Iranian Journal of science and Technology (B: Engineering)
Volume:32 Issue: 2, April 2008

Composite Reinforced Concrete (RC) wall system refers to a cantilever composite wall, where steel or Fiber Reinforced Polymer (FRP) components are embedded in or attached to an RC wall. The results of an analytical and parametric study on the effectiveness of using externally bonded steel plates and FRP sheets on RC shear walls as a retrofit technique so as to improve their seismic behavior have been investigated in this paper. Calibration and verification of a base RC wall has been done by comparing the results of the finite element model and also the experimental model. Analytical results are used to evaluate the capacity curves (Load-Displacement relationships) of strengthened RC shear walls. Analysis results of a model with an optimized thickness of a steel jacket instead of an over-hanging part of the boundary element show the ductile behavior of a strengthened wall close to the behavior of the base RC wall with boundary elements; this achievement would lead to the theory that steel jacketing could be an alternative for the boundary elements of RC shear walls. The application of externally bonded Carbon Fiber Reinforced Polymer (CFRP) sheets is an effective seismic strengthening procedure in order to improve the behavior of reinforced concrete shear walls. In the retrofit method, using CFRP sheets, the flexural and shear strength would be increased by applying the CFRP sheets with the fibers oriented in the vertical or horizontal direction. The carbon fiber sheets are used to increase the precracked stiffness, the cracking load (up to 35%) and the ultimate flexural capacity (up to 18%) of the RC walls. Finally, a wrapped CFRP sheet around the plastic hinge area of the RC wall in parallel with boundary elements, provides not only enough shear strength, resulting in a ductile flexure failure mode, but also the confinement of concrete in the plastic hinge leads to an increase in the ductility of the RC wall.

A modified predictive optimal linear control (MPOLC) algorithm is proposed for controlling the seismic response of elastic structures. This algorithm compensates for the time delay that occurs in real control applications by predicting the structural response in the modified optimal linear control equation. Since the environmental loads and disturbances are not measured during real-time control, they are not involved in the derivation of the control algorithm. Therefore the predictive optimal linear controller (POLC) is a proportional feedback of the only predicted current state. In the modified control algorithm (MPOLC), using a logical assumption, the immeasurable disturbances are considered in the state space equation and also in the derivation of the control algorithm, so that the controller is a combination of the control force in the last step and the proportional feedback of the predicted states in the last two steps. Hence, the control performance of the modified control algorithm is superior to that of the original one. The feasibility and effectiveness of the proposed control algorithm is verified through frequency-domain and time-domain analyses, and compared with the original one. The tendon control system of a three-degree-of-freedom structure is illustrated to demonstrate the control effectiveness of the modified predictive control algorithm.

In this research the Discrete Element Method is employed to determine the seismic three dimensional bearing capacity of rectangular foundations. A rigid but moving slip body resting on its base is assumed to define the failure mechanism under the footing. A soil mass enclosed in a three dimensional space with assumed failure surfaces is considered as several discrete blocks connected with Winkler springs. The geometry of the failure surface under the foundation is not fixed and can be altered due to all of the factors affecting the problem. This geometry is determined by six independent angles. The seismic loading can be applied to the soil mass, soil surcharge and foundation loading in a pseudo-static manner. This paper includes the derivation of 3D DEM formulation in a three dimensional state, and several examples solved by means of a developed DEM program to explain the capability of the method and to compare the results with the other methods.

In recent years determining bearing capacity of piles from in-situ testing data as a complement of static and dynamic analysis has been used by geotechnical engineers. In this paper, different approaches for estimating the bearing capacity of piles from SPT data have been explained and compared. A new method based on the N-value from SPT is presented and calibrated. Data averaging, failure zone extension, and plunging failure of piles has been noticed in the proposed approach. A data base has been compiled including 43 full scale static pile load tests and 17 dynamic testings which were analyzed with the signal matching technique by CAPWAP. The SPT data were performed close to pile locations are also included in the data base. A comparison of current methods by error investigation with cumulative probability and Log-Normal approaches demonstrates that the proposed method predicts pile capacity with more accuracy and less scatter than other methods. Results of prediction with good agreement to measured capacities indicate that the proposed method can be used as an alternative for determining the bearing capacity of piles in geotechnical practice.

Abstract– Two dimensional finite element (FEM) and boundary integral equation methods (BIEM) are used to determine the uplift forces on a half-buried submarine pipeline in a sandy seabed. The main assumptions are potential flow theory for water, linear elastic stress-strain for soil, and Darcy''s law for pore fluid flow. Dynamic pressures around the pipe and uplift forces are calculated based on BIEM and FEM. Also, dynamic uplift forces on a pipeline with variable burial depths are calculated. The results of the numerical approach are compared with some analytical formulations based on the potential flow theory and experimental data, and good agreement is shown with both analytical and experimental data. Parameters in this study have been discussed in relation to the uplift forces.

In this paper, the bending behavior of unbraced CSB is investigated and some empirical equations are proposed to predict the bending coefficient of Cb. The acquired results are compared with some published papers in the technical literature, and by applying the proposed modification factor Cc on the relations of I-sections, a very good agreement is gained.

In this study, the behavior of nine steel frames having various infill properties under reversed-cycling loading were investigated experimentally. The steel frame systems consist of a single story with span/height ratios of 1, ½ and 2. The selected infill properties are no infill, brick-wall infill and brick-wall + plaster infill. The reversed-cycling loading was applied to test the specimens laterally to simulate the seismic load. Then, the displacements occurring at the specimens were measured. Strength envelopes, rigidity decreases and energy dissipation properties of the infilled frames were determined and the results obtained are compared.

Underground excavations are of immense interest to mining engineers worldwide. Underground projects are often complex in nature where geological features, geomechanical parameters of rock mass and stress play important role. The present research has conducted 2D, Quasi-3D and 3D continuum analyses of the underground excavation of the extension phase at the Masjed-e-Solaiman hydroelectric project in Iran’s southwestern province of Khuzestan. The effects of weak zones and the formation of multiple openings in the inhomogeneous rock mass have, in particular, been taken into account during those analyses. This study reveals that 2D is more deformed than the other models, whereas 3D analysis yields the best results comparable with in-situ measurements.

This paper proposes a new ant colony based optimizer to improve the traffic flow in a city. For this reason, a new structure of urban traffic control system has been introduced, which uses an ant colony optimizer as its main part. To study the performance of such system, we simulated the ACO based system as an adaptive path planner. Results show a very good optimization of path length and path traffic. To apply ACO on this problem we have changed the original version of ACO and the modified algorithm can be used for other applications such as designing intelligent data routers, intelligent data mining, etc.

The probable maximum precipitation (PMP) for many stations in Iran and other places using the Hershfield formula is routinely estimated as the mean plus 15 standard deviations processed from one-day yearly maximum rainfall values. However, the value of 15 may not be suitable for all stations with different climatic specifications. In this paper, yearly maximum one day rainfall data of 20-36 years for 30 stations in the Atrak watershed region in the northeast of Iran were analyzed in an attempt to estimate PMP for a one day duration based on an appropriate frequency factor. Based on the actual maximum daily rainfall data of these stations, the highest value of these frequency factors was found to be 9.63 for a one day duration. This frequency factor was subsequently used to estimate one day PMP values. Using these PMP estimates, a generalized pattern for the spatial distribution of one day PMP was demonstrated. It was found that one day PMP over the Atrak watershed ranges from 97 to 295 mm, and the mean ratio of PMP to the highest observed one day rainfall was about 2.51. The PMP maps are considered important tools to determine reliable and consistent estimates for any location in the Atrak watershed for large hydraulic structure designs.