JOURNAL OF FACULTY OF ENGINEERING (UNIVERSITY OF TABRIZ)
Year:2008 | Volume:35 | Issue:3 (51) CIVIL ENGINEERING|Papers Count:10

The durability of concrete in corrosive ambient has been a matter of concern for concrete researchers. Natural and artificial pozzolans in replacement with cement have performed very well in concrete structures situated in such environments. In order to investigate the performance of Iranian pozzolans, concrete specimens incorporating Type 2, ordinary cement natural pozzolans (Sabalan tuff, Ansarod pumice) and silica fume were made and stored maintained in simulated Oroumia lake conditions (free air, submerged and wetting-drying) for 6 months. All the considered mixtures have been made with two different water-cement ratios (0.4 & 0.45). Three size of concrete cover (2, 3.5, 5 cm) have been used. Tests such as corrosion potential measurement, electrical resistivity, reinforcement corrosion intensity, carbonation depth, chloride ion concentration and compressive strength were carried out at different ages. Results show that the wetting-drying condition has had a great influence on the durability of concretes. Pozzolanic mixtures have shown better performance in comparison with Type 2 mixtures. Concretes containing silica fume showed the best durability and performance.  The use of 450 kg/m3 cement and water - cement ratio less than 0.4 had a great influence on the protection of concrete against corrosive ions and thus their durability enhancement.

In past decades, steel shear walls (SSWs) have been used as a new lateral resistance structures in tall buildings and high seismic risk regions due to appropriate seismic specifications. SSWs are constructed in two forms of unstiffened and stiffened types. The unstiffened form is the best choice for designers, because of its simple constructional details and lower cost. There are three types of design procedures for SSWs. in all procedures, the designing process is performed Base on shear strength, and the bending strength is neglected. In tall buildings, significant bending forces occur in addition to shear forces. Hence in the present study, the behavior of SSWs in tall buildings was assessed, by applying into account both bending forces and shear forces. The analysis was performed by advanced nonlinear finite element program ANSYS®. The analysis results represented incapability of current SSWs design procedure in tall buildings. Some recommendations including modifying boundary conditions using feasible structural systems and modifying design procedure, in order to implementing this type of resistance systems, were proposed. The performed nonlinear collapse analysis demonstrates the effectiveness, reliability and validity of the proposed approach.

Climatic indices are used to forecast seasonal stream flow through the application of neural network techniques. This research has been carried out in Nazloochay River Basin in northwest of Iran. The spring season stream flow of this basin is about 80% of the annual flow, and the previous research shows that it is influenced by the Southern Oscillation Index (SOI) and North Atlantic Oscillation (NAO). A feed-forward three layers Artificial Neural Network (ANN) is used to forecast the spring stream flow with one-year lead time. It is believed that considering the lead time of one year and the long distance between the basin in Iran and the locations of climatic phenomenon (SOI and NAO), the findings in this paper are very important and distinguished, both from water resources management aspects and teleconnections outlook.

Seismic performance of dual steel moment-resisting frames with mixed use of rigid and semi-rigid connections is investigated. To this end, nonlinear seismic response of three groups of frames with three, eight and fifteen story is evaluated. These frames with rigid, semi-rigid and combined configuration of rigid and semi-rigid connections are subjected to five earthquake records and in ultimate limit state of rigid frame, their response is compared. This study shows that in all frames, it can be find a state of semi-rigidity and connections configuration which behaves better than rigid frame, because of base shear and storey drifts. This optimization should be done with respect to the factors such as geometrical and mechanical properties of frame, strength and rigidity of connections and properties of design earthquake record.

Steel shear wall is a novel system used to resist against the lateral loads of wind and earthquake. Nowadays, due to the special benefits of this innovative system, in comparison with the other lateral loading-resistant systems such as concrete shear walls and moment frames, shear steel walls are used widely in the construction  practice, especially in tall buildings in North America and Japan. In the present paper, the collapse behavior of shear steel walls is studied. The finite element method has been used to investigate into the effects of various parameters on the collapse behavior of these systems. All of the analyses have been undertaken using ANSYS. In order to verify the accuracy and validity of the finite element modeling, the theoretical results, obtained from material and geometric nonlinear static analyses, have been compared with the available experimental results of steel shear walls. It has been found that the finite element model is reliable enough to be used to undertake nonlinear collapse analysis for parametric investigation. The effects of these parameters have been studied: post buckling behavior, type of connections of frames, material model, type of connection of shear steel wall to the frame, and slenderness ration of plate.

In this investigation, the effect of different parameters has been studied experimentally on behavior specialties of three-dimensional, turbulent and steady inclined turbidity currents. One of the important specialties that show the structure of hydrodynamics of turbidity currents is velocity profile and in this investigation, it has been measured by ADV (Acoustic Doppler Velocimeter). In all of the experiments, kaolin with specific gravity of 2.65 kg/m3 was used as suspended materials. The mean particle diameter is D50=20 micron approximately. The experimental results show an increase in the entrance volume flux of turbidity current into the tank of fresh water, is increased always the depth or height of turbidity current and an increase in entrance concentration and slop, is decreased often the height of turbidity current. In addition to, for the reason that intense entrainment in the lateral and the longitudinal directions, along the interface of water and turbidity current is increased height of turbidity current after enter under of fresh water. Investigation of velocity profiles in this turbidity current is showed for the reason that, existing of inertia forces in the beginning of traveling of current into the tank. The rate of maximum and average velocity always is more than the end of tank. While we are traveling to the end of tank, is observed always the location of maximum and average velocity is shifted to up. Increase in volume flux, is increased rate of maximum and average velocity and I Increase in entrance concentration with the exception of the entrance regime, in other regions is increased rate of maximum and average velocity. After coming into under of fresh water, turbidity current spreads and then arrives to the state established flow and   the entrainment is at least rate.

Construction of hydraulic structures or other structures compact the soils layers and create hydrostatic pressure (excess pore water pressure) in saturated fine grained soils. While the excess pore water pressure dissipates, stresses on the soil skeleton (effective stress) gradually increase; thus soil undergoes deformation or strain in vertical direction (consolidation settlement). By the use of compression index, Cc, which is obtained from consolidation test, one can estimate the among of field settlement. These expressions correlate Cc to the soil properties or physical indices such as Atterberg limits, void ratio and specific gravity. In this research we have attempted to find some expressions for the soils of Ahwaz region. To do this, consolidation tests and tests for determination of soil physical properties and Atterberg limit have been carried out on 29 undisturbed samples which were prepared from different locations and depths. The results showed that there is a good correlation between Cc and initial void ratio.

In this research, the strength and ductility of reinforced concrete columns made of lightweight aggregates are studied. Twelve square reinforced concrete columns were manufactured and tested. In the specimens, the shape and spacing of transverse reinforcement and compressive strength of specimens varied. For all specimens, the eccentricity of axial loading was 60mm. Test results show that the confinement of transverse reinforcement has a positive effect on ultimate strength and ductility. Test results have been compared with the provisions of ACI Code for normal strength concrete. The comparison shows that the reinforced concrete columns made of natural lightweight aggregates can be used in structures if they include appropriate transverse reinforcement and have a good mix design.

A guyed tower consists of a mast which is laterally supported by pre-tensioned guyed cables. In this study, the variations of axial forces in mast elements were investigated including chords, struts, diagonals and the changes of sections in elements in height, using several towers subjected to the combination of dead and wind load. Non-Linear analysis of all towers has been carried out using a finite element package-written by the former writer-and then the model and the results have been validated by Sap2000 package. The truss elements have been used to model the latticed mast. The guys have been modeled using non-linear cable elements. The results of analysis showed that the chord forces varied considerably with height increasing. Thus cross section of legs in mast can be reduced by height increasing. Also, the variations of maximum axial forces in diagonals and struts in panels are not significant in height; therefore the change of cross section of those members can be ignored in height.