A complete research of seismic risk assessment is presented herein focused on the existing build- ings of the extended urban region of Athens in Greece. The seismic risk assessment is fulfilled by discriminating the c...A complete research of seismic risk assessment is presented herein focused on the existing build- ings of the extended urban region of Athens in Greece. The seismic risk assessment is fulfilled by discriminating the current study in two approaches, probable and actual, conducting afterwards between them a comparison analysis. In the first part, a pilot methodology is developed for the seismic loss assessment in monetary terms regarding the buildings damages, consistent with the National Programme for Earthquake Management of Existing Buildings (NPEMEB). The building stock consists of typical building types of Southern Europe and refers to 750,085 buildings (18.80% of buildings in Greece) situated in the entire region of Athens according to the results of the 2000-1 statistical census. A wider research of seismic risk assessment could include direct losses of infrastructures and indirect economic losses. The evaluation of loss due to building damage in a certain region requires an assessment of both seismic hazard and vulnerability of the building stock in the study area. Four different existing damage scenarios are applied for the vulnerability assessment. The results of the seismic risk assessment for the four different aspects of the es- timated damage and the different soil conditions are presented in a map of the study region. The existing vulnerability curves corresponding to defined types of buildings have been derived from the National Technical Chamber of Greece and also from recently developed DPMs. The last DPMs were obtained in a previous research (Eleftheriadou, 2009) from the process of a created damage database after the 7th of September 1999 Parnitha’s earthquake and comprised 180,945 buildings which developed damage of varying degree, type and extent. In the second part of the research, the seismic risk is evaluated from the available data regarding the mean statistical repair/ strengthening or replacement cost for the total number of damaged structures (180,427 buildings) after the same (1999 Parnitha’s) seismic event. Data regarding the compatible (budget approved according to the ministry’s provisions) repair cost has been collected. The structural losses in monetary terms for the 180,427 buildings damaged structures are evaluated equal to 2450.0 Μ€, 1887.8 Μ€ and 2118.9 Μ€ based on the previously mentioned statistical seismic risk data. The statistically derived repair cost for Attica is compared with the results of the economic loss esti- mation for buildings using the aforementioned risk assessment methodology. From the analysis results, the seismic scenario based on the recently developed DPMs (Eleftheriadou, 2009) pre- sented the better correlation (2627.77 M€) with the total statistically evaluated repair cost (2450.02 M€). It is important to stress that the inclusion of the coefficient parameter S overes- timates significantly the seismic losses. The last result should be taken into consideration in future risk researches. The comparison of the estimated economic loss with the statistical repair cost calibrates the reliability of the commonly used risk assessment method and serves in the im- provement of seismic security prioritizing the criteria for seismic rehabilitation programmes of existing buildings.展开更多
Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced dama...Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced damage to the rocking wall resulting from seismic loading can provide an extremely valuable tool to evaluate the status and safety of structural concrete walls following earthquakes. In this study, the behavior and the damage state of monolithic, self-centering, rocking walls, as a new type of concrete rocking wall, are investigated. The nonlinear mechanical behavior of the wall is first modeled numerically, and subsequently the mechanical parameters from the numerical simulation are used to generate the local damage index. The results from the damage index model are compared with the full-scale test results, confirming the viability of the numerically based damage index method for estimating the seismically induced damage in concrete walls. Moreover, the estimated damage can be utilized as a qualitative and quantitative scale to assess the status of the wall following seismic loading events.Finally, an equation is proposed to estimate the repair cost based on the predicted damage state for the studied structural system.展开更多
The reliability of the product sold under a warranty is usually maintained by the manufacturer during the warranty period. After the expiry of the warranty, however, the consumer confronts a problem about how to maint...The reliability of the product sold under a warranty is usually maintained by the manufacturer during the warranty period. After the expiry of the warranty, however, the consumer confronts a problem about how to maintain the reliability of the product. This paper proposes, from the consumer's perspective, a replacement policy after the extended warranty, under the assumption that the product is sold under the renewable free replacement warranty (RFRW) policy in which the replacement is dependent on the repair-cost threshold. The proposed replacement policy is the replacement after the extended warranty is performed by the consumer based on the repair-cost threshold or preventive replacement (PR) age, which are decision variables. The expected cost rate model is derived from the consumer's perspective. The existence and uniqueness of the optimal solution that minimizes the expected cost rate per unit time are offered. Finally, a numerical example is presented to exemplify the proposed model.展开更多
Most warranty cost models based on preventive maintenance operations are assumed that products improve at each preventive maintenance(PM)operation and the failure rate is reduced to the failure rate of new products or...Most warranty cost models based on preventive maintenance operations are assumed that products improve at each preventive maintenance(PM)operation and the failure rate is reduced to the failure rate of new products or to some specified level.To make warranty cost models more suitable to real operations,a modeling method of the PM warranty cost was proposed with the situation where each PM operation slowed the rate of product degradation.A warranty cost model was built on PM operations.On the basis of the cost model,both without and with reliability limit PM warranty policy,algorithms were presented to derive the optimal PM number and the optimal PM interval with an objective of minimizing expected total warranty cost over a finite warranty period.Finally,to demonstrate the feasibility of the presented modeling method,Weibull distribution cases were tested by numerical simulations.The simulation results indicate that the proposed modeling method is feasible and valid for resolving the optimal solution of the product warranty cost.展开更多
Owing to high costs and unnecessary inspections necessitated by the traditional inspection planning for ship structures, the risk-based inspection and repair planning should be investigated for the most cost-effective...Owing to high costs and unnecessary inspections necessitated by the traditional inspection planning for ship structures, the risk-based inspection and repair planning should be investigated for the most cost-effective inspection. This paper aims to propose a cost-benefit assessment model of risk-based inspection and repair planning for ship structures subjected to corrosion deterioration. Then, the benefit-cost ratio is taken to be an index for the selection of the optimal inspection and repair strategy. The planning problem is formulated as an optimization problem where the benefit-cost ratio for the expected lifetime is maximized with a constraint on the minimum acceptalbe reliability index. To account for the effect of corrosion model uncertainty on the cost-benefit assessment, two corrosion models, namgly, Paik＇ s model and Guedes Soares＇ model, are adopted for analysis. A numerical example is presented to illustrate the proposed method. Sensitivity studies are also providet. The results indicate that the proposed method of risk-based cost-benefit analysis can effectively integrate the economy with reliability of the inspection and repair planning. A balance can be achieved between the risk cost and total expected inspection and repair costs with the proposed method, which is very. effective in selecting the optimal inspection and repair strategy. It is pointed out that the corrosion model uncertainty and parametric uncertaintg have a significant impact on the cost-benefit assessment of inspection and repair planning.展开更多
Mesh hernia repair is one of the commonest open techniques of inguinal hernia repair.The main limiting factor in the use of new meshes is the cost.We carried out a prospective randomized double blind study and compris...Mesh hernia repair is one of the commonest open techniques of inguinal hernia repair.The main limiting factor in the use of new meshes is the cost.We carried out a prospective randomized double blind study and comprising of a hundred patients with 100 inguinal hernias admitted consecutively for elective surgery,divided into the polypropylene mesh(PPM)group and the mosquito net mesh(MNM)group each containing fifty patients.All cases were completed successfully and results revealed no difference in two groups.The results of the present study,in consistent with the published literature,reveal that the cheap indigenous mosquito mesh,which has similar properties of an imported mesh,can be safely used for tension-free inguinal hernia repair in adults.Further trials with a larger number of patients and longer follow-ups are justified and recommended.展开更多
One-shot systems such as missiles and extinguishers are placed in storage for a long time and used only once during their lives. Their reliability deteriorates with time even when they are in storage, and their failur...One-shot systems such as missiles and extinguishers are placed in storage for a long time and used only once during their lives. Their reliability deteriorates with time even when they are in storage, and their failures are detected only through inspections for their characteristics. Thus, we need to decide an appropriate inspection policy for such systems. In this paper, we deal with a system comprising non-identical units in series, where only minimal repairs are performed when unit failures are detected by periodic inspections. The system is replaced and becomes “as good as new” when the nth failure of the system is detected. Our objective is to find the optimal inspection interval and number of failures before replacement that minimize the expected total system cost per unit of time.展开更多
Background: It is unknown whether stapling the mesh affects recurrence rate, incidence of neuralgia, and port-site hernia. We chose to fix it to the exterior reducing port size, cost and pain, at the same comparing th...Background: It is unknown whether stapling the mesh affects recurrence rate, incidence of neuralgia, and port-site hernia. We chose to fix it to the exterior reducing port size, cost and pain, at the same comparing this with traditional mesh stapling. Methods: We conducted a prospective trial for laparoscopic TAPP inguinal hernia repair on 120 patients in which we fixed the mesh to the anterior abdominal wall using either two prolene threads that passed to the exterior and tied in place or traditional mesh stapling. Results: The operative time is ranged from 35 to 70 minutes for external fixation, 30 to 60 minutes for mesh stapling, and 4 to 51 months for follow-up, and no recurrence occurred in both groups during the procedure. Two cases with post TAPP pain in mesh stapling patients are discussed with reduction of the cost and port size in external fixation patients. Conclusion: It is not necessary to secure the mesh during laparoscopic TAPP inguinal hernia repair from the interior and it is fixed only to the exterior allowing a reduction in size of the ports and considerable reduction in cost with elimination of TAPP associated post operative pain.展开更多
Optimum maintenance and availability of a series system whose components are subject to imperfect repairs are studied in this paper. Imperfect corrective maintenance is treated in a way that after it the life of each ...Optimum maintenance and availability of a series system whose components are subject to imperfect repairs are studied in this paper. Imperfect corrective maintenance is treated in a way that after it the life of each component in the system will be decreased to a fraction of its immediately previous one and the repair time will be increased to a multiple of the one immediately preceding it, where successive failure free times are independent and so are successive repair times. Under such an assumption, the limiting system availability, mean time between system failures or repairs are derived based on some related results. A numerical example is presented to compare with Barlow and Proschan's availability model. Two classes of maintenance cost models are proposed and the optimum maintenance policies are also discussed for series system with n components in this paper.展开更多
文摘A complete research of seismic risk assessment is presented herein focused on the existing build- ings of the extended urban region of Athens in Greece. The seismic risk assessment is fulfilled by discriminating the current study in two approaches, probable and actual, conducting afterwards between them a comparison analysis. In the first part, a pilot methodology is developed for the seismic loss assessment in monetary terms regarding the buildings damages, consistent with the National Programme for Earthquake Management of Existing Buildings (NPEMEB). The building stock consists of typical building types of Southern Europe and refers to 750,085 buildings (18.80% of buildings in Greece) situated in the entire region of Athens according to the results of the 2000-1 statistical census. A wider research of seismic risk assessment could include direct losses of infrastructures and indirect economic losses. The evaluation of loss due to building damage in a certain region requires an assessment of both seismic hazard and vulnerability of the building stock in the study area. Four different existing damage scenarios are applied for the vulnerability assessment. The results of the seismic risk assessment for the four different aspects of the es- timated damage and the different soil conditions are presented in a map of the study region. The existing vulnerability curves corresponding to defined types of buildings have been derived from the National Technical Chamber of Greece and also from recently developed DPMs. The last DPMs were obtained in a previous research (Eleftheriadou, 2009) from the process of a created damage database after the 7th of September 1999 Parnitha’s earthquake and comprised 180,945 buildings which developed damage of varying degree, type and extent. In the second part of the research, the seismic risk is evaluated from the available data regarding the mean statistical repair/ strengthening or replacement cost for the total number of damaged structures (180,427 buildings) after the same (1999 Parnitha’s) seismic event. Data regarding the compatible (budget approved according to the ministry’s provisions) repair cost has been collected. The structural losses in monetary terms for the 180,427 buildings damaged structures are evaluated equal to 2450.0 Μ€, 1887.8 Μ€ and 2118.9 Μ€ based on the previously mentioned statistical seismic risk data. The statistically derived repair cost for Attica is compared with the results of the economic loss esti- mation for buildings using the aforementioned risk assessment methodology. From the analysis results, the seismic scenario based on the recently developed DPMs (Eleftheriadou, 2009) pre- sented the better correlation (2627.77 M€) with the total statistically evaluated repair cost (2450.02 M€). It is important to stress that the inclusion of the coefficient parameter S overes- timates significantly the seismic losses. The last result should be taken into consideration in future risk researches. The comparison of the estimated economic loss with the statistical repair cost calibrates the reliability of the commonly used risk assessment method and serves in the im- provement of seismic security prioritizing the criteria for seismic rehabilitation programmes of existing buildings.
文摘Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced damage to the rocking wall resulting from seismic loading can provide an extremely valuable tool to evaluate the status and safety of structural concrete walls following earthquakes. In this study, the behavior and the damage state of monolithic, self-centering, rocking walls, as a new type of concrete rocking wall, are investigated. The nonlinear mechanical behavior of the wall is first modeled numerically, and subsequently the mechanical parameters from the numerical simulation are used to generate the local damage index. The results from the damage index model are compared with the full-scale test results, confirming the viability of the numerically based damage index method for estimating the seismically induced damage in concrete walls. Moreover, the estimated damage can be utilized as a qualitative and quantitative scale to assess the status of the wall following seismic loading events.Finally, an equation is proposed to estimate the repair cost based on the predicted damage state for the studied structural system.
基金supported by the National Natural Science Foundation of China(7147114771631001)+1 种基金the Basic Research Project of Natural Science in Shaanxi Province(2015JQ7273)the 111 Project(B13044)
文摘The reliability of the product sold under a warranty is usually maintained by the manufacturer during the warranty period. After the expiry of the warranty, however, the consumer confronts a problem about how to maintain the reliability of the product. This paper proposes, from the consumer's perspective, a replacement policy after the extended warranty, under the assumption that the product is sold under the renewable free replacement warranty (RFRW) policy in which the replacement is dependent on the repair-cost threshold. The proposed replacement policy is the replacement after the extended warranty is performed by the consumer based on the repair-cost threshold or preventive replacement (PR) age, which are decision variables. The expected cost rate model is derived from the consumer's perspective. The existence and uniqueness of the optimal solution that minimizes the expected cost rate per unit time are offered. Finally, a numerical example is presented to exemplify the proposed model.
基金National Natural Science Foundation of China(No.60574054No.70771065No.70671065)
文摘Most warranty cost models based on preventive maintenance operations are assumed that products improve at each preventive maintenance(PM)operation and the failure rate is reduced to the failure rate of new products or to some specified level.To make warranty cost models more suitable to real operations,a modeling method of the PM warranty cost was proposed with the situation where each PM operation slowed the rate of product degradation.A warranty cost model was built on PM operations.On the basis of the cost model,both without and with reliability limit PM warranty policy,algorithms were presented to derive the optimal PM number and the optimal PM interval with an objective of minimizing expected total warranty cost over a finite warranty period.Finally,to demonstrate the feasibility of the presented modeling method,Weibull distribution cases were tested by numerical simulations.The simulation results indicate that the proposed modeling method is feasible and valid for resolving the optimal solution of the product warranty cost.
文摘Owing to high costs and unnecessary inspections necessitated by the traditional inspection planning for ship structures, the risk-based inspection and repair planning should be investigated for the most cost-effective inspection. This paper aims to propose a cost-benefit assessment model of risk-based inspection and repair planning for ship structures subjected to corrosion deterioration. Then, the benefit-cost ratio is taken to be an index for the selection of the optimal inspection and repair strategy. The planning problem is formulated as an optimization problem where the benefit-cost ratio for the expected lifetime is maximized with a constraint on the minimum acceptalbe reliability index. To account for the effect of corrosion model uncertainty on the cost-benefit assessment, two corrosion models, namgly, Paik＇ s model and Guedes Soares＇ model, are adopted for analysis. A numerical example is presented to illustrate the proposed method. Sensitivity studies are also providet. The results indicate that the proposed method of risk-based cost-benefit analysis can effectively integrate the economy with reliability of the inspection and repair planning. A balance can be achieved between the risk cost and total expected inspection and repair costs with the proposed method, which is very. effective in selecting the optimal inspection and repair strategy. It is pointed out that the corrosion model uncertainty and parametric uncertaintg have a significant impact on the cost-benefit assessment of inspection and repair planning.
文摘Mesh hernia repair is one of the commonest open techniques of inguinal hernia repair.The main limiting factor in the use of new meshes is the cost.We carried out a prospective randomized double blind study and comprising of a hundred patients with 100 inguinal hernias admitted consecutively for elective surgery,divided into the polypropylene mesh(PPM)group and the mosquito net mesh(MNM)group each containing fifty patients.All cases were completed successfully and results revealed no difference in two groups.The results of the present study,in consistent with the published literature,reveal that the cheap indigenous mosquito mesh,which has similar properties of an imported mesh,can be safely used for tension-free inguinal hernia repair in adults.Further trials with a larger number of patients and longer follow-ups are justified and recommended.
文摘One-shot systems such as missiles and extinguishers are placed in storage for a long time and used only once during their lives. Their reliability deteriorates with time even when they are in storage, and their failures are detected only through inspections for their characteristics. Thus, we need to decide an appropriate inspection policy for such systems. In this paper, we deal with a system comprising non-identical units in series, where only minimal repairs are performed when unit failures are detected by periodic inspections. The system is replaced and becomes “as good as new” when the nth failure of the system is detected. Our objective is to find the optimal inspection interval and number of failures before replacement that minimize the expected total system cost per unit of time.
文摘Background: It is unknown whether stapling the mesh affects recurrence rate, incidence of neuralgia, and port-site hernia. We chose to fix it to the exterior reducing port size, cost and pain, at the same comparing this with traditional mesh stapling. Methods: We conducted a prospective trial for laparoscopic TAPP inguinal hernia repair on 120 patients in which we fixed the mesh to the anterior abdominal wall using either two prolene threads that passed to the exterior and tied in place or traditional mesh stapling. Results: The operative time is ranged from 35 to 70 minutes for external fixation, 30 to 60 minutes for mesh stapling, and 4 to 51 months for follow-up, and no recurrence occurred in both groups during the procedure. Two cases with post TAPP pain in mesh stapling patients are discussed with reduction of the cost and port size in external fixation patients. Conclusion: It is not necessary to secure the mesh during laparoscopic TAPP inguinal hernia repair from the interior and it is fixed only to the exterior allowing a reduction in size of the ports and considerable reduction in cost with elimination of TAPP associated post operative pain.
文摘Optimum maintenance and availability of a series system whose components are subject to imperfect repairs are studied in this paper. Imperfect corrective maintenance is treated in a way that after it the life of each component in the system will be decreased to a fraction of its immediately previous one and the repair time will be increased to a multiple of the one immediately preceding it, where successive failure free times are independent and so are successive repair times. Under such an assumption, the limiting system availability, mean time between system failures or repairs are derived based on some related results. A numerical example is presented to compare with Barlow and Proschan's availability model. Two classes of maintenance cost models are proposed and the optimum maintenance policies are also discussed for series system with n components in this paper.
