نشریه مهندسی عمران مدرس
سال دهم شماره 4 (زمستان 1389)

There are a lot of approximation techniques for structural optimization. Among them, four outstanding approximation methods have been selected for trusses optimization. These approaches have been developed or modified by previous ones. Based on these schemes, a lot of trusses have been optimized by author's program. This study shows that the abilities of the mentioned methods are not the same and some of them have deficiencies. Reaching a better solution, lesser analysis time, oscillation of response, numerical stability and also using a variety of the design variables are among the findings of this work. A brief of these obtained results has been given in the conclusion part.

Direct calculation of free term coefficients for linear isotropic problems in three dimensional displacement boundary integral equations is presented in details. In addition, the shape functions of 9 node non-continuous and semi-continuous elements for modeling the crack surfaces, layers interface, infinite boundary and other similar problems have been demonstrated. This proposed method for calculating cij coefficients has been verified comparing with some solved problems.

Plastic shrinkage occurs in fresh concrete within few hours after mixing the concrete. When the plastic concrete is allowed to shrink freely, it never cracks. But, generally, removal of unsound material or damaged concrete is a part of repair operation. Thus usually the surface of the substrate is rough, the repair concrete will be under restrained condition, which will result in the development of tensile stresses in the plastic concrete and will create cracks on the surface of the concrete. Four types of repair materials were used in this work: plane selfconsolidating concrete (SSC), SCC containing silica fume (S.F.), SCC containing S.F. and latex (Styrene Butadiene Rubber), and SCC containing S.F., latex and fiber. To roughen the surface of the substrate base, dents with different degree, referring to restraint indices, RI, were used to provide restraints. RI is defined as the ratio of the surface area dents to smooth surface area of the slab. The panels were subjected to sever combination of wind, temperature and relative humidity. The test program includes: settlement strains, free and restrained shrinkage strains, evaporation and bleeding rates, and cracks characteristic measurements. The results showed that, while the rate of evaporation and bleeding affected the shrinkage properties, it was over shadowed by properties of the repair materials and restraints indices. The results also indicated that, for a given repair concrete, the restrained strain increasedas the R.I. increased. A significant improve was observed for the SCC with latex and fiber, exhibiting the lowest plastic settlement, shrinkage strains and crack area, and the highest time to the first crack.

One of the main reasons of weakness in airport system management and capacity insufficiency of its various sections is the lack of detailed information or reliable assessments of services of those sections of the airport. Proper airport management requires a thorough understanding of the performance of the different components and the airport system, as a whole. In this paper, a model of airport assessment and ranking is proposed after identifying and classifying the factors influencing the efficiency and level of service of the various sections of an airport based on the results of previous researches and a survey to gather the opinion of the experts in this field. The importance of the above factors and their sub-factors is determined using Analytical Hierarchy Process and the data gathered from the experts. The results of this model can help to identify airport weaknesses and strengths per airport section, make possible a quantitative comparison of airports and their ranks and also may be applied to identify the potentials of the different sections of an airport system. The results indicated that the efficiency factors (76.7%) are about three times more important than the level of service factors (23.3%). Also the two most important factors are runways (26.11%) while taxiways (9.6%) and the least important ones are baby changing stations (0.1%) and vending machines (0.11%).

There are known techniques for cyanide remediation from contaminated soil such as soil washing, soil oxidation and biological degradation. However, there is very little research forelectrokinetic remediation of cyanide from soil. This study investigates the application of electrokinetic remediation to contaminated soil with high clay content and low coefficient of permeability. The experiments were conducted with two electrodes as cathode and anode poles, which were placed inside the soil using the direct electrical current. Thus cyanide ions were transported to the anode pole and caused the remediation of the soil. The contaminated soil from tailing dam of Takab gold processing plant was used. Contaminated soil with the concentration of 420 mg/kg, distilled water and NaOH were employed in the electrokinetic cell. The experiments were conducted on the optimum moisture content of clayed soil at two voltage gradients (1.0 and 1.5 VDC/cm for the duration of 7 and 14 days) in order to assess the effect of voltage gradient when employing 1M NaOH solutions and distilled water at the anode pole. For each test, cyanide removal efficiency, the pH of the soil, moisture content, electrical conductivity and the electrical current and flow were determined. The measurements were conducted for the entire duration of electrokinetic experiments and at the end of the test. The results indicated that the cyanide removal obtained in 7 and 14 days was approximately 65% and 80%, respectively. The results also showed the pH of the soil was changed from 8.83 to 1-2 for the anode and to 12-13 for the cathode pole. The cyanide transported to the cathode and the pH were the most important dominant factors for cyanide remediation.

The effect of two types of common initial geometric imperfections on the reliability of steel frames was investigated. These imperfections are the coordinates of connection nodes and crookedness of members. Most of the finite element reliability analyses in the past haveneglect this source of uncertainty. For this purpose, static non-linear pushover structural analysis was used in the present work from which reliabilities were estimated based on the FORM and Monte Carlo sampling methods. Furthermore, to investigate the importance of uncertain parameters, reliability sensitivity analysis was performed by the use of direct differentiation method, which was implemented in the object oriented framework of OpenSees software. It was demonstrated that some of these geometric imperfections have significant influence on the reliability assessment of steel frames.

The effects of natural pozzolan, fly ash and silica fume as cementitious materials on strength development and absorption water capacity were investigated. Cubic specimens (100×100×100 mm) from 13 mix designs with 2 water-cement ratios of 0.3 and 0.46 were made. The specimens at the age of 28 days were dried and then immersed in water from 30 minutes to 7 days based on BS 1881, part 122, to study their cavity volume. The cement type 2 was replaced (by weight) with natural pozzolan and fly ash with 15, 30, 15 and 25 percent, respectively. Furthermore, in 0.3 water cement ratio specimens, the cement was replaced with silica fume at three percentages of 5, 8 and 11. It was concluded that natural pozzolan caused the decrease of compressive strength at both the early and later ages. Fly ash also caused the decrease of compressive strength at the early age, however, at the later age, it improved the compressive strength. Silica fume improved the compressive strength from the second day to the later ages. In 0.46 water cement ratio specimens, the absorption water capacity was decreased when the cement replacement with natural pozzolan and fly ash was 15%. Silica fume decreased the absorption water content when the immersion time was 7 days. In 0.3 water cement ratio specimens, the pozzolan materials had no considerable effect on the absorption water capacity.

The experience of last earthquakes has shown the vulnerability of most of structures. This has been caused the speeding up of the seismic evaluation and retrofitting of projects in Iran. In this regard, the instructions for seismic rehabilitation of the existing buildings have been published and are currently beiong used in the evaluation and retrofitting projects. The experience of retrofitting the structures in the past has shown that one of the most important problems in Iran is seismic evaluation and retrofitting of the foundations. The evaluation procedures are usually done such that they results in huge retrofitting plans for foundations and this opinion has been raised that seismic evaluation and retrofitting of the structures is not economical. This paper presents some suggestions for accurate seismic evaluation of structural and geotechnical components of foundations. The results showed that by using the correct relations and understanding the behavior of structure exactly, the retrofitting procedure do not result in massive strengthening.

Appealing to the principle of vertical residence and stemming the horizontal expansion of the city, the Tehran Milad Tower is being built on 35000 sm3 site with the total area of 220000 sm3. With a height of over 170m, this 56-story concrete building is in the final stages of construction and would be the highest residential building of Iran. Since Tehran is located in a high-risk earthquake zone, all of its structures must be designed for seismic loads. In this building, the lateral loads are carried with three main shear walls, which are located in an angle of 120 degrees and the gravity loads are transferred from the concrete slabs to the secondary shear walls. Since the introduction of Tuned Mass Dampers (TMD) by Frahm in 1909, as a passive control system, numerous investigations have been carried out to examine the effect of these devices in reducing seismic response of the structures. The objective of incorporating a TMD into a structures is to reduce the energy dissipation demand on the primary structural members subjected to external forces. This reduction is accomplished by transferring some of the structural vibration energy to the TMD and dissipating the energy at the damper of TMD. The purpose of this paper is to design and evaluate the effectiveness of TMD for response reduction of the Tehran tower under seismic excitations. A lumped mass model of the building was provided with 112 translational and 56 rotational degrees of freedom using solid and shell elements. Time history analyses were performed to calculate the response of the structure subjected to some earthquake records. The same procedure was followed for the models with attached TMD. The control effectiveness of TMD was evaluated by comparing the tower's responses with those of the towers without control device. Furthermore, multiple tuned mass dampers are suggested as a solution for insufficiency of TMD.

There are a lot of approximation techniques for structural optimization. Among them, four outstanding approximation methods have been selected for trusses optimization. These approaches have been developed or modified by previous ones. Based on these schemes, a lot of trusses have been optimized by author's program. This study shows that the abilities of the mentioned methods are not the same and some of them have deficiencies. Reaching a better solution, lesser analysis time, oscillation of response, numerical stability and also using a variety of the design variables are among the findings of this work. A brief of these obtained results has been given in the conclusion part.