Scientia Iranica
Volume:28 Issue: 2, Mar-Apr 2021

Estimation of bridge backwater has been one of practical challenges in hydraulic engineering for decades. In this study, Genetic Programming (GP) has been applied for estimating bridge backwater for the first time based on the conducted literature review. Furthermore, two new explicit equations are developed for predicting bridge afflux using Genetic Algorithm (GA) and hybrid MHBMO-GRG algorithm. The performances of these models are compared with Artificial Neural Network (ANN) and several explicit equations available in the literature considering both laboratory and field data. Based on five considered performance evaluation criteria, the two new explicit equations outperform the ones available in the literature. Furthermore, GP and ANN achieve the best results in favor of four out of five considered criteria for train and test data, respectively. To be more specific, ANN improves the MSE and R2 values of the explicit equation developed using GA by 44% and 12% for the test data while GP enhances the corresponding values by 62% and 9% for the train data. Finally, the results demonstrate that not only artificial intelligence models considerably improve bridge afflux estimation than the explicit equations but also the suggested equations significantly improve the accuracy of the available explicit ones.

The worker’s absence considerably affects the performance of the labor-intensive construction projects. Identifying the worker’s absence pattern assists construction project managers in preparing the proper project organization, reducing the absence rate, and improving the project performance. Despite its critical role, no study has investigated the absence pattern in the construction industry in Iran. This study addresses this gap by identifying the worker’s absence pattern and providing recommendations to reduce the absence rate. First, a comprehensive literature review is conducted on the impacts and influential factors of the worker’s absence. Then, a questionnaire-based survey is designed and distributed among project managers, work supervisors, and human resource experts in different construction companies. The absence rate of seven percent achieved for the construction industry in Iran is among the high rates compared to the rates reported for other countries. The organizational policies, the national holiday season and the size of the working groups are among the main influential factors. Enhancing teamwork spirit, enforcing severe implications for the worker’s absence, and increasing managers’ site visits are among the recommended policies for reducing the absence rate. The identified pattern in this research is applicable for evaluating and improving the performance of construction companies in Iran.

Despite appropriate design of beams under bending and shear, the deflection of long steel beams usually exceeds the allowable range, and therefore the structural designers encounter challenges in this regard. Considering significant features of the cables, namely, low weight, small cross section, and high tensile strength, they are used in this research so as to control the deflection of beams. In this study, for the first time, theoretical relations are developed to calculate the increase in pre-tensioning force of steel cables under external loading as well as the deflection of steel beam with different support conditions and different patterns of cable. Moreover, required cross-sectional area of steel cable has been calculated to reach allowable deflection in steel beams with different support conditions and different patterns of cable. The obtained results show that the theoretical relations can appropriately predict the deflection of beam with different support conditions and different patterns of cable. In this study, simply supported as well as fixed supported beams are pre-stressed with V-shaped and modified V-shaped patterns of the cable. According to the obtained results, the modified V-shaped pattern of the cable is more efficient than V-shaped pattern one.

Modal parameters of large civil engineering structures such as modal damping ratios (MDRs) are determined mainly by output-only modal identification. In this paper, MDRs of a double layer grid were obtained using output-only modal identification. For this purpose, a double layer grid constructed from ball-joint system was tested. Doing some random tapping on the structure, the acceleration response in multiple locations was measured. The acquired data was processed using output-only modal identification to arrive at MDRs. The MDRs corresponding to the first eight modes of the grid were extracted by five output-only modal identification techniques; namely enhanced frequency domain decomposition (EFDD), curve-fit frequency domain decomposition (CFDD) and three different methods of data-driven stochastic subspace identification. To determine the appropriate model order used in SSI methods, a sensitivity analysis was carried out and the resulting number of order was 200. The proper frequency resolution of 1600 was also determined to estimate the MDRs of the grid by EFDD and CFDD. The results showed that the MDRs of the grid, obtained from different methods, are in good agreement with each other. The grid has very low MDRs, as the MDRs of the modes measured from different methods varied from 0.06% to 0.11%.

The main structural elements of reinforced concrete (RC) bridges deteriorate with time under such uncertain hazards as scouring and corrosive conditions. In this paper, a multi-hazard framework is proposed to assess the performance of bridges subjected to the main effective uncertain natural hazards during their lifetime. In this assessment, the uncertainties associated with the combined effects of multiple hazards including pier scour, earthquake, carbonation, and corrosion are considered. Therefore, for each of the hazards, their severity relationships have been extracted over time, and the effects of these hazards on concrete elements are presented as resistance dimming parameters. The annual and cumulative losses due to these hazards in unit currency are estimated using the life-cycle costs. For decision making, the present value of the expected cumulative cost associated with the retrofit or design scenarios is evaluated using a cost-benefit analysis. The results for a case study bridge, using the proposed framework, indicate the significant impact of the different scenarios on reducing the expected value of damages or incurred losses due to multiple hazards.

Sheet piles are of general water retaining structures. The discharge flow rate beneath sheet plies is an important parameter in the design of these structures. In this study, the Gene Expression Programming (GEP) as an Artificial Intelligence (AI) method is used for developing a model to predict the discharge flow rate. The input parameters include the sheet pile height, upstream head and hydraulic conductivity anisotropy ratio. In order to achieve better performance, the flow rate is normalized and selected as an output of the model. A database including 1000 cases are created from the Scaled Boundary Finite Element Method (SBFEM) for the seepage beneath sheet plies is employed to develop the model. The GEP-based model predictions demonstrate a reasonable agreement with the simulated data, which indicates the efficiency of the developed model. The results of the sensitivity analysis indicate that the upstream head is the most influential parameter in the discharge flow rate beneath the sheet piles. Furthermore, the outputs of the parametric analysis show the reasonable performance of the model in the prediction of normalized discharge flow rate.

Nowadays, the benefits of continuous welded rails and engineers’ tendency toward such types of tracks have increased the importance of railways’ lateral stability. For increasing railways’ stability, lateral resistance development mechanism should be reinforced. One of the methods for reinforcing the passive pressures’ mechanism at sleeper’s end and, therefore, increasing tracks’ durability is the utilization of winged sleepers. In this paper, lateral resistance of conventional and winged sleepers is examined and compared using laboratory and field tests. The tracks’ lateral resistant force was measured by single sleeper push test and track panel loading test. In the laboratory, single sleeper push tests showed 101% increase in lateral resistance in the winged sleeper compared with the conventional sample. In the field test, the test track was divided into three parts, namely conventional sleeper part, winged sleeper part and mixed part. The lateral resistance of each part was measured by LTPT. In the field test, 96% increase in lateral resistance was obtained. Winged sleeper panels and mixed sleeper panels showed 71% and 59% resistance increase, respectively, compared with the conventional panel. By using winged sleepers in tracks, lateral displacements decreased by increasing the shoulder and crib ballast’s volume through the passive pressure mechanism.

In recent years, the studies have been focused on using the surface wave methods in determining the soil specifications. The surface layer of the soil with lateral variation was modeled at different angles in finite element software. The shot was applied on two sides of the geophone array and the seismic wave data were recorded by geophones. Using the windowing methods of different lengths and moving along the array, the various geophone data were placed in different windows. Next, for each windowing, the frequency-wavenumber spectrum was obtained using the double Fourier transform and then, the dispersion curve was plotted. In this regard, the variations in the resolution of frequency-wavenumber spectrum and dispersion curve were investigated for different window lengths. The results show that for the media with lateral variation at different angles, the dispersion curves could be obtained along the array and the location of the start and end of lateral variation along with the corresponding phase velocity range could be achieved with an acceptable accuracy, and the estimated phase velocity could be used as initial velocities in the inversion and specification of soil surface layers.

This paper aims to propose a framework by which decision-makers can evaluate and compare alternatives for sustainable island-based tourism development. The uncertainties and risks involved in information and judgment within the evaluation process are taken into account by using a hybrid approach, which combines the Delphi method, fuzzy set theory, and a discrete multi-criteria method based on prospect theory called TODIM (an acronym in Portuguese of interactive and multiple criteria decision making). The decision making model examines three different techniques of aggregating the viewpoints of different decision-makers and explores how the aggregation technique affects the ranking of the alternatives. To demonstrate the potential application of the proposed approach, it is examined for development of Hendourabi Island (Iran) for tourism. Results show that among the three development alternative plans, decision-makers prefer the medium-size development alternative, since it offers a balance between benefits of tourism market and costs of project development under an uncertain future. It also allows for adaptive management. Results also showed that the proposed approach which reduces loss regret in decision-making under uncertain future can be used effectively for planning the island development under an uncertain dynamic future considering the risk and uncertainty associated with human judgment.

In order to estimate the seismic performance of structures, performing incremental dynamic analysis, and obtaining fragility curves are essential. Since producing these curves is time-consuming due to performing a large number of nonlinear dynamic analyses, the selection of appropriate earthquake ground motion records which give reliable responses with sufficient accuracy is important. Due to the lack of a solid framework, the selection of an appropriate ground motion recordset is still a challenging problem. In this paper, the primary goal is to select a suitable set of records from a general set of records in order to reach reliable limit-state capacities prediction of structures. To achieve this goal, incremental dynamic analysis is conducted for an equivalent single degree of freedom under a general set of records, and an optimization algorithm is employed to solve the problem by minimizing the error between the mean incremental dynamic analysis curves of each selected subset and the mean incremental dynamic analysis curve of a general set of records. The fragility curves obtained by all records and selected ones are compared and the results show that the fragility curves corresponding to the selected records estimate the target fragility curves appropriately.

The increasing use of technologies based on Internet of Things in cars and other transportation vehicles, as well as innovations in tracking systems and spatial information systems, have created the opportunity to collect tolls on urban roads in a more intelligent, more efficient, and a wider way. Considering the cultural and infrastructure variables in different cities, different approaches have been designed for this purpose, but so far no work has been done in this area in Tehran. Therefore, in this research, a system of hardware and software based on the Internet of things was developed based on GPS / GSM for automated urban tolls in Tehran, which manages the location of a user's car and manages toll payments at any given moment. In addition, in this system, considering the cultural issues in the country, the infrastructure in the metropolis of Tehran, and important issues of the city, the trespass submission system is designed in accordance with the existing surveillance cameras and an infrared-based structure was used to reduce the burden of image processing in order to improve efficiency. The data obtained from this system will have more potential than only the urban toll management.