ORIGINAL_ARTICLE
Fine Sand Model Ground during Shaking Using a Laminar Box
A fiber reinforced soil behaves as a composite material in which fibers of relatively high tensile strength are embedded in a matrix of soil. Shear stresses in the soil mobilize tensile resistance in the fibers, which in turn imparts greater strength to the soil. This strength mobilization is highly dependent on the level of confining pressure. In this paper a study on the influence of synthetic fibrous materials in improving the dynamic strength characteristics of a fine sandy soil under low confining pressure is reported. The project is aimed at converting fibrous carpet waste into a value-added product for soil reinforcement. A series of shaking table tests using laminar box were carried out on Toyoura sand specimens reinforced with randomly distributed geotextile strips. The dynamic strength characteristics of the reinforced sand are defined in terms of shear modulus and damping ratio. The effect of fiber content under low confining pressure has been delineated. The results indicate the effectiveness of the reinforcement in improving the dynamic properties of fine sand under low confining pressure.
http://www.jsee.ir/article_240678_28997f7f235bb121025c14d36b06fff9.pdf
2009-01-01
195
203
H.
Ghiassian
1
Iran University of Science and Technology
AUTHOR
R.
Jamshidi Chenari
jamshidi_reza@yahoo.com
2
Faculty of Engineering, Guilan University
LEAD_AUTHOR
H.
Shahnazari
3
Iran University of Science and Technology
AUTHOR
A.
Tabarsa
4
Civil Engineering Department, Golestan University
AUTHOR
ORIGINAL_ARTICLE
Comparing the Performance of RC Buildings Designed by Direct Displacement Based Method and Standard-2800 (3rd Edition)
Direct displacement based design method, which has been presented by Priestley, is the newest performance design method of RC buildings recently noticed by many researchers. It refers to the seismic behavior of buildings and their performance during strong earthquakes. This method has a new point of view in comparison to the ordinary well-known forced based design method. This paper compares seismic behavior of RC buildings designed by two basically different design methods; DDBD method and the forced based method in the Iranian Code of Practice; Standard-2800 (the 3rd edition). For each design method, four RC Buildings: 4, 8, 12, and 16-story two dimensional special moment resisting frame are designed based on a specific design spectrum. Seismic performance of all buildings using the dynamic inelastic time history analysis is evaluated against two seven-member artificial records. The members of the first group are synthesized by SIMQKE1 and for the second group a new proposed (by authors) simple approach based on the Fourier transform modifies the real accelerograms. All members of the two groups have response spectra match to the specified design spectrum of the buildings. Extensive analysis shows that all buildings designed by DDBD have a strong and regular behavior and meet their performance criterion (2% drift ratio), while the buildings designed by Standard-2800 can not perform well such that they do not meet their performance criteria even with those designed based on.
http://www.jsee.ir/article_240680_23b9941ccb92a99030624e21413c6c74.pdf
2009-01-01
217
229
M.
Kaffashian
1
IIEES
AUTHOR
O.
Bahar
omidbahar@iiees.ac.ir
2
IIEES
LEAD_AUTHOR
ORIGINAL_ARTICLE
Using Ambient Array Method in Evaluating the Shear Wave Velocity Profile of a Site in Tehran
In order to evaluate the capability of ambient array method for estimating the underground shear wave velocity (Vs) profile, a series of microtremor array measurement was performed in a site in Tehran. Fifteen seismometers were used simultaneously as 3 concentric circles with a radius of 25, 35 and 50m and the data were recorded continuously for 15 hours. Using the Nakamura H/V technique, the records of each station were processed individually and the natural period of the site was evaluated. The frequency wave number (F-K) and Spatial Autocorrelation (SPAC) methods were used to process the ambient array records and the extracted results were compared with the previous down hole and PS logging results. To obtain the shear wave velocity profile of subsurface layers, inversion of dispersion curve was performed using the neighborhood algorithm. Based on the obtained average results from F-K and ESPAC processing methods, it seemed that the Vs profile derived from ESPAC technique was more consistent with previous site investigation results. It was also concluded that by using multi layer model for the site with at least the layer number as the real, the extracted Vs profile fits better with previous investigations. By increasing the suggested layer number from real one, little variation can be shown in the Vs profile of the site.
http://www.jsee.ir/article_240679_72ca63d797932757a06a5b95e01924a2.pdf
2009-01-01
205
215
M.
Davoodi
m-davood@iiees.ac.ir
1
IIEES
LEAD_AUTHOR
E.
Haghshenas
2
IIEES
AUTHOR
M.
Mirjalili
3
IIEES
AUTHOR
ORIGINAL_ARTICLE
Experimental and Analytical Evaluation of the Seismic Behavior of Masonry Walls
Masonry non-engineered buildings suffer major failure in earthquakes, due to their poor lateral strength. Problem with these buildings are usually associated with their poor understanding of their behavior and more so lack of a well defined methodology for their analysis. Many methods such as distinct element, finite element, equivalent frame model and finally code regulations are used for their constructions but each having their shortcomings. In this paper, the results of three full scale tests of masonry walls and ways of loading and test set up is presented for better understanding of the behavior. Then, by using equivalent frame methodology these results are calibrated, and are compared with code regulations which have shown good agreements meaning the benefits of equivalent method. Analysis of both static and dynamic have been applied and results are obtained. In all, very good agreements are provided by equivalent frame methodology for modeling these walls.
http://www.jsee.ir/article_240681_4bad6f60aeb05641794a1a7370856b55.pdf
2009-01-01
231
242
F.
Alemi
f-alemi@iiees.ac.ir
1
IIEES
LEAD_AUTHOR
F.
Nateghi-Alahi
2
IIEES
AUTHOR
M.
Ziyaeifar
3
IIEES
AUTHOR
ORIGINAL_ARTICLE
Spectral Investigation on Behaviour of Mass Isolated Structures and Their Semi-Active Control against Earthquakes
In this paper, the seismic behaviour of mass isolated structures against the earthquake is studied. These structures are assumed to be consisted of two subsystems. Mass subsystem possesses low lateral stiffness but carries the major part of mass of the system. Stiffness subsystem, however, controls the deformation of the mass subsystem and attributes with much higher stiffness. The isolator layer is, therefore, located in between the mass and the stiffness subsystems and assumed to be a semi-active damper layer. The analytical model used for this investigation is a dual mass-spring model which is an extended form of the three-element Maxwell model. In this study, the ability of mass isolation techniques in reducing earthquake effects on buildings with two approaches, parametric and numerical approaches, is studied. In the parametric approach, by defining an isolation factor for structure and determining the dynamic characteristics of system, the relative optimum value of the isolator damping coefficient is obtained. Finally, in the numerical approach, the spectral responses of these structures due to the earthquake are investigated. The results show a noticeable decrease in earthquake input force to mass isolated structures in comparison with non-isolated structures and also show a suitable performance in control case.
http://www.jsee.ir/article_240682_2b5b7b4f3e30962aa6defd5d0546dd38.pdf
2009-01-01
243
252
M.
Nekooei
nekooei@iiees.ac.ir
1
IIEES
LEAD_AUTHOR
M.
Ziyaeifar
2
IIEES
AUTHOR
ORIGINAL_ARTICLE
Seismic Control of the Phase II Base Isolated Benchmark Problem by A Proposed Semi-Active Algorithm
Performance of a proposed semi-active control algorithm is investigated during the seismic control of a base isolated 8-storey benchmark building. The building, which is equipped by nonlinear isolators, has been developed by other researchers to evaluate the performance of various control algorithms in MATLABĀ® and SIMULINKĀ®. The proposed algorithm creates an artificial nonlinear damping force, so that the base shear hysteresis curve show a high energy dissipation capability while limiting the maximum base shear. The idea is taken from the hysteresis curve generated by friction bearings and modifications were made to reduce the demerits while keeping the merits of this type of isolators. A numerical model of a MR damper is employed in the analysis. To compare the results, a passive viscous damping system, as well as a variable damping system controlled by skyhook algorithm is utilized. Seven pairs of earthquakes provided by the developers of the benchmark problem are used for the time history analysis. The resulted base-shear hysteresis curves are presented for the three studied cases. The comparison of the performance indices indicates that the employed semi-active control methods have better performance than the passive method. The base displacement values are mostly less in the model controlled by the proposed algorithm. However, it resulted in larger floor accelerations, which is originated by the sudden changes in the damping force.
http://www.jsee.ir/article_240683_c4e1e926668e4ba52676985ddf710023.pdf
2009-01-01
253
262
A.
Kalantari
a.kalantari@iiees.ac.ir
1
IIEES
LEAD_AUTHOR
ORIGINAL_ARTICLE
Analytical and Experimental Study on Using Yielding Steel Shear Keys in Girder-Slab Bridges Supported on Rubber Bearings
In girder-slab bridges supported on conventional rubber bearings, shear keys are usually designed to support the girders against lateral seismic loads. Shear keys are relatively stiff elements and transfer the lateral load of the superstructure to the substructure during an earthquake. Due to relatively large mass of superstructure, the lateral seismic load could damage the substructure. In this paper, an innovative idea is proposed in which the conventional shear keys are replaced with yielding steel shear keys with high ductility. During an earthquake seismic energy is dissipated within the proposed shear keys resulting in significant reduction of seismic demand on the substructure. Experimental study has been conducted to evaluate the behavior of the proposed shear keys. Test results indicate that these shear keys can sustain large inelastic deformation without strength degradation under cyclic loading. A two span concrete bridge has also been analyzed to evaluate the performance of bridges equipped with the proposed shear keys. The results of analyses indicate that seismic demand on substructure reduces by about 50 percent if conventional shear keys are replaced by the proposed shear keys.
http://www.jsee.ir/article_240684_1d65ba8b89d81471bc0e1d17ea44510d.pdf
2009-01-01
263
270
A.
Vasseghi
vasseghi@iiees.ac.ir
1
IIEES
LEAD_AUTHOR
H.
Rostamian
2
IIEES
AUTHOR