Papers by Ferhad R . Karim
CONSTRUCTION, Dec 21, 2023
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CONSTRUCTION
Ultra-high performance fiber reinforced concrete (UHPFRC) is a high-performance cementitious mate... more Ultra-high performance fiber reinforced concrete (UHPFRC) is a high-performance cementitious material with enhanced tension, compression, and toughness, strengths in the post crack region with high ductility, toughness, and durability. The companies prefer to use it to construct highly durable structures such as high-rise buildings, towers, and bridges. In addition, the thickness of the flat slab produced by UHPFRC might be thinner than the conventional concrete. One problem that has always been a concern in a flat slab is the punching shear failure since this failure is brittle and occurs suddenly without any previous notice. Besides, the position of the critical section for punching shear could be changed based on the thickness of the drop panel and the inclusion of fiber in the concrete. This paper highlights the effect of drop panels dimension on the punching shear resistance in UHPFRC flat slabs. The four two-way interior UHPFRC supported flat slab panels, consisting of one con...
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International Journal of Research in Engineering and Technology, 2016
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The International Journal of Engineering and Science (IJES), 2020
The use ofFiber-reinforced polymerscomposite materials in repairing and strengthening damaged str... more The use ofFiber-reinforced polymerscomposite materials in repairing and strengthening damaged structural parts,especially those made of reinforced concrete, is wide spreads. However, each FRP composite that used in the strengthening of beams must carefullychose, there are many techniques used in the strengthening of beams such as externally bonded reinforcement (EBR) and near-surface mounted (NSM) and FRP composite applied to the surface of the beam in different shape and forms such as U-anchorage, a bottom face, strips, plates, laminates, and sheets. This paper highlights the effect of different FRP composite,and strengthening techniques on the flexural strength of the reinforced concrete beams. The results showed that the flexural strength of reinforced concrete beams improved up to170.2 %, 53%,50 %, and 45.1 % due to strengthening by CFRP composites, aramid FRP composite,GFRP composite, graphite FRP composite, and prestressed CFRP,respectively. Moreover, the jacketing techniques with two vertical and two horizontal of the CFRP plate are the most suitable way for flexural strengthening, which improves up to 235%.
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American Journal of Engineering Research (AJER) , 2020
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Saudi Journal of Civil Engineering , 2020
This paper highlight, the techniques used to analyses symmetric structures subject to general loa... more This paper highlight, the techniques used to analyses symmetric structures subject to general loading. After an extensive review of previous work in this field, the paper introduces the most public way of structure analysis, based on conventional three methods which is force, matrix stiffness and column analogy techniques. It shows how this approach can systematically simplify a structural analysis and clarify a technique which is best known to structural engineers. For each method, a portal symmetry plane frame considered for analyzing with an explanation of the analysis calculation procedure, and it also shows that the influences of symmetry can observe and utilization in different methods to simplify the analysis procedure.
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Saudi Journal of Civil Engineering , 2020
This paper highlights the review of the behavior and strength of strengthening reinforced concret... more This paper highlights the review of the behavior and strength of strengthening reinforced concrete columns by reinforced concrete jacketing. Even with the fact that on a massive scale, numerous experimental studies on column strengthening with the assistance of reinforced concrete jacketing are performed after which suggested, however, there may be nonetheless an apparent need for locating and executing new approaches to improve the performance of classical RC jacketing. As in the case of RC structure, columns are subjected to uniform and non-stop loading, which increases with the boom in a number of stories and might cause partly damage or even general failure of the column. To overcome the whole failure of RC columns, instant attention is needed in and the broken part of reinforced concrete repaired by way of reinforced concrete jacketing. This paper additionally focuses on the effect of presenting dowel rebar by way of drilling holes and using concrete jackets made with particular types of concrete. The results show that each use of dowel rebar and distinctive kinds of concrete will increase the bond strength, basic load wearing capability, and primary crack load. Critical cases clarified to avoid such as reinforcing limit and form, type and property of concrete, types of surface preparation, and a recommendation for high temperature.
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The International Journal of Engineering and Science (IJES), 2020
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East African Scholars Journal of Engineering and Computer Sciences , 2020
This research highlights the contribution of concrete cover to improve the torsional resistance o... more This research highlights the contribution of concrete cover to improve the torsional resistance of peak load of under-reinforced fibrous high-strength concrete beams. The thickness of concrete cover is the main variable which was varied from 17 mm to 53 mm in this research. To investigate the influence of thickness of concrete cover on the behavior of under-reinforced fibrous, high strength concrete beams subjected to pure torsional loading, four rectangular solid beams were cast and tested. The test results showed that the torsional resistances at peak load was improved up to 80.6%. Furthermore, all of the twisting angle, shear strain in concrete, strain in transverse reinforcement, and strain in longitudinal reinforcement were reduced at peak loads up to 70.2%, 90%, 50.6%, and 34.5%, respectively.
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The tension stiffening index is a critical factor which improved their effect on the torsional be... more The tension stiffening index is a critical factor which improved their effect on the torsional behavior of fibrous reinforced concrete beams which included the bond strength between the reinforcement and the concrete, and the amount of reinforcement indexes. Thus, this paper highlights the effect of the tension stiffening index on the torsional resistance of ultra-high performance fiber reinforced concrete (UHPFRC) beams under pure torsion. Therefore, four under-reinforced ultra-high performance fiber reinforced concrete beams were cast and tested under pure torsion which contains the fixed amount of longitudinal and transverse reinforcements, while the grade and the rib pattern on the surface of reinforcement have been changed. Test results verified that the torsional resistance, stiffness of the cracked section and the twisting angle were improved at the crack and peak loads due to a reduction in the tension stiffening index. However, the axial strains in transverse and longitudinal reinforcements. List of notation : Bond strength between transverse reinforcement and the matrix of ultra-high performance fiber reinforced concrete, MPa : Bond strength between the longitudinal reinforcement and the matrix of ultra-high performance fiber reinforced concrete, MPa : Linear variable differential transformer : Tension stiffening index, MPa VC: Visco Crete UH: Ultra-High Performance fiber reinforced concrete : Transverse reinforcement index, MPa : Longitudinal reinforcement index, MPa Φ: diameter of fiber, mm INTRODUCTION Non-fibrous concrete beams are designed for resisting torsional moment, the compressive strength and dimensions of the section are taken into account before cracking, while the yield stress of transverse reinforcement in stress-strain curve, stirrup dimensions and spacing between stirrups are considered at peak load [1, 2]. In contrast, the compressive strength and split tensile strength in fibrous concrete were influenced by the inclusion of steel fiber [3-5]. Consequently, the bond strength between reinforcement and the matrix of fibrous concrete improved proportionally with compressive strength [6]. However, the spacing between spiral cracks and the width of crack at failure were influenced by the bond strength between reinforcement and the matrix of concrete [7]. Although, the amount of reinforcement has effect on the strain in reinforcement [2], the strain in reinforcement embedded steel bar in concrete was less than the strain of reinforcement corresponding to yield stress in stress-strain curve which is known as tension stiffening [8]. In addition, the strain in longitudinal reinforcement has been influenced on the shear strain in diagonal compression strut
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This investigation highlights the influence of double idealized shear flow zones on the torsional... more This investigation highlights the influence of double idealized shear flow zones on the torsional resistance for under-reinforced fibrous normal strength concrete beams subjected to pure torsion. The beam sections were double reinforced by transverse and longitudinal reinforcements, once was located in the idealized shear flow zone and the other one was located in the idealized tension zone. To study the influence of double idealized shear flow zones on the torsional resistance of under-reinforced fibrous normal strength concrete beams, four fibrous concrete beams were cast and tested under pure torsion. The under-reinforced beams designed based on ACI 318-14. The main transverse and longitudinal reinforcements in the shear low zone are kept constant in the beams while the transverse reinforcement in the idealized tension zone was covered different percentage of this zone. The test results were confirmed that the torsional resistance at peak loads was improved up to 23.7% while the area enclosed by stirrup in core zone has extended to 46.2%. In addition, the twisting angle at peak loads was enhanced up to 60.9%and the shear strain in concrete and the strain in longitudinal reinforcement were enhanced whereas the strain in transverse reinforcement was decreased. The spacing between spiral cracks and the inclination angle of crack at failure were increased with inclusion of reinforcement in core zone. The space truss model was modified to cover the influence of double shear flow zones. The proposed modification model was showed that it has a good agreement with test results. Index Terms-Double shear flow zone, Fibrous normal strength concrete, Pure torsion, andSpace truss analogy,.
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In this paper, the existing models for predicting compressive, split tensile, and flexural streng... more In this paper, the existing models for predicting compressive, split tensile, and flexural strength with modulus of elasticity of fibrous high strength concrete are reviewed. This paper highlights the improvement of compressive and split tensile strengths in fibrous high strength concrete with use of varying volume fraction of fibre, which contained the same amount of different size of fibre, and the ratio of long to total amount of fibre in the mix. The main variables which affect the strength of this kind of concrete statistically were analyzed using statistical techniques. In this research, the predicted models confirmed that the amount of cement, silica fume, aspect ratio of steel fibre and maximum size of aggregate affect the compressive strength whereas split tensile and flexural strength are affected by volume fraction of steel fibre and the amount of super-plasticizer. It was found that the use of different size of steel fibres improves both tensile and compressive strengths more than the improvement obtainable from the use of single size of steel fibre. The proposed models for predicting compressive and split tensile with the simple relation between them prove that they have a good agreement with results.
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This investigation examines experimentally and statistically the behavior and ultimate strength o... more This investigation examines experimentally and statistically the behavior and ultimate strength of L-shape reinforced high strength concrete beams under combined bending and shear. The experimental investigation consists of casting and testing of nine beams which were tested under bending and shear. The effect of compressive strength, longitudinal reinforcement on the load carry capacity and the effect of transverse reinforcement on the shear strength is studied. An increase in compressive strength by (65.56%) causes an increase in load carrying capacity and shear strength at cracking load by (21.47% and 162.9%) respectively. An increase in longitudinal reinforcement ratio for bending by (153.8%) caused an increase in load carrying capacity by (46.37%) when the longitudinal reinforcement ratio is kept constant, an increase in transverse reinforcement index by(59.25% %) causes an increase in shear strength at ultimate load by (6.55 %). By using multiple nonlinear stepwise regression method, based on data in this research and from other literature; equations were proposed for predicting shear strength at cracking and ultimate loads. These proposed equations show good agreement and they are conservative when compared with equations given by Codes of practice. Keywords: High strength concrete, L-shape beam, bending and shear. ﻤﻘﻁﻊ ﺫﺍﺕ ﺍﻟﻌﺘﺒﺎﺕ ﺴﻠﻭﻙ ﻗﺹ ﻭ ﻋﺯﻭﻡ ﺘﺤﺕ ﺍﻟﻤﻘﺎﻭﻤﺔ ﻋﺎﻟﻴﺔ ﻜﻭﻨﻜﺭﻴﺕ ﻤﻥ ﻤﺼﻨﻭﻋﺔ L ﺍﻟﺨ ﻼ ﺼ ﺔ ﻭﺍﻟﻘﺹ ﺍﻻﻨﺤﻨﺎﺀ ﺘﺎﺜﻴﺭ ﺘﺤﺕ ﺍﻟﻌﺘﺒﺎﺕ ﻭﻤﻘﺎﻭﻤﺔ ﺴﻠﻭﻙ ﻟﺩﺭﺍﺴــﺔ , ﺘﻡ ﻓﺤـﺹ ﻭ ﺼـﺏ ﺘ ﻋﺘﺒﺎﺕ ﺴﻌﺔ ﺨﺭﺴﺎﻨﻴﺔ ﺍﺨﺫ ﻤﻊ ﺍﻟﻤﻘﺎﻭﻤﺔ ﻋﺎﻟﻴﺔ ﺍﻟﺨﺭﺴﺎﻨﺔ ﻤﻥ ﻤﺼﻨﻭﻋﺔ ﻤﺴﻠﺤﺔ ﺒﻨﻅـﺭ ﺍﻻﻋﺘﺒ ﺍﻟ ﺘﺴﻠﻴﺢ ﻨﺴﺒﺔ ﺎﺭ ﻁﻭﻟﻲ ، ﻭﻤﺅﺸﺭ ﺍﻟ ﺒـﻴﻥ ﺍﻟﻤﺴﺎﻓﺔ ﻨﺴﺒﺔ ﻭ ﺍﻟﻌﻤﻭﺩﻱ ﺘﺴﻠﻴﺢ ﺘﺴـﻠﻴﺢ ﺍﻟﻘ ﺍﻟﻰ ﺹ ﺍﻟ ﻌﻤﻕ ﺍﻟ ﻟﻠﻌﺘﺒﺔ ﻔﻌﺎل. ﺍﻟﻰ ﺒﻨﺴﺒﺔ ﺍﻻﻨﻀﻐﺎﻁ ﻤﻘﺎﻭﻤﺔ ﺯﻴﺎﺩﺓ ٦٥،٥٦ % ﻴـﺅﺩﻱ ﻓﻲ ﺯﻴﺎﺩﺓ ﺍﻟﻰ ﻭ ﺍﻟﻘﺼﻭﻯ ﺍﻟﻘﺎﻭﻤﺔ ﺒﻤﻘـﺩﺍﺭ ﺍﻟﻘﺹ ﺠﻬﺩ ٢١،٤٧ ﻭ ١٦٢،٩ % ﻋﻠـﻰ ﺍﻟﺘﻭﺍﻟﻲ. ﺍ ﺜﺎﺒﺘﺎ ﺍﻟﻌﻤﻭﺩﻯ ﺍﻟﺘﺴﻠﻴﺢ ﻜﺎﻥ ﺫﺍ , ﻓـﺎﻥ ﺯﻴـﺎﺩﺓ ﺘﺴـﻠﻴﺢ ﻨﺴـﺒﺔ ﺒﻤﻘـﺩﺍﺭ ﺍﻻﻓﻘـﻰ). ١٥٣،٨ (% ﻓﻲ ﺯﻴﺎﺩﺓ ﺍﻟﻰ ﻴﺅﺩﻱ ﺍﻟﻘﺼﻭﻯ ﺍﻟﻤﻘﺎﻭﻤﺔ ﺒﻤﻘﺩﺍﺭ) ٤٦،٣٧. (% ﺍ ﻜﺎﻥ ﺍﺫﺍ ﻤﺎ ﺜﺎﺒﺘﺎ ﺍﻻﻓﻘﻲ ﺍﻟﺘﺴﻠﻴﺢ ، ﺒﻤﻘﺩﺍﺭ ﺍﻟﻌﻤﻭﺩﻱ ﺍﻟﺘﺴﻠﻴﺢ ﻭﺍﻀﻴﻑ) ٥٩،٢٥ (% ﻓ ﺍﻻﻀﺎﻓﺔ ﻬﺫﻩ ﺘ ﺯﻴﺩ ﺍﻻ ﺍﻟﻘﺹ ﺠﻬﺩ ﻤﻥ ﺒﻤﻘﺩﺍﺭ ﻗﺼﻰ) ٦,٥٥ .(% ﺍﻻ ﺍﻻﺒﺤﺎﺙ ﻭ ﺍﻟﻌﻤل ﻟﻬﺫﺍ ﺍﻟﻤﻭﺠﻭﺩﺓ ﺍﻟﺒﻴﺎﻨﺎﺕ ﻋﻠﻰ ﺍﻋﺘﻤﺎﺩﺍ ﺨﺭﻯ , ﺍﻗﺘﺭﺤﺕ ﺍﻟﻤﻌﺎﺩﻻﺕ ﺒﻌﺽ ﺍﻟﻘﺹ ﻭﺠﻬﺩ ﺍﻻﻗﺼﻰ ﺍﻟﻘﺹ ﺒﺠﻬﺩ ﻟﻠﺘﻨﺒﺄ ﺍﻟ ﻤﺴﺒﺒﺔ ﻭ ﺍﻻﻗﺼﻰ ﺍﻻﻨﺤﻨﺎﺀ ﻋﺯﻡ ﻤﻊ ﻟﻠﺸﻘﻭﻕ ﻋﺯﻡ ﺍﻻﻨﺤﻨﺎﺀ ﺍﻟ ﺍﻟﺸﻘﻭﻕ ﻤﺴﺒﺏ. ﺠﻴﺩﺓ ﻨﺘﺎﺌﺞ ﺍﻟﻤﻘﺘﺭﺤﺔﺍﻅﻬﺭﺕ ﺍﻟﻤﻌﺎﺩﻻﺕ ﻫﺫﻩ ﻭ ﻤﻘﺎﺭﻨﺘﻬـﺎ ﻋﻨﺩ ﺍﺨﺭﻯ ﻤﻌﺎﺩﻻﺕ ﻤﻊ .
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This research highlights the effect of concrete cover on the behavior of ultra-high performance f... more This research highlights the effect of concrete cover on the behavior of ultra-high performance fiber reinforced concrete rectangular solid beams under pure torsion. The main parameter in this research is the thickness of concrete cover which is varying between 21 and 52 mm. For this purpose, four under-reinforced ultra-high performance fibre reinforced concrete rectangular solid beams were cast and they were tested under pure equilibrium torsion. The test results verified that the torsional resistance at peak and crack loads were improved up to 113% and 134%, respectively, of the estimated value based on thin walled tube theory. Moreover, all of the twisting angle at ultimate load and shear strain in concrete were found to decrease up to 64.9%, 40.1%, respectively. In addition, both strain in longitudinal reinforcement and strain in stirrup were reduced up to 50%. The space truss analogy was modified to be compatible with this parameter effect. The modified model showed that it has a good agreement with test results.
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This study highlights the effect of additional reinforcements in the idealized core zone of fibro... more This study highlights the effect of additional reinforcements in the idealized core zone of fibrous high strength concrete beams for resisting pure torsional loading. The transverse and longitudinal reinforcements were added in the area considered as idealized core zone which is supposed to be in tension condition plus the traditional reinforcements located in the main idealized shear flow zone. Four fibrous high strength under-reinforced concrete solid beams were cast and tested under pure torsion to verify the influence of secondary shear flow zone on the torsional resistance. The tested beams were designed according to ACI318-14. The transverse and longitudinal reinforcements were kept constant in the idealized main shear flow zone while the covered area in the idealized core zone by reinforcements was added as a different percentage of this zone. The test results show that torsional resistance at peak load and torsional resistance provided by reinforcement and fibre were improved up to 14.18% and 146%, respectively, due to covering of 85.4% of the idealized core zone area by transverse and longitudinal reinforcements. In addition, due to contribution of reinforcement in the idealized core zone, the strains in transverse and longitudinal reinforcements were reduced up to 60% and 69.4%, respectively. Index Term-Fibrous high strength concrete, Idealized core zone, Pure torsion, and Secondary shear flow zone.
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In this paper, the methods for evaluating torsional strength of fibrous concrete beams are review... more In this paper, the methods for evaluating torsional strength of fibrous concrete beams are reviewed and highlighted the basic assumptions in these methods.The variables which include in the proposed model in these methods for predicting of torsional strength in shallow under-reinforced and plain fibrous concrete beams are explained. The proposed models indicated that volume fraction of steel fibre, aspect ratio of fibres, tensile strength of fibres, geometry of the section and inclination angle of spiral crack have an impact on the torsional strength in pre-cracking stage, whereas longitudinal and transverse reinforcement ratios, enclosed area by stirrups as well as stirrup spacing have influence on the ultimate torsional strength.Likewise, the impact of these variables on the torsional strength in prior of cracking and post-cracking stages improved by the experimental researcher's .It was noticed that there is a gap between assumption and experimental variables. While in space truss analogy method, the enclosed area by stirrups is considered in the prediction of ultimate torsional strength, whereas according to the basic assumptions the same area is ignored. Likewise, the area of concrete outside of stirrups is considered as a basic assumption whereas this area is completely ignored in the evaluating ultimate torsional strength. Moreover, the material's strength is limited in the predicting models. Consequently, these limits make an efficient torsion design of fibrous concrete beams difficult.
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this investigation highlights the influence of glass powder and cement content on the compressive... more this investigation highlights the influence of glass powder and cement content on the compressive strength in ultra-high performance concrete. The cement content and replacement of cement by glass powder were selected as the parameters in this research. To study the influence of cement content and replacement of cement by glass powder, 117 cubes were cast and tested under compression. The test results were claimed that the compressive strength was enhanced by including extra cement content to the mix and replacement of cement by glass powder up to 14% and 5%, respectively. The SPSS software package was used to proposed equation to predict compressive strength includes mix proportion of UHPC using nonlinear multiple regression. The proposed model was showed that it has a good agreement with test results.
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This paper highlights the influence of thickness of concrete cover on the torsional resistance in... more This paper highlights the influence of thickness of concrete cover on the torsional resistance in the fibrous rectangular solid concrete beams under pure torsion. In this investigation, thickness of concrete cover vary between 18 and 53 mm. To study the influence of concrete cover in under-reinforced fibrous normal strength concrete, four fibrous concrete beams were cast and test under pure torsion. The under-reinforced concrete beams was designed based on ACI-318-14. The transverse and longitudinal reinforcement indexes are kept constant in the beams. While the aspect ratio of the beam cross section and span to depth ratio of the beams are 1.22 and 5.75, respectively. The test results were claimed that the torsional resistance provided by concrete and reinforcements plus fibre were enhanced at crack and peak loads up to 76.4% and 64.4%, respectively. In contrast, twisting angle, shear strain in concrete, strain in transverse and longitudinal reinforcements were reduced up to 57.8%, 65%, 89.3% and 95.6%, respectively. The spacing between cracks and the angle of inclination of crack at failure was increased whereas the number of cracks reduced. The dimensional analysis was used to proposed equations to predict torsional resistance at crack and peak loads including the contribution of concrete cover. In addition, the Buckingham П theorem was used for this purpose. Based on the 34 data from previous researches and the data in this research, nonlinear multiple regressions in Minitab software version 16 was used to predict the coefficients of the proposed П-groups equations. The proposed models have shown a good agreement with test results.
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Papers by Ferhad R . Karim