Damage tolerance requirements for integrally stiffened composite wing skins are typically met using design allowables generated by testing impact-damaged subcomponents, such as three-stringer stiffened panels. To improve these structures, it is necessary to evaluate the critical design parameters associated with three-stringer stiffened-panel compressive behavior. During recent research and development programs, four structural parameters were identified as sources for strength variation: (a) material system, (b) stringer configuration, (c) skin layup, and (d) form of axial reinforcement (tape versus pultruded carbon rods). The relative effects of these parameters on damage resistance and damage tolerance were evaluated numerically and experimentally. Material system and geometric configuration had the largest influence on damage resistance; location and extent of the damage zone influenced the sublaminate buckling behavior, failure initiation site, and compressive ultimate strength. A practical global-local modeling technique captured observed experimental behavior and has the potential to identify critical damage sites and estimate failure loads prior to testing. More careful consideration should be given to accurate simulation of boundary conditions in numerical and experimental studies.
The response of structural steel columns to high temperatures is investigated. Both numerical prediction and experimental testing are carried out. The material properties of the steel are obtained from a series of tensile coupon tests at various temperatures and two different strain rates. A high strain rate was used to determine instantaneous material properties, while a low strain rate allowed some creep strain to be included implicitly. These strain rate dependent material properties are incorporated in a finite element analysis (FEA) to simulate the results of stub column buckling tests, conducted at range of temperatures up to 600°C. Good agreement has been obtained between the numerical simulations and the tests.
An analytical model is presented to predict the response of restrained steel columns to elevating temperatures due to fire. A locally heated column was idealised as stub column in series with a spring representing restraint from the structure. The model incorporates thermal, creep and elasto-plastic effects which represents the most important material factors of the behaviour of steel columns when exposed to fire. The significance of these effects at different stages of a fire is clearly identified. Axial deformation due to creep was found to dominate at high load levels, with thermal effects dominating at low load levels. The results obtained will be compared with future experimental testing.
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