Remigijus Šalna

The influence of shear span ratio on load capacity of fibre reinforced concrete elements with various steel fibre volumes

Abstract This paper analyses the influence of steel fibre volume and shear span ratio on the strength of fibre reinforced concrete elements in various states of stress. 36 beams with three different shear spans (a/h = 1, 1,5, and 2 %) and three different fibre volumes (1, 1,5, and 2 %) were tested to examine how these factors influence the behaviour of such elements. Test results suggest that steel fibre volume and shear span can increase load capacity, plasticity and cracking. Experimental research showed that steel fibre volume has different influence at different shear span ratios. Regression analysis of experimental data was carried out and empirical approach showing different effect of these factors was proposed. Furthermore, test results were compared with different theoretical and empirical approaches of other authors.

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.

Probability based design of punching shear resistance of column to slab connections

AbstractThe paper analyzes the dependence of punching shear strength reliability index β, calculated according to EN 1992-1-1:2004 (2004) and STR 2.05.05:2005 (2005) in reinforced concrete floor slab-to-column joint on the values of random factors. The paper deals with theoretical research of the influence of independent random variables, such us the value of the characteristic compressive strength fck of concrete, the area As of the longitudinal reinforcement, effective cross-section depth d and the ratio of the self-weight and the effective load on the value of the reliability index β. The paper presents experimental results of reinforced concrete slabs with different longitudinal reinforcement ratio ρ subjected to a concentrated load. It was determined that when the effective load makes around 50% of the construction self-weight load, i.e. Gk /Qk = 2 and when minimal variation coefficient estimates are taken (for concrete strength δfc = 0.1, for effective depth δd = 0,1 and for the area of longitudinal...

Probability-based design of an optimal elastic–plastic truss

Abstract According to Eurocode EN 1990 and Lithuanian Technical Regulation of Construction STR 2.05.03:2003, structures should be designed to satisfy reliability requirements. The reliability of a structure can be achieved using one of 3 methods: partial factor (PF), PF assisted by testing and direct probability-based method. When PF methods are used, the determined reliability of a structure is often greater than required; therefore the direct probability methods allow a more cost-efficient design. The reviewed literature suggests that even greater economical effect can be achieved by combining probability-based design methods with optimization. Unfortunately, the literature presents very few such methodologies. This article focuses on an optimal design of a truss under variable repeated loading at shakedown. The authors propose a model of a truss volume minimization problem with direct probabilistic evaluation of safety margin. The developed technique allows finding minimum volume of desirable reliabili...

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.

Experimental study of flexural behaviour of layered steel fibre reinforced concrete beams

AbstractThe building of structures from steel fibre reinforced concrete (SFRC) in the external and conventional reinforced concrete (RC) in the internal layer represents an economical alternative of structures effectively using SFRC. The paper presents test results of flexural behaviour of layered beams with SFRC external layers and RC internal layer. The behaviour of these beams is compared to test results of SFRC and conventional RC beams. The test results show, that the flexural load capacity for all series of beams is nearly similar, but the deflections of layered beams are less comparing to monolithic ones. It also been shown that the equations indicated in the Eurocode 2 can be used to design the flexural reinforcement in layered SFRC beams.