Question

γ G=1.35 for permanent actions and γ Q =1.5 for variable actions Why do we apply a γ factor to the permanent and variable actions and why are they different values? [2 marks]

Answer 1

The gamma factors, γG and γQ, are applied to account for the uncertainties and variabilities in the actions that a structure experiences. Different values are used for γG and γQ because the uncertainties and variabilities associated with permanent actions are generally more predictable and better understood compared to the uncertainties.

Step-by-step explanation:

The gamma factors, γG and γQ, are applied to account for the uncertainties and variabilities in the actions that a structure experiences. The gamma factor, γ, is a coefficient that is used to increase the characteristic value of an action to ensure that the structure is designed with a margin of safety. Hence, by applying a gamma factor to the permanent and variable actions, we can consider the uncertainties and variabilities in these actions and design a more reliable structure.

The reason why different values are used for γG (1.35) and γQ (1.5) is because the uncertainties and variabilities associated with permanent actions (such as self-weight of the structure) are generally more predictable and better understood, compared to the uncertainties and variabilities associated with variable actions (such as live loads and wind loads) which are more unpredictable and can vary significantly in magnitude.