Key Engineering Materials Vol. 691

Abstract: The presented paper brings comparison of design accuracy of slender concrete column coming from levels of approximation after MC 2010 and SIA 262, which are compared with the Method of nominal curvature for calculation of 2. order moment after EN 1992-1-1. Results were also compared with nonlinear analysis accounting for 2nd order effects, nonlinear behavior of concrete in compression and influence of cracking, creep and shrinkage.

Abstract: In the production of structures made of concrete it is sometimes required to make a completed structure contain a minimum amount of free water. From the point of view of effectiveness of the production process it is also preferred to dry the concrete in a short time and at a reasonable cost. Required for free water content can be limited by various factors (e.g. construction covered by flooring sensitive to humidity, frost resistance, etc.).The moisture characteristic of concrete is verified in civil engineering provided that the concrete is located in the environment with normal atmospheric pressure. By solving the project “Development of methods for structure of thermal vacuum insulated containers” we have met a requirement to produce concrete with extremely low moisture content. It was found out that information about moisture content of concrete obtained by currently used method was unsatisfactory for concrete in the environment with extremely low atmospheric pressure. The research has indicated that usual methods of concrete drying are not sufficient for concrete subjected to vacuum because they don´t eliminate physically bound water.

Abstract: It is shown that alternative procedures for probabilistic assessment of design impact forces given in EN 1991-1-7 leads to similar results. The impact forces are up to three times greater than the recommended indicative values given in the main text of EN 1991-1-7. Provided that no other safety measures are undertaken, the structures designed for recommended lower bound of impact forces may have insufficient reliability. Application of the upper limit of impact forces should be recommended for key bridges where the bridge columns are situated near road intersections or in the adverse configuration of the terrain.

Abstract: Balanced cantilever method is one most used method for the large span concrete bridge construction. Generally non-homogenous concrete structures with changing the structural system within its erection are sensitive to the deformation and stress prediction in time. Long-term monitoring system has become very important tool which enables to obtain basic information about actual structural behavior in time about stress and deformation level. It can also cover the other structural effects for example the temperature influence which can significantly affect to the later structural behavior. Generally bridge designers in practice do not have enough information about these influences within the structure erection over the time. Underestimating such above mentioned effects often causes that predicted values of stresses or deformation does not corresponded with the reality as was published for example in [1]. In boundary cases unexpected excessive deformations or crack opening due to the stresses distribution may lead to the serviceability problems, deterioration of aesthetics, and even early reconstruction of the bridge eventually. In this paper we would like to present some experiences with the long-term monitoring of bridge structure and performed structural analysis considering the real load history and structural scheme changing. Recorded strains development was compared with the numerical model results based on the expected behavior of prestressed concrete structure according to the European standard models, [3, 4].

Abstract: The article presents the results and analysis of long-term monitoring of the bridge across the Odra River on the D47 freeway in the Czech Republic near Ostrava. Structural system of this bridge is formed by a continuous composite box girder with spans from 49 to 102 m. Total length of the bridge is 402 m. The bridge was equipped by strain gauges and force sensors during the construction. The monitoring has been kept on for 10 years. The measured values are compared with the results of calculations.

Abstract: Concrete is the most used man made material nowadays. The environmental impact associated with cement production is very significant due to the extent of concrete use. At the same moment cement production is associated with large energy consumption and high amount of greenhouse gas emissions. Development of concrete technology during last twenty years has lead to a significant quality shift of technical parameters and also of related environmental impacts. New types of optimized concrete mixes have significantly improved characteristics from the perspective of strength, mechanical resistance, durability and resistance to extreme loads. The use of alternative non-steel reinforcement from various types of fibres can increase reliability, durability and reduction of environmental impacts. Due to optimization of production technology, concrete is gradually becoming a building material appropriate and advantageous for sustainable construction of buildings. In this context increase of reliability and durability within whole life cycle is essential. New approaches in concrete technology like utilization of high performance and ultra high performance concretes, use of textile reinforcement, shape optimization and conceptual approach for integrated life-cycle assessment of concrete structures are presented in the paper. Some of principles are demonstrated on results of experimental research performed by author and his team at the Czech Technical University in Prague (CTU).

Abstract: The paper deals with cylindrical tanks. Structures of this type have been used in hydraulic engineering, e.g. water towers, sewerage plant tanks. In recent years, cylindrical tanks have been also used in biogas management as fermentation and storage tanks.While the standard hydrostatic load acts symmetrically, it evokes the rotary symmetric load. During the seismic event, the load acts in one direction only, i.e. in the direction of earthquake. This load imposes a non-symmetrical loading of a structure. By a combination of individual loads the resulting forces are slightly non-symmetrical.Specific tank has been modeled. In one model, the solution is made using the quasi-static load induced by the hydrodynamic pressure according to the standard EC1998, part 4 [12]. The other model is presented as a calculation using the modal and spectral analyses under the seismic load. At the conclusion, these two solutions have been compared.

Abstract: This article discusses the properties of concrete within the piers of the Old Bridge in Bratislava (former Franz Joseph Bridge). It was the first permanent bridge across the river Danube in Bratislava as well as within the present territory of Slovakia. Mechanical, physical and chemical properties were verified on core drills, some of them being almost 23 m long. The concretes were tested for dynamic and Young’s elasticity module and compressive strengths. Subsequently the fines of concrete specimens were studied by the X-ray diffraction, TG-DTA and mercury intrusion porosimetry techniques and also by chemical analyses and SEM observations. The piers were made from 5 different concrete kinds. The concrete in the caissons and in the piers does not fulfil the criteria for structural concrete defined in the present European standards. This finding seriously suggests that carrying capacity of the piers after the reconstruction of the bridge, without any strengthening would become questionable.

Abstract: The paper deals with formation and development of cracks up to the failure of two span post-tensioned concrete girder. It is focused on influence of different bond between prestressing units and surrounding grout. Monitored and analysed phenomena affected by different bond are as follows: crack initiation, crack spacing and crack width of the prestressed girder. Sources of analysis are results from experimental program focused on influence of oil based corrosion protection agents on bond of prestressing units. Two span post-tensioned girders were subjected to the loading in laboratory till the bending failure has occurred. Girders were in two cases prestressed with bonded tendons. Other two girders were post-tensioned with unbonded tendons and two girders with tendons with decreased bond, due to corrosion protection coatings. Girders have demonstrated different behaviour by loading regarding to the bond level of prestressing units. Experimental results are faced with the results of the theoretical calculation of crack width according to European standards.

Abstract: Over the past few years, punching shear has been in the forefront of both research teams and professional public due to a new approach to its verification according to Model Code 2010. From this topic, the task of flat slabs strengthening against punching shear has arisen. This problem, and in particular the problem of flat slabs strengthened by additional concrete column heads, is the focus of this paper. Structures are analysed using a 3D FEM models including material and geometric nonlinearity. The way of modelling is validated against experiments on non-strengthened flat slabs subjected to punching shear. At first, strengthening with a rigid connection at the interface between structures is considered and then, several different types of connection at the interface are evaluated. Finally, strengthening of structures with varying lengths of top flexural reinforcement in the slab is modelled while minimum anchorage length outside the additional column head is verified.