Reda Farag - Academia.edu (original) (raw)

Papers by Reda Farag

Journal of Offshore Mechanics and Arctic Engineering, Jun 3, 2016

Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic ... more Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic evaluations and an improved response surface method denoted as IRSM-second-order reliability method (SORM). It is a hybrid approach consisting of an IRSM, SORM, and several advanced factorial schemes. For this type of sophisticated analysis, simulation-based algorithm is impractical to implement. The concept is applied to estimate the risk of an existing MDS at the shore of Nile Delta. It is a large diameter steel-pile embedded in the sea bed. The Pile–Soil-System is represented by a nonlinear finite element model (NLFEM). In NLFEM, the steel pile is assumed to behave linearly under the considered working loads, but the soil is considered to behave nonlinearly. Moreover, the contact nonlinearity between the pile and the soil is taken into account. It is demonstrated that the reliability information on MDS can be extracted using tens of deterministic evaluations. It has been found that incorporation of the contact nonlinearity into analysis has no effect on the pile behavior. In the probabilistic analysis, the uncertainties in loading, material properties, and geometric details are taken into account. Both operational and structural limit states are considered. For the MDS considered in this study, it has been observed that the strength limit state (flexural) is more critical than the operational limit state (drift). The most important variables are the mooring loads, the radius and thickness of the pile, and the modulus of elasticity of steel.

Because of its critical effect and significant destructive nature during and after the seismic ev... more Because of its critical effect and significant destructive nature during and after the seismic events, the lateral ground spreading has seen an increasing interest in the geotechnical earthquake engineering. This paper introduces a quick method to predict pile-failure under lateral spread. The method integrates the limit equilibrium method (LEM) with the second order reliability method (SORM). In the procedure, the Finite element method (FEM), is used to build up a limit equilibrium, LE-based finite element model. This model is coupled with (SORM) via the response surface method (RSM). In the finite element model the soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by elastic 3D beam element. The proposed method is validated using Monte Carlo Simulation (MCS). Numerical examples are used for further illustration. Both operational and structural limit states are used. For the considered example, the soil pressure and the r...

New Approaches in Engineering Research Vol. 10, 2021

The lateral ground spreading has witnessed an increase in interest due to its serious effect and ... more The lateral ground spreading has witnessed an increase in interest due to its serious effect and major destructive character during and after seismic events. This paper describes a quick method for predicting pile failure due to lateral spread. The proposed technique integrates the limit equilibrium method (LEM) with the second order reliability method (SORM). In this technique, a limit equilibrium-based finite element model is coupled with (SORM) via the response surface method (RSM). In the finite element model the soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by elastic 3D beam element. Monte Carlo Simulation (MCS) is used to validate the suggested method through numerical example. Both operational and structural limit states are involved. For the considered example, the soil pressure and the pile radius are found to be the most sensitive variables.

The large amount of uncertainties in liquefaction-induced lateral spreading particularly leads to... more The large amount of uncertainties in liquefaction-induced lateral spreading particularly leads to pile damage after many earthquakes. This paper presents a simplified safety analysis method of the single piles subjected to lateral spread in three layered soils. With the suggested method the analyst can get a quick estimate of the pile safety using few simulations of the pile-soil structural model. The method integrates a limit equilibrium-based finite element model with the response surface method as well as the first or the second order reliability method (FORM/SORM). In the finite element model, the assumptions of limit equilibrium method are simply applied. The soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by an elastic 3D beam element. The simplified procedure not only estimates the safety but also determines the most sensitive basic pile and soil parameters affecting the response. Both serviceability and ultimate ...

INAE Letters

A novel reliability analysis concept for large Structural/Mechanical systems represented by finit... more A novel reliability analysis concept for large Structural/Mechanical systems represented by finite elements using multiple deterministic analyses is presented in this paper. The intent is to extract reliability information by conducing only tens instead of millions of deterministic analyses as an alternative to the classical Monte Carlo Simulation. It is particularly applicable when a deterministic analysis requires a considerable amount of computational time to satisfy the underlying physics. It is developed by integrating the second-order reliability method and an improved response surface method by removing its deficiencies. The efficiency of the integrated scheme is further improved by using advanced statistical and factorial schemes producing compounding beneficial effect. The concept is elaborated using two different illustrative examples. To validate the procedure, the underlying reliabilities are estimated by using the basic Monte Carlo simulation technique to develop the reference or benchmark value. Then, the accuracy and efficiency of the method are compared and verified.

Journal of Offshore Mechanics and Arctic Engineering, 2016

Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic ... more Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic evaluations and an improved response surface method denoted as IRSM-second-order reliability method (SORM). It is a hybrid approach consisting of an IRSM, SORM, and several advanced factorial schemes. For this type of sophisticated analysis, simulation-based algorithm is impractical to implement. The concept is applied to estimate the risk of an existing MDS at the shore of Nile Delta. It is a large diameter steel-pile embedded in the sea bed. The Pile–Soil-System is represented by a nonlinear finite element model (NLFEM). In NLFEM, the steel pile is assumed to behave linearly under the considered working loads, but the soil is considered to behave nonlinearly. Moreover, the contact nonlinearity between the pile and the soil is taken into account. It is demonstrated that the reliability information on MDS can be extracted using tens of deterministic evaluations. It has been found that in...

Ain Shams Engineering Journal, 2015

Assessment of the reliability of wall-frame structures using simulation based method is often pro... more Assessment of the reliability of wall-frame structures using simulation based method is often prohibited by the costly and lengthily computations. The present paper introduces a response surface based technique to quickly extract the reliability and safety information. The proposed method couples the finite element (FE) model of wall-frame structure, an improved response surface scheme and the second order reliability method (SORM). At the beginning, the large number of the random variables is reduced via preliminary sensitivity analysis. Then, the failure region is reached through a repetitive strategy integrated with recommended experimental designs. The efficiency and accuracy of the scheme are verified using Monte Carlo simulation. Moreover, both serviceability and flexural limit states are used in the verification. Tens of simulations are used instead of hundreds or thousands. The method is simple, efficient and can be easily implemented. For the considered example, the lateral load and the wall stiffness are the most important variables.

Coupling the finite element model of pile under lateral spread with the Monte Carlo Simulation is... more Coupling the finite element model of pile under lateral spread with the Monte Carlo Simulation is frequently prohibited by excessive lengthily computations. In the present paper, a simplified pseudostatic method is integrated with an improved response surface scheme to evaluate the reliability of pile subjected to lateral spread. The pseudostatic model takes both geometric and soil nonlinearities into account, while, the response surface formulation takes; load, geometry, material and model uncertainties into consideration. First; the improved response surface scheme is suggested and validated with the help of a simple example. Then, the pseudostatic model of a full size pile under lateral spread is integrated with the improved response surface scheme in order to assess the pile reliability. In the considered example, for both operational and structural possible modes of failure, it has been found that the most influential random variables are lateral displacement, and pile radius, respectively.

Proceedings of the 5th Asian-Pacific Symposium on Structural Reliability and its Applications, 2012

Vulnerability, Uncertainty, and Risk, 2011

A mooring dolphin structures (MDS), consisting of steel-pipe-piles and soil around them, are impo... more A mooring dolphin structures (MDS), consisting of steel-pipe-piles and soil around them, are important elements of marine structures. The reliability analysis of such complicated systems is very challenging. The limit state functions for them are implicit in nature. Reliability evaluation using the classical Monte Carlo simulation technique may not be practical since each deterministic evaluation will require several hours of computer time. A new hybrid method is presented in this paper. The system is represented by finite elements and its reliability is estimated by intelligently integrating the stochastic finite element, response surface methods, and advanced factorial schemes. The procedure is verified with the help of an example.

A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic ... more A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic loading applied in time domain is presented. For this class of problems, the performance functions are expected to be function of time and implicit in nature. Available first- or second-order reliability method (FORM/SORM) will be challenging to estimate reliability of such systems. Because of its inefficiency, the classical Monte Carlo simulation (MCS) method also cannot be used for large nonlinear dynamic systems. In the proposed approach, using only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the reliability information. A hybrid approach, consisting of the stochastic finite element method (SFEM) developed by the author and his research team using FORM, response surface method (RSM), an interpolation scheme, and advanced factorial schemes is proposed. The method is clarified with the help of several numerical ...

Journal of Offshore Mechanics and Arctic Engineering, 2014

A novel reliability evaluation procedure is proposed for analysis and design of offshore mooring ... more A novel reliability evaluation procedure is proposed for analysis and design of offshore mooring dolphin structures (MDS). It is a hybrid approach consisting of an improved response surface method (IRSM), second-order reliability method (SORM), and several advanced factorial schemes. It is denoted as IRSM-SORM. Several schemes of IRSM-SORM are proposed and clarified with the help of an illustrative example.

Advances in Structural Engineering, 2012

A general purpose novel reliability analysis method to estimate low probability of failure events... more A general purpose novel reliability analysis method to estimate low probability of failure events for large complicated real nonlinear structures excited by dynamic loadings including seismic loading applied in time domain is presented. In this approach, only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the required reliability information. It is a significant improvement over other methods currently being developed in other disciplines. Several areas of response surface method are improved and advanced factorial design concepts are presented. The method is elaborated with the help of two informative examples. The proposed method found to be robust, efficient, and accurate. It can be used to estimate reliability of large complicated civil engineering systems.

Ain Shams Engineering Journal, 2016

A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic ... more A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic loading applied in time domain is presented. For this class of problems, the performance functions are expected to be function of time and implicit in nature. Available first-or second-order reliability method (FORM/SORM) will be challenging to estimate reliability of such systems. Because of its inefficiency, the classical Monte Carlo simulation (MCS) method also cannot be used for large nonlinear dynamic systems. In the proposed approach, only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the reliability information. A hybrid approach, consisting of the stochastic finite element method (SFEM) developed by the author and his research team using FORM, response surface method (RSM), an interpolation scheme, and advanced factorial schemes, is proposed. The method is clarified with the help of several numerical examples.

Journal of Offshore Mechanics and Arctic Engineering, Jun 3, 2016

Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic ... more Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic evaluations and an improved response surface method denoted as IRSM-second-order reliability method (SORM). It is a hybrid approach consisting of an IRSM, SORM, and several advanced factorial schemes. For this type of sophisticated analysis, simulation-based algorithm is impractical to implement. The concept is applied to estimate the risk of an existing MDS at the shore of Nile Delta. It is a large diameter steel-pile embedded in the sea bed. The Pile–Soil-System is represented by a nonlinear finite element model (NLFEM). In NLFEM, the steel pile is assumed to behave linearly under the considered working loads, but the soil is considered to behave nonlinearly. Moreover, the contact nonlinearity between the pile and the soil is taken into account. It is demonstrated that the reliability information on MDS can be extracted using tens of deterministic evaluations. It has been found that incorporation of the contact nonlinearity into analysis has no effect on the pile behavior. In the probabilistic analysis, the uncertainties in loading, material properties, and geometric details are taken into account. Both operational and structural limit states are considered. For the MDS considered in this study, it has been observed that the strength limit state (flexural) is more critical than the operational limit state (drift). The most important variables are the mooring loads, the radius and thickness of the pile, and the modulus of elasticity of steel.

Because of its critical effect and significant destructive nature during and after the seismic ev... more Because of its critical effect and significant destructive nature during and after the seismic events, the lateral ground spreading has seen an increasing interest in the geotechnical earthquake engineering. This paper introduces a quick method to predict pile-failure under lateral spread. The method integrates the limit equilibrium method (LEM) with the second order reliability method (SORM). In the procedure, the Finite element method (FEM), is used to build up a limit equilibrium, LE-based finite element model. This model is coupled with (SORM) via the response surface method (RSM). In the finite element model the soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by elastic 3D beam element. The proposed method is validated using Monte Carlo Simulation (MCS). Numerical examples are used for further illustration. Both operational and structural limit states are used. For the considered example, the soil pressure and the r...

New Approaches in Engineering Research Vol. 10, 2021

The lateral ground spreading has witnessed an increase in interest due to its serious effect and ... more The lateral ground spreading has witnessed an increase in interest due to its serious effect and major destructive character during and after seismic events. This paper describes a quick method for predicting pile failure due to lateral spread. The proposed technique integrates the limit equilibrium method (LEM) with the second order reliability method (SORM). In this technique, a limit equilibrium-based finite element model is coupled with (SORM) via the response surface method (RSM). In the finite element model the soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by elastic 3D beam element. Monte Carlo Simulation (MCS) is used to validate the suggested method through numerical example. Both operational and structural limit states are involved. For the considered example, the soil pressure and the pile radius are found to be the most sensitive variables.

The large amount of uncertainties in liquefaction-induced lateral spreading particularly leads to... more The large amount of uncertainties in liquefaction-induced lateral spreading particularly leads to pile damage after many earthquakes. This paper presents a simplified safety analysis method of the single piles subjected to lateral spread in three layered soils. With the suggested method the analyst can get a quick estimate of the pile safety using few simulations of the pile-soil structural model. The method integrates a limit equilibrium-based finite element model with the response surface method as well as the first or the second order reliability method (FORM/SORM). In the finite element model, the assumptions of limit equilibrium method are simply applied. The soil is represented by 3D solid elastoplastic (Drucker-Prager failure criterion) while the pile is represented by an elastic 3D beam element. The simplified procedure not only estimates the safety but also determines the most sensitive basic pile and soil parameters affecting the response. Both serviceability and ultimate ...

INAE Letters

A novel reliability analysis concept for large Structural/Mechanical systems represented by finit... more A novel reliability analysis concept for large Structural/Mechanical systems represented by finite elements using multiple deterministic analyses is presented in this paper. The intent is to extract reliability information by conducing only tens instead of millions of deterministic analyses as an alternative to the classical Monte Carlo Simulation. It is particularly applicable when a deterministic analysis requires a considerable amount of computational time to satisfy the underlying physics. It is developed by integrating the second-order reliability method and an improved response surface method by removing its deficiencies. The efficiency of the integrated scheme is further improved by using advanced statistical and factorial schemes producing compounding beneficial effect. The concept is elaborated using two different illustrative examples. To validate the procedure, the underlying reliabilities are estimated by using the basic Monte Carlo simulation technique to develop the reference or benchmark value. Then, the accuracy and efficiency of the method are compared and verified.

Journal of Offshore Mechanics and Arctic Engineering, 2016

Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic ... more Reliability of complicated mooring dolphin structures (MDS) is estimated using few deterministic evaluations and an improved response surface method denoted as IRSM-second-order reliability method (SORM). It is a hybrid approach consisting of an IRSM, SORM, and several advanced factorial schemes. For this type of sophisticated analysis, simulation-based algorithm is impractical to implement. The concept is applied to estimate the risk of an existing MDS at the shore of Nile Delta. It is a large diameter steel-pile embedded in the sea bed. The Pile–Soil-System is represented by a nonlinear finite element model (NLFEM). In NLFEM, the steel pile is assumed to behave linearly under the considered working loads, but the soil is considered to behave nonlinearly. Moreover, the contact nonlinearity between the pile and the soil is taken into account. It is demonstrated that the reliability information on MDS can be extracted using tens of deterministic evaluations. It has been found that in...

Ain Shams Engineering Journal, 2015

Assessment of the reliability of wall-frame structures using simulation based method is often pro... more Assessment of the reliability of wall-frame structures using simulation based method is often prohibited by the costly and lengthily computations. The present paper introduces a response surface based technique to quickly extract the reliability and safety information. The proposed method couples the finite element (FE) model of wall-frame structure, an improved response surface scheme and the second order reliability method (SORM). At the beginning, the large number of the random variables is reduced via preliminary sensitivity analysis. Then, the failure region is reached through a repetitive strategy integrated with recommended experimental designs. The efficiency and accuracy of the scheme are verified using Monte Carlo simulation. Moreover, both serviceability and flexural limit states are used in the verification. Tens of simulations are used instead of hundreds or thousands. The method is simple, efficient and can be easily implemented. For the considered example, the lateral load and the wall stiffness are the most important variables.

Coupling the finite element model of pile under lateral spread with the Monte Carlo Simulation is... more Coupling the finite element model of pile under lateral spread with the Monte Carlo Simulation is frequently prohibited by excessive lengthily computations. In the present paper, a simplified pseudostatic method is integrated with an improved response surface scheme to evaluate the reliability of pile subjected to lateral spread. The pseudostatic model takes both geometric and soil nonlinearities into account, while, the response surface formulation takes; load, geometry, material and model uncertainties into consideration. First; the improved response surface scheme is suggested and validated with the help of a simple example. Then, the pseudostatic model of a full size pile under lateral spread is integrated with the improved response surface scheme in order to assess the pile reliability. In the considered example, for both operational and structural possible modes of failure, it has been found that the most influential random variables are lateral displacement, and pile radius, respectively.

Proceedings of the 5th Asian-Pacific Symposium on Structural Reliability and its Applications, 2012

Vulnerability, Uncertainty, and Risk, 2011

A mooring dolphin structures (MDS), consisting of steel-pipe-piles and soil around them, are impo... more A mooring dolphin structures (MDS), consisting of steel-pipe-piles and soil around them, are important elements of marine structures. The reliability analysis of such complicated systems is very challenging. The limit state functions for them are implicit in nature. Reliability evaluation using the classical Monte Carlo simulation technique may not be practical since each deterministic evaluation will require several hours of computer time. A new hybrid method is presented in this paper. The system is represented by finite elements and its reliability is estimated by intelligently integrating the stochastic finite element, response surface methods, and advanced factorial schemes. The procedure is verified with the help of an example.

A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic ... more A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic loading applied in time domain is presented. For this class of problems, the performance functions are expected to be function of time and implicit in nature. Available first- or second-order reliability method (FORM/SORM) will be challenging to estimate reliability of such systems. Because of its inefficiency, the classical Monte Carlo simulation (MCS) method also cannot be used for large nonlinear dynamic systems. In the proposed approach, using only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the reliability information. A hybrid approach, consisting of the stochastic finite element method (SFEM) developed by the author and his research team using FORM, response surface method (RSM), an interpolation scheme, and advanced factorial schemes is proposed. The method is clarified with the help of several numerical ...

Journal of Offshore Mechanics and Arctic Engineering, 2014

A novel reliability evaluation procedure is proposed for analysis and design of offshore mooring ... more A novel reliability evaluation procedure is proposed for analysis and design of offshore mooring dolphin structures (MDS). It is a hybrid approach consisting of an improved response surface method (IRSM), second-order reliability method (SORM), and several advanced factorial schemes. It is denoted as IRSM-SORM. Several schemes of IRSM-SORM are proposed and clarified with the help of an illustrative example.

Advances in Structural Engineering, 2012

A general purpose novel reliability analysis method to estimate low probability of failure events... more A general purpose novel reliability analysis method to estimate low probability of failure events for large complicated real nonlinear structures excited by dynamic loadings including seismic loading applied in time domain is presented. In this approach, only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the required reliability information. It is a significant improvement over other methods currently being developed in other disciplines. Several areas of response surface method are improved and advanced factorial design concepts are presented. The method is elaborated with the help of two informative examples. The proposed method found to be robust, efficient, and accurate. It can be used to estimate reliability of large complicated civil engineering systems.

Ain Shams Engineering Journal, 2016

A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic ... more A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic loading applied in time domain is presented. For this class of problems, the performance functions are expected to be function of time and implicit in nature. Available first-or second-order reliability method (FORM/SORM) will be challenging to estimate reliability of such systems. Because of its inefficiency, the classical Monte Carlo simulation (MCS) method also cannot be used for large nonlinear dynamic systems. In the proposed approach, only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the reliability information. A hybrid approach, consisting of the stochastic finite element method (SFEM) developed by the author and his research team using FORM, response surface method (RSM), an interpolation scheme, and advanced factorial schemes, is proposed. The method is clarified with the help of several numerical examples.