AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2013 | Volume:45 | Issue:1|Papers Count:10

The need for ductility in Concentrically Braced Frames (CBF) has driven researches to study the different parameters which influence the ductile performance of this kind of structure. Brace end clearance in gusset plates is one of the most important of these parameters, which is considered by seismic codes to improve the seismic behavior of these structures.This study examines the effect of brace end clearance on the behavior of CBFs. Both rectangular andtapered gusset plates are considered in order to gain a deep insight into this issue. Nonlinear analyses using the detailed inelastic finite-element model (FEM) are employed to perform this research. The equivalent plastic strain concept is used to determine the limits of ductile behavior and to predict fracture and failure in these models. Results shows that while in tapered gusset observing 2tp clearance (which is recommended by codes) provides the optimum ductile behavior, in rectangular gusset plates, it is possible to reduce this distance and obtain a smaller gusset plate to maintain the ductile behavior of the frame.

Deterioration of concrete structures in sulfate environments is a well-known phenomenon. Cement chemistry is an important parameter in coping with sulfate attack. C3A and CA (OH)2 lead to expansion, cracking and strength reduction. The use of rice husk ash (RHA) can improve the sulfate resistance of concrete. It was observed that the sulfate resistance of blended cements was significantly higher in sulfate environments. This study investigates the effect of RHA replaced by cement on the durability of concrete due to sulfate attack. Three RHA replacement levels were considered in the study which is 7%, 10% and 15% by the weight of cement. After the specified initial moist curing period (28 days), concrete specimens were immersed in sodium sulfate & magnesium sulfate solution. The degree of sulfate attack was evaluated by measuring the compressive strength reduction of concrete cubes and their weight losses in both continuous immersed and wetting-drying conditions. Expansion observed in the ordinary Portland cement mortar prisms was larger than expansion for the RHA mortar prisms. Moreover, microstructure of the mortar and concrete incorporating Rice Husk Ash were studied through SEM tests.

In this paper, a GIS based model for locating urban rail stations is suggested. The Purpose of the model is maximizing the number of passengers who are attracted to the rail. The model at first generates different combinations of stations along the rail line. Following that, the model evaluates the rail trip attraction from the station-covered areas in each combination of stations. Finally, the model prioritizes the location and combinations of stations. Based on this, the optimized locations of stations are determinable. The suggested model considers local conditions, user characteristics and rail specifications.

Removal of silica impurities on Reshm bentonite sample of Semnan province in Iran was investigated. Two processes of hydrocyclone and sedimentation treatment with sodium hexametaphosphate were used aiming for nanoclay production. Mineralogical studies indicated that the treated sample was a low grade Na-bentonite. The dominant impurities were cristobalite and quartz with low amounts of feldspar, gypsum, dolomite, calcite and zeolite. The Purification of the sample was processed by two methods of hydrocyclone and sedimentation treatment with sodium hexametaphosphate as depressant. The purified product was intercalated with octadecylamine. The evaluation of products was performed by XRD analysis. The purification results showed that hydrocyclone process failed to produce a purified montmorillonite product suitable for nanoclay application. Using sedimentation treatment with sodium hexametaphosphate as a depressant, a product with impurities of less than 5 percent, suitable for nanocaly application, can be produced. Intercalation of purified montmorillonite by octadecylamine showed that the application of sodium hexametaphosphate increase the basal spacing up to 36o A.

Using geotextiles as a material with more tensile strength than soil has attracted attention of different researchers and organizations, particularly for road construction. In this research, first, the effect of geotextiles on pavement bearing has been investigated by laboratory model. Dimensions were determined in a way that boundaries have minimum effect on results. The free-end or fixed-end needle punched geotextiles were placed under a layer of sand (as sub-base) and over a layer of soft clay (as sub-grade). The results indicated that Fixed-End or Free-End conditions of geotextiles are similar to each other and geotextiles increase pavement bearing. This effect increases as displacement increases.

Recently steel shear walls have been considered as a resistant system against lateral loads. Also researchers have seen different effects of earthquakes of near and far from the fault. These researches shows that mappings of near fault have less effective time than mappings of far from the fault and have one or more special pulse, large domain and medium to large frequency which causes to increase the domain of response spectrum in large period zones. In this article four moment resisting steel frames each of which has four spans 3, 7, 15 and 25 stories that only their mid span has steel shear wall with thin plate (strip model) have been analyzed under near or far from the fault and Iranian Earthquake 2800 Code spectrums. By the assumption of well acting of strip model, results showed that base shearing and relative roof displacements of 3 and 7 stories under the near fault spectrum was 2 to 32 percent less than the cases under far from the fault and Iranian Earthquake 2800 Code spectrums and at 15 and 25 stories the consequence was vice versa and averagely 22 and 52 percent more than the amounts of far from the fault and Iranian Earthquake 2800 Code spectrums.

The purpose of this article is the study of effects of high voltage AC stray current (220 and 380 VAC) on the durability of concrete. In rainy condition, high voltage AC current can leakage into water saturated concrete power pole by creeping AC current through their insulators. In Iran, large budgets are annually spent for replacing degraded concrete power poles with new ones. There is not any research on the above mentioned subject and the history of this research is related to the authors of this paper. Therefore, this study is a new work in the field of concrete.In this study, the degradation effects and mechanisms of the AC stray current on water saturated concrete were investigated via laboratory tests. They included electrical and electrochemical tests. Based on the results of the tests, AC stray currents can reduce the durability of water saturated concrete by non-distribution current, thermal and shrinkage stress mechanisms. Application of silica fume and reducing w/c ratio increases the resistance of concrete against destructive effects of the AC stray current and increases its durability.

In this research, behavior of exterior concrete beam-column joints made of normal concrete (NC) and self-consolidating concrete (SCC) is investigated. The variables include the type of beam longitudinal bar anchorage in joint, transverse reinforcement of joint and strength of concrete. Experimental and analytical investigation of joint behavior is carried out. In the experimental part, 10 semi-scale exterior beam-column joints were manufactured and subjected to a constant column axial load and beam quasi-static cyclic load. In the analytical part, the ABAQUS software is used for modeling and analyzing of test specimens. Based on the results, the experimental and analytical joint capacities are in good agreement. Results show that using self-consolidating concrete in joints, apart from easier concrete placement, can increase the workability and ductility of connection and result in a better bond with reinforcing bars. Also, by increasing the concrete strength, the failure mechanism of a connection may change from shear failure in joint to flexural failure in beam.

Significant wave height is mean of one third of the largest wave heights in a certain marine condition. Investigation and prediction of the significant wave height have been recently considered in marine system analysis including loadings over marine structures and sediment transport for designing, operation and marine researches. The capability of chaos theory in engineering particularly marine engineering has been gaining considerable interest in recent times. In this research, dynamic characteristics of the significant wave height time series in Caspian Sea at Anzali entrance are considered and the prediction has been performed using ideas gained from chaos theory. To reconstruct phase space, the time delay and embedding dimension are needed and for this purpose, autocorrelation function and algorithm of false nearest neighbors are used. Correlation dimension method is applied for investigating chaotic behavior of the significant wave height, which is the resultant of correlation dimensions, expresses chaotic behavior in the time series. Local prediction algorithm is used for time series prediction and results illustrate good and acceptable accuracy of chaos theory in quantitative prediction of seas significant wave height.