Concrete Compressive Strain Research Articles

Performance of Reinforced Concrete Flat Slabs Having GFRP Gratings

A thorough study of the literature indicated that there is not much relevant research on the application of GFRP gratings. Otherwise, extensive study has been done on FRP bars, laminates, sheets, strips, and rods. This study proposes a novel approach to improve the punching shear resistance of flat slab column connections by inserting GFRP gratings across the slab thickness. The results of seven specimens tested under vertical static loading are presented, considering the influence of the grating’s characteristics. All specimens were tested as simply supported slabs under one point of static loading. Experimental results, including crack patterns, slab deflection, concrete compressive strain, tensile steel strain, GFRP grating strain, and failure load, were recorded using extensive electric instrumentation. Test results revealed an enhancement in the failure load ranging between 9.03% and 27.67% for the specimens provided with the GFRP grating. In addition, a nonlinear finite element numerical model analysis was carried out using the ANSYS 15 program. Correlational studies based on the load-deflection response and crack patterns were utilized, resulting in a good agreement between numerical simulations and experimental results with differences ranging from 1.0% to 8.0%.

Experimental investigation of the dynamic mechanical properties of concrete under different strain rates and cyclic loading

To investigate the effects of strain rate and cyclic loading on the mechanical parameters of concrete compressive strength, residual strain, peak strain and elastic modulus, a series of cyclic loading tests over concrete were conducted by setting different numbers of cycles, magnitude factors, and cycle frequencies/periods based on the FST-1000 alpine geotechnical dynamic and static triaxial test system. The quantitative relationships between the mechanical parameters of concrete and the parameters of cyclic loading as well as the strain rate were also proposed. The results show that as the strain rate increases, the concrete compressive strength and elastic modulus increase linearly, while the residual strength and peak strain show a decreasing trend. Under cyclic loading, the compressive strength was quadratically related to each cyclic loading parameter, and the elastic modulus was quadratically related to the cyclic number and magnitude factor. The trend of the concrete compressive strength rate sensitivity undergoes a change at the specific thresholds of 0.145 for the magnitude factor and 1.93 Hz for the frequency. The minimum value of the peak strain rate sensitivity corresponds to the specific thresholds of 6023 for the number of cycles, 0.14 for the magnitude factor, and 1.38 Hz for the frequency thresholds, respectively. Additionally, the enhancement of the elastic modulus rate sensitivity occurs when the number of cycles exceeds 918 or when the magnitude factor surpasses 0.33. The results can provide a theoretical basis for the design of concrete structures and seismic engineering.

Comparative Study of and Voided Slab System and Conventional RCC Slab

This paper presents the flexural capacities of R.C.two-way hollow flat slabs with plastic voids. Recently, various types of slab systems which can reduce the self-weight of slabs have been studied as the height and span of building structures rapidly increase. To verify the flexural behaviour of this voided slab such as flexural stiffness, ultimate load, deflection, stresses and concrete compressive strain were studied.FEM model was created in ANSYS workbench 2022 for both conventional solid flat slab and voided slab. U-Boot beton from “daliform group building innovation Italy” was used as void former in this study. The dimensions of U-boot is 520×520mm and with 180mm and 160mm height. Dimension of FEM slab model is 8500×8500 mm with 500×500 column support at all four corners. Three different slab of 280mm, 300mm and 320mm was created. In addition, manual analysis of solid slab and voided slab was carried out using direct design method as per IS-456(2000). And further, design is checked to verify that it satisfies all design and serviceability criteria given as per IS-456(2000).Results obtain via theoretical calculation and FEM model simulation for both solid and voided slab were compared. The aim of this paper is to discuss and compare flexure behaviour of solid slab and voided slab and to study changes in inertia, stiffness and reduction in weight, of the slab by void formation.

Comparison of calculation models for flexural capacity of RC beams strengthened with TRC in China and Germany

AbstractThe new innovative composite material textile reinforced concrete (TRC) has been intensively investigated in Germany since the end 1990s. It has become increasingly important in the construction industry. Compared with conventional steel reinforcement, TRC has advantages such as higher load‐bearing capacity, higher strength‐to‐weight ratio, better ductility, and non‐corrosive behavior. This made them a subject of extensive research and diverse applications both nationally and internationally. In 2004, Xu et al. started research on bond properties of TRC in China in cooperation with Hans‐Wolf Reinhardt et al. from the University of Stuttgart in Germany. Since then, there have been numerous researches on TRC in China. This article introduces a calculation method for the flexural capacity of reinforced concrete (RC) beams strengthened with TRC in China. For comparison, the dimensioning procedure in Germany is also presented. Subsequently, the two models are compared with each other in a case study. Both models in China and Germany have the same mathematical background and also provide similar results. However, they have some differences in definitions of material characteristics (e.g., design concrete compressive strength, strain, and stress distribution) and consideration of the damage resulting from the preloading stage.

Compression behavior of GFRP reinforced hybrid fibre reinforced concrete short columns subjected to eccentric loading

This paper presents the results of an experimental study carried out on the GFRP reinforced hybrid fibre concrete short columns subjected to eccentric compression. In this study, hybrid fiber-reinforced concrete was prepared in different volume ratios of hybrid fibers and the cooperative effect of the GFRP reinforcement and the steel-PVA hybrid fibre concrete with different fibre ratios under eccentric loading was explored. 10 GFRP reinforced hybrid fibre concrete short columns and 2 plain reinforced concrete short columns were tested to investigated their eccentric compressive properties. The tests results are presented in terms of failure modes, longitudinal reinforcement strain, concrete compressive strain and compressive load capacity of GFRP reinforced hybrid fibre concrete eccentrically compressed short columns. The results show that the concrete on the compressed side was crushed when the specimen under both the initial eccentricity of 50 mm and 100 mm the reinforcement were pulled on the tension side of specimen under a larger initial eccentricity of 100 mm. The addition of fibres can effectively prevent the crack generation and development and improve the bonding property between reinforcement and concrete. Besides, the addition of steel fibre contributes a better performance on the ultimate compressive capacity of specimen under a lager initial eccentricity with an optimal ratio of steel fibre at 1.4 %. PVA fibre effectively improve the ductility of the concrete, so that the hybrid fibre concrete elements remain relatively its integrity after failure. Finally, considering the effect of GFRP reinforcement and different ratios of steel fibre and PVA fibre on the compressive capacity of short concrete columns, the equation for the calculation of the ultimate compressive capacity of partial sections of eccentric columns is proposed, and a good agreement was observed between the tested and calculated value.

Computational modeling and simulations for predicting the nonlinear responses of reinforced concrete beams

PurposeThe ultimate capacity and ductility behavior of a reinforced concrete (RC) beam generally depends on its constituent material properties. This study aims to use ANSYS to accentuate the nonlinear parametric finite element (FE) simulations of RC sections under monotonic loading.Design/methodology/approachThe concrete matrix and steel reinforcement are the primary constituent materials of RC beams. The material properties such as tensile reinforcement area, tensile bars yield strength, concrete compressive strength and strain rate in tensile reinforcement at nominal strength have significantly influenced the ultimate response of RC beams. Therefore, these intensive parameters are considered in this study to ascertain their effect on the RC beam's ultimate behavior. The nonlinear response up to the ultimate load capacity and the crack evolutions of RC beams are predicted efficiently.FindingsThe parametric study reveals that increasing the tensile steel reinforcements (from Ast = 213–857 mm2) significantly improves the ultimate load capacity by 229% and yield deflections by 20%. However, it declines the ultimate deflection by 47% and ductility by 56% substantially. Varying the strain limit (?tn = 0.010–0.0015) of tensile reinforcement has proficiently increased the ultimate load-resisting capacity by 20%, whereas the ductility declined by 62%. When the concrete strength increases (from fck = 25–65 MPa), the cracking load increases profoundly by 51%, whereas the ultimate capacity has found an insignificant effect.Originality/valueThe load-deflection response plots extracted from the proposed numerical model exhibit satisfactory accuracy (less than 9% deviation) against the experimental curves available in the literature, which emphasizes the proficiency of the proposed FE model.

Size effect on dynamic compressive failure mode and mechanical properties of recycled concrete

AbstractIn order to study the size effect behavior of recycled concrete under dynamic compression load, a meso‐scale model of recycled concrete was established. The particle size of coarse aggregate, replacement ratio of recycled coarse aggregate, and section size were used as parameters to explore the mechanical properties of recycled concrete under uniaxial dynamic compression load, such as failure mode, compressive strength, peak strain, and residual strength. The effects of strain rate, particle size of recycled coarse aggregate, and replacement rate of recycled coarse aggregate on the size effect of dynamic compression of recycled concrete were further analyzed. The results showed that under uniaxial dynamic compression load, the damage degree of recycled concrete deep and along with the change of the strain rate change, recycled concrete dynamic compression strength and strain rate were positively correlated. There is the critical strain rate is 1/s, which weaken the influence of the size effect, when the strain rate reaches 10/s, the dynamic compressive strength of recycled concrete increases with the increase of section size. At the same time, when the strain rate is high, the particle size of recycled coarse aggregate and the replacement rate of recycled coarse aggregate have little effect on the size effect behavior of recycled concrete.

Test and design of eccentrically-loaded slender circular tubed columns filled with high-strength concrete and reinforcement

The tubed-reinforced concrete (TRC) column is an original reinforced concrete column in which the stirrups are mostly replaced with the steel tube to enhance the confinement to the concrete core. In this study, the eccentrically-loaded behavior of slender circular TRC (CTRC) columns with high-strength materials was experimentally and numerically investigated. Six slender columns with high-strength concrete of 81 MPa and high-strength rebar of 583 MPa were tested to failure under eccentric loading, considering the main parameters of length-to-diameter ratio and load eccentricity. A three-dimensional finite element (FE) model was established and verified for conducting parametric studies and investigating the moment magnification and eccentricity magnification which reflect the second-order effect on the strength of slender columns. The results indicate that all columns fail in a bending mode and show good deformability, even with the use of high-strength materials, and the strength of high-strength rebars can be fully utilized due to the enhanced concrete compressive strain and ductility. Based on the test results and parametric study, a design method is proposed to assist designers to evaluate the load capacity of slender CTRC columns.

Effect of polyethylene terephthalate fibres on the structural performance of reinforced concrete beams with openings in the shear region

The provision of transverse openings in the shear region of beams to allow passage of services reduces the cracking and ultimate load capacities of the beams and increases deflection under the openings, especially when the size of the opening exceeds 25 % of the overall beam depth. Strengthening of the pre-planned opening regions by use of special steel reinforcements causes reinforcement congestion and difficulties in compaction, calling for alternative ways of strengthening beams with openings. In this study, concrete material was modified by the use of Polyethylene Terephthalate (PET) fibres produced from waste plastic bottles to improve the tensile properties and hence reduce the cracking around the openings and improve the overall performance of the beams. To evaluate the performance of PET fibres in beams with openings, eight (8) reinforced concrete beams with and without fibres of dimensions (150 × 250 × 2000 mm) were cast with varying opening sizes. The horizontal position of the openings was fixed at 300 mm from the support while the vertical position was maintained at the mid-depth of all beams. This performance was evaluated in terms of ultimate and first cracking loads, mid-span deflections, ductility, crack patterns and failure modes, and strain behavior. Test data showed that incorporating PET fibres in beams with openings resulted in a slight increase in ultimate load of 4.1 % and 5.82 % for 0.25 h and 0.35 h beam opening sizes respectively, beyond which the strength was reduced by 9.57 % for beams with 0.45 h opening size, where h was the overall depth of the beam. The first cracking loads increased by 44.12 %, 48.48 %, and 9.38 % for 0.25 h, 0.35 h, and 0.45 h opening sizes, respectively. In addition, a slight improvement in the ductility of PET fibre beams for all opening sizes was observed. The PET fibre beams exhibited a slight change in the mode of failure from dominant shear failure to combined shear and flexure failure characterized by multiple cracks in the flexure region with minimal spacing. An increase in the concrete compressive and tensile strains accompanied by a reduction in concrete and steel shear strains was observed because of the tension stiffening effects of the fibres. The incorporation of PET fibres, therefore, showed a slight improvement in the ultimate performance of beams with 0.25 h and 0.35 h opening size, with no improvement for the control beam and 0.45 h opening sized beam. However, a significant improvement in the serviceability performance for all PET reinforced beams was observed.

Investigation of Nonlinear Behavior of the Reinforced Concrete Columns for Different Confined Concrete Models

Stress-strain and moment-curvature behavior of the reinforced concrete (RC) square columns have been analytically investigated according to different confined concrete models. The effect of transverse reinforcement diameter, transverse reinforcement spacing and concrete grade on the behavior of RC column models were investigated. For different confined concrete models, the confinement effectiveness coefficient, effective lateral confining stress, confined concrete compressive strength, strain at maximum concrete stress and ultimate concrete compressive strain values were calculated. In the second part, a parametric investigation was carried out for examining the effects of different design parameters on the moment-curvature relationships. Analytical moment-curvature relationships were obtained for RC cross-sections by using the TBEC (2018), Mander model (1988), Saatcioglu and Ravzi (1992) confined concrete models. The effects of the design parameters on the RC square column behavior were evaluated in terms of moment capacity and the curvature of the cross-section. In RC column models, stress-strain and moment-curvature relationships are obtained and compared according to different parameters. Confined concrete strength and the ultimate moment values obtained from the Mander model were higher than the Saatcioglu and Ravzi model when the transverse reinforcement close to the minimum spacing values. The results obtained from the Mander model and TBEC (2018) are close to each other.

The Design of Concrete Beams Reinforced with GFRP Bars Based on Crack Width.

Since glass fiber-reinforced polymer (GFRP) bars have a lower modulus than steel bars, the design of GFRP-reinforced concrete (GFRP-RC) is often governed by the serviceability limit state (deflection and cracking) rather than the ultimate state. A new design method has been proposed in this paper for GFRP-RC beams based on the flexure crack width. The state when the maximum flexure crack width in the tensile zone reaches the limit of 0.5 mm specified by ACI 440.1R-15 was used as the design limit state. The concrete compressive strain at the extreme compression fiber of concrete under the design limit state was obtained by four-point bending tests of eight full-scale GFRP-RC beams and finite element analysis. Based on the concrete compressive strain under the design limit state and cross-sectional analysis, a design method for calculating the longitudinal reinforcement ratio of GFRP-RC beams under the design limit state is proposed. This design method is proven to be feasible by the experimental and the finite element results. In addition, the flexural capacity coefficient was discussed to investigate the safety reserve of the design method.

Flexural behaviour of concrete-basalt FRC beams with steel bars under concentrated load

In this work, the experimental investigation and theoretical analysis on the flexural behavior of steel-reinforced concrete-basalt fiber reinforced concrete (RC-BFRC) beams were conducted. The formulae for calculating the cracking, yielding and ultimate moments, and the deflection of RC-BFRC beams were proposed and validated through experiments. Experimental results demonstrated significant enhancement in load-carrying capacity, deformation ability, and crack resistance for the RC-BFRC beam compared with the ordinary reinforced concrete (RC) beam. And the ultimate deflection of the RC-BFRC beam was slightly smaller than that of the steel-reinforced basalt fiber reinforced concrete (RBFRC) beam at the same fiber content. To gain a deeper understanding of the flexural performance of the RC-BFRC beam, a parametric study was also conducted based on the proposed methods. The results indicated that yield and ultimate moments increased but ultimate curvature in case of under-reinforced failure decreased with the increase of yield strength and amount of steel reinforcement. In case of under-reinforced failure, curvature ductility and energy dissipation of the whole stage decreased with the increase of yield strength and amount of steel reinforcement but increased with the increase of concrete compressive strength and concrete ultimate compressive strain.

Flexural Strength of Concrete Beam Reinforced with CFRP Bars: A Review.

Conventional reinforced concrete (RC) structures are commonly associated with the corrosion of steel reinforcement. The application of carbon fiber reinforced polymer (CFRP) bars as flexural reinforcement has become a new promising option. This paper presents a state-of-the art flexural strength on concrete beams reinforced with CFRP bars. Concrete compressive and CFRP bar tensile strain, reinforcement ratio, types of surface treatment on CFRP bar and concrete compressive strength were identified as aspects of behavior. Significant findings in the literature had manifested all aspects of behavior that were affecting the flexural strength, deflections and crack characteristics of CFRP RC beams. In addition, the experimental result on 98 specimens of CFRP RC beams from the literature show that ACI 440.1R-15 and CSA S806-12 standards underestimate the ultimate flexural moment capacity of CFRP RC beams. On the other hand, Kara and Ashour predictions are more accurate with the experimental values. Moreover, hotspot research topics were also highlighted for further considerations in future studies.

Modified Time-Dependent Model for Flexural Capacity Assessment of Corroded RC Elements

The corrosion of embedded steel bars in concrete is one of the severe deterioration processes that can escalate the risk and reduce the durability and lifetime of concrete structures. Based on the literature, simultaneous corrosion of longitudinal and transverse bar is considered to estimate section capacity. In this research, a flexible multi-stage approach is proposed to differentiate between corrosion levels on longitudinal and transverse reinforcement based on their corrosion initiating time. The result indicated that the multi-stage approach provides higher capacity and curvature for the sections. A significant reduction in reinforced concrete (RC) sections’ ductility after corrosion of confining bars and before starting corrosion of longitudinal rebars was observed, which illustrates the importance of stirrups corrosion effects on the sections’ ductility. In the higher values of corrosion intensity, confined concrete’s ultimate strain tends to reach the unconfined state. Using the energy-based method of calculating ultimate concrete compressive strain instead of approximate methods, a higher value of curvature ductility of corroded RC cross-sections is obtained.

Concrete compressive strain behavior and magnitudes under uniaxial fatigue loading

Recent advances in concrete technology and construction have promoted an increasing utilization of concrete in fatigue-critical structures, such as wind turbine towers. While research into concrete fatigue is not a new topic and has been going on for several decades, a large majority of this research has primarily been focused on the determination of concrete fatigue capacity. However, understanding and advancing concrete fatigue behavior (e.g., fatigue stress vs. strain response) has received limited attention, even though this is also crucial, especially considering the inherently nonlinear behavior of concrete. To address this knowledge gap and further advance our understanding of concrete fatigue behavior, an experimental investigation consisting of uniaxial compressive fatigue testing of concrete cylinder specimens until failure was undertaken, and axial strains were recorded throughout the duration of fatigue loading. The behavior and evolution of concrete axial strains, including the rate of accumulation of strains, through the fatigue loading process were extensively analyzed and are reported. Additionally, the influence of key parameters, such as peak stress levels and number of cycles to failure, on peak strain evolution were investigated and are described. Magnitudes of peak axial strain at the end of the stable strain accumulation phase, as well as at failure, are also reported, and recommendations are made for estimating strain magnitudes at these critical junctures when conducting fatigue analysis and design. The results will help advance the understanding of concrete axial strain behavior under compressive fatigue loading. The results also provide guidelines for estimating the magnitudes of concrete strains under fatigue loads, which in turn will be beneficial to designers, as it allows them to also consider structural performance during the analysis and design of fatigue critical concrete structures.

Flexural behavior of concrete beams cast with high-performance materials

The use of ultra-high strength concrete (UHSC) is advantageous in construction. In fact, a combination of UHSC with regular reinforcement steel still has problems with corrosion after years in service, typically in exposed structures. This effect is more profound by climate changes (i.e., extensive heat waves or unexpected long and cold winter). This research investigates the flexural performance of concrete beams, cast with UHSC and high-performance reinforcement (HPR) steel; which is characterized by its high-strength and high-corrosion resistance. The testing matrix consisted of 8 concrete beams, cast with UHSC and high-strength concrete (HSC), in combination with ASTM A1035 Grade 830 steel and ASTM A615 Grade 420 steel. For each flexural test, along with measuring the applied loading and deflection, the variation in concrete compressive strain and steel tensile strain were monitored through a number of strain gauges. Experimental results revealed that Grade 830 can enhance the flexural capacity by 33% as compared to Grade 420 steel. On the other hand, UHSC can enhance the flexural capacity by 11% and decrease the concrete strains by up to 26% as compared to HSC.

TBDY 2018 Ve Mander Modeline göre Sargılı Betonun Gerilme-Şekil Değiştirmesinin Araştırılması

In this study, stress-strain relationships for confined reinforced concrete columns were investigated according to TBEC 2018 and Mander models. For the proposed confined concrete models, the lateral confining stress on core concrete, the compressive strength of confined concrete and stress-strain relations in the confined concrete were investigated. In order to better understand the behavior of the confined concrete, stress-strain relations and information about the confined concrete models are given. To investigate the behavior of confined concrete, square cross-section reinforced concrete column models with different transverse reinforcement diameters and transverse reinforcement spacing have been designed. The effect of the diameter and spacing of the transverse reinforcement on the confined concrete compressive strength was investigated. Stress-strain relations of square cross-section columns were investigated by considering the different confined concrete models. The stress-strain curves were obtained by calculating the confined concrete compressive strengths and strain at maximum concrete stress in the square cross-section column models designed. The results obtained from the analysis results were compared and interpreted according to different parameters. Results obtained with TBEC 2018 and Mander model were compared and interpreted. It has been concluded that the use of transverse reinforcement with different diameters and spacing in the models affects the lateral confining stress on core concrete from transverse reinforcement and compressive strength of confined concrete in reinforced concrete column sections designed with different parameters.

Effect of boundary element confinement configuration on the performance of GFRP-Reinforced concrete shear walls

Recent advances in reinforcing lateral-load resisting systems with glass-fiber-reinforced-polymer (GFRP) bars have highlighted the need for farther experimental investigations. With the elastic behavior of GFRP-bars, ensuring sufficient plastic deformations become challenging. The current study presents the experimental work performed on six full-scale GFRP-reinforced concrete shear walls with boundary elements. The mid-rise building shear walls were tested under reversed quasi-static cyclic loading, with an emphasis on how varying the configuration of the boundary-element confinement would influence their strength and deformation performance. Two shear walls had boundaries reinforced with square GFRP spiral stirrups, while a third had boundaries reinforced with circular GFRP spiral stirrups. The remaining three shear walls had higher confinement in the boundary elements; one had a square GFRP spiral stirrups embedded inside rectangular GFRP spiral stirrups. The second had a rectangular GFRP spiral stirrups with two GFRP ties in the middle, and the third had two square spiral stirrups overlapped side-by-side. The overall performance of each specimen was characterized by investigating the hysteretic response, the cracking patterns, the drift ratio, the strength capacity, and the behavior of energy dissipation. Also, the strain progressing in the longitudinal, horizontal, stirrups, and concrete was investigated. The obtained results demonstrate that increasing the confinement level in the boundary elements enhanced deformation capacity and increased the overall strength of the GFRP-reinforced shear walls by developing a higher level of concrete compressive strains and a better distribution of shear deformations over the height.

Seismic Fragility of Ordinary Reinforced Concrete Shear Walls with Coupling Beams Designed Using a Performance-Based Procedure

The seismic performance of ordinary reinforced concrete shear walls, that are commonly used in high-rise residential buildings in Korea (h < 60 m), but are prohibited for tall buildings (h ≥ 60 m), is evaluated in this research project within the framework of collapse probability. Three bidimensional analytical models comprised of both coupled and uncoupled shear walls exceeding 60 m in height were designed using nonlinear dynamic analysis in accordance with Korean performance-based seismic design guidelines. Seismic design based on nonlinear dynamic analysis was performed using different shear force amplification factors in order to determine an appropriate factor. Then, an incremental dynamic analysis was performed to evaluate collapse fragility in accordance with the (Federal Emergency Management Agency) FEMA P695 procedure. Four engineering demand parameters including inter-story drift, plastic hinge rotation angle, concrete compressive strain and shear force were introduced to investigate the collapse probability of the designed analytical models. For all analytical models, flexural failure was the primary failure mode but shear force amplification factors played an important role in order to meet the requirement on collapse probability. High-rise ordinary reinforced concrete shear walls designed using seven pairs of ground motion components and a shear force amplification factor ≥ 1.2 were adequate to satisfy the criteria on collapse probability and the collapse margin ratio prescribed in FEMA P695.

Nonlinear 3D finite element simulation of CFST columns under different confined concrete material’s models

Nowadays everything expands rapidly and growth with time, including the service structures to accommodate an acceptable level of service to the community. The concrete filled steel tubes is a new technique that provides some features compared with the normal concrete columns.in this study three concrete compressive stress strain models behavior have been studied to validate the adopted experimental work and find the best model that can simulate the actual data, using nonlinear finite element analysis in Abaqus. Then, three type of concrete strength where considered (C25, C40, and C60) with three Diameter of tube thickness ratios are; 165,100, and 50 for each concrete class type. Tests results have shown that the confinement effect in high strength concrete was higher than other types of concrete types, in addition to a noticeable enhancement in the ductility behavior. The adopted model was able to capture concrete compressive behavior accurately, for all curve’s stages.