Cracking and strength of reinforced concrete structures in flexure strengthened with carbon fibre laminates

The article presents the analysis of the cracking moment and the strength of beams reinforced with external carbon fibre. Experimental research of beams strengthened in this way has been carried out. Three different methods of anchoring external reinforcement were applied to strengthen the beams. The influence of anchorage on the cracking moment and the strength of the beams has been defined. Design methods for defining the cracking moment and the strength have been presented. The design procedure for defining the cracking moment evaluates the curvilinear stress diagrams of concrete under tension and compression. The design procedure for defining the strength of the structures evaluates the stiffness of the contact between the carbon fibre and the concrete. The design results are provided. Comparative analysis of the experimental and the theoretical results has been performed. Anglies pluoštu armuotų lenkiamųjų konstrukcijų pleišėtumas ir stiprumas Santrauka Straipsnyje analizuojamas sijų su išorine anglies pluošto armatūra plyšių susidarymo momentas ir stiprumas. Atlikti anglies pluoštu sustiprintų sijų eksperimentiniai tyrimai. Trys skirtingi išorinės armatūros inkaravimo būdai buvo pritaikyti sijoms stiprinti. Nustatyta inkaravimo įtaka plyšių susidarymo momentui ir stiprumui. Pateikti skaičiavimo metodai plyšių susidarymo momentui ir stiprumui nustatyti. Plyšių susidarymo momento skaičiavimo metodika pagrįstos kreivalinijinės tempiamojo ir gniuždomojo betono įtempių diagramos, o konstrukcijų stiprumo skaičiavimu įvertintas anglies pluošto ir betono kontakto standumas. Pateikti skaičiavimo rezultatai. Atlikta eksperimentinių ir teorinių rezultatų palyginimo analizė. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: išorinė anglies pluošto armatūra, stiprinimas, plyšių susidarymo momentas, stiprumas

Deflection of reinforced concrete beams strengthened with CFRP

This paper presents the results of an experimental study to investigate the deflection of reinforced concrete beams strengthened with external CFRP reinforcement. The influence of anchoring of external reinforcement was investigated. CFRP reinforcement was anchored in three different ways. Steel clamps, fibre wraps and steel pins were used for anchoring. Also different prepressing levels and different areas of steel clamps were used. The analysis of results of experimental research shows that anchoring of external reinforcement affects the performance and deflection of the strengthened reinforced concrete beams

RC Beams strengthened with HPFRCC: Experimental and numerical results

The study analyses the behaviour of reinforced concrete beams strengthened with high-performance fibre-reinforced cementitious composite (HPFRCC). Six beams were divided into two equal groups and strengthened. In total, nine beams were tested, including three control beams that were not strengthened. Control beams were over-reinforced. The beams of the first group were strengthened in the compressed part while those of the second group were strength­ened in the compressed and tensioned parts of the section. The experimental results of all tested beams were compared with numerical results. The positive and negative effects of strengthening the resistance and serviceability of the beams were experimentally determined. The obtained results showed that the load-carrying capacity of all strengthened beams increased and their deflections decreased; however, crack width in the beams of the second group increased while that of the beams of the first group decreased. The width of cracks increased because the number of cracks decreased. The findings of this study show a comparison of strains, deflections, cracking and load-carrying capacity and indicate that strengthening changed the failure of the beams

Flexural capacity and stiffness of monolithic biaxial hollow slabs

The article presents a research on flexural behaviour of hollow monolithic reinforced concrete slabs. It focuses on the results of experimental investigation into full-size hollow reinforced concrete slabs and analyses their flexural capacity and stiffness. The self-weight of the slabs directly depends on the shape and number of hollows. An increase in the hollowness of a slab significantly reduces the load caused by self-weight. This allows increasing the estimated length of the slab under the same payload. An increase in the amount of hollows of the slab changes the stiffness of the slab cross-section that has a direct impact on slab deflection. Considering the shape of the slab cross-section, theoretical calculations of the flexural capacity and deflection of experimental slabs were made. The design of a new type of slabs and variations in different parameters of the slab experience difficulties in conducting a large amount of experimental tests. Therefore, the initial analysis may apply to numerical simulation. The paper describes the principles of designing a numerical model. The calculations were made using DIANA software. The stiffness and flexural capacity of the hollow slabs were established employing numerical simulation compared to the results of experimental investigations. The findings indicate that numerical simulation can be applied for analysing the stress state of the examined structures

Analysis of Strain State and Cracking of Cocnrete Sleepers

Prestressed concrete sleepers are the most common type of the sleepers used on the railroad. They serve as rail supports and absorb loads induced by trains. Sleepers are important for the durability and safety of the railroad and are exposed to various loads and an agressive environment during exploitation. Therefore, different types of appearing damage can determine their reliability. The article briefly discusses possible causes of damage and the deterioration of prestressed concrete sleepers. End cracking and damage at the rail seat was determined during the inspection of used sleepers. Therefore, the strain state and cracking of the rail seat of the sleeper was analysed under static and dynamic loads. The paper provides the obtained results of experimental research of used and new sleepers

Deflection of flexural reinforced concrete structures with external non-metallic reinforcement (experimental and theoretical investigation)

In many cases concrete structures with prestressed steel being sufficiently strong do not meet requirements for stiffness. It is possible to avoid steel prestressing in concrete structures by means of providing additional non-metallic reinforcement, which gives opportunity to increase stiffness of beams significantly. Experimental investigations of reinforced concrete beams with external non-metallic reinforcement were made. Method for calculation of deflection of beams with external non-metallic reinforcement is presented in this article. Theoretical calculations of deflections using the proposed method were performed. Sufficiently good agreement with experimental deflection values was obtained. Frist Published Online: 30 Jul 201

Analysis of behaviour of contact between the profiled steel sheeting and the concrete

In designing composite structures it is necessary to verify the following three sections: normal, diagonal and horizontal. The behaviour of composite steel‐concrete structures with external profiled reinforcement is directly dependent on the deformability and contact strength. In contact behaviour between concrete and profiled steel sheeting three stages are distinguished: the first ‐ until chemical bond is effective, the second ‐ after failure of chemical bond, the third ‐ after failure of mechanical bond when composite action is provided by friction and anchors. Deformability and contact strength is substantially influenced by the shape of the profiled sheeting, the pre‐compressing force acting perpendicularly to a contact plane and the horizontal forces restraining transversal strains of concrete. It was established by investigations that a shear strength of contact between concrete and profiled steel sheeting increases and shear strain decreases with an increase of contact between concrete and sheeting pre‐compressing forces and concrete transverse strain restraining forces. Plieninio profiliuotojo lakšto ir betono kontakto standumo įtaka kompozitinių konstrukcijų elgsenai Santrauka Skaičiuojant sluoksniuotąsias konstrukcijas, būtina tikrinti pjūvius: statmenąjį, įstrižąjį ir horizontalųjį. Kompozitinių plieninių ir betoninių konstrukcijų su išorine profiliuotąja armatūra kontakto deformatyviškumas ir stiprumas turi tiesioginę įtaką konstrukcijų elgsenai. Betono ir plieninio profiliuotojo lakšto kontakto elgsenoje išskiriamos trys stadijos: pirmoji – kol nepažeistas cheminis sukibimas, antroji – pažeidus cheminį sukibimą, trečioji – pažeidus mechaninį sukibimą, kai bendrą elgseną užtikrina trintis ir inkarai. Kontakto deformatyviškumui ir stiprumui didelę įtaką turi profiliuotojo lakšto forma ir kontakto apspaudimo jėga. Eksperimentinių tyrimų metu bandinių kontaktas buvo apspaustas kontakto plokštumai statmena jėga. Tyrimais nustatyta, kad, didėjant kontakto apspaudimo jėgos dydžiui, kontakto tarp betono ir plieninio profiliuotojo lakšto stipris didėja. Veikiant apspaudžiančiajai jėgai, kontakto šlyties deformacija mažėja. Raktiniai žodžiai: profiliuotasis plieninis lakštas, betonas, jungtis, stipris, slydimas. First Published Online: 14 Oct 201

Reinforcement characteristics of prestressed concrete beams with fiber-reinforced polymer (FRP) tendons

The basic advantages of fiber-reinforced polymer (FRP) reinforcement are reviewed. FRP tendons exhibit linear elastic response to rupture without yielding and thus failure is expected to be brittle. Structural beahaviour of beams prestressed with FRP tendons is different from that of beams with traditional steel reinforcement. Strength design approach for prestressed beams with FRP tendons is based on the concept of brittle ratio, reinforcement ratio at which concrete fails in compression at the same time as FRP tendon ruptures. Depending on reinforcement ratio, the flexural behaviour of the beam can be devided into several groups. If reinfrocement ratio is equal to brittle ratio, beams fail by rupture of tendons and crushing of concrete simultaneously. Beams with reinforcement ratio, less than brittle ratio, are under-reinforced and will fail by rupture of tendons. When reinforcement ratio is greater than brittle ratio, concrete fails in compresion prior to rupture of tendons. Brittle ratio was calculated by different expressions proposed in scietific literature, and particular results were given. It has been shown, that brittle ratio is influenced by the mechanical properties of FRP and concrete. Lenkiamųjų iš anksto įtemptų gelžbetoninių elementų armavimo kompozitine armatūra ypatumai Santrauka Straipsnyje aptariamos pagrindinės iš anksto įtempto gelžbetonio kompozitinės armatūros (FRP) savybės. Kompozitinė armatūra iki pat lenkiamųjų gelžbetoninių ar iš anksto įtempto gelžbetonio elementų laikomosios galios netekimo išlaiko tampriąsias savybės. Šia armatūra armuotų sijų, lyginant su tradicine plieno armatūra, elgsena skiriasi. Galimi keli kompozitine (FRP) armatūra armuotų lenkiamųjų elementų suirimo atvejai. Konstrukcijų su kompozitine (FRP) armatūra suirimo pobūdis gali būti nustatytas remiantis mokslinėje literatūroje pasiūlytomis formulėmis racionaliam armavimo procentui apskaičiuoti. Gauti skirtingi skaičiavimų rezutlatai. Parodyta, kaip armavimo procentas priklauso nuo mechaninių betono ir neplieninės (FRP) armatūros savybių. First Published Online: 16 May 2013 Reikšminiai žodžiai: anglies pluoštas, armavimo procentas, išankstinis įtempimas, tamprumo modulis, relaksacij

Technological-structural peculiarities of reinforced concrete structures strengthened with carbon fiber-reinforced polymer

Carbon fiber‐reinforced polymer is used for strengthening of reinforced concrete structures with externally bonded reinforcement. This fiber has more strength and better deformation properties than steel. During glueing, the glue is absorbed in the surface layer of concrete. It changes physical and mechanical properties of concrete. This effect depends on the structure of concrete. Experimental investigations sustained absorbing of glue and strengthening of concrete. The rigidity between concrete and carbon fiber polymer layer is smaller in cracked zones. Shear deformations decrease rigidity and strength in a contact zone. The authors methods were investigated in fastening carbon fiber‐reinforced polymer to concrete. The efficiency of these methods was definited. Theoretical results are compared with experimental results. Gelžbetoniniu konstrukciju stiprinimo anglies pluoštu technologiniai ir konstrukciniai ypatumai Santrauka Konstrukcijoms stiprinti paskutiniu metu naudojamas anglies pluoštas, kuris yra kur kas stipresnis už plieną ir turi geresnių deformacinių savybių. Klijuojant pluošta klijai įsigeria į paviršinius betono sluoksnius. Tai pakeičia fizines ir mechanines betono savybes, kurios priklauso nuo jo struktūros. Eksperimentiniai gelžbetoninių sijų tyrimai patvirtino klijų įsigėrimo į betoną ir betono sustiprėjimo prielaidą. Nustatyta, kad supleišėjus gelžbetoninių konstrukcijų tempiamajai zonai, betono ir anglies pluošto jungties standumas sumažėja. Jungtyje išryškėjusios šlyties deformacijos sumažina sustiprinto elemento standumą ir stiprumą. Buvo nagrinėti ir papildomi anglies pluošto tvirtinimo būdai. Nustatyta jų įtaka stiprinimo efektyvumui. Pateikta sustiprintų elementų stiprumo skaičiavimo metodika, leidžianti įvertinti anglies pluošto ir betono jungties standumą. Gauti rezultatai palyginti su eksperimentinių tyrimų rezultatais. First Published Online: 21 Oct 2010 Reikšminiai žodžiai: gelžbetoninės konstrukcijos, stiprinimas, anglies pluoštas, tvirtinimo būdai, jungties standumas, efektyvuma

Inžinierius Pranas Markūnas

Knygoje rašoma apie iškilų statybos inžinierių, tarpukariu suprojektavusį ir pastačiusį labai daug tiltų, visuomeninių ir gamybinių pastatų, gyvenamųjų namų. Pranas Markūnas yra laikomas gelžbetonio konstrukcijų plėtros Lietuvoje patriarchu. Jis buvo beveik visų stambiausių tarpukario pramoninių statybų projektuotoju. Pranas Markūnas daug metų dirbo pedagoginį darbą Vytauto Didžiojo universitete, dėstė statybinių konstrukcijų dalykus, vadovavo diplomantams, skatino jaunimą vykdyti mokslinius tyrimus. Leidinys skirtas plačiajai visuomenei, besidomintiems mokslo ir technikos raida Lietuvoje, studijuojančiam jaunimui