18
1735-0522
379
Seismic Geotechnique
Study on Pullout Behavior of Uniaxial HDPE Geogrids Under Monotonic and Cyclic Loads
Nayeri
Arash
Fakharian
Kazem
1
12
2009
7
4
211
223
30
12
2009
11
01
2014
Abstract: This paper presents the results of pullout tests on uniaxial geogrid embedded in silica sand under monotonic and cyclic pullout forces. The new testing device as a recently developed automated pullout test device for soil-geogrid strength and deformation behavior investigation is capable of applying load/displacement controlled monotonic/cyclic forces at different rates/frequencies and wave shapes, through a computer closed-loop system. Two grades of extruded HDPE uniaxial geogrids and uniform silica sand are used throughout the experiments. The effects of vertical surcharge, sand relative density, extensibility of reinforcement and cyclic pullout loads are investigated on the pullout resistance, nodal displacement distributions, post-cyclic pullout resistance and cyclic accumulated displacement of the geogrid. Tell-tale type transducers are implemented along the geogrid at several points to measure the relative displacements along the geogrid embedded length. In monotonic tests, decrease in relative displacement between soil and geogrid by increase of vertical stress and sand relative density are the main conclusions structural stiffness of geogrid has a direct effect on pullout resistance in different surcharges. In cyclic tests it is observed that the variation of post-cyclic strength ranges from minus 10% to plus 20% of monotonic strength values and cyclic accumulated displacements are increased as normal pressure increase, but no practical specific comment can be made at this stage on the post-cyclic strength of geogrids embedded in silica sand. It is also observed that in loose sand condition, the cyclic accumulated displacements are considerably smaller as compared to dense sand condition.
380
Clay Reinforcement Using Geogrid Embedded In Thin Layers of Sand
Abdi
M.R.
Sadrnejad
S. A.
Arjomand
M.A.
1
12
2009
7
4
224
235
30
12
2009
11
01
2014
Large size direct shear tests (i.e.300 x 300mm) were conducted to investigate the interaction between clay
reinforced with geogrids embedded in thin layers of sand. Test results for the clay, sand, clay-sand, clay-geogrid, sandgeogrid
and clay-sand-geogrid are discussed. Thin layers of sand including 4, 6, 8, 10, 12 and 14mm were used to
increase the interaction between the clay and the geogrids. Effects of sand layer thickness, normal pressure and
transverse geogrid members were studied. All tests were conducted on saturated clay under unconsolidated-undrained
(UU) conditions. Test results indicate that provision of thin layers of high strength sand on both sides of the geogrid
is very effective in improving the strength and deformation behaviour of reinforced clay under UU loading conditions.
Using geogrids embedded in thin layers of sand not only can improve performance of clay backfills but also it can
provide drainage paths preventing pore water pressure generations. For the soil, geogrid and the normal pressures
used, an optimum sand layer thickness of 10mm was determined which proved to be independent of the magnitude of
the normal pressure used. Effect of sand layers combined with the geogrid reinforcement increased with increase in
normal pressures. The improvement was more pronounced at higher normal pressures. Total shear resistance provided
by the geogrids with transverse members removed was approximately 10% lower than shear resistance of geogrids
with transverse members.
381
New Predictive Models for the v max/a max Ratio of Strong Ground Motions using Genetic Programming
Kermani
E.
Jafarian
Y.
Baziar
M. H.
1
12
2009
7
4
236
247
30
12
2009
11
01
2014
Although there is enough knowledge indicating on the influence of frequency content of input motion on the
deformation demand of structures, state-of-the-practice seismic studies use the intensity measures such as peak ground
acceleration (PGA) which are not frequency dependent. The v max/a max ratio of strong ground motions can be used in
seismic hazard studies as the representative of frequency content of the motions. This ratio can be indirectly estimated
by the attenuation models of PGA and PGV which are functions of earthquake magnitude, source to site distance,
faulting mechanism, and local site conditions. This paper presents new predictive equations for v max/a max ratio based
on genetic programming (GP) approach. The predictive equations are established using a reliable database released
by Pacific Earthquake Engineering Research Center (PEER) for three types of faulting mechanisms including strikeslip,
normal and reverse. The proposed models provide reasonable accuracy to estimate the frequency content of site
ground motions in practical projects. The results of parametric study demonstrate that v max/a max increases through
increasing earthquake moment magnitude and source to site distance while it decreases with increasing the average
shear-wave velocity over the top 30m of the site.
382
Comparison of Different Methods of Wavelet and Wavelet Packet Transform in Processing Ground Motion Records
Ghodrati Amiri
G.
Asadi
A.
1
12
2009
7
4
248
257
02
01
2010
11
01
2014
Future design procedures for civil structures, especially those to be protected from extreme and blast relatedloads, will need to account for temporal evolution of their frequency content. There are, however, several instanceswhere acceleration time histories are required as seismic input. For example, to determine the ultimate resistance andto identify modes of structures’ failure, a nonlinear time history analysis is needed. In other cases, acceleration timehistories are required for linear analyses. Many seismic codes require this type of analysis for buildings which haveirregularities. The process of time-frequency analysis made possible by the wavelet transform provides insight into thecharacter of transient signals through time-frequency maps of the time variant spectral decomposition that traditionalapproaches miss. In this paper an approach is examined and a new method for processing the ground motion which ismodeled as a non-stationary process (both in amplitude and frequency), is proposed. This method uses the best basissearch algorithm with wavelet packets. In this approach, the signal is expressed as a linear combination of timefrequencyatoms which are obtained by dilations of the analyzing functions, and are organized into dictionaries aswavelet packets. Several numerical examples are given to verify the developed models.
383
The Effects of Variability of the Mathematical Equations and Project Categorizations on Forecasting S-Curves at Construction Industry
Banki
M. T.
Esmaeili
B.
1
12
2009
7
4
258
270
02
01
2010
11
01
2014
Cash flow forecasting is an indispensable tool for construction companies, and is essential for the survivalof any contractor at all stages of the work. The time available for a detailed pre-tender cash flow forecast is oftenlimited. Therefore, contractors require simpler and quicker techniques which would enable them to forecast cash flowwith reasonable accuracy. Forecasting S-curves in construction in developing countries like Iran in compare withdeveloped countries has many difficulties. It is because of uncertainty and unknown situation in nature of constructionindustry of these countries. Based on knowledge of authors there is a little attempt for cash flow forecasting inconstruction industry of Iran. As a result authors produced An S-curve equation for construction project from historicaldata which has reasonable accuracy. A sample of 20 completed projects was collected and classified in to the threedifferent groups. In order to model S-curves for each group, a simple and reliable method of S curve fitting has beenused. S-curves were fitted into each group by using different techniques. Errors incurred when fitting these curves weremeasured and compared with those associates in fitting individual projects. At the end, accuracy of each model hasbeen calculated and an equation has been proposed to forecast S-curves.
245
Water-Hydraulic Structure
Total Pressure around Chute Blocks of SAF Stilling Basins
Farhoudi
Javad
^{
n
}
^{
n
}The University of Tehran
1
12
2009
7
4
271
279
16
07
2009
ABSTRACTInduced total pressure by flow, including mean and fluctuating components, around a selected chute block in SAF stilling basins downstream of an ogee spillway was studied. Several pressure holes were selected on various faces of a selected chute block to get enough information regarding the total pressure field. This paper reports the results of an experimental work and measurement of mean and fluctuation pressures around chute blocks of SAF stilling basins. The observations showed that the maximum total pressure varies inversely with Froude number of incoming flow while its position of occurrence follows a quadratic polynomial relation ship. Statistical analysis also showed that the peak instantaneous pressure fluctuations could be as large as ±4.5times the RMS value.It is concluded that pressure fluctuation around the chute blocks may double the magnitude of pressure field around the chute blocks and can not be overlooked in designing such appurtenances.
385
Pullback Test for Seismic Performance Evaluation of Safe Rooms
Mazloom
M.
Mehrabian
A.A.
1
12
2009
7
4
280
288
02
01
2010
11
01
2014
Pullback test has no scrupulous theoretical establishment. It is based on the hypothesis that the response ofthe structure can be related to the response of an equivalent single degree-of-freedom (SDOF) system. This implies thatthe response is controlled by a single mode. In fact, the steel frame of each safe room, which is introduced within theunreinforced masonry buildings for protecting the lives of residents in catastrophic earthquake failures, contains aSDOF structural system. In pullback test, the steel frame carries its gravity load first, and then it will be pushed underan incremental lateral roof displacement pattern, which is imposed to its center of mass. This paper expresses theresults of 13 pullback tests executed by the authors on the steel frames of safe rooms. The results show that pullbacktest is a practical method for seismic performance evaluation of safe rooms. Also the performance of these frameslocated in a collapsing three storey masonry building is presented with favorable conclusions. In fact, the results ofpullback test of the safe room located at the ground-floor level were compared with the requirements of Iranian codefor seismic resistant design and it was concluded that the steel frame had an acceptable performance against seismiceffects.