10 research outputs found
Interaction Strength of Hanger and Horizontal Steel Reinforcement of Dapped End Beams
No full textThe dapped end beam members have a special end with low depth at the support area, which results in a weak area against shear stresses. Classical structural analysis doesn't capture the precise steel reinforcement interaction at the dapped zone area. The main objectives of this study are to investigate the strength of the dapped end area and to analyze stresses in the steel reinforcement to evaluate the shear failure mechanism at the re-entrant corner. The experimental tests conducted on RC beam samples, in addition to the numerical simulation of these samples by a finite element program, have been compared with a mathematical model. The experimental program highlighted the strains in the steel reinforcement in the dapped region to calculate the magnitude of the stresses in the steel reinforcement. In the experimental program, six dapped beams were fabricated with a length of 3 m, a width of 150 mm, and a depth of 300 mm. The notched end has a 150-mm depth and 150-mm height. These beams were loaded by a concentrated load near support to investigate the shear strength capacity. From the results for steel reinforcement strain, it is found that hanger and horizontal steel reinforcements interact to provide dapped end shear strength. The study proposes a new approach to computing shear strength capacity at the re-entrant corner by adding the contributions of the horizontal and hanger steel reinforcement using an appropriate proportion strain factor. This method revealed greater carrying capacity for the dapped end beam compared with other common structural methods. The results of the numerical analysis were done by the ABAQUS finite element program, showing the same behavior as the experimental work. This study proved the common contribution of hanger and horizontal re-entrant corner steel reinforcement and proposed a new formula to determine the updated nominal shear strength. Doi: 10.28991/CEJ-2023-09-12-015 Full Text: PD
Torsional Behavior of CFRP Strengthening of SCC Box Beams with Web Openings under Repeated Loading
No full textMonotonic and repeated torsional loading frequently occur in many concrete structures. The loading and unloading action of repeated torsion places structures under greater damage and risk of failure than other types of loading. Therefore, keeping old infrastructure maintained, repaired, and upgraded has become an important priority and requirement. In this research, experimental work was done on pre-cracked self-compacted reinforced concrete box beams repaired (strengthened) with CFRP sheets to investigate the effect of web openings and CFRP sheets on the torsional behavior of tested specimens. Two groups of sixteen half-scale CFRP-strengthened RC box beams with different numbers of circular openings in the web, with a diameter of about 30% of the hollow box depth, were investigated. The first group (I), tested under monotonic torsional loading, comprised four unstrengthened RC beams and another four beams strengthened with CFRP strips, whereas the second group (II) consisted of the same details as the first one tested under repeated loading. The range of the repeated loading was about 30% and 60% of the ultimate load of the monotonic tests. The effect of opening and repairing (strengthening) with CFRP on the ultimate and cracking Torques, Torque-Twist Angle, steel strains, and modes of failure were displayed and discussed. Cracking and ultimate torques and the angle of twist of the tested beams were significantly reduced due to openings in the web, accompanied by increased values for the steel strains due to the presence of openings. However, the results showed that using CFRP strengthening techniques increased torsional strength, angle of twist, and decreased steel strain for all the tested beam specimens. Results revealed that repeated loading causes inelastic deformations in proportion to the number of loading cycles, more than static load deformations. Doi: 10.28991/CEJ-2023-09-12-06 Full Text: PD
Effect of Openings on the Torsional Behavior of SCC Box Beams Under Monotonic and Repeated Loading
No full textRepeated Torsional loading occurs in many concrete structures, such as offshore structures, freeways, multistory parking garages, and other structures; however, repeated torsional loading is still poorly understood. This study aims to investigate the effect of openings on the ultimate and cracking torques, angle of twist, and modes of failure of self-compacted R.C. box beams under monotonic and repeated loading. Two groups of eight half-scale box beams with different numbers of circular openings in the web with a diameter of about 30% of the hollow box dimension were investigated. The first group (I) included four beams: one was the control box beam without openings, whereas the rest of the beams were hollow with one, two, or three openings in the web tested under monotonic loading. The second group (II) consisted of the same details as the first one tested under repeated loading. The range of the repeated loading was about 30% and 60% of the ultimate load of the monotonic tests. The study showed that the cracking and ultimate torques and the angle of twist of the tested beams were significantly reduced due to openings in the web. Results revealed a more pronounced effect for monotonic loading, with a maximum reduction of 20% and 26.8% in cracking and ultimate torsional strength, respectively, compared to monotonic loading. Moreover, results revealed that repeated loading causes inelastic deformations in proportion to the number of loading cycles. Doi: 10.28991/CEJ-2023-09-09-015 Full Text: PD
Behavioral Investigation of Reinforced Concrete T-Beams with Distributed Reinforcement in the Tension Flange
No full textCurrent design codes and specifications allow for part of the bonded flexure tension reinforcement to be distributed over an effective flange width when the T-beams' flanges are in tension. This study presents an experimental and numerical investigation on the reinforced concrete flanged section's flexural behavior when reinforcement in the tension flange is laterally distributed. To achieve the goals of the study, numerical analysis using the finite element method was conducted on discretized flanged beam models validated via experimentally tested T-beam specimen. Parametric study was performed to investigate the effect of different parameters on the T-beams flexural behavior. The study revealed that a significant reduction in the beam flexural strength with increasing deflection is encountered as a sizable percentage of reinforcement is distributed over the wider flange width. The study recommended that not more than 33% of the tension reinforcement may be distributed over an effective flange width not wider than ℓn/10. This result confirms and agrees well the ACI 318 limit on the effective width to be less than ℓn/10
Structural Behavior of Prestressed RC Dapped Beam with Openings Strengthened Using CFRP Sheets
No full textThis research examines the strengthening efficiency of prestressed concrete dapped end beam with opening under monotonic point load. The study concerns with the position of the opening relative to the dapped end, the shape of opening, as circle or square, in addition, the effect of CFRP strengthening around the opening. The experimental program consisted of testing nine scaled down prestressed concrete dapped end beam specimens with single opening near the dapped end. Beam specimens consisted of one control beam and the remaining eight beams classified into two groups. The first group contained four unstrengthened specimens, whereas the second group included beams with opening strengthened using CFRP sheets. A full wrapping configuration for the opening region was adopted in this research. The results presented the detrimental influence of the openings on the shear strength of the dapped beam and the additional strength achieved from strengthening. This study concludes that the shear strength of the prestressed dapped beam decreased by the presence of openings in the web with maximum reduction about 20% when the opening was located close the dapped end. Based on the test results, the strengthened beams recovered significant part of their original load carrying capacity. Generally, prestressed dapped beams regain a maximum of 92% of their strength when openings with different configurations and locations were strengthened with full CFRP wrap
Enhancing Post-Fire Performance of Lightweight RC Slabs Using Expanded Polystyrene and Steel Fibers: An Experimental Study
No full textAggregate significantly influences the mechanical properties of concrete material and has a crucial role in post-fire behavior. This research focuses on investigating the post-fire behavior of a fiber-reinforced one-way slab made from lightweight expanded polystyrene (EPS) aggregate concrete. The experimental study consisted of testing fourteen fiber-reinforced self-compacting concrete (SCC) one-way slabs with EPS as a partial replacement of coarse aggregate. All specimens have identical dimensions of 1800×500×125 mm. The main parameters investigated included fire exposure, EPS replacement ratio, and steel fiber content. The tested specimens were divided into two groups. The first group included seven specimens tested under monotonic static load, whereas the seven specimens of the second group were tested under monotonic static load after being exposed to a steady-state temperature of 700°C for one hour. Following exposure to fire, results revealed a dramatic decrease in the structural performance of the slab specimens, including cracking load, ultimate load, stiffness, absorbed energy, and ductility, especially for the non-fibrous lightweight samples. However, adding EPS beads in the concrete mixture helps in reducing strength degradation due to fire exposure, and the higher the EPS content, the less strength degradation. This result exposed the positive impact of EPS on the structural performance of RC lightweight slabs exposed to fire due to their thermal properties. Moreover, results revealed a significant enhancement in post-fire stiffness, ductility, and absorbed energy of the RC slab due to steel fiber inclusion, showing their constructive impact on the slab performance
Geometric Nonlinear Synthetic Earthquake Analysis of Base Isolated Tall Steel Buildings Under Site-Specific Seismic Loading
No full textPre- and Post-Cracking Resistance of Steel Fiber Reinforced Concrete Flexural Members with GFRP Bars
No full textThis research investigates the pre- and post-cracking resistance of steel fiber-reinforced concrete specimens with Glass Fiber Reinforced Polymer (GFRP) bars subjected to flexural loading. The purpose is to modify the ductility and cracking resistance of GFRP-reinforced beams, which are prone to early cracking and excessive deflections instigated by the low modulus of elasticity of GFRP. Six self-compacting concrete specimens (1500×240×200 mm), incorporating steel fibers of two lengths (25 mm and 40 mm) with varying distribution depths, were tested to assess their structural performance. The results indicate significant enhancements in cracking resistance, stiffness, energy absorption, ductility, and flexural strength. Tested beams reinforced with 40 mm-long steel fibers exhibited a 23.9%–24.2% development in the ultimate moment capacity associated with the steel-reinforced specimens, whereas those with 25 mm fibers showed smaller increases (2.7%–3.1%). The cracking resistance improved by up to 33.3% in beams with 40 mm-long fibers and by 16.67%–20% in those with 25 mm-long fibers, associated with a non-fibrous GFRP specimen. Additionally, the inclusion of 40 mm hooked-end steel fibers significantly enhanced ultimate deflection, with peak deflections increasing by 30.2%–44.8% compared to steel-reinforced beams. Fibrous GFRP-reinforced beams exhibited up to 154% higher energy absorption under ultimate load than a non-fibrous GFRP beam. All fibrous GFRP-reinforced beams achieved deformation-based ductility indices between 4.2 and 6.9, exceeding the minimum threshold of 4 for adequate deformability. These findings confirm that incorporating 40 mm steel fibers significantly improves the structural behavior of GFRP-reinforced concrete specimens, offering valuable insights for optimizing their design
AI-Driven Shear Capacity Model of Steel Studs in Composite Structural Systems
No full textIn composite steel-concrete structures, shear connectors in the form of headed steel studs are commonly utilized to transfer longitudinal shear force developed at the interface between the two materials. To overcome the shortcomings of design codes, which frequently understate shear capacity and fail to take advantage of sophisticated computational methods, this paper presents an optimization attempt to estimate the shear strength of headed steel studs utilizing the Grey Wolf Optimizer (GWO) technique using MATLAB software. Data from 234 experimental tests are employed to identify and highlight key input parameters influencing the shear strength of headed steel studs. These key parameters include concrete compressive strength (f’c), diameter (D), and tensile strength of the steel stud shank (fu). After identifying and examining the limits of the experimental data, the proposed model has been developed using about 80% of the mixed raw dataset. The remaining 20% of the raw data is utilized to validate the proposed model. The predicted shear strength of headed steel studs closely matched the experimental results. This research offers an innovative strategy to measure the steel stud's shear capacity employing GWO, showing the current code's limitations. The GWO model showed excellent accuracy in predicting the shear strength with an R-value of 0.9922, indicating that the predicted value is in good agreement with experimental observations. Interestingly, the model's mean absolute error with 100 wolves in the GWO method was only 7.51%, showing the proposed model provides an improvement in shear capacity forecasting for practical structural engineering applications
Color Masking Ability of Guided Enamel Regeneration with a Novel Self-Assembling Peptide and Resin Infiltration on Artificial Enamel Lesions Under Various Challenges: An In Vitro Spectrophotometric Analysis
No full textThe color masking ability of resin infiltration (RI) and curodont repair fluoride plus–self-assembling peptide (CRFP-SAP) was investigated under various simulated oral challenging conditions. Sixty-four extracted caries-free human canines were randomly divided into two groups: Group 1 (RI) and Group 2 (CRFP-SAP). The baseline color values of samples were recorded using a spectrophotometer (VITA Easyshade® Advance 4.0 VITA Zahnfabrik, Bad Sackingen, Germany). The samples were stored in a demineralization solution for 4 days to induce artificial enamel lesions (AELs). The AELs of Groups I and II were treated with RI (Icon, DMG, Hamburg, Germany) and CRFP-SAP (vVARDIS, Zug, Switzerland), respectively, followed by color measurements. Each group was subjected to challenges such as remineralization, pH cycling, staining, and thermocycling, followed by color measurements. The difference between the mean ∆E (color difference value) of sound enamel and both treatment groups was less than 3.7 1-week post treatment. Meanwhile, the difference between the mean ∆E of RI-treated samples and all kinds of challenges was more than 3.7, while for the CRFP-SAP-treated samples, it was less than 3.7 for all kinds of challenges, except for the thermocycling, for which the mean ∆E difference was 4.3. RI and CRFP-SAP treatments were effective in masking the discoloration caused by AELs. However, the color was not stable for RI-treated samples, whereas it was stable for CRFP-SAP-treated samples under all challenges, except for thermocycling
