Structural Health Monitoring and Engineering Structures

This work proposes the weight optimization of a 10-bar truss structure using nine advanced optimization algorithms namely Rao-1 algorithm, Rao-2 algorithm, Rao-3 algorithm, self-adaptive multi-population Rao-1 (SAMP Rao-1) algorithm, SAMP Rao-2 algorithm, SAMP Rao-3 algorithms, quasi-oppositional-based Rao-1 (QO Rao-1) algorithm, QO Rao-2 algorithm, and QO Rao-3 algorithm. These Rao algorithms and their variants are simple and independent of algorithm-specific control parameters. The optimization problem is of a 10-bar truss structure that consists of ten design variables with 36 design constraints. The stresses induced in each member and the displacement at each node are considered as design constraints. The optimization is carried out for three different cases of search space. The results obtained using Rao algorithms and their variants are compared with the results obtained by other researchers and methods in previous studies. The comparison revealed that the Rao algorithms and their variants obtained better designs of the 10-bar truss structure with minimum weight.

This paper presents a convergence study and CPU time analysis between equilibrium optimizer (EO) and Cuckoo search (CS) algorithms. Both optimization techniques are used as an inverse problem to calibrate a finite element (FE) model of a frame structure based on measurements. Different iterations and populations to test the accuracy of both optimization techniques are provided for healthy and damaged frame structures. The investigated results have shown that EO had good convergence with less CPU time compared with CS based on the number of populations and iterations selected.

Due to the importance of preventing unexpected structural failures, vibration-based damage detection methods have been widely studied to monitor the health of various structures. These methods are considered as efficient and reliable non-destructive techniques for damage detection of structures. In this study, a novel model is developed to predict damage severity in beam-like structures based on the finite element method (FEM) and multilayer perceptron (MLP) neural network. In this way, empirical data are obtained using FEM, then MLP neural network is used to predict damage’s severity. The first five frequencies and severity of the damage of the beam are considered as inputs and outputs of the neural network, respectively. Based on the inputs and outputs, the network creates a nonlinear activation function and is trained to predict the severity of the damage. Results obtained indicate that the model created by the network can detect any single damage in beam-like structures with high accuracy (R > 0.9) by having natural frequencies of the damaged beam.

The present work presents the results of experimental investigation of semi-solid preparation billet of ADC12 Al alloy using a cooling slope. The experiments have been carried out following central composite design. Three-key process variables at five different levels (pouring temperature, slope angle, and length of travel of the melt) have been considered for the present experimentation. Regression analysis and analysis of variance (ANOVA) have also been performed to develop a mathematical model for particle size of evolution of primary α-Al phase using response surface methodology. Finally, the best processing condition has been identified for optimum particle size (48.27) as slope angle of 65°, pouring temperature of 580 ℃, and 300 mm length of travel of the melt. The effect of pouring temperature, slope angle, and length of travel of the melt were identified to find the most important effects.

GPS in the cable-stayed bridge monitoring system is used to provide overall deformation measurements of the bridge. During GPS data acquisition, data may be lost under the impact of various factors. This paper investigates the application of the artificial neuron network (ANN) method to recover lost GPS data under the influence of factors such as wind speed, air temperature, and stress of structure. Monitoring data of an actual cable-stayed bridge were extracted for study. The proposed method results are compared with actual monitoring data to evaluate the accuracy. These results indicate that GPS—RTK data supplemented by the ANN method completely ensure accuracy and reliability.

For existing stay cables, bending stiffness and boundary conditions at cable ends often differ from those of the design owing to the degradation of cable materials and complexity at the cable supports. This paper presents a method for vibration-based cable tension estimation using artificial neural networks (ANNs) regardless of the uncertainties of cable boundary conditions and unknown cable bending stiffness. Finite difference formulation of a discretized cable with rotational restraint ends is developed to generate datasets for training, validation, and testing in ANNs. The proposed method was applied to identify tensions in cables of an existing bridge as a case study. Results showed that the suggested that suggested methodology is highly capable of identifying cable tension with unknown cable bending stiffness and uncertain boundary conditions.

This paper presents the reduction phenomenon of the added damping in a stay cable caused by static wind loads acting on a cable with an external damper. First, an equation of motion of a sagging cable is derived that takes the consideration of dead loads including cable self-weight and static wind loads into account. Second, a finite difference formulation (FDF) for cable vibration is introduced to address the equation of motion and to determine the added cable damping. Third, the impacts of cable bending stiffness, damper support stiffness and various types of boundary conditions at cable ends consisting of hinged, fixed and rotational restraint ends on cable vibration characteristics are investigated. The results showed that in the presence of static wind loads acting on a cable, the global stiffness of a cable increases, leading to an increase in vibration frequency and a decrease in the added cable damping.

This paper presents the method for estimating the characteristics of the load-carrying capacity and displacements of semi-rigid steel frames with fuzzy variables. A nonlinear inelastic analysis method based on the refined plastic hinge method is employed to predict the load-carrying capacity and displacements of the structure since this approach yields the acceptably accurate results in much shorter analysis time compared to the plastic-zone methods. In addition, the nonlinear behaviors of semi-rigid connections are modeled by using the zero-length element and the Kishi–Chen three-parameter power model, and the generalized displacement control algorithm is applied to solve the nonlinear equilibrium equations. The α-cut method, where the lower- and upper-bounds are calculated by using the micro-genetic algorithm, is used to present the fuzzy characteristics of the structure. A semi-rigid two-story space frame example is studied. The numerical results show that the proposed method yields better results with much smaller required structural analyses compared to the Monte Carlo simulation method. In addition, the load-carrying capacity and displacements of the frame are the fuzzy variables, and the proposed method is reliable, efficient, and accurate.

In this paper, the authors present an optimization problem of nonlinear inelastic rigid steel frames that considers both load combinations and frequency constraints for the first time. Direct analysis-based on the beam–column approach is employed to account for the non-geometric and nonlinear behaviors of the structure. The objective function is the total cost of the structure which is simplified as a function of total weight. The constraints of the optimization include the strength and serviceability conditions, and structural frequency requirements. An improved differential evolution algorithm is employed to solve the proposed optimization problem that effectively reduces the number of structural analyses. A three-bay five-story planar frame is studied to illustrate this work. The numerical results show that the optimization design of structures considering both load combinations and structural frequency constraints improves the performance of the structure. Furthermore, the proposed optimization problem was more complicated than the optimization problem without considering structural frequency constraints.

This paper presents damage identification method for 10 and 25-bar plane truss structures based on inverse problem. Models for both structures are built in MATLAB software using FEM. A new optimization technique investigated recently, namely a chimp optimization algorithm (ChOA), is used. The objective function is based on measured and calculated frequencies and mode shapes, and used to analyse the convergence study of the fitness and damaged elements. Modal assurance criteria (MAC) are used to represent the mode shape in the objective function. The ChOA provided good results for both structures after a few iterations.

Nowadays, optimization problems have been one of the most challenges for solving real-work problems. Because of the importance of practical problems in other fields, more and more intelligent search algorithms have been proposed. Each algorithm has both advantages and disadvantages. It is difficult to find a suitable algorithm to solve real problems. In this article, the comparison of four robust algorithms including two classical algorithms such as particle swarm optimization (PSO) and artificial bee colony (ABC), and two algorithms which are presented recently, i.e., cuckoo search (CS) and gray wolf optimizer (GWO). To make a diversity in comparison, the first ten benchmark test functions were chosen to compare items such as convergence rate and accuracy of the algorithms. Moreover, the high dimensions (n = 30) in the search space are also examined to evaluate the effectiveness of the algorithms in the variable dimension problems. Through the results achieved, an algorithm which is achieved a balance between the convergence rate, and the accuracy level is submitted.

Vibration-based damage detection methods are widely used to monitor the health of structures. Various methods presented in the literature have different performances. Therefore, the use of a proper method can be useful to find correctly and fast the location and severity of damage in structures. The purpose of this study is to introduce a novel objective function in the optimization problem of damage detection of structures based on the residual force method (RFM) and finite element method (FEM). Then, the proposed objective function is optimized using two algorithms called particle swarm optimization (PSO) and genetic algorithm (GA) to compare their performances in damage detection of a beam-like structure. The effectiveness of two algorithms is evaluated by detecting the location and severity of a damaged beam for several damage scenarios. Results show that the PSO algorithm can predict the location as well as the severity of damage in beam-like structure in both single and multiple damage scenarios better than the GA algorithm based on the accuracy and convergence to the optimum solution.

This article studies the main features of wave transmission of a semi-rigid structure, i.e., a soil–cement column. A numerical model of the rigid pile is created, and its response due to a dynamic excitation applied on the pile head is tentatively analyzed. The study is in the near field and the far field. In the near field, the soil–structure interaction is replaced by the link elements, including a q–w and damper at the pile tip and t–z spring along the pile shaft. For studying the semi-rigid structure, the stiffness of the pile model is intentionally reduced to the same extent as normally practiced in the real construction works and the wave propagating characteristics is examined inside the pile shaft and outside to the surrounding soil medium. The defects are deliberately created including necking 50%, bulging 20% in diameter, low material rigidity (one-third of the original E value); and the velocity response of the pile/column could be examined. Pile impedance is investigating between the theoretical curves and numerically computed ones. The results indicate that the defected semi-rigid column shows no change in the impedance, some high frequencies dominate, and the velocity decreases from head to tip. In the far field, by considering the vibrational transmission from the defected pile/column shaft to the outside medium, the results indicate that velocity of the responsive vibration from the semi-rigid column propagates and attenuates nearly to zero at the distance not farther than 20 m. This study partially points out the difficulty in applying the impact test to the semi-rigid structures and the effects of each kind of defect of piles and columns on the responsive velocity of the ground surface. Some non-destructive techniques in diagnosing the defects of the semi-rigid structures like soil–cement columns are strongly suggested.

The shear strength of concrete beams strengthened with embedded through-section (ETS) fiber-reinforced polymer (FRP) bars considering bonding-based approach is investigated in this study. A series of pullout tests was firstly collected to assess the bond response between the ETS FRP rods and concrete. An analytical method for assessing the ETS bars–concrete interfacial profile is then identified. The bond model is then utilized to propose a simple method to predict the contribution of the ETS shear strengthening system. By using bonding-based method, an attempt is made to estimate the ETS FRP shear contribution via the mechanical approach and the regressing approach. The results obtained from this study show that the bonding-based method can provide reasonable predictions for the ETS FRP shear contribution. Further, through model validation against the experimentally accessible data base, the bonding-based method incorporating with the mechanical approach exhibits the powerful estimations of the ETS shear resisting forces in the ETS-strengthened beams.

This paper aims to analyze the dynamic behavior of structural components affected by deep localized damage. In order to obtain frequency values at different degrees of damage, beam models undamaged and damaged by notches were tested through free vibration tests. The experimentations are performed both with homogeneous beam model and reinforced concrete (RC) beam. The beam models have been notched with different damage degree; the damages have been concentrated at the midspan zone. The experimental campaign is organized with the aim to obtain the envelope of frequency response functions (FRFs), that is elaborated and correlated to the degree of damage both for homogeneous and for RC beam models. The behavior of beams with notches under free vibration has been also studied adopting finite element method (FEM). The numerical analysis has been developed assuming boundary conditions adopted in the tests: simply supported beam for homogeneous model and with free-free ends for RC beam model. Finally, it shows a comparison of experimental and theoretical outcomes.

Cracking in concrete is one of the main reasons to decreasing both the quality and the service life of buildings. This study mainly evaluated the effect of fly ash on the length changes and the cracking resistance of concrete. High CaO fly ash was used as a replacing cement material by decreasing the cement in the ratio of 30% by weight. Concrete mixtures with a controlled slump were tested in this study. The experiment programmes included on a compressive strength, length changes under free and internal restrained conditions and a cracking resistance according to ring test of concrete in the laboratory. Compressive strength of concrete is decreased by using fly ash. However, the compressive strength of concrete containing fly ash continually increases until later ages when compared to that of concrete without fly ash. Both free shrinkage and restrained shrinkage of concrete were reduced in the case of fly ash concrete. Especially, the use of fly ash significantly delayed a cracking age of concrete under the external restrained condition according to ring test as compared to cement only concrete.

This study numerically investigates the dynamic response of concrete-filled double skin tube segmental columns (CFDST-SC) under blast loads. A numerical model of the CFDST-SC developed in LS-DYNA is verified against the available data on the open literature. The dynamic response of the CFDST-SC under different blast load scenarios is then compared to a monolithic CFDST. It is found that owing to the opening of the segment joints, the CFDST-SC exhibits less concrete damage, less flexural cracks, and smaller residual displacement than its counterpart. Concrete crushing at the segment joint corners including bottom, top and middle joints are normally observed on the CFDST-SC while there are flexural cracks in both sides of the CFDST. However, the CFDST-SC normally exhibits higher maximum displacement due to the lower lateral stiffness as compared to the monolithic one. Increasing the blast pressure on the columns by increasing the mass of the TNT charge, more joint openings are observed on the CFDST-SC which leads to the increase of the tensile force in the tendon. Therefore, the tensile fracture of the tendon is likely to occur in the CFDST-SC. Furthermore, the effect of three critical parameters, i.e. number of segments, hollowness ratios, and steel thicknesses on the blast performances of the CFDST-SC is also investigated in this study.

The goal of this work is to assess the effect of technology factors on superplastic deformation of AA7075 sheets. The factors considered include strain temperature T, initial strain rate $$ \dot{\varepsilon } $$ ε ˙ , while the response is maximum superplastic elongation (δ). Firstly, the experimental follow thermomechanical regime have determined, the result obtained is microstructural features of material with fine stable and grain size (~13 µm). Subsequently, a set of experiments were conducted in superplastic conditions such as strain temperature from 470, 500, 530, 550 °C and the initial strain rates from 5 × 10−4 s−1, 10−3 s−1, 1.5 × 10−3 s−1. Finally, an assessment of the effect of process parameters was used to determine the best superplastic deformation conditions. The results indicated that the maximum superplastic elongation of 280% could be obtained at 530°C and 10−3 s−1 strain rate. This work is expected as a significant contribution to determine a reasonable technology regime for superplastic deformation of AA7075 aluminum alloy.

One of the reasons making cracks in the concrete structure is due to thermal problems. Thermal cracking mainly relates to the temperature development during the hydration process and the variation in ambient temperature. In actual construction conditions, the temperature differences between the inside zone and the surface of concrete blocks are the cause of thermal cracking. It is noted that these differences in temperature may vary in different parts depending on the shape, size, and operating conditions of the structure. Especially, the formation of thermal cracks occurs not only in mass concrete structures but also in any others. Additionally, these cracks may exist in structures at both early age and extraction stages. Thermal cracks may affect the integrity of concrete structures and cause costly maintenance. This article presents an overview of thermal cracks in concrete structures with the basic issues to be understood. The causes of crack formation in concrete structures have been analyzed and evaluated in detail by using Finite Element Method (FEM) and experimental study. Also, the review analyzes the basic measures to minimize the risk of thermal cracking in concrete structures. These measures take notes and establish appropriate plans to prevent cracks in design and construction processes. Besides, the conclusion mentions the new approach for further study in this field.

Expanded PolyStyrene concrete (EPS-C) is known as a lightweight material. The grade of EPS-C has lower strength than conventional concrete but has their advantages such as lighter, higher thermal, and better sound insulation properties. Thanks to its characteristics, the EPS-C could be used for a wide range of applications in civil engineering. Since the last decades, EPS-C has been studied and applied in the structural building component. In this article, an experimental campaign has been carried out, aim at studying the flexural behavior of reinforced lightweight concrete slabs using recycled expanded polystyrene on load-bearing capacity and deflection. Specimens with the same recycled expanded polystyrene contents were produced and tested herein to determine the mechanical properties of the EPS-C. Three full-scale EPS-C slabs were then subjected to four-point bending flexural test. Based on Eurocode 2 requirements, the result showed that load-bearing capacity of 100 mm thickness slab, spanning 2 m, reaches 4 kN/m2 with EPS-C density lower than 1200 kg/m3. This value of load-bearing capacity is approximately 45% of the ultimate load. The findings reveal that it is possible to use the prefabricated reinforced lightweight EPS-C slab in civil engineering applications.

This paper focuses on linear vibration analysis of uncracked and cracked pipes. Finite element analysis (FEA) of the pipes is done by using the ANSYS software where three mode shapes have been extracted and plotted for different depths of crack, situated in the midpoint of the pipe. An experimental analysis has been also done to validate the developed model. A comparison between the obtained results from cracked and uncracked pipes haves been done to identify the influence of the crack’s depth on the behavior of the pipe. Various specimens of pipe’s configurations have been analyzed, and the sensitivity of the used mesh has been also studied. These aspects play an important role in the determination of the real response of the pipes where the measured frequencies depend on the significance of the crack’s depth and the chosen type of mesh.

This study investigated cracking behavior of reinforced concrete (RC) beams repaired in flexure by steel fiber-reinforced concrete (SFRC) composite. The deformation mechanism of the members subjected to a corrosion process was first examined. SFRC materials were then fabricated to rehabilitate deteriorated zone of corroded RC beams. Afterward, the bending tests were monitored to investigate cracking properties of repaired beams. The load–crack width response, effects of steel fiber volume in SFRC, and corrosion degree on the test specimens were assessed to achieve new findings as follows. The shear behavior of corroded beams changed beam action to arch action. The members subjected to 17%-corrosion degree furnished smaller crack width than that for members with 12%-corrosion degree. Increasing load, the SFRC-repaired beams failed primarily by the detachment of SFRC to old parts (concrete and steel). The load capacity of the beam leveled by 17% of corrosion degree and repaired using SFRC contained 1.5%-steel fibers was approximately 10% greater than load-carrying capacity of the other tested beams. Additionally, the beams subjected to high corrosion degree repaired by large fraction of steel fibers in SFRC resisted maximally the crack opening.

Strain hardening fiber-reinforced cementitious composite (SHFRCC) is a new generation of cement-based material that exhibits high tensile strength, high ductility, and multiple microcracking behavior under direct tensile test. SHFRCC is expected to be a promising material for marine structural applications. This paper intends to evaluate durability of SHFRCC exposed to chloride environment by measuring electrical resistivity. Two types of steel fiber, hook and twisted fiber, were used in producing SHFRCC with a volume of 2%. The uncracked and precracked SHFRCC specimens were subjected to wet–dry cycling in 3.5% sodium chloride solution. The electric resistivity was measured at 0, 7, 14, 21, 49, 70, and 98 cycles. The results showed that the electrical resistivity reduced significantly as the number of chloride cycles increased. The electrical resistivity of SHFRCC was strongly dependent on the fiber type and the width of microcracks. SHFRCC with twisted fibers produced lower electrical resistivity at all measured cycles than those with hooked fibers. The precracked specimens exhibited much lower electrical resistivity than uncracked specimens. Furthermore, the measurement of electrical resistivity could deliver valuable information with respect to chloride and moisture penetration into uncracked and precracked SHFRCC.

This paper aims to study the effects of measuring errors during the process of structural health monitoring (SHM) on the reliability index (RI) of a building. A six-story plane frame model of a flexible long-span building is studied in which defects are randomly occurred both in the superstructure and its foundation. The response of the building due to different damage patterns would be collected, analyzed, and the outputs as raw data sending to the measuring the system would be deliberately changed to obtain a perturbed data set of signals. The RI of the system would be computed using the first-order reliability method (FORM), and the effects of modeling and measuring errors (noises) on the index would be examined. These uncertainties both in aleatoric aspect (load, section, limit stress and quality of material) and epistemic (modeling device instrumentation and signal transformation method) aspect affect remarkably the reliability analysis. Findings are the order of importance of each factor involved, the percentage of contribution to the RI and an approach for computing the RI of the structural system using the Taylor series expansion. Some recommendations for the measuring procedure, the variation in frequency of the response, and the change in the performance of the building concerning various kinds of defects are studied and the RI in terms of different damage patterns and variables (i.e., kinds of errors) are suggested.

In the bridge structure, the superstructure attracts much attention from scientists in the world, while the substructure also plays an essential role in the load-carrying capacity. Among the parameters of the structure, the vibration parameters reflect relatively clearly the actual conditions of the structure. The natural vibration frequency is made up of two main parameters which are the modal participating stiffness and the modal participating mass in that frequency. In order to better understand the behavior of bridge piers, the paper proceeds to determine the actual modal participating stiffness, the modal participating mass of the beam corresponding to this vibration case. This paper using the Rayleigh method analyzed for the case of simply supported beam bridge pier, the results modal participating mass and stiffness obtained by the proposed method are compared with the original assumptions and received high-reliability results.

A billboard is present in many localities in Vietnam, with the typical form is a large surface and structure made of steel, so the main load is wind load and it can be corroded. In the southern region of Vietnam, during the rainy season, there are usually thunderstorms accompanied by strong winds, causing many billboards to be damaged. To avoid such damage, the structure of the billboard, in addition to the standard design, must be assessed for reliability by random variables such as wind load, material strength, and cross-section geometry. This study analyzed the reliability of billboard structure according to random design parameters using Monte Carlo simulation. The results show that there may be a high risk for the safety of the work of the billboard, even if the structures are implied by the design code.

This paper introduces a newly proposed “loss factor function (LF)” and its application to bridge condition assessment based on the structure monitoring data. First, a viscoelastic model is integrated in the equation of motion of a beam. In this model, material characteristics contained two components such as elastic modulus and viscous coefficient. Viscoelastic model, different with linear elastic model, is nonlinear, and therefore, it reflects real state of the structure precisely. Secondly, LF is calculated from amplitudes and frequencies of power spectral density of random vibration signals and is concerned with mechanical parameters in detecting structural changes. Vibration of beams was investigated in case different random excitations are used to simulate ambient load in the process of varying material properties. Based on theoretical analysis and simulation result, this study reveals more effective in condition assessment of structure.

The stability of tunnels is influenced by the diversity of ground properties and characteristics of the support systems for tunnel construction. Tunnel excavation in the ground causes displacements and creates possibilities for deformation in the tunnel’s interior. This distortion may result in changing the stress–strain of the vicinity rock in the tunnel. This paper provides a stability analysis of tunnels using distortion strain energy theory for the analytical design of the tunnel providing another understanding of the stability of the tunnel.

Rapid urbanization in Vietnam creates an increasing demand for expanding both above ground and underground areas in the urban cities. Urbanization brings several challenges such as inadequate cultural spaces, environmental pollution, and overlap of the utility systems. Urban processing in Vietnam faces to the lack of a unified-based policy for planning in cities in depth. This paper analyzes possible multi-utility tunnel applications for Vietnam’s urban cities regarding urban characteristics, planning challenges, and management construction of multi-utility tunnel (MUT) for urban sustainability.

Internet of Things (IoT) is at the top of the most popular technology in the industry, also applied to many aspects of life. In that case, data collection is one of the key processes in every IoT system. In order to collect data, we need a data collection system that facilitates the process of data collection in real time, allowing specific, structured information to be gathered in a systematic fashion, subsequently enabling data analysis to be able to conduct the best analysis and prediction on the collected data. Most of the data collection solution today relies on specialized electronic devices located far apart and then perform data collection and analysis based on a fixed schedule. In this paper, we are going to present the results of research and build an integrated monitoring system (IMS) based on IoT technology. Our objective is to propose a solution to connect IoT sensors, digitize data and exploit the existing network infrastructure to conduct data exchange on cloud computing platforms. The collected data in IMS can be used to cater to the different requirements from the various environment.

Structural health monitoring system (SHMs) for bridge involves the use of sensor types to continuously monitor bridge responses under the effects of load types. The database of SHMs is used to analyze and diagnose the health of bridges to identify reasonable maintenance strategy. Structural health monitoring technologies today often use a combination of sensors and IoT technology to track structural responses in real time. This paper summarizes the issues of designing, installing the monitoring system, structural diagram of SHMs, analyzing and determining health warning thresholds of three bridges: Thuan Phuoc, Dragon and Tran Thi Ly across the Han River, Da Nang city. The results obtained from this three-bridge monitoring system can be referenced for the design and operation of long span bridge monitoring systems in the future.

In order to cope with the safety hazards in the long-term operation of the steel structure of platform canopy in advance and reduce maintenance cost of the platform canopy, a health monitoring system is developed in this research. With the in-depth study on the health monitoring system of steel structure for railway platform canopy in active service, the efficiency of BIM model loading process is a key problem for further utilization. As the size of the data increases continuously, the performance of the system decrease tremendously. In the system proposed by this research, BIM model data is stored in the external database in advance, which can greatly reduce the loading time of BIM model by adopting optimistic method. In addition, when the health system monitoring is running, users can interact with external databases at the same time. Based on the size of the query data volume and the frequency of repeated use of the data volume data query operation and data storage space are deeply optimized. In order to avoiding unpacking and boxing during the operation, the data is sorted and saved with a novel efficient pattern. Through the design and optimization of the system, lightweight network communication of the health monitoring systems is realized, and furthermore, the safety and stability of the system are also guaranteed. This research provides a new idea to improve the overall performance of a railway canopy monitoring system.

The motivation of this study is to present a numerical simulation for identification of the loss of prestress force in prestressed concrete structures using electro-mechanical impedance responses. In order to achieve the objective, the following approaches are implemented. Firstly, the theories of electro-mechanical impedance responses using PZT (Lead Zirconate Titanate) sensor and four damage indices based on the change in the impedance responses are outlined. Secondly, a finite element model of prestressed concrete beam’s cable anchorage system is simulated by using ANSYS software. The loss of prestress force is investigated with different levels. The reliability of the numerical results is verified by comparison to pre-published experimental results. Finally, the damage indices are determined to identify the loss of prestress force in beam. The results from this study show that the impedance-based damage detection method is high effectiveness for monitoring the loss of prestress force in prestressed concrete structures.

Steel slag has been classified as an industrial waste formed from steel-making process. A large amount of steel slag in excess is really an environmental risk. Therefore, widening the application of steel slag has highly attracted interest from many researchers. In this study, some mixtures, including steel slag and crushed stone (size of 0–5 mm), were designed and examined for applying them at road-pavement base. The ratios of steel slag/crushed stone were tested as follows: 100/00 (named S1.0C0.0), 80/20 (named S0.8C0.2), 70/30 (named S0.7C0.3) and 60/40 (named S0.6C0.4). The S0.7C0.3 produced the best performance in terms of resilient modulus and CBR value. Besides, some material properties of the mixtures were also measured and reported.

The article mentions a case in situ on slope stability solutions with 60 m high for the infrastructure of Nhan Co Industrial Zone, Dak Nong, Vietnam. The embankment is finished in February 2020, obstructing the troughed tributary streams of about 14 ha. The retaining wall at 6–8 m high and the embankment has 5 benches with grade of side slope m = 1:1.50 for each one. The first bench is adjacent to the top filled by closed cement concrete slabs, whereas the other times using the open ones; the materials are mainly K90 well-compacted basalt in place. On April 4th, 2020, there is a 150 m-in-length, 70 m-in-width and 40 m-in-height landslide [1]. The pit crest has a 15-meter subsidence. The landslide is moved out of the embankment slope covering the wall. The expected movement is about 10–15 m long. The survey data is made right after the landslide showed that the physical properties of the embankment have changed, especially the groundwater level rises [2]. The groundwater flowing into the site is about 2.6 m3/day/m of the retaining wall. The analysis results show that the safety factor (SF) of the embankment is stable with SF = 1.0564 and it is unstable when the groundwater level rises in rainy seasons with SF = 0.8420. We have proposed the solutions for underground drainage and slope stability of the project to put into use and operation.

There are a lot of soft grounds in Ho Chi Minh City that make a few problems when expanding and developing infrastructure. Therefore, the first steps have to improve the soft soil to make strong background for the building that makes avoiding some accident and unstability. Preloading with prefabricated vertical drains (PVDs) is a popular improvement method that was applied in many big projects is help to increase drainage in the underground. And the most important factor to predict the consolidation process is coefficient vertical and horizontal of consolidation. The paper is focused to analyse the relationship of two coefficient and hence find these specific characteristics for soft soil in Nha Be District, Ho Chi Minh area.

Currently, shaft-grouted bored piles are being used more and more widely for high-rise buildings in Vietnam thanks to the increase in bearing capacity compared to non-grouted piles of the same size. However, estimation of the bearing capacity of this type of pile has not been prescribed with national standards and depends entirely on the experts of contractors. This study aims to analyze the increase in bearing capacity of bored piles using the shaft-grouting method by comparing the results from the Osterberg cell tests of a project in Ho Chi Minh City area. These tests were conducted on two full-scale and fully instrumented trial piles, of which one is non-grouted and the other is shaft-grouted. The results show that the shaft-grouting method increases the shaft resistance of the corresponding pile section by more than 110%, which increases the pile’s bearing capacity. In addition, the result from the test of the shaft-grouted pile was back analyzed to suggest a simple model to estimate the unit friction resistance in correlation with the standard penetration test (SPT) results. The correlation fs = 8.76NSPT can be used to reliably estimate the unit friction resistance for bored piles using shaft-grouting technique in the studied area.

According to the latest count of General Department of Fire Prevention, Fire Fighting and Rescue in Vietnam, there were 3790 cases of fire nationwide in 2019 that caused 85 deaths and 126 injuries; the estimation of lost properties was approximately 1527 billion VND. Notably, the victims died mainly because of inhaling a great amount of poisonous gases. On the other hand, Pinaceae wood materials, which have been widely used in Vietnam, produce a variety of poisonous gases when they are burned. Hence, in this work, we determine the toxicity of fire products when Pinaceae wood materials are burned, and factors that affect the toxicity of the fire products.

We have successfully fabricated the composites of α-Fe2O3 nanorods and SnO2 nanorods through hydrothermal treatment method. Morphologies of α-Fe2O3 and SnO2 nanorods and their composites with different weight ratios were studied by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Liquefied petroleum gas (LPG)-sensing properties of the sensor made from the α-Fe2O3 nanorod/SnO2 nanorod composites were explored. At optimum operating temperature of 370 ℃, the sensor made from the composites of 75 wt% a α-Fe2O3/25 wt% SnO2 shows the highest response to LPG. This attributed to the successful fabrication of a LPG—leak detection device, which is based on a sensor made from the composites of α-Fe2O3 nanorods and SnO2 nanorods, to detect and warn the risks of fire and explosion.

This study aims to determine aerodynamic drag coefficients of cable-stayed bridge pylons with different shapes through a computational fluid dynamics (CFD) approach. The approach is based on a three-dimensional model of the turbulent wind flow around pylon using the finite element ANSYS CFX software. Numerical models of the flow around simple objects are first carried out and the results are validated with the previous work in the literature. To identify the most suitable turbulent modeling approach, numerical analyses of five turbulent models including k-epsilon, k-omega, shear stress transport, BSL Reynolds stress, and SSG Reynolds stress are performed on a single pylon. Next analyses for other examined pylons of cable-stayed bridges in Vietnam are conducted to determine their aerodynamic drag coefficients. Surface pressure acting on each pylon is also investigated. Finally, the discussion on the effects of the pylon shapes on drag coefficients and surface pressures as well as vortex flows is presented in detail.

The concept of the representative volume element (RVE) is widely used in geomechanical, geotechnical applications, and related field issues, especially in multi-scale modeling. However, the RVE existence and its size determination are not always evident and have been crucial subject of numerous research works for a long while. In the present research, the paper focuses on the RVE made of 2D circular grains, by using discrete element modeling (DEM). Numerical simulations were then carried out, and the results were served as ingredients for statistical analysis with objective function was homogeneous RVE stress–strain responses. The results show that RVE could achieve statistically homogeneous behavior by increasing its size. Besides this, the findings also suggest that the existence of RVE is found in linear or hardening phases while the response is rather scattering in softening regime. The latter relates to the loss of uniqueness which is due to the inherent strain-softening exhibited by the granular material.

This paper is based on the energy absorption of Expanded polystyrene (EPS) into a motorcycle helmet to evaluate the impact resistance on a flat anvil in the shock absorption test of QCVN:2008. The paper is divided into two sections: In the first section, the EPS liner of either helmet is experimentally determined its density and stress-strain curve used in FEA models. The other is tested shock absorption at SMEQ in order to measure the acceleration value at the peak position, 3 ms and 6 ms of acceleration curve which is required in the standard. In the second section, a basic model with three layers (head form, EPS, and shell) is built in Solidworks and simulated in LS-DYNA under experimental conditions. After compared with experimental values, the model is optimized to obtain an error of less than 5%. In order to investigate the behavior of this model with different thicknesses, the EPS layer thickness of the optimized model is modified from 10 to 20 mm. As a result, the acceleration values depend on the EPS layer thickness, the peak acceleration increase rapidly in proportion to the thickness from 10 to 14 mm and then the acceleration decreases to a limit value of 20 mm thickness. The simulation result also shows that the stress of the ABS shell is concentrated in at the impact point which is the center of the circle and slightly decreases from the center. By using simulation technology in the impact tests, the shock absorption of EPS is controlled by its thickness which is 16 mm or more for better protection.

The dynamic analysis of duct drilling structure to the wave loading with consideration of the ballast water inside is studied in this paper. The research content is based on the actual model of Tam Dao 05 self-jacking rig selected to apply simulation and analysis. The structural system of offshore structure with the ballast water inside is modeled by finite element method in ANSYS Workbench. The analysis results show that the change in ballast water height inside the rig body has affected the fluctuation cycle of the rig and changed the behavior of the rig structure under the combination of wind and wind and waves.

Temperature changes affect pavement performance such as strength reduction at elevated temperature or crack initiation and development at low thermal conditions. Thermal diffusivity of paving materials is one of parameters helps to determine exactly temperature distribution in pavement structures. Currently, the thermal diffusivity can be determined through thermal conductivity, mass density of material, and specific heat capacity. Nevertheless, the specific heat capacity is quite complicated to obtain for composite materials. Literature reported different experimental methods used for determining the thermal conductivity of building materials such as heat flow method (ASTM C 518), guarded-hot-plate approach (ASTM C 177), hot wire technique (ASTM C 1113), and transient plane heat source solution (ISO 22007-2:2015). However, these methods were found not suitable for pavements due to large granular sizes and heterogeneous properties of pavement materials. This study developed a device to determine the thermal diffusivity of pavement materials in the laboratory without the needs of heat capacity and thermal conductivity of the composites. The temperature distributed in the hot mixed asphalt concrete type 19 having air void content of 9.7%, bitumen content of 4%, and density of 2.14 (T/m3) was first measured by this device. The thermal diffusivity was then determined based on the heat transfer theory, and the result was 4.556 × 10−7(m2/s), consistent with the one from previous studies.

Cabinet facility is known as a high-frequency nonstructural component, and its failure is directly affected by dynamic characteristics of ground motions (i.e., frequency content, amplitude, and duration). This study aims to investigate the seismic vulnerability of a nonstructural component in the nuclear power plant (NPP) induced by the predominant frequency of the ground motions. Time history analysis is performed for eighty ground motions of low- and high-frequency motions. The results indicate that the high-frequency ground motions significantly increase the peak acceleration at the top of the cabinet. In contrast, the low-frequency content motions have less impact on structural seismic behavior.

Axial force plays an important role in determining the bending capacity of columns. Results from a shaking experiment on a steel building conducted in 2007 on the E-Defense showed the obvious evidence of column bending moment capacity deterioration. In this test, local buckling behavior was observed in the column ends which were subjected to simultaneous biaxial moment and axial force. The occurrence of local buckling resulted in the decrease in the base shear capacity and consequent structural collapse. Out of some former studies on the experiment, this paper additionally clarifies the different deteriorating patterns of all columns in this building specimen. It is because the column axial force magnitudes closely relating to the column locations differ considerably during the seismic movement of the structure. Moreover, this paper provides a further interpretation of the building response in terms of energy, in which energy input and the dissipation mechanism at the collapse excitation state are evaluated.

The objective of our work is to develop a fast and efficient code to compute the damped parameters (the complex eigenvalues, the damped eigenfrequencies, and the corresponding loss factors) of viscoelastic twisted multilayer beams rotating at a constant angular speed. The beam is twisted, and its cross section is uniform. The governing equations are developed using the Hamilton principle and discretized using the finite element method. The related nonlinear eigenvalue problem is resolved by combining the homotopy method and the asymptotic numerical method. The obtained complex eigenparameters are coherent with those found in the literature. In addition, our calculation code makes it possible to directly compute the loss factors without using the bandwidth method used in some commercial codes.

This research applies the polygonal finite element method (PFEM) to deal with the incompressible steady Navier–Stokes (N-S) fluid problems. Two numerical examples are presented in this paper. The first one is the lid-driven cavity flow that is widely utilised to evaluate the numerical methods in solving the N-S equations. The second one is an example of a flow suddenly expands and flows through an obstacle. In this research, all numerical tests are coded and programmed by MATLAB program.

One of the potential risks of damage to steel members in real structures is the existence of available micro-cracks in steel material which is unavoidable in the process of production, assembly as well as operation. These cracks could appear as a result of the effect of the welding process or available defect in steel material, corrosion, or fatigue failure of steel members. The investigation appraises the effect of pre-existing cracks in steel material on the behavior of steel beams under the four-point bending experiment. The steel beam samples were made of high carbon steel. Pre-existing cracks were created on the flanges in certain positions which were corresponding to designed steel beam samples to investigate the effect of pre-existing cracks on the behavior of steel beam. The calculation was implemented at the same time with experiments to verify the experimental results.