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Showing 5 results for Damping Ratio

M. Khanzadi, G. Ghodrati Amiri, G. Abdollahzadeh Darzi,
Volume 5, Issue 1 (3-2007)

According to performance-based seismic design method by using energy concept, in this paper it is tried to investigate the duration and damping effects on elastic input energy due to strong ground motions. Based on reliable Iranian earthquake records in four types of soils, structures were analyzed and equivalent velocity spectra were computed by using input energy. These spectra were normalized with respect to PGA and were drawn for different durations, damping ratios and soil types and then effects of these parameters were investigated on these spectra. Finally it was concluded that in average for different soil types when the duration of ground motions increases, the input energy to structure increases too. Also it was observed that input energy to structures in soft soils is larger than that for stiff soils and with increasing the stiffness of the earthquake record soil type, the input energy decreases. But damping effect on input energy is not very considerable and input energy to structure with damping ratio about 5% has the minimum value.
A. Haddad, Gh. Shafabakhsh,
Volume 5, Issue 2 (6-2007)

Local site conditions have a strong effect on ground response during earthquakes. Two important soil parameters that control the amplification effects of seismic motions by a soil column are the soil hysteretic damping ratio and shear wave velocity. This paper presents the results of in situ damping ratio measurements performed using continuous surface wave attenuation data at a site in Semnan University campus and analysis used to obtain the near surface soils damping ratio profile. Once the frequency dependent attenuation coefficients are determined, the shear damping ratio profile is calculated using an algorithm based on constrained inversion analysis. A computer code is developed to calculate the shear damping ratio in each soil layer. Comparisons of the in situ shear damping ratio profile determined from continuous surface wave with cross hole independent test measurements are also presented. Values of shear damping ratio, obtained using continuous surface wave measurements, were less than the measured using cross hole tests, possibly because of the higher frequencies used in cross hole tests.
A. Hassanipour, A. Shafiee, M.k. Jafari,
Volume 9, Issue 4 (12-2011)

Shear modulus and damping ratio are important input parameters in dynamic analysis. A series of resonant column tests was

carried out on pure clays and sand-clay mixtures prepared at different densities to investigate the effects of aggregate content,

confining stress, void ratio and clay plasticity on the maximum shear modulus and minimum damping ratio. Test results revealed

an increase in the maximum shear modulus of the mixture with the increase in sand content up to 60%, followed by a decrease

beyond this value. It was also found that the maximum shear modulus increases with confining stress, and decreases with void

ratio. In addition, minimum damping ratio increases with sand content and clay plasticity and decreases with confining stress.

Finally, on the basis of the test results, a mathematical model was developed for the maximum shear modulus.

Mohsen Gerami, Ali Kheyroddin, Abbas Sivandi-Pour,
Volume 14, Issue 1 (1-2016)

Steel-concrete hybrid systems are used in buildings, in which a steel structure has been placed on a concrete structure to make a lighter structure and have a faster construction. Dynamic analysis of hybrid structures is usually a complex procedure due to various dynamic characteristics of each part, i.e. stiffness, mass and especially damping. Dynamic response of hybrid structures has some complications. One of the reasons is the different stiffness of the two parts of structure and another reason is non-uniform distribution of materials and their different features such as damping in main modes of vibration. The available software is not able to calculate damping matrices and analyze these structures because the damping matrix of these irregular structures is non-classical. Also an equivalent damping should be devoted to the whole structure and using the available software. In the hybrid structures, one or more transitional stories are used for better transition of lateral and gravity forces. In this study, an equation has been proposed to determining the equivalent uniform damping ratio for hybrid steel-concrete buildings with transitional storey(s). In the proposed method, hybrid buildings are considered to have three structural systems, reinforced concrete, transitional storey and steel. Equivalent uniform damping ratio is derived by means of a semi-empirical error minimization procedure.

Dongdong Zhang,
Volume 14, Issue 8 (12-2016)

This paper compares the seismic load of a 5MW wind turbine supported by a 100-m-high prestressed concrete tower calculated via time history analysis and response spectrum analysis using elastic acceleration spectrum provided by the China Aseismic Code for Buildings. With 5% damping ratio, the fixed-based Multi-degree of freedom model and Finite element model considering soil structure interaction are used for response spectrum analysis and time history analysis, respectively. The results indicated that the seismic load calculated by response spectrum analysis is significantly larger than the results associated with the time history analysis method. It implies that the seismic load determined from common building code procedures along with other loads for wind turbine foundation design is too conservative. Within this paper, the effects of damping ratio, horizontal acceleration amplitude, spring stiffness and damping coefficient of foundation on the seismic load of the prestressed concrete wind turbine tower are discussed. It is shown that the seismic load with mode damping ratio for the prestressed concrete wind turbine tower is not significant when compared with traditional tubular steel designs. The maximum moment demand at the base of the tower may be controlled by earthquake loading as the seismic fortification intensity lever is more than seven. The foundation spring stiffness has a immensely impact on the base bending moment and the natural frequency. Finally, seismic load should be considered in more detail when designing wind turbines that are supported by concrete towers, particularly for turbine’s over 100-m tall and located in seismically active zones.

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