Applied Mechanics and Materials Vol. 769

Abstract: The paper presents the way of estimating the wind force acting on straight or curved elements with circular cross-section. These elements can be positioned at any angle to the wind direction. They may also be bent into the form of a torus or a helix, laid horizontally or sloped. The first part of the article briefly presents the results of the air flow computer simulations. The second part of the work shows the analytical approach to the problem, solved by decomposition of the wind velocity vector to the normal, binormal and tangent components, estimation of the pressure distribution around the elements cross-section and finally integration of the pressure over the whole surface. Because there were observed significant differences between the data obtained from the analytical and numerical method, some empirical correction functions had to be attached to the analytical equations. The last part consists of the engineering applicable advices, presented in the form of a table of coefficients.

Abstract: The paper deals with a dynamic response of footbridge structure which is loaded by a movement of pedestrians. Interaction between crowd and footbridge structure is a complex problem. It is important to take into account load generated by the movement of pedestrians during the computation, but also change of load influenced by a response of the structure. It means practically that the response of the structure has influence on the movement of pedestrians. Computation of the response has to be performed in several steps. The first step is backward modification of load represented by the crowd movement. Next step is recalculation of the structure with newly compiled load. This approach can bring near the real behaviour of the structure which is exposed by the continuous movement of pedestrians..

Abstract: This paper deals with solution of air flowing around the object - atypical cross section. Result is an important parameter of pressure coefficient on the structure, what is necessary for design of buildings and structures in terms of wind load calculations. Wind tunnel measurements of wind flow and wind pressures distribution around part of the circle were performed in BLWT STU in Bratislava for 24 wind directions and different wind speeds. Measurements were performed using pressure scanner DSA 3217 (Scanivalve) and have shown significant differences between peaks of suction due to wind direction. These results were used for comparison with CFD calculations of flow around the section. This comparison of known pressure coefficient for atypical shape of cross section is the first step for testing other shapes, which are not described in Eurocode.

Abstract: The paper is devoted to structural health monitoring using a non-destructive method based on the method of direct stiffness determination combined with the model updating method. The primary aim of the paper is to determine the change in bending and torsional stiffnesses. In the first part of the work it was necessary to prepare a simple experimental scale model of the bridge which was made from two materials – wood and plaster boards. The same bridge model was created in the finite element commercial codes RFEM5 - Dlubal (a more detailed 3D analysis) and ANSYS (a 2D analysis). The last numerical model consists of beam elements with lumped mass elements. The modal analysis was made and these results were used as a comparative base for measurements. In either case data for the original and the damaged models were acquired. Analysis of the measurement data led to the identification of vertical and torsional mode shapes. Last part of the paper is devoted to identification of the damage by application of the direct stiffness calculation method.

Abstract: The cable-stayed bridge at the inner ring road in Prague in the Czech Republic was put into operation in 1997. In 2008 a crack was found in the bridge structure area where the end beam was connected with the upper deck of the box section and where the bridge expansion joint system was anchored. The basic objective of diagnostic works, which were started immediately after the finding of the crack, was obtaining the basis for bridge structure modifications, among other things, to prevent formation of similar damages in the future. A series of diagnostic methods was used for determination of the bridge actual state and the real static and dynamic bridge behavior. One of these methods was the dynamic load test. It was focused on an examination of the bridge forced vibration which was caused by dynamic effects of a usual traffic flow. An arrangement of the test was not quite usual because the experiment was concentrated on dynamic behaviour of bridge support areas especially. The abutment area, the pylon area and the area of a pillar with the bearing with a tensile structural element were observed on the investigated bridge. The dynamic load test was performed in two stages. The first stage was focused on investigation of bridge dynamic behaviour in original structural conditions and on obtaining the basis for design of bridge adjustments. The second stage was realized after bridge reconstruction in December 2012 and verified the effectiveness of bridge modifications.

Abstract: Paper discusses the implementation of sectional analysis in a custom program developed by authors. The program is devoted to nonlinear analysis of reinforced concrete frames. Analysis consists of two interrelated iterative procedures, global frame analysis and sectional analysis. The latter works with the discretized cross section into finite number of concrete fibres and reinforcement layers. Each fibre is analysed separately to determine axial stresses on them. However, equilibrium and compatibility requirements are satisfied for the cross section as a whole. For determination of stresses on fibres is used Disturbed Stress Field Theory (DSFM) model. Paper summarizes the concept of the global and sectional analysis and DSFM. Finally it shows the proposed implementation of cross section discretization for the sectional analysis in respect with consideration of the cover layer if the concrete.

Abstract: This paper deals with a problem of eigenfrequencies of filled cylindrical tank rested on elastic foundation. For an ANSYS analysis of eigenfrequencies some numerical models of gravel subgrade are used and finally results got by these models are compared. In final part of the paper some crucial results are presented both in a graphical and numerical way.

Abstract: This paper deals with the determination of eigenfrequencies of high steel cylindrical storage tank. The eigenfrequencies have been determined for empty tank and also for the tank with fluid. Water levels varied in the range from 10 cm to 80 cm, with the step 10 cm. The task was solved by 3D computing model. The results were verified by the tests made on real structure in scale 1:1. Total dimensions, a material, the description of created computing model, applied loads, the descriptions of measuring devices and the tests are mentioned here. Obtained results and future plans are discussed at the end of the paper.

Abstract: This article is devoted to the calculation of natural frequencies of concrete slabs. Natural frequencies of a solid slab and a hollow core slab have been compared. Solid slab and lightened slab with reduced self-weight and stiffness have been modeled using FEM software ANSYS as 2D model using shell elements. Third model was made from 3D elements as a hollow core slab. Two types of boundary conditions have been considered: a simply supported slab and a clamped slab. The changes in natural frequencies according to aspect ratio of the slab were compared, too. Numerical methods have been compared with simplified method of calculation of natural frequency of slabs, as e.g. an equivalent plate approach; approximation presented by Hearmon and compilation of formulas by Bachmann.

Abstract: The pressure coefficients on duo-pitched roofs of separated buildings are well described by several standards. Nowadays, there are various commercial or non-commercial programs which can predict the pressure coefficients. However, the most accurate method is to perform a wind tunnel test. The aim of this paper is to simulate the airflow over a gable roof with different elevations under ANSYS Fluent 14.0 program. Examined elevations of the gable roof are 5°, 15° and 30°. Classical two equation k-ε turbulence models based on Reynolds Averaged Navier-Stokes (RANS) equations simulation were performed. Performance of each turbulence model with the increasing angel of the roof was compared.