فهرست مطالب

Iranian Journal of Science and Technology Transactions of Civil Engineering
Volume:36 Issue: 2, 2012

  • تاریخ انتشار: 1391/06/29
  • تعداد عناوین: 11
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  • A. Kaveh, M. Ahangaran Page 121
    This paper presents a social harmony search algorithm to solve optimization problems with continuous design variables. Although the Harmony Search (HS) algorithm (HSA) has proven its ability in finding near global regions within a reasonable time, it is rather inefficient in performing local search. The proposed method applies the harmony search optimizer for global optimization and normal distribution is employed to update the position of each design variable of a new harmony found by the first rule of the HS (memory consideration) in every stage to rapidly attain the feasible solution space. Normal distribution works as a global search in early iterations and as a local search in final iterations to improve HS in order to quickly converge and find better solutions. Various benchmark optimization problems are used to illustrate the effectiveness and robustness of the proposed method. Finally, the experimental results reveal the superiority of the proposed method in quick convergence and finding better solutions compared to the classic HS, its recently developed variants, and some other optimization algorithms.
    Keywords: Social harmony search, normal distribution, meta, heuristics, optimization, diversification, intensification
  • A. Kaveh Massoudi Page 139
    This paper presents an ant colony system model for cost optimization of a composite floor system based on the load and resistance factor design (LRFD) specification of the AISC. The model formulation includes the cost of concrete, steel beam, and shear studs. The objective function is considered as the cost of the structure, which is minimized subjected to serviceability and strength requirements. Examples of composite floor systems are presented to illustrate the performance of the present algorithm. A parametric study is also included to investigate the effects of beam spans and loadings on the cost optimization of composite beams.
    Keywords: Ant colony system (ACS), cost optimization, composite floor systems, structural optimization, load, resistance factor design
  • S. C. Dutta, R. Roy Page 149
    Structures, seldom designed with adequate safety to blast hazards, are often designed for earthquake. At this backdrop, presented herein is an attempt to achieve safety against explosive hazard through aseismic design methodology. The possibility of blast damage to ‘solitary’ structures appears to be comparable to that due to earthquake beyond a critical standoff distance of explosion. The study develops an equivalency of blast parameters (charge weight, critical stand-off distance) and earthquake characteristics (PGA) along with ductility capacity (represented by R) so as to yield similar damage. For example, beyond a critical stand-off distance of about 25m, structures designed elastically for earthquake with PGA of 0.2g may endure little damage (similar to that at R = 2 during earthquake) due to the explosion of 500 kg charge-weight. This not only helps to ascertain the level of safety of seismically designed buildings under blast, but also to decide the distance of fencing to be constructed to protect an important structure in accordance with their functionality. However, the response in an urban setting due to similar blast action may be relatively subdued. The detailed results presented in the study may be useful to prepare codified load combinations to mitigate blast hazard.
    Keywords: Blast, low, rise building, seismic, stand, off, damage, state, of, the, art, urban setting
  • K. Badv, T. Sayadian Page 167
    The Shahid-Kalantari highway between Urmia and Tabriz cities in Iran, has experienced more than one meter of settlement 7.8 Km east of Urmia city. The soil investigations revealed that the existence of a peaty foundation (Urmia peat) caused this settlement. This motivated a research to investigate the geotechnical characteristics of Urmia peat. A series of consolidation and direct shear tests were conducted on samples of Urmia peat and the relationship between the key mechanical and physical properties was investigated. The results show that the amount of organic matter (degree of decomposition) and initial void ratio are two important factors which control the mechanical behaviour of this soil. It was also found that the Cα/Cc concept of compressibility is applicable for Urmia peat.
    Keywords: Peat, organic content, initial void ratio, compressibility, shear behavior
  • A. Totonchi, F. Askari, O. Farzaneh Page 181
    It is well known that the plan curvature of curved slopes has an influence on the stability of the slopes.This paper aims to present a method of three-dimensional stability analysis of concave slopes in plan view based on the Lower-bound theorem of the limit analysis approach. The method’s aim is to determine the factor of safety of such slopes using numerical linear finite element and lower bound limit analysis method to produce some stability charts for three dimensional (3D) homogeneous concave slopes. Although the conventional two and three dimension limit equilibrium method (LEM) is used more often in practice for evaluating slope stability, the accuracy of the method is often questioned due to the underlying assumptions that it makes. The rigorous limit analysis results in this paper were found to be closely conservative results to exact solutions and therefore can be used to benchmark for solutions from other methods. It was found that using a two dimensional (2D) analysis to analyze a 3D problem will lead to a significant difference in the factors of safety depending on the slope geometries. Numerical 3D results of the proposed algorithm are presented in the form of some dimensionless graphs, which can be a convenient tool for use by practicing engineers to esti­mate the initial stability for excavated or man-made slopes. The results obtained using this 3D method show that the stability of concave slopes in plan view increases as the relative curvature R/H and the relative width of slope decrease.
    Keywords: Three, dimensional slope, slope stability, limit analysis, lower, bound, limit equilibrium
  • A.Totonchi, F. Askari, O. Farzaneh Page 195
    In this paper, application of stress fields in computation of seismic active lateral forces on retaining walls is considered using the lower bound method of limit analysis. Finding the exact solution of boundary value problems in engineering fields is a complicated problem in most applied cases and from this point of view, use of the limit state methods is very beneficial for engineers. In limit analysis method, in spite of exact solution of the problem, the upper and lower bound of the limit load are determined. The lower bound of the exact solution can be obtained by use of different admissible stress fields in different regions of the media divided by stress discontinuity surfaces. Earthquakes have unfavorable effects of increasing active and decreasing passive lateral earth pressure, so to investigate how the lateral earth pressure is affected, extensive numerical results based on the limit analysis method reported by Chang and Chen. This paper is devoted to finding an Analytical solution to investigate the lateral force affection on retaining walls, using mathematical relations based on lower bound limit analysis method. This process include the calculation of direction and magnitude of active lateral earth pressure. Numerical results of the proposed algorithm are presented in some practical dimensionless graphs.
    Keywords: Limit analysis, stress discontinuity surfaces, lateral pressure, retaining wall
  • S. H. Sadeghi, S. F. Mousavi, S. S. Eslamian, S. Ansari, F. Alemi Page 209
    A new analytical procedure taking into account the non-uniform outflow profile for hydraulic analysis and design of multiple outlets pipelines is presented. The method is developed based on presenting a new friction head loss distribution along the lateral. The proposed method simulates pressure and outflow profiles along the trickle or sprinkler irrigation laterals and manifolds, as well as gated pipes. The velocity head change was considered, whereas minor head losses were neglected. The presented technique was compared with the accurate step by step (SBS) method to justify its accuracy for lateral design. The comparison test for various design combinations indicated that the proposed method is sufficiently accurate. The suggested method could be applied in designing irrigation laterals.
    Keywords: Pressure head distribution, lateral pipeline, head loss, non, uniform outflow
  • M. Karamouz, M. Fallahi, S. Nazif Page 225
    Floods are one of the most important natural disasters causing extensive loss of life and properties every year all over the world. Occasional tropical or Mansoon rain can produce floods that are sometimes considered as a lifesaver due to water scarcity in arid and semi-arid regions. By simulating the hydrograph of probable floods in each year, action plans can be implemented to reduce damages and also to better plan for utilizing water resources potential of floods. By simulating future rainfall, and estimating the resulted runoff, it can be determined whether a severe flood will occur or not. The simulated flood hydrograph is affected by uncertainties in future rainfall simulation and runoff modeling that should be considered when flood prevention plans are developed. In this study, a long lead flood simulation model is developed, considering the uncertainties in the simulation process. The SDSM (Statistical Downscaling Model) is used to generate hourly and daily rainfall data, needed for flood simulation, based on General Circulation Models (GCM) outputs. The extreme simulated rainfalls in each year are considered as the probable flood and a rainfall-runoff model developed in HEC-HMS software environment is used for simulation of the corresponding hydrograph. The uncertainties in hydrograph development are considered through variation of curve number (CN) and time of concentration (Tc). The effect of climate change on flooding probability is evaluated by comparing the Cumulative Distribution Function (CDF) of the simulated floods with historical floods. The proposed model for long lead flood simulation has been applied to the Kajoo basin located in the south-eastern part of Iran.
    Keywords: Uncertainty, long lead flood simulation, downscaling, rainfall, runoff model
  • M. C. Tuna Page 239
    Scour holes formed downstream from a stepped spillway may affect the safety and stability of a structure. The development of such scour hole can cause failure of the structure by undermining the riverbed, thus it is important to develop criteria that result in understanding how such a scour hole can develop. The literature contains many studies dealing with energy dissipation, aeration and oxygen transfer in stepped spillways. However, their downstream scour hole depth and geometry is not well documented. In this study, a physical model is employed to study the impact of offtake channel base angle of stepped spillways on the scour hole. The area of the longitudinal profile of the scour hole is used to evaluate the amount of scour at downstream from the stepped spillways. Experimental results showed that the takeoff angle of 30o is the optimum angle which gives minimum longitudinal area and maximum depth of the scour hole.
    Keywords: Stepped spillway, offtake channel base angle, scour hole geometry, scour depth
  • F. Salmasi, M. R. Chamani, D. Farsadi Zadeh Page 253
    Stepped gabion spillways have many applications in dam structures, river engineering, and soil conservation works. They are more stable and flexible than their rigid (impervious) counterparts. Moreover, their stilling basins can be constructed at lower costs as energy dissipation in these spillways is high due to both over-flow and through-flow. This study aims to study the over-flow and through-flow in gabion stepped spillways and to evaluate their energy dissipation. For this purpose, eight physical models of gabion stepped spillways with three different porosities (38, 40 and 42%) and two slopes (1:1 & 1:2) (V:H) were made with permeable and impermeable faces of both horizontal and vertical types. Results showed that at higher discharges, energy dissipation was greater in pervious (gabion) spillways than those with impermeable horizontal or vertical faces. At lower discharge rates, however, energy dissipation was greater in impervious stepped spillways. On the other hand, steps with impervious vertical faces had more energy dissipated than those with impervious horizontal faces. Increasing gabion porosity increased energy dissipation, but this effect was minor at higher discharges. Finally, it was found that decreasing slope led to more energy dissipated.
    Keywords: Energy dissipation, porosity, spillway slope, stepped gabion spillway
  • A. Akbari, M. Ardestani, J. Shayegan Page 265
    This article discusses the distribution of total petroleum hydrocarbons (TPH) contamination in soil within areas of the South Pars Gas Complex (S.P.G.C.), located on the northern shore of the Persian Gulf. To assess the potential risk to groundwater, in situ contaminant mobility was also examined in vertical soil profiles. Sampling was conducted in two rounds, and TPH was determined in accordance with standard methods of TPH analysis. The maximum detected concentration was 10268 +785 mg/kg in the area of the waste disposal site. Significant heterogeneity in natural attenuation of different hydrocarbon compounds during transport in the soil was observed. Although the groundwater samples did not show evidence of contamination, vertical contamination profiles clearly showed that groundwater contamination will occur in the near future if no remedial action is taken immediately. It is worth noting that the refineries have been brought to production just in the last 5 years. Also, relevant soil and contamination properties were investigated to recommend an appropriate remediation approach. Bioventing and biopiling were suggested as remediation technologies. However, the result of this study highlights the necessity for national regulations to address cleanup standards and the preventive and remedial guidelines for petroleum hydrocarbon contamination in soil or groundwater.
    Keywords: Contamination, total petroleum hydrocarbon (TPH), soil, gas refinery