A method is presented to estimate the axial force in a bar which is part of a built-up structure. The estimation is based on the modal characteristics of the bar or, alternatively, on its operational deflection shape, as determined from a local vibration test. Timoshenko beam theory is assumed and, in addition, the rotational inertia of the bar and the mass of the sensors are accounted for. A major advantage of the proposed method is its generality. When data from five or more sensors along the length of the bar are available, no information on the connection of the bar to the remainder of the structure is required. The method can therefore be used for any beam or truss element. The method is first verified numerically using finite element simulations. Finally, a set of laboratory experiments is performed in order to ascertain the applicability and accuracy of the proposed method.
The paper aims at exploring damage assessment in masonry structures at an early stage by vibration measurements. One arch replicate of historical constructions was built as reference, undamaged, state. Afterwards, progressive damage was induced and sequential modal identification analysis was performed at each damage stage, aiming to find adequate correspondence between dynamic behaviour and internal crack growth.
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In order to maintain the reliability of civil engineering structures, considerable effort is currently spent on developing a non-destructive vibration testing method for monitoring the structural integrity of constructions. The technique must be able to observe damage, secondly to localize the damage; and finally to give an idea of the severity of the damage. Within the framework of relating changes of measured modal parameters to changes in the integrity of the structure, it is important to be able to determine the dynamic stiffness in each section of the structure from measured modal characteristics. A damaged structure results in a dynamic stiffness reduction of the cracked sections. The dynamic stiffnesses provide directly an indication of the extension of the cracked zones in the structure. The dynamic stiffness reduction can also be associated with a degree of cracking in a particular zone. In an experimental programme, a concrete beam of 6 m length is subjected to an increasing static load to produce cracks. After each static perload, the beam is tested dynamically in a free–free set-up. The change in modal parameters is then related to damage in the beam. The technique that will be presented in the paper to predict the damage location and intensity is a direct stiffness derivation from measured modal displacement derivatives. Using the bending modes, the dynamic bending stiffness can be derived from modal curvatures. Using the torsional modes, the dynamic torsion stiffness can be derived from modal torsion rates.
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In order to estimate the wind loads on circular cylindrical shell structures, the pressure coefficient as a function of the Reynolds number is given for an isolated cylinder in Eurocode 1 - Part 2-4: Actions on structures - Wind actions. As cylinders are often placed in groups and the configuration of these groups largely influences the pressure distribution around the cylinders, a computation of the wind flow provides a more realistic estimation of the pressure coefficients. First, the transient 2D turbulent air flow around a single cylinder at a Reynolds number of 12.4 millions is computed using the SST turbulence model and the results are compared with the pressure coefficients in Eurocode 1 and with experimental data. The minimum pressure coefficient is underestimated, while the base pressure coefficient is slightly overestimated. Unsteady simulations are performed for the flow around a group of 2 by 2 and of 8 by 5 cylinders. Vortex shedding occurs both from the group as a whole, and from individual cylinders. The group configuration drastically changes the time-averaged pressure distribution around the cylinders. High values of suction are present at the location of the small gaps between the cylinders and upstream of the separation points of the cylinders on the side corners of the groups. The cylinders at the borders of the groups experience high drag or lift forces, while these forces are considerably lower in the middle of the group.
Link Between CAD Systems and Analysis Programs as a Step of an Integrated Approach of the Building Process G. De Roeck, G. Degrande, PH. Geyskens Pages 458-464 (1987 Proceedings of the 4th ISARC, Haifa, Israel, ISSN 2413-5844) Abstract: The link between CAD-systems and FE-programs seems to be very promising because they use in some sense the same data: geometry as well as some information about mechanical properties are normally contained in the CAD-system. The inclusion of FE entities in the Initial Graphics Exchange Standard (IGES) may be an illustration of this statement. Experience will be reported in linking CAD-systems and FE-programs on mainframe as well as on microcomputers. Access to the database and programming facilities offered by the CAD-system are crucial. We believe that our experience concerning interface possibilities is also valuable for other situations (e.g. planning of the building process). Keywords: No keywords DOI: https://doi.org/10.22260/ISARC1987/0030 Download fulltext Download BibTex Download Endnote (RIS) TeX Import to Mendeley
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