Journal of Numerical Methods in Civil Engineering
Volume:7 Issue: 3, Mar 2023

The spread of different material processing technologies has led to the novel methods developed for reinforcing structural members. One of these approaches is to add the carbon nanotubes (CNTs) with different distributions through the matrix phase of composite materials to improve its properties. Due to superior properties such as lightweight and high values of elastic modulus, elastic strain, and failure strain, CNTs can be used to reinforce structures and elements. The present paper aims to investigate the effect of adding CNTs as reinforcement of matrix on the buckling capacity of columns. The meshless local Petrov-Galerkin (MLPG) method is applied for buckling analysis of CNT-reinforced columns. Since the MLPG method uses some scattered nodes through the domain and boundaries for discretization (rather than the meshing), the functionally graded (FG) variation of material properties can be conveniently modeled under the influence of reinforcing elements (CNTs). Four types of volume fraction exponent functions are considered for modeling the FG variation of the CNT volume fraction to examine the effect of CNTs distribution on the buckling capacity of the column and determine the most optimal distribution of CNTs. Effective mechanical properties of the CNT-reinforced column are estimated based on the extended rule of mixture. Results show that reinforcing the polymer matrix with a low volume fraction of CNTs with appropriate distribution can significantly increase its buckling capacity. Using the obtained results, one can determine the best distribution pattern of CNTs in the longitudinal direction of the column at various boundary conditions.

In this paper, the seismic performance of reinforced concrete moment-resisting frame with cold-joint subjected to monotonic lateral load has been studied numerically using Pushover analysis. Two modes of fracture may occur for cold-joint in a frame subjected to in-plane loading. The modes are Mode-I (stress orthogonal to the local plane of the crack surface) and Mode-II (stress parallel to the crack surface but orthogonal to the crack front). In order to model cold-joint and verify its behavior in mode I and mode II fracture mechanics, first the three-point bending beam with an initial notch in the middle of the span and then the S-shaped specimen, used in the push-off test, have been modeled and validated. Furthermore, a single-story single-span bare frame has been monotonically modeled at first and validated by laboratory results. Then cold-joint has been added to this frame and analyzed. Moreover, to investigate the effect of the number of spans, the considered frame has been analyzed with two and three spans in both monolithic (MJ) and with the cold-joint (CJ) statuses. In order to investigate the seismic performance, parameters such as ultimate lateral capacity, stiffness, and ductility have been evaluated. The results of this study show that in general, the presence of cold-joint in the frame has little effect on the ultimate lateral capacity and stiffness but has a significant impact on the ductility of the frame.

Tensegrity structures have a high degree of indeterminacy. Occurrence of initial partial failure at one point of these structures can lead to the propagation of failure throughout the structure. One of the influential factors in the propagation of initial failure is the initial starting point of failure. The first failure can occur in a member that is considered as "critical member" and causes further damage to the structure, or it can occur in a member that has caused minor damage to the structure and maintain the overall stability of the structure. Identification of critical members in tensegrity barrel-vaults, due to the application of these structures in the roof covering of meeting halls, passenger terminals, industrial halls and aircraft hangars, etc. can lead to important and effective results in preventing the occurrence of progressive collapse and possible damages. Therefore, in this paper, the critical members of a two-layer tensegrity barrel-vaults consisting of square simplexes are identified by performing nonlinear dynamic analyzes using Abaqus software. Abaqus software uses the Model Change settings to simulate the initial failure. The stability of the structure under the dynamic effects of failure of different members is investigated and finally, the critical and non-critical members is introduced. It was found that failure of members of the modules are closer to the center of the structure in the longitudinal direction of the barrel vault show more critical behavior than the members of other modules. It was also observed from the results of the analysis that members with maximum stress are not among the most critical members.

These days, there is more need for natural air conditioning, which means there is more demand for air conditioning by open windows. Perhaps this is a reaction to the “Sick Building Syndrome” that is frequently used to describe irregular HVAC use. In the buildings, implementation of such mechanical systems to improvise a continuous comfort shows the lack of awareness and no consideration towards environmental issues including the enormous energy wastes. The results of all the conducted research conclude that the façades require a greater design in a way that is well equipped to encounter the elements including wind, rain, heat, and humidity. In this regard, Dual Skin Facades, which have recently become widespread in European architecture, provide the possibility of natural ventilation while regulating sound, wind, and rain. Heat, cold, light, wind, and outside noise may all be adjusted and compensated with Dual Skin Facades, allowing residents to be more comfortable without energy losses. The purpose of the following paper is to perform a numerical investigation of natural air conditioning in various Dual Skin Façade systems. The buildings under consideration are located in Iran's "Hot and Arid" climate in the city of Kerman, and they will benefit from natural air conditioning in the most months of the year. Also the parameters impacting the flow field, such as velocity and temperature in winter and summer, as well as throughout the day and night, were studied in this study for various opening sizes. The results of modeling showed that regarding the climatic conditions, the appropriate selection of the dual skin facade system, the air-gap width, the ventilation method, the location, and the dimensions of the openings, significantly made the buildings with dual skin facade unnecessary from mechanical heating and cooling facilities. And leads to energy saving.

The main goal of this research is the performance evaluation of the sampled moment-resisting steel structure against 3D simulated blast loading. In the first stage of the present research, the numerically simulated blast wave is verified by comparing with the relevant renowned numerical and experimental previous researches. In the second stage, the sensitivity of blast-induced pressure to the finite element mesh size and the surrounding air cube dimensions are investigated considering the 3D one-story building block with real dimensions based on Computational Fluid Dynamics (CFD) using AUTODYN hydrocode. The innovation of this stage is to present the optimum mesh size and air cube dimensions for the numerical results compared with the relevant empirical relationships toward the realistic simulation of blast-induced pressure on structures. Finally, in the last stage, the performances of two seismically-designed buildings with 1 and 10 stories against the achieved numerical blast-induced pressure time histories and the empirical formulations, based on the UFC 3-340-02 guideline, are studied. To assess the structural performance, the sampled buildings are modeled using the finite element tool OpenSEES. Performance assessment of sampled structures reveals that empirical formulation of blast loading will lead to underestimation of structural response, especially for the lower scaled distance scenarios.

This paper analyzes freight production and attraction and their relationship with traffic analysis zone (TAZ) features. The effects of some parameters on the production and attraction of industrial, agricultural and livestock, food, and fruit and vegetable freight were evaluated using over 300 explanatory variables, i.e., land-use types, the numbers and areas of businesses, the characteristics of residents and employees, employment, land price, vehicle ownership per capita, and road network, and TAZ descriptors. The 2019 comprehensive master plan of Shiraz, Iran, in 325 TAZs was employed. A vehicle survey and roadside interviews were used to collect data in three cordons involving 143 stations. Vehicles of different types were counted in the vehicle survey, and the roadside interview forms included questions on the travel time, vehicle type, vehicle capacity, freight amount, freight type, and travel origin and destination. Then, the freight origin-destination (O-D) matrix was constructed. To evaluate the effects of variables on the production and attraction of industrial, agricultural and livestock, food, and fruit and vegetable freight using aggregated data in the TAZs of Shiraz, Iran, for different freight, modeling was performed based on minimizing the residual sum of squares, proposing a total of eight models. The adjusted coefficient of determinations (adjusted R2) was calculated to be larger than 0.55 for all eight models. In addition, the models were found to have root-mean-square errors (RMSE) below 130.

In the context of increasing aging in the cities, elderlies with different characteristics such as sociodemographic, mental, and physical problems may face many barriers to their mobility. We need new mathematical models to understand and predict how different factors affect the subway system, which helps older adults to eliminate their obstacles and experience a flexible and independent trip while using the subway system. This research provides a comprehensive methodology for identifying the factors and calculate their impact on subway usage in three steps, namely survey design, model estimation, and forecasting subway usage by elderlies with different characteristics. To achieve this purpose, we use stated preference data gathered from elderly people in Tehran during April and May 2021. To estimate the model, we calculate the elderly’s attitudes and features toward subway choice and anticipate subway usage through a hybrid discrete choice model. The findings from the case study indicate that improving mental satisfaction followed by facility and service coverage satisfaction and education will increase the probability of elderly’s subway usage. By contrast, physical problems, staff services and lack of facilities, aging, illness, and high income had adverse effects.

Joints, which are usually located in the abutments of dams, play a vital role in the seismic stability evaluation of arch dams. This paper presents a comprehensive numerical investigation of the influence of uplift pressure in joints on the seismic response of an arch dam, with a focus on the interaction between the dam and the rock wedges. For this study, the Bakhtiari arch dam, having one rock wedge at each abutment, was chosen as a case study, and three distinct finite element models of the dam were developed. Three components of El Centro were applied to the dam's foundation, and the influences of dam-rock wedge interaction on the crest displacement time history and tensile damage of the arch dam were investigated. Four different scenarios were taken into account. The results indicated that taking uplift pressure in joints into account has important effects on the dam responsesWedge;Arch dam.