البحوث الخاصة بالتدريسي أ.م.د.علي هادي عظيم

قائمة البحوث
  • عنوان البحث : Nonlinear Finite Element Modelling and Parametric Analysis of Shear Strengthening RC T-Beams with NSM CFRP Technique

    ملخص البحث :

    In this study, a robust three-dimensional finite element (FE) model has been developed for reinforced concrete beams strengthened in shear with near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) rods. The FE models were developed and validated against existing experiments and presented various nonlinear constitutive material laws and interfacial relations. A detailed parametric study was performed to investigate the effects of various parameters on the performance of strengthened member. It was shown that increasing the concrete compressive strength ( fc ′ ) from 20 to 50 MPa, leads to an increase in the beam’s ultimate load and contribution of NSM CFRP reinforcement. While for NSM reinforcement ratio (휌f), the ultimate load slightly increased when 휌f is 0.14–0.22%, and then increased by 11% in average when 휌f increased to 0.28%. Varying the percentage of existing steel stirrups (휌sw) from 0.11 to 0.36%, leads to an increase in ultimate load from 8 to 15% compared to the control un-strengthened specimen. However, the further increase in 휌sw (more than 0.36%) caused a reduction in the contribution of NSM CFRP technique because of the changing in the failure mode. The distance between existing steel stirrups and NSM reinforcement does not affect the behaviour. In addition, the model predictions were used to evaluate several design formulas available in the literature for this technique. It was found that some theoretical equations were conservative as long as the governing failure mode is shear.
    • سنة النشر : 2019
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Finite element modelling and parametric analysis of FRP strengthened RC beams under impact load

    ملخص البحث :

    In this study, a non-linear three-dimensional finite element model was developed to study the impact behaviour of reinforced concrete beams strengthened in shear and/or flexure with carbon-FRP (CFRP) sheets. Concrete damage plasticity model was used for the concrete part, a traction-separation law for the CFRP-concrete interface, and Hashin criteria for rupture in CFRP. Comparisons with experimental data from literature, for various properties, confirmed the accuracy of developed model. A detailed parametric analysis was performed focusing on: the impact location as a ratio (α) from support to mid-span, impact velocity (v); and several geometrical properties related to CFRP technique. Increasing α from 0.26 to 0.79 results in increasing the maximum displacement (Δmax) for both un-strengthened and strengthened beams. CFRP strengthening resulted in decreasing Δmax for different values of α and v and prevented global concrete failure for v ¼ 8.86 m/s. Δmax is also decreased by 13% when a round corner and an arched soffit were used to prepare the beam substrate for bonding the transverse sheets instead of a sharp corner. Furthermore, the paper presents detailed discussions and implications for the above parameters and two additional ones, namely: configuration of transverse sheets (continuous wraps or discontinuous strips) and thickness of CFRP longitudinal sheets.
    • سنة النشر : 202
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Parametric 3D finite element analysis of FRCM-confined RC columns under eccentric loading

    ملخص البحث :

    Fiber reinforced cementitious matrix (FRCM) is emerging as a viable retrofit and confinement technique, in lieu of fiber reinforced polymer (FRP) system which suffers from a number of issues related to the use of synthetic binders. While many studies have been conducted on the use of FRCM in shear and flexural applications, few were dedicated to confinement of slender columns, particularly those related to finite element (FE) analysis. In this study, a nonlinear three-dimensional FE model has been developed to study the behavior of reinforced concrete (RC) columns confined by (FRCM) jackets, and loaded concentrically and eccentrically. Drucker-Prager (DP) concrete model, which has several improvements over traditional DP models, was used to model the concrete core. Composite failure in the fibers comprising FRCM system and column buckling were also considered in the developed FE model. The model was validated by comparing its predictions with those of three control and 8 FRCM-confined RC columns from literature. Consequently, a parametric study utilizing 96 additional models, was performed on five parameters, namely: crosssectional shape (square, circle, hexagon, and octagon), and for rectangular columns; aspect (h/b) ranging from 0.5 to 3, at 0.5 increment; slenderness (KL/r) ratio, considering four values, 10, 25, 50, and 75; load eccentricity (e) as a ratio (e/h) to side length (h), varying from 0 to 2.5; and concrete compressive strength (f́ c), studying three values: 20, 35, and 50 MPa. Effects of these parameters on the column’s maximum load (Pmax) and general behavior, are discussed in details in Section 6 and summarised in the conclusions part. In general, Pmax increased by 0–32% as a result of applying one layer of FRCM jacket, and showed great dependence on the examined parameters
    • سنة النشر : 2020
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : A robust 3D finite element model for concrete columns confined by FRCM system

    ملخص البحث :

    Fibre reinforced cementitious matric (FRCM) is a recent application of fibre reinforced polymer (FRP) reinforcement, developed to overcome several limitations associated with the use of organic adhesive [e.g. epoxies] in FRPs. It consists of two dimensional FRP mesh saturated with a cement mortar, which is inorganic in nature and compatible with concrete and masonry substrates. In this study, a robust three-dimensional (3D) finite element (FE) model has been developed to study the behaviour of slender reinforced concrete columns confined by FRCM jackets, and loaded concentrically and eccentrically. The model accounts for material nonlinearities in column core and cement mortar, composite failure of FRP mesh, and global buckling. The model response was validated against several laboratory tests from literature, comparing the ultimate load, loadlateral deflection and failure mode. Maximum divergence between numerical and experimental results was 12%. Following the validation, the model will be used later in a comprehensive parametric analysis to gain a profound knowledge of the strengthening system, and examine the effects of several factors expected to influence the behaviour of confined member
    • سنة النشر : 2019
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Predictive Capability of Existing Confinement Models for FRCM Composites Confined Concrete

    ملخص البحث :

    Concrete confinement by the means of external fiber reinforced polymer (FRP) jacketing has been proved to be an effective method to increase the compressive strength and ductility, as well as mitigating deterioration due to aging, chemical attacks, overloading, and seismic activity. Concerns about the organic matrices used in FRP resulted in the development of fiber-reinforced cementitious mortar (FRCM) as a costeffective and sustainable alternative system, used to repair reinforced concrete beams in shear and flexure, or in column confinement. Several theoretical models have been proposed for FRCM confined concrete elements, based on limited laboratory tests. In this study, the predictive capability of four design models has been tested by comparing their predictions for confined concrete compressive strength (fcc) and ultimate axial strain (εcc) with a large experimental database of 137 samples found in the literature. The model developed by Ombres and Mazzuca [6] provided the highest calibrations with test data, although it still needs further improvements to include the effects of key geometric and material variables. Further efforts should be made to improve the performance of the design models and provide an accurate theoretical confinement model for FRCM-wrapped columns, for design and evaluation purposes.
    • سنة النشر : 2020
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Employment of damage plasticity constitutive model for concrete members subjected to high strain-rate

    ملخص البحث :

    Concrete damage plasticity (CDP) model is used to model the concrete damage through using ABAQUS software. Among several input parameters that should be defined in CDP model, the dilation angle (ψ), eccentricity parameter and tensile behaviour, have been identified as a significant influence on the finite element (FE) results for concrete modelling under static loading while limited studies examined these parameters for concrete subjected to impact load and high-strain rate. This study aims to focus on numerical modelling of impact-loaded concrete, examine and calibrate the above CDP model parameters using three-dimensional FE modelling. Several values of dilation angles, ψ, of 30 to 550 and eccentricity parameter of 0.1 to 0.2 have been used to capture the test behaviour. The model tensile softening behaviour was also investigated using three models, bilinear stress-strain, tri-linear stress-strain and stress-crack opening displacement. The FE results revealed that the value of dilation angle ranged 45-500 , the eccentricity parameter and tri-linear stress-strain model of tensile softening provided better correlations with test results in terms of displacement-time plots and cracking paths.
    • سنة النشر : 2020
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Flexural Behavior of Lightweight Aggregate Concrete One-Way Slabs

    ملخص البحث :

    The lightweight aggregate concrete had become a wide spectrum use at civil structures nowadays. The main aim of this research is towards evaluating the efficiency of lightweight aggregate in the structural behavior of reinforced concrete slabs. A three-dimensional finite element model suitable for the analysis of lightweight concrete one-way slabs (LWC) was used through this study. This analysis has been adopted by using the finite element principles with a system computer program (ANSYS V.17.2). The ordinary reinforced concrete and LWC slabs were modeled by 8 node isoparametric brick elements, while the steel reinforcing bars were modeled as axial members (bar elements) connecting opposite nodes in the brick elements with a full interaction assumption. In the present study, some important factors were studied by using numerical model to investigate their effect on the behavior of LWC one slabs. The parameters that considered were: (1) Type of lightweight aggregate (crushed brick and porcelenite types applied. Results explained the ultimate load increasing by (17.33 %) for crushed brick concrete and decreased by (27%) for porcelenite concrete when compared with normal concrete. Using crush than porcelenite aggregates
    • سنة النشر : 2018
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Shear Strengthening of RC Beams with FRCM Technique

    ملخص البحث :

    Nowadays, utilizationof Fibre Reinforced Polymer (FRP) in rehabilitation and strengthening of Reinforced Concrete (RC) beams is commonly used with a proper type of epoxy. Fabric Reinforced Cementitious Material (FRCM) presentsan alternative technique instead of the traditional epoxy. This paper investigates the shear performance of RC beamsusing FRCM strengthening. Finite Element method was adopted in modelingthe FRCM strengtheningfor RC beams in shear using ANSYS software with nonlinear and 3D analysis. In the beginning, the FE model was verified through comparing with the tests in the literature in terms of load-mid span deflection response, ultimate load, strain readings of reinforcement at mid-spanand the mode of failure. It was found that the FE model was capable to capture the behavior of FRCM strengthened RC beams with a high level of accuracy. This validated model has been employed later in studying some of parameters which have a potential effecton efficiency of this technique such as concrete compressive strength, number of fiber layers, and the arrangement of the fiber. Generally, it was found that the concrete compressive with high strength has significant impact in increase the efficiencyof FRCM strengthening system.
    • سنة النشر : 2019
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Flexural Performance of Hybrid Fiber Reinforced Cement Composites Under Elevated Temperatures

    ملخص البحث :

    Historically, the flexural behavior of hybrid fiber cement composites is not completely understood using the traditional test methods. This research presents the results of an experimental investigations on a high performance cement composites (HPCC) containing both micro steel fibers (SF) and micro polypropylene fibers (PP) before and after elevated temperature exposure. The experimental program was developed to study the flexural performance (flexural strength, toughness and stiffness) under high temperature using mono and hybrid (SF) and (SF + PP) fibers. Mixtures were divided into eight different groups, with constant w/c of 0.28 and different fibers content. Based on the results of this research, the replacing of micro (SF) in high performance cement composites by 15 % of micro (PP) fibers is recommended at high temperature exposure due to the fact that all hybrid fiber HPCC specimens show slight decreasing in flexural behavior compared to samples reinforced with 1% volume fraction of mono steel fibers after high temperature exposure.
    • سنة النشر : 2018
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل

  • عنوان البحث : Finite Element Analysis of RC Beams Strengthened in Shear with NSM FRP Rods

    ملخص البحث :

    This study presents three-dimensional FE models on RC T-beams strengthened in shear with near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods, with various rod spacing, strengthening pattern, and internal shear reinforcement ratios. The FE models utilized different constitutive material relations for concrete, steel, and FRP and implemented a mixed-mode bond-slip law at the NSM FRP rod-concrete interface. Comparisons, such as ultimate loads and load-deflection history, validated the accuracy of the developed models. More importantly, the FE models were able to predict the brittle shear failure of the beams and debonding of the NSM rods. For an accurate simulation of shear failure, the shear retention factor (β) should be less than 0.2. The correlated models will be used in further research to examine the effects of various parameters expected to influence the behavior of the retrofitted beams, in an effort to strengthen the knowledge on this topic
    • سنة النشر : 2018
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل

  • عنوان البحث : NUMERICAL MODELLING OF CFRP STRENGTHENED REINFORCED CONCRETE BEAMS UNDER IMPACT LOADING

    ملخص البحث :

    : In the recent years, externally bonded carbon fibre reinforced polymer (CFRP) composites are commonly used to strengthen existing reinforced concrete (RC) structures. In everyday practice, there are many situations under which deteriorated structures are subjected to impact loads. Thus, it is essential to have a comprehensive understanding of the response of CFRP strengthened RC beams subjected to impact load. This paper aims at providing a numerical model which is able to represent the behaviour of this kind of structures. It is worth noting from previous studies that CFRP strengthened RC beams can fail in several scenarios including flexural and shear failure in concrete (or mix between them), debonding of the CFRP layers and rupture in the CFRP. Thus, it is important to build a numerical model can capture all possible failure modes that could occur in the case of CFRP strengthened RC beams subjected to impact loads. The damage criteria were used for the concrete, CFRP and contact between concrete and CFRP to capture the failure that may occur. The proposed numerical model was then validated against set of samples tested in previous studies. It was found that the numerical model can capture the test results with high level of accuracy
    • سنة النشر :
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل

  • عنوان البحث : Optimizing the accelerated hardening of sawdust light weight concrete with carbon dioxide gas

    ملخص البحث :

    Recent increases in the amount of industrial wastes to be removed has made dealing with such waste products and gases an issue that needs to be solved with some urgency. The accelerated hardening mechanisms of light weight concrete (LWC) using carbon dioxide gas were thus studied in an experimental study to investigate the mechanical performance of concrete incorporating waste sawdust. The final results were optimised to maximise strength and minimise density using two different parameters: gas concentrations and sawdust percentages. All samples were subjected to tests of their mechanical and physical properties, including compressive strength, splitting tensile strength, water absorption, and density using the relevant standards. Parts of the samples were also submitted to thermogravimetric analysis (TGA) following the process of accelerated curing in order to quantify the consumed calcium hydroxide (Ca(OH)2) and the produced calcium carbonate (CaCO3). The results of the study showed an improvement in the physical and mechanical properties of all investigated specimens using the accelerated CO2 curing method. In addition, a 7% sawdust addition with 53% CO2 concentration resulted in higher strength in all cases. The TGA results proved that the carbonation curing resulted in lower Ca(OH)2 and higher CaCO3 content, with associated enhancement in the mechanical performance. This indicates that CO2-rich industrial emissions could find a value adding use in carbonation curing of sustainable wood-based concrete.
    • سنة النشر :
    • تصنيف البحث : بحث اكاديمي
    • منشور في : Scopus
    • تحميل

  • عنوان البحث : Shear Behavior of Precast-Prestressed Concrete Beam with Reactive Powder Concrete Slab

    ملخص البحث :

    The present experimental and theoretical investigation aims to study the shear behavior of composite concrete members which consisting from precast-prestressed concrete beams and reactive powder concrete slabs, as well as knowledge the impact and effectiveness of using the reactive concrete powder slab on the shear behavior of the composite member compared to conventional concrete slab for the same composite member, that was studied in this research as well. Experimental work included casting and testing seven composite concrete members and the only difference between them was the quality of the concrete slab either precast-prestressed concrete beam was similar for all of them. The results showed that the shear behavior has been improved when using the reactive powder in concrete slab compared with traditional concrete slab. The ultimate shear strength (Vu) and diagonal cracking load (Vcr) increased to (20.31%) and (13%) respectively with using the reactive powder concrete slab compared to composite concrete member with normal concrete slab (SB7). It was found that the increase of steel fiber volumetric ratio (Vf) % form (0 to 1%) increased ultimate shear strength Vu by (12.63 to 31.82%) respectively. Also, it was found that the increase of shear-span to depth ratio (a/d) from (2 to 3.5) decreased both diagonal cracking load Vcr by (7.15 to 28.57%) and ultimate shear strength Vu by (8.34 to 31.8%). For this analysis, a system of computer program (ANSYS V.12.1) is used for this study. The precast-prestressed concrete, reactive powder concrete and normal concrete slab were modeled by 8-noded isoparametric brick elements (Solid 65), while the steel reinforcing bars and prestressed strand were modeled as axial members (bar elements Link8) connecting opposite nodes in the brick elements with full interaction assumption. Good agreement with the experimental tests of some previous studies was obtained using ANSYS solution. The maximum difference with experimental test is found to be less than 6%.
    • سنة النشر :
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل

  • عنوان البحث : FIRE FLAME EFFECT ON THE STRENGTH OF SELF – COMPACTING CONCERETE

    ملخص البحث :

    This study aims to investigate the effect of fire flame on some mechanical properties of self-compacting concrete specimens. To determine the workability, different test methods are adopted in this research such as slump-flow, T50 slump-flow, L-box, U-box and V-funnel. The concrete specimens were subjected to fire flame at the lower surface only to reach temperatures around 400,500 and 600 ° C for one hour, then they were cooled gradually to room temperature. After that, they were tested for weight loss, compression, splitting and flexural and compared with specimens not subjected to fire flame (reference mix). Based on the results of this work, it may found that the compressive strength of selfcompacting concrete decreases with fire temperature exposure. The residual values of compressive strength were (71-88) % of the strength for the reference specimens. The flexural strength is more sensitive to fire flame temperatures. The residual flexural strengths were in the range of (58- 81) % of the flexural strength for the reference specimens. The splitting tensile strength was extra sensitive than the compressive strength. The residual splitting tensile strength were in the ranges of (58- 90) % of the splitting strength for the reference specimens. The weight loss of concrete specimens increases with increasing fire temperature.
    • سنة النشر : 2012
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل

  • عنوان البحث : FLEXURAL BEHAVIOR OF PRECAST-PRESTRESSED CONCRETE BEAM WITH REACTIVE POWDER CONCRETE SLAB

    ملخص البحث :

    The present experimental and theoretical investigation aims to study the flexural behavior of composite concrete members which consisting of precast-prestressed concrete beams and reactive powder concrete slabs, as well as knowing the impact and effectiveness of using the reactive concrete powder slab on the flexural behavior of the composite member compared to conventional concrete slab for the same composite member, that was studied in this research as well. Experimental work included casting and testing four composite concrete members and the difference between them was the quality of the concrete slab but the precast-prestressed concrete beam was similar for all of them. The results showed that the flexural behavior has been improved when using the reactive powder in concrete slab compared with traditional concrete slab. The ultimate load (Pu) increased to (19.91%) with using the reactive powder concrete slab compared to composite concrete member with normal concrete slab. It was found that the increase of steel fiber volumetric ratio (Vf) % from (0 to 1%) increased ultimate load Pu by (19 to 31.9%) respectively. For this analysis, a system of computer program (ANSYS V.12.1) is used for this study. The precast-prestressed concrete, reactive powder concrete and normal concrete were modeled by 8-noded isoparametric brick elements (Solid 65), while the steel reinforcing bars and prestressed strand were modeled as axial members (bar elements Link8) connecting opposite nodes in the brick elements with full interaction assumption. Good agreement with the experimental tests of some previous studies was obtained using ANSYS solution. The maximum difference with experimental test is found to be less than 5%.
    • سنة النشر : 2016
    • تصنيف البحث : بحث اكاديمي
    • منشور في : غير ذلك
    • تحميل