The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hy...The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.展开更多
To further exploit the potential of marine composites applications in building ship hulls,offshore structures,and marine equipment and components,design approaches should be improved,facing the challenge of a more com...To further exploit the potential of marine composites applications in building ship hulls,offshore structures,and marine equipment and components,design approaches should be improved,facing the challenge of a more comprehensive and explicit assessment of appropriately defined limit states.The structure ultimate/limit conditions shall be verified in principle within the whole structural domain and throughout the ship service life.What above calls for extended and reliable materials characterization on the one hand and for accurate and wide-ranging procedures in structural analyses.This paper presents an overview of recent industrial developments of marine composites limit states assessments and design approaches,as available in open literature,focusing on pleasure crafts and yachts as well as navy ships and thus showing a starting point to fill the gap in this respect.After a general introduction about composites characterization techniques,current design practice and rule requirements are briefly summarized.Both inter-ply and intra-ply failure modes and corresponding limit states are then presented along with recently proposed assessment approaches.Three-dimensional aspects in failure modes and manufacturing methods have been identified as the main factors influencing marine composite robustness.Literature review highlighted also fire resistance and hybrid joining techniques as significant issues in the use of marine composites.展开更多
In the U.S., the current Load and Resistance Factor Design （LRFD） Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of...In the U.S., the current Load and Resistance Factor Design （LRFD） Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are on the same reliability-based platform. Since these extreme loads are time variables, combining them with not considered frequent. non- extreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively,展开更多
The current design philosophy for submarine hulls,in the preliminary design stage,generally considers as governing limit states material yielding along with various buckling modes.It is common belief that,beyond the d...The current design philosophy for submarine hulls,in the preliminary design stage,generally considers as governing limit states material yielding along with various buckling modes.It is common belief that,beyond the design pressure,material yielding of the shell plating should occur first,eventually followed by local buckling,while global buckling currently retains the highest safety factor.On the other hand,in the aeronautical field,in some cases structural components are designed in such a way that local instability may occur within the design loads,being the phenomena inside the material elastic range and not leading to a significant drop in term of stiffness.This paper is aimed at investigating the structural response beyond a set of selected limit states,using nonlinear FE method adopting different initial imperfection models,to provide the designers with new information useful for calibrating safety factors.It was found that both local and global buckling can be considered as ultimate limit states,with a significant sensitivity towards initial imperfection,while material yielding and tripping buckling of frames show a residual structural capacity.In conclusion,it was found that the occurrence of local buckling leads to similar sudden catastrophic consequences as global buckling,with the ultimate strength capacity highly affected by the initial imperfection shape and amplitude.展开更多
Goal based and limit state design is nowadays a well-established approach in many engineering fields.Ship construction rules started introducing such concepts since early 2000.However,classification societies’rules d...Goal based and limit state design is nowadays a well-established approach in many engineering fields.Ship construction rules started introducing such concepts since early 2000.However,classification societies’rules do not provide hints on how to verify limit states and to determine the structural layout of submerged thin-walled stiffened cylinders,whose most prominent examples are submarines.Rather,they generally offer guidance and prescriptive formulations to assess shell plating and stiffening members.Such marine structures are studied,designed and built up to carry payloads below the sea surface.In the concept-design stage,the maximum operating depth is the governing hull scantling parameter.Main dimensions are determined based on the analysis of operational requirements.This study proposes a practical conceptdesign approach for conceptual submarine design,aimed at obtaining hull structures that maximize the payload capacity in terms of available internal volume by suitably adjusting structural layout and stiffening members’scantling,duly accounting for robustness and construction constraints as well as practical fabrication issues.The proposed scantling process highlights that there is no need of complex algorithms if sound engineering judgment is applied in setting down rationally the hull scantling problem.A systematic approach based on a computer-coded procedure developed on purpose was effectively implemented and satisfactorily applied in design practice.展开更多
基金The National Natural Science Foundation of China(No.51878160,52008100,52078128).
文摘The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.
文摘To further exploit the potential of marine composites applications in building ship hulls,offshore structures,and marine equipment and components,design approaches should be improved,facing the challenge of a more comprehensive and explicit assessment of appropriately defined limit states.The structure ultimate/limit conditions shall be verified in principle within the whole structural domain and throughout the ship service life.What above calls for extended and reliable materials characterization on the one hand and for accurate and wide-ranging procedures in structural analyses.This paper presents an overview of recent industrial developments of marine composites limit states assessments and design approaches,as available in open literature,focusing on pleasure crafts and yachts as well as navy ships and thus showing a starting point to fill the gap in this respect.After a general introduction about composites characterization techniques,current design practice and rule requirements are briefly summarized.Both inter-ply and intra-ply failure modes and corresponding limit states are then presented along with recently proposed assessment approaches.Three-dimensional aspects in failure modes and manufacturing methods have been identified as the main factors influencing marine composite robustness.Literature review highlighted also fire resistance and hybrid joining techniques as significant issues in the use of marine composites.
基金Federal Highway Administration at the University at Buffalo under Contract No.DTFH61-08-C-00012
文摘In the U.S., the current Load and Resistance Factor Design （LRFD） Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are on the same reliability-based platform. Since these extreme loads are time variables, combining them with not considered frequent. non- extreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively,
基金The research activity on this topic is still under development in the frame of the ASAMS(Aspetti specialistici e approccio metodologico per progettazione di sottomarini di ultima generazione)project(2019-2022)which has been funded by the Italian MoD–Segredifesa,in collaboration with Fincantieri.
文摘The current design philosophy for submarine hulls,in the preliminary design stage,generally considers as governing limit states material yielding along with various buckling modes.It is common belief that,beyond the design pressure,material yielding of the shell plating should occur first,eventually followed by local buckling,while global buckling currently retains the highest safety factor.On the other hand,in the aeronautical field,in some cases structural components are designed in such a way that local instability may occur within the design loads,being the phenomena inside the material elastic range and not leading to a significant drop in term of stiffness.This paper is aimed at investigating the structural response beyond a set of selected limit states,using nonlinear FE method adopting different initial imperfection models,to provide the designers with new information useful for calibrating safety factors.It was found that both local and global buckling can be considered as ultimate limit states,with a significant sensitivity towards initial imperfection,while material yielding and tripping buckling of frames show a residual structural capacity.In conclusion,it was found that the occurrence of local buckling leads to similar sudden catastrophic consequences as global buckling,with the ultimate strength capacity highly affected by the initial imperfection shape and amplitude.
基金Supported by the Italian Ministry of Defense-Segredifesa,in collaboration with Fincantieri under Grant of the ASAMS(Aspetti specialistici e approccio metodologico per progettazione di sottomarini di ultima generazione)project(2019-2022).
文摘Goal based and limit state design is nowadays a well-established approach in many engineering fields.Ship construction rules started introducing such concepts since early 2000.However,classification societies’rules do not provide hints on how to verify limit states and to determine the structural layout of submerged thin-walled stiffened cylinders,whose most prominent examples are submarines.Rather,they generally offer guidance and prescriptive formulations to assess shell plating and stiffening members.Such marine structures are studied,designed and built up to carry payloads below the sea surface.In the concept-design stage,the maximum operating depth is the governing hull scantling parameter.Main dimensions are determined based on the analysis of operational requirements.This study proposes a practical conceptdesign approach for conceptual submarine design,aimed at obtaining hull structures that maximize the payload capacity in terms of available internal volume by suitably adjusting structural layout and stiffening members’scantling,duly accounting for robustness and construction constraints as well as practical fabrication issues.The proposed scantling process highlights that there is no need of complex algorithms if sound engineering judgment is applied in setting down rationally the hull scantling problem.A systematic approach based on a computer-coded procedure developed on purpose was effectively implemented and satisfactorily applied in design practice.
