This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlin...This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).展开更多
The commonly used Mohr-Coulomb(M-C) failure condition has a limitation that it overestimates the tensile strength of cohesive soils. To overcome this limitation, the tensile strength cut-off was applied where the pred...The commonly used Mohr-Coulomb(M-C) failure condition has a limitation that it overestimates the tensile strength of cohesive soils. To overcome this limitation, the tensile strength cut-off was applied where the predicted tensile strength is reduced or eliminated. This work then presented a kinematical approach to evaluate the active earth pressure on subgrade retaining walls in cohesive backfills with saturated seepage effects. An effective rotational failure mechanism was constructed assuming an associative flow rule. The impact of seepage forces, whose distribution is described by a closed-form solution, was incorporated into the analysis. The thrust of active earth pressure was derived from the energy conservation equation, and an optimization program was then coded to obtain the most critical solution. Several sets of charts were produced to perform a parameter analysis. The results show that taking soil cohesion into account has a distinct beneficial influence on the stability of retaining walls, while seepage forces have an adverse effect. The active earth pressure increases when tensile strength cut-off is considered, and this increment is more noticeable under larger cohesion.展开更多
Purpose： The results for fixation of comminuted posterior wall acetabular fractures are not very promising with reported complications in terms of osteoarthritis, nonunion and malunion which subsequently require conv...Purpose： The results for fixation of comminuted posterior wall acetabular fractures are not very promising with reported complications in terms of osteoarthritis, nonunion and malunion which subsequently require conversion to total hip arthroplasty. The conversion to total hip arthroplasty is possible in patients over 50 years of age but not in younger patients. So this requires new methods for salvage of the native hip in young patients. Methods： There were six patients in our series with highly comminuted posterior wall acetabular frac- tures where the fragments were excised and the gap filled with tricortical anterior iliac-crest strut autograff, fixed with screws and plate. Results： Good results were achieved in four out of six patients analyzed clinically using the Merle d＇Aubinge score modified by Matta and radiologically by Matta scoring. These patients have returned to original work and are walking independently. The good result in one patient deteriorated from good to poor between one and two years. One patient developed infection and excision arthroplasty was done, The graft incorporated well in five out of six patients. Conclusion： The use of iliac crest autograff is a better, advanced and promising technique as it provides a new wall to the weight bearing dome of the acetabulum for articulation with the femoral head. The rates of nonunion, malunion, post traumatic osteoarthritis are less as compared to the fixation of the comminuted fragments. The need for conversion to total hio arthroolastv is also less.展开更多
文摘This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).
基金Projects(51538009,51674115,51804113) supported by the National Natural Science Foundation of China。
文摘The commonly used Mohr-Coulomb(M-C) failure condition has a limitation that it overestimates the tensile strength of cohesive soils. To overcome this limitation, the tensile strength cut-off was applied where the predicted tensile strength is reduced or eliminated. This work then presented a kinematical approach to evaluate the active earth pressure on subgrade retaining walls in cohesive backfills with saturated seepage effects. An effective rotational failure mechanism was constructed assuming an associative flow rule. The impact of seepage forces, whose distribution is described by a closed-form solution, was incorporated into the analysis. The thrust of active earth pressure was derived from the energy conservation equation, and an optimization program was then coded to obtain the most critical solution. Several sets of charts were produced to perform a parameter analysis. The results show that taking soil cohesion into account has a distinct beneficial influence on the stability of retaining walls, while seepage forces have an adverse effect. The active earth pressure increases when tensile strength cut-off is considered, and this increment is more noticeable under larger cohesion.
文摘Purpose： The results for fixation of comminuted posterior wall acetabular fractures are not very promising with reported complications in terms of osteoarthritis, nonunion and malunion which subsequently require conversion to total hip arthroplasty. The conversion to total hip arthroplasty is possible in patients over 50 years of age but not in younger patients. So this requires new methods for salvage of the native hip in young patients. Methods： There were six patients in our series with highly comminuted posterior wall acetabular frac- tures where the fragments were excised and the gap filled with tricortical anterior iliac-crest strut autograff, fixed with screws and plate. Results： Good results were achieved in four out of six patients analyzed clinically using the Merle d＇Aubinge score modified by Matta and radiologically by Matta scoring. These patients have returned to original work and are walking independently. The good result in one patient deteriorated from good to poor between one and two years. One patient developed infection and excision arthroplasty was done, The graft incorporated well in five out of six patients. Conclusion： The use of iliac crest autograff is a better, advanced and promising technique as it provides a new wall to the weight bearing dome of the acetabulum for articulation with the femoral head. The rates of nonunion, malunion, post traumatic osteoarthritis are less as compared to the fixation of the comminuted fragments. The need for conversion to total hio arthroolastv is also less.
