Scientia Iranica
Volume:20 Issue: 3, 2013

This paper attempts to present a method for differentiating between multi-attribute decision procedures and to identify some competent procedures for major decision problems, where a matrix of alternative-measure of effectiveness and a vector of weights for the latter are available. In this respect, several known multi-attribute analysis procedures are chosen, and the same procedures are exploited to evaluate themselves, based on some evaluation criteria. This is done from an engineering viewpoint and in the context of a transportation problem, using a real case light rail transit network choice problem for the City of Mashhad, and the results are presented. Two concepts have been proposed in this respect and used in this evaluation; peer evaluation and information evaluation, which are investigated in this paper.In the evaluation of five multi-attribute decision procedures, based on nine criteria, and with the help of these procedures themselves in the context of the case under study, the results revealed that these procedures found Electre, Linear Assignment, Simple Additive Weighting, TOPSIS, and Minkowski Distance better than others, in the same order as given. This is backed by a wide range of sensitivity analyses. Nevertheless, despite specific conclusions made regarding the better decision procedures among those evaluated, this paper finds its contribution mainly in the approach to such evaluations and choices.

This paper presents an optimal design of three dimensional multi-story reinforced concrete structures using recently developed meta-heuristic algorithms, namely; the charged system search and the enhanced charged system search. The design is based on the ACI 318-05 code and loadings are based on ASCE7-05. Analysis of the structures is performed by the standard stiffness method. All members are subjected to biaxial moments and axial loads. Pre-determined sections are assumed for beams and columns, and the corresponding interaction curves are utilized to check whether the selected section for each member is acceptable. The objective function is taken as the weight of the structure, and constraints consist of the slenderness of compression members, the maximum allowable drift of the structure and the natural frequency of the structure. It should be mentioned that second order effects are also considered and that the end moments of the columns are magnified when needed.First, a 7-story frame with 3 spans is considered and optimized. Then, a sensitivity analysis is performed by optimal design of nine frames having 3 stories and 2 spans. In each story, different span lengths and loading conditions are assumed, and the results are compared.

In the present paper, Mindlin’s solutions are used (Mindlin, 1936) to estimate the load–displacement relationship for a circular foundation for ground anchors. Constant, linearly and parabolically varied anchor loads are applied to the foundation. The closed form analytical solutions derived by Selvadurai are used in the analysis. Effects of the length of the anchor region, its depth of location and the distribution of load within the anchor region are investigated in this article. The analytical solutions are also compared with finite element analysis and the results are given.

This paper presents a new application of the Group Method Of Data Handling (GMDH), to predict pile scour depth exposed to waves. The GMDH network was developed using the Levenberg–Marquardt (LM) method in the training stage for scour prediction. Scour depth due to regular waves was modeled as a function of five dimensionless parameters, including pile Reynolds number, grain Reynolds number, sediment number, Keulegan–Carpenter number, and shields parameter. The testing results of the GMDH-LM were compared with those obtained using the Adaptive Neuro-Fuzzy Inference System (ANFIS), Radial Basis Function-Neural Network (RBF-NN), and empirical equations. In particular, the GMDH-LM provided the most accurate prediction of scour depth compared to other models. Also, the Keulegan–Carpenter number has been determined as the most effective parameter on scour depth through a sensitivity analysis. The GMDH-LM was utilized successfully to investigate the influence of the pile cross section and Keulegan–Carpenter number on scour depth.

In the method of a combination of elementary mechanisms utilized in the plastic analysis of frame structures, a search is carried out to find the collapse load factor of a frame by checking every possible combination of its elementary mechanisms. In this paper, the ant colony system and charged system search algorithms are employed to optimize the process of finding the collapse load factor of planar frames. The efficiency of these algorithms is compared through four numerical examples.

Seismic hazard assessment is a basic tool for rational planning and designing in areas of different seismic activity. The Bayesian probability estimation was applied in this study to assess seismic hazard. The estimation procedure provides a posterior probability distribution that integrates prior estimates based on the knowledge of the process, and the likelihood of occurrence based on historical data. The Bayesian approach was applied to calculate the probability that a certain cut-off magnitude would be exceeded at certain time intervals in different regions of Iran. The results for the cut-off magnitude of 6.5 indicate that the highest probability of seismic hazard exists in the Alborz, Kopeh-Dagh, Bandar-Abas, Kerman, and Zagros regions. The seismic hazard is lowest for the Esfahan–Sirgan region, the Arabian Platform, the Persian Gulf, and Kavir in Central Iran. The comparison between the Bayesian results and the seismotectonic models of Iran reveals that it is possible to partition the spatially distributed epicenters of earthquake events into different regions. In general, these regional divisions agree with previously proposed seismotectonic provinces of Iran.

A recent method in the seismic assessment of structures is Endurance Time Analysis (ETA). ETA is a time–history-based dynamic pushover procedure, in which structures are subjected to gradually intensifying acceleration functions called Endurance Time Acceleration Functions (ETAFs), and their performances are evaluated based on the equivalent intensity level that they can endure while satisfying required performance goals. In this paper, the accuracy of the ETA in the seismic assessment of steel moment resisting frames is compared with the Time History Analysis (THA) and Incremental Dynamic Analysis (IDA) methods. For this purpose, a set of mid-rise and high-rise frames were selected as a case study. Three sets of second generation ETAFs were used as input in the ETA method, and seven scaled ground motions were used for THA and IDA. It was found that ETA can estimate THA results in an equivalent target time, and also the general trend of IDA curves, with acceptable accuracy, while ETA requires considerably less computational effort in comparison with THA, and, especially, the IDA method.

The flexibility of floor diaphragms has a significant influence on the behavior of building structures. Commonly, in analyzing structures, floor diaphragms are considered rigid. This assumption distributes lateral loads between the resistant elements according to their rigidities, and decreases the degree of freedom that creates easier analysis. However, in steel structures with braced frames and long span floors, diaphragms usually behave flexibly. The seismic responses of such structures vary to the expected response of typical rigid floor structures. Ignoring the effects of diaphragm flexibility can lead to non-economic or unsafe structural design. In this paper, the nonlinear responses of braced steel buildings with flexible concrete block-joist floor diaphragms are investigated under both static lateral load and dynamic ground motion, and they are compared with the responses of structures with the assumption of rigid diaphragms. This study demonstrates that span ratio is an important parameter in the flexibility of floor diaphragms, and if this ratio exceeds three, the variation of results between the two assumptions of flexible and rigid diaphragms may not be ignored. In addition, results show that diaphragm flexibility changes the seismic response of the structures and linear analysis is not sufficient to explain this behavior.

A hybrid numerical model is introduced for simulation of cohesive sediments concentration profiles in a surf zone. For this purpose, wave height reduction must be considered, due to muddy beds and wave breaking. Models, such as Sanford and Maa’s erosion model, Krone’s sedimentation model, Tajima’s wave breaking model and the visco-elastic–plastic rheological model, are used to investigate the interaction of wave and bed and to predict the concentration profile. A splitting algorithm has been used to split the three-dimensional advection–diffusion equation into a horizontal, two-dimensional equation, and a vertical, one-dimensional equation, due to different length scales. The one-dimensional equation is discretized over a non uniform grid, and, then solved implicitly using the QUICKEST scheme (third order in time and space). The two-dimensional equation is divided into two parts (advection and diffusion) and each part is separately solved at different time steps. A suitable mesh, regarding space and time intervals, is chosen for considering the stability of the present model. The computational domain extends from the shoreline to the deepwater zone. Finally, the results are analyzed and compared with experimental and field data and other models. Good agreement has been obtained with the data and other numerical models.