Mục lục

Modelling school travel mode choice – the case of hanoi, vietnam

Trang: 778-788 Minh Hieu Nguyen
Tóm tắt

The COVID-19 outbreak has resulted in adopting massively social distancing measures to tame the human-to-human transmission of the new coronavirus and protect public health. These intervention policies have caused changes in travel behavior, thereby expressing a need to update profiles of factors associated with mode choice. To respond to this research gap in part, this current study aims to model children’s mode decisions for school trips in the post-pandemic time in Hanoi. As regards mode usage, cycling is the main mode of active transport with a share at 23.3%, doubling the rate of 11% for walking. The dominant mode of traveling to school is the motorized modes (i.e., cars and motorcycles) with a proportion of 60%, meanwhile, school buses account for only 6.2%. As regards the determinants, when growing up, children tend to shift from being driven to traveling actively. The availability of cars increases the likelihood of using other modes compared to cycling. An opposite association is seen for the availability of bicycles. The flexibility in terms of a mother’s job is involved in a higher possibility of being driven for a child. A home-school distance less than 1 km is more suitable for walking compared to cycling; however, an inverse relationship is witnessed for a distance between 1 and 2 km. A distance over 2 km is more appropriate for motorized modes and school buses. To promote active transport to school, children’s travel demand should be taken transport planning into consideration. Developing cycling and walking facilities is essential, especially in urban districts. Additionally, limiting the use of private motorized modes would be useful.

Characteristics and corrosion protection of polypyrrole doped with salicylate anions on CT3 steel passivated by molydate

Trang: 789-799 Hoang Thi Tuyet Lan, Lai Thi Hoan
Tóm tắt

In recent years, the conducting polymers have attracted much attention in research and development because of their applications in medical and civil engineering. Here, the salicylate doped polypyrrole films were prepared on the carbon steel surface and their corrosion protection in 3 % NaCl solution were studied. Polypyrrole (Ppy) film was electrochemically synthesised with constant current techniques in a sodium salicylate solution (0.05M, 0.1M, 0.15M) and 0.1M pyrrole monomer on mild CT3 steel electrode passivated by molybdate. The morphological, structural, composition and thermal properties of salicylate doped Ppy films were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) techniques. The anti-corrosion ability of these films was assessed by electrochemical measurements in 3 % NaCl solution. The obtained results suggested that salicylate anions contributed in corrosion protection ability of Ppy films for mild steel electrode. The concentration of sodium salicylate of 0.1M and pyrrole of 0.1M is most suitable for preparation of good protection coating. The self-healing mechanism has been also mentioned for salicylate doped Ppy films on CT3 steel substrate.

Exploring factors associated with red-light running: a case study of Hanoi city

Trang: 800-810 Chu Tien Dung
Tóm tắt

Red-light running (RLR) is the most significant factor involved in traffic crashes and injuries at signalized intersections. In Vietnam, little knowledge of factors affecting RLR has been found. This paper applied an ordered probit model to investigate factors associated with RLR using questionnaire data collected in Hanoi. Generally, this paper found that males and motorcyclists have a higher likelihood of RLR than females and car drivers. In addition, the younger and lower-income road users and the ones who are businessmen and who have a commuting trip in off-peak hours are more likely to run the red light. By contrast, the road users who go to school and the people who understand traffic law are less likely to violate the red light. In the future, it is necessary to collect data in different cities to generalize the results. In addition, may need to apply a more powerful method such as the latent class model, which can discover hidden facts among respondents. In the new model, other factors such as weather, waiting time, and countdown signal will be considered to investigate their effects on RLR.

Structural analysis of steel-concrete composite beam bridges utilizing the shear connection model

Trang: 811-823 Phung Ba Thang, Lai Van Anh
Tóm tắt

Shear connector (typically shear studs) plays a vital role as a transfer zone between steel and concrete in steel-concrete composite bridge girder. In the previous studies, the connection between steel beam and reinforced concrete slab were considered as continuous joint. However, in practice, this connection is discrete, which allows the slipping and peeling phenomenon between two layers (the influence of peeling is usually very small and could be ignored). To reflect this actual working mechanism, this study proposed a model of shear connection in the form of discrete points at the actual positions of studs for structural analysis. The model was simulated utilizing Timoshenko beam theory considering transverse shear effects. The numerical applications are carried out in order to compare two types of connections. The obtained results indicated that the proposed model properly reflected the actual performance of the structure and in some necessary cases, we should consider discrete connection for more accurate local results.

Experimental evaluation on engineering properties and microstructure of the high-performance fiber-reinforced mortar with low polypropylene fiber content

Trang: 824-840 Vu Viet Hung, Nguyen Tuan Cuong, Nguyen Huu Duy, Ngo Nguyen Ngoc Tho, Huynh Trong Phuoc
Tóm tắt

Recently, high-performance fiber-reinforced mortar/concrete (HPFRM) has been researched and developed in many fields such as repair, maintenance, and new construction of infrastructure works due to its high strain capacity and tight crack width characteristics. Optimizing the design of mixture proportions and structures using HPFRM is still a complex mechanical and physical process, depending on the design principles, specific site conditions, and their local materials. This study aims to develop an HPFRM with low polypropylene fiber content by using locally available ingredients in Southern Vietnam to address the deficiencies commonly observed in traditional cement grout mortars. Three mixture proportions were prepared with different water-to-binder (w/b) ratios of 0.2, 0.25, and 0.3. Then, the performance of HPFRM was evaluated in both fresh and hardened stages. Additionally, the microstructural characteristics of each mix design were also assessed through scanning electron microscope observation. The experimental results showed that the optimum w/b of 0.25 and a fixed dosage of 0.6% polypropylene fiber produced positive impacts on the rheological, mechanical properties, and also ductility of the high-performance mortar. It was concluded that HPFRMs are promising for cost-effective and sustainable cement mortars.

Impacts of the specific cake resistance on mbr fouling for wastewater treatment

Trang: 841-849 Christelle Guigui, Vu Thi Thu Nga
Tóm tắt

Membrane bioreactor (MBR) has been increasingly used for municipal wastewater treatment and reuse due to its good effluent quality. However, membrane fouling remains the major limitation of MBR. Understanding fouling is still a key issue for a more sustainable operation of MBRs. Thus, this research presents the influence of specific cake resistance (α) on the fouling propensity in the MBR. Correlation between α value with fouling resistance (Rf), fouling rate (dTMP/dt), especially of peak height 100-1000 kDa protein-like SMPs was investigated. The result reported that the α value was strongly correlated with the dTMP/dt in the MBR (R2 value of close to 1). In this study, however, there is an obvious discrepancy between the fouling resistance calculated from the resistance in the series model and the α value in the supernatant filtration. These observations demonstrated that the fouling propensities of the membrane could be monitored by the transmembrane pressure and the fouling characteristics, include fouling resistance and specific cake resistance in the filtration cell.