Investigating Alternate Load Paths and Damage Tolerance of Structures Optimized for Multiple Load Cases

Redundancy in structures can provide load carrying capacity for the structure under multiple load cases, damaged conditions, or different configurations. Since these different load paths arise due to some changes in conditions, they are also referred to as “alternate paths”. The damage tolerance of a structure is a function of its ability to develop alternate load paths that effectively transfer loads to support points. A robust multi-path structure should be able to develop multiple alternate load paths that can survive loading and perform its intended function regardless of large variations in changes of loads, stiffness, or configuration. Previous work on design of redundant truss structures for robust damage tolerance and progressive failure response has shown that redundancy by itself does not guarantee that a structure can provide effective alternate load paths. Redundant structures must be tailored explicitly to develop such alternate load paths. This paper investigates design optimization methods for robust design of redundant multiple load path structures. Different mathematical definitions for load paths are presented and compared. Topology optimization for damage tolerance is developed to generate candidate designs for alternate load path investigations. Procedures for identifying alternate paths are developed and used in formulating and solving optimization of multiple load path structures.