The load sequence effects on structures’ ultimate limit strength evaluation

This paper intends to draw attention to the consideration of load sequence effects on the structures’ installation and upgrading/reinforcement practice. The paper first summarises four types of load sequence effects encountered in structural engineering practice. In order to investigate the ultimate strength performance of structures with the variation of support conditions and member stiffness (due to the installation of reinforcement on members) during the structures’ life time, a practical engineering evaluation procedure is presented. The load sequence effects, which are often ignored in the daily engineering practice, are studied through the modelling of a typical offshore module frame structure subjected to a large number of load cases. From the study it is concluded that the changes of the support conditions and the added stiffness from the reinforcements may slightly change the global stiffness of the structure, while they do influence the local stiffness and reaction forces on reinforced members or members close to the supports and the reinforced members, and may therefore be unconservative. A general proposal for a simplified analysis by taking the effects aforementioned into account is presented. Furthermore, methods for capacity check and practical recommendations for increasing the efficiency of the reinforcement are also given. Finally, suggestions for further studies are also given.