Exploring the performances of the vibrating barriers for the seismic protection of the Zoser Pyramid

In this paper we aim to investigate the use of the Vibrating Barrier (ViBa) as a potential strategy to mitigate the effects of the seismic action on the Zoser Pyramid. The Vibrating Barrier is a structure buried in the soil that is able to absorb a significant portion of the dynamic energy arising from the ground motion. The working principle exploits the dynamic interaction among vibrating structures resting on a compliant semi-infinite space, namely the structure–soil–structure interaction. A reliable numerical simulation of the Zoser Pyramid and the surrounding soil undergoing a stochastic ground motion excitation representing the seismicity in Saqqara is presented. Due to the unique structural form, the ViBa is herein optimized through an ad-hoc procedure to minimize a response strain energy spectral density used as a synthetic performance parameter. Various layouts of the ViBa have been considered and presented in the paper. The efficiency of the ViBa is assessed by numerical simulation of the finite element model of the ViBa-Soil-Pyramid system. Results from a pertinent Monte Carlo study show an evident reduction of the stresses in the Pyramid manifesting the feasibility of this novel strategy to protect historic structures from earthquake-induced ground motion

Embedment effects of flexible foundations on control of structures

In the design of controller for earthquake-excited building benchmark, it is common to inquire about the present relationships between controlled building performance and the considering soil-foundation-structure interaction (SFSI) effects for description of the earthquake excitation. The SFSI effects can drastically affect the response of the structures subjected to earthquake motion. The effects of embedment depth on the control of structures, under plane-strain conditions, have been studied by substructure approach for buildings supported by rigid foundations embedded into a homogeneous, isotropic and elastic half-space. It is assumed that control devices are installed on all the floors. It is concluded that deeply embedded structures may increase the energy dissipated by control devices for the case of considering SFSI effects than expected from the fixed-base model and decrease the H2 norm of the system transfer function than control of structures with surface supported foundations. The effects are intensified for structures located on relatively soft soils. The inter-story drifts for control of squat structures with embedded foundations may reduce than the one controlled according to the fixed-base model, while it may increase the demand of inter-story drifts for the case of control of slender interacting systems. According to these results, considering SFSI effects on structural control can make some unexpected damages. Hence, for structures rested in or on soft soil that are controlled by active or semi-active control devices, SFSI effects in controller design should be considered. © 2010 Elsevier Ltd

A review on the current trends on computational modelling of masonry-infilled reinforced concrete frames

A review of methods applicable to the study of masonry-infilled reinforced concrete frames (MIRCF), consisting both traditional and advanced solutions, and located in seismic zones is presented in this research. Firstly, this research presents a brief discussion about the main challenges on modelling the RC frames, masonry infills and interaction between them for structures located in seismic zones. Then, simplified and sophisticated approaches, which are actually used or developed for modelling both RC frames and masonry infills recently, are discussed. The main available strategies including simplified methods, and sophisticated finite element solution are considered with regard to their realism, computer efficiency, data availability and real applicability to large structures.</p

Embedment effects of flexible foundations on control of structures

In the design of controller for earthquake-excited building benchmark, it is common to inquire about the present relationships between controlled building performance and the considering soil-foundation-structure interaction (SFSI) effects for description of the earthquake excitation. The SFSI effects can drastically affect the response of the structures subjected to earthquake motion. The effects of embedment depth on the control of structures, under plane-strain conditions, have been studied by substructure approach for buildings supported by rigid foundations embedded into a homogeneous, isotropic and elastic half-space. It is assumed that control devices are installed on all the floors. It is concluded that deeply embedded structures may increase the energy dissipated by control devices for the case of considering SFSI effects than expected from the fixed-base model and decrease the H2 norm of the system transfer function than control of structures with surface supported foundations. The effects are intensified for structures located on relatively soft soils. The inter-story drifts for control of squat structures with embedded foundations may reduce than the one controlled according to the fixed-base model, while it may increase the demand of inter-story drifts for the case of control of slender interacting systems. According to these results, considering SFSI effects on structural control can make some unexpected damages. Hence, for structures rested in or on soft soil that are controlled by active or semi-active control devices, SFSI effects in controller design should be considered. © 2010 Elsevier Ltd

Dynamic stiffness of monopile supporting offshore wind turbine generators

Very large diameter steel tubular piles (up to 10 m in diameter, termed as XL or XXL monopiles) and caissons are currently used as foundations to support offshore Wind Turbine Generators (WTG) despite limited guidance in codes of practice. The current codes of practice such as API/DnV suggest methods to analysis long flexible piles which are being used (often without any modification) to analyse large diameter monopiles giving unsatisfactory results. As a result, there is an interest in the analysis of deep foundation for a wide range of length to diameter (L/D) ratio embedded in different types of soil. This paper carries out a theoretical study utilising Hamiltonian principle to analyse deep foundations ( L/ 2 D≥ ) embedded in three types of ground profiles (homogeneous, inhomogeneous and layered continua) that are of interest to offshore wind turbine industry. Impedance functions (static and dynamic) have been proposed for piles exhibiting rigid and flexible behaviour in all the 3 ground profiles. Through the analysis, it is concluded that the conventional Winkler-based approach (such as p–y curves or Beanon-Dynamic Winkler Foundations) may not be applicable for piles or caissons having aspect ratio less than about 10 to 15. The results also show that, for the same dimensionless frequency, damping ratio of large diameter rigid piles is higher than long flexible piles and is approximately 1.2–1.5 times the material damping. It is also shown that Winkler-based approach developed for flexible piles will under predict stiffness of rigid piles, thereby also under predicting natural frequency of the WTG system. Four wind turbine foundations from four different European wind farms have been considered to gain further useful insights

Investigation of beneficial and detrimental effects of soil-foundation-structure interaction on the seismic response of shear buildings

The frequency content of earthquake ground motions shows the different influences on the performance of the structural response while the Soil-Foundation-Structure Interaction (SFSI) is considered. In this study, the periods with crucial effects on the response of a structure are quantitatively detected by considering the wavelet energy spectrum. The effects of SFSI under plane-strain conditions are studied using the substructure approach for the structural frames supported by rigid foundations embedded into a homogeneous, isotropic and elastic half-space. The effective-mass formulation is developed for the system with and without considering SFSI. Three ranges of periods on the energy spectrum of the response ratio are identified. The proposed ranges of periods on the energy spectrum and the band of possible predominant periods of free-field motion illustrate the beneficial or the detrimental effects of Soil-Foundation-Structure (SFS) system by determining the ratio of base-shear or structural inter-story drifts for flexible base structure and fixed base structure cases. © 2014 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg

Practical Method to Estimate Foundation Stiffness for Design of Offshore Wind Turbines

Offshore wind turbine structures (OWTs) are dynamically sensitive due to their shape and form (slender column supporting a heavy rotation mass) and also due to the different forcing functions (wind, wave, and turbine loading) acting on the structures. Designers need to ensure that the first Eigen natural frequency is not close to forcing frequencies to avoid dynamic associated effects such as resonance and fatigue damage. Such damages may result in higher maintenance costs and a lower service life. Therefore, it is crucial to get the best prediction of the first natural frequency during the early stages of a project. Other design requirements include the serviceability limit state (SLS) criteria which imposes strict pile head deflection and rotation limits. These calculations require foundation stiffness and the aim of this chapter is to provide practical methods to predict the stiffness of the foundations for any ground profile (nonuniform or layered soils) through the use of standard methods. The foundation stiffness values can then be used as an input to predict the first natural frequency of OWT system as well as checking SLS requirements. An example problem is taken to show the application of the method