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Showing 7 results for Seismic Loading

Kimiaei M., Shayanfar M.a., Hesham Ei Naggar M., Agha Kouchak A.a.,
Volume 2, Issue 2 (6-2004)
Abstract

The seismic response of pile-supported offshore structures is strongly affected by the nonlinear behavior of the supporting piles. Nonlinear response of piles is the most important source of potentially nonlinear dynamic response of offshore platforms due to earthquake excitations. It is often necessary to perform dynamic analysis of offshore platforms that accountsfor soil nonlinearity, discontinuity condition at pile soil interfaces, energy dissipation through soil radiation damping and structural non linear behaviors of piles.In this paper, an attempt is made to develop an inexpensive and practical procedure compatible with readily available structural analysis software for estimating the lateral response of flexible piles embedded in layered soil deposits subjected to seismic loading. In the proposed model a BNWF (Beam on Nonlinear Winkler Foundation) approach is used consisting of simple nonlinear springs, dash pots and contact elements. Gapping and caving-in conditions at the pile-soil interfaces are also considered using special interface elements. This model was incorporated into a Finite Element program (ANSYS), which was used to compute the response of laterally excited piles. A linear approach was used for seismic free field ground motion analysis. The computed responses compared well with the Centrifuge test results.This paper deals with the effects of free field ground motion analysis on seismic non linear behavior of embedded piles. Different parts of a BNWF (Beam on Nonlinear Winkler Foundation) model, together with quantitative and qualitative findings and conclusions for dynamic nonlinear response of offshore piles, are discussed and addressed in detail. The proposed BNWF model (only using the existing features of the available general finite element software) could easily be implemented in a more comprehensive model of nonlinear seismic response analysis of pile supported offshore platforms.
H. Moharrami, S.a. Alavinasab,
Volume 4, Issue 2 (6-2006)
Abstract

In this paper a general procedure for automated minimum weight design of twodimensional steel frames under seismic loading is proposed. The proposal comprises two parts: a) Formulation of automated design of frames under seismic loading and b) introduction of an optimization engine and the improvement made on it for the solution of optimal design. Seismic loading, that depends on dynamic characteristics of structure, is determined using "Equivalent static loading" scheme. The design automation is sought via formulation of the design problem in the form of a standard optimization problem in which the design requirements is treated as optimization constraints. The Optimality Criteria (OC) method has been modified/improved and used for solution of the optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of active set of constraints and calculation of corresponding Lagrange multipliers. The modification has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal design problems. Two examples have been provided to show the procedure of automated design and optimization of seismic-resistant frames and the performance and capability of the proposed algorithm.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)
Abstract

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
M. Afzalirad, M. Kamalian, M. K. Jafari, A. Sohrabi-Bidar,
Volume 12, Issue 1 (1-2014)
Abstract

In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)
Abstract

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
C. Vieira,
Volume 12, Issue 1 (1-2014)
Abstract

This paper presents a simplified approach to estimate the resultant force, which should be provided by a retention system, for the equilibrium of unstable slopes. The results were obtained with a developed algorithm, based on limit equilibrium analyses, that assumes a two-part wedge failure mechanism. Design charts to obtain equivalent earth pressure coefficients are presented. Based on the results achieved with the developed computer code, an approximate equation to estimate the equivalent earth pressure coefficients is proposed. Given the slope angle, the backslope, the design friction angle, the height of the slope and the unit weight of the backfill, one can determine the resultant force for slope equilibrium. This simplified approach intends to provide an extension of the Coulomb earth pressure theory to the stability analyses of steep slopes and to broaden the available design charts for steep reinforced slopes with non-horizontal backslopes
A. Reyes-Salazar, E. Bojorquez, J.l. Rivera-Salas, A. Lopez-Barraza, H.e. Rodriguez-Lozoya,
Volume 13, Issue 3 (9-2015)
Abstract

The linear and nonlinear responses of steel buildings with perimeter moment resisting frames (PMRFs) are estimated and compared to those of equivalent buildings with spatial moment resisting frames (SMRFs). The equivalent models with SMRFs are designed by using an approximated procedure in such a way that, not only their fundamental period, total mass and lateral stiffness are fairly the same as those of the corresponding buildings with PMRFs, but also other characteristics to make the two structural "as equivalent" as possible. The numerical study indicates that the interstory shears of the PMRFs building may be significantly larger than those of the SMRFs building. The main reasons for this are that the buildings with PMRFs are stiffer and that the dynamics properties of the two types of structural systems are different. The interstory displacements are similar for both structural systems in many cases. For some other cases, however, they are larger for the model with SMRFs, depending upon the closeness between the earthquake corner periods and the periods of the buildings. The global ductility and story ductility demands are larger for the buildings with PMRFs, implying that, since larger ductility demands are imposed, the detailing of the connections will have to be more stringent than for the buildings with SMRFs. It can be concluded, that the seismic performance of the steel buildings with SMRFs may be superior to that of steel buildings with PMRFs. The findings of this paper are for the particular models used in the study. Much more research is needed to reach more general conclusions

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