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PL
W pracy przedstawiono wyniki badań eksperymentalnych żelbetowych belek o przekroju prostokątnym o wymiarach 1100x120x80 mm wykonanych z betonów z wykorzystaniem kruszywa z recyklingu oraz belek kontrolnych jednorodnych wykonanych z użyciem kruszywa naturalnego. Badania w zakresie doraźnym obejmują ugięcia, odkształcenia, nośność i rysy belek z zastosowaniem kruszywa z recyklingu. Ponadto w pracy przedstawiono badania materiałowe zastosowanych betonów.
EN
The paper presents the results of experimental tests of reinforced concrete beams with a rectangular cross-section with dimensions of 1100x120x80 mm, made of concrete with the use of recycled coarse aggregate, and homogeneous control beams made of natural aggregate. Ad hoc tests include deflections, deformations, load capacity and cracks of beams using recycled aggregate. In addition, the paper presents material tests of the concretes used.
2
Content available remote Prefabrykacja belek do budownictwa mostowego
3
Content available remote Badania na ścinanie belek zbrojonych podłużnie i poprzecznie prętami FRP
PL
W artykule przedstawiono przegląd literatury w dziedzinie badania na ścinanie belek zbrojonych podłużnie i poprzecznie prętami FRP. Przegląd badań obejmuje zestawienie parametrów różnych zmiennych: rodzaju zastosowanego zbrojenia; wysokości użytecznej elementu; szerokości belek; smukłości ścinania; wytrzymałości betonu na ściskanie; stopnia zbrojenia podłużnego i poprzecznego; modułu sprężystości prętów; kształtu strzemion; porównania z elementami zbrojonymi prętami stalowymi, a także schematu statycznego. Na podstawie przeglądu wiedzy zaproponowano program badań własnych.
EN
This article presents a review of research in the field of shear tests of beams with longitudinal and transverse FRP reinforcement. The research review includes a summary of the parameters of various variables: type of reinforcement, depth of the element, width of the beams, shear span to depth ratio, compressive strength of concrete, longitudinal and transverse reinforcement ratio, modulus of elasticity of bars, shape of stirrups, comparison with elements reinforced with steel bars, as well as the static scheme. Based on the foreign studies the own research program has been proposed.
EN
Due to the increase in traffic volume, load level, and service life of existing bridges, the bending bearing capacity of reinforced concrete beams (hereinafter referred to as RC beams) has decreased, leading to safety issues. In order to solve the problem of insufficient flexural bearing capacity of RC beams, this article adopts the method of ultra-high performance concrete (UHPC) flexural strengthening RC beams, establishes a finite element model of UHPC-RC reinforcement system, and conducts stress analysis with reinforcement thickness, reinforcement range, reinforcement form, and reinforcement height as parameters to determine the optimal scheme of the reinforcement system. Based on the calculation results, a theoretical formula for the maximum principal stress and maximum deflection of the reinforcement system is proposed. To verify the feasibility of the plan, a reinforcement design was carried out on an existing beam, and it was found that the bending bearing capacity of the RC beam increased by 21%; the high tensile strength of UHPC and the addition of steel fibers have a good limiting effect on cracks; The steel plate of the reinforcement system can be used as a template, reducing construction costs and having good economy.
5
Content available remote Wpływ otworów technologicznych na nośność belek żelbetowych
PL
Zastosowanie otworów technologicznych w belkach pozwala na bardziej ekonomiczne wykorzystanie dostępnej przestrzeni budynku. Otwór w elemencie konstrukcyjnym, nawet jeśli jest mały, powoduje istotne zaburzenie w rozkładzie naprężeń i odkształceń. Z tego powodu w miejscach występowania małych otworów należy zapewnić dodatkowe zbrojenie przenoszące siłę tnącą. W artykule przedstawiono dwie metody wyznaczania niezbędnego zbrojenia wokół otworu: metodę standardową oraz metodę kratownicową.
EN
The use of technological openings in beams allows for more economical use of the available building space. An opening in a structural element, even if it is small, causes a significant disturbance in the distribution of stresses and deformations. For this reason, in places with small openings, additional reinforcement should be provided to transfer cutting force. The article presents two methods of determining the necessary reinforcement around the opening: the standard method and the truss method.
PL
W artykule przedstawiono propozycję prostego podejścia do szacowania nośności belek żelbetowych wzmocnionych taśmami CFRP, które zostało oparte na wynikach badań eksperymentalnych 10 belek żelbetowych. Badania 2 belek referencyjnych i 8 wzmocnionych taśmami CFRP wklejonymi w betonową otulinę (metoda NSMR) wykonano, symulując rzeczywiste warunki wykonywania wzmocnień. Belki zostały wzmocnione pod obciążeniem w pozycji sufitowej. Wyniki nośności belek uzyskane z badań porównano z wynikami obliczeń na podstawie zaproponowanego podejścia, przyjmując wytrzymałość betonu i stali z badań próbek towarzyszących, a także z normy dla zastosowanej klasy betonu i stali. Porównanie wskazuje na bezpieczne szacowanie nośności.
EN
The article presents a proposal for a simple method of estimating the load-bearing capacity of RC beams strengthened with CFRP strips, based on the results of experimental tests of 10 beams. Tests of two reference beams and eight beams strengthened with CFRP strips glued into the concrete cover (NSMR method) were carried out by simulating the real conditions of strengthening. The beams were strengthened under sustained loading were the strip was applied in the bottom side. The beam load-bearing capacity results obtained from the tests were compared with the calculation results based on the proposed simple method. To estimate the load-bearing capacity, the strength of concrete and steel from the accompanying tests and those provided in the standard regulations was adopted. The comparison indicates a safe estimation of the load capacity.
EN
“Polyurea coatings as a possible structural reinforcement system” is a research project aimed at exploring possible applications of polyurea coatings for improving structural performance (including steel, concrete, wooden and other structures used in the construction industry). As part of the project, this paper focuses on evaluating the performance of bent reinforced concrete (RC) beams covered with a polyurea coating system. Easy polyurea application and its numerous advantages can prove very useful when existing RC structural elements are repaired or retrofitted. Laboratory tests of three types of RC beams with three different longitudinal reinforcement ratios were performed for the purposes of this paper. The tests were designed to determine the bending strength, performance and cracking patterns of the coated RC beams. In addition, a theoretical model was developed to predict the impact of the polyurea coating on the bending strength of the RC beams. On this basis, the effect of the coating on the bending strength and the performance of the coated beams at the ultimate limit state (ULS) was examined and analyzed. The results showed that the use of the polyurea coating has a positive impact on the cracking state of the RC beams subject to bending and little effect on their bending strength.
EN
The torsional behavior of RC beams is a complex work involving interactions of different design parameters and mechanisms. Considering the limitations and lower accuracy of traditional calculation theories, two machine learning models, including artificial neural network (ANN) model and random forest (RF) model, were applied for the frst time to predict the cracking torque and initial or pre-cracking torsional stiffness of RC beams. A comprehensive database consisting 159 experimental results of RC beams with solid or hollow sections was compiled, with input variables including dimension parameters of cross-section, compressive stress of concrete, elastic modulus and strength ratio of reinforcements. The performance of the models was appraised by various statistical estimators and safety ratio, and compared with different theories for cracking torque and initial stiffness. Among all the calculation models, RF model achieved the best overall prediction performance with the highest coeffcient of determination (R2=0.985 for cracking torque and R2=0.978 for initial stifness) and lowest root-mean-square error (RMSE=5.867 for cracking torque and RMSE=3.994 for initial stiffness). However, theories for cracking torque, i.e., plastic theory, Bredt thin-tube theory and skew-bending theory, gave huge underestimation, whereas greatly exaggerated initial stiffness was obtained by elastic theory and simplified soften membrane model for torsion theory. Besides, input variable importance analysis was conducted, revealing that dimension parameters of cross-section were the most critical features to decide prediction performance for pre-cracking torsional performance of RC beams. The achievements of this paper may provide references to the establishment of new predicting model for pre-cracking torsional response of RC beams.
EN
In order to study the influence of load position and chamfer opening on the shear performance of reinforced concrete (RC) beams with double openings, five 1/3 RC beams were subjected to three equal point loading tests and ABAQUS finite element analysis. The study revealed that the position of the opening in the structure has a significant impact. When the opening is located in the bend-shearing section, shear force cannot be transmitted, resulting in brittle shear failure of the top chord. In contrast, if the opening is in the pure bending section, bending failure of the specimen occurs. The top chord's cross section exhibits a neutral axis, resembling a short beam, leading to the redistribution of normal stress at the opening. Shear capacity decreases as the loading point moves inward from the outside of the opening. Rectangular openings demonstrate better mechanical properties compared to chamfered openings. The findings from finite element analysis (FEA) suggest that the shear performance of RC beams with double openings is mainly influenced by the length of the opening in the bend-shearing section. The shear capacity relies on the presence of shear stirrups with the same length of the opening in the bend-shearing section. As a result, a revised calculation method for the shear bearing capacity of RC beams with double openings, based on different countries' standards, has been proposed. The revised approach was validated using experimental and FE specimens from this study, along with 32 RC beams with double openings from the previous literature. The calculated results demonstrate a satisfactory level of safety, with the revised Chinese standard deviation within 10%.
EN
In the building industry, it is a frequent cause of damage to elements at different stages: during transportation, operation, installation, etc. Since replacing an element is not always possible due to various circumstances, it entails significant financial losses, logistics, and others. For this reason, the expediency of studying the effect of damage on the bearing capacity of reinforced concrete elements is growing. This effect is dependent on its type and has significant variability. In the case of the combination of the defect and damage in reinforced concrete elements, the complexity of the research of this element increases significantly. In this article is discussed: a review of damaged reinforced concrete elements; researching the influence of the damage and additional factors on the element; developed testing methodology for bending reinforced concrete elements with damage to concrete in a compressed zone with insufficient reinforcement, when performing damage to the action of the load and during the action of the load, is presented; the influence on the deformability and bearing capacity of the variability of damage on the sample with insufficient reinforcement is reflected, taking into account the factor of change in the load at which the damage is performed; a comparison is made of the dependence of the change in the actual height of the compressed zone on the change in the load on the elements; implementation of conclusions on the result of the study.
11
Content available remote Modelling of strengthening of concrete beams with FRP in Ansys software
EN
The purpose of this article is to confirm an accuracy of Cohesive Zone Model (CZM) implemented in Ansys for modelling concrete beams strengthened with fiber reinforced polymer (FRP) tapes. Only mode II of debonding was taken into account, which is sufficient for a case of bent beam strengthened with FRP tape glued to its bottom. Results show satisfying coincidence of used model with experimental data and therefore confirm usefulness of CZM for solving the above mentioned problems.
PL
Celem artykułu jest weryfikacja dokładności modelu Cohesive Zone Model (CZM), zaimplementowanego w programie Ansys, w modelowaniu numerycznym belek żelbetowych wzmacnianych taśmami z polimerów zbrojonych włóknami (FRP). Wzięto pod uwagę jedynie postać II utraty przyczepności, co jest wystarczające w przypadku belek zginanych wzmocnionych taśmą przyklejoną do ich spodu. Wyniki pokazują zadowalającą zgodność użytego modelu z danymi eksperymentalnymi i tym samym potwierdzają użyteczność CZM do rozwiązywania ww. zagadnień.
PL
Dodatek włókien jest obiecującym rozwiązaniem, poprawiającym zachowanie belek żelbetowych przy zginaniu. Wpływa na poprawę właściwości tych belek w zakresie obciążenia szczytowego, plastyczności i absorpcji energii. Nieefektywne włókna mono w betonie działają bardzo efektywnie, gdy są połączone poprzez hybrydyzację i przyczyniają się do zwiększenia wytrzymałości. Hybrydyzacja włókien zapewnia poprawę właściwości mieszanki betonowej i stwardniałego betonu. Dla zapewnienia optymalnych właściwości użytkowych ważniejszy jest synergiczny efekt włókien. Wprowadzenie dwóch rodzajów włókien do matrycy betonowej skutecznie mostkuje rysy. W celu zbadania wpływu hybrydyzacji włókien na zginanie, przygotowano belki żelbetowe, przeprowadzono doświadczenia i porównano wyniki z belkami kontrolnymi. W niniejszej pracy zamierzano ocenić i porównać wpływ włókien stalowych i bazaltowych, w postaci mono i hybrydowej, na przebieg zginania, a mianowicie pierwsze obciążenie przy pęknięciu, zachowanie się pod wpływem obciążenia, plastyczność, szerokość pęknięcia i wytrzymałość na zginanie belek żelbetowych. Do oceny właściwości mechanicznych betonu zbrojonego włóknami klasy M40, wybrano udziały objętościowe włókien wynoszące 0,25%, 0,5% i 0,75%. Połączenie włókien bazaltowych z włóknami stalowymi, w znacznym stopniu poprawia właściwości poprzez synergię działania. Na podstawie ogólnej oceny właściwości mechanicznych ustalono, że połączenie włókien bazaltowych i stalowych w ilości odpowiednio 0,25% i 0,75%, dało najlepsze wyniki. Optymalne udziały objętościowe tych włókien zastosowano do wykonania belek. Tam, gdzie było to możliwe, wyniki prób zginania były weryfikowane z normami indyjskimi.
EN
Addition of fiber is a promising solution, to enhance the flexural behaviour of reinforced cement concrete [RCC] beams. It improves the peak load, ductility and energy absorption characteristics of RCC. Ineffective mono fibers in the concrete perform very effective, when combined through the hybridization and contribute towards the strength. Fiber hybridization offers appreciable improvement in fresh and hardened properties of concrete. To achieve optimum performance, synergetic effect of fibers is more important. Incorporation of two fibers in concrete matrix, bridges the cracks effectively. Hence to investigate the effect fiber hybridization in the flexural performance, RCC beams were cast, experimented and the results were compared with the control beams. In the present study, it is intended to evaluate and compare the impact of steel and basalt fibers in mono form and hybrid form, on the flexural parameters such as first crack load, load response behaviour, ductility, crack width and flexural strength of RCC beams. To evaluate the mechanical properties of M40 grade fiber reinforced concrete, volume fractions chosen were 0.25%, 0.5% and 0.75%.Comparatively addition of basalt fibers with steel fibers, improves synergetic response to a considerable extent. From overall assessment of the mechanical properties, it was established that the combination of basalt and steel fibers at 0.25% and 0.75% respectively, produced optimum results. Optimum volume fraction of fibers identified is used in the casting of RCC beams. Wherever possible, flexural parameters were cross checked, with Indian Standards.
EN
Damage occurring on a reinforced concrete beam (e.g. spalling) can reduce beam’s capacity to withstand external loads. The damage becomes more critical if it is occurred in the shear span since it may lead to shear failure. Patching to the damage zone by suitable patch repair material could be the best option in restoring the shear capacity of the beam. This research investigates the shear recovery of patched reinforced concrete beams with web reinforcement. The patching material used is unsaturated polyester resin mortar. The shear recovery is assessed on the basis of the patched beam’s behavior under flexure-shear load in comparison with those of normal beams. The behavior observed include cracking failure mode, strains of the reinforcements, and load-deflection behavior. The results indicate that the UPR mortar is capable to restore the strength of the damage reinforced concrete beam. The characteristic of UPR mortar (low elastic modulus and high strength) can be the origin of the overall behavior of the patched reinforced concrete beams.
EN
The paper presents the research on reinforced concrete (RC) beams strengthened with carbon fibre reinforced polymer (CFRP) strips with various configurations in terms of anchoring and tensioning. The five full-scale RC beams with the total length of 6.0 m were strengthened with passive strips, without and with mechanical anchorages at their ends, as well as with strips tensioned by the novel prestressing system with three various prestressing levels ranging from 30 to 50% of the CFRP tensile strength. All RC beams were tested under static flexural load up to failure and they were investigated in a full range of flexural behaviour, including the post-debonding phase. The main parameters considered in this study include the use of mechanical anchorages, the effect of tensioning the strips and the influence of the various prestressing levels. Several performance indicators have been established to evaluate the beams’ behaviour. The study revealed that the RC beams strengthened using tensioned CFRP strips exhibited a higher cracking, yielding and ultimate moments as compared to the beams with passively bonded CFRP strips. Moreover, increasing the beams’ prestressing level has a significant positive influence on the performance of strengthened beams. However, it did not affect the ultimate load-bearing capacity of the beams. The optimal prestressing level for the novel system has been determined as 60% of CFRP tensile strength.
15
PL
Konstrukcje żelbetowe w czasie eksploatacji pracują w różnych warunkach środowiskowych, które wywołują korozję prętów zbrojeniowych i betonu o różnej intensywności. Wówczas mamy do czynienia z uszkodzeniami korozyjnymi, którym towarzyszą zarysowanie oraz ubytki betonu, zmniejszenie przekroju prętów zbrojeniowych, a także obniżenie parametrów cech mechanicznych betonu i stali zbrojeniowej. W konsekwencji wpływa to na dalsze bezpieczeństwo oraz użyteczność konstrukcji żelbetowych. W artykule przedstawiono przykłady oceny nośności i odkształcalności belek żelbetowych o różnym stanie oraz zakresie uszkodzeń korozyjnych betonu i prętów zbrojeniowych. Przeprowadzone analizy wykazały, że uszkodzenia korozyjne prętów zbrojeniowych oraz betonu mogą spowodować istotny spodek nośności i zwiększone ugięcie belek żelbetowych.
EN
Reinforced concrete structures work in various environmental conditions during their service life, which cause corrosion of reinforcing bars and concrete of various intensity. In such cases we are dealing with corrosion damage, which is accompanied by scratching and loss of concrete, reduction of cross-sectional area of reinforcing bars as well as lowering the parameters of mechanical properties of concrete and reinforcing steel. Consequently, this affects the further safety and usability of reinforced concrete structures. This paper presents an analytical method and examples of evaluating the load-bearing capacity and deformability of reinforced concrete beams with different state and scope of corrosion damage to concrete and reinforcing bars. The analyses have shown that corrosion damage to rebar and concrete can cause a significant decrease in the load-bearing capacity and increased deflection of reinforced concrete beams.
EN
The present study gives an up-to-date, state-of-the-art review of the application of fiber-reinforced polymer (FRP) composites as an external shear strengthening material for reinforced concrete (RC) flexural members. Based on the critical review of more than a hundred experimental studies, this study discusses the influence of different parameters on the shear behavior of FRP strengthened RC beams. In addition, the present study discusses some of the widely used existing design guidelines for the prediction of the shear contribution of FRP composites. Along with these, this study also briefly discourses the application of numerical methods and soft-computing tools in the field of rehabilitation of shear-deficient RC flexural members using EB-FRP composites. Based on the parametric investigation, the current study empowers readers to recognize the existing gaps in the literature that should be examined in the future. Finally, the article concludes by summarizing key points of the shear strengthening of RC beams comprising FRP composites.
EN
The paper deals with the working peculiarities of the support zones of reinforced concrete elements subject to bending with due account of the eccentric compression and tension. The authors performed simulation of the stress-strain behaviour of the indicated structures with the aid of “Lira” software which results are shown in the graphical and tabulated form. The performed simulation allowed of tracing the work of the studied sample beams till collapse. Such approach made it possible to single out and generalize the main collapse patterns of the inclined cross-sections of the reinforced concrete elements subject to bending on which basis the authors developed the improved method to calculate their strength (Karpiuk et al., 2019).
EN
Determination of shear-load-bearing capacity of reinforced concrete beams (according to the current normative documents), comprises particular recommended values, which do not depend on the parameters of the sample or load. This article de-scribes the methodology for determination the shear strength with suggestions for calculation the coefficient CRd,c and compressed element tilt angle Ѳ while reinforced concrete elements` calculation with the use of “truss model”. In order to confirm the methodology 4 reinforced concrete beams were tested. Tests were performed in order to investigate each particular inclined section separately. Variable parameter was the relative shear span a/d, with its values a/d=2, a/d=1,5 and a/d=1. Another parameter was the usage of composite strengthening system, made for relative shear span a\d=2. Samples were tested as single-span beams subjected to short-term loading. The calculation with the use only the values, given in norms showed significant divergence of results. Using the refined parameter values provided the convergence of results within 16-29% toward overestimation of the experimental data. The composite reinforcement system calculation showed the overestimation of 23%, which is within the same limits as for the control samples.
EN
In this work on the basis of the developed and tested mathematical model, the numerical experiment is conducted in order to study in more detail the specifics of performance of concrete beams` with combined reinforcement. For this purpose nine series of reinforced concrete beams with different combination of steel bars (A400C, At800, A1000) and ribbon reinforcement (C275) were modeled. In the developed series two classes of concrete were used: C50/60, C35/45. The functions derived on the basis of mathematical modeling allow us to determine the recommended percentage of high-strength reinforcement of common reinforced concrete structures with single reinforcement. Therefore, the possibility is obtained to reduce the total structures` reinforcement percentage, increasing their deformability by the specified value without affecting the bearing capacity.
20
PL
Belki żelbetowe wzmacnia się na ścinanie stosując strzemiona na obrzeżach przekroju poprzecznego. Strefa rdzeniowa przekroju, w której występuje duże naprężenie ścinające, jest zazwyczaj niezbrojona. Prowadzi to do nagłego pojawienia się i rozprzestrzeniania pęknięć oraz do kruchych uszkodzeń pod wpływem ścinania. W artykule przedstawiono badania nowego sposobu wzmocnienia elementów żelbetowych na ścinanie za pomocą siatki spawanej z drutu stalowego, umieszczonej wzdłuż belki w strefie rdzeniowej przekroju. Wyniki wskazują na to, że zastosowana siatka bardziej skutecznie przenosi ścinanie, zmieniając zarazem mechanizm zniszczenia z kruchego na plastyczny.
EN
The present practice of using shear reinforcement in the form of stirrups, which go round near to the periphery in reinforced concrete beams, leaves the core zone of the cross-section, where there is the existence of high shear stress, un-reinforced. This leads to sudden appearance and propagation of cracks, leading to brittle failures under shear. This paper presents an experimental study on the new way of using the welded wire mesh [WWM] for resisting shear in reinforced concrete members. The method consists of using a prefabricated mesh such as welded wire mesh as core zone reinforcement, placed longitudinally apart from conventional rectangular stirrups/ties. The study indicated improved performance compared to the shear resistance of RC beams with conventional stirrups.
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