Seismic stability of vibration-insulated turbine foundations depending on the frequency composition of seismic impact

The seismic resistance of vibration-insulated turbine foundations is a complex and multifaceted problem that includes many aspects. The turbine foundation is a special building structure that unites parts of the turbine and generator unit into a single machine and it is used for static and dynamic loads accommodation. The number of designed and constructed power plants in high seismic level areas is large and steadily growing. In addition, engineers and designers deal with the issue of the frequency composition of the seismic impact influence on the seismic resistance of vibration-insulated turbine foundations. Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismic displacements (deformations of vibration isolators). The results of the calculation experiments proved a significant effect of seismic action frequency composition on the behavior of the vibration-insulated turbine foundations. Calculations of foundations, taking into account earthquakes of the same intensity, but with different values of the prevailing frequencies of the impact, lead to the differing by several times values of the maximum seismic accelerations at the turbine level and seismic displacements.

Optimal design and performance evaluation of tuned mass damper inerter in building structures

This paper concerns the numerical performance evaluation of multi-degree-of-freedom systems equipped with Tuned Mass Dampers-Inerter (TMDIs); a passive control device used for the mitigation of mechanical vibrations induced by dynamic loads. The inerter device is commonly used to increase the apparent mass of classics tuned mass dampers (TMDs), improving its seismic performance. To evaluate the TMDI action, three case studies are employed, determined from three real buildings of Medellin city from low, medium to high rise (30 meters, 97 meters, and 144 meters, respectively). Optimum design parameters are found using a metaheuristic optimization based on the differential evolution method, first, for the minimization of the horizontal peak displacements, and then, for the minimization of the root mean square (RMS) response of displacements. Besides, the case studies are assessed using eight seismic accelerations records representative of the literature. Finally, the seismic performance is evaluated on each case study considering different levels of inertance induced by the inerter device: 5%, 20%, and 50% with respect to the total mass of the building, for which it is observed a better dynamic behavior when TMDIs with lower values of inertance are implemented.

Dynamic Behavior of Quay Walls According to N-values of Backfill and Amplitude of Seismic Accelerations

Sand soil discharge, which seemed to be the liquefaction damage, was observed in the backfill of a quay wall structure during the Pohang earthquake in 2017. This discharge occurred because the bearing capacity decreased owing to the loss of effective stress, which was caused by the increase in the excess pore-water pressure with the dynamic loads from the earthquake. In this study, the effects of the variations in the N-value of the backfill of the quay structure and the seismic acceleration coefficient were investigated for increasing excess pore-water pressure and decreasing effective stress, owing to the dynamic load from earthquakes.

Rehabilitation of bearings of a major earthquake damaged railway bridge

<p>The Clarence River Rail Bridge is a 478 m long steel truss girder bridge located 40 Km north of Kaikoura. The cast iron fixed and guided pinned bearings of the bridge suffered significant damage during the November 2016 Kaikoura Earthquake, likely caused by vertical seismic accelerations in excess of 1g.</p><p>Replacement of the damaged cast iron guided pinned bearings involved the design of new bespoke pinned steel bearings with modern stainless steel and approved sliding material (ASM) surfaces newly introduced to AS5100.4:2017.</p><p>The use of modern bearing materials and established detailing principles have led to rehabilitating an earthquake damaged 80-year-old bridge with design and construction of the earthquake repairs completed in less than 12 months.</p>

New Mexico City International Airport - Control Tower

<p>The New International Airport in Mexico City is being built on some of poorest ground conditions that exist in Mexico City, or indeed anywhere. The ground is extremely soft, rapidly sinking and exposed to a major and unique seismic site hazard. This paper discusses the performance–based engineering design of the 90 m tall Control Tower. The tower is base isolated to significantly reduce the seismic accelerations which would approach 1.0 g with a fixed-base design. The airport site is predicted to settle by 5 m over the 75-year design life due to regional subsidence. A practical, efficient and elegant solution was developed using a shallow pile-enhanced and compensated raft, and a transfer truss which supports the lightweight braced steel tower on seismic base isolator bearings, allowing the building to be founded on the soft soils while accommodating regional subsidence by moving down with it. The design accommodated seismic joint movements of 1.4 m.</p>

Análise simplificada do efeito de ações sísmicas em edifícios de concreto armado dimensionados pela norma brasileira

<p class="Normal1">Earthquakes are natural events, caused mainly due to the relative movement between tectonic plates (interplate earthquakes) and in faults between rocky blocks (intra-plate earthquakes), or induced by human activity. It is possible to observe a relation between the regions located in areas with greater seismicity and the areas that are close to several intraplate failures and shale gas reserves in Brazil. According to NBR 15421/2006, this condition results in a map of seismic accelerations characteristic of the design. Such accelerations can be used to estimate equivalent horizontal loads. However, it is not usual to consider these effects in the design of reinforced concrete buildings. Therefore, this work aims to evaluate the global stability of reinforced concrete buildings with different bracing systems, subject to seismic accelerations provided for in NBR 15421/2006. Initially, the global stability was verified considering the wind and vertical actions by the γz coefficient. Therefore, all the frames analysed in this paper behaved as non-sway structures (γz ≤ 1,10). Then the wind actions were replaced by seismic ones since it is improbable that both phenomena occur simultaneously. Finally, global stability was re-evaluated by means of the γz coefficient. Therewith, it was observed that all the buildings analysed started to behave as structures of mobile nodes (γz &gt; 1,10), that is, susceptible to the second-order global effects.</p>

Seismic impacts influence on the slope stability on the example of Abrau Peninsula (Russian sector of black sea coast)

Some aspects of seismic impact on the stability of massive seismogravitational solid masses are examined. An example of the slope stability calculation using separate accounting for seismic accelerations in blocks is shown. The influence of the relief on the change in seismic effects is considered. Some aspects of seismic impact on the stability of massive seismogravitational solid masses are examined. An example of the slope stability calculation using separate accounting for seismic accelerations in blocks is shown. The influence of the relief on the change in seismic effects is considered. The comparative impact of longitudinal and transverse seismic waves from the earthquake focuses located in front of the slope foot and behind the slope ridge is evaluated.

A Comparison of Time Domain Seismic Analysis Methods for Offshore Wind Turbine Structures: Using a Superelement Approach

Recently, wind farm development has gained more traction in Asian countries such as Taiwan, which are seismically active. Compared to Europe, the offshore wind structures need to be designed for these additional extreme environmental conditions. For monopiles, these calculations can typically be performed in an integrated way in the wind turbine load calculation, but for jackets the superelement (SE) approach remains preferred. At the time of writing different approaches are being applied in the industry to apply the SE approach for seismic time domain analysis. This work explains and compares three different methods, based on calculations performed in offshore strength assessment tool Sesam and aeroelastic tool BHawC. When including additional interface nodes at the foundation model bottom into the SE to which the seismic accelerations can be applied in BHawC similarly as in the re-tracking run in Sesam, the results between BHawC and Sesam are nearidentical. Using a normal SE, which only includes an interface node for the connection to the wind turbine tower bottom, and including the response due to seismic displacements into the SE load file gives a match between BHawC and Sesam, and closely matches the results of the case with additional interface nodes. Doing the same but only including the dynamic response of the interface point relative to a frame of reference moving with the rigid body motions as caused by the seismic accelerations into the SE load file, significant differences occur. This is due to the lack of the loading effect of rigid body motions. The same conclusions on how these methods compare can be drawn when using different wind and wave cases. The presented results give insights into the differences between the methods and how the choice of method may influence the results.