نشریه مهندسی عمران مدرس
سال دوازدهم شماره 2 (تابستان 1391)

The remediation of heavy metal contaminated soils is one of the known challenges of researches in many industrial countries. The use of EDTA (Na2EDTA.2H2O) is one of the common soil-washing methods. In spite of several research conducted on this subject, the optimization of the use of EDTA for heavy metal removal from contaminated soils, specifically soils with relatively high surface area, are not well addressed in the literature. The main objective of this research is to evaluate the optimization of the use of EDTA in remediation of Pb-contaminated bentonite. To achieve the above mentioned objective, bentonite samples were laboratory contaminated with different concentrations of lead nitrate. Lead nitrate at concentrations of 0.001, 0.005, 0.01, 0.5 and 0.7 mol/l (1, 5, 10, 50 and 70 cmol/kg-soil) was used to laboratory contaminate bentonite. After drying the contaminated samples, they were exposed to different concentrations of EDTA. EDTA at concentrations of 0.001, 0.005, 0.01, 0.05, and 0.1 mol/l (1, 5, 10, 50, and 100 cmol/kg-soil) was used in 1:10 soil:electrolyte ratio in accordance to EPA. For sample preparation, 20 ml of EDTA at the required concentration was added to 2 grams of a dried contaminated bentonite. Samples were shaken for 2 hours on a horizontal shaker. Then, they were kept for 96 hours to reach equilibrium. In these 96 hours of equilibrium, soil samples in centrifuge tubes were shaken 2 hours in each 24 hours. Finally, samples were centrifuged with 4000 rpm to separate the solid and electrolyte. Then, the efficiency of Pb removal from samples was measured by analyzing the electrolyte. It should be emphasized that to prevent precipitation of lead ions in electrolyte, nitric acid was added to electrolyte to keep the pH less than 2. The achieved results show that the quantity of removed Pb ions by the application of EDTA is relatively equal to the concentration of applied EDTA. In other words, as the 1, the quantity of lead removal by EDTA is equal to EDTA concentration. This quantity of lead removal is neither a function of lead concentration nor to the number of soil washing by EDTA. In addition, since the quantity of removed Pb is only a function of EDTA/Pb ratio, therefore such a removal is not dependent to the pH variations caused by different concentrations of Pb or EDTA. This approves that the high buffering capacity of bentonite in comparison to other variables of environment has the minimum impact on the interaction process of EDTA and heavy metal contaminated bentonite.

Nowadays, fluid storage tanks are as important as fluids in urban life. The dynamic behavior of this important structure is different from common structures. Baffles as a passive control device can reduce the effects of sloshing which reduces the structural response to seismic excitation. In this study, the effect of baffles on seismic response of cylindrical vertical liquid storage tanks is investigated. The considered baffle is an annular plate with constant level from the base and constant inner diameter fixed on wall of the tank. Considering Laplace equation as the governing equation of fluid domain, and using boundary element method, a rigid tank is analyzed in the frequency and time domains. Afterwards, the baffle effects on natural frequency (in the frequency domain), and on base shear and overturning moment (in the time domain) due to El Centro and Erzincan earthquakes are investigated. Based on the results of mentioned analyses, it is observed that when the baffle is installed, the natural frequency of liquid domain reduces. Moreover, by installing the baffle, the base shear slightly increases whereas overturning moment remarkably reduces.

Scouring is one of the main causes of failures of bridges and piles in rivers and marine environment. So the estimation of scour depth around bridge piers and piles is of great importance. On the other hand, since the scour depth properties should be considered in designs by the designers, the importance of acceptable accuracy to estimate the scour depth properties will be quite highlighted. Regarding the importance of scouring investigation, there are several empirical formulas that have been presented by researchers but acceptable results have not been provided yet. Considering the fact that the prediction of scour depth around a pile is complicated and is affected by sediment characteristics and sediment transport mechanism, current properties and pile geometries, new approaches other than empirical ones are being sought by researches. Recently alternative methods like data mining approaches have been widely applied to simulate complicated problems. Artificial Neural Networks (ANN) as a famous data mining approach has been successfully used to estimate the scour properties around a pile. However, performances of Support Vector Machines (SVM) as another type of data mining approach are not explored yet. SVM has been recently applied in fields of particle identification, face identification, text categorization and bioinformatics. In this study SVM is applied to estimate the scour depth around a pile and the results are compared with those of the ANN by MLP network with one hidden layer and back propagation training algorithm. Performances of all methods are tested by experimental data sets and the results are compared using statistical measures. Results of statistical measures of verification stage indicate that SVM provides a better estimation of scour depth than ANN and empirical formulae. They also indicate that data mining approaches provide better prediction than empirical approaches.

A search of the published literature reveals that studies related to the effects of the degree of bolt tightness on the behavior of space structural joints and consequently on the member behavior and the overall response of space structures are rather limited. An experimental investigation of the effects of bolt tightness on the rigidity of double layer grids, carried out previously by the authors, had revealed the significance of the degree of bolt tightness on the overall rigidity of the tested structures. The present research is concerned with an investigation of the effects of the degree of bolt tightness on the end conditions and consequently on the effective lengths and the slenderness ratios of compression members of double layer space structures. An experimental program of work was conducted on more than 40 test specimens consisting of typical pyramidal modules of representative double layer grids to observe the influence of the degree of bolt tightness on the effective length and load carrying capacity of diagonal compression web members of such modules. Each module was fabricated by practically identical tubular members and the matching MERO type ball joints. However, different modular specimens were constructed using tubular members with different diameters and cross sectional properties. In each individual test specimen, it was attempted that the bolts connecting the members to the ball joints be tightened by the same applied torque to achieve an identical degree of tightness in all its joints. However, different values of applied torques were used to tighten different test specimens. Following the preparation of the test specimens tightened with different applied torques, a monotonically increasing concentrated load was applied at the upper node of each specimen. The tests were continued up to failure and in each test the displacement of the central top node just underneath the applied load was measured as the main component of the response of the test module. The observations indicate that the degree of bolt tightness has a significant influence on the effective lengths and consequently the load carrying capacity of compression members of such modules. However, over-tightening may cause failure of connection sleeves. Also, bolt pre-stressing shall not be made to a degree that causes brittle fracture of pre-stressed bolts or premature tearing of member to end cone welded connections under additional applied tension. On the basis of the observed behavior and supporting theoretical studies, the effects of the bolt tightness on the behavior of double layer space structures have been discussed in the context of design assisted by testing emphasized in Chapter 7 of the Iranian Code of Practice for Space Structures. With due consideration of different aspects of the influence of the degree of bolt tightness on the behavior of joints, members and modules, as well as the overall structural behavior, some practical recommendations have been presented to improve the reliability of structural performance through increasing rigidity and load carrying capacity of such double layer space grid structures, that can be achieved as a result of a proper choice of the bolt tightening procedure.

This paper examines the dynamic behavior of steel moment-resisting frames with steel-concrete composite beams with welded connections. One story-two bay frames with and without composite beams with rigid and simple connections were modeled with ABAQUS software and analyzed under earthquake accelerations. The distribution pattern of plastic hinges, rotation of plastic beam to column joints, plastic energy dissipation capacities of frame components and crack mechanism of slabs near the interior and exterior connections were studied. The results revealed that the frames with composite beams and welded rigid connections have the lowest values of period, plastic energy dissipation capacity, plastic rotation of joints and early frame mechanism. Failure mechanism in the exterior connection was in the form of concrete pre-tensioning from the starting at the corner of the column stretching in oblique around the edges of the slab. At the interior connections, it was in the form of concentrated compressive stress over the outer flange of the column. Strength and ductility of steel in tension and compression capacity of concrete in steel-concrete beams (composite beams) make this system suitable for long spans and considerable growth in recent years. In Euro Code 8, rules are stated for mechanisms between concrete slab and steel column in bending and sagging moment modes. The mechanism in bending and sagging moment regions, where concrete slab has enclosed steel column, is shown in Figure 1. In the first mechanism, the compressive stress is applied directly onto the outer side flange of the column. Whereas in the second mechanism, the concrete slab exerts pressure through a 45 degree angle to the column web. The performance of the first mechanism leads to removal of contact friction between the concrete slab and the column. But the second mechanism leads to removal of contact element (Hard Contact) between the concrete slab and the inner core of the column web and flange. Therefore, activation of both mechanisms manifests a better performance of the system. Formation the plastic hinges in frames generally start at the column base, particularly at the middle column and then expand to other members, connections and the concrete slab. In this study, the use of composite beam, instead of steel beam, causes plastic hinges to form in the connections instead of beams. In composite frames with simple connections, due to stress concentration, the major plastic hinges are formed at the welded connections. In these frames, the first plastic hinge is formed earlier than others. But the failure capacity of these frames is higher than rigid ones. In rigid connections, the added rigidity due to enclosure by concrete slab causes initial stiffness for the frame and delays the formation of the first plastic hinge. However, it induces sudden stresses on the welds at the upper part of the beam. Thus will eventually lead to weld rupture and slab failure. This produces early failure in the frames.

Minimum Spanning Tree (MST) is a mathematical programming problem that may be applied for analyzing transportation network structure and its performance, like its connectivity and link prioritization. Generally, the cost associated with each link is its Free Flow Travel Time (FFTT), however in this paper this concept is developed to the case of a loaded network with capacity constraints and its application to transportation network planning is examined for times of disaster, when the life of many people is involved. In this paper equilibrium travel time for a loaded network is proposed as the link cost and the problem is formulated and solved for Tehran province network. Results show that based on equilibrium travel times, the total cost of MST will have an 8 percent increase from 25973 to 28081 seconds and about 30 percent of the links in the new MST will change. It is also observed that if the MST based on FFTT is used for computing the total cost of the loaded network, the total cost will be 30232 seconds which demonstrates 17 percent increase in cost and 9 percent in error.

In this paper, the finite element code (ABAQUS) is used to present numerical modeling of strike-slip North Tabriz fault. To investigate the frictional behavior of fault the slip weakening law is assigned to the fault. This law is based on stick- slip instability mechanism. Fault modeling has been done in three-dimensional using ABAQUS software. The model involves a vertical strike-slip planar fault that resides in elastic crust. In this model only the upper solid part of With this analysis, verification of the constitutive relation of friction has been done. The second analysis crust is simulated and topography effects have been ignored. The fault is simulated as 2D vertical contact elements. The results have been verified with geological data such as rate of displacement on fault and verifications demonstrate satisfied convergence. For friction of fault, the results with two coefficient factors are compared with GPS data and coefficient factor of 0.1 showed better convergences.

One of the important applications of Expanded Polystyrene (EPS) in Iran is its use as infill block in Block and Joist Reinforced Concrete Floors. The properties and performance of EPS blocks in this floor system, including reaction-to-fire, mechanical properties, thermal resistance and acoustical performance of the system, was studied. Fire behavior of blocks was tested with ISO 5660 cone calorimeter test method. The fire properties of standard and flame retarded types of EPS were measured and discussed, including time to ignition, average and peak values of heat release rate and total heat release. The influence of type of EPS on its fire behavior was investigated. The results showed that the time-to-ignition and total heat release parameters can not be a characteristic value for distinction between standard and fire retarded types of EPS under cone calorimeter test condition. The reason is that both types are flammable and burn completely at fire temperatures. The peak value of heat release rate (PHRR) of EPS is the mostimportant parameter that can be utilized for distinction of Standard and flame retarded types of EPS with cone calorimeter test method. PHRR values higher than 300 kW/m 2 were achieved for standard types, but the results for flame retarded ones were less than 250 (and mostly less than 200) kW/m.

During the past decades, there has been an ever increasing demand for construction of new wharves and port facilities in Iran. This is partly because of the recent rapid demographic, social and economic developments, increase in offshore oil and gas activities and also long coastlines available in the country. Wharves، Piers and jetties are lifeline structures, which provide a cost effective means for transporting large quantities of goods and raw materials into and out of a region. Harbor structures also play a central role in management of an abnormal condition such as an earthquake. For long structures such as wharves and jetties, transient ground deformations inducedby seismic wave passage and effects from the spatial difference in ground motion become important. On the other hand, if a port facility is located close to the seismic source, it will become subject to the near field pulse type excitations. An analytical approach has been used to address the problem. Linear and non-linear response of simplified structural models to near-fault and far-fault strong ground motions is investigated. The model approximates a structure by an equivalent oscillator consisting of a rigid beam supported by several rigid mass-less columns. Bi-linear rotational springs connect the columns to the deck and the base of the structure. The system has been studied under two pulses type (fault-normal pulse and fault-parallel pulse) and 108 near field and far field earthquake excitations. In this study closed form solutions for the dynamic response of multi span pile and deck structures have been developed. Material non-linearity, large deformations and P   effects are taken into consideration. The central difference method is employed to solve the nonlinear equations of motion. The model is then used to analyse the structure under incident pulse type near-field excitations. Effects from strain-hardening, columns height, the seismic source distance, magnitude of the excitation, type of the excitation (pulse or random), have been investigated and compute the reduction factor and compare with the common design rules. In general it has been found that the classic design criteria for the strength reduction factors provide non-conservative results in a number of occasions.

Sensible vibration of steel beams in long spans is undesirable issue in the buildings. These beams may be vibrated during people passage, although the strength calculations of this beams to be performed, accurately and drift control index based on buildings codes to be considered. Iranian Steel Buildings Code has offered a formula for controlling of vibration of beams in building frames with pin connections in serviceability phase. However, this code has not presented criteria for beams include fixed connections. Since these beams have the considerable portion of building frames, their vibration control needs special attentions. The presented equations for determination of beams frequency are complicated and have been not used for control of buildings floor vibration. In this paper, the mentioned formula in forenamed codes has been discussed. The dynamic analysis, finite element method (FEM) and artificial neural networks (ANN) techniques have been adopted to constitute the frequency equations of the fix ends and cantilever steel beams. Comparison of resulted frequency from presented equations and ANN showed that the error is low. Furthermore, it is suggested that use proposed equations for determination of frequency of moment connection beams.