Quarterly Report of RTRI Vol. 58(2017) No. 3

In the fiscal year 2015, RTRI conducted research into around 300 themes. Among them were about 45 dealing with rolling stock, covering a wide range of practical areas such as increasing train running speeds and improving ride comfort, applied research such as running stability and vehicle crashworthiness, and finally, basic research such as elucidating the mechanisms underlying wheel wear.
This paper introduces three of these themes, namely, "A new type of bogie for reducing the risk of derailment," "Carbody safety evaluation method for reducing passenger injury in the event of a level crossing accident" and "Small and low-cost pneumatic centering cylinder for tilting vehicles."

The Railway Technical Research Institute has been researching a variety of technologies related to railway structures. These include technologies for maintenance (inspection, diagnosis, prediction, repair, renewal), earthquake countermeasures, construction and environmental impact assessment. This review gives some overview of recent research and development trends in maintenance and construction technologies for "geotechnical structures" (earth retaining walls, soil structures and tunnels) conducted at the Railway Technical Research Institute.

Maintenance of ground facilities account for approximately half the running costs of local railway companies. Moreover, as measures are taken to cut the workforce in these companies, this ratio is rising. There is therefore a general consensus that the cost of the ground facility maintenance is the main factor causing financial difficulties for local railway companies. This paper presents recent RTRI R&D into cutting the cost of local track maintenance, which can contribute to alleviating the financial burden on local railway companies.

The vertical vibration of railway vehicle carbodies induced by the rotation of wheelset(s) with a small mass imbalance needs to be suppressed to improve ride comfort. For this reason, a displacement-dependent rubber bush, which is used for connecting the bogie frame to the carbody was developed. This paper presents a displacement-dependent rubber bush for yaw dampers. To confirm the vibration suppression performance of the devised rubber bush, rotating excitation tests and running tests were performed. Results demonstrated that the vertical vibration of the carbody induced by the rotation of imbalanced wheelsets was reduced by use of the developed displacement-dependent rubber bush.

The Japan Freight Railway Company has developed an inverter-controlled diesel hybrid shunting locomotive, type HD300, to replace aging DE10 diesel shunting locomotives. In the early stage of development, it was difficult to secure sufficient tractive effort just after starting. Therefore, a re-adhesion control method was developed to minimize torque reduction by improving the delay in wheel rotational acceleration signals, used to determine when torque reduction is stopped during anti-slip re-adhesion control, thereby increasing the average tractive effort. The results of running tests verified an increase of 5% or more in the average tractive effort. The developed control method has been applied to the mass-production of the HD300 model.

Almost all railway vehicles have brake systems which use the tangential force between rails and wheels. It is difficult to stabilize braking performance and to prevent wheel damage because the tangential force is influenced by various conditions, such as weather, the contact surfaces of the rails and the wheels, etc. Wheel slide protection systems (WSP) are one solution adopted on many vehicles. However, in existing WSP systems, braking force is controlled using limited information from the rotational speed of the wheel. Therefore, they do not always offer optimal control when the tangential force varies frequently. This study proposes a new WSP system which can determine the quality of the tangential force from the brake cylinder pressure when wheel slips occur. The performance of the new WSP was verified through bench tests. As a result, application of the new WSP method reduced braking performance loss.

Tsunami tests were conducted, to gain further insight into the phenomenon where, in the area close to concrete bridge girders, flow speeds fall when water levels rise, and there are differences in water levels upstream and downstream around girders. Based on results a method was proposed for calculating fluid forces acting on girders. The proposed method enables calculation of fluid forces generated around the bearing surfaces between concrete girders and bridge piers, using information about the bridge and assuming height and speed of the tsunami.

Steel truss bridges consists of many different trussed members and it is important to clarify the possibility of bridge collapse following the fracture of a member. This study evaluates the safety margin on a standard steel railway through-truss bridge after the fracture of certain members, using 3-D finite element analysis. Results showed that the safety margin remains fairly high with surviving members after the fracture of lower chord members, because floor members can make up for the lost sectional force from the fractured members. Finally, the degree of importance of each member was evaluated.

Preventing concrete spalling is very important in tunnel maintenance because it can be a direct hazard to the operational safety of trains. This paper deals with the applicability of sprayed polyurea as a method to prevent spalling of tunnel linings. Model tests and trials using the method were carried out. According to the model tests, when the arch crown displacement reached 30mm, bending compressive fractures appeared around the shoulder of the lining, no spalling occurred in the lining because the polyurea covered the exfoliated concrete. The model tests therefore confirmed the effectiveness of polyuria application against spalling. For the trials in an actual tunnel, 3 kinds of surface were prepared before application of the polyurea spray, which enabled evaluation of bonding strengths and execution time.

Gas pressure welding is commonly used for rail welding in Japan. This technique however requires specialist skills for the rail-end surface grinding stage and the rail heating process using a burner. In anticipation of a decrease in the number of skilled welders, a new simplified and standardized gas welding method with minimal requirement for expert training has therefore been studied and developed.
This paper describes the newly developed gas pressure welding process, and presents the performance test results of the gas pressure welds prepared according to this process.

Today, tamping machines and rail grinding machines are used to maintain ballasted tracks and to remove rail surface irregularities, respectively. Even though maintenance cycles could be extended and the total cost of maintenance could be reduced by efficiently combining these two machines, they are usually operated independently. As such, in order to estimate the effect of combining both these machines (combined maintenance), a model has been designed along with a scheduling system, as a simple method for preparing maintenance schedules which combine tamping and grinding. Investigations were also carried out to establish how long this type of maintenance lasts, and determine the optimum level of combined maintenance.

It is important for the design and verification of rail fastening system performance to clarify the permissible lateral force it can tolerate. This study proposes a method for predicting the fatigue life of rail clips. The validity of the method was confirmed on the basis of the relationship between the applied loads and stress on the rail clip, established in laboratory tests. The fatigue life of the rail clip was then estimated using the proposed method and the permissible lateral force for a conventional fastening system was derived using this estimation.

The following correction should be made to the original paper: May, 2017 Vol.58, No.2 Page 89, in Fig. 5 (b), the notation " ●：騒音測定点" should read " ● ： Measuring point".