of the mentioned

The question was posed to me in an international level competition.

I'm obligated to ask this question of IS Code of Practice for Design of Raft Foundations in portion Shallow Foundations of Geotechnical Engineering II

Answer 1

Right answer is (c) Column support reaction acting downwards

Explanation: The first system of forces consists of i) uniformly distributed bearing pressure w acting upwards along the entire area of the raft ii) the column support reaction acting vertically downwards obtained by treating the raft as an inverted floor carrying the uniformly distributed load w with the reaction at the point of loading.