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Ljubljana, Slovenia

Rodman U.,ELEA IC | Saje M.,University of Ljubljana | Planinc I.,University of Ljubljana | Zupan D.,University of Ljubljana
International Journal of Structural Stability and Dynamics

This paper presents the stability analyses of glulam arches subjected to distributed vertical loading. The present analysis employs a strain-based formulation of a nonlinear geometrically exact three-dimensional beam theory. The influence of the relative height of the arch on the lateral buckling load is studied. The buckling load is determined by bisection method with observing the sign of the determinant of the tangent stiffness matrix. The post-critical load deflection path is traced by a modified arc-length method. Such influences are shown for arches with a constant cross-section or constant volume. After determining the most favorable height of the arch, the influence of the number and position of lateral supports is shown. We also compare the deflections, bending, and radial stresses at the lateral buckling states to the limit values which are recommended by European standards. © World Scientific Publishing Company. Source

Isakovia T.,University of Ljubljana | Zevnik J.,ELEA IC | Fischinger M.,University of Ljubljana
Structural Control and Health Monitoring

The stiffness of rubber bearings typically increases during weak earthquakes. This can reduce the efficiency of the isolation and jeopardize the equipment installed in structures isolated with such bearings. The problems and the parameters influencing the response of the equipment in structures isolated by high-damping rubber bearings (HDRB) have been systematically analyzed in the accompanying article. To improve the response of rubber isolators in the case of lower seismic intensities, a new isolation device, which adjusts itself to the intensity of the load, has been developed. It is made from a magnetically controlled elastomer (MCE), i.e. a rubber-like material whose stiffness can be varied by applying a magnetic field. The main topic of this research is the evaluation of the efficiency of this new device. In order to be able to test it, appropriate numerical models of the device and the control algorithm have been developed. The efficiency of the new MCE device for the protection of equipment subjected to weak earthquakes has been systematically studied using non-linear acceleration floor spectra. It was found that the majority of the parameters influencing the response in structures isolated by conventional HDRB also influence the effectiveness of the new device. Besides these parameters, the effectiveness of the new MCE was found to be heavily dependent on the stiffness of the superstructure and on the thresholds of the control algorithm of the device. The MCE is more effective in the protection of equipment installed in very stiff structures. Copyright © 2010 John Wiley & Sons, Ltd. Source

Isakovic T.,University of Ljubljana | Zevnik J.,ELEA IC | Fischinger M.,University of Ljubljana
Structural Control and Health Monitoring

The seismic response of secondary oscillators mounted on structures isolated by high-damping rubber bearings (HDRB) and subjected to earthquakes weaker than the design earthquake is analyzed in the first of two joint articles. The shear modulus of rubber can substantially increase at small deformations. Consequently, the initial and post-elastic tangent stiffness of HDRB can be significantly different. Hence, the effective stiffness of HDRB can considerably increase and the effectiveness of the seismic isolation can be substantially reduced when they are subjected to earthquakes weaker than the design earthquake. This can jeopardize the equipment mounted on the structure, since the seismic demand can be even larger for weak earthquakes than for the design earthquake. The effects of the increased effective stiffness of HDRB on the response of the equipment were studied using floor spectra. The main parameters that influence the floor spectra at low-seismic intensities were identified and analyzed. They are the following: the effective stiffness of the bearings, which depends on the intensity of the seismic load and the deformation of the rubber, the periods (stiffnesses) of the isolated and the non-isolated superstructure, the initial stiffness of the bearings, the non-linearity of the bearings, the effective damping of the bearings, the effective damping of the superstructure as well as the effective damping of the equipment, and the higher modes of vibration (the position of the equipment in the building). In the case of weak earthquakes, the floor spectra are quite sensitive to the numerical model of the bearings. Copyright © 2010 John Wiley & Sons, Ltd. Source

Klopcic J.,University of Ljubljana | Zivec T.,ELEA IC | Zibert M.,ELEA IC | Ambrozic T.,University of Ljubljana | Logar J.,University of Ljubljana
Geomechanik und Tunnelbau

The Šentvid tunnel had first been designed as twin tube doublelane tunnel. Later on, the design included the third traffic lanes and connecting ramp tunnels. The underground junctions required the construction of large caverns. A small diameter exploration gallery was excavated in order to find the optimum locations for both caverns in foliated Perm-Carboniferous soft rock conditions and to provide geotechnical model and material parameters for the design. The exploration gallery furthermore enabled displacement measurements ahead of the excavation face of the main tunnel during its construction. This paper presents some details of the exploration gallery and the results obtained from it, showing the results of displacement measurements ahead of the tunnel face and comparisons of the observed displacements ahead of the tunnel face with geological conditions. The tunnel construction won international attention due to its complexity and as an example of best practice in the construction of very large excavations in diverse geotechnical conditions. During the decision making process, an international panel of recognized experts from consulting companies and universities was involved. Later on, the panel regularly monitored the progress of tunnelling works and contributed to the decisions during critical steps of the project. The decision to involve international experts with different experiences and approaches permitted the client to keep the construction risks within acceptable limits. © 2013 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

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