The article presents experimental tests of a new type of composite bar that has been used as shear reinforcement for concrete beams. In the case of shearing concrete beams reinforced with steel stirrups, according to the theory of plasticity, the plastic deformation of stirrups and stress redistribution in stirrups cut by a diagonal crack are permitted. Tensile composite reinforcement is characterized by linear-elastic behavior throughout the entire strength range. The most popular type of shear reinforcement is closed frame stirrups, and this type of Fiber Reinforced Polymer (FRP) shear reinforcement was the subject of research by other authors. In the case of FRP stirrups, rupture occurs rapidly without the shear reinforcement being able to redistribute stress. An attempt was made to introduce a quasi-plastic character into the mechanisms transferring shear by appropriately shaping the shear reinforcement. Experimental material tests covered the determination of the strength and deformability of straight Glass Fiber Reinforced Polymer (GFRP) bars and GFRP headed bars. Experimental studies of shear reinforced beams with GFRP stirrups and GFRP headed bars were carried out. This allowed a direct comparison of the shear behavior of beams reinforced with standard GFRP stirrups and a new type of shear reinforcement: GFRP headed bars. Experimental studies demonstrated that GFRP headed bars could be used as shear reinforcement in concrete beams. Unlike GFRP stirrups, these bars allow stress redistribution in bars cut by a diagonal crack.
The paper presents the results of tests for flexural tensile strength (fct,fl) and fracture energy (Gf) in a three-point bending test of prismatic beams with notches, which were made of steel fibre reinforced high-strength concrete (SFRHSC). The registration of the conventional force–displacement (F–δ) relationship and unconventional force-crack tip opening displacement (CTOD) relationship was made. On the basis of the obtained test results, estimations of parameters fct,fl and Gf in the function of fibre reinforcement ratio were carried out. The obtained results were applied to building and validating a numerical model with the use of the finite element method (FEM). A non-linear concrete damaged plasticity model CDP was used for the description of the concrete. The obtained FEM results were compared with the experimental ones that were based on the assumed criteria. The usefulness of the flexural tensile strength and fracture energy parameters for defining the linear form of weakening of the SFRHSC material under tension, was confirmed. Own equations for estimating the flexural tensile strength and fracture energy of SFRHSC, as well as for approximating deflections (δ) of SFRHSC beams as the function of crack tip opening displacement (CTOD) instead of crack mouth opening displacement (CMOD), were proposed.
This paper investigates composite reinforcement with regard to its use as longitudinal reinforcement. The methods used to calculate the shear strength of concrete members reinforced with fibre-reinforced polymer (FRP) bars are analysed. The main parameters having a bearing on the shear strength of beams reinforced with composite bars are defined. A comparative analysis of the shear strength calculating algorithms provided in the available design recommendations concerning FRP reinforcement and formulas derived by others researchers is carried out. A synthesis of the research to date on sheared concrete members reinforced longitudinally with FRP bars is made. The results of the studies relating to shear strength are compared with the theoretical results yielded by the considered algorithms. A new approach for estimating the shear capacity of support zones reinforced longitudinally with FRP bars without shear reinforcement was proposed and verified. A satisfactory level of model fit was obtained—the best among the available proposals. Taking into account the extended base of destructive testing results, the estimation of the shear strength in accordance with the proposed model can be used as an accompanying (non-destructive) method for the empirical determination of shear resistance of longitudinally reinforced FRP bars.
This paper discusses the rheological properties of normal (ordinary) strength concrete. The results of tests aimed at determining the creep strains and shrinkage strains in normal strength concretes modified with steel fibre reinforcement are presented. The tests were divided into three groups. Steel fibre reinforced concretes (SFRCs) with a different composition were studied in each of the groups. Hook steel fibres, 50-mm long and 0.8 mm in diameter, were used in the tested SFRCs. The latter had an average compressive strength of 35.17Á59.18 MPa and a steel fibre content of 0, 25, 35, 50 and 65 kg per 1 m 3 of the concrete mixture respectively. Functional dependences for the increase in shrinkage and creep strains over time are given. The problem of the effect of aggregate grading on creep strains is addressed. Conclusions concerning the rheological deformability of steel fibre reinforced concrete are drawn.
This paper deals with problems connected with the design and operation of thin-walled steel silos for storing pelleted materials. A failure of a faultily designed silo is described and its causes are examined. The parameters of the stored material were determined. The exceptional (unforeseen) loads produced by arching and their consequences were analysed. In order to compare the effect of calculation assumptions on the degree of use of the load-bearing capacity of the stringer its buckling capacity under the stored material load alone was checked. On the basis of the analyses the probable course of the events leading to the failure was determined. It is pointed out that the exceptional loads and the disturbance of the bulk material flow by silo structural and technological fittings need to be taken into account in the design of silos. Reference to this paper should be made as follows: Antonowicz, R.; Bywalski, C.; Kamiński, M. 2014. Analysis of loads and structural capacity of steel silo with corrugated wall for pelleted material, Journal of Civil Engineering and Management 20(3): 372-379. http://dx.
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