Mục lục

A machine learning approach to risk assessment of expressway bridges

Trang: 661-673 Le Duc Anh, Dao Duy Lam, Thai Thi Kim Chi, Bach Thi Diep Phuong
Tóm tắt

The expressway network in Vietnam is developing strongly, playing the role of the backbone of the national road system, in which bridge construction accounts for a large proportion. With many specific characteristics and complex risks always hidden in all stages of the expressway project, risk assessment to have solutions and plans to prevent and respond to risks, limiting the impacts of quality assurance and operational safety of the works is essential. However, the current risk assessment and forecasting models still have many limitations. The application of Machine Learning to all aspects of life is getting more popular. This article develops the algorithms, models and program to assess the technical risks in the period of construction and service of expressway bridges in Vietnam using Machine Learning, in order to solve the current limitations in this work. The selection of key influencing factors is especially important in the field of risk assessment. It improves the classification model's performance by focusing only on the most important factors in the data. Via the applications of artificial neural networks and the Random Forest Algorithm in data processing, the performance risks for bridge management can be analyzed, and performed in more detail and exactly. The possible multiple and non-linear relationships of the risks can be investigated. Based on the results, the proposed model helps the managers to make optimum decisions on managing the risks in advance and to obtain sustainable solutions

Upper bound on the number of determining modes for the 2D g-bénard problem

Trang: 674-687 Nguyen Dinh Thi, Tran Quang Thinh, Trinh The Anh
Tóm tắt

The "determining modes" concept introduced by Foias and Prodi in 1967 say that if two solutions agree asymptotically in their P projection, then they are asymptotical in their entirety. In this paper, we consider the 2D g-Bénard problem in domains satisfying the Poincaré inequality with homogeneous Dirichlet boundary conditions. We present an improved upper bound on the number of determining modes. Moreover, we slightly improve the estimate on the number of determining modes and obtain an upper bound of the order G. These estimates are in agreement with the heuristic estimates based on physical arguments, that have been conjectured by O.P. Manley and Y.M. Treve. The Gronwall lemma and Poincaré type inequality will play a central role in our computational technique as well as the proof of the main result of the paper. Studying the properties of solutions is important to determine the behavior of solutions over a long period of time. The obtained results particularly extend previous results for 2D g-Navier-Stokes equations and 2D Bénard problem.

Physical, thermal, and mechanical properties of calcium aluminate cement-based refractory conerete at elevated temperature

Trang: 688-702 Manh Tien Tran, Xuan Hong Vu, Emmanuel Ferrier
Tóm tắt

In the past decade, calcium aluminate cement is widely used to manufacture refractory concrete for infrastructure works which frequently were subjected to elevated temperature thanks to the thermal stability by the high content of aluminum. This paper presents experimental results of the physical, thermal, and mechanical properties of calcium aluminate cement-based refractory concrete specimens. As experimental results, with a calcium aluminate content of about 50%, the refractory concrete provides remarkable physical, thermal, and mechanical properties. The high density and low water content were characterized for this concrete. The thermal diffusivity coefficient of refractory concrete is lower from 3 to 4 times than that of normal concrete while the conductivity is around of 1.05 (W/m.K). Furthermore, from the thermomechanical tests, the direct tensile strength and Young’s modulus of refractory concrete were identified at different temperature levels. The effect of elevated temperature on the performance of this refractory concrete was analyzed and highlighted

Experimental investigation on the tensile strength degradation in curved reinforcement of textile reinforced concrete

Trang: 703-712 Hoai Ho, Huu Tai Dinh, Huy Cuong Nguyen, Dang Dung Le, Thanh Tam Nguyen
Tóm tắt

Recently, textile reinforced concrete (TRC) has become a new approach for strengthening the existing reinforced concrete and masonry structures. When TRC wraps around the structural members, the direction of textile reinforcements changes according to the curvature radius of the structural corner. This paper presents an experimental investigation into the tensile strength degradation in curved glass and carbon reinforcement of TRC specimens. The results show that the ultimate tensile load decreases as the diameter of the semi-circle parts reduce. At the same diameter, the carbon TRC specimens have a higher tensile load-bearing capacity than glass textile-reinforced concrete. The failure modes of all the experiment cases are the fracture of the textile reinforcement in the middle of the semi-circle parts or at the transition region of the straight and curved region. The tensile strength degradation of both glass and carbon textile reinforcement has a linear relationship with the diameter of the semi-circle parts of the TRC specimens. The value only reaches up to 41% and 60% tensile strength of the individual filaments for glass and carbon fiber, respectively.

A high gain wideband array antenna based on metasurface for ETC application

Trang: 713-723 Khuat Dinh Chinh, Tran Thi Lan
Tóm tắt

Free flow electronic toll collection (FFETC) has played an important role in building convenient and safe transportation systems in many countries. The most challenging problem when researching and developing this system is shortening the payment cycle so that vehicles passing through the stations do not need to stop or keep going at a speed greater than 60 Km/h. Designing roadside unit (RSU) reader antennas with high gain and suitable radiation pattern is the most feasible and economical solution. This paper proposes a left-handed circularly polarized (LHCP) 2×4 array antenna using sequential phase rotation power dividers at 5.8 GHz band. The element antenna is a square patch antenna with a slit in the middle for better impedance matching, six trapezoidal parasitic patches added to either side of the main patch to create resonance at high frequencies, and a metasurface placed on top of the main patch. The proposed metasurface is a 4×4 array of dual circular unit cells to improve gain and extend axial ratio (AR) bandwidth. The proposed antenna array has a high gain of 17 dBi, -3 dB vertical and horizontal beamwidths of 33.20 and 17.10, which cover over one lane, are expected for any ETC system to avoid interference with other lanes. Impedance bandwidth and AR bandwidth are 2.19 GHz (37.75%) and 2.06 GHz (35.52%), respectively. The overall dimensions of the proposed array antenna are approximately 152×76×6.4 mm3. With the above merits, this antenna is a suitable candidate for the RSU reader antenna in the FFETC

A practical approach for modeling twin-tunnel excavation in Ho chi minh city

Trang: 724-734 Hong Lam Dang, Thi Quynh Chi Dang, Ba Dong Nguyen
Tóm tắt

The prediction of ground settlement under tunnel excavation is still challenge. Almost engineer uses Mohr-Coulomb model in practice due to the conventional geotechnical investigation data. This paper describes the study of tunnel lining behaviors and ground surface settlement under tunneling process with a typical case study of twin tunnels excavation in Ho Chi Minh city, Vietnam. The advanced material model namely Hardening Soil model is used to investigate the proposing twin-tunnel with numerical approach. The internal forces of tunnel lining and ground settlement, which achieved from Hardening Soil model and the available results from Mohr-Coulomb model, are then made comparison between two models which yields some important differences for analysis. Since the experimental works for qualifying stiffness parameters in Hardening Soil model are missed in the Metro Line 1 project in Ho Chi Minh city, an empirical formula is proposed in the paper as a guide for estimating the required data in modelling process