Trang: 317-327 Yen-Lien T. NguyenTóm tắtThis paper analysed the real-world driving data to determine the representative parameters of driving cycle for the purpose of the typical driving cycle development of bus in Hanoi. The real-world driving data of bus in Hanoi were collected by using the Global positioning system technique with 1Hz data update rate. The real-world driving data of fifteen bus routes in the inner city were collected continuously, on weekdays as well as at weekends. The data, then, were used to calculate 33 kinematics parameters reflecting the realistic driving characteristics, including vehicle-specific power. The hierarchical agglomerative clustering method was used to determine a minimal set of representative variables from the 33 kinematics parameters. The 14 representative parameters of the real-world driving cycle of bus in Hanoi were determined.
Trang: 328-335 Nguyen Luong HaiTóm tắtLeadership behavior is one of the fundamental functions of management principles, especially meaningful to the public management in terms of road infrastructure development in the context of scarce capital and complicate investment implementation as well. The article is aimed to clarify the impact of leadership behaviors on public management efficiency in the context of road infrastructure development in Vietnam. Through a linear regression analysis, the results have synthesized the critical leadership behaviors and figured out factors related to authority assignment, communication encouragement and motivation promotion, which influences significantly (p << 0. 05) to the management performance (MP). Research results contribute significantly to both knowledge-body and practices of public management and sustainability of road infrastructure development in Vietnam.
Evaluating the maiden BRT corridor in Vietnam
Trang: 336-346 Huy Nghia Nguyen, Sy Sua Tu, Minh Hieu NguyenTóm tắtBus Rapid Transit (BRT) is one of the most effective solutions to meet an enormous growth of travel demand in developing countries’ urban areas where urban rail systems are on the plan or under construction but not in reality yet. Based on collection and synthesis of successful and outstanding experience over the world (e.g. in Bogota (Colombia), Guangzhou (China), Ahmedabad (India)), the Bus Rapid Transit Standard (BRTS) was introduced to provide guidelines to the following creation of BRT. It is a measurement to clarify what are strengths and shortcomings of each case, which contributes to propose approaches to deal with disadvantages and enhance operation. Hanoi inaugurated the first BRT corridor at the beginning of 2017; however, it has performed more poorly than expected. In this paper, it is assessed by the BRTS to show (1) which level it reached compared with international BRT systems, (2) its main limitations and (3) potential remedies for its poor performance. The findings emphasize that its design meets the Bronze standard; however, its actual operation achieves the Basic level only. Its major issues are low (design) capacity, low frequency, limited speed, lack of reliability and convenience. To address them, implementing technical packages to give prioritized signals at intersections and provide multimodal real-time information together with reducing interval at peak hours would be the most important and feasible solutions. Although being ineffective now; BRT would play a vital role in the process of limiting the use of private vehicles, especially motorcycle.
A methodology of re-generating a representative element volume of fractured rock mass
Trang: 347-358 Hong-Lam DANG, Phi Hong THINHTóm tắtIn simulation of fractured rock mass such as mechanical calculation, hydraulic calculation or coupled hydro-mechanical calculation, the representative element volume of fractured rock mass in the simulating code is very important and give the success of simulation works. The difficulties of how to make a representative element volume are come from the numerous fractures distributed in different orientation, length, location of the actual fracture network. Based on study of fracture characteristics of some fractured sites in the world, the paper presented some main items concerning to the fracture properties. A methodology of re-generating a representative element volume of fractured rock mass by DEAL.II code was presented in this paper. Finally, some applications were introduced to highlight the performance as well as efficiency of this methodology.
Trang: 359-367 Ta Duy HienTóm tắtIn general, the fluctuation of the elastic modulus of materials is crucial in structural analysis. This paper develops a stochastic finite element method (SFEM) for analyzing a nonuniform column considering the random process in elastic modulus. This random process of elastic modulus is assumed as a one-dimensional Gaussian random field. The weighted integration method is used to discretize the random field and establish the stochastic finite element formulation to compute the first and second moments of displacement fields. The results of the proposed approach are validated with those of the previous study. The response variability of displacement of column and effect of the parameter of the random field is investigated in detail.
Trang: 368-379 Tran Khac Duong, Do Quoc CuongTóm tắtEfficiency analysis of bus transit at the route level is critical to understand the existing performance of individual routes within a bus system and identify operational problems as well as effectively optimise their performance. This article applies the Data Envelopment Analysis (DEA) model to examine the performance of 38 bus routes in Hanoi, Vietnam. The results indicated the best and the inefficient bus routes within the given sample and identified the internal sources of inefficiency, including: number of stops and vehicles. The findings provide bus agencies in the case study with additional and useful information for decision making.
Trang: 380-387 Dang Thuy Chi, Le Minh CuongTóm tắtBond behavior between the reinforcement steel bars and surrounding concrete is considered as an important characteristic for reinforced concrete structures, including lightweight aggregate concrete ones. This paper presents an experimental investigation on the bond behavior of 14 mm diameter steel bars embedded in lightweight aggregate concrete. The bond slip relationship between rebar and lightweight aggregate concrete shows a conventional behavior, similar to traditional reinforced concrete. The development length of 14 diameter steel embedded in lightweight aggregate concrete is smaller than the requirement in ACI 318-11.
Trang: 388-402 Tuan-Anh NguyenTóm tắtThis paper deals with a geometrically nonlinear finite element formulation for the analysis of torsional behaviour of RC members. Using the corotational framework, the formulation is developed for the inclusion of nonlinear geometry effects in a multi-fiber finite element beam model. The assumption of small strains but large displacements and rotations is adopted. The principle is an element-independent algorithm, where the element formulation is computed in a local reference frame which is uncoupled from the rigid body motions (translations and rotations) of the reference frame. In the corotational based frame, strains and stresses are measured from corotated to current, while base configuration is maintained as reference to measure rigid body motions. Corresponding to the requirement of corotational based, in the local frame, taking into account the torsional effect conducts to nonlinear strain assumption, thus require some specific development using a new kinematic model. Second order strain is accounted in the axial term, however lateral buckling is neglected, therefore this formulation is recommended to use in case of solid cross-section with arbitrarily large finite motions, but small strains and elastic material behaviour, such as slender of long-span reinforced concrete beam-column under flexion-torsional effect following serviceability limit state design. The enhanced formulation is validated in linear and nonlinear material range by several examples concerning beams of rectangular cross-section.
Trang: 403-418 Le Dinh Thuc, Pham Phu CuongTóm tắtPublic–Private Partnership (PPP) has emerged as an effective procurement in delivering infrastructure and public service in many countries over the world since last few decades. It brought more benefits for sustainable development compared to traditional procurement in many developing countries. However, in order to determine whether a project is successful or not has still remained an ambiguous perception. Therefore, this study will rank the successful level for PPP transportation infrastructure projects in Vietnam via case studies. Fifteen success criteria were identified by the comprehensive review. The fuzzy TOPSIS method was then applied to evaluate and rank the success level for case studies. The result showed that project 2 is considered as the most successful until this recent time with a satisfactory degree of 0.489. Project 1 and project 3 are ranked second and third with a satisfactory degree of 0.482 and 0.435, respectively. Although the projects were judged as effective. Nevertheless, the success index of these expressway project still lower than 0.5. Therefore, project managers need to propose effective solutions to improve the success of these projects in the future. This result can help participants to be a good insight into the PPP project success in developing countries in general and Vietnam in particular.
Modeling of contact interface between two material layers in hybrid structures
Trang: 419-430 Nguyen Thi Thu Nga, Tran Nam HungTóm tắtIn hybrid structures, material layers of different mechanical properties are integrated to increase bearing capacity. When the difference in mechanical properties or thickness of the material layers is very large, debonding usually occurs along the interface between the two layers. This study uses a homogenization procedure combined with asymptotic algorithm applied on weaker/thinner materials to determine the interface stiffnesses for such structures. All the material layers and the interface are assumed to be linear elastic. Comprising with the available methods and numerical simulation results showed that the proposed model is more suitable with the work of the structures in reality. Furthermore, in this method the interface stiffnesses can be easily determined through the number and length of cracks and the dry or saturated state of the medium are also considered.
Trang: 431-443 Van Thao Le, Dinh Si Mai, Tat Khoa Doan, Quang Huy HoangTóm tắtIn the wire arc additive manufacturing (WAAM) process, the geometry of single welding beads has significant effects on the stability process and the final quality and shape of manufactured parts. In this paper, the geometry of single welding beads of 308L stainless steel was predicted as functions of process parameters (i.e. welding current I, voltage U, and travel speed v) by using the response surface methodology (RSM). A set of experimental runs was carried out by using the Box-Behnken design method. The adequacy of the developed models was assessed by using an analysis of variance (ANOVA). The results indicate that the RSM allows the predictive models of bead width (BW) and bead height (BH) to be developed with a high accuracy: R2-values of BW and BH are 99.01% and 99.61%, respectively. The errors between the predicted and experimental values for the confirmatory experiments are also lower than 5% that again confirms the adequacy of the developed models. These developed models can efficiently be used to predict the desirable geometry of welding beads for the adaptive slicing principle in WAAM.
Strengthening soft soil for approach road after abutment by cement and fly ash
Trang: 444-457 Nguyen Dinh HungTóm tắtApproach road is an important structure of a bridge. Serviceability of a bridge is affected by the settlement of approach road, especially that on soft soil. One method that is usually applied for minimizing effect of settlement of approach road is to replace soft soil by hill soil. This method however may increase cost of projects in Mekong Delta area with a larger depth of soft soil. In this paper, soft soil strengthened by mixing it to cement and fly ash at different mix proportions was investigated. Test results from unconfined compression test and direct shear test of strengthened soft soil are compared to those of hill soil to determine the optimal mix proportion. Results showed that mixing 25kg cement and 75kg or 100kg fly ash to 1m3 soft soil increased its unconfined compressive strength and shear strength and are higher compared to those of hill soil. Strengthening in situ soft soil by using fly ash, industrial waste from thermal power plant, reduces cost of project and at the same time contributes to solving environmental problems.
