Applied Mechanics and Materials Vol. 837

Abstract: Unburned clay was used for the traditional engineering works for thousands years. Its qualities have not been too appreciated in the last few decades. Because of that, its material characteristics were never researched very rigorously. In last years, we could see increasing demand for use of this building material in building practice and research. The basic problem that should be mitigated by civil engineers handling unburned clay is its considerable shrinkage during drying. The degree of shrinkage depends on the amount of mixture water and on the amount and type of clay minerals. In the unburned clay, like in the cement, clay minerals play role of the binder. The problem is that clay minerals are causing volume changes. This paper is focused on the degree of shrinkage and its dependence on the species and quantity of clay mineral.

Abstract: We are going to present in this article an actual problem in the production of prestressed concrete prefabricated elements. There is a problem of high transport costs in the case of bridges, that are made from prefabricates. In the production of T type or double T type cross section we can have a situation that the form could be more than 100 m long and prestressing force is self-fixed. Putting the polystyrene in the form we can produce 10 or more beams in one step. From a viewpoint of theoretical background this steel form represents a problem of stability and friction. A special steel assembled frame for the production of prestressed prefabricates could be arranged close to the bridge site. Horizontal deformations represent a special problem. Friction effect is introduced as the simplification of elastic support. Non-linear solution has been used.

Abstract: Mathematical modeling of boundary value problems in linear theory of viscoelasticity. Definitions and basic principles in the mathematical modeling theory. Constitutive functional and its transformation into a form of Stieltjes integral. Application of theory of algebraic sets and corresponding subsets. Riesz theory of representation and its application for derivation of constitutive equations. Integral and differential operator forms of stress-strain relationships for a solid-phase continuous media.

Abstract: The submitted paper deals with a dynamic analysis of the footbridge, which has been exposed to the effects of vandalism and crossing pedestrians. The loading produced by pedestrians was considered for two typical states. Firstly, the analysis was aimed at the ordinary traffic where pedestrians were discretized by the SDOF damped biodynamic models and secondly, the movement of single pedestrian, which was based on the inverted pendulum and biodynamic properties of human body, was evaluated. The jumping vandals were replaced by the motion of SDOF undamped biodynamic model. The calculations have been done at the computational model of the real footbridge across Opatovska Street in Prague.

Abstract: Each structure should be designed so that the entire intended lifetime fulfilles its objectives in terms of usability, resistance and stability without significantly lowering its usefulness and without excessive, unpredictable maintenance costs. Therefore, each time selecting the appropriate fastener at the design stage of the load it must be determined how it can act on it during operation. Typically, the calculation takes into account the normal conditions. In reality, however, the fastener can operate in abnormal conditions. Effects of operating temperature and humidity onto a load-bearing capacity of fasteners of various types have been determined by the work. The study was conducted for concrete with different strength.

Abstract: The Port Bridge across Danube in Bratislava is about 461 m long with 4 spans. The bridge was designed for both a highway and simultaneously for two railway tracks. Nowadays the construction is overloaded and that is why the structural health monitoring of the bridge is being developed. The test setup consists of two measuring polygons. This setup needed an original LabVIEW program, which has been developed in cooperation with experts – electrical engineers and experts on structural mechanics. Main problem was to achieve a synchronization of both measuring polygons connected by Wi-Fi antennas. Except of software difficulties there were complications during in-situ measurement, like cable connection between highway and railway level and especially the time synchronization of the traffic video and measurement. The measurement has been done and some eigenmodes have been identified from ambient data.

Abstract: Geomaterials with typical low unit weight and high porosity are significantly prone to liquefaction as a result of dynamic – seismic load. Investigation of geomaterials that are prone to liquefaction due to seismic load can use certain SPT and CPT penetration tests. The method of investigating liquefaction caused by seismic activity was developed based on numerous penetration tests of sandy or silty–sandy soils and was elaborated in detail at the Workshop on Evaluation of Liquefaction Resistance of Soil, NCEER, Salk Lake City, USA, 1996. In the present paper, the results of penetration CPT test conducted at the ash impoundment in Zemianske Kostoľany are analyzed using methodology NCEER.

Abstract: In the paper the results of laboratory tests performed on a simplified model of a slab-column connection were presented. The aim of investigations was to find out at which value of the load the destruction of such a connection occurs due to a rupture of the bars above the column. In respective models the column was situated axially or eccentrically with respect to span of bars. In each case the reinforcement passing above the column consisted of bars with a diameter of ø8 mm, ø12 mm or ø16 mm. The obtained results of laboratory tests and calculations permitted to determine the relations between the exerted load and the displacement of the column in time and also were compared with the guidelines contained in the standards CSA A23.3 and ACI 352R. Based on the results, the reduction of the load bearing capacity of the reinforcement bars due to bending was determined.

Abstract: Concrete hardening and setting processes are the most critical phases during construction work, influencing the properties of concrete structure. For this reason applying non-destructive testing in the early age of concrete lifetime can be useful. Acoustic emission method is a powerful tool for determination of lifetime concrete structures. Nevertheless, its application in civil engineering area is not easy because many building structures are inhomogeneous. This method can describe material changes during concrete lifetime. Acoustic Emission Method monitors concrete structure continuously. Changes in the whole concrete structure are recorded. The acoustic emission phenomenon is directly associated with nucleation of cracks in building materials, therefore the changes result from the volumetric expansion causing formation micro and macro cracking in structure, which we can recognize. Application of Acoustic Emission Method during concrete hardening and setting with different water-cement ratio will be the aim of this article and his influence on parameters of acoustic emission. A comprehension of microstructure-performance relationships is the key to true understanding of material behaviour.

Abstract: Slab-column structures used in design and construction work are one of the typical kinds of structures used in building industry. The emergence of factors unexpected at the designing stage can lead to collapse of the structures. The paper presents experimental investigations of the central field of the continuous floor. The research was conducted on a nine-field slab with dimensions 9300×9300×100 mm. The aim of the research was to observe the behaviour of the experimental model in the time when excessive load is exerted. The model was prepared using high ductility steel (ε_uk>7.5%) in order to determine the possibility to induce tensile membrane action. The paper presents basic geometrical and material data, the research methodology, the description of the system of loading, the description of the measurement system, and the obtained measurement results. The last part summarizes the conducted investigations.