Practical techniques for determining of average stress-strain relationships for concrete from experimental data of rc bending members

Straipsnyje aprašomi nauji pasiekimai, plėtojant neseniai pasiūlytą metodą [1–5], kuriuo ič lenkiamų gelžbetoninių sijų eksperimentinių duomenų gali bųti nustatytos betono vidutinių įtempių-deformacijų diagramos. Turint eksperimentines momentų-kreivių ir momentų-deformacijų diagramas, gaunama pilna tempiamo betono vidutinių įtempių-deformacijų diagrama, įskaitant ir jos krentančiają dalį. Taip pat, net neturint duomenų apie betono savybes, pakankamai tiksliai galima rasti ir gniuždomo betono diagramą. Skaičiavimas pagrįstas nauja idėja, kai tempiamo ir gniuždomo betono vidutinių įtempių-deformacijų diagramos skaičiuojamos kraštiniams lenkiamo elemento sluoksniams. Turint eksperimentines kraštinių sluoksnių deformacijas, kiekvienai apkrovos pakopai nustatomi tų sluoksnių įtempių prieaugiai. Kiekvienoje apkrovos pakopoje gautos diagramos taikomos kitiems mažiau deformuotiems sluoksniams. Pasiūlytasis metodas patikrintas skaitiškai. Remiantis šiuo metodu, pasiūlytos dvi inžinerinės skaičiavimo metodikos, įvertinančios eksperimentinių duomenų išsibarstymą. Pirmaja metodika, turint vieną eksperimentinę momentų-vidutinių deformacijų (kreivių) diagramą, nustatoma tempiamo betono vidutinių įtempių-deformacijų kreivė. Šiuo atveju gniuždomo betono įtempių-deformacijų kreivė yra laikoma žinoma. Antraja metodika, turint dvi eksperimentines momentų-vidutinių deformacijų (kreivių) diagramas, iteraciniu būdu nustatomos tiek tempiamo, tiek gniuždomo betono vidutinių įtempių-deformacijq kreivės. Pastaruoju atveju laikoma, kad betono diagrama yra žinomos parabolės formos, o ją apibrėžiantys dydžiai—betono tamprumo modulis ir prizminis (arba cilindrinis) stipris nustatomi skaičiavimu. First Published Online: 26 Jul 201

Deflection Calculation of RC Beams: Finite Element Software versus Design Code Methods

The paper investigates accuracy of deflection predictions made by the finite element package ATENA and design code methods ACI and EC2. Deflections have been calculated for a large number of experimental reinforced concrete beams reported by three investigators. Statistical parameters have been established for each of the technique at different load levels, separately for the beams with small and moderate reinforcement ratio

Editorial

„Editorial" Journal of Civil Engineering and Management, 15(1), p. 5-6 First Published Online: 14 Oct 201

A life dedicated to science: on the occasion of the 70th birthday of Editor-in-Chief Edmundas Kazimieras Zavadskas

„A life dedicated to science: on the occasion of the 70thbirthday of Editor-in-Chief Edmundas Kazimieras Zavadskas" Journal of Civil Engineering and Management, 20(3), p. 311-31

Performance of Distributed Optical Fiber Sensors (DOFS) and Digital Image Correlation (DIC) in the monitoring of RC structures

Distributed Optical Fiber Sensors (DOFS) are strain measuring tools whose potential had been discovered in the latest years only, in particular related to the civil engineering field. A unique utility lies in the possibility of bonding these extremely thin sensors (125µm of diameter) to steel reinforcement bars which will later be embedded in Reinforced Concrete (RC) elements in order to monitor its mechanical strains. These measurements encircle the features of reliability, accuracy, completely dist8ributed nature and desired frequency. The present paper presents the results of an experimental campaign developed at UPC´s Structure Technology Laboratory that saw the tensing of two RC tensile members (ties) with DOFSinstrumented steel rebars providing strain readings every 7.5mm. The first of the two members was designed not to crack while the second one yes, giving insight on the steel rebar’s strain profile when surrounded by cracking concrete. The described results are novel in their essence as measurements as accurate, completely-distributed, experimentally extracted, both before and after concrete cracking, have been, up until now, impossible. The internal strain measurements are additionally integrated with an external Digital Image Correlation (DIC) monitoring which provides data on the displacements and strains of the members’ surfaces in order to check the feasibility, reliability and accuracy of both monitoring techniques. The present research represents the beginning of an in-depth experimental campaign aimed at providing reinforcement strain data for multiple loaded RC ties that encompass different geometrical features (concrete cover, reinforcement ratio, bar diameter and more). This is fundamental for an improved understanding of phenomenon that rely on the knowledge of steel strains (such as steel-concrete bond and tension stiffening) which have always resorted to theoretical, empirical or numerical solutions.Postprint (published version

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

Generalised tension-stiffening relationship conforming to Chinese Design Code GB 50010-2010

A generalised stress-strain tension-stiffening relationship conforming to the Chinese Code for Design of Concrete Structures GB 50010-2010 is proposed. Based on the provisions in GB 50010-2010 for rigidity and curvature calculations of reinforced concrete flexural members, tension-stiffening relationships were derived from moment-curvature relations by means of the inverse technique for deformation analysis. A parameterized stress block for tension-stiffening was suggested. The proposed tension-stiffening model was applied to nonlinear finite element analysis of reinforced concrete beams. Good agreement between the analysis results based on the proposed model and those based on the codified formulas in GB 50010-2010 was achieved. The proposed model will be able to serve as a design aid for serviceability evaluation of concrete beams in general

Tension-stiffening behaviour of reinforced concrete ties of various strength classes

A new law of tension-stiffening for reinforced concrete (RC) ties is proposed in the present study. It is based on the test data of 11 experimental programs of RC elements of various strength classes reported in the literature. The experimental programs covered a wide range of characteristics of mechanical and geometrical parameters of specimens such as compressive strength of concrete, reinforcement ratio and diameter of reinforcement bars. By eliminating the effect of shrinkage from the test load-strain diagrams of the ties, a simple model with no dependence on reinforcement ratio could be derived. The proposed tension-stiffening law is compared with the formulation in Eurocode 2. Statistical analysis of strain predictions of RC ties based on Eurocode 2 was conducted. It is found that the Eurocode 2 significantly underestimated strains in the RC ties with the errors reaching 50% for the lightly reinforced members. Nevertheless, when shrinkage effect was accounted for in the test load-strain diagrams, the predictive capability of the Eurocode 2 formulation could be significantly improved

Modelling the behavior of I-shape concrete beams reinforced with fibers and prestressed steel and GFRP bars

This paper reports the behavior of I-shaped fiber reinforced concrete (FRC) beams flexurally reinforced with prestressed steel and glass fiber reinforced polymer (GFRP) bars. The use of steel fibers aims to enhance the durability of pre-fabricated concrete structures by partially or completely replacing steel stirrups. In addition, GFRP and steel bars/tendons are combined as flexural reinforcement, creating a hybrid reinforcement system. GFRP bars are immune to corrosion and are positioned with minimum concrete cover, while steel reinforcement has adequate concrete cover thickness to minimize its risk to corrosion and ensure the required flexural capacity in a fire occurrence. Nonlinear finite element analysis (NLFEA) software was utilized for a critical analysis on the use of smeared crack model for predicting the behavior of this type of beams, including deflection, crack pattern, load-carrying capacity, and failure modes.The first author gratefully acknowledges the financial support of “Fundação para a Ciênciae Tecnologia” (FCT-Portugal), through the PhD grant SFRH/BD/09253/2020. The authors acknowledge the support provided by FCT through the project FemWebAI, reference PTDC/ECI-EST/6300/2020, and PID2021-125553NB-I00 (MCI/AEI/FEDER, UE). This work was partly financed by FCT / MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020, and under the Associate Laboratory Advanced Production and Intelligent Systems ARISE under reference LA/P/0112/2020

FRP reinforcement for concrete structures: state-of-the-art review of application and design

Fiber reinforced polymers (FRPs) are considered to be a promising alternative to steel reinforcement, especially in concrete structures subjected to an aggressive environment or to the effects of electromagnetic fields. Although attempts to develop effective reinforcement have been followed, the application of FRPs remains limited by the solution to simple structural problems that mainly appear due to the absence of design codes, significant variation in the material properties of FRP composites and limited knowledge gained by engineers as regards the application aspects of FRP composites and structural mechanics of concrete elements reinforced with FRPs. To fill the latter gap, the current state-of-the-art report is dedicated to present recent achievements in FRPs applying practice to a broad engineers’ community. The report also revises the manufacturing process, material properties, the application area and design peculiarities of concrete elements reinforced with FRP composites. Along the focus on internal reinforcement, the paper overviews recent practices of applying FRP reinforced concrete (RC) elements in structural engineering. The review highlights the main problems restricting the application of FRPs in building industry and reveals the problematic issues (related to the material properties of the FRP) important for designing RC following the formulation of targets for further research