Improving Bond Performance of Near-Surface Mounted Steel Ribbed and Threated Rods in the Concrete

Sabry Fayed,Emrah Madenci,Yasin Onuralp Özkiliç,Mohamed H. Zakaria 한국콘크리트학회 2024 International Journal of Concrete Structures and M Vol.18 No.2

In this study, the experimental findings of twenty pull-out tests on the bond efficiency of threaded/ribbed steel rods used in near-surface mounting (NSM) are presented. On a groove (20 × 20 mm) that was slotted in one of the sides of a concrete block measuring 250 × 250 × 200 mm, a pull-out experiment was performed. The primary factors are the slot-filling materials (substrate concrete and epoxy paste), bonded length (equal to 5, 7, 10, and 15 times the rod diameter), surface pattern conditions (conventional ribbed reinforcing rebar and threaded bolt), use of nuts or rings welded at the free end of the bonded length, and use of straight or spiral wire welded along the length of the bonded length. The tested specimens' ultimate bond strength, slip, bond stress–slip response, failure patterns, stiffness, and ductility are recorded and assessed. The results showed that the ultimate bond strength and corresponding slip of ribbed rods cemented with epoxy were higher by 11.11% and 199%, respectively, than those of ribbed rods submerged in the substrate. Over the controls, all NSM epoxy-rods exhibited a greater ductility. As the bonded length increased, the ultimate bond strength of NSM rods fell by 12–32%. As the bonded length increased, the stiffness decreased. On the other hand, the ductility of NSM epoxy-rods increased as the bonded length increased. All applied schemes such as nuts, rings, longitudinal bars, and spiral bars significantly improved the ultimate bond strength (maximum = 25.93%) and corresponding slip (maximum = 166.67%) of NSM threaded rods as compared to the control ones.

Evaluate the effect of steel, polypropylene and recycled plastic fibers on concrete properties

Fayed, Sabry,Mansour, Walid Techno-Press 2020 Advances in concrete construction Vol.10 No.4

The impacts of reinforcing concrete matrix with steel fibers, polypropylene fibers and recycled plastic fibers using different volume fractions of 0.15%, 0.5%, 1.5% and 2.5% on the compressive and tensile characteristics are experimentally investigated in the current research. Also, flexural behavior of plain concrete (PC) beams, shear performance of reinforced concrete (RC) beams and compressive characteristics of both PC and RC columns reinforced with recycled plastic fibers were studied. The experimental results showed that the steel fibers improved the splitting tensile strength of concrete higher than both the polypropylene fibers and recycled plastic fibers. The end-hooked steel fibers had a positive effect on the compressive strength of concrete while, the polypropylene fibers, the recycled plastic fibers and the rounded steel fibers had a negative impact. Compressive strength of end-hooked steel fiber specimen with volume fraction of 2.5% exhibited the highest value among all tested samples of 32.48 MPa, 21.83% higher than the control specimen. The ultimate load, stiffness, ductility and failure patterns of PC and RC beams in addition to PC and RC columns strengthened with recycled plastic fibers enhanced remarkably compared to non-strengthened elements. The maximum ultimate load and stiffness of RC column reinforced with recycled plastic fibers with 1.5% volume fraction improved by 21 and 15%, respectively compared to non-reinforced RC column.

Parametric studies on punching shear behavior of RC flat slabs without shear reinforcement

Galal Elsamak,Sabry Fayed 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.25 No.4

This paper proposed a numerical investigation based on finite elements analysis (FEA) in order to study the punching shear behavior of reinforced concrete (RC) flat slabs using ABAQUS and SAP2000 programs. Firstly, the concrete and the steel reinforcements were modeled by hexahedral 3D solid and linear elements respectively, and the nonlinearity of the used materials was considered. In order to validate this model, experimental results considered in literature were compared with the proposed FE model. After validation, a parametric study was performed. The parameters include the slab thickness, the flexure reinforcement ratios and the axial membrane loads. Then, to reduce the time of FEA, a simplified modelling using 3D layered shell element and shear hinge concept was also induced. The effect of the footings settlement was studied using the proposed simplified nonlinear model as a case study. Results of numerical models showed that increase of the slab thickness by 185.7% enhanced the ultimate load by 439.1%, accompanied with a brittle punching failure. The punching failure occurred in one of the tested specimens when the tensile reinforcement ratio increased more than 0.65% and the punching capacity improved with increasing the horizontal flexural reinforcement; it decreased by 30% with the settlement of the outer footings.

Experimental and numerical analysis of the punching behavior of RC isolated footings

Walid Mansour,Sabry Fayed,Ali Basha 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5

In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200x1200 mm2 to 1500x1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

Flexural strengthening of RC beams using externally bonded aluminum plates: An experimental and numerical study

Elsamak, Galal,Fayed, Sabry Techno-Press 2021 Advances in concrete construction Vol.11 No.6

This research investigated the flexural strengthening of RC beams using Aluminum plates (AP). An experimental program including 8 RC beams were carried out. The width and depth of the beam were 150 and 300 mm respectively while the effective span of the beam was 1560 mm. The tensile reinforcement ratios of the beams were 0.38 and 0.548%. The external APs ratios (the cross sectional area of AP to the beam cross sectional area) were 0.10, 0.37 and 0.74% while the AP length to the beam length was 0.93. A Finite element analysis (FEA) was investigated to study many variables that influenced on the ultimate load and the behavior of the AP-strengthened beams such as AP length, using shear connectors, using various techniques of the end anchorages and using anchored/unanchored U-shaped APs. It was noticed that the improvement ratios of the ultimate load and the ductility of strengthened beams with tensile reinforcement ratio of 0.38% was better than the beams with tensile reinforcement ratio of 0.548%. The AP length to the beam span ratio had a significant effect on the ultimate load, the ductility and the failure mode of the beams. The ultimate deflection and the ultimate load of the AP strengthened beams that used shear connectors increased by 165 and 54 % respectively compared to the beam without shear connectors. Using U-shaped AP jacket accompanied with end anchorages enhanced the ultimate load by 109%. The ultimate load of the beams with bolted U-shaped AP jacket increased by 128%.

Flexural strengthening of RC one way solid slab with Strain Hardening Cementitious Composites (SHCC)

Basha, Ali,Fayed, Sabry,Mansour, Walid Techno-Press 2020 Advances in concrete construction Vol.9 No.5

The main aim of the current research is to investigate the flexural behavior of the reinforced concrete (RC) slabs strengthened with strain hardening cementitious composites (SHCC) experimentally and numerically. Seven RC slabs were prepared and tested under four-points loading test. One un-strengthened slab considered as control specimen while six RC slabs were strengthened with reinforced SHCC layers. The SHCC layers had different reinforcement ratios and different thicknesses. The results showed that the proposed strengthening techniques significantly increased the ultimate failure load and the ductility index up to 25% and 22%, respectively, compared to the control RC slab. Moreover, a three dimensional (3D) finite element model was proposed to analyze the strengthened RC slabs. It was found that the results of the proposed numerical model well agreed with the experimental responses. The validated numerical model used to study many parameters of the SHCC layer such as the reinforcement ratios and the different thicknesses. In addition, steel connectors were suggested to adjoin the concrete/SHCC interface to enhance the flexural performance of the strengthened RC slabs. It was noticed that using the SHCC layer with thickness over 40 mm changed the failure mode from the concrete cover separation to the SHCC layer debonding. Also, the steel connectors prevented the debonding failure pattern and enhanced both the ultimate failure load and the ductility index. Furthermore, a theoretical equation was proposed to predict the ultimate load of the tested RC slabs. The theoretical and experimental ultimate loads are seen to be in fairly good agreement.

Buckling performance of pultruded glass fiber reinforced polymer profiles infilled with waste steel fiber reinforced concrete under axial compression

Emrah Madenci,Sabry Fayed,Walid Mansour,Yasin Onuralp Özkılıç 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5

This study reports the results of a series of tests of pultruded glass fiber reinforced polymer (P-GFRP) box section composite profile columns, geometrically similar with/without concrete core, containing 0-1-2-3% steel fiber, with different lengths. The recycled steel wires were obtained from waste tyres. The effects of steel fiber ratio on the collapse and size effect of concrete filled P-GFRP columns under axial pressure were investigated experimentally and analytically. A total of 36 columns were tested under compression. The presence of pultruded profile and steel wire ratio were selected as the primary variable. The capacity of pultruded profiles with infilled concrete are averagely 9.3 times higher than the capacity of concrete without pultruded profile. The capacity of pultruded profiles with infilled concrete are averagely 34% higher than that of the pultruded profiles without infilled concrete. The effects of steel wire ratio are more pronounced in slender columns which exhibit buckling behavior. Moreover, the proposed analytical approach to calculate the capacity of P-GFRP columns successfully predicted the experimental findings in terms of both pure axial and buckling capacity.

Flexural rigidity and ductility of RC beams reinforced with steel and recycled plastic fibers

Walid Mansour,Sabry Fayed 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.3

This study compares between the mechanical properties of concrete either reinforced with recycled plastic (RP) or end-hooked steel (EHS) fibers with volume fractions of 1, 2 and 3%. Also, the effects of the fiber type and volume fraction on flexural responses were investigated using experimental program composed of seven reinforced concrete (RC) beams. Generally, results showed that the RP and EHS fibers remarkably enhanced both the mechanical characteristics of concrete and the flexural capacity of RC beams. Specifically, concrete matrix that reinforced with 2% volume fraction of RP or EHS fibers exhibited the highest capacities among all tested specimens. On the other hand, the compressive and the tensile strengths of the fibrous concrete which strengthened with 3% volume fraction (either RP or EHS fibers) were lower than their counterparts that reinforced with lower volume fraction (2%). As the fiber volume fraction increased up to 2%, the peak load of the RC beams increased followed by a reduction for higher fiber volumes. The peak load of the RC beam specimens reinforced with 2% of RP and EHS fibers were 57.1 kN and 60.7 kN, respectively compared to 39.6 kN for the control RC beam. Both RP and EHS fibers had a positive effect on the (effective/gross) flexural rigidity ratio, especially when used with volume fraction lower than 3%. RC beams reinforced with 1% of RP and EHS fibers yielded higher ductility in comparison with 2 and 3%. An analytical model constructed based on the distribution of stress-strains along the height of the RC beam was used to estimate the bending moments at different stages. Results well agreed with the experimental records.

Flexural Behavior of Cracked RC Beams Retrofitted with Strain Hardening Cementitious Composites

Ali Basha,Sabry Fayed,Galal Elsamak 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.6

In the present research, the efficiency and the effectiveness of different Ultra High Performance Strain Hardening Cementitious Composites (UHP-SHCC) schemes for flexure retrofitting of a cracked RC beams were investigated experimentally, numerically and analytically. The experimental program consisted of six RC beams. The control specimen was loaded until failure. The middle third part of the control specimen was replaced with UHP-SHCC, then, it was loaded again until failure. The other five beams were loaded until 52% of the failure load of the control beam, then they were retrofitted with a layer of UHP-SHCC casted at tension side. The main parameters were thickness and the reinforcement ratio of UHP-SHCC layer with two different lengths of UHP-SHCC layer. The test results showed that using UHP-SHCC layer is a highly effective technique to increase the flexural capacity and the ductility of RC beams. As the reinforcement ratio of the layer increased, the flexural capacity increased. The flexural capacity of the beams with a layer length of 75% beam span was less than the capacity of the beams having a layer length equal to the beam span. Analytical and numerical results agreed with the experimental results.

Experimental Study on Effect of Recycled Reinforced Concrete Waste on Mechanical Properties and Structural behaviour of the Sandy Soil

Ali Basha,Fatma khalifa,Sabry Fayed 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.6

In recent years, constructing natural aggregates as a base layer for the roads has increased. Natural resources will run out as long as human consumption of them continues. Recycled concrete aggregate (RC) has thus emerged as a substitute material for the building of road base layers. Additionally, RC can be utilized to create interior city highways. The base layer for roads must have sufficient strength to support the working load on the pavement surface without damage deforming. As a result, the focus of this paper is on enhancing the structural performance of sandy soil reinforced with various RC percentages. The three key factors are relative soil density (Dr = 83 and 97%), recycled concrete aggregate reinforcing levels (RC = 0,5,10,15,20,25,30,40,50 and 100%), and reinforcement layer thickness (Rd = 0.0B, 0.5B, B, and 2B where B is the footing model width). Numerous laboratory experiments were conducted in order to examine the impact of important parameters on the properties of the mixtures. The plate bearing tests were carried out using a footing model (250 × 250 mm) inside a tank (1500 × 1500x1000 mm) to ascertain the stress–strain response, bearing capacity ratio (BCR), ultimate bearing capacity, and modulus of elasticity of the tested mixtures. It is clear that raising the RC has no effect on the diameters of the grains. It was found that as RC increased, the mixture's bulk density increased but specific gravity decreased. Maximum dry density rose as RC rose, whereas water content fell. It was noted that BCR unquestionably increased as RC increased for all RC levels and all values of settlement ratios. The appropriate reinforcing layer thickness is suggested to be no more than 2B. As the RC concentration in the sand and Rd increased, the difference between two pressure-settlement curves of densities 83% and 97% significantly decreased. Furthermore, when RC reaches 50%, two curves are roughly comparable. At RC = 50%, it is advised that the relative density of 83% is sufficient to produce the same behavior as the relative density of 97%. It was found that as RC and Rd grew, the tested mixtures' ultimate bearing capacity and elasticity modulus increased as well. A novel proposed formulas are developed to compute bearing capacity ratio, ultimate bearing capacity, and elasticity modulus of the tested mixtures taking into account the influence of RC, reinforcement layer depth, settlement ratio, and the relative density, and its results agree with the experimental results.