نشریه مهندسی عمران فردوسی
سال بیست و چهارم شماره 2 (بهار و تابستان 1392)

Abstract The aim of this paper is to present four strategies to increase the accuracy and speed of optimization of truss structures under the constraint of Structural System Failure Probability (SSFP). In the first strategy based on the probability rules, a criterion is defined to avoid producing many correlated paths and obtain more accurate upper bound of SSFP. In the second strategy, the force method formulation is improved and employed to analyze trusses with different topologies. In the third strategy two intelligent agents are utilized to identify the repeated paths and determine the fitness of the best chromosomes in each generation. Using the fourth strategy, the chromosomes, whose SSFP is much larger or smaller than the allowable value, are identified during the analysis and the analysis is terminated at that stage.

Abstract Accurate calculation of reliability index is very important for the reliability analysis of structures. In some limit state functions with nonlinear characteristic and several local optimum design points, the computational reliability methods may not appropriately determine the failure probability, and iterative reliability approaches may be converged to local optimum design points. In this paper, formulation of nonlinear conjugate gradient methods such as: Fletcher & Reeves (FR) and Dai & Yuan (DY) were proposed for computing the reliability index. Then, the efficiency, capacity and robustness of the conjugate gradient were investigated through several reliability problems. The FR and DY algorithms were diverged in some examples. Therefore, a new modified nonlinear conjugate gradient method was proposed by using the hybrid optimization algorithm to ensure accurate convergence of reliability index. The results illustrated that the modified nonlinear conjugate gradient methods were converged with less run-times and number of iterations in comparison with the FR and DY methods, and robust, efficient and stable algorithms are to calculate the structural failure probability.

Compressibility characteristics of fine-grained soils are often the most important parametersfor settlement evaluation of the founded layers. The compression index which is the slope of virgin curve is usually for determination of settlement potential of fine grained soils. In this research, the effects of different physical and index properties of soil samples were investigated on compression index in order to find the most compatible properties and reliable equation based for a wide range of soil samples collected from different sites of Iran. For this purpose, one-dimensional consolidation tests were conducted utilizing conventional oedometer test on 26 soil samples at three different levels of void ratio. The compression index of each specimen was determined using data obtained from test results and correlation analysis was made using statistical software, SPSS. The results showed that the compression index, c C, has a significant correlation with the most of index properties where its coefficient of correlation with structural properties was strongly greater than those related to inherent properties. Therefore the empirical equations which do not consider at least one structural parameter and use only intrinsic properties could not estimate the compression index properly. Furthermore a very simple and reliable equation was developed for estimation of the compression index and virgin curve of unconsolidated and normally consolidated fine-grained soils. Statistical analysis demonstrated that the proposed relationship predicts the compression index accurately in comparison with the existing relationships.

A large number of bridges and buildings that are currently used, are made of slabs withopening. Some of these buildings and bridges have been severely damaged because of natural disasters such as earthquake, storm and other effects such as materials fatigue and alkaline and corrosive agents.Therefore, retrofitting and strengthening of these structures is essential and affordable. In this research, by applying experimental models, the flexural behavior of reinforced concrete slabs with opening strengthened with different FRP systems and steel sheets have been studied. Eight specimens of reinforced concrete slabs designed according to the Iranian code ABA with the dimensions of 150×45×20 cm were manufactured. In these slabs, the amount of tensile reinforcement was equal to 0.25 ρ b. Two openings across the length of each slab with 10 cm diameter were created. One slab was considered as reference (not strengthened) and seven other slabs were strengthened with CFRP laminates, GFRP sheets and steel sheets, and tested. Forces, strains and deflections were recorded during the tests. The results of this research show that the flexural strength increases about 43% in the strengthened slabs with FRP laminates, about 57% with CFRP sheets, 45% with GFRP sheets and 15% with steel sheets.

In practice, foundations are settled on the soft layers of soil, so the ground must be designed aswell as the structure. Wave propagation and hysteresis damping of soil layers may alter the seismicresponse of flexible-base design in comparison to controversial fixed-base. Lots of uncertainties aboutthis issue, necessitate most of seismic design standards including Iranian standard No. 2800 to neglectthe soil – structure interaction (SSI) effects on seismic response of structures. A simplified finite elements method is proposed in this research and applied according to the Standard No. 2800 criteria on reinforced concrete structures. The accuracy and efficiency of this method is compared with four other similar researches, and the results of time history and modal analyses for descriptive reinforced concrete systems are ilusterated in the form of figurs and charts.

Concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars exhibit large deflections and crack widths as compared with steel reinforced concrete beams due to the low modulus of elasticity of GFRP bars. Different studies show that ACI 318 equation for the effective moment of inertia Ie does not predict deflection well for FRP reinforced concrete beams. The purpose of this paper is to propose new equations for estimating the effective moment of inertia of FRP reinforced concrete beams based on genetic algorithm and experimental results. Genetic algorithm is used for optimization of error function between experimental and analytical responses. In the experimental part of the study, nine beam specimens were manufactured and tested. The parameters of reinforcement ratio and concrete compressive strength were selected as the variables for the beam specimens. Also fifty five beam specimens tested by other researchers were used for experimental database. In this paper, the effect of elastic modulus of FRP bars, reinforcement ratio and the applied level of loading on the effective moment of inertia is taken into account. In addition, the proposed equations are compared with different code provisions and the existing models for predicting deflection of FRP reinforced concrete beams. Also, the calculated values by the proposed equations are compared with different test results. The experimental results correlated well with the values predicted by the proposed equations especially in high reinforcement ratios and high levels of loading.

So far, different methods have been applied to clean up soils contaminated with oil. Bioremediation is one of the clean up technologies which uses microorganisms or microbial processes to degrade oil contaminations in soils. This study evaluates the applicability of cow manure as bioremediation alternative for soils spiked with petroleum hydrocarbons. Target contaminant of this research was diesel fuel which was spiked at 60000 mg/kg sample on a dry weight basis. The major goal of this research was to find the appropriate mix ratio of cow manure for enhancing diesel fuel degradation during contaminated soil composting. The ratios of contaminated soil to cow manure were 1:0.15, 1:0.3, 1:0.5 and 1:1 as wet weight basis in 3 replicates. To examine the circumstances conditions on degradation process, we determined the C/N, C/P and total bacterial count (TBC) of treatments at start, week 5 and week 11(end of study). Total petroleum hydrocarbons (TPH) were measured by USEPA standard method 8015B using GC-FID. The degradation of diesel fuel was significantly enhanced by the addition of cow manure as compared to the control treatment and TPH degradation results were better described using a second- order kinetic model. The experimental data indicated that the most degradation rates occurred in the first 5 weeks. By week 5, 50% of the original TPH was removed in the1:1 treatment. After this period, degradation trend of diesel fuel showed a lower removal rate. At the end of study, the most active degradation of TPH was observed at the soil to cow manure mix ratio of 1:1 with 62% removal whereas the 1:0.5 treatment degraded 58% of TPH contamination. No statistically significant difference was observed between 1:1 and 1:0.5 treatments (p<0.05). Statistical analysis showed high correlations among the amount of TPH degraded and TBCs(r = 0.733).

Hot or cold weather condition affects the quality of the concrete in different ways, which one of them is increase or decrease in the initial temperature of the concrete. In this study, the impact of the initial temperature of the concrete on its quality in concrete kerbs made by dry pressing method with Portland cement is examined. Concretes with similar mix designs and initial temperatures of 17, 25, 29, and 39  C were made and cured in the standard laboratory condition. Then, in different ages some tests were carried out on them. The test results showed that the temperature of the concrete during placement is a parameter that affects the strength and durability properties of the concrete. For the initial temperature of 39  C, the quality of the concrete had a significant decrease. For the temperature range in this study, the initial temperature of 25 C resulted in the highest quality of the concrete. In the 7 and 42 days of age, the concrete with 25C initial temperature obtained the highest compressive strength and the lowest water absorption. The highest electrical resistivity in high ages was related to the concrete with 17C initial temperature.

Labyrinth spillway is an appropriate option to pass PMF discharge. The most advantages of this type of spillway are higher discharge capacity, easy aeration as well as low fluctuations of flow surface. It is essential to find the optimum geometry considering the maximum passing discharge under specific hydraulic conditions with minimum construction cost. In this study, fuzzy inference system (FIS) and genetic algorithm (GA) were used to optimize the spillway's geometry and satisfy the hydraulic conditions. Applying FIS to evaluate coefficient based on available input - output pattern, ANFIS was employed. Finally, based on GA and ANFIS model output a cost function was defined to minimize the expense under appropriate hydraulic condition.