Strain Of Longitudinal Reinforcement Research Articles

The Effect of Concrete Cover Thickness on the Torsional Resistance of Fibrous, High-strength, Under-reinforced Concrete Beams

This study focuses on the role of concrete cover in enhancing the torsional resistance of peak load in under-reinforced fibrous high-strength concrete beams. In this study, the primary variable that varied from 17 mm to 53 mm was the concrete cover thickness. Four rectangular solid beams were cast and tested to determine the effect of concrete cover thickness on the behaviour of under-reinforced fibrous, high strength concrete beams subjected to pure torsional loading. The test results revealed an 80.6% improvement in the torsional resistance at peak load. In addition, at maximal loads, the twisting angle, shear strain in concrete, transverse reinforcement strain, and longitudinal reinforcement strain were reduced by 70.2%, 90%, 50.6%, and 34.5%, respectively. It is therefore possible to draw the conclusion that the concrete cover has a new function, which is an improvement in torsional resistance at ultimate load that is in addition to protecting the reinforcement from corrosion.

Experimental Study on Flexural Performance of Recycled Steel Fiber Concrete Beams

We sorted the waste from mechanical processing to form recycled steel fibers. In order to study the flexural mechanical properties of reinforced concrete beams after the addition of recycled steel fibers, four recycled steel fiber concrete beams (RSFCBs) and one normal concrete beam (NCB) were designed and poured using the volume fraction of steel fibers (0%, 0.5%, 1%, 1.5%, 2%) as the variables. Normal section bending tests were conducted on them under a concentrated load. We obtained experimental data such as the cracking load, ultimate load, mid-span deflection, and steel and concrete strain of the beam by gradually loading the test beam, and we observed and recorded the development of cracks. The results indicate that the NCB exhibits crushing failure, while the RSFCBs exhibit equilibrium failure. The addition of recycled steel fibers effectively controls the extension of cracks, resulting in a better bending toughness of the beam. The bending performance of RSFCBs with different volume additions shows a trend of first increasing and then decreasing with the increase in steel fiber content. The peak value was reached when the steel fiber content was 1.5%, which increased the bending bearing capacity by 54.72% compared with the NCB. With the increase in steel fiber content, the required load value for tensile steel bars to yield also increases, reaching a peak at a content of 1.5%, which increases the bending bearing capacity by 44.64% compared with the NCB. The addition of recycled steel fibers enables the beam to improve its bearing capacity while limiting the development of longitudinal reinforcement strain, allowing the longitudinal reinforcement to yield under higher loads and improving the overall bending performance of the beam.

Experimental Study on Structural Performance of Cast-in-Place Frame Printed Concrete Wall

A growing number of nations and regions have printed concrete structures thanks to the application of 3D printing technology in the field of civil engineering. However, the houses built with printed concrete are mostly printed concrete wall structures with composite load-bearing walls and cast-in-place frames. This structure solely takes into account the performance of the structure under vertical loads, which does not address its ability to withstand horizontal loads. In this paper, wall specimens were designed and tested under horizontal reciprocal loads in order to investigate the structural performance of this cast-in-place border-frame printed concrete wall structure under horizontal loads. Four factors are examined in order to determine how well the cast-in-place frame printed concrete wall structure performs when subjected to horizontal loads: column longitudinal reinforcement strain, hysteresis curve, skeleton curve, and energy dissipation capacity. According to the test results, the addition of the wall increased the bearing capacity and accumulated energy dissipation of the specimen, but the increase in stiffness also caused the structural ductility to decrease. As a result, cracks were more likely to generate at the wall–column joints, so the stiffness matching between the printed concrete wall and the cast-in-place side frame needed to be further coordinated to obtain a higher ductility. It turns out that the wall sections have little impact on the seismic performance of the members.

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.

Experimental studies on tensile behavior of reinforced engineered cementitious composite members with double steel rebars

AbstractThis paper investigates the tensile behavior of reinforced engineering cementitious composite (ECC) members. Twelve reinforced ECC members were tested in uniaxial tension. The stress‐average strain curves, failure modes, and the strain of longitudinal reinforcement at selected sections were obtained during testing. The influence of reinforcement ratio on the load resistance and deformation capacity of members was determined. Test results showed that the tensile behavior of reinforced ECC members could be divided into three stages, namely, the elastic stage, the microcracking stage and the major cracking stage. ECC significantly contributed to the load resistance of reinforced ECC members before the formation of major cracks through tension stiffening effect. The load capacity and deformation capacity of reinforced ECC members increased with the increase of reinforcement ratios. For members with ungrooved steel bars, the ultimate load and ultimate strain increased by 130.0% and 115.2% with the reinforcement ratio increased from 1.01% to 2.26%. For members with grooved steel bars, the ultimate load and ultimate strain increased by 123.6% and 98.7% with the reinforcement ratio increased from 0.78% to 2.04%. Based on the test results, the failure mechanism of reinforced ECC members was analyzed and equations for predicting the load capacity of members were proposed. Comparisons between experimental and calculated load capacities suggested that the calculated results were in good agreement with the experimental values. The study on the tensile behavior of reinforced ECC members provides useful results for the design and application of reinforced ECC members.

Numerical analysis of reinforced concrete columns strengthened with sleeve wedge bolts and a self compacting concrete layer

With the development of technology in the field of structural analysis, it has now become possible to computationally model more complex structures, each with its own peculiarity, such as those with structural reinforcement. With regard to the non-linear analysis of structural elements in reinforced concrete, the Finite Element Method is ideal, since it is only possible with the use of computational resources. For columns subjected to flexion compression, elements that are highly susceptible to second-order effects and which have as an important function the global stability of buildings, software for numerical analysis, such as ATENA, become especially applicable for the study of behavior structural of these elements. Marques et al. (2015) carried out a study on the performance of columns reinforced through casing with self-compacting concrete and wedge bolts applied to prevent slipping between these materials. Based on this study, then, in this work, 5 numerical models were developed in the ATENA software: PO, PR, P150-18, P150-26 and P75-50. The first two are references (original column and reference column, respectively), while the others are reinforced, whose nomenclature distinguishes them in terms of the quantity and disposition of wedge bolts on the compressed face of the element. The relationships and parameters that allowed the analysis of the models were: rupture load versus displacement, specific strains in longitudinal reinforcement, cracking and stresses in wedge bolts at failure. Good results were obtained, both with regard to the variation between the experimental results and those obtained numerically, and for the performance of the structural reinforcement technique, which represents the reliability of the computational modeling and the adopted methodology. The variation between such results respected the 15% limit established by the comments of the ACI 318 (2011) standard, with the exception of the PO, and the reinforcement technique, in turn, resulted in the growth of the initial strength of the column in its original condition (PO). The present study allows, therefore, to guarantee and disseminate the application of numerical simulation for the analysis and design of reinforced concrete elements.

Seismic performance and flexible connection optimization of prefabricated integrated short-leg shear wall filled with ceramsite concrete

A new type of prefabricated integrated shear wall that can be integrally prefabricated in a factory and assembled during construction can significantly improve the assembly rate of prefabricated shear wall structures and effectively reduce energy consumption. In this study, three integrated shear walls with ceramsite concrete infill walls were constructed, and their pseudo-static tests were conducted under cyclic lateral loading. The failure mode, bearing capacity, stiffness, ductility, and energy dissipation capacity of the three specimens were obtained. The test results showed that bending failure of the wall limbs and bending–shear failure of the coupling beams occurred under a horizontal seismic action on the prefabricated integrated shear walls. Moreover, as the heights of the coupling beams increased, the failure form of the infill walls changed from corner failure to overall bending–shear failure. In the finite element (FE) analysis conducted using the ABAQUS platform, the prefabricated integrated shear wall specimens, loading rigid beams, and bottom beams were modeled in detail by discrete models. The hysteretic curve, failure mode, and longitudinal reinforcement strain of the wall limbs obtained using the FE model were in good agreement with the results of the pseudo-static tests, verifying the accuracy and applicability of the modeling method proposed in this paper. Finally, based on numerical simulation, the structural form between the infill walls and wall limbs was studied, and a structural optimization scheme of a flexible connection was proposed. The effects of the lengths of the infill walls, section heights of the shear wall limbs, and strength of ceramsite concrete on the seismic performance of the prefabricated integrated shear walls were also examined by numerical simulation.

Seismic Performance Test of Double-Row Reinforced Ceramsite Concrete Composite Wall Panels with Cores

The research objective of this study was the seismic performance of double-row reinforced ceramsite concrete sandwich wall panels. The feasibility of upgrading a new wall panel from a non-load-bearing partition wall to a load-bearing seismic wall was examined by conducting cyclic load tests on five wall panel specimens. The test piece was a sandwich thermal insulation structure that could achieve a good protection distance between the thermal insulation material and the fire source so that the fire prevention problem could be solved. At the same time, the problem of easy fall-off of the insulation system was also solved. The specimens were divided into three groups, including three double-row reinforced ceramsite concrete sandwich wall panels with different dosages of alkali-resistant glass fiber, a double-row reinforced ordinary concrete sandwich wall panel, and a solid concrete ceramic wallboard. The effects of different dosages of alkali-resistant glass fiber, construction forms, and bearing side plate materials on the seismic performance of the sandwich wall panels were investigated separately for the specimens. From the analysis of the specimen results (damage characteristics, hysteresis curves, energy dissipation capacity, bearing capacity, ductility, longitudinal reinforcement strain, and stiffness degradation), it could be seen that among the five types of wallboard, the double-row reinforced ceramsite concrete sandwich wall panel with 0.3% fiber content had the best ductility and energy dissipation capacity. Adding fiber could solve or improve the problem of the low ultimate bearing capacity of ceramsite concrete as the wallboard’s bearing material. Compared with the same size solid ordinary concrete wallboard, the bearing capacity of the double-row reinforced ceramic concrete sandwich panel was slightly reduced. However, the additional seismic performance indexes were relatively superior. Through the analysis of the test results, it was shown that, when considering the thermal performance and seismic capacity, the new wall panel had good prospects for engineering applications.

Numerical analysis on shear resistance of ultra‐high performance concrete‐normal strength concrete composite beam

AbstractUltra‐high performance concrete‐normal strength concrete (UHPC‐NC) composite beam is a brand‐new composite structure. UHPC‐NC composite beam not only has the interfacial problem of the two materials, but its shear resistance should be investigated, which directly determines the mechanical performance and engineering value. In this article, the finite element analysis (FEA) method combined with the UHPC‐NC composite beam shear experiment are used to analyze the shear resistance of the composite beam and the influence of the interfacial zone on the shear behavior. The shear span‐to‐depth ratio, UHPC layer, and longitudinal reinforcement of specimens are designed to study the shear mechanism. Then the FEA model is used to simulate the cooperative working properties of the concrete beam and the UHPC layer, which includes two conditions—slip and no‐slip. The shear resistance, load‐span deflection curve and the strain of longitudinal reinforcement of the UHPC‐NC composite beams are analyzed and studied in combination with the results of shear experiment. The results show that the UHPC‐NC composite beam can effectively improve the ultimate shear resistance and ductility of the beam. At the same time, the interfacial zone of UHPC‐NC composite beam at the ultimate stage is a weak area, the cracking of that will has adverse effects on the mechanical properties of the composite beam, which needs to be paid attention to in the structural design.

Experimental Study on the Shear Performance of Reinforced Concrete Beams Strengthened with Bolted Side-Plating

To investigate the residual shear capacity of post-fire bolted side-plated (BSP) reinforced concrete (RC) beams with different depths of steel plate and types of anchor adhesive, i.e., magnesium oxychloride cement (MOC) and HIT-RE500, a control beam and five BSP beams were fabricated, of which two were exposed to fire in accordance with ISO834 temperature curve. Four-point bending shear tests were conducted to investigate the influence of elevated temperature on the failure mode, cracking load, shear capacity, stiffness, ductility and strain development, etc. The shear capacities of RC beams were found to be improved significantly by using the BSP technique. However, the stiffness of BSP beams was seriously degraded after exposed to fire, but the reduction in shear capacity was negligible, whereas the ductility and the strain of longitudinal reinforcement were obviously increased. Thus, the failure-mode was changed from shear failure to flexural failure. Regarding the adhesive mortar used for bolt anchorage, magnesium oxychloride cement (MOC) achieved higher shear capacity and better ductility but lower stiffness for BSP beams compared with HIT-RE500. Additionally, increasing the depth of bolted steel plates effectively improved the shear performance of BSP beams. In the tests, uneven relative slips were observed on the plate-RC interface due to the shear deformation of bolt shafts and the plates’ tensile principal stress perpendicular to the main diagonal crack, which proved the deformation lag of the bolted steel plates with respect to the RC beam. The outcomes of this study provide a better understanding on the shear performance of BSP beams at room temperatures and at fire conditions.

Flexural performance of reinforced self-consolidating concrete beams containing hybrid fibers

Flexural performances of twelve reinforced self-consolidating concrete (SCC) beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their combinations were studied at room temperature. The major test variables were fiber types, fiber contents and longitudinal reinforcement ratios. Cracking load, yielding load, ultimate load, mid-span deflection, longitudinal reinforcement strain and crack pattern of the reinforced SCC beams were investigated. It was found that the addition of mono steel fiber and hybrid fibers enhanced the ultimate bearing capacity but reduced the mid-span deflection of reinforced SCC beams. With the increase in fiber content, the longitudinal reinforcement strain, crack width and crack spacing decreased significantly. The hybrid use of steel fiber and micro polypropylene fiber did not have a further beneficial effect on the flexural performance of SCC beams at room temperature. Compared to micro polypropylene fiber, the macro polypropylene fiber displayed a more significant effect on the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC beams at room temperature was proposed, which takes into consideration the effects of hybrid fibers. Comparisons were drawn between the predicted results of this proposed model and other previous models with experimental data in this study and previous literature. The results indicate that the proposed model can reasonably estimate the ultimate bearing capacity of SCC beams containing hybrid fibers subjected to flexural loading at room temperature.

Dynamic behavior of reinforced concrete panels subjected to blast loading

This paper presents experimental and analytical results for dynamic response of reinforced concrete one-way slab under blast loading. Steel frame with massive concrete foundation to minimize rigid movement was prepared for fixed-fixed boundary condition. Two 1500×2350×150 mm RC slabs were tested under surface bursts of 50 kg TNT and 100 kg TNT at standoff distance of 20 m. Types of measured data related to structural response includes strain of longitudinal reinforcement at mid-span, and longitudinal strain on unloaded side concrete at midspan. Incident pressures were measured at 15 m, 20 m, and 25 m to check if full detonation occurs. All measured data were compared with results of AUTODYN. Difference of peak reinforcement strains is 3 %, and one of concrete strains at surface of unloaded side is 11 %, showing that prepared numerical analysis can be used to estimate behavior of reinforced concrete one-way slab under explosion.

Experimental study of intermediate length coupling beams subjected to monotonic load

Experimental study is conducted on four reinforced concrete coupling beams, with length to depth ratios of 2.5 and 3.1. The beams are designed to fail in shear after yielding of longitudinal reinforcement. The longitudinal reinforcement contents are 0.76 and 1.14 percent, while shear reinforcement varies from 0.2 to 0.5 percent. The beams are loaded monotonically until failure. It is found that the shear stiffness of such beams reduces to 0.1 of the initial stiffness upon yielding of reinforcement. An empirical equation is proposed to assess the shear strength degradation of the beams based on axial strain of longitudinal reinforcement.

Improving the Failure Mode of Over-Reinforced Concrete Beams Using Strain-Hardening Cementitious Composites

AbstractOver-reinforced sections fail suddenly by compression concrete crushing when their ultimate compressive strain has been exceeded but the longitudinal reinforcement strain has not yielded. This study investigates the use of cementitious repair materials for the compression side of over-reinforced concrete beams to change their failure mode to ductile failure. In this study, 11 over-reinforced concrete beams were cast (1 as a control specimen and 10 as strengthened beams). The study’s strengthening material was an ultra-high-performance strain-hardening cementitious composite (UHP-SHCC). The effect of shear connectors with the strengthening material was investigated. Meanwhile, replacement of the concrete cover, use of a welded wire mesh inside the additional layer, and concrete strength were tested. Crack pattern and failure modes were noted, and deflection behavior, failure loads, steel strains, and crack width were measured. The tests results showed that using strengthening UHP-SHCC material is a...

Testing on Axial Compression of Damaged RC Columns Reinforced by Winding Steel Wire

Four groups of specimens of damaged RC columns reinforced by winding steel wire were tested for axial compressions. One group was undamaged RC columns; the others were damaged RC columns, the width of crack developing was regarded as damage index, they were respectively 0.3mm, 1.0mm and 1.5mm, the helically-wound method was adopted for reinforcement, and winding spacing was 50mm. The testing results showed that under reinforcement the load of damaged columns improved a bit in comparison with undamaged ones, but with a little range, however, the strain of longitudinal reinforcement, stirrup and concrete could improve greatly, which indicated that it had a good effect to reinforce the damaged columns by winding steel wire, meanwhile, the ductility of damaged columns was improved apparently.

Construction of the interaction curve of concrete-encased composite columns based on the deformation domains of reinforced concrete sections

AbstractThis paper proposes a methodology for obtaining the interaction curve for composite steel-concrete sections subject to combined compression and bending based on the deformation domains of reinforced concrete structures defined by ABNT NBR 6118 [1]. For this, were developed expressions for the axial force, the moment and the strains of concrete, longitudinal reinforcement and the elements comprising the metal profile in each deformation domain.Based on these expressions a computer program called MDCOMP (2014) was created. In this study the same limit values of longitudinal reinforcement strain defined by ABNT NBR 6118 [1] were used for the steel profile strains. To verify the numerical implementations performed, the interaction curves and the plastic resistance of the section obtained by MDCOMP program were compared with those determined from the recommendations of Eurocode 4 [2], of ABNT NBR 8800 [3] or literature responses.

The Analysis of Relationship between Stirrup and Longitudinal Reinforcement with Regression Analysis

Regional confined concrete is a method which can strengthen constraint in the most needed position, it can make concrete, longitudinal reinforcement and transverse stirrup to form a more effective binding, and provide a stronger restraint in required regional giving full play the role of constraints. In the result analysis of the regional confined column specimen load test, we found that longitudinal reinforcement and stirrup strains have certain relationship. This article analyses the relationship between the two from the stirrup and longitudinal reinforcements strains in the contingency load, references are provided for the further development of regional confined concrete theory. Taking the two specimens as examples, the regression analysis was carried on between longitudinal reinforcement and stirrup strain, the relationship equation was obtained

Yield curvature for seismic design of circular reinforced concrete columns

Significant research efforts have been devoted in recent years to the development of displacement-based seismic assessment and design methodology, recognising the shortcomings of traditional, code-specified force-based procedures. Recent advances in direct displacement-based seismic design of columns rely on the estimates of yield curvature for determining seismic design forces to satisfy the specified seismic performance levels. This paper presents simple expressions for estimating the effective yield curvature for normal- and high-strength circular reinforced concrete columns based on moment–curvature analyses of a large number of column sections. Such expressions can be programmed into spreadsheet format and can be used for the direct displacement-based design of circular reinforced concrete columns. Influences of different parameters on the effective yield curvature have been quantified. Effective yield curvature is presented in terms of the gross diameter of the section and the yield strain of longitudinal reinforcement together with three modification factors that take into account the effects of the strength of concrete, axial load ratio and the amount of longitudinal reinforcement. An example illustrating the preliminary design of bridge columns based on the developed expressions is presented.

Experimental Study on Deep Four-Pile Caps with Different Reinforcement Layouts Based on 3D Strut-and-Tie Analogy

Based on 3D strut-and-tie analogy developed for analyzing the load-transferring mechanism of deep pile cap, this paper focuses on the effect of different longitudinal reinforcement layouts at the lower part of cap on the mechanical behaviors of deep four-pile cap. Besides a common layout of uniformly distributed reinforcement by the flexural theory, three different layouts of concentrated reinforcement over piles were designed by 3D strut-and-tie analogy. All specimens were limited in same reinforcement percentages, dimensions, materials and test procedures. Four specimens with the scale ratio of 1/5 were tested under the statically incremental gravity loading. The load capacity, deflection, strain of longitudinal reinforcement of specimens were measured, and the failure mode, crack propagation, deformation of specimens and stress distribution of reinforcement were analyzed. Through comparisons of the test results among all specimens, it was found that deep pile cap failed in shear and corner-pile punching whether with concentrated or uniform reinforcement, and the reinforcement concentrated over each two adjacent piles, similar to the tension bars in the strut-and-tie model, had considerable advantages than common uniform reinforcement layout. The ultimate strength of deep pile cap with concentrated reinforcement was significantly increased, while the improvement of deformation resistance and brittleness of deep pile cap was limited. According to above findings, the appropriate reinforcement layouts for deep pile cap were suggested in this paper.

Strain and bond stress distributions in tension lap joints in reinforced concrete

Fifteen reinforced concrete tension specimens were tested, each reinforced with a pair of lapped rods. Longitudinal reinforcement strain distributuions were measured using electrical resistance strain gauges installed within the reinforcement, and strain concentration gauges were used to obtain very detailed information at the ends of some rods. Thirteen of the specimens were loaded incrementally to study short-term effects and the other two were used for a preliminary investigation of sustained loadings. Results show the changing nature of the strain distributions, first as transverse cracks were developed and subsequently as lap failure was approached. The test results have been compared with the theoretical work of Tepfers. Peak and mean bond stresses at the formation of each crack were calculated and compared and bond stress distributions at lap failure are discussed.