The ductility of reinforced concrete beams is very important, since it is essential to avoid a brittle failure of the structure by ensuring adequate curvature at the ultimate limit state. One of the ...procedures used to quantify ductility is based on curvatures, namely, curvature ductility. It is necessary to know the curvature ductility of singly reinforced high-strength concrete (HSC) sections for determining a maximum permissible tensile reinforcement ratio or a maximum depth of the concrete compression area in design codes. The requirements of several codes and methods of prediction of the curvature ductility are based on the experimental results of normal strength concrete (NSC). The rules derived for NSC sections may not be appropriate for HSC sections, and verifications and modifications may be required for the evaluation of curvature ductility of HSC sections. In this study, the major factors affecting the curvature ductility of a singly reinforced HSC beam section are investigated. Based on numerical analyses, a parametric study has been carried out to evaluate the effects of various structural parameters on the curvature ductility of reinforced HSC beam sections.
The shear failure of reinforced concrete beams is one of the fundamental problems in civil engineering; however, the diagonal tension strength of reinforced concrete (RC) beams without stirrups is ...still in question. This paper focuses on the prediction of diagonal cracking strength of RC slender beams without stirrups. In slender beams, flexural cracks develop in the tension zone prior to a diagonal cracking. Using the basic principles of mechanics, but cracking included, and theory of elasticity, a diagonal cracking strength equation is proposed for both normal and high strength concrete beams. The proposed equation, the requirements of six codes of practice and seven equations proposed by different researchers are compared to the experimental results of 282 beams available in the literature. It is found that the predictions from the proposed equation are in good agreement with the experimental results.
The paper presents method of calculation of eigenfrequencies of the cracked reinforced concrete beams including discreet model of crack. The described method is based on the stiff finite elements ...method. It was modified in such a way as to take into account local discontinuities - cracks. In addition, some theoretical studies as well as experimental tests of concrete mechanics based on discrete crack model were taken into consideration. The calculations were performed using the author's own numerical algorithm. Moreover, other calculation methods of dynamic reinforced concrete beams presented in standards and guidelines are discussed. Calculations performed by using different methods are compared with the results obtained in experimental tests.
This study is devoted to the investigation of the vibration of a cracked cantilever beam under moving mass load. The present formulation contains inertial, centripetal and Coriolis forces that depend ...on mass and the velocity of the moving load. The existence of crack induces a local flexibility which is a function of the crack depth, thereby changing its vibration behavior and the eigen-values of the system. The response of the system is obtained in terms of Duhamel integral. The differential equation which involves complicated terms on the right side is solved via an iterative procedure. It has been shown that the centripetal and Coriolis forces make an effect to decrease the deformations on the beam since the deformed beam remains concave during the passage of the moving load. It has also been detected that the previous solutions for the case of moving constant force had several mistakes. The results are exemplified for various values of the variables.
This paper deals with the analysis of cracked flexural reinforced concrete structures with special highlighting of modelling the interaction between concrete and reinforcement. A new approach based ...on the bond stress distribution through the transfer length between the zero-slip and the cracked sections is proposed. Since the cracking phenomenon of concrete occurs, the fracture energy changes in order to appeal to the interaction between concrete and steel. The increment of stresses is evaluated by the bond-slip distribution by means of one-dimensional problem. Besides, the 2D nonlinear description of components behaviour, concrete and steel are considered.
On numerical modelling level, the interaction property is obtained from a variety of fundamental pull out and push out tests, for the most part this phenomenon does not very well represent the bending members. For this object, this study presents a numerical approach, which can compute the distribution stresses at the steel-concrete interface near flexural crack in reinforced concrete beams. Finally, predictions made by the non-linear finite element analysis program and the non-linear material models for concrete, reinforcing bars and bond slip are in good agreement with the experimental results.
This study presents alternative cracking shear strength equations for slender reinforced concrete (RC) beams without stirrups. More than 80 data has been obtained from existing sources of RC beam ...shear test results covering a wide range of beam properties and test methods. The proposed cracking shear strength equations are applied to existing test data for normal strength concrete (NSC) and high-strength concrete (HSC) slender beams and the results are compared with those predicted by the ACI 318 equations. It can be also noted that the test results are in better agreement with proposed cracking shear strengths. However, because the test data for high-strength concrete members are very limited, further research is required to verify these equations.
There are many methods to calculate castellated steel beams; however, neither of these methods determines the rational cross-section selection. Selecting the rational cross-section induces a ...significant reduction in the quantity of steel. A new algorithm for selecting the rational dimensions of the castellated beams is presented in this paper. In future works it may be adopted and used for design. 12 m long beams, web thickness 6-12 mm and web depth 500-1000 mm are analysed in this paper. Opening size used varies from half of the web depth to the total web depth minus 100 mm. The chosen cross-sectional area of two flanges is equal to the cross-sectional area of the web. The thickness of the flanges is twice as big as the thickness of the web. The finite element method was used for geometrical and physical non-linear analysis of the castellated beams under a uniformly distributed load. The upper flanges of the beams are restrained out of the plane. The results are presented in relevant charts.
The study is divided into two parts: (i) in the first one, the plate girder (Fig 1) is considered to be exposed to quasi-constant loading (ie to loads which are either constant or repeated in a very ...small number of cycles), while (ii) in the other one, the girder is assumed to be subjected to repeated loading. Then it is understandable that the objective of the first part should be to look into the influence of initial imperfections on the static ultimate load of the girder related to the formation of a plastic failure mechanism in it, while that of the second part was to study the effect of imperfections on the stress state under considerably lesser loads, viz under such as to correspond to the development of fatigue cracks in the girder and, consequently, to its fatigue limit state. In this case the state of stress was measured by bending stresses developing in the crack-prone areas (Fig 4) of the web "breathing" under the repeated loads, which -as demonstrated by the Prague experiments - occur at the toes of the fillet welds connecting the "breathing" web with the girder flanges and stiffeners. In both parts, the results of the theoretical investigation were compared with the conclusions of numerous tests carried out at the Institute of Theoretical and Applied Mechanics in Prague. The correlation was found to be very good; for example, the experimental load-carrying capacity of the girders tested in Prague was close to the mean value of the corresponding theoretical solutions performed for the same girders. Thereby the analytical model applied in the theoretical investigation can be regarded as verified.
The theoretical analysis was based on a non-linear variant of the finite element method, the girder being modelled by means of shell elements and the ANSYS program being applied. All input imperfections were considered to be random quantities. The statistical distributions were introduced according to both experimentally obtained results and data given in literature. Random realisations of input random quantities were simulated by the LHS (Latin Hypercube Sampling) method. By way of sensitivity analysis it was studied to what extend the variability of initial imperfections was reflected in the variability of stresses in the crack-prone areas of the girder.
The main conclusion can be formulated as follows: While the effect of (and sensitivity to) the initial out-of-flatness of the girder web, in the case studied of a plate girder whose web is subjected to predominant shear, on the static load-carrying capacity is (see the results of the first part of the study) very small (only a few p.c), the same effect on the stress state occurring in the crack-prone areas of the "breathing" web under service loads can be (see the other part of the study) very important. This is also one of the main explanations of the large scatter of the results of the fatigue tests conducted in Prague.
This paper deals with a theoretical and a numerical analysis of local stability of web of tapered beams subjected to a pure bending moment. A standard FEM code COSMOS/M has been used for a numerical ...estimation of a critical load multiplier. It has been assumed that the critical stress of the web of tapered beam could be calculated in an analogous way as for uniform member just with an additional correction factor α
b.w
. A large number of simulations carried out within a wide range of the ratios of second moments of area allowed to determine the proper values of that factor. In the paper there was investigated the influence of steel grade, relative slenderness and beam's ends cross-section moments of inertia ratio to the local stability of web of the tapered beam subjected to pure bending.
The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made ...of reinforced normal concrete and high-performance concrete (HPC).
The reinforced concrete composite beams used in the tests were prepared in full scale with the cross-section of 120 × 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of high-performance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.
PDF
