Juozas Valivonis

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 in- crease of contact between concrete and sheeting pre-compressing forces and concrete transverse strain restraining forces.

A model for strength and strain analysis of steel fiber reinforced concrete

Abstract The article proposes a model for strength and stain analysis of steel fiber reinforced concrete (SFRC). The model is based on general principles for creating and modelling structural composites and on reinforced concrete code. Differently from other examples, the elastic and plastic properties of the components (concrete and steel) of the introduced model are directly taken into account. The model gives an opportunity to determine tension and compression strength, the elasticity modulus of fiber concrete and the main parameters of its elasticity and plasticity. A good agreement between the obtained results and those of experiments performed by other investigators was confirmed. Differences between the ratios of theoretical and experimental values are insignificant and vary within the limits of 1.06–1.10. This model may be used for the analysis of reinforced concrete members reinforced by steel fibers (SFRC) in a dispersible way assuming stress distribution diagrams.

Study on shear resistance of fiberreinforced polymer–reinforced concrete beams:

This article is aimed to investigate the shear resistance of the beams reinforced with fiber-reinforced polymer stirrups. Together with theoretical analysis of the existing shear resistance provisions in design codes and literature, an experimental research was performed. During the experimental investigation, four doubly reinforced rectangular concrete beams were designed, produced, and tested to failure. A new analytical calculation method (including, but not limited to statistical validation) to investigate the shear response of fiber-reinforced polymer–reinforced concrete beams has been developed. A database with 102 beams was compiled, in order to evaluate the guideline provisions and proposed analytical calculation method. The experimental results were compared with theoretical results obtained by the proposed analytical calculation method. Correlation between analytical and experimental results is more accurate than using the existing provisions in design codes and literature for fiber-reinforced polymer–reinforced concrete 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.

PECULIARITIES OF STRUCTURAL PROPERTIES OF MASONRY FROM HOLLOW BLOCK UNITS AND THEIR ESTIMATION

Summary Performed analyses of investigations have shown that properties of masonry from hollow blocks depend on many factors, and on material type and shape of the blocks including. But there is no unified method for determining the main structural properties-the compressive strength and modulus of elasticity. Theoretical investigations into masonry from hollow blocks and analysis of character of failure have shown that horizontal stress due to vertical loads has great influence on the strength of such masonry. The failure is initiated by vertical cracks crossing transverse webs. Values of strengths of concentrically compressed masonry calculated according to codes [2, 3] lead to different deviations from experimental results. Lower deviations for masonry of blocks are obtained according to [2] than according to [3]. Strength of masonry of calcium silicate blocks calculated by [3] is greater than that determined by experiments. Modulus of elasticity of such type masonry is lower than that of the same stre...

RC Beams strengthened with HPFRCC: Experimental and numerical results

AbstractThe 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 th...

Kompozitinės armatūros inkaravimo betone ypatumai@@@Anchorage Characteristics of Non-Metallic Reinforcement for Concrete

Santrauka Straipsnyje nagrinėjamos kompozitinės armatūros inkaravimo betone problemos. Pateikiamos projektavimo normų (ACI, STR, JSCE) ir rekomendacijų (fib MC 2010) metodikos armatūros inkaravimo ilgiui nustatyti. Atlikta eksperimentinių rezultatų ir teorinių skaiciavimų lyginamoji analizė. Aptarti eksperimentiniai armatūros ir betono sukibties stiprio nustatymo būdai, betono ir armatūros sukibimą veikiantys veiksniai. Remiantis sio darbo rezultatais nustatyta, kaip armatūros inkaravimo ilgis priklauso nuo armatūros ir betono mechaninių savybių, geometrinių parametrų. Pateikiamos sių veiksnių ir kompozitinės armatūros inkaravimo ilgio priklausomybės.

Gelžbetoniniu konstrukciju stiprinimo anglies pluoštu technologiniai ir konstrukciniai ypatumai

Santrauka Konstrukcijoms stiprinti paskutiniu metu naudojamas anglies pluostas, kuris yra kur kas stipresnis už pliena ir turi geresniu deformaciniu savybiu. Klijuojant pluosta klijai isigeria i pavirsinius betono sluoksnius. Tai pakeicia fizines ir mechanines betono savybes, kurios priklauso nuo jo struktūros. Eksperimentiniai gelžbetoniniu siju tyrimai patvirtino kliju isigerimo i betona ir betono sustiprejimo prielaida. Nustatyta, kad supleisejus gelžbetoniniu konstrukciju tempiamajai zonai, betono ir anglies pluosto jungties standumas sumažeja. Jungtyje isryskejusios slyties deformacijos sumažina sustiprinto elemento standuma ir stipruma. Buvo nagrineti ir papildomi anglies pluosto tvirtinimo būdai. Nustatyta ju itaka stiprinimo efektyvumui. Pateikta sustiprintu elementu stiprumo skaiciavimo metodika, leidžianti ivertinti anglies pluosto ir betono jungties standuma. Gauti rezultatai palyginti su eksperimentiniu tyrimu rezultatais.

Load-bearing capacity of flexural reinforced concrete members strengthened with fiber-reinforced polymer in fracture stage

The article examines the behavior of flexural reinforced concrete members, strengthened with fiber-reinforced polymers (FRP), under the ultimate loading conditions (in fracture stage). One of the main problems of such elements is sudden and brittle failure mode caused by FRP debonding. The method for the calculation of load-bearing capacity of the normal section of flexural reinforced concrete members, strengthened with various types of FRP, is proposed in this article. This method is based on the theory of fracture mechanics of solids. The reduction of overall member stiffness due to the slip between concrete and FRP is estimated by reducing the FRP stress according to the built-up bars theory. Such reduction allows the prediction of load-bearing capacity of strengthened members sufficiently precisely even for sudden and brittle FRP debonding failure mode. The numerical results are compared with experimental ones. In total, 55 reinforced concrete beams, strengthened with externally bonded or near surface mounted carbon fiber-reinforced polymer and glass fiber-reinforced polymer sheets, plates, strips, and rods, are analyzed in this comparison. Experimental results were collected from various scientific publications. A focus is made on the depth of the crack in critical normal section and FRP strain–stress relationship.