OSAMA M. ALI - Academia.edu (original) (raw)

Papers by OSAMA M. ALI

Aswan University Journal of Sciences and Technology

Research on the effects of blast loads on concrete structures has been conducted extensively in r... more Research on the effects of blast loads on concrete structures has been conducted extensively in recent decades. This is primarily due to the increasing risk of deliberate explosive attacks, accidental explosions, and other types of explosion-related failures that structures worldwide are facing. The magnitude of blast loads generated by most explosions far exceeds the design loads considered in traditional structural design. Consequently, this heightened awareness has prompted building owners, government agencies, and design professionals to prioritize the ability of buildings to withstand blast loading and ensure the survival of structures in the face of constant global terrorist attacks. This research paper focuses on the modeling and dynamic analysis of the foundation of a steam turbine generator, which is an important and valuable element. While there have been previous studies on the behavior of reinforced concrete (RC) structures under blast loads, this paper specifically examines the nonlinear dynamic responses and failure behaviors of the supporting structure of turbine generators subjected to blast loads using Explicit Dynamic Analysis in Ansys Workbench. The study investigates the effects of middle-rate impact loading stresses on the blast responses of RC structures. By conducting dynamic analysis using Ansys Workbench, the researchers found that the RC structure is significantly influenced by the blast load. Moreover, they observed that the effect of the blast load decreases as the distance between the TNT source and the RC structure increases.

Advances in Structural Engineering, 2012

This paper presents the results of a parametric study on the seismic behavior of self-centering h... more This paper presents the results of a parametric study on the seismic behavior of self-centering hybrid walls as a new seismic retrofit method for reinforced concrete (RC) frames. A special base connection that isolates the wall from its foundation ensures the controlled rocking behavior of the self-centering hybrid wall. This seismic retrofit scheme is very appealing because of its relatively low cost, substantially large stiffness and reasonably low base shear demand. A parametric study has been carried out to investigate the effects of several factors including strength and initial stiffness of hysteretic dampers, and others pertaining to PT tendons on the seismic behavior of the self-centering hybrid wall as the primary lateral force resisting system in a retrofitted RC frame structure. The results from a nonlinear time history analysis of a three-bay, three-story RC frame structure subjected to selected earthquake ground motions, reveal that the self-centering shear wall is fair...

Durability of reinforced concrete bridges placed in non-aggressive environments is notably satisf... more Durability of reinforced concrete bridges placed in non-aggressive environments is notably satisfactory. However, under certain environmental conditions, there are external factors that significantly reduce their lifetime. Referring to existing design codes, lifetime assessment of deteriorating structures nowadays focuses on the isolated effects of the main deterioration processes (corrosion, growth of loads…etc). However, it is paramount to study the coupled effects of various deterioration processes because such interactions could reduce structural integrity. At a certain level of deterioration, strengthening is an essential tool to compensate strength losses and/or to support additional loads. Externally bonded fiber reinforced polymer (FRP) composites are an increasingly adopted technology for the renewal of existing concrete structures. In order to encourage the further use of these materials, a timedependent reliability analysis that considers the uncertainty inherent in (1) material properties, (2) models and their parameters, (3) environmental factors and (4) traffic loading, is needed. The scope of the present study is to propose a time dependent reliability analysis of FRP strengthened RC beams. Two deterioration factors were considered: corrosion of steel reinforcement and growth of live load over time. Models to describe variations in the constitutive materials properties, dimensions and the structural loadings are drawn from the literature. Techniques for reliability analysis are compared; First Order Reliability Method FORM, Monte-Carlo MC simulation and, a method developed within the present research work: Monte-Carlo simulation based on Neural Network MC-NN. In parallel, existing works of externally bonded FRP are surveyed. This leads to identify the limit states, failure modes and their corresponding analytical design formulas to integrate in the time-dependent reliability analysis. Three main objectives were considered in the present study. First one is to propose timedependent probabilistic models of steel reinforcement and live load. Second objective is to perform probabilistic analysis in term of time dependent failure probability or reliability index. The reliability analysis is based on the Load and Resistance Factor Design (LRFD) that provides an ideal framework for reliability consideration. Failure modes of FRP strengthened RC beam included in the survey were probabilistically simulated (e.g. concrete crushing, FRP debonding, FRP rupture …etc) using FORM method. These failure modes are based on analytical expressions and simplified formulas reported in previous studies. The third objective is to develop a Monte-Carlo simulation based on Neural Networks and Finite Element Method MC-NN-FEM which aims at verifying the results of reliability analysis Abstract xii using FORM method in terms of calculated time to strengthening. Simulation results show that MC-NN-FEM method provides eventually more accurate reliability and structural analyses than that obtained using FORM and simplified analytical design formulas. Simulations results reveal that the combined effects of corrosion and growth of live loads over time strongly influence the reliability of RC beam, leading to large reduction in expected lifetime. Furthermore, the effectiveness of FRP strengthening on the reliability profile of RC beam depends on failure mode included in considered ultimate limit state ULS: concrete crushing or FRP debonding...etc. It is also concluded that the level of deterioration before strengthening does not affect the increase in the reliability due to strengthening. Unlike the ULS, serviceability limit state-deflection-is significantly affected, in terms of reliability, by the growth of live load regardless deterioration due to corrosion. The results of this work bring to light the many variables affecting the reliability of strengthened members and the need for continuing research to better describe these variables. Two variables of particular significance, requiring extensive further study, are the state of the existing structure when strengthening is applied and the complexity of loads acting on the structure.

The present study aims to estimate effectiveness of applying FRP strengthening in order to enhanc... more The present study aims to estimate effectiveness of applying FRP strengthening in order to enhance the seismic structural reliability of RC frames. Two FRP strengthening configurations were compared: applying flexural FRP strengthening to members – beams/columns – of the RC frame and applying FRP confinement to columns of the frame. Seismic reliability was expressed in term of fragility estimates which involves performing nonlinear time history analysis recoding the maximum lateral top drift as a dynamic demand. A nonlinear time history analysis was carried out using finite elements method FEM. In order to reduce the computational effort, an efficient meta-modeling using Polynomial Dimensional Decomposition PDD in conjunction with the Monte-Carlo Simulation (MCS) was used. In addition, a sensitivity analysis using Sobol indices and Morris screening method were applied to evaluate importance of each random variables considered in the analysis . The proposed approach was applied to a ...

Parasite (Paris, France), 2017

Plasmodium vivax is the most widely distributed human malaria parasite. Outside sub-Saharan Afric... more Plasmodium vivax is the most widely distributed human malaria parasite. Outside sub-Saharan Africa, the proportion of P. vivax malaria is rising. A major cause for concern is the re-emergence of Plasmodium vivax in malaria-free areas. Oman, situated in the south-eastern corner of the Arabian Peninsula, has long been an area of vivax malaria transmission but no locally acquired cases were reported in 2004. However, local transmission has been registered in small outbreaks since 2007. In this study, a local outbreak of 54 cases over 50 days in 2014 was analyzed retrospectively and stained blood slides have been obtained for parasite identification and genotyping. The aim of this study was to identify the geographical origin of these cases, in an attempt to differentiate between imported cases and local transmission. Using circumsporozoite protein (csp), merozoite surface protein 1 (msp1), and merozoite surface protein 3 (msp3) markers for genotyping of parasite DNA obtained by scrappi...

Reliability Engineering & System Safety, 2014

Construction and Building Materials, 2012

Construction and Building Materials, 2021

Abstract Finite element (FE) simulation of confined RC columns is a complex task, as it involves ... more Abstract Finite element (FE) simulation of confined RC columns is a complex task, as it involves the precise representation of a concrete material model that could express the volumetric change of concrete under a triaxial state of stress. The problem of confining RC columns using fiber-reinforced polymer (FRP) is more complex. This is due to the passive nature of FRP containment. Recently, the concrete damage plasticity (CDP) model available in an FE software product (ABAQUS) has been widely used to represent RC columns subjected to axial loading. The present paper aims to calibrate the concrete dilatancy angle and viscoplastic regularization parameters in the CDP model for the applications of square RC columns confined with FRP sheets. Ten experimental FRP-confined RC column specimens are incorporated in the calibration. In addition, a parametric study is investigated, including 96 cases, to obtain the influence of various design variables on the ratio between the confined to unconfined concrete compressive strength (fcc/fc). Four design variables are considered (i.e., the corner radius, concrete compressive strength, FRP reinforcement ratio, and cross-sectional size of columns). The study also focuses on assessing the reliability of four design codes: ACI-440, ECP-208, CSA-S806 and FIB-Bulletin-14. The numerical results show that a viscoplastic regularization with a fixed value equal to 0.0005 could provide accurate behavior. Nevertheless, the dilation angle cannot be considered a fixed value and should be related to the confinement degree coefficient Cd, which depends on the cross-sectional geometrical and FRP properties. Among the four considered design codes, ACI-440 and ECP-208 provide more accurate behavior than CSA-S806 and FIB-Bulletin-14.

Ain Shams Engineering Journal, 2020

This article presents a numerical Concrete Damage-Plastic (CDP) model for investigating the compl... more This article presents a numerical Concrete Damage-Plastic (CDP) model for investigating the complex behavior of the RC slab-column connection under monotonic loading. The proposed numerical model is verified versus both the experimental data from the literature and various international design codes of practices, as well. The basic CDP model parameters (i.e. concrete dilation angle, the shape of the yield surface in the deviatoric plane, the softening simulation behavior, and the fracture energy) will be calibrated. Then, a comprehensive numerical investigation is conducted for studying the influences of different design variables. The numerical investigation also focuses on the damage initiation, propagation and evolution for a very wide range of connections cases. The numerical results displayed the ability of the calibrated CDP model to predict with fair accuracy the overall behavior of the connection demonstrating the impact of each investigated parameter.

This paper presents the time-variant flexural reliability analysis of a RC highway bridge strengt... more This paper presents the time-variant flexural reliability analysis of a RC highway bridge strengthened with CFRP. Three deterioration factors are dealt with. The first is the growth of traffic live load over time. The second is the resistance deterioration of steel reinforcing bars due to corrosion. The third is the deterioration due to aging of CFRP. The reliability analysis is performed implementing five flexural failure modes. A Monte-Carlo simulation is used to develop time-dependent statistical models for steel areas and daily live load extreme effects. The reliability of a RC bridge CFRP-strengthened interior beam, designed in accordance to AASHTO-LRFD (Load and Resistance Factor Design) specifications, is evaluated under various traffic volumes, different corrosion environments and strengthening configurations. The results of the analysis have shown that, among the deterioration factors, corrosion has the most significant effect on a bridge service life followed by live load ...

AICSG, 2019

Explosion effects on structures have been an area of research over the last decades. This is main... more Explosion effects on structures have been an area of research over the last decades. This is mainly due to the fact that structures all over the world are increasingly being exposed to the threat of premeditated explosive attacks, accidental explosions and other forms of explosion related failures. The magnitude of blast loads produced by most explosions are significantly higher than the design loads for conventional structural design. Consequently, this has increased awareness of building owners, government departments as well as design professionals to the vulnerabilities and survivability of structures to blast loading as global terrorist attacks continue at an increasing rate. The finite element modeling and dynamic analysis of massive and elevated foundation of steam turbine generator is considered in this paper. Despite many studies existing in the literature on the investigation of reinforced concrete (RC) structures under blast loads separately, this paper numerically evaluates the nonlinear dynamic responses and failure behaviors of turbine generators supporting structure subjected to blast loads using Explicit Dynamic Analysis-Ansys Workbench. The effects of the middle-rate impact loading stresses on the blast responses of RC structures are studied. The results of dynamic analysis by Ansys Workbench showed that the RC Structure is greatly affected by the explosive load whenever the effect of blast load decreases by increasing the distance between the source of TNT and RC structure.