Aydın Turkey based Adnan Menderes University’s Civil Engineering Faculty Professor Mehmet E Uz has published results of “Modeling the Impact of Hailstones on Flat Steel Roofing Membranes for Residential Buildings” in Nature. Metal roof panels are commonly used on residential and commercial buildings. Steel panels exposed to hail have not yet been adequately tested for dent resistance. A finite element model was used to analyze the entire test setup. To compare artificial hailstones with natural hailstones, which remained intact after impact, different steel sheets were struck by different sizes of artificial hailstones at different terminal velocities. The simulation and the material properties are assessed by comparing the experimental results with the FE model. An equation to predict the dent depth based on kinetic energy and stress is also presented. The following factors are considered in this study: sheet thickness, material thickness, batten spacing, distance of the dent center of gravity from the closest edge and hail size. For inelastic steel, the dent depth is independent of the hailstone diameter. A smaller hailstone with a larger impact produces a similar permanent dent and the same impact energy as a larger hailstone with a smaller impact. The plastic distortion noted with the proposed equation agrees well with the experimental results. The dent depth in this case is not inversely proportional to the square root of the plate thickness or to the vibration-induced yield stress. The FE models were not able to provide accurate predictions of deformation depths shown in experiments compared to analytical models. Numerical models were able to accurately represent approximately 82% of the experimental results of permanent deformation of the plate. The elastic response of steel plates is generally overestimated by FE models. It is also necessary to conduct a separate study to accurately determine the strain sensitivity of the artificial hailstone in relation to the hardness of the hailstone, which determines the impact force at the point of contact. Based on these findings, new design methods for hail-resistant steel sheets can be developed that have a wider range of applications. A resistance factor of 0.80 is recommended for use with the equation in order to achieve the target reliability index of 4. Relative to the current AISC specification’s equation, which has a resistance factor of 0.75 as specified in the code, the use of the proposed equation will facilitate structural design that are more economical yet reliable. The results of this study provide a better understanding of the failure modes of hail and roof panels and their effects on dent resistance. In this study, the results of observations and numerical simulations agreed well with those of analytical models. The result is that the proposed equation overestimates the dent depths compared to the dent depths obtained with finite element models, while the equation leads to an underestimation of the dent depths found in the steel sheets.
Aydın Turkey based Adnan Menderes University’s Civil Engineering Faculty Professor Mehmet E Uz has published results of “Modeling the Impact of Hailstones on Flat Steel Roofing Membranes for Residential Buildings” in Nature. Metal roof panels are commonly used on residential and commercial buildings. Steel panels exposed to hail have not yet been adequately tested for dent resistance. A finite element model was used to analyze the entire test setup. To compare artificial hailstones with natural hailstones, which remained intact after impact, different steel sheets were struck by different sizes of artificial hailstones at different terminal velocities. The simulation and the material properties are assessed by comparing the experimental results with the FE model. An equation to predict the dent depth based on kinetic energy and stress is also presented. The following factors are considered in this study: sheet thickness, material thickness, batten spacing, distance of the dent center of gravity from the closest edge and hail size. For inelastic steel, the dent depth is independent of the hailstone diameter. A smaller hailstone with a larger impact produces a similar permanent dent and the same impact energy as a larger hailstone with a smaller impact. The plastic distortion noted with the proposed equation agrees well with the experimental results. The dent depth in this case is not inversely proportional to the square root of the plate thickness or to the vibration-induced yield stress. The FE models were not able to provide accurate predictions of deformation depths shown in experiments compared to analytical models. Numerical models were able to accurately represent approximately 82% of the experimental results of permanent deformation of the plate. The elastic response of steel plates is generally overestimated by FE models. It is also necessary to conduct a separate study to accurately determine the strain sensitivity of the artificial hailstone in relation to the hardness of the hailstone, which determines the impact force at the point of contact. Based on these findings, new design methods for hail-resistant steel sheets can be developed that have a wider range of applications. A resistance factor of 0.80 is recommended for use with the equation in order to achieve the target reliability index of 4. Relative to the current AISC specification’s equation, which has a resistance factor of 0.75 as specified in the code, the use of the proposed equation will facilitate structural design that are more economical yet reliable. The results of this study provide a better understanding of the failure modes of hail and roof panels and their effects on dent resistance. In this study, the results of observations and numerical simulations agreed well with those of analytical models. The result is that the proposed equation overestimates the dent depths compared to the dent depths obtained with finite element models, while the equation leads to an underestimation of the dent depths found in the steel sheets.
