Tension Reinforcement Research Articles

Design Issues about the Bar Lay-Out at the Dapped Ends of Simply-Supported One-Way R/C Slabs

Directly-or indirectly-supported R/C slabs are frequently used in the covers of small-to-medium underground facilities, where the service loads are often rather limited, but very severe loads cannot be ruled out in accidental situations.To have fresh information on the structural performance and cracking of R/C slabs simply supported along their short sides via corbels (dapped ends), four rectangular slabs subjected to transversely distributed or concentrated loads have been recently tested in Milan (b x L = 1.30 x 2.20 m; simply-supported span = 2.10 m; thickness = 15 cm). The load was applied either at mid-span (in the bending tests, not presented in this paper), or at 1/10 of the span (in the shear tests).Two bar arrangements were investigated with straight or bent-up bars in the main body, and straight bars or hooks in the corbels.In the D zones of the slabs tested in shear, the concentrated load induces a rather complex 3-D crack pattern, with a limited reduction in the bearing capacity, compared with the cross-wise distributed load.Rather simple strut-and-tie models applied to the slabs with bent-up bars and hooks, and the equations provided by European and North-American codes for the beams devoid of transverse reinforcement are shown to yield realistic predictions for the bearing capacity at the ultimate limit state. In the former case, however, modelling the bond along the tension reinforcement of the corbel requires some care, because of bond local and global effects. Last but not least, refining bar layout confirms – once more – that slab performance can be markedly improved with little extra effort.

Flexural Performance of Reinforced High-Strength Concrete Beams with EAF Oxidizing Slag Aggregates

This study evaluates the flexural behavior of reinforced high-strength concrete beams with electric arc furnace (EAF) oxidizing slag aggregates. The main test parameters include the type of aggregates, compressive strength of concrete, and tension reinforcement ratio. A total of eight simply supported beam specimens subjected to four point loads are cast and tested in flexure. Two types of aggregates, natural and EAF oxidizing slag aggregates, are used in this study. The compressive strength of the concrete is designed to have normal- and high-strengths of 24 MPa and 100 MPa, respectively. The tension reinforcement ratios of beam specimens are 0.3 and 0.5 times the balanced reinforcement ratio for flexure. The experimental results indicated that the flexural strength of specimens was not affected by the type of aggregate, whereas the flexural ductility of specimens with EAF oxidizing slag aggregates was superior to that of specimens with natural aggregates, regardless of the compressive strength of concrete and the tension reinforcement ratio.

Dual potential capacity model for reinforced concrete beams subjected to shear

AbstractThe shear resistance mechanisms of a reinforced concrete (RC) member with shear reinforcement can be divided into the contributions of the concrete and the shear reinforcement. The shear resistance mechanisms of concrete can be further divided into the shear resistance of the intact concrete in the compression zone, the aggregate interlock in the cracked tension zone and the dowel action of the longitudinal tension reinforcement. The shear demand curves and potential shear capacity curves for both tension and compression zones have been derived in this study, with the assumption that the shear failures of RC members are dominated by the flexural‐shear strength. The shear capacity model was also proposed on this basis. In the proposed model, the crack width and the local stress increase in reinforcement were calculated based on the bond behaviour between the reinforcement and its surrounding concrete. Further, the crack concentration factor was introduced to consider the formation and propagation of the critical shear crack that developed from the flexural cracks. The results of a total of 1,018 shear tests were collected and compared with the analysis results provided by the proposed model. It was demonstrated that the proposed model provides a good estimate of the shear strengths of RC beams.

Behaviour of RC Beams with non-bonded flexural reinforcement: A numerical experiment

The present work is concerned with a numerical investigation of the behaviour of reinforced-concrete beams with non-bonded flexural tension reinforcement. The numerically-established behaviour of such beams with and without transverse reinforcement is compared with its counterpart of similar beams with bonded reinforcement. From the comparison, it is found that the development of bond anywhere within the shear span inevitably leads to inclined cracking which is the cause of 'shear' failure. On the other hand, the lack of bond within the shear span of the beams is found, not only to prevent cracking within the shear span, but, also, to lead to a flexural type of failure preceded by the formation of horizontal splitting of concrete in the compressive zone. It is also found that delaying the extension of horizontal splitting through the provision of transverse reinforcement in the beam mid span can lead to flexural failure after yielding of the tension reinforcement. Yielding of the tension reinforcement before the horizontal splitting of the compressive zone may also be achieved by reducing the amount of the latter reinforcement.

Influences of location of reinforcement corrosion on seismic performance of corroded reinforced concrete beams

The seismic performance of corroded reinforced concrete beams was investigated experimentally in this research. Corrosion was induced by the electrochemical accelerated corrosion method to reinforcement at various locations in the beams. After accelerated corrosion, the beams were tested under cyclic loading to investigate their seismic performance. Test results showed that as the corrosion level in tension reinforcement increased, the failure mode of the beam changed from flexural shear due to crushing of core concrete to flexural tension due to fracture of tension reinforcement. Corrosion of longitudinal tension reinforcement had a significant negative effect on the yield drift, yield load, and peak load, and on the ultimate drift when the failure was due to fracture of tension reinforcement. It had no or some degree of positive effect on the ultimate drift when the failure mode was flexural shear. Corrosion in compression reinforcement adversely affected the yield drift and had a minor negative effect on the ultimate drift when the failure mode is flexural shear. It had little effect on the yield load and peak load, and on the ultimate drift when the failure was due to fracture of tension reinforcement. Corrosion in transverse reinforcement had a negative impact on the yield drift and ultimate drift when the failure mode was flexural shear. It had insignificant effect on the yield load and peak load, and on the ultimate drift when the failure mode was caused by fracture of tension reinforcement.

Concrete Cover Separation in FRP-Plated RC Beams: Mitigation Using FRP U-Jackets

AbstractConcrete cover separation is a common failure mode of RC beams strengthened with a fiber-reinforced polymer (FRP) plate externally bonded to the tension face (FRP-plated RC beams). This failure mode initiates at the critical plate end and then propagates at the level of steel tension reinforcement in the direction of increasing moment. Plate-end anchorage by FRP U-jackets has been specified in some design guidelines as a mitigation measure to delay or suppress concrete cover separation, although its effectiveness is far from clear. This mitigation method is more attractive than other options because the same strengthening material is used and the installation procedure is simple. This paper presents the first systematic experimental study on the use of FRP U-jackets for mitigating plate-end concrete cover separation failure, with particular attention to the effect of inclination angle between the U-jacket and the beam axis. A total of 10 full-scale FRP-plated RC beams were tested. The test results...

Size effect on shear strength of reinforced concrete beams with tension reinforcement ratio

It is well known that shear stress at peak of reinforced concrete beams decreases with increasing effective depth. Thus, several existing design codes and models have included various forms of formulas considering the size effect on shear strength of reinforced concrete beams; however, past experimental researches show that tension reinforcement ratio is also associated with the shear strength of reinforced concrete beams. To examine the effect of tension reinforcement ratio and effective depth on shear strength of reinforced concrete beams, this study has conducted experiments in which the effective depth (150, 300, 500, and 780 mm) and tension reinforcement ratio (1%, 2%, and 3%) are employed as variables. Besides, a formula for the shear strength considering both variables is proposed based on data samples collected from the present experiment and previous research. The proposed formula gives predictions comparable to the results of existing shear tests. Furthermore, rational predictions are made for effective depth of beams, compressive strength of concrete, shear span-to-depth ratio, and even tension reinforcement ratio exceeding 3%.

Finite-element analysis of a piled embankment with reinforcement and subsoil

In 2014, the authors of this paper considered predictions of reinforcement tension in a piled embankment from British standard BS 8006 published in 2010 and the 2012 amended version, and compared the results with finite-element model predictions. In keeping with BS 8006, any contribution from the subsoil beneath the embankment was ignored. The present paper extends that earlier work by also considering the potentially beneficial contribution of a lightly overconsolidated clay subsoil layer, both in the finite-element predictions and as a simple modification to the BS 8006 predictive method. It is assumed that there is no ‘working platform’ (granular) material below the pile cap level, and that the water table in the subsoil does not drop, since either of these factors would be likely to significantly reduce the ability of the subsoil to carry load from the embankment. As anticipated, the subsoil support reduces reinforcement tension. When compared to the finite-element results the proposed modified BS 8006 prediction is quite accurate. The BSI 2012 modified prediction is ‘best’ (but sometimes slightly unconservative), whereas the BSI 2010 modified prediction is conservative in all cases considered.

Performance of R.C. slabs with lap splices using headed bars

This paper presents an experimental investigation on the behavior and strength of reinforced concrete slabs with lap splice of tension reinforcement using headed bars. Nine simply supported reinforced concrete one-way slabs were tested to study the effect of lap splices length, confinement at the splice zone, debonding of bars in the splice zone, and applying repeated gradually increasing cyclic loading. It was concluded that implementation of lap splice length as stated by ACI 318-14 for headed bars, but without adding confinement in the splice zone, and using cut-off ratio equal to 100%, led to brittle failure of the slab and the ductility was reduced. When the tested slabs were provided with confinement in the splice zone, the strength of slabs was improved and ductility of these slabs was remarkably increased. Additionally, the integrity of the lap joint was preserved when subjected to repeated gradually increasing cyclic loading.

Curvature ductility of high strength concrete beams according to Eurocode 2

Recently, the high-strength concrete is increasingly used in the construction of reinforced concrete structures due to its benefits, but this use is influenced negatively on the local ductility of structural elements. The objective of this study is the prediction of a new approach to evaluate the curvature ductility factor of high strength concrete beams according to Eurocode 2. After the presentation of the Constitutive laws of materials and the evaluation method of curvature ductility according to the Eurocode 2, we conduct a parametric study on the factors influencing the curvature ductility of inflected sections. The calibrating of the obtained results allows predicting a very simple approach for estimating the curvature ductility factor. The proposed formula allows to calculate the curvature ductility factor of high strength concrete beams directly according to the concrete strength <TEX>$f_{ck}$</TEX>, the yield strength of steel <TEX>$f_{yk}$</TEX> and the ratio of tension and compression reinforcements <TEX>${\rho}$</TEX> and <TEX>${\rho}^{\prime}$</TEX> respectively, this proposed formula is validated by theoretical and experimental results of different researchers.

Evaluation of Shear Strength of HSRC beams without web reinforcement

Abstract Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems rely on design is usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches have been calculated and analyzed on 18 simple span HSRC deep beams without web reinforcement were tested under monotonic two point loads at the mid span to examine the contribution of various parameters on the shear capacity of HSRC beams like; f International Conference on Civil and Architecture Engineering ICCAE-11-2016cu=60 MPa, three values of tension reinforcement (0.73%,1.21% &1.83%) and shear span to effective depth ratio ( 2,1.5 &1) were selected to mainly study the behavior of deep beams, where typical shear failure can be anticipated.

An investigation on bond between FRP stay-in-place formwork and concrete

FRP stay-in-place (SIP) formworks are designed to act as a support for casting concrete and as a tension reinforcement when the concrete is cured. For composite action between the formwork and concrete, proper bond between them is essential. This investigation focuses on the role of adhesives for the bond development. Two different bond mechanisms, aggregate bonding and adhesive bond, are investigated using three different adhesives. A novel experimental set up is prepared to evaluate the bond. The load capacities and failure modes were examined. Load–deflection, load-slip and load-strain curves have been plotted to evaluate the bond mechanisms. A finite element model is developed that is able to accurately predict the ultimate pullout load and load-slip relationships. The results show that the types of resins have a great impact on the bond. It is recommended to use the wet-bond technique with special adhesives.

Assessment of design methods for punching through numerical experiments

The work is intended to demonstrate that the loss of bond between concrete and flexural steel which led in recent years a number of flat-slab structures to punching collapse under service loading conditions is also relevant to ultimate limit-state design. It is based on a comparative study of the results obtained from numerical experiments on flat slab-column sub-assemblages. The slabs were designed for punching either in compliance with the EC2 code requirements, which do not allow for such loss of bond, or in accordance with the compressive force-path method which considers the loss of bond between concrete and the flexural reinforcement in tension as the primary cause of punching. The numerical experiments are carried out through the use of a nonlinear finite element analysis package for which, although ample published evidence of its validity exists, additional proof of its suitability for the purposes of the present work is presented.

EXPERIMENTAL STUDY ON SHEAR STRENGTH BEHAVIOR OF SUPER PLASTICIZED FIBER REINFORCED CONCRETE BEAMS WITH HIGH REACTIVE METAKAOLIN

Experimental investigation is carried out to study the behavior of Metakaolin reinforced concrete in comparison to fly ash reinforced concrete with and without steel fibers on compressive strength and under shear strength. The weakness in tension of conventional concrete is overcome by incorporating steel fibers into the matrix while the Metakaolin and Fly ash can increase many properties of concrete and also reduces the cementing consumption. 12 beams of length 1500mm, breadth 150mm and depth 200mm having 4-12mm diameter bars as tension reinforcement and 2L, 8mm diameter bars spaced at 130mm c/c as stirrups were casted and cured for 28 days and tested under two point loading applied at 1/3 span points.

Bond between FRP formworks and concrete-effect of surface treatments and adhesives

FRP stay-in-place (SIP) formworks are designed as a support for casting concrete and as a tension reinforcement when concrete is cured. Bond development between SIP formwork and concrete is critical for FRP tension element to be effective. This paper reports the bond strength between FRP formwork and concrete for different interfacial treatments. A novel experimental setup is prepared for observing the bond behaviour. Three different adhesives with varying workability have been investigated. Along with the load-deformation characteristics, bond slip and strains in the formwork have been measured. A finite element numerical simulation was conducted for the experiments to understand the underlying mechanism. The results show that the adhesive bonding has the best bond strength.

Effects of improper moist curing on flexural strength of slabs cast under hot weather conditions

Inadequate moist curing can have adverse effects on the properties of concrete, especially during hot weather concreting (HWC). This research aims at gaining a better understanding of the effects of inadequate moist curing on the flexural behavior of reinforced concrete (RC) slabs cast during severe HWC. Five RC slabs and field-cured cylinders and cubes were cast and cured under peak temperatures as high as 50°C, relative humidity as low as 6%, and relatively strong winds. Two additional slabs were control specimens which were cast and cured under lab conditions. The slabs were tested in a four-point loading setup to study their flexural behavior. The experimental results showed a general reduction in the properties of the concrete cast and cured outdoors, especially the concrete which did not receive adequate moist curing. The flexural strengths of the slabs cured outdoor were smaller than those of the lab-cured slabs by 6–29%. In addition, considerable decreases in the flexural stiffness were observed. The compressive strength of cores drilled from the slabs cast outdoors and not cured with moisture was smaller than that of the lab-cured control slab by 39%. The flexural strength of the slabs was calculated using the flexure theory and ACI code equations based on the compressive strength of the drilled cores and the field-cured cylinders. Using the reduced compressive strengths for the outdoor slabs did not lead to capturing the actual reduction in the flexural strength. However, the strength calculations remained conservative for all slabs, with strain hardening in the tension reinforcement being one of the contributors to this conservatism.

Prestressed glulam beams reinforced with CFRP bars

This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure of glued laminated timber (glulam) beams using bonded-in carbon fiber reinforced polymer (CFRP) bars. A series of four-point bending tests were conducted till failure on unreinforced, passively reinforced and prestressed Douglas fir glulam beams in a simply-supported scheme. The focus of this research was to evaluate the reinforcing efficiency of both passively reinforced and prestressed beams. Test results showed that the flexural capacity of the reinforced, prestressed, prestressed & reinforced (bottom prestressed and top reinforced) beams greatly increased by 64.8%, 93.3% and 131%, respectively. While the maximum improvement of the bending stiffness reached 42.0%. Another important finding was that the extreme fiber tensile strain of timber beams at failure could be remarkably increased due to the presence of the tension reinforcement, which indicated it overcomes the effects of local defects and therefore the failure mode was changed from brittle tension failure to ductile compression failure. Based on the experimental results, a theoretical model was proposed to predict the flexural capacity of unreinforced, reinforced and prestressed timber beams, which was validated by the test data.

Structural behaviour of reinforced concrete beams containing a novel lightweight aggregate

This paper reports the results of an experimental investigation into the structural behaviour of reinforced concrete beams incorporating a novel EPS-based lightweight aggregate (LWA) called stabilised polystyrene (SPS) aggregate. Four concrete mixtures with water to cement (W/C) ratio of 0.8 were used. The replacement levels of natural aggregate by SPS were 0%, 30%, 60% and 100%. The volume ratio to manufacture SPS aggregate was 8:1:1 (80% waste EPS: 10% cement: 10% clay). A total of 24 beams were cast and tested at 28-day age. Three types of tension reinforcement were used: 2 bars, 3 bars and 2 bars + shear links. There were no compression bars at the top for all beams. Four point-loading flexural tests were conducted up to failure. In general, it can be observed that the structural behaviour of SPS concrete beams is similar to that of other types of lightweight aggregate concretes used around the world.

Regression Based Analysis and Visualization of for Identifying Flexural Behaviour of M60 Beams under Repeated Compressive LOAD Based on Observational Data Sets

In this paper, we are focusing on exploring the impact of linear regression based statistical analysis of observed civil data sets that can be used to identify the eqation to improve the efficiency and effectiveness of future data collection and further refinement of activities in various civil engineering applications. The cutting edge technology in modern day construction emphasizes the quest for high strength concretes to ultra-high strength concretes. The high strength concretes are manufactured invariably by the selective addition of several mineral admixtures like silica fume, metakaoline, flyash, rice husk ash, ground granulated blast furnace slag, etc. The manifold applications of concrete desired to have a compressive strength ranging from 60 to 100MPa has made a paradigm shift for the need of High Strength Concrete (M60) in the construction scenario. The present paper of this research work focuses on the flexural response of M60 beams under cyclic loading. We are taking the datasets of volume fraction and compressive strength of concrete as two independent variables to generate equation using linear regression. The data sets are gathered by means of perfoming real-time experiments. The experimental programme consisted of six M60 beams prepared by the addition of 8% silica fume at a constant water-cement ratio of 0.36 with different percentages of tension reinforcement and variation in spacing of shear reinforcement. All the beams are designed for under reinforced condition. The steel ratio is modified in terms of 1.0%, 1.25% and 1.5% and the shear reinforcement is spaced at 100 and 200mm c/c combinations. The purpose of variation in tension steel ratio and shear reinforcement spacing is to find out the effect of confinement in strength, ductility and cracking. The test on beams is carried out under cyclic loading till failure to obtain the engineering performance and other associated properties. The test results indicated that there has been a wide range of enhancement in parameters like strength, deformation, ductility, and minimization of cracks and crack width. Also the experimental results are validated with the analytical model developed using regression analysis computed using Minitab software.

PERFORMANCE OF RCC BEAMS WITH AND WITHOUT CURTAILMENT

SYNOPSIS In R.C rectangular beams, theoretically there is no effect of curtailment of steel in flexure. The objective of this work is to establish Load vs Deflection and Load Vs Crack width relationships for RC beams with same Ast but with and without curtailment of tension reinforcement. An experimental study was conducted on 2 RCC beams of 0.23 m x 0.23 m x 1.5 m size with same Astcorresponding to Moment of Resistance of 40 kN_m. From the study, it was observed that curtailment improved the Moment carrying capacity and displacement ductility.