Showing 13 results for Ahmad
Mivehchi Mahmood R., M.t. Ahmadi, Hajmomeni A.,
Volume 1, Issue 1 (September 2003)
Abstract
Ambient vibration test is an effective and economical method for identification of dynamic properties of structures such as dams. Mathematical models generally are developed for the design purpose. Structural and material parameter are assumed from similar projects or limited material tests. Therefore it is usually desirable to verify the results obtained from mathematical model by performing vibration test on the actual as-built structure and process its, data correctly. There are addressed in this paper. A modification of mathematical model could then be performed.
Pakbaz M.c., Ahmadi C.,
Volume 1, Issue 2 (December 2003)
Abstract
This research include, more than 400 erosion tests performed on coarse and fine grain suspension materials. The purpose of tests was to determine erosion characteristics of mixtures of different materials. Samples of the .same constituents in different groups were cured tit two different setting time of // and 16 !tours before they were subjected to the constant hydraulic heads of 20 and 40 cm for ct time period of 30 urinates. The amount of erosion was measured as the weight loss of the samples offer the test. /n general the lower setting tune and the higher hydraulic head for a large group of samples showed higher erosion. For uniform sand samples when the cement content was 60-70 % the percentage of erosion (PE) was below 2. For the mixture of sand-cement, with the clay content below, 20% the percentage of erosion was below 2 and it increased to 15.5 for the clan, content of 58dc. Die addition of bentonite in the soil-cement mixtures in general did not affect the erosion.
A.a. Ramezanianpour, M. Mahdi Khani, Gh. Ahmadibeni,
Volume 7, Issue 2 (June 2009)
Abstract
Rice Husk Ash (RHA) is a by-product of the agricultural industry which contains high amount of silicon dioxide (SiO2). In this research, for the first time in the Middle East, in order to supply typical RHA, a special furnace was designed and constructed in Amirkabir University of Technology. Afterwards, XRD and XRF techniques were used to determine the amorphous silica content of the burnt rice husk. Attempts were made to determine the optimum temperature and duration of burning. Results show that temperature of 650 degrees centigrade and 60 minutes burning time are the best combination. Then various experiments were carried out to determine properties of concretes incorporating optimum RHA. Tests include compressive strength, splitting tensile strength, modules of elasticity, water permeability and rapid chloride permeability test. Results show that concrete incorporating RHA had higher compressive strength, splitting tensile strength and modulus of elasticity at various ages compared with that of the control concrete. In addition, results show that RHA as an artificial pozzolanic material has enhanced the durability of RHA concretes and reduced the chloride diffusion.
R. Abbasnia, M. Kanzadi, M. Shekarchi Zadeh, J. Ahmadi,
Volume 7, Issue 2 (June 2009)
Abstract
Drying shrinkage in concrete, which is caused by drying and the associated decrease in moisture content, is
one of the most important parameters which affects the performance of concrete structures. Therefore, it is necessary
to develop experimental and mathematical models that describe the mechanisms of drying shrinkage and damage build
up in concrete. The main objective of this research is the development of a computational model and an experimental
method for evaluation of concrete free shrinkage strain based on the internal moisture changes. For this purpose and
for modeling of moisture losses in concrete members a computational program based on finite element approach and
the modified version of Fick's second law in which the process of diffusion and convection due to water movement are
taken into account, is developed. Also the modified SDB moisture meter was used to measure the internal moisture
changes in concrete. Based on the obtained results, calculated humidity is in good agreement with measured data when
modified Fick's second law with diffusion coefficient from Bazant method were used, and are very reasonable for
determining the moisture gradient. Also, the predicted value of shrinkage strain from the proposed method is in good
agreement with measured data and also the established relationship can be used for determine the distribution of
shrinkage strains in concrete members.
A. Ghanbari, M. Ahmadabadi,
Volume 8, Issue 2 (6-2010)
Abstract
Inclined retaining walls with slopes less than perpendicular are appropriate candidates in several
engineering problems. Yet, to the knowledge of authors, only a few analytical solution for calculation of active earth
pressure on such walls, which will be usually smaller than the same pressure on vertical ones, has been presented
neither in research papers nor in design codes. Considering limit equilibrium concept in current research, a new
formulation is proposed for determination of active earth pressure, angle of failure wedge and application point of
resultant force for inclined walls. Necessary parameters are extracted assuming the pseudo-static seismic coefficient
to be valid in earthquake conditions. Moreover, based on Horizontal Slices Method (HSM) a new formulation is
obtained for determining the characteristics of inclined walls in granular and or frictional cohesive soils. Findings of
present analysis are then compared with results from other available methods in similar conditions and this way, the
validity of proposed methods has been proved. Finally according to the results of this research, a simplified relation
for considering the effect of slope in reduction of active earth pressure and change in failure wedge in inclined
retaining walls has been proposed.
H. Shakib, F. Omidinasab, M.t. Ahmadi,
Volume 8, Issue 3 (September 2010)
Abstract
Elevated water tanks as one of the main lifeline elements are the structures of high importance. Since they are extremely vulnerable under lateral forces, their serviceability performance during and after strong earthquakes is a matter of concern. As such, in recent years, the seismic behavior of water tanks has been the focus of a significant amount of studies. In the present work, three reinforced concrete elevated water tanks, with a capacity of 900 cubic meters and height of 25, 32 and 39 m were subjected to an ensemble of earthquake records. The behavior of concrete material was assumed to be nonlinear. Seismic demand of the elevated water tanks for a wide range of structural characteristics was assessed. The obtained results revealed that scattering of responses in the mean minus standard deviation and mean plus standard deviation are approximately 60% to 70 %. Moreover, simultaneous effects of mass increase and stiffness decrease of tank staging led to increase in the base shear, overturning moment, displacement and hydrodynamic pressure equal to 10 - 20 %, 13 - 32 %, 10 - 15 % and 8 - 9 %, respectively.
P. Ghoddousi, R. Ahmadi, Mahdi Sharifi,
Volume 8, Issue 4 (December 2010)
Abstract
Superior performances of Self-Compacting Concrete (SCC) in fresh state to achieve a more uniform distribution encourage the addition of fibers in concrete which is a motivation for structural application of fiberreinforced concrete. Fiber addition reduces the workability of Self-Compacting Fiber Reinforced Concrete (SCFRC). To provide required workability of the SCFRC, more paste is needed in the mixture. Therefore, the coarse aggregate content shall be adjusted to maintain its workability. The purpose of this study is to drive a model for estimating the aggregate contents for SCFRC. This model is based on constant covering mortar thickness theory. In this paper, all parameters which are participated in coarse aggregate content are discussed and presented in a relation. Then another relation is developed for predicting the void volume in the fibrous concrete. These relations are combined and a mathematical relation is deduced for predicting the coarse volume content in the function of the fiber factors. Proposed model is validated by conducting a rheological test. The result shows that the proposed model is simple, applicable and can be used as starting point in practical project. Finally in order to complete the proposed model, another relation has been derived that can show the interaction of parameters involved in SCFRC rheology behavior.
Malik Shoeb Ahmad, S. Salahuddin Shah,
Volume 8, Issue 4 (December 2010)
Abstract
Roadways have a high potential for utilization of large volume of the fly ash stabilized mixes. In this study, an attempt has been made to investigate the use of Class F fly ash mixed with lime precipitated electroplating waste sludge–cement as a base material in highways. A series of tests were performed on specimens prepared with fly ash, cement and lime precipitated waste sludge. California bearing ratio (CBR) tests were conducted for 70%-55%fly ash, 8%cement, and 30%-45%waste sludge combinations. Results show that the load bearing strength of the mix is highly dependent on the waste sludge content, cement as well as curing period. The CBR value of fly ash mixed with electroplating waste sludge and cement has been increased to manifold and results the reduction in the construction cost of the pavement. The study also encourages the use of two potentially hazardous wastes for mass scale utilization without causing danger to the environment, vegetation, human and animal lives.
S. N. Moghaddas Tafreshi, Gh. Tavakoli Mehrjardi, M. Ahmadi,
Volume 9, Issue 4 (December 2011)
Abstract
The results of laboratory model tests and numerical analysis on circular footings supported on sand bed under incremental
cyclic loads are presented. The incremental values of intensity of cyclic loads (loading, unloading and reloading) were applied
on the footing to evaluate the response of footing and also to obtain the value of elastic rebound of the footing corresponding
to each cycle of load. The effect of sand relative density of 42%, 62%, and 72% and different circular footing area of 25, 50,
and 100cm2 were investigated on the value of coefficient of elastic uniform compression of sand (CEUC). The results show that
the value of coefficient of elastic uniform compression of sand was increased by increasing the sand relative density while with
increase the footing area the value of coefficient of elastic uniform compression of sand was decreases. The responses of footing
and the quantitative variations of CEUC with footing area and soil relative density obtained from experimental results show a
good consistency with the obtained numerical result using “FLAC-3D”.
R. Ahmadii, P. Ghoddousi, M. Sharifi,
Volume 10, Issue 4 (December 2012)
Abstract
The main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (SFRC) behavior
under four point bending test (FPBT). In this model all the force components at the beam section (before and after cracking)
are formulated by applying these assumptions: a bilinear elastic-perfectly plastic stress-strain response for concrete behavior
in compression, a linear response for the un-cracked tension region in a concrete constitutive model, and an exponential
relationship for stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical
cracked section is calculated by applying these assumptions and satisfying equilibrium lawat critical cracked section. After that,
parametric studies have been done on the behavior of SFRC to assess the sensitively of model. Finally the proposed model has
been validated with some existing experimental tests.The result shows that the proposed solution is able to estimate the behavior
of SFRC under FPBT with simplicity and proper accuracy.
Masoud Ahmadi , Hosein Naderpour , Ali Kheyroddin ,
Volume 15, Issue 2 (Transaction A: Civil Engineering 2017)
Abstract
Concrete filled steel tube is constructed using various tube shapes to obtain most efficient properties of concrete core and steel tube. The compressive strength of concrete is considerably increased by the lateral confined steel tube in circular concrete filled steel tube (CCFT). The aim of this study was to present an integrated approach for predicting the steel-confined compressive strength of concrete in CCFT columns under axial loading based on large number of experimental data using artificial neural networks. Neural networks process information in a similar way the human brain does. Neural networks learn by example. The main parameters investigated in this study include the compressive strength of unconfined concrete (f'c), outer diameter (D) and length (L) of column, wall thickness (t) and tensile yield stress (fy) of steel tube. Subsequently, using the reliable network, empirical equations are developed for the confinement effect. The results of proposed model are compared with recently existing model on the basis of the experimental results. The findings demonstrate the precision and applicability of the empirical approach to determine capacity of CCFT columns.
Abdullah Ahmad, Rajat Rastogi,
Volume 15, Issue 4 (Transaction A: Civil Engineering 2017)
Abstract
Sufficient literature is available on approaches to deal with heterogeneous traffic on mid-blocks in developing countries, but not much work is done on roundabouts. The estimation of passenger car unit (PCU) for different vehicles to convert heterogeneous traffic into homogeneous traffic is a well-accepted procedure. But the parameters used for mid-blocks may not be helpful on roundabouts as traffic flow characteristics on the two locations are different. Suggested PCU values on roundabouts from developing countries are not recent, and needs a relook. It is also not clear whether to use static or dynamic PCU values on account of possible temporal and spatial variations across locations. This paper presents an estimation approach for PCUs on roundabouts, as well as, suggests using static value instead of dynamic. The problem to deal with re-estimation of PCU values at different locations, due to possible traffic flow variations, is dealt with by proposing a Heterogeneity Equivalency Factor (H-Factor). The factor is multiplicative and converts heterogeneous traffic (veh/h) into homogeneous traffic (pcu/h).
Ahmad Soltanzadeh, Iraj Mohammadfam, Abbas Moghim Beygi, Reza Ghiasvand,
Volume 15, Issue 7 (Transaction A: Civil Engineering 2017)
Abstract
Construction industries are the most dangerous worksites with high risk of occupational accident and bodily injuries, which ranges from mild to very severe cases. The aim of this study was to explore the causal factors of accident severity rate (ASR), in 13 of the biggest Iranian construction industries. In this analytical cross-sectional study, the data of registered accidents from 2009 until 2013 were obtained from an official database. Data of HSE risk management systems and HSE training were also gathered from comprehensive accident investigation reports. Data analysis and regression modeling were done using SPSS statistical software (version 22). The mean and SD of ASR of studied construction worksites was 257.52±1098.95. The results show that the system associated with HSE and HSE risk management established only 41.8 and 18.4%, respectively. The results of multiple linear regression indicated that some individual and organizational factors (IOFs), HSE training factors (HTFs), and Risk Management System factors (RMSFs) were significantly associated with ASR (p<0.05). The study revealed the causal factors of ASR. Hence, these findings can be applied in the design and implementation of a comprehensive HSE risk management system to reduce ASR.