ASAS
Year:2009 | Volume:11 | Issue:24|Papers Count:7

In recent years, bridge construction had become more important in Iran. Researches pay more attention to reinforced concrete bridge that usually built as thin walled prestressed or post tension concrete. To keep the prestressed force and reduce the amount of losses as much as possible, it is possible to use high strength concrete. For majority of cases in thin walled concrete sections, the congestion of steel rebars is the main vibration of concrete. Nowadays using Self Compacting Concrete, SCC is a new type of concrete which doesn't need any vibration; it will compact under its own weight and follow easily in steel congestion area. This technology causes the fundamental revolution on construction of prestressed concrete structures.This research show the comparison between laboratory results of loading Prestressed SCC-T-Beams of 9m length (loading accordance to the Iranian bridge code of practice) and results of finite element modeling on flexure, shear and ductility. It was concluded that a good agreement is available between two methods.

This paper presents an accurate analytical model to evaluate the efficiency of using longitudinal restrainer cables for preventing unseating of concrete cantilever curved viaducts. Since the dynamic behavior of bridge support and especially longitudinal restrainer cables are so complex and their results with linear analytical methods don't have enough accuracy, ANSYS software is used and different curve radiuses and different earthquake records are selected and then nonlinear time history analysis is conducted on the 3D finite element model of "Karoon" bridge. With this model, high concentration of seismic forces in some cables is observed. Also it is found that the nonsymmetrical distribution of impact forces, because of not synchronizing movements of spans close to the expansion joints, increases the probability of vulnerability in the cables and isolation bearing supports.In general, longitudinal restrainer cables decrease the probability of deck unseating. Also these cables prevent the effect of high amount of impact forces on the spans close to expansion joints. On the other hand, to avoid the failure of restrainer cables, much attention is needed to nonlinear behavior of bridge regarding its geometric properties such as curve radius and characteristics of isolation bearings.

This paper discusses an object- oriented neural network model that was developed for predicting traffic flow- speed fundamental diagram on a section (Gange) of the Ghazvin- Rasht road and 50 kilometers from Rasht, Gilan, Iran. The feasibility of this approach is demonstrated through multi layer perseptron network (MLP) that uses back propagation approach (BP) for training data, which was developed for predicting hourly speed data and Traffic Flow data up to one hour in the future. The results obtained indicate that the MLP is capable of predicting mean speed and traffic flow up to one day in the future with a high degree of accuracy. (99% for predicting mean speed and 97% for predicting traffic flow on non-holidays). Similar models which were developed for predicting mean speed and traffic flow on the similar facility, using regression approach, were successful in short term traffic forecasting with lower degree of accuracy. The results which is obtained in this paper shows the high capability of neural network approach for short term traffic prediction.

In chevron and reversed chevron cross braces two members of bracing meet each other in the middle of the beam opening so out of balanced force obtained from difference between tensile and straining resistance of cross braces can have much effect on cyclic behavior of frame.There is one major problem in these frames, when whole construction's height is set in mechanism state, destruction total mechanism formation.In order to overcome this problem, last floor cross braces are designed in a way that when all the straining cross braces has buckled and sewing columns gave in, the structure would remain inelastic range. In designing sewing columns, designing method is applied upon capacity basis which this design method prevents plastic joints and complete rupture mechanism formation in beams.In this paper by studying seismic system behavior which named zipped frames, seismic resistance increase of structure and its absorption and energy distribution amount is being investigated by applying limited components software and along an appropriate (suitable) method introduction to achieve above objectives, it also will be determined (recognized) that as structure's height increases, behavior coefficient of zipped cluster piles also increases and continuously this coefficient is about 30% more than behavior coefficient of chevron cluster piles.

During an earthquake, the input energy in a structure can be used as a criterion to assess the seismic performance of a structure. In the present study, the effects of near and far field earthquake records on input energy of SMRF (Special Moment Resistant Frame), SCBF (Special Concentric Braced Frame), flexural EBF (Eccentric Braced Frame) with hinge and rigid connections, flexural KBF (Knee Braced Frame), RBS (Reduced Beam Section) and BRBF (Buckling Restrained Braced Frame) are compared. The Perform software with three records (El Centro, Imperial Valley and Tabas for far field and near field) are used for nonlinear analysis of systems. The P-Delta effect is included and the action-deformation of nonlinear component is assumed to be elastic-perfectly plastic. The effects of PGA variation and height of the frames are also considered in this study. The results show that the input energy to SCBF system is more than all in far field records and the least is belong to RBS system. Also the least and more input energy in near field records, are belong to SCBF and EBF (H) respectively.

In recently years, there has been an increase in the use of industrial and agricultural residues in the production of concrete. Thousands of tones of these agricultural residues and industrial bypro ducts are produced every year. Therefore, the study of their characteristics and possible applications becomes a priority as their use brings benefits in technical, economic, power and environmental terms. Different materials with pozzolanic properties such as silica fume, fly ash, blast-furnace slag, rice-husk ash and bagasse ash have played an important part in the production concrete. This paper presents a laboratory study on the properties of mortar containing "Karun Argo Industries Co." bagasse ash and Different materials with pozzolanic properties. For this purpose-A total of 19 mixtures with different mix designs were prepared, 9 of them with baggase ash, 3 mixes with rice-husk ash, 3 mixes with silica fume and 3 mixes with truss were prepared. These different pozzolanic materials was added as partial cement replacement. 1 mix was prepared as control mixture. This research shows that bagasse ash, could be used as a pozzolanic material to produce concrete.

In construction of modem buildings many pipes and ducts are necessary to accommodate essential service like water supply, sewage, air-conditioning, electricity, computer and telephone network.These pipes and ducts are placed underneath of the beams and for aesthetic reasons are covered by a suspended ceiling, thus creating a dead space in each floor.The height of dead space is added to the overall building height and depended on the number and depth of ducts to be accommodated.If these ducts are passed through the transverse opening of the floor beams, the dead space will be significantly reduced. But, presence of opening in beam's web leads to reduction of its ultimate strength. Therefore a particular design procedure is necessary for reinforce concrete members.In this paper the effects of opening created in beams and obtimom length of openingin beam's web to prevent reduction of their ultimate strength are studied.