Enhancement of Diana capabilities for creep analysis including aging effect: improvement of the NEN 6720 creep model and creation of a usersupplied creep model

A request from Bouwdienst Rijkswaterstaat about modelling aging effect with the NEN 6720 creep model has lead to a reflection on possible improvements about visco elastic analysis for long-term behaviour study of concrete structures. In this context, this document deals with the following points: specification of an aging parameter for the NEN 6720 creep model; creation of a user-supplied subroutine for definition of aging creep model.