The stiffness of rubber bearings, which are widely used for the seismic isolation of different types of structures, changes under different seismic intensities. These bearings are typically designed considering only lateral displacements induced by design earthquakes. At lower displacements, induced by weaker earthquakes, the stiffness of rubber bearings is typically increased, and the efficiency of the seismic isolation is thus reduced. To improve the response of rubber isolators at lower seismic intensities, a new isolation device, which can adjust itself to the intensity of the load, has been developed. It is fabricated from a magnetically controlled elastomer (MCE), whose stiffness can be varied by applying a magnetic field. Variation of the device stiffness is regulated by a specifically designed control unit. The seismic response of this new device was tested experimentally and analytically. This study showed that the new device can substantially reduce the seismic demand, particularly in the case of fairly stiff structures, and the equipment installed in such structures. It was found that the group of equipment, which is critical in the case of weak earthquakes, can be substantially reduced or even completely eliminated when stiff structures are isolated using MCE devices.
COBISS.SI-ID: 5657185
Bridges are one of the most critical components of transport systems. However, the literature devoted to these important engineering structures and in particular to their seismic performance is quite limited compared to that related to building structures. This book is an important contribution to the literature related to the seismic behavior of bridges. It focuses on the use of inelastic analysis methods for the seismic assessment and design of bridges, on which substantial work has been carried out in recent years, and they have been gradually included to the modern standards. These methods have been mostly developed for the analysis of buildings. Since the seismic response of bridges is significantly different from that of buildings, researchers as well as designers face with numerous dilemmas when applying these methods to bridges. The key objective of this book is therefore twofold: 1) to present all important methods (including all the specifics in the case of bridges) belonging to the aforementioned category in a uniform and sufficient way for their understanding and implementation, and 2) to provide also a critical perspective on them by including selected case-studies wherein several methods are applied to a specific bridge, and by offering some critical comments on the limitations of the individual methods and on their relative efficiency. In this respect, this book is a valuable tool for both researchers and practicing engineers dealing with seismic design and assessment of bridges, by both making accessible the methods and the analytical tools available for their implementation, and by assisting them to select the method that best suits the individual bridge projects that each engineer/researcher faces. This book includes the research performed by members of the TG11 – »Seismic design, assessment and retrofit of bridges«, which was set up in the frame of European Association for Earthquake Engineering.
COBISS.SI-ID: 5829729
The extended N2 method has been developed, which takes into account higher mode effects both in plan and in elevation. The extension is based on the assumption that the structure remains in the elastic range when vibrating in higher modes. The seismic demand in terms of displacements and storey drift can be obtained by combining the results of basic pushover analysis and those of standard elastic modal analysis. In the paper, the proposed procedure was summarized and applied to a test example which represents an actual 8-storey reinforced concrete building. The results obtained by the extended N2 method were compared with the results of nonlinear response history analysis and basic N2 analysis without the consideration of higher modes. The extended N2 method was able to provide fair, conservative estimates of response in the case of the test example. In comparison to the basic N2 method, the predictionof seismic demand was greatly improved in the upper part of the building and at the flexible edges.
COBISS.SI-ID: 5591649
The sensitivity of the seismic response parameters to the uncertain modelling variables of the infills and frame of four infilled reinforced concrete frameswas investigated using a simplified nonlinear method for the seismic performance assessment of such buildings. This method involves pushover analysis of the structural model and inelastic spectra that are appropriate for infilled reinforced concrete frames. Structural response was simulated by using nonlinear structural models that employ one-component lumped plasticity elements for the beams and columns, and compressive diagonal struts to represent the masonry infills. The results indicated that uncertainty in the characteristics of the masonry infills has the greatest impact on the responseparameters corresponding to the limit states of damage limitation and significant damage, whereas the structural response at the near-collapse limitstate is most sensitive to the ultimate rotation of the columns or to thecracking strength of the masonry infills. Based on the adopted methodology for the seismic performance assessment of infilled reinforced concrete frames,it is also shown, that masonry infills with reduced strength may have abeneficial effect on the near-collapse capacity, expressed in terms of the peak ground acceleration.
COBISS.SI-ID: 5776993
Most of historical masonry buildings in Slovenia were built out of local stone or stone and brick with lime-based mortars. An efficient technique for improving the mechanical properties of stone or stone-brick walls is grout injection. In order to evaluate the quality and compatibility of commercially available injection grouts with materials present in historical masonry buildings, several types of hydraulic lime-pozzolana, lime-cement and cement grouts were tested. Chemical, physical and mechanical criteria to select optimal grout mixture for strengthening of historical masonry buildings were proposed, by which tested grouts were classified in three quality classes A, B and C. Only two commercial lime-cement grouts and one cement grout were able to meet the set requirements and were qualified in class B as medium quality grout (one lime-cement grout) or in class C as low quality grouts. Therefore, the design of hydrated lime-based grouts was carried out in continuation of our study, in order to obtain a grout that is highly compatible with the historical masonry in Slovenia. Among available limes, hydrated lime in powdered state and lime putty were used. Ground granulated blast furnace slag (GGBS), volcanic tuff, and limestone powder were used as mineral additives. It was found that the added combination of limestone powder and supplementary cementitious material (GGBS or tuff) has a beneficial influence on the properties of designed grout compositions.
COBISS.SI-ID: 5886561