Scientia Iranica
Volume:22 Issue: 6, 2015

Damage identi cation in Structural Health Monitoring (SHM) involves three main steps: signal acquisition, signal processing, and feature extraction and interpretation. Recently, the authors presented a review of recent articles on signal processing techniques for vibration-based SHM. This article presents a review of journal articles on feature extraction and classi cation techniques in order to assess the health condition of a structure in an automated manner. This review is limited to civil structures such as buildings and bridges. The methods reviewed are neural networks, wavelets, fuzzy logic, support vector machine, linear discriminant analysis, clustering algorithms, Bayesian classi ers, and hybrid methods. Further, two novel algorithms with potential for feature classi cation in SHM are suggested.

Central Force Optimisation (CFO) is a nature-inspired conceptual framework with roots in gravitational kinematics, a branch of physics that models the motion of masses moving under the in uence of gravity. This paper presents a review of CFO, its variants, and applications to engineering problems. Example applications include electric circuit design, antenna design, water pipe network design, and training of arti cial neural networks.

Seismic loads on bridges may cause large damaging forces in the substructure. Isolation and energy dissipating elements or a combination of the two have been used to reduce the transmitted forces caused by seismic loading. The benefits of these systems are mainly attributed to the increase of structure’s natural period of vibration and damping. This paper investigates a new device that works on the same principles. This device is composed of sliding bearings and air springs or airbags. Several bridges are analyzed using the Nishimura’s model for air springs and the sensitivity of seismic response of bridges due to variable spring parameters is investigated and optimum values are obtained. Then, using these parameters for the air spring and solving the equation of motion the variation of air spring internal parameters with time are investigated. Results show that air springs are very efficient in reducing the effects of seismic forces.

The development of transportation in large cities requires the construction of twin-tunnels or the construction of new tunnels close to the existing ones. Since both the relative position of tunnels and the construction procedure a ect the soil movement, this paper presents analysis of this issue with a particular interest for the optimization of both the relative position of the twin-tunnels and the construction procedure. Since the soil is composed of discrete particles with di erent sizes, modeling using nite element methods based on the mechanics of a continuous medium is not completely consistent with reality (especially, modeling of con ning e ect with depth). Therefore, in this study, discrete element method is used to model the discontinuum nature of soils. For these concerns, using software PFC2D based on Discrete Element Method (DEM), the static analysis of circular twin-tunnels has been performed, and in uence of the two factors on the soil settlement resulting from the tunnel construction has been investigated. Analyses were conducted for three con gurations of the twin-tunnels: aligned-horizontally, vertically, and inclined. The results are compared with the FEM results. The comparison shows influence of modeling the discontinuous nature of coarse-grain alluvial soils with respect to continuous media modeling.

This paper describes an experimental study conducted to investigate the properties of concretes produced with recycled aggregates and normal aggregates for two different concrete classes (C20/25, C30/37). Tests of compressive strength, splitting tensile strength, ultrasonic pulse velocity, rebound hammer, wet and dry density and freeze-thaw resistance were conducted on specimens of the concretes. Moreover slump test was conducted on fresh concrete. The results showed that the slump of recycled aggregate concrete (RAC) was less than that of normal aggregate concrete (NAC). For class C20/25, the average compressive strength, rebound hammer and density of the RAC were 26%, 17% and 16.6% less, respectively, than those of NAC. The splitting tensile strength of RAC was 3.5% greater that of NAC. Moreover for C30/37 the average compressive strength, splitting tensile strength, rebound hammer and density of the RAC were 32.5%, 12%, 21% and30% less, respectively, than those of NAC. For class C20/25 and class C30/37 the ultrasonic pulse velocity of RAC was 17% and 18% smaller than that of NAC, respectively. RAC for C20/25 lost 2.5% more weight than NAC in freeze-thaw resistance tests and RAC for C30/37 lost 29% more weight than NAC in this test.

In this article Thermo-Hydro-Mechanical (THM) response of saturated clays has been studied. For this purpose, the finite element program PISA, which is able to simulate coupled THM analysis, has been employed. Due to the effects of temperature on the mechanical behavior of soil, two temperature-dependent constitutive models have been implemented in PISA. For verification of the developed numerical model, ATLAS large scale experiment has been simulated in different conditions and the simulations results have been compared with in-situ measurements. Comparison of predictions and measurements reveals that using coupled formulation along with thermoplastic constitutive models, the main aspects of the THM behavior of saturated clays can be captured. The results indicate that for accurate simulation of advection phenomenon, two-dimensional finite element model should be used.

The study is undertaken with the aim ofdeveloping a 1-D numerical analysis of flow over side weirs ondifferential quadrature method (DQM). The numerical results were compared with relevant experimental data for both the simple and labyrinth side weirs. The results showed that the numerical methodology can effectively predict the discharge and flow profile associated with labyrinth side weirs. The deviation (from experimental data) was found not exceeding 4.5%. Furthermore, the contribution from different terms of the governing equation was assessedthrough a comprehensivesensitivity analysis. The results show that, in order to simplify the governing equation, the channel slope and the friction slope can be eliminated.

The determination of the thermal conductivity coefficient of construction materials is very important in terms of fulfilling the condition of comfort, durability of construction materials, the economy of country and individual. In this study, linear regression, adaptive neural based fuzzy inference system (ANFIS), and artificial neural networks (ANN) models were developed to estimate the thermal conductivity coefficient values fromthe surface density (dry specific gravity/thickness) and the unit weight of construction materials. Validations of the developed models were investigated by statistical analysis. In predictive models, while the lowest determination coefficient (R2) and the highest root mean square error (RMSE) were obtained from linear regression, the highest R2 and lowest RMSE were obtained from the ANFIS model. The results of the ANN model according to results of linear regression, while R2 increased by approximately 6%, RMSE decreased by 30-39%. The results of the ANFIS model revealed that while R2 increased by approximately 12%, RMSE decreased by 59-71%. As a result, it is suggested that together the surface density and unit weight with ANFIS, the most appropriate method in the used methods, can be used as an alternative approach to estimate the value of thermal conductivity.

In this paper, a new traffic assignment model is proposed based on fuzzy equilibrium condition where perceived travel times of users are assumed to follow fuzzy values. First, a new method is proposed to determine membership function based on link congestion levels using probabilistic models. Then, a new index is presented based on percentage of users’ risk-acceptance for comparison of fuzzy numbers. Using this index, two approaches, fuzzy Dijkestra shortest path algorithm and defuzzification method, are established for solving shortest path problem. Fuzzy equilibrium condition is defined based on the two proposed fuzzy shortest path methods and a traffic assignment model is developed with consideration of fuzzy equivalency equilibrium condition. Frank-Wolfe Algorithm and fuzzy shortest path method are combined to solve the proposed traffic assignment problem. The assignment model is applied to a small and medium-sized network. Sensitivity analysis for link flows is performed under different levels of users’ risk-acceptance to understand the route choice of different types of users. To apply the model to a large-scale network, the network of Mashhad, Iran is considered as a case study. The fuzzy traffic assignment model provides more accurate estimation of volume compared to conventional traffic assignment.

Confining of concrete columns by means of fiber reinforced polymer (FRP) composites is the most common method used for enhancing strength and ductility of concrete compression members. The shape of the column section is from the significant parameters affecting the efficiency of composite in confinement. In rectilinear columns, due to stress concentration at corners, the concrete is non-uniformly confined and the effectiveness of confinement is much reduced compared to circular columns. In this study, the compressive behavior of 9 rectilinear RC columns confined with CFRP strips is experimentally examined. To improve the confinement effectiveness in the columns, some of the specimens are locally strengthened with CFRP strips at corners, before the application of horizontal CFRP wrapping. The number of confining layers and the shape of rectilinear section (square or rectangular) are the main parameters under investigation. Based on results of the current study,local reinforcement at the corners of rectilinear columns before horizontal wrapping eliminates stress concentration at the corners and avoids premature rupture of CFRP confining layers at these parts; thus increases the efficiency of composite in confinement. Furthermore, local reinforcement of corners of column section is more effective in RC columns with square sections compared to rectangular sections.

In this paper, the semi-rigid connections such as Double-angle Web (DW) connections, which are welded to the beam web and bolted to the column flange, are investigated. This study tries to establish the effect of clearance setback between beam end and column flange and/or web. When the beam rotates, it is desirable to avoid the bottom flange of the beam bearing against the column as this can induce large forces in the connection. The usual way of achieving this, is to ensure that the connection extends at least a few millimeters beyond the end of the beam. For this purpose, several connections are designed and considered, based on two different shear capacities for the beam. For each connection, two different bolt gage distances and three values for clearance setback are analyzed. Analyses are performed to establish the moment–rotation relationship for this type of connection and the stress distribution of each specimen is observed. In this study, connections are subjected to shear loads. Material and geometric non-linearities, as well as contact and friction have also been implemented in the model. The model is validated through comparison with experimental data, found in the literature.

A better understanding and modeling of breaking waves is important for coastal engineering. This article concerns the plunging wave break over a slope bottom considering unsteady, incompressible viscous flow with free surface. The method solves the two dimensional Naiver-Stokes equations for conservation of momentum, continuity equation, and full nonlinear kinematic free-surface equation for Newtonian fluids, as the governing equations in a vertical plane. A new mapping was developed to trace the deformed free surface encountered during wave propagation by transferring the governing equations from the physical domain to a computational domain. Finally a numerical scheme is developed using finite element modeling technique to predict the plunging wave break. The Arbitrary Lagrangian Eulerian (ALE) algorithm is employed in modeling wave propagation over sloping beaches. The results compared with other researches and show the good result.

Two one-story, single-span concrete frames with different bay to height ratios (B/H1) are considered in order to evaluate the vulnerability of concrete structures equipped with metallic yielding elements (YE) against earthquakes. The nature of damages in structures is based on the rate of absorbed energy. Therefore, investigating the behavior of structures based on energy concept is considered as one of the most important methods toward the designed structures against earthquake load. It is required to concentrate the absorbed energy in some yielding elements, in order to reduce and/or avoid damages the main elements. One powerful technique to retrofit existing structures and seismically design new concrete structures is the use of metallic yielding dampers. The metallic dampers function similar to a fuse by deforming during earthquake, which subsequently can be replaced with new ones. In this study, parametric studies based on static analysis are carried out to determine the best place and angle of these elements in the frames. Furthermore, the responses of these frames against three earthquakes are presented and the comparison of results is performed. It is revealed that yielding element can dissipate up to 60 percent of earthquake energy in a concrete reinforced structure.

In this paper, a General Hybrid Cellular Automata (GHCA) model is hybridized with two of the most reliable heuristic search methods, namely Genetic Algorithm (GA) and Ant Colony Optimization Algorithm (ACOA), for the simultaneous optimal design of layout and size of pumped and/or gravity sewer networks. GHCA model is recently proposed by the authors for the optimal size determination of the sewer network with fixed layout. The model has shown to be able to optimally design pumped and/or gravity sewer networks, if required. In proposed hybrid models, the heuristic search algorithms are used to create trial layout for the network while GHCA is used to design the network by determining the pipe diameters, pipe slopes, drop height and pump height, if required. An ad-hoc engineering based method is used to determine feasible layouts by GA, while a Tree Growing Algorithm (TGA) is used to construct feasible layout using ACOA. The proposed hybrid models are tested against two benchmark sewer networks and the comparison of results to those of some existing methods indicates that proposed models, and in particular the ACOA-GHCA method, are more efficient and effective than some alternative methods for the optimal design of layout and size of sewer networks.