W artykule omówiono zmodyfikowany program merytoryczny ćwiczeń laboratoryjnych prowadzonych w ramach przedmiotu Konstrukcje betonowe na studiach pierwszego stopnia na Wydziale Inżynierii Lądowej Politechniki Warszawskiej. Zadaniem, jakie studenci mają do wykonania w ramach tych ćwiczeń, jest grupowe zaprojektowanie belki żelbetowej tak, aby przy narzuconych ograniczeniach przeniosła jak największe obciążenie. Studenci, będący po zaledwie jednym semestrze studiowania konstrukcji betonowych („świeże głowy”, bez doświadczenia) projektują belkę, samodzielnie ją wykonują, a następnie badają jej zachowanie pod obciążeniem aż do zniszczenia. Podczas wspólnych zajęć podsumowujących są dyskutowane: sposoby zniszczenia belek, błędy popełnione podczas ich projektowania lub to, co spowodowało, że pewne belki przeniosły obciążenie większe niż inne.
EN
The article presents the modified content of the laboratory exercises conducted as part of the course Concrete Structures in the first-cycle studies at the Faculty of Civil Engineering of the Warsaw University of Technology. The task that students have to perform in these exercises is to design a reinforced concrete beam in groups so that it can carry the greatest possible load within the imposed constraints. Students with just one semester of studying concrete structures („fresh minds”, with no experience) design a beam, build it themselves, and then study its behavior under load until failure. During the joint debriefing sessions, the following are discussed: ways in which beams were damaged, errors made during their design, or what caused some beams to carry a greater load than others.
Przedstawiono uproszczony model tkaniny Peirce’a oraz na podstawie dostępnej literatury opisano podstawowe naprężenia działające na tkaniny, takie jak przy rozciąganiu, zginaniu i ścinaniu. Uwaga została skupiona na współczynniku podatności tkanin na formowanie odzieży, który ma decydujący wpływ na jej układalność oraz dopasowanie do sylwetki człowieka. Wykazano również jak można zapobiegać trudnościom związanym ze złą podatnością na formowanie.
EN
A simplified Peirce fabric model is presented and the basic stresses acting on fabrics, such as in tension, bending and shear, are described based on the available literature. Attention was focused on the formability coefficient of fabrics, which has a decisive effect on the garment’s drapeability and fit the human figure. It is also shown how the difficulties associated with a poor fabric formability can be prevented.
W artykule przedstawiono i porównano wybrane metody wyznaczania wartości sprężystych naprężeń krytycznych przy ścinaniu stalowych środników z żebrami podłużnymi na dwóch poziomach. Analizę porównawczą oparto o procedury podane w projekcie normy prEN 1993-1-5:2021 oraz o wyniki analiz numerycznych. Obliczenia przeprowadzono dla trzech grubości środników i dla różnych przekrojów żeber podłużnych. Wykonane analizy uwidoczniły istotne różnice w wynikach obliczeń w zależności od stosowanego podejścia obliczeniowego.
EN
The article presents and compares selected methods for determining elastic critical shear stress values of steel webs with longitudinal stiffeners. The comperative analysis is based on the procedures given in the draft standard prEN 1993-1-5:2021 and on the results of numerical analyses. The calculations were carried out for three web thickness and for different cross-sections of longitudinal stiffeners. The analyses showed significant differences in the calculations results depending on the calculation approach.
The paper investigates the effect of stirrup spacing s and stirrup diameter φs on the shear capacity of beams with non-metallic reinforcement. Stirrups of φ8 were used with a spacing of 120 mm, and stirrups of φ12 were used with a spacing of 270 mm, maintaining a uniform transverse reinforcement ratio Ρw = 0,33%. The influence of stirrup spacing was analysed in beams with two different longitudinal reinforcement ratios: Ρl = 2.9% and Ρl = 3.7%. The paper presents the quantitative and qualitative influence of these parameters on the shear capacity and behaviour of the beams.
PL
W artykule przeanalizowano wpływ rozstawu strzemion s i ich średnicy φs na nośność na ścinanie belek ze zbrojeniem niemetalicznym. Przyjęto strzemiona φ 8 w rozstawie co 120 mm oraz strzemiona φ 12 w rozstawie co 270 mm, zachowując jednolity stopień zbrojenia poprzecznego Ρw = 0,33%. Analizowano wpływ rozstawu strzemion w belkach o dwóch różnych stopniach zbrojenia podłużnego: Ρl = 2,9% oraz Ρl = 3,7%. Przedstawiono ilościowy i jakościowy wpływ tego parametru na nośność na ścinanie oraz zachowanie się belek.
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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.
This paper presents an analysis of variable parameters on the shear capacity of elements reinforced with FRP bars: longitudinal reinforcement ratio; transverse reinforcement ratio; axial stiffness of reinforcement; shear slenderness; concrete compressive strength; spacing of stirrups; depth; shape of beam cross-section; inclination of transverse reinforcement and bond behaviour of stirrups.
PL
W artykule przedstawiono analizę parametrów zmiennych na nośność na ścinanie elementów zbrojonych prętami FRP: stopnia zbrojenia podłużnego; stopnia zbrojenia poprzecznego; sztywności osiowej zbrojenia; smukłości ścinania; wytrzymałości betonu na ściskanie; rozstawu strzemion; wysokości użytecznej; kształtu przekroju poprzecznego belki; nachylenia zbrojenia poprzecznego oraz przyczepności strzemion.
This paper focuses on confined masonry walls. Confined walls are very popular in the seismic regions and are used as the prevention of excessive cracking, displacement and a loss of structural integrity. In terms of structural engineering, confined walls, similarly to walls in conventional buildings with conventional load-bearing wall structure, can function as the structure restraint, and not only the walls under mainly vertical load. This paper presents the original proposition of the algorithm that determines stiffness of a single area of the confined wall without openings and with openings, which is based on the S-T (strutand-tie) method in accordance with European standards EN 1996-1-1:2010, draft Eurocode 6 (prEN 1996-1-1:2017), having regard to American standards FEMA 274 and FEMA 306.
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Bamboo scrimber beams are prone to brittle failure, and I-shaped steel beams are prone to buckling and out-of-plane instability. To address these issues, the failure process, failure mechanism, deformation and bearing capacity of composite beams made by combining I-shaped steel and bamboo scrimber plates with structural adhesive are studied, taking the shear span ratio (λ) as a variable. The failure modes of the composite beam are mainly bottom-up layer-by-layer tearing of the bamboo scrimber and slight out-of-plane deformation of the I-shaped steel in the late loading period. Meanwhile, the ultimate bearing capacity, load‒displacement curve, load–strain relationship and strain distribution of the mid-span section of the composite beams are obtained, indicating that the overall working performance of these beams is excellent and that the comprehensive effect of the components is remarkable. The shear capacity of the composite beam increases with decreasing shear span ratio. By referring to the existing calculation formula of the shear capacity and fitting the test results, we obtain a calculation model of the shear capacity of a composite beam. The average error between the theoretical values and the test values is 11%, indicating that the method can predict the shear capacity well.
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In this new work, we will investigate the application of a higher-order shear deformable model for elastostatic higher-order displacement, strain, and stress analyses of a shear deformable cylindrical shell. The composite structure is assumed to be composed of a Cu-based matrix reinforced with foldable nanographene, in a thermal environment. The cylindrical shell is reinforced with graphene origami auxetic metamaterial subjected to mechanical and thermal loads. The constitutive relations are extended in thermal environment using three-dimensional Hooke's law where using the mathematical and statistical approach, the effective materials characteristics are experimentally derived as some modification coefficients of foldability, content of reinforcement, and thermal load. The principle of virtual work is used to derive governing equations taking thermal loading into consideration. One can arrive at a parametric analysis and a numerical result investigation through employing an analytical approach to explore elastostatic displacement/strain/stress along the radial coordinate with changes of thermal loads, folding, content characteristics, and other parameters.
Purpose: The study aims to determine the effect of the treatment of alkali solution concentration and soaking time on the mechanical properties of coconut fibre. Design/methodology/approach: The study consists of preparing materials and equipment, immersion of coconut fibre in an alkali solution, drying in a furnace, testing, analysis of test results, and conclusions. Materials and equipment used are coconut fibre, alkali solution, polyester matrix, distilled water, furnace, hydrolysis test, tensile test, and SEM analysis. The sample had two treatments; the first was coconut fibre, which was soaked in the sodium hydroxide solution with 5%, 10%, 15%, and 20% concentrations for 3 hours. The second treatment was coconut fibre soaked in the sodium hydroxide solution with a concentration of 20% for 1, 5, 7, 9, and 11 hours. The samples were then dried in a furnace at 90ºC for 5 hours, and then a hydrolysis test, tensile test, pull-out test, and SEM analysis were carried out. Findings: The results suggest that for immersion in an alkali solution of 20%, the highest tensile strength of coconut coir fibre was obtained in soaking for 3 hours at 280.94 N/mm2, and the highest bonding strength between coconut coir fibres with a matrix polyester was obtained at 5 hours immersion at 7.86 N/mm2. Research limitations/implications: In the given study, coconut fibre was treated by soaking it in 5%, 10%, 15%, and 20% sodium hydroxide solution. Then, a single fibre tensile test was carried out, and a pull-out test was carried out to determine the mechanical properties of coconut fibre as a required effect that had been given. Subsequent studies can be carried out with other treatments using other chemical solutions, such as hydrogen peroxide or potassium permanganate. Originality/value: The tensile strength of coconut fibre without treatment was 186.42 N/mm2, whereas after being immersed in 20% sodium hydroxide solution, the tensile strength became 280.94 N/mm2. Likewise, the shear strength of the interface between the fibre and the polyester matrix was 1.85 N/mm2 for untreated coconut fibre to 3.09 N/mm2 for coconut fibre soaked in a 20% sodium hydroxide solution. The results of the study are intended as data for the use of coconut fibre as a natural fibre-reinforced composite material, for example, as a raw material for fishing boat walls.
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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%.
W artykule przedstawiono rodzaje kotew metalowych stosowanych do betonu i sposoby przekazywania obciążenia z ich korpusu na podłoże. Omówiono różnice i ograniczenia wynikające z budowy poszczególnych kotew. Przedstawiono modele zniszczenia i zachowanie się kotew na skutek ich wyciągania bądź ścinania. Poruszono także niezwykle ważny aspekt instalacji kotew w podłożu zarysowanym.
EN
The paper presents the types of metal fasteners used in concrete and the ways of transferring the load from their body to the concrete. Differences and limitations resulting from the construction of particular fasteners are discussed. Models of failure and behaviour of the fasteners due to tension or shear are presented. An extremely important aspect of anchor installation in cracked concrete is also discussed.
W pracy przedstawiono sposoby wzmacniania elementów żelbetowych przy użyciu biernych i czynnych systemów wzmacniania materiałami z włóknami węglowymi CFRP przyklejanymi na powierzchni betonu lub wklejanymi w betonowe bruzdy. Omówiono zagadnienia wzmocnień dotyczące zginania i ścinania sposobem biernym oraz czynne systemy wzmocnień. Zaprezentowano wyniki badań własnych prowadzonych w Katedrze Budownictwa Betonowego PŁ w zakresie wzmocnień na zginanie metodami EBR oraz NSMR przy użyciu biernych i czynnych technik. Dodatkowo przedstawiono wyniki badań własnych wzmocnień na ścinanie przy użyciu taśm i mat przyklejanych na zewnętrznej powierzchni oraz taśm wklejanych metodą NSMR.
EN
The paper presents strengthening methods of reinforced concrete elements using passive and active strengthening systems with CFRP carbon fibre materials bonded on the concrete surface or embedded in concrete grooves. The issues of passive and active flexural and shear strengthening have been discussed. The results of own research, carried out at the Department of Concrete Structures, have been presented in the field of flexural strengthening by EBR and NSMR methods, using both passive and active techniques. Additionally, the results of the own research on shear strengthening using strips bonded on the surface using the NSMR method have been presented.
This study presents an improvement of the graphical method for plotting the shear and moment diagrams for the structural members under linearly varying loads (triangular and trapezoidal loads). Based on the parabolic nature of the shear function, when the loading varies linearly, and on the relations among load, shear, and moment, a mathematical equation is developed to locate the zero-shear point, while a geometric technique is presented to calculate the parabolic shear area. Five comprehensive examples of beams loaded with linearly varying loads are selected to illustrate the steps of the solution for the proposed techniques. The results demonstrated the applicability of the presented method, and gave exact diagrams compared with the basic graphical method. It is concluded that the proposed improved method is generally more convenient, less time-consuming, and has less computational efforts because it does not require sectioning, solving equilibrium equations, and quadratic formulas compared with the basic graphical method.
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.
The paste content in the self-compacting concrete is about 40% in unit volume. The rheological properties of paste directly determine the properties of self-compacting concrete. In this paper, the effect of silica fume (2, 3, 4, and 5%), limestone powder (5, 10 and 15%), and the viscosity modified admixture (2, 3, 4, 5, 6, and 7%) on the rheological properties were investigated. The effect of admixtures on shear thickening response was discussed based on the modified Bingham model. The results indicate that yield stress and plastic viscosity increased with increased silica fume and viscosity modified admixture replacement. The paste’s yield stress increases and then decreases with limestone powder replacement. The critical shear stress and minimum plastic viscosity are improved by silica fume and viscosity modifying admixture. The critical shear stress first increases and decreases as the limestone powder replacement increases. A reduction in the shear thickening response of paste was observed with silica fume and viscosity modified admixture replacement increase.
Przedstawiono analizę wyników badań ścian wykonanych z bloczków ABK, wzmocnionych nowoczesnymi materiałami FRP. Omówiono zmiany parametrów wytrzymałościowych, odkształceniowych i sposobu zniszczenia ścian wzmocnionych w odniesieniu do ścian niewzmocnionych. Potwierdzono pozytywny wpływ zbadanego ułożenia mat CFRP, wskazując jednocześnie na ograniczenie przy stosowaniu mat GFRP.
EN
The paper presents an analysis of the test results for walls made of AAC blocks strengthened using modern FRP materials. A detailed discussion of changes in strength and deformation parameters as well as the mode of failure of strengthened walls in relation to unstrengthened walls is presented. Tested arrangement of CFRP sheets has been proven to have a positive effecl. At the same time, limitation in the use of GFRP sheets was indicated.
Przedstawiono postępowanie przy sprawdzaniu nośności przekroju ściany ścinanej przy wykorzystaniu wykresu interakcji, zbudowanego według zaleceń Eurokodu 6 (prEN 1996-1-1:2019). Sformułowano niezbędne równania określające nośność przekroju w funkcji pionowego obciążenia NEd. Przeanalizowano wpływ kształtu ściany oraz mimośrodu obciążenia pionowego na kształt wykresu interakcji.
EN
This paper describes the procedure for verifying shear load capacity by means of the interaction diagram drawn as specified in Eurocode 6 (prEN 1996-1-1:2019). Necessary equations for determining load-carrying capacity of cross-section against vertical load NEd were worked out. The effect of wall shape and eccentricity of vertical load on the shape of the interaction diagram was analysed.
The evaluation of friction is an important element in the verification of stability and the determination of the bearing capacity of piles. In the case of cyclic stress, the soil-pile interface has a relaxation which corresponds to a fall in the horizontal stress which represents the normal stress at the lateral surface of the pile. This paper presents an explicit formulation to express the degradation of the normal stress after a large number of shear cycles as a function of cyclic parameters. In this study we are interested in the exploitation of the cyclic shear tests carried out by Pra-ai with imposed normal rigidity (CNS) in order to demonstrate the phenomenon of falling of the normal stress. The approach presented in this paper consists in proposing a simple expression for estimating the degradation of normal stress as a function of cyclic shear parameters after a large number of cycles. The validation of this approach is verified by the application of this formulation to a real case where the comparison of the simulations made by this approach with those recorded on site shows the good adaptation of this approach to this type of problems.
Development of self-compacting concrete (SCC) is a very desirable achievement in the reinforced concrete (RC) structures for overcoming issues associated with many problems such as congestions of steel reinforcement. This non-vibrating concrete is not affected by the skill of workers, and the shape and amount of reinforcing bar arrangement of a structure. Due to the high fluidity and resisting power of reinforcing of SCC, it can be pumped longer distances. In this study, the finite element (FE) modeling of three SCC beams in shear while taking into account, the flexural tensile strength of concrete is computed and the results are compared with the available experimental tested reinforced SCC beams. The stirrups are located at 75 mm apart from the end of beams up to the loading point. The electrical strain gauges (ESGs) have been embedded on the stirrups and their strain readings are taken for every step of load increment. For modeling longitudinal steel reinforcing bars and concrete, the 3-D elements with 2-node and 8-node, are used respectively. The comparison of results obtained by two methods is indicated that a good satisfactory agreement is achieved.
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