AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2012 | Volume:44 | Issue:1|Papers Count:11

Fracture mechanics approach is to assess the process of crack propagation in a known stress field. The amount of material strength against the crack propagation is named fracture toughness. In this research, different cracked samples are used to determine the fracture toughness of different rocks. The methods proposed by ISRM (International Society for Rock Mechanics) are two tests, i.e. three point bend test and short rod. The present research is based on the three point bent test. Also, in these tests two levels are utilized, 1-load control 2-displacement control, but in the present tests the level I is chosen for two types of rocks.

Determination and prediction of damage imposed on the structures is one of the most important topics related to the performance based design. In this regard, the standards regarding the performance based design have introduced some levels & limitations. The main objective of this research is to evaluate these levels by comparison of damage indices calculated from dynamic & pushover analysis. IN addition, performance of ABA & 2800 codes in limiting damage of structures is evaluated. For this purpose, seven earthquake records, which are appropriate for site effects under consideration, are selected & scaled in such a way that average response spectrum of them has minimum difference with Iranian code 2800 design spectrum. then damage analysis is performed on several reinforced concrete moment resisting frames. Results represented that drift criterion introduced by standards such as FEMA273 & ATC40 can lead to incorrect results in determination of seismic performance of structures. it was illustrated that ABA& 2800 codes have proper performance in limiting damage of structures at Life Safety level.

Rock mass behavior is closely depends on rock joints characteristics, rock joint behavior is depends on its surfaces roughness. There are several methods to measure joint surfaces roughness by two or three dimensional. Three dimensional methods are expensive and advanced technology, thus to obtain high precision roughness of joint surfaces a new apparatus is designed and developed for first time in Iran. Using the designed apparatus the joint surfaces measurement with high precision is possible with low expenses. The apparatus is made up of two parts consisting hardware and software. Hardware consists of: laser head, cross table, and digital camera. The measured data is processed in software to obtain three dimensional surfaces roughness. As an advantageous of the developed apparatus it is possible to determine surface roughness using non-destructive method and same sample could be used for mechanical laboratory testing. To verify the apparatus performance a rock joint specimen roughness profiles is measured with 1mm intervals and the surface topography of joint surface is obtained with 1mm*1mm cell size. In this paper the apparatus assembly and its application along with the results are illustrated.

The tunnel form buildings are used for mass construction in many countries. This construction method is very interesting because of its fast construction technique and low cost. But there is deficiency of researches about tunnel form building in comparison to the other conventional building systems. There are no special requirements for seismic analysis and design of this type of buildings. According to high risk of earthquake and using of this construction method in many projects in Iran, some more studies should be done to evaluate seismic behaviour of tunnel form buildings. In this paper, an experimental program was performed in which the testing of two three-story 1.5-scale of the tunnel form building were carried out to clarify the seismic behaviour of structures. The experimental program consisted of some cyclic loadings and forced vibration tests in order to study the failure mechanisms and the effects of cracking on the fundamental period. The behavior of the specimens was simulated by finite element model and a good correlation was obtained between experimental and numerical results. This study showed that the tunnel form buildings have low level of ductility and brittle failure mechanism was observed.

The outer part of curve in meandering rivers are suitable places for diversions, as the secondary currents in this locations cause the transfer of the river-bed sediments towards the convex bank. Flow diverting from the outer bend causes the formation of a transverse flow component in depth to surface flow, having an opposite alignment with the secondary current and consequently transferring a part of the sediment load of the river to intake mouth. Besides diversion of the flow will cause the change of the flowing currents pattern in the river bend and decrease the energy of the secondary current in this location, which is important in sediment transportation. This research carried out on the physical model of Sinuosity River. The results has showed that along with low ratios of flow diversion to the intake mouth has a little effect on the secondary current, and also this current causes the repelling of sediments from the outer bend of river. Along with the increase of the ratio of diverted flow, the energy of secondary currents decrease and the ratio of sediment diversion increases. In a ratio of flow diversion, the secondary flow energy fully damped. After that, the sediments entering to the intake mouth has a higher increase compared to the previous situation. The results of Research have showed that the graph curve comparing the changes of diverted sediments to the intake structures, with the flow diversion generally follows the pattern similar to the S shape. The flow depth in the outer part of curve is also the effective parameters on secondary flow. The Increasing of river depth causes intensity in secondary energy and thus decreasing in sediment entering to the intake. In this paper, the effects of flow diversion ratio to sediments ratio entering to the intake structure by considering different flow depths with 90-degree diversion angle was presented.

The instrument performs protection, preservation and control dam behavior, failure detection and timely treatment to prevent the occurrence of the risks and increase the longevity of the dam during construction and operation. In this paper, Zayandeh-Rud dam instrumentation data were analyzed and the stability condition of the dam, foundation and abutments are evaluated. Finally, considering the position of the instruments the distinct element method was employed. The effect of shear and normal stiffness on body and foundation displacements was investigated and the actual values of the shear and normal stiffness were selected as the input model. In this study, Mohr-Coulomb criterion are used for joint behaviors, which are defined as boundary between rock foundation and dam body and boundary between concrete arch blocks, and comparison between measured and calculated values by numerical models has been investigated and good agreement between the results obtained. Results of numerical modeling and measurements have shown that the dam body and foundation are stable. Due to poor geological condition of right wall of dam, the displacements obtained in comparison with the left wall are higher. Also demonstrates that stress and deformation of dam body and foundation, strongly influenced by variation of lake water level.

Recently, Nanotechnology has caused a vast breakthrough worldwide and scientists in different fields have used it. Nano particles have been gaining increasing attention and been applied in many fields to fabricate new material with novel function due to their unique physical and chemical properties. Therefore, using Nano-silica as a Nano-scale additive in concrete is under further inspection by researchers. Recent contribution to the development of building materials compromise adding colloidal Nano-silica to concrete. In this paper, the influence of Nano-silica addition on mechanical and durability properties of concrete as compared with silica fume has been studied. Tests include compressive strength, water permeability, rapid chloride penetration and electrical resistance test. Moreover, microstructure of the cement paste incorporating Nano-silica and Silica-fume were studied through X-ray diffraction and Scanning electron microscope tests. The experimental results show that Nano-silica as an artificial pozzolanic material can improve the compressive strength, water penetration resistance and electrical resistivity of concrete and reduce the chloride diffusion more effectively than SF at early ages. In addition, utilizing NS in cement paste improve its microstructure at early days.

The conceptual hydrologic HEC-HMS model that includes a library of different event-based models for simulating rainfall-runoff process has been gained a significant attention in different applications. Automatic calibration of HMS model has been considered in this study using particle swarm optimization (PSO) algorithm and its application has been assessed in modeling Tamar basin in North of IRAN. The PSO algorithm has been coded in MATLAB where the HMS model is called and run from through transferring to DOS applications. Firstly, Model calibration is performed in single event scenarios and the results were compared with Nelder and Mead local search algorithm method built in HMS model. The results revealed the outperformance of the proposed PSO-HMS model. Since no unique parameter set was obtained in single event scenarios, the model was employed to calibrate three calibration events jointly. Then all candidate parameter sets obtained from single and jointly-event calibration scenarios were tested in verification stage in which parameters of initial abstraction coefficients were recalibrated. The procedure resulted in choosing more suitable parameter sets to be screened out, although no unique parameter set can be obtained.