Atstumo tarp pagrindinių plyšių armuoto betono elementuose modelis

The intention of the present study is to develop a unified approach for serviceability analysis reinforced concrete tensile and flexural elements, with a focus on mean crack spacing. The current research is mainly quantitative in nature, with the development of the strain compliance approach based on collected data of 170 tensile and 96 flexural specimens. Furthermore, statistical analysis and individual physical parameter impact on the crack spacing and accuracy in general are provided. The key feature of the proposed strain compliance concept is the merging of two distinct cracking analysis methods, referred to as the stress transfer and the mean deformation approaches. Compatibility is ensured by equating the mean reinforcement strains, as estimated by the referred techniques individually. Thus, the lack of knowledge on the spatial strain distribution in the mean deformation approach is addressed by the stress transfer technique, which contains such knowledge. The technique has been derived for tensile elements with the inclusion of a reference element notion, that is defined by reference values of bar diameter and reinforcement ratio. Moreover, the mean crack spacing must also be known. Consequently, the bond stresses can be evaluated for this reference case and the predictions can then be extended to alternative configurations of ratios of reinforcement and bar diameters. The concept has been extended with modifications to the assumed strain profile for flexural elements. The notion of the reference element has been eliminated with bond stresses accounted for directly from selected models, such as design codes. A central zone concept is introduced, which governs the averaged behaviour of the reinforcement strains within the middle between consecutive primary cracks. A constitutive length model was derived. In-depth comparisons with experimental data and parametric investigations were carried out. With the rise of machine learning in the field of civil engineering, it is imperative that research stays ahead of the trend to be able to analyse the implications. A multipurpose study was carried out, resulting in the development of an artificial neural network for estimating the spacing between cracks with very good generalisation abilities, good adequacy in terms of accuracy and consistency. Incidentally, the gathered experimental data was validated for robustness and the general features of the strain compliance method were found to be in good agreement with the neural network predictions and the experimental results. The research concludes with the validation of the strain compliance technique as a more adequate approach in terms of scatter and accuracy than the present design codes. Moreover, the concept has been shown to be mechanically sound.Dissertatio

Predicting crack spacing of reinforced concrete tension members using strain compliance approach with debonding

A novel technique based on strain compliance for investigating the crack spacing of reinforced concrete (RC) tension members has been developed. The new method is based on the mean strain and the partial interaction (stress-transfer) approaches. The strain compliance principle is established by equating together the mean strains of a reinforced concrete block between adjacent primary cracks estimated by the mean strain and the stress-transfer approaches. The distribution of reinforcement strains within the RC block must be known to apply the stress-transfer approach. This technique is intended for the stabilized cracking stage, where formation of new primary cracks has ceased. This work accounts for local effects – fully damaged bond between the concrete and reinforcement near the cracks. Knowledge of a benchmark data point obtained from a reference element is required. The point is defined by the reinforcement ratio, bar diameter and mean crack spacing values. This data point enables the estimation of the mean crack spacing for other RC tension elements. A comparative investigation was carried out, with two different mean strain approaches, following the free-of-shrinkage tension stiffening law and provisions in Eurocode 2. The obtained results provide reasonably accurate estimates of crack spacing compared to experimental values

Calculation technique for stress-strain analysis of rc elements subjected to high-cycle compression / Daugiacikle gniuždymo apkrova veikiamų gelžbetoninių elementų įtempių ir deformacijų skaičiavimo metodika

Theoretical models for the evaluation of fatigue on reinforced concrete structures most commonly fall into two major groups. The first and more widely used group of models is based on S-N curves and the static stress state. These models provide the final load cycle count until structural failure but do not consider redistribution of stresses within the structure or strain evolution over time. The second group accounts for deterioration of concrete over time. However, due to difficulties in application and high computational costs, these models are not fully evolved. A new simplified iterative method for reinforced concrete columns based on previous research by Zanuy et al. (2009) is presented in this paper. This model allows for estimation of stress redistribution and progressive degradation of concrete under high-cycle loading. Santrauka Teoriniai modeliai, taikomi gelžbetoninių konstrukcijų nuovargio poveikiui vertinti, paprastai yra skirstomi į dvi pagrindines grupes. Pirmoji modelių grupė, kuri ir yra labiausiai paplitusi, remiasi S-N kreivėmis ir statiniu konstrukcijos įtempių būviu. Šie modeliai pateikia tik galutinį apkrovos ciklų skaičių iki konstrukcijos suirimo ir juos taikant neatsižvelgiama į betono įtempių persiskirstymą ar deformacijų kitimo raidą. Antroji grupė apima irimo teorijos modelius, kuriuose atsižvelgiama į laipsnišką betono silpnėjimą. Tačiau dėl pernelyg sudėtingo realaus konstrukcinio pritaikymo ir dėl per didelių skaičiavimo programų resursų poreikio praktinis šių modelių taikymas nėra išvystytas. Todėl, remiantis Zanuy et al. (2009) pasiūlytu mode­liu, kuris leidžia įvertinti laipsnišką betono įtempių degradaciją ir jų perskirstymą, buvo sukurtas ir išplėtotas supaprastintas ir aiškus gelžbetoninių kolonų, veikiamų daugiacikle apkrova, iteracinis analizės metodas. Reikšminiai žodžiai: ciklinė apkrova; degradacija; gelžbetonis; nuovargis; S-N kreivės

Reinforcement Strains in Reinforced Concrete Tensile Members Recorded by Strain Gauges and FBG Sensors: Experimental and Numerical Analysis

Experimental and numerical studies have been carried out on reinforced concrete (RC) short tensile specimens. Double pull-out tests employed rectangular RC elements of a length determined not to yield any additional primary cracks. Tests were carried out with tensor strain gauges installed within a specially modified reinforcement bar and, alternatively, with fibre Bragg grating based optical sensors. The aim of this paper is to analyse the different experimental setups regarding obtaining more accurate and reliable reinforcement strain distribution data. Furthermore, reinforcement strain profiles obtained numerically using the stress transfer approach and the Model Code 2010 provided bond-slip model were compared against the experimental results. Accurate knowledge of the relation between the concrete and the embedded reinforcement is necessary and lacking to this day for less scattered and reliable prediction of cracking behaviour of RC elements. The presented experimental strain values enable future research on bond interaction. In addition, few double pull-out test results are published when compared to ordinary bond tests of single pull-out tests with embedded reinforcement. The authors summarize the comparison with observations on experimental setups and discuss the findings

Reinforcement Strains in Reinforced Concrete Tensile Members Recorded by Strain Gauges and FBG Sensors: Experimental and Numerical Analysis

Experimental and numerical studies have been carried out on reinforced concrete (RC) short tensile specimens. Double pull-out tests employed rectangular RC elements of a length determined not to yield any additional primary cracks. Tests were carried out with tensor strain gauges installed within a specially modified reinforcement bar and, alternatively, with fibre Bragg grating based optical sensors. The aim of this paper is to analyse the different experimental setups regarding obtaining more accurate and reliable reinforcement strain distribution data. Furthermore, reinforcement strain profiles obtained numerically using the stress transfer approach and the Model Code 2010 provided bond-slip model were compared against the experimental results. Accurate knowledge of the relation between the concrete and the embedded reinforcement is necessary and lacking to this day for less scattered and reliable prediction of cracking behaviour of RC elements. The presented experimental strain values enable future research on bond interaction. In addition, few double pull-out test results are published when compared to ordinary bond tests of single pull-out tests with embedded reinforcement. The authors summarize the comparison with observations on experimental setups and discuss the findings.This article belongs to the Section Physical SensorsThis research was funded by the European Social Fund according to the activity ‘Improvement of researchers’ qualification by implementing world-class R&D projects’ of Measure No. 09.3.3-LMT-K-712 (Project No. 09.3.3-LMT-K-712-01-0145)

Short-term deformation analysis of reinforced beams made of lightweight concrete

This paper investigates the accuracy of selected design codes predicting deflections of reinforced beams made of lightweight concrete (LWC). Three well-known design codes, namely European EN, American ACI, and Lithuanian STR have been considered. The moment-curvature data of 26 LWC beams reported by the authors and other investigators were used for the analysis. The authors’ viewpoint is that a prediction is safe, if the code overestimates the deflection. Unfortunately, the obtained results reveal that the design code models were unable to predict deformations with acceptable level of safety: the average prediction errors (on the unsafe side) are equal to 26%, 9%, and 18% for the European, American, and Lithuanian codes, respectivelyLietuvos energetikos institutas (LEI)Vilniaus Gedimino technikos universitetasVilniaus Gedimino technikos universitetas, [email protected] Gedimino technikos universitetas, [email protected] Gedimino technikos universitetas, [email protected] Gedimino technikos universitetas, [email protected]