Ferdowsi Civil Engineering
Year:2014 | Volume:25 | Issue:2|Papers Count:11

Accurate identification of seismic hazard and the estimation of associated seismic demands are the key components in the performance-based seismic design (PBSD). Although nonlinear time history (NTH) analysis is the most precise procedure to evaluate the seismic demands of buildings structures, it is relatively complex and time-consuming for routine applications. Nonlinear static procedures (NSPs) are now prevalently used in engineering practice instead of nonlinear time history analysis for the prediction of seismic demands in building structures. Current Instruction for Seismic Rehabilitation of Existing Buildings (No. 360) uses invariant load distributions. While those invariant load distributions (such as inverted triangle, uniform, or mass proportional) are based on the assumption that the response is primarily in its fundamental mode of vibration, it can lead to incorrect estimates for structures with significant higher mode contributions. The objective of this paper is evaluation of the assumptions, approximations and limitations of pushover analysis and the differences between static and dynamic methods to estimate seismic demands in building structures subjected to both far- and near-fault ground motions. Analytical results show that lateral load pattern used to estimate demands can have a significant influence on the computed demands. When compared to nonlinear time history estimates, pushover methods tend to underestimate demands at the upper levels signifying the relevance of high mode participation in mid to high rise structures.

Many shape and topology optimization methods have been inspired from the nature. In this paper, two different optimization algorithms based on the adaptive biological growth (ABG) have been applied to some structural elements. The first algorithm is developed for the shape optimization and is applied to a plate with a central hole as well as a fillet plate. The second algorithm is the soft kill option (SKO) that is applied to a cone cantilever beam and a beam with variable cross section where the optimum topology of them are sought. The results show that the fatigue life of the plate with a central hole is increased by 40 times. Also, the maximum normalized first principle stress is 6% lower and finally, the volume of the optimum structure is less than those obtained by other researchers.

Determination of volume change of unsaturated soils during loading and suction change is one of the most important difficulties in testing unsaturated specimens. It is revealed from literature review that various attempts have been made to invent an apparatus that can be used in testing on unsaturated soil specimens, simply and accurately. In this research, details of design and manufacture of a fully automatic 3-axial apparatus is explained, that can be used in measurement of volume change in unsaturated soils. Calibration procedure is also explained. To determine SWCC, some tests were conducted in anisotropic conditions. Results confirm the operation of apparatus. It is shown that SWCC is a function of excreted load.

Utilizing considerablepetroleum products, increasing soil contamination and need to its clean-up is one of serious environmental issues. Soil vapor extraction is a common and very wide used method for soil remediation because of its Easy operation, low cost and high efficiency. In this paper, influence of soil type and heating, as two important parameters in efficiency of soil vapor extraction method is examined. The used soil is blown sand, which is mixed with different percentages of kaolinite clay. Establishing pilot and running experiments, the result of soilsremediationout of aliphatic hydrocarbons in gas-oil is reported. The results indicate thatenhancement of clay percentage leads to great reductioninclean-up efficiency. After 24 hours test running, removal efficiencyreached to 78.4% for the soil with 20% clay content, while this efficiency fell down to 23.75% for the soil with 40%of clay content. Having no clay within the soil, soil-heated vapor extractionmethod did not causenoticeable increasing in clean-up efficiency. However, heating has the most influence and increases clean-up efficiency for 20.6% with presence of 20% clay within the soil, while presence of %40 clay decreases the efficiency to 12.57%.

Concrete is one of the most utilized construction materials in the world. Nowadays, Nano silicate usage due to its special property attracted considerable attention. On this basis, studying its environmental functions is an essential issue. Accordingly, the behavior of normal concrete and the one with Nano silicate were compared via taking advantage of Life Cycle Assessment (LCA) method in this investigation. In addition, due to ASTM recommendation, the abovementioned method was utilized to compare these two concrete mixtures economically, too. Concluding the outcomes, the economic and environmental assessments were mixed via multi-criteria decision-making method. Reducing environmental impacts via substitution of cement with 1.5% Nano silicate, global warming criterion and fossil fuel consumption have been reduced 26.5 and 10.88 percent, respectively. Having the same substitution in concrete production, economic assessment indicates 10% reduction in life cycle expenses for this mixture. The mixture assessments for both normal and mixture with Nano silicate concrete ranked them 47.6 and 52.8, respectively.

Study of the effect of confinement of concrete on the seismic performance and behavior of permanent shuttering concrete panel structures is the subject of this paper. For this purpose, a few building models with different heights, but similar planar layout of walls, with and without considering the effect of confinement, i.e. execution of boundary elements, are taken into consideration. For this study, the PERFORM 3D software is employed for the modeling of nonlinear behavior of these structures by the possibility of using a multi layer shell element with fiber sections. For finite element modeling of these sections two types of concrete fibers, confined and non-confined, are employed. After modeling and carrying out nonlinear analyses, performance of each of specimens at two different risk levels is determined. The obtained results indicate that although execution of the boundary elements in these structural systems does not considerably improve the seismic performance but the confinement is a major factor in improving some parameters such as ductility, the probable maximum strength and the loss of energy that have a positive influence on the seismic performance of the structure.

Today, corrosion in reinforcements is an important issue in many structures, especially those made in off-shore, resulting of reduction of the structural capacity under gravitational and lateral loads. Using FRP polymer can reduce this effect to some extents. A numerical and experimental investigation has been conducted on three different concrete beams to find out the effect of replacing steel stirrups with FRP ones under static loading. So, three beams were tested under concentrated loading on the middle of the span. One of the three beams, as the reference had steel stirrups, while the other two contained in-place FRP made stirrups. Longitudinal steel reinforcements were used in all three specimens. Also, two different beams with steel and FRP stirrups were analyzed by finite element method in ANSYS. After calibration, two other groups of concrete beams were modeled and analyzed. The results demonstrated that FRP stirrups had the better shear capacity performance compared to steel stirrups and the final strain in FRP stirrups reached %0.8 which is two times of the value suggested by design code provisions.

Optimal operation of reservoir is one of the most important problems of water resource engineering addressed by many researchers. Mathematical and traditional optimization methods have been extensively used to solve reservoir operation problem. Nowadays, meta-heuristics methods such as Ant Colony Optimization (ACO) algorithms, however, are being used more and more to solve this problem. ACO algorithms refer to a family of search methods based on the foraging behavior of real ant colonies. In this paper, the application of four ACO algorithms namely, Ant System, Elitist Ant System, Ranked Ant System and Max-Min Ant System is used to solve the simple and hydropower reservoir operation problems. The efficiency of these methods is tested against the benchmark example of «Dez» reservoir and the results are presented and compared. The results indicate the superiority of Max-Min Ant System over other algorithms to solve reservoir operation problem.

In this paper, based on soil plasticity and pseudo-static methods, necessary equations have been derived for determination of total active thrusts due to layered backfill on rigid retaining walls using limit equilibrium approach. For this purpose, the reaction force applied on the failed wedge due to granular backfill has been determined using Kotter’s equations. The total lateral thrust and the angle of the failed wedge in the backfill with the horizontal direction has also been computed for both active and passive conditions. In addition, heights of application points of these thrusts have been calculated and compared with those obtained from earlier research work. Moreover, the method has been expanded for layered backfill. The results show that the total resultant thrust obtained from this study is well in accordance with the Coulomb method. In addition, it has been shown that the point of application of the resultant thrust depends on the backfill layering and backfill properties. Moreover, the developed method has shown that for retaining walls rotating sufficiently about their toes, overturning moments computed from the Coulomb method are on the safe side.

Basic dynamic characteristics of a 1:12 scaled experimental model of a 4 stories 3-D steel frame are obtained using different methods. The frequency sweep method is used to calculate the modal damping ratio and mode shapes of the frame. The optimal values of the TMD different parameters are evaluated using try and error method. Then the associated TMD system is constructed and installed on the top story and the model is tested under support harmonic excitation. The experimentally measured results of the model frame under resonant harmonic support excitation show the significant effectiveness of the proposed TMD system in reducing the model frame response. The above model is also analytically examined under 23 world-wide earthquake accelerogrames with different level of frequency content.

The main role ofcore in earth dams is to reduce and control the seepage flow through the dam. In order to achieve this purpose, the core material is usually selected from pure or mixed clays. Due to very small coefficient of permeability, the clay cores can prevent water leakage easily. However, pore water pressures developed inside the core during construction, can not be dissipated quickly. As a result, increasing the rate of embankment filling during the construction stage, may lead to large development of the pore pressure inside the core. In this study, based on a hardening elasto-plastic constitutive model, the total stresses and pore pressures inside the core of MASJED-E-SOLEYMAN rockfill dam, are calculated using the PLAXIS software during the construction and first reservoir filling stages. The analysis is in term of effective stress coupled with consolidation analysis. In order to verify the result of the numerical analysis, the measurment data from installed instruments in the rockfill dam have been compared with the numerical results. This comparsion shows that the numerical analysis results are in a good agreement with the instrument results. Excess amount of pore pressures in the core of this dam is due to very small coefficient of permeability and high rate of embankment filling.