سال:1393 | دوره: | شماره: |تعداد مقالات:10

Con ned masonry construction is made up of masonry walls and con ning ties, which are built on all four sides of each wall. This system is a conventional form of house construction, as well as a good alternative for post-disaster reconstruction of seismically damaged and/or collapsed buildings in many countries. Window and door openings appear in many panels of con ned masonry buildings, but many codes do not consider the eect of these openings in the strength and stiness of con ned masonry panels. In this study, the inuence of masonry panel openings on the stiness and strength of con ned masonry walls is investigated. A nite element program, DIANA, is used for the nite element modeling of fully grouted con ned masonry walls, walls with un lled head joints, two-story walls, walls with a lintel band and walls with added vertical ties on the opening sides. All specimens have openings and are constructed according to the Iranian seismic code (Standard No.2800-05). Models are validated by the results of the tests performed on two fully grouted one-story one-bay con ned masonry walls, and a two-story one-bay con ned masonry wall, constructed in Iran. Simple equations are proposed that predict the eect of central openings on the stiness of dierent types of con ned masonry wall and the cracking strength of fully grouted walls with openings.

The optimal groundwater bioremediation design problem is complex, nonlinear, and computationally expensive. In this paper, an improved Ant Colony Optimization (ACO) algorithm is employed for optimizing a groundwater bioremediation problem, and the BIOPLUMEII model is used to simulate aquifer hydraulics and the bioremediation process. Injection and extraction pumping rates and well locations are treated as decision variables. Optimization results show that the proposed approach performs better than the Genetic Algorithm (GA), Simulated Annealing (SA) and the hybrid SA-GA algorithm, called Parallel Recombinative Simulated Annealing (PRSA), and reduces the computational time of a number of function evaluations compared with the mentioned algorithms. Applying the optimal dynamic pumping strategy in the second stage reduces bioremediation costs by 13: 3%.

In order to evaluate the dynamic behavior of oating oshore wind turbines, the authors consider two approaches. A numerical method is used to investigate Tension Leg Platform (TLP) oshore wind turbine response behavior under a parked condition. This code considers nonlinearities due to changes in the tension of tethers. The o-diagonal components of stiness, damping and mass matrices are considered to calculate coupling. This code solves the nonlinear equation of motion at each time step. However, in order to validate the data generated by the code, a scaled-down model was fully tested in the marine laboratory. The importance of these series of experiments is due to the fact that this model possesses a unique design and speci cations to which no other model can be compared. Measurement of three degrees of freedom under environmental load is the goal of the experiments. Also, the results clearly show that the direction of encountering waves is an extremely important factor. It can be concluded that wind loads can dampen the oscillation of the model and prevent the impact of large loads on the tethers. The results show that the discrepancy between experimental and numerical results, with dierent degrees of freedom, is suciently acceptable.

In this paper, the Mixed Discrete Least Squared Meshless (MDLSM) method is used for solving quadratic Partial Dierential Equations (PDEs). In the MDLSM method, the domain is discretized only with nodes, and a minimization of a least squares functional is carried out. The least square functional is de ned as the sum of the residuals of the governing dierential equation and its boundary condition at the nodal points. In MDLSM, the main unknown parameter and its rst derivatives are approximated independently with the same Moving Least Squares (MLS) shape functions. The solution of the quadratic PDE does not, therefore, require calculation of the complex second order derivatives of MLS shape functions. Furthermore, both Neumann and Dirichlet boundary conditions can be treated and imposed as a Dirichlet type boundary condition, which is applied using a penalty method. The accuracy and eciency of the MDLSM method are tested against three numerical benchmark examples from one-dimensional and two-dimensional PDEs. The results are produced and compared with the irreducible DLSM method and exact analytical solutions, indicating the ability and eciency of the MDLSM method in ecient and eective solution of quadratic PDEs.

In situ soil properties are spatially variable parameters causing soil deposits to be heterogeneous. Heterogeneity consists of two components: (i) A deterministic trend and (ii) The residual component. This paper presents the eect of dierent components of soil heterogeneity on the ultimate bearing capacity of a vertically loaded shallow foundation resting on clay deposits. The numerical model used in this study is based on nite dierence simulations, employing FLAC 5.0. Results of numerical analysis are compared with other simple and analytical solutions. For heterogeneous soil deposits, considering both linear and bi-linear deterministic trends, nite dierence tools were found to be able to reect salient features of heterogeneity in bearing capacity estimation. An equivalent homogeneous analysis solution is introduced, in order to allow for heterogeneity, by adopting a representative depth for shear strength measurements. Stochastic variation of shear strength is shown to induce under conservatism by solely relying upon deterministic estimations.

The use of short link beams in Eccentrically Braced Frames (EBFs) is generally preferred to long ones, mainly due to their high rotation capacity and energy dissipation under cyclic loadings. However, long links have the advantage of providing openings in the braced spans of EBFs. Based on a few tests conducted on long link behavior in the literature, Seismic Provisions (AISC-341-05) limits their rotation capacity to a small value of 0: 02 rad. In this paper, a three dimensional nite-element model using ABAQUS is developed for the inelastic nonlinear analysis of long links to investigate their rotation capacity. It was found that using some new intermediate stieners, in addition to those speci ed in the Seismic Provisions, a large rotation capacity for long links can be achieved.

In this research, the impact of climate change on extreme rainfall events in the Chenar-Rahdar Basin, Shiraz, Iran, was investigated utilizing three statistical downscaling methods, namely, change factor, LARS-WG, and SDSM. Daily precipitations with dierent recurrence periods were projected for the future period of 2011-2040 (2020s), based on two AOGCM output data (HadCM3 and CGCM3), under an A2 emission scenario. In summary, HadCM3 (for three downscaling methods) projected an increasing trend (of up to 21.8%) in extreme rainfall events for the period of 2011-2040, with respect to the base period. On the other hand, CGCM3 showed an increasing trend for extreme rainfall events for the rst two methods (up to 24.7%), while the SDSM method resulted in an increasing trend (up to 3.6%) for recurrence periods of 20 and 25 years and a very small decreasing trend (down to -2%) for recurring periods of 50 and 100 years. Relatively low correlation coecients in multiple regressions obtained for both AOGCMs reect the limitations of SDSM in downscaling precipitation data in the study area. Comparing the three downscaling techniques utilized in this study, it is concluded that using change factor or LARS-WG downscaling methods would be conservative enough in climate change impact assessment for the next 30 years.

Rubble-mound breakwaters are common marine structures that provide a safe area for human coastal activities. The stability of these structures against sea-waves requires their seaward slope to be protected by an armor layer consisting of natural rock or concrete units. To provide a safe breakwater, it is reasonable to establish a relation between the exerted wave loads and the stability of the armor units. However, up to now, the empirical design equations, derived from model tests, relate wave parameters to armor weight, and keeps the eect of wave loads in a black box. In this paper, a new approach, based on numerically-derived wave loads on the armor, is presented to evaluate the stability of these protective units. Results indicate that by increasing wave height, the weight of the armor units does not necessarily increase. Wave breaking type strongly inuences the applied loads and stability of the armor units. New dimensionless numbers are introduced to provide relationships between wave parameters and stability indices of breakwater armor units at dierent locations. This approach clari es the ambiguities of the design process caused by the complex ow eld, especially the wave breaking type near the breakwater.

In this paper, we examine uid ow and associated dispersion around a circular cylinder under progressive surface wave motion. The ow eld and vortex shedding patterns were studied using ow visualization and Particle Image Velocimetry (PIV). Several patterns of vortex shedding were identi ed around a single cylinder. The vortex shedding patterns under progressive wave motion are similar to those observed in planar oscillatory ow, except in the way the vortices form and in the orientation they take. The observed vortex patterns in progressive wave motion are more unstable than those in planar oscillatory ow. Using particle tracking and the Lagrangian dispersion method, the dispersion coecients were calculated for various ow regimes. The observations con rm the calculations in general. It was also found that wave steepness can aect the shedding pattern. The vortices tend to shed more frequently in a wave direction at low wave steepness.

The main concern of this investigation is to evaluate the ability of the Delft3D- ow package in studying the distribution of Suspended Sediment Concentration (SSC) over the depth in the Dithmarschen Bight. The area consists of tidal channels and tidal ats, with a prevailing semi-diurnal tide, and is tidally dominated. Required eld data were prepared using the data collected by a transmissometer and a mechanical sampler. A factor of two of the measured SSC was used to evaluate the performance of the model, and some dissimilarity was found between the modeled and measured SSC. To verify the reason, two comparing procedures were carried out. First, evolutions of the vertical pro le of the SSC from the model and the eld were prepared and compared. In another procedure, snapshots of the distribution of SSC during dierent phases of a tidal cycle were prepared for both model results and eld data. It was found that the predicted SSC values are in good agreement with eld data during the periods of ood phase and low slack water. However, spatial dissimilarities are observed during the periods of high slack water and the ebb phase. Aninsucient supply of sediment from the tidal at predicted by the model was considered to be responsible.