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Showing 22 results for Experimental Study

Baziar M.h., Ziaie Moayed R.,
Volume 1, Issue 1 (9-2003)
Abstract

An experimental study was carried out to evaluate the influence of silt content on cone penetration measurements and its implication for soil classification. The investigation includes twenty-seven peizocone tests in saturated salty sand samples, which had been prepared in a big rigid thick walled steel cylinder-testing chamber. The samples were prepared with several different silt contents ranging from 0 to 50 percent and were consolidated at three-overburden effective stresses including 100, 200 and 300 kPa. This study showed that, the amount of silt content in sand is an important parameter affecting CPT results. As the silt content increases, the cone tip resistance decreases. The recorded excess pore water pressure during sounding was increased with increasing silt content. It is also concluded that friction ratio, in general, increases with increasing silt content. The method presented by Robertson and Wride [25] and Olsen [17] to evaluate soil classification are also verified.
Baziar M.h., Asna Ashari M.,
Volume 2, Issue 3 (9-2004)
Abstract

An experimental study was carried out to evaluate the liquefaction resistance of silty sand utilizing laboratory techniques. In this study, liquefaction potential of silty sand by using cyclic triaxial tests on frozen samples retrieved from calibration chamber and constructed samples by dry pouring method were investigated. Correlation between cone penetration resistance and cyclic strength of undisturbed silty sand samples are also examined using CPT calibration chamber and cyclic triaxial tests. The cone penetration tests were performed on silty sand samples with fine contents ranging from 0% to 50% and overburden stresses in the range of 100-300 kPa. Then the soil sample in calibration chamber, in the same way that soil samples were prepared during CPT sounding, was frozen and undisturbed soil specimen retrieved from frozen soil sample were tested using cyclic triaxial tests. Analysis of results indicates that the quality of frozen samples is affected by fine content and overburden pressures. Also, using data obtained in this research, the relationship between cone tip resistance and cyclic resistance ratio (CRR) for silty sand soils will be presented. These correlations are in relatively good agreement with field case history data. Also increasing confining pressure in silty sand material increases the cone tip resistance and generally, cyclic resistance ratio increases by increasing silt content.
M. Heidarzadeh, A.a. Mirghasemi, S. Etemadzadeh,
Volume 5, Issue 1 (3-2007)
Abstract

A new chemical grouting method has been developed for conglomerate formations based on the experimental studies. Due to the lack of chemical grouting experience of conglomerate formations, the testing programs were performed to evaluate the performance of chemical grouting in the water sealing of part of conglomerate foundation of Karkheh earth dam using a combination of field and laboratory tests. First, the chemical grouts alone were examined with regard to viscosity-time behavior, gelation time, temperature-influence, stability, and deformability. These laboratory tests, led to the selection of the final chemical grout which was a solution of sodium silicate, water, and ethyl acetate as reactant. The second step tested grout-soil interaction: The injectability and permeability reduction of the selected chemical grout was examined in field injection tests. In this step two field tests were performed including shallow test holes without hydrostatic pressure and full scale tests under dam real hydrostatic pressure head. Based on these two field injection tests, performed in the conglomerate foundation of Karkheh dam, a new chemical grouting method for conglomerate formations is proposed and satisfactory results led to the recommendation of this method for eventually successful application.
S. Eshghi, V. Zanjanizadeh,
Volume 5, Issue 3 (9-2007)
Abstract

This paper presents an experimental study on seismic repair of damaged square reinforced concrete columns with poor lap splices, 90-degree hooks and widely spaced transverse bars in plastic hinge regions according to ACI detailing (pre.1971) and (318-02) using GFRP wraps. Three specimens were tested in “as built” condition and retested after they were repaired by glass fiberreinforced plastic sheets. They were tested under numerous reversed lateral cyclic loading with a constant axial load ratio. FRP composite wraps were used for repairing of concrete columns in critically stressed areas near the column footings. Physical and mechanical properties of composite wraps are described. Seismic performance and ductility of the repaired columns in terms of the hysteretic response are evaluated and compared with those of the original columns. The results indicated that GFRP wraps can be an effective repair measure for poorly confined R/C columns due to short splice length and widely spaced ties with 90-degree anchorage hooks. Both flexural strength and ductility of repaired columns were improved by increasing the existing confinement in critical regions of them.
Ali Pak, Zahra Zahmatkesh,
Volume 9, Issue 2 (6-2011)
Abstract

Geotextiles are one of the most widely used synthetic materials in filtration and drainage applications. Since in real

applications, geotextiles are subjected to various hydraulic gradients and confining stresses, hydraulic behavior of geotextiles

under different circumstances is of great practical importance. In this study filtration and drainage properties of several

nonwoven needle-punched geotextiles with different properties and unit mass per area of 200g/m2, 400g/m2, 500g/m2 and

800g/m2, under various confining stresses and hydraulic gradients, were studied using standard permittivity

and transmissivity equipments. Prepared samples were subjected to hydraulic heads in the range of 10cm to 60cm and

confining stresses up to 1000kPa and their hydraulic behavior was investigated accordingly. In this study the flow regime

through the geotextile fibers and also the anisotropic behavior of geotextile permeability were investigated. The results show

that transmissivity will decrease exponentially with increasing the normal stress until a residual value is reached, and

permittivity and transmissivity coefficients were seen to decrease with increasing the hydraulic gradient. The flow regime has

found to be non-turbulent in all cases.The Geotextile hydraulic behavior is of great usage in the design of landfill covers,

design of embankments and irrigation structures drainage systems, and in the design of protection systems in river

engineering.


M. Khorami, J. Sobhani,
Volume 11, Issue 4 (12-2013)
Abstract

Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2 % and 4 % of waste agricultural fibers in combination with and without 5 % replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.
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.
Jose Bogas, Augusto Gomes,
Volume 12, Issue 2 (6-2014)
Abstract

This paper aims to characterize the elastic modulus of structural modified normal density (MND) and lightweight aggregate concrete (LWAC) produced with different types of expanded clay lightweight aggregates (LWA). A comprehensive experimental study was carried out involving different concrete strengths ranging from 30 to 70 MPa and density classes D1.6 to D2.0. The influence of several factors on the LWAC elastic modulus, such as the cement content, initial wetting conditions, type and volume of coarse LWA and the partial replacement of normal weight coarse and fine aggregates by LWA are analyzed. The strength and deformability of LWAC seems to be little affected by the addition of high reactive nanosilica. Reasonable correlations are found between the elastic modulus and the compressive strength or concrete density. The obtained LWAC elastic moduli are compared with those reported in the literature and those estimated from the main normative documents. In general, codes underestimate the LWAC modulus of elasticity by less than 20%. However, the MND modulus of elasticity can be greatly underestimated. In addition, the prediction of LWAC elastic modulus by means of non-destructive ultrasonic tests is studied. Dynamic elasticity modulus and ultrasonic pulse velocity results are reported and high correlated relationships, over 0.95, with the static modulus are established.
R. Perumal, K. Nagamani,
Volume 12, Issue 4 (12-2014)
Abstract

An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.
A. R. Rahai, M. Mortazavi,
Volume 12, Issue 4 (12-2014)
Abstract

During the past years the use of buckling restrained braces (BRBs) have had a dramatic growth due to their better performance comparing to conventional braces. BRBs have more ductility and energy absorption capacity by excluding the overall brace buckling. However, even these kinds of braces have some problems restricting their use in some projects, i.e. high tolerance of applying unbonding material, concrete placing difficulties and their weight. Accordingly, many researchers have conducted experiments to find the possibility of shortening or even eliminating the infill material of the braces. The following study has addressed the effect of debonding material friction ratio, shortening the concrete fill, and finally eliminating it if possible, by reshaping the core element with constant section area. The operated analysis has been carried out both numerically and experimentally. ABAQUS finite element software was applied for numerical analysis and the results were verified by an experimental study in two groups of models each including four full-scale brace models. With a constant core section area, results revealed that without the risk of buckling, the concrete cover length could be reduced. With a special core profile, the infill may be fully omitted and the restrainer would be made up of only a steel tube, which may happen without any changes made to the cross sectional area of the core profile.
D. F. Cao, W. J. Ge, B. Y. Wang, Y. M. Tu,
Volume 13, Issue 1 (3-2015)
Abstract

In order to investigate the flexural behaviors of RC beams after freeze-thaw cycles, compressive strength test of concrete cubes after 0, 50, 100, 125 freeze-thaw cycles were made, and static flexural experiment of 48 RC beams after 0, 50, 100, 125 freeze-thaw cycles were made. The relationships of relative compressive strength, mass loss rate, relative dynamic elastic modulus and numbers of freeze-thaw cycles were analyzed. The influences of different numbers of freeze-thaw cycles on the flexural behaviors of RC beams with different concrete grades were studied. The results show that concrete cubes’ mass, relative dynamic elastic modulus and compressive strength decrease with the increasing of freeze-thaw cycles, and high-strength grade concrete could slow down the damage caused by freeze-thaw cycles. Experimental values of test beams stiffness under short-term load were smaller than theory value. Some under-reinforced RC beams occurs over-reinforced failure mode after freeze-thaw cycles. Boundary reinforcement ratio of RC beams after certain numbers of freeze-thaw cycles was derived and its correctness was verified by experiment. Current code for design of concrete structures about crack load and ultimate load are still suitable for RC beams after freeze-thaw cycles.
F. Tootoonchy, B. Asgarian, F. Danesh,
Volume 13, Issue 2 (6-2015)
Abstract

Despite the rapid growth of engineering science especially in the modern structural engineering and application of new materials in civil engineering, a significant percentage of world population in different countries are living in adobe buildings made from mud-bricks. In this paper, by performing experimental study on scaled mud-brick walls under monotonic load, in-plane behavior of the walls have been investigated for different levels of vertical load. After recognizing damage mechanisms from experiment, a simple retrofitting method has been presented to upgrade wall performance. Experimental behavior of retrofitted walls was also studied. The proposed retrofitting method consists of using polypropylene lace and tarpaulin belts. As a result, a better performance of the walls in terms of shear capacity, ductility and energy absorption are observed by using proposed retrofitting method. Meanwhile, Proposed retrofitting method has significant effect in rocking mechanism delay and prevention of wall sudden collapse.
Dr M. Khodaparast, Dr A.m. Rajabi, Mr. M. Mohammadi,
Volume 13, Issue 2 (6-2015)
Abstract

The Dynamic Probe is an effective tool used in site investigation. It is more economic than the use of direct drilling, particularly in explorations with moderate depth. This paper presents an experimental study to investigate the capability of using dynamic probing to evaluate the shear strength and compaction percent of fine soil. A series of dynamic probe tests were carried out at 6 different sites in the Khozestan, Hormozgan and Qom provinces in the central and southern regions of Iran. The repeatability of the results is considered and new empirical equations relating the dynamic point resistance to undrained shear strength and compaction percent are proposed. For undrained shear strength evaluation of fine soils, i.e. clay and silty clay soils, a reliable site-specific correlation between qd and Cu can be developed when considering the correlation between log qd and log Cu. Also compaction present can be evaluated by qd. These equations can be developed to provide site-specific relationships based upon geotechnical data at each new location. Using this approach an estimation of the undrained shear strength Cu and compaction percent CP can be determined from dynamic probe tests with acceptable accuracy. The present paper also encourages the wider application of dynamic probing for site investigation in fine soils.
M. Mojezi, M.k. Jafari, M. Biglari,
Volume 13, Issue 3 (12-2015)
Abstract

Experimental study of the cyclic behavior of unsaturated materials is more complex than that of the saturated materials due to the required equipment, experience and time. Furthering investigations in the field of unsaturated materials is necessary to better understand its complexity and sensitivity of unsaturated cyclic parameters to different determinants such as suction path, stress path, loading speed, deviatoric stress amplitude, physical specifications, and etc. To this end, the main focus of this study has been to analyze the effects of factors such as mean net stress and deviatoric stress levels in fast cyclic loading on the cyclic behavior of a normally consolidated unsaturated fine-grained trade soil, namely the Zenoz kaolin. Various unsaturated tests were performed in three mean net stress levels and three amplitudes of cyclic deviatoric stress levels. Results showed that increase of suction in the same strain level leads to increase in stiffness in normally consolidated samples (i.e. increase in elastic modulus and shear modulus and decrease in damping ratio). Also, in the same suction value and strain level, increase of the mean net stress during the isotropic consolidation causes to the denser normally consolidated samples and results to increase of elastic modulus and shear modulus, and decrease of damping ratio.


S.m. Zahrai,
Volume 13, Issue 3 (9-2015)
Abstract

Seismic retrofit of masonry slabs in existing steel or masonry buildings has found special significance in current codes as failure of unstable jack arch slabs has been reported as a major reason for collapsing structures in Middle East deadly earthquakes. In this paper, three retrofit schemes are investigated and compared. The proposed rehabilitation techniques consist of a single X strapping, SXS, a double X strapping, DXS, and a two-way jack arch slab supported by a steel grid. Using experimental studies, advantages and disadvantages of each scheme are evaluated. In-plane stiffness and capacity of the diaphragm are adopted as the seismic performance index of each rehabilitation scheme. According to the obtained results, the jack arch slab systems designed and constructed based on proposed retrofit methods provide an appropriate alternative to other forms of flooring in seismic zones. DXS can greatly improve diaphragm performance in terms of in-plane stiffness, capacity and even energy dissipation of the diaphragm compared with the other two techniques. The second place belongs to SXS while the steel grid scheme has a minor effect on the in-plane stiffness of the diaphragm.
A.r. Sattarifar, M.k. Sharbatdar, A. Dalvand,
Volume 13, Issue 4 (12-2015)
Abstract

In this paper, an experimental study has been conducted on strengthening of reinforced concrete (RC) connections by FRP sheets. The innovation of this research is using narrow grooves on critical regions of connection to increase the adherence of FRP sheets and prevent their early debonding. Therefore, four RC connections were made and tested under a constant axial load on the column and an increasing cyclic load on the beam. The first specimen, as the standard reference specimen, had close tie spacing in ductile regions of beam, column and panel zone based on seismic design provisions, and the second specimen, as the weak reference specimen did not have these conditions in all regions. Two other weak specimens were strengthened using two different strengthening patterns with FRP sheets one by ordinary surface preparation and the other with surface grooving method for installing FRP sheets on the connection. The results showed that ultimate load and ductility of the weak specimen compared to standard specimen decreased 25% and 17%, respectively. The shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened specimens. Also, it was observed that early debonding of FRP sheets was prevented in the strengthened connection with grooving pattern and so had desirable ductility and bearing capacity similar to the standard specimen.


L. Zeng, Q. Zhou, Ch. Xu, Y. Wu, X. Tu,
Volume 13, Issue 4 (12-2015)
Abstract

To study seismic performance of concrete-encased composite columns with T-shaped steel cross-section, twelve half-scale columns were tested under quasi-stastic cyclic loading. The result indicates that concrete-encased composite columns with T-shaped steel section possess good seismic performance. The failure modes include bending failure, shear-bond failure, shear compression failure and shear-composition failure. Unsymmetrical phenomenon of positive and negative hysteresis loop was shown evidently. Span ratio has a great influence on failure mode. The ductility performance decreases with increasing of axial compression level. As stirrup ratio increases, ductility and bearing capacity of columns are improved greatly, and energy dissipation capacity after yielding is enhanced. Cross tie can enhance ultimate bearing capacity, and lower strength attenuation and stiffness degradation on the later loading stage


Fatemeh Kazemi, Dr Saeed Reza Khodashenas, Hamed Sarkardeh,
Volume 14, Issue 1 (1-2016)
Abstract

Stilling basins dissipate energy in order to form hydraulic jumps and rotational flows. Hydraulic jump and rotational current phenomenon produces pressure fluctuation at the bottom of stilling basins. In the present study, pressure fluctuations and their locations have been studied in a physical model of Nimrod Dam. Results showed that fluctuations in presence of jump in the basin are high and therefore the fluctuation factors are respectively high. Regarding available empirical equations, the thickness of slab for different hydraulic conditions were calculated and compared in 1D and 2D conditions. By analyzing collected data, it was observed that, results of 1D were underestimated in comparison by 2D calculations.


Hossein Soltani-Jigheh,
Volume 14, Issue 7 (10-2016)
Abstract

The main objective of present study is to possible use of plastic waste materials for reinforcing clayey soils. An experimental study was planned to investigate compressibility and undrained shear behavior of clayey soil mixed with plastic waste. The mixtures were prepared with various amount of plastic waste (i.e. 0%, 0. 5%, 1.0%, 1.5% and 3.0% in dry weight) and interactive effect of plastic waste, plastic flexibility, confining pressure and initial density on the behavior of clayey soil was studied by performing compaction, consolidated undrained triaxial and oedometer consolidation test. The results show that plastic wastes do not affect compaction characteristics of clayey soil considerably and adding them to the clay more than a specific value (i.e. 1.0% in this research) causes to change undrained behavior of samples from contractive to dilative. In addition, beyond this specific value, it improves shear strength and reduces compressibility of clay. The rate of increase in shear strength and decrease in compressibility depends on the confining pressure, flexibility of plastic and initial density of samples. It is more noticeable when plastic waste in mixtures is relatively rigid and density and confining pressure are high. Moreover, plastic waste has a negative effect on the free swelling, swelling pressure and swelling index of samples, so that these parameters for plastic waste mixed clay are higher than the associated values of plain clay.


Hyun-Ki Choi,
Volume 15, Issue 4 (6-2017)
Abstract

This study investigated the structural behaviors of reinforced concrete shear walls containing opening and slab. A series of three half-scale shear wall specimens were tested: a solid wall (WS-Solid), a wall with opening and slab (WS-023), and a wall with opening but no slab (WB-0.23). Using the experimental results, the reduction in the load-carrying capacity of the wall due to the loss of cross section was evaluated. Its contribution to the moment resisting capacity of the total system of coupling elements and its structural behavior was also examined. The results of experiments conducted on the WS-0.23 specimen with artificial damage due to installation of the opening, showed that the load-carrying capacity of the wall decreased as a result of the opening. It is apparent that the influence of cutting reinforcing bars and reduction of effective sectional area lead to early first yield of the reinforcing bars before the allowable limit of the drift ratio of the shear walls is reached. This decrease in the load-carrying capacity of the shear wall because of installation of openings is significantly different from the results of previous studies. This is because slabs and the remaining wall function as coupling elements for the shear wall. The contribution of slabs and residual wall to the lateral load resisting system was investigated via an empirical test and finite element analysis. During the experiment, a U-shaped critical section of coupling slab was observed and its effective width and the total length of the critical section examined. The critical section of coupling slab that functions as a coupling element for shear wall varied marginally from the results of previous studies. The results of the analysis conducted show that slabs and residual walls contribute approximately 30% to the lateral load resisting system.



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