Concrete Tension Research Articles

Effects of varying temperature on the performance of reinforced concrete

To obtain a more robust understanding of the effects of temperature on crack widths, stiffness, strength and short term creep behaviour of reinforced concrete elements to improve structural assessment techniques. Crack widths are monitored in four small scale reinforced concrete tension specimens, while exposed to temperature cycles. Four large scale beams, two at room temperature and two at −20 °C, are loaded under four point bending for 48 h at service load before being tested to failure. Crack width behaviour and mid-span deflections are monitored. A comparison of the room temperature and low temperature test results show that the crack widths tend to decrease at lower temperatures in members that are free to expand and contract. The beams also saw an increase in strength that was dependent on the failure mode, but saw no noticeable increase in stiffness. Lastly, short-term creep behaviour was reduced in the low temperature beams. The observed cracking behaviour and beam test results indicate the potential for an increase in shear capacity for beams at lower temperatures.

Laboratory tests of fungal biocorrosion of unbonded lubricated post-tensioned tendons

In unbonded post tensioned concrete used in buildings, parking structures, and bridges utilizing steel cable, protection against stress corrosion is provided by grease. Microbiologically influenced corrosion (MIC) of prestressing steel mainly due to bacteria has been reported in literature while only few papers report on the role of fungi in the corrosion failure of unbonded lubricated tendons.The aim of this research was to evaluate to which extent three ubiquitous fungi (Aspergillus flavus, Penicillium commune and Fusarium solani) and an acidotolerant black yeast (Acidomyces acidophilum) could cause the corrosion of post tensioned lubricated tendons.The ability of the chosen fungi to degrade a commercial calcium based grease (OVOLINE 71C), used as lubricant in post-tensioning tendons was evaluated, followed by small scale sample experiments. The fungal colonization and extent of corrosion was studied by SEM microscopy and by FTIR spectra to analyze the organic acid produced.The results showed that all fungal strains were able to utilize the grease as sole carbon source and, through the production of organic acids, they were able to produce diffused pits on steel surface. No Stress Corrosion Cracking (SCC), however, was noticed on the steel surface under tensile strength.Results showed that the fungi may cause an indirect steel corrosion through the release of organic acids following grease utilization as carbon source.

Unified Formulation for a Triaxial Elastoplastic Constitutive Law for Concrete.

A constitutive model to describe the triaxial load-response spectrum of plain concrete in both tension and shear was developed. The inelastic phenomena are described using the plastic flow with direction determined by the gradient of the plastic potential. A new plastic potential is introduced and experimentally fitted to ensure better estimate of the load direction. This approach allows to control the inelastic dilatancy in terms of the inelastic deformation of the material. By overlaying the plastic potential on modified Etse and Willam’s yield surface (both defined on the Haigh–Westergaard coordinates), the results showed that the two curves do not undergo similar stress states for a given strength level. It is, therefore, necessary that each surface goes through the current stress state to ensure adequate evaluation of normal vectors. A closed-form solution to accurately predict the triaxial stress state in concrete has been proposed. The predictive capabilities of the proposed model are evaluated by comparing predicted and measured stresses. The proposed model is shown to be accurate in predicting stress state of concrete.

Dynamic fracture of concrete compact tension specimen: Experimental and numerical study

Compared to quasi-static loading concrete loaded by higher loading rates acts in a different way. There is an influence of strain-rate and inertia on resistance, failure mode and crack pattern. With increase of loading rate failure mode changes from mode-I to mixed mode. Moreover, theoretical and numerical investigations indicate that after the crack reaches critical velocity there is progressive increase of resistance and crack branching. These phenomena have recently been demonstrated and discussed by Ožbolt et al. (2011) on numerical study of compact tension specimen (CTS) loaded by different loading rates. The aim of the present paper is to experimentally verify the results obtained numerically. Therefore, the tests and additional numerical studies on CTS are carried out. The experiments fully confirm the results of numerical prediction discussed in Ožbolt et al. (2011). The same as in the numerical study it is shown that for strain rates lower than approximately 50/s the structural response is controlled by the rate dependent constitutive law, however, for higher strain rates crack branching and progressive increase of resistance is observed. This is attributed to structural inertia and not the rate dependent strength of concrete. Maximum crack velocity of approximately 800m/s is measured before initiation of crack branching. The comparison between numerical and experimental results shows that relatively simple modeling approach based on continuum mechanics, rate dependent microplane model and standard finite elements is capable to realistically predict complex phenomena related to dynamic fracture of concrete.

Estimating on Creep Strain for Ready-Mixed Concrete during Shrinkage

This paper presents the development of formulas to estimate the creep strain of the reinforced concrete specimens. The experimental part of the work focused on the dispersion of shrinkage strain between reinforced concrete and plain concrete specimens, as well as the equilibrium condition between concrete tension and reinforcement compression. Based upon the experimental data and development formula, the creep strain and concrete age curves of the reinforced concrete specimens are drawn. Moreover, the characteristics of the creep strain are analyzed in detail. The creep strain formula can provide the important data and theoretic basis to “the code for design of concrete structures”（GB50010－2010）.

Estimation of Tensile Capacity of Single Anchors Including Edge Effect Using Neural Networks

The demand for more flexibility in the design and strengthening of concrete structures has resulted in an increased use of anchoring systems. Adhesive anchors are widely used in seismic strengthening applications to add new structural members or sections to existing concrete members. To safely design such anchors, it is very important to know their tensile capacity under axial tensile forces. This paper explores the pullout capacity of single adhesive anchors loaded in tension in un-cracked concrete. To this end 142 single anchor tests including edge effect (located near a concrete edge) were obtained from literature. The formulated three-layered artificial neural network method (ANN) was trained using 75% of the data set by using different learning algorithms. The methods were tested with the remaining 25% of the data set. The variables taken into account in this study are anchor diameter, embedment length, concrete body height and edge distance. It was determined that experimental data can be estimated to a notably close extent via the ANN model.

Non-linear analyses model for composite box-girders with corrugated steel webs under torsion

A composite box-girder with corrugated steel webs has been used in civil engineering practice as an alternative to the conventional pre-stressed concrete box-girder because of several advantages, such as high shear resistance without vertical stiffeners and an increase in the efficiency of pre-stressing due to the accordion effect. Many studies have been conducted on the shear buckling and flexural behavior of the composite box-girder with corrugated steel webs. However, the torsional behavior is not fully understood yet, and it needed to be investigated. Prior study of the torsion of the composite box-girder with corrugated steel webs has been developed by assuming that the concrete section is cracked prior to loading and doesn't have tensile resistance. This results in poor estimation of pre-cracking behaviors, such as initial stiffness. To overcome this disadvantage of the previous analytical model, an improved analytical model for torsion of the composite box-girder with corrugated steel webs was developed considering the concrete tension behavior in this study. Based on the proposed analytical model, a non-linear torsional analysis program for torsion of the composite box-girder with corrugated steel webs was developed and successfully verified by comparing with the results of the test. The proposed analytical model shows that the concrete tension behavior has significant effect on the initial torsional stiffness and cracking torsional moment. Finally, a simplified torsional moment-twist angle relationship of the composite box-girder with corrugated steel webs was proposed based on the proposed analytical model.

Modelling the structural behaviour of frost-damaged reinforced concrete structures

A methodology is introduced to predict the mechanical behaviour of reinforced concrete structures with an observed amount of frost damage at a given time. It is proposed that the effects of internal frost damage and surface scaling can be modelled as changes of material and bond properties, and geometry, respectively. These effects were studied and suggestions were made to relate the compressive strength and dynamic modulus of elasticity, as the indicators of damage, to the response of the damaged concrete in compression and tension, and to the bond behaviour. The methodology was applied to concrete beams affected by internal frost damage, using non-linear finite element analyses. A comparison of the results with available experimental data indicated that the changes in failure mode and, to a rather large extent, the effect on failure load caused by internal frost damage can be predicted. However, an uncertainty was the extension and distribution of the damaged region which affected the prediction of the load capacity.

Study on reinforced lightweight coconut shell concrete beam behavior under shear

Lightweight concrete has been produced using crushed coconut shell as coarse aggregate. The shear behavior of reinforced concrete beam made with coconut shell is analyzed and compared with the normal control concrete. Eight beams, four with coconut shell concrete and four with normal control concrete were fabricated and tested. Study includes the structural shear behavior, shear capacity, cracking behavior, deflection behavior, ductility, strains in concrete and in reinforcement. It was observed that the shear behavior of coconut shell concrete is comparable to that of other lightweight concretes. The results of concrete compression strain and steel tension strain showed that coconut shell concrete is able to achieve its full strain capacity under shear loadings. However, the failure zones of coconut shell concrete were larger than for control concrete beams.

Missing subjects

This commentary engages with Kevin Cox’s (2013) “Notes on a Brief Encounter: Critical Realism, Historical Materialism and Human Geography.” Identifying a trajectory in historical geographical materialism that focused on the material social practices of everyday life fully attuned to the social relations of production and social reproduction of space, place, and nature, I argue that Marxist geography was perhaps less in need of the methodological corrective that Cox suggests critical realism offered. The rich empirical research associated with this strand of history in our field kept the ricochet between abstract and concrete in dialectical tension, exposing and examining some of the material social practices through which new structures are created, which is at the heart of what Cox wants to understand. Finally, I note a persistent silence. At the same time as the engagements between critical realism and historical geographical materialism were taking place in the 1980s—crystallized for some around the locality debates—feminist geographers were producing work that offered a different perspective on the `elaboration of new structures of social relations,' which Cox finds so resonant in critical realism. This scholarship was largely occluded in the debates between critical realism and historical geographic materialism, as it is again in the present piece, but it offers some powerful resolutions of—or productive struggles with—the contradictions of structure and agency, necessity and contingency, pluralizing and totalizing, or abstract and concrete that can haunt and confound those working in a critical realist or narrowly class-focused Marxist tradition.

Experimental Comparative Study on Composite RC T-Beams Behavior with Diverse Distributions of Headed Studs in Sagging –Moment Tensioned Concrete Media(English)

لغرض تقييم تأثير أعداد ونمط ترتيب روابط القص الوتدية ذوات الرؤوس في العتبات الخرسانية المسلحة بسيطة الارتكاز ذوات الوترات المصبوبة جزئيا والمرتبطة داخليا بحديد ساقية عند أسطحها السفلى ، تم تنفيذ منهاج تجريبي باستخدام ثلاث حالات من أعداد الأوتاد وتوزيعها إضافة إلى حالة السيطرة الخالية من الأوتاد . لقد تبين إن حالة العتبة الحاوية على عدد معتدل من الأوتاد وغير متجانسة التوزيع بمسافات داخلية بين الأوتاد لا تقل عن عرض وترة العتبة تجمع المزايا الساندة للعتبتين الآخريتين اللتين تضمان أوتاد متجانسة التوزيع إحداهما غزيرة والأخرى متباعدة مع تحاشي عيوبها المحتملة . على وجه التحديد ، فان مجالات أفضلية العتبة المثلى هي : الجساءة والمطاوعة والمقاومة القصوى الإنثنائية ، إضافة إلى تقييد الانزلاق النسبي وخصائص الوحدة التمامية . رغم احتجاز الخرسانة في نطاق حديد الساقية ، فان انخفاضات حادة في مستويات مقاومة الانحناء القصوى والوحدة التمامية قد حصلت عند إزالة روابط القص .

Numerical analysis of thermal and composite stresses in pre-stressed concrete pavements

One of the major benefits of the pre-stressed concrete pavements is the omission of tension in concrete that results in a reduction of cracks in the concrete slabs. Therefore, the life of the pavement is increased as the thickness of the slabs is reduced. One of the most important issues in dealing with the prestressed concrete pavement is determination of the magnitude of the pre-stress. Three dimensional finite element analyses are conducted in this research to study the pre-stress under various load (Boeing 777) and thermal gradient combinations. The model was also analyzed under temperature gradients without the presence of traffic loading and the induced stresses were compared with those from theoretical relationships. It was seen that the theoretical relationships result in conservative values for the stress.

Prediction of tensile capacity of adhesive anchors including edge and group effects using neural networks

AbstractAdhesive anchors are widely used in seismic strengthening applications to add new structural members or sections to existing concrete members due to their high tensile and compressive strengths, low cost, and easy and fast installation. To safely design such anchors, it is very important to know their pullout capacity under axial tensile forces. This paper explores the pullout capacity of both single and groups of adhesive anchors loaded in tension in uncracked concrete. Quadruple anchor groups were considered for group effect. To this end, 142 single anchor tests including edge effect (located near a concrete edge) and 175 quadruple group anchor tests (totally 317 tests) were obtained from literature. The formulated three-layered artificial neural network method (ANN) was trained using 75% of the data set by using different learning algorithms. The methods were tested with the remaining 25%. The variables taken into account in this study are anchor diameter, embedment length, concrete compressive strength, concrete body height, edge distance (for single anchors), and anchor spacing (for group anchors). It was determined that experimental data can be estimated to a notably close extent via the ANN model.

Evaluation of tension stiffening effect on the crack width calculation of flexural RC members

Building codes consider the tension stiffening when calculating the crack width of the flexural members. A simple analytical procedure is proposed for the determination of forces, stresses and strains acting on a reinforced concrete section subjected to flexure considering the concrete contribution in tension up to tensile concrete strain corresponding to the cracking strength of concrete. This analytical method gives the minimum value (lower bound) of tension stiffening. Also, a commercial Finite Element Program (ABAQUS 2007) was used to perform non-linear analysis in order to evaluate the total contribution of the tensioned concrete in carrying loads which may be considered as the upper bound of tension stiffening. In addition, a comparison is carried out among the different codes using four reinforced concrete rectangular models to compare and evaluate the tension stiffening with proposed analytical lower bound tension stiffening and upper bound as obtained by ABAQUS. The models include different percentages of flexural steel ratio. The comparison revealed that the codes’ equations always consider tension stiffening lying between lower and upper bound of tension stiffening proposed in this study. Also, the study showed that the tension stiffening decreases with the increase of the percentage of the flexural reinforcement ratio.

A Computer Method for Rapid Design of Composite Steel-concrete Cross-sections

This paper presents an efficient numerical procedure for the rapid design of arbitrary-shaped composite steel-concrete cross-sections that are subjected to biaxial bending and axial force. The design procedure allows cross-sections to be designed by solving directly for the reinforcement required to provide a cross-section with adequate strength. The new numerical procedure developed in this paper shows very good stability in the presence of strain softening effect exhibited by the concrete in compression and tension and convergence stability is not affected by the shape of stress-strain relation-ships of concrete, the type and amount of reinforcements or the residual stress distribution in encased steel elements. A computer program was developed, aimed at obtaining the ultimate strength capacity and reinforcement required by rein-forced and composite cross-sections subjected to combined biaxial bending and axial load. In order to illustrate the pro-posed method and its accuracy and efficiency, this program was used to study several representative examples, which have been studied previously by other researchers. The examples run and the comparisons made prove the effectiveness of the proposed numerical procedure.

Tension Stiffening and Cracking of Hybrid Fiber-Reinforced Concrete

An experimental program has been carried out to study the effect of hybrid fibers on the tension stiffening and cracking characteristics of high-performance concrete (HPC). A total of 24 axially reinforced concrete tension members were cast and tested under uniaxial tension. The main variables considered were the volume fraction of: 1) crimped steel fibers (0.5 and 1.0%); and 2) polypropylene fibers (0.1, 0.15, and 0.2%). Load-deformation response was recorded and analyzed. Crack width and crack spacing were also measured at all stages of loading. Test results indicate that the addition of fibers in hybrid form significantly improves the tension stiffening effect and resistance to cracking. The combination of 1% steel fiber and 0.1% polypropylene fiber showed better performance than the other combinations considered in this study. A method is proposed to predict the crack width of hybrid fiber-reinforced, high-performance concrete tension members, and the computed values compared satisfactorily with the test results.

Influence of Concrete Tension Softening Properties on the Steel-Liner Reinforced Concrete Penstock

In combination with the practice of a large hydropower station, concrete damaged plasticity model is introduced into the steel-liner reinforced concrete penstock for the nonlinear analysis, the damage distribution rules of the surrounding concrete and the stresses of the steels are furtherly studied under the different tension softening characteristic curves, the conclusions can provide the reference for damage assessment of the surrounding concrete and the optimization allocation of the reinforcement for the penstock.

High-Temperature Behaviour of Concrete in Tension

The mechanical properties of concrete at high temperature and in fire conditions have been the subject of a number of investigations over the past 50 years. Nonetheless, the wide range of materials at hand, especially after the advent of high-performance and high-strength concretes, makes these results difficult to be generalized. This is particularly true of tensile response, due to the challenging experimental conditions and to the still not standardized test methods: “;hot” vs. residual test conditions, direct vs. indirect tensile loading, restrained vs. free strain localization, notched vs. unnotched specimens are only some of the possible options that make the comparison between tests from different sources a really difficult task.In this paper, the results collected by the authors on several different concrete mixes are illustrated, with the twofold objective of clarifying the relations among the most common direct and indirect testing techniques and to sketch any possible general trend in the tensile properties of ordinary and special concretes exposed to high temperature.Among the conclusions are the variable influence of the restraint exerted on the specimen ends in direct tension, the relatively good reliability of the splitting tests, the strong influence of specimen size and increasing material deformability in the bending tests, and the good agreement between the thermally induced decays of tensile strength and modulus of elasticity.

Study on reinforced lightweight coconut shell concrete beam behavior under flexure

Coconut shell has been used as coarse aggregate in the production of concrete. The flexural behavior of reinforced concrete beam made with coconut shell is analyzed and compared with the normal control concrete. Twelve beams, six with coconut shell concrete and six with normal control concrete, were fabricated and tested. This study includes the moment capacity, deflection, cracking, ductility, corresponding strains in both compression and tension, and end rotation. It was found that the flexural behavior of coconut shell concrete is comparable to that of other lightweight concretes. The results of concrete compression strain and steel tension strain showed that coconut shell concrete is able to achieve its full strain capacity under flexural loadings. Under serviceability condition, deflection and cracking characteristics of coconut shell concrete are comparable with control concrete. However, the failure zones of coconut shell concrete were larger than for control concrete beams. The end rotations of the coconut shell concrete beams just prior to failure values are comparable to other lightweight concretes. Coconut shell concrete was used to produce hollow blocks and precast slab in 2007 and they are being subjected to some practical loading till today without any problems such as deflection, bending, cracks, and damages for the past five years.

Deriving stress–strain relationships for steel fibre concrete in tension from tests of beams with ordinary reinforcement

One of the most critical points in the theory of steel fibre reinforced concrete (SFRC) is quantifying the residual stresses in tension. Due to concrete interaction with fibres, a cracked section is able to carry a significant portion of tensile stresses, called the residual stresses. Because of a great diversity in the shape and aspect ratio of fibres and, consequently, varying bond characteristics, there are no currently available reliable constitutive models. In present practices, residual stresses needed for strength, deflection and crack width analysis are quantified by means of standard bending tests. However, such tests require relatively sophisticated and expensive equipment based on the displacement-controlled loading. Besides, the test results are highly scattered. This paper investigates an alternative approach for defining the residual stresses. The approach aims at deriving equivalent stress–strain relations of cracked tensile concrete using test moment–curvature relationships of flexural concrete members with ordinary reinforcement and steel fibres. Tests on eight lightly reinforced beams (reinforcement ratio 0.3%) with different contents of steel fibres (0%, 0.5%, 1.0%, and 1.5% by volume) have been carried out. Based on the proposed technique, equivalent stress–strain relations were defined for each of the beams and further used for curvature and crack width analyses.