Seismic evaluation of fluid-elevated tank-foundation/soil systems in frequency domain

Livaoglu, R.,Dogangun, A. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.1

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequency-dependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

Investigation of wall flexibility effects on seismic behavior of cylindrical silos

Livaoglu, Ramazan,Durmus, Aysegul Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.1

This paper is concerned with effects of the wall flexibility on the seismic behavior of ground-supported cylindrical silos. It is a well-known fact that almost all analytical approximations in the literature to determine the dynamic pressure stemming from the bulk material assume silo structure as rigid. However, it is expected that the horizontal dynamic material pressures can be modified due to varying horizontal extensional stiffness of the bulk material which depends on the wall stiffness. In this study, finite element analyses were performed for six different slenderness ratios according to both rigid and flexible wall approximations. A three dimensional numerical model, taking into account bulk material-silo wall interaction, constituted by ANSYS commercial program was used. The findings obtained from the numerical analyses were discussed comparatively for rigid and flexible wall approximations in terms of the dynamic material pressure, equivalent base shear and bending moment. The numerical results clearly show that the wall flexibility may significantly affects the characteristics behavior of the reinforced concrete (RC) cylindrical silos and magnitudes of the responses under strong ground motions.

Soil interaction effects on sloshing response of the elevated tanks

Livaoglu, Ramazan Techno-Press 2013 Geomechanics & engineering Vol.5 No.4

The aim of this paper is to investigate how the soil-structure interaction affects sloshing response of the elevated tanks. For this purpose, the elevated tanks with two different types of supporting systems which are built on six different soil profiles are analyzed for both embedded and surface foundation cases. Thus, considering these six different profiles described in well-known earthquake codes as supporting medium, a series of transient analysis have been performed to assess the effect of both fluid sloshing and soil-structure interaction (SSI). Fluid-Elevated Tank-Soil/Foundation systems are modeled with the finite element (FE) technique. In these models fluid-structure interaction is taken into account by implementing Lagrangian fluid FE approximation into the general purpose structural analysis computer code ANSYS. A 3-D FE model with viscous boundary is used in the analyses of elevated tanks-soil/foundation interaction. Formed models are analyzed for embedment and no embedment cases. Finally results from analyses showed that the soil-structure interaction and the structural properties of supporting system for the elevated tanks affected the sloshing response of the fluid inside the vessel.

Seismic evaluation of fluid-elevated tank-foundation/soil systems in frequency domain

R. Livaoglu,A. Dogangun 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.1

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequencydependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

Effect of Geometric Properties on Dynamic Behavior of Historic Masonry Minaret

Ramazan Livaoglu,Mehmet Hüdai Bastürk,Adem Dogangün,Cavit Serhatoglu 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6

Historical minarets are quite sensitive structures against horizontal loads as they are tall, slender and masonry constructions. Due to their special characters, significant damages are occurred in critical part by devastating earthquakes. These damages lead to more comprehensive studying about minarets. In this study; the effect of geometrical features was investigated for dynamic behavior of seven historical masonry minarets in Bursa. However, dynamic character identification of historical masonry minarets are so difficult. Therefore, ambient vibration test were performed with aim of defining modal parameters of the minarets. Since the structural behavior of historical minarets were also represented with mathematical models, three dimensional (solid) models were implemented by using the finite element software Abaqus Cae. Model updating was performed in order to match the natural frequencies arising from the experimental investigation with those from numerical results. According to the results obtained from both forms, effect of geometric features on the dynamic behavior of minarets was evaluated. The relationships are between the first mode period of the minarets and the structural properties such as height, cross section, boundary condition. Then, the analytical formula was derived from the relationships for rapid estimation of the fundamental period of the typical Ottoman minarets. Finally, it was found that the period of the minarets from the formula close enough to modal test and modal analysis results.

Hydrodynamic pressures acting on the walls of rectangular fluid containers

Dogangun, Adem,Livaoglu, Ramazan Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.2

The dynamic response characteristics of a rectangular fluid container are investigated by using finite element method. The fluid is assumed to be linear-elastic, inviscid and compressible. A displacement-based fluid finite element was employed to allow for the effects of the fluid. A typical rectangular fluid container, which is used in recent studies, is considered for the numerical analysis. The North-South component of El Centro Earthquake records is used as input ground acceleration. Rigid and flexible fluid containers solutions are obtained for the chosen sample tank. Hydrodynamic pressures and sloshing motions are determined using Lagrangian fluid finite element. The results obtained from this study are compared with the results obtained by boundary-finite element method (BEM-FEM) and requirements of Eurocode-8. Based on the numerical analysis, some conclusions and discussions on the design considerations for rectangular fluid containers are presented.

Experimental analysis on FEM definition of backfill-rectangular tank-fluid system

Cakir, Tufan,Livaoglu, Ramazan Techno-Press 2013 Geomechanics & engineering Vol.5 No.2

In the present study, the numerical and experimental investigations were performed on the backfill- exterior wall-fluid interaction systems in case of empty and full tanks. For this, firstly, the non-linear three dimensional (3D) finite element models were developed considering both backfill-wall and fluid-wall interactions, and modal analyses for these systems were carried out in order to acquire modal frequencies and mode shapes by means of ANSYS finite element structural analysis program. Secondly, a series of field tests were fulfilled to define their modal characteristics and to compare the results from proposed approximation in the selected structures. Finally, comparing the theoretical predictions from the finite element models to results from experimental measurements, a close agreement was found between theory and experiment. Thus, it can be easily stated that experimental verifications provide strong support for the finite element models and the proposed procedures themselves are the meritorious approximations to the real problem, and this makes the models appealing for use in further investigations.

The role of slenderness on the seismic behavior of ground-supported cylindrical silos

Demir, Aysegul Durmus,Livaoglu, Ramazan Techno-Press 2019 Advances in concrete construction Vol.7 No.2

This paper reports on the results of a parametric study, which examines the effects of varying aspect ratios on the dynamic response of cylindrical silos directly supported on the ground under earthquake loading. Previous research has shown that numerical models can provide considerably realistic simulations when it comes to the behavior of silos by using correct boundary conditions, appropriate element types and material models. To this end, a three dimensional numerical model, taking into account the bulk material-silo wall interaction, was produced by the ANSYS commercial program, which is in turn based on the finite element method. The results obtained from the numerical analysis are discussed comparatively in terms of dynamic material pressure, horizontal displacement, equivalent base shear force and equivalent bending moment responses for considered aspect ratios. The effects experienced because of the slenderness of the silo in regards to the seismic response were evaluated along with the effectiveness of the classification system proposed by Eurocode in evaluating the loads on the vertical walls. Results clearly show that slenderness directly affects the seismic response of such structures especially in terms of behavior and the magnitude of the responses. Furthermore the aspect ratio value of 2.0, given as a behavioral changing limit in the technical literature, can be used as a valid limit for seismic behavior.