Additional Longitudinal Forces Research Articles

Appropriate locations of fixed bearings of continuous beams considering rail-bridge thermal interaction.

Due to the rail-bridge thermal interaction, the high additional axial force in continuously welded rails on continuous bridges may lead to rail buckling or breaking. However, there is little research on the influence of the location of the fixed bearing of continuous beam on the additional force of rail. In order to study the influence of bridge bearing arrangement on the additional longitudinal force of CWR, the thermal interaction model is established for rail, and simple and continuous beams considering nonlinear stiffness and the methods are proposed to determine the locations of fixed bearings of continuous beams corresponding to the maximum additional forces in rail reaching minimum values. Multiple continuous beams with several different lengths and simple beams with three types of bearing arrangements are taken into account to find the effect laws of the locations of the fixed bearings of continuous beams on the maximum additional forces in rail. The results show that as long as the same number of continuous beams, the ratios of the distances of adjacent two fixed bearings to the distance between the two fixed bearings of the simple beams neighbour to the first and last continuous beams respectively are approximately equal to each other. Furthermore the appropriate locations of the fixed bearings of continuous beams are recommended. The results can guide designing the location of the fixed bearing of continuous railway bridge while reducing the additional axial force in continuously welded rails due to bridge thermal effect.

Stress-strain state of hybrid timber-reinforced concrete multy-storey buildings considering creep deformation

Problem statement. The new solutions of hybrid constructions of multi-storey buildings are being developed, in which the main structural material is timber and reinforced concrete or steel is used to ensure spatial rigidity. The problem in developing such projects is a significant difference in the deformation characteristics and rheological properties of timber and concrete, which can significantly affect the load-bearing capacity and serviceability of the hybrid building. At present time the issues of joint work of these materials in the elements of structural systems are insufficiently studied. The purpose of the article is to investigate the stress-strain state of hybrid wood-reinforced concrete multi-storey buildings taking into account the influence of creep deformations. Conclusion.The method of taking into account the peculiarities of deformation and creep of timber and concrete in the calculation of hybrid multi-storey buildings is presented. Using the software complex "Lira" the modeling of the stress-strain state of multi-storey buildings of hybrid construction with columns and beams made of glued laminated timber and the reinforced concrete rigidity core. It is established that the characteristics of deformation and creep of materials significantly affect the value of displacement of the frame elements. The values of vertical displacements, taking into account the creep, are 1,57…1,66 times higher than those determined in the elastic stage. Non-uniform deformation of vertical structures causes skew of the storey cells, redistribution of forces between the elements of the frame and the appearance of additional longitudinal forces in the floor beams. Thus, for design multi-storey hybrid wood-reinforced concrete buildings, it is necessary to take into account the influence of deformation and rheological characteristics of wood and concrete on the parameters of the stress-strain state.

Applicability of small resistance fastener on long-span continuous bridges of high-speed railway

Ballastless tracks have been widely applied in high-speed railway (HSR). The adaptability research between continuous welded rails (CWR) and long-span bridges of HSR is of great practical engineering significance. Based on the HSR long-span continuous bridges, the integrative spatial finite element model of track-bridge-pier-foundation system was established with the nonlinear spring element simulating the longitudinal resistance between track and bridge. Comparative study on the various additional longitudinal forces of CWR using the common fasteners and small resistance fasteners was carried out. Analysis results indicate that the additional expansion forces and additional rail-breaking forces in long-span ballastless continuous girders can be reduced evidently by 40%–50% after adopting small resistance fasteners, but lead to greater rail broken gap. The small resistance fasteners have little influence on the additional force only caused by vertical load, but can reduce the additional force caused by vertical load combined with braking load by over 10%. Besides, transient analysis method is proved to be more accurate and safe in calculating additional longitudinal forces when the train running or braking on the bridge, compared with the traditional static method.

Force Characteristics of Longitudinally Coupled Slab Track Turnout on Bridges under Temperature Action

With a longitudinally coupled slab track turnout on LeiDa Bridge on the Wuhan–Guangzhou passenger dedicated line in China as an example, an integral finite element model of a turnout (crossover)–slab track–bridge–pier was developed. This model considered two No. 18 welded turnouts with movable frogs in the form of crossover, longitudinally coupled slab track, bridges, and piers as one system. The computational results included the temperature force and the displacement regularity of the turnouts, slab track, bridges, and piers. Their effect parameters, such as the extensional stiffness of the track slab, the friction coefficient of the sliding layer, and the setting of the anchor point, were also investigated. The key findings are that (a) the additional longitudinal forces and the displacement of rails induced by temperature changes increased with reduced slab extensional stiffness, whereas the corresponding forces of the turnout components decreased significantly; (b) the longitudinal distortions of the track structure were insensitive to the failure of the sliding layer but posed negative impacts on the forces and anchor points of the piers; and (c) it was necessary to arrange anchor points on large-span bridges to prevent rail displacement and reduce the negative effects of forces on the piers.

Mechanics model of additional longitudinal force transmission between bridges and continuously welded rails with small resistance fasteners

A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement among the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.

THE LONGITUDINAL FORCES ARISING IN A WAY BEFORE THE BRAKING TRAIN

The results of experiment on definition of the additional longitudinal forces arising in a railway ahead of a braking train are considered in the article.

Four-Wheel Drive Cars Without Intermediate Differential Gear: Impact on Tire Tread Wear

Abstract Longitudinal tire forces on four-wheel drive cars, both with and without a differential gear between the axles, are compared with those on two-wheel drive cars; tests were made on a curved trajectory. A “critical speed” may be defined which depends solely on characteristics of the car and test tires; this is usually of the order of a few tens of kilometers per hour. Above that speed, for the lateral accelerations normally reached, the additional longitudinal forces caused by lack of an intermediate differential do not increase the relative tread wear rate relative to that on a two-wheel drive car. Cars almost always operate above this critical speed. Below it, however, the additional longitudinal forces caused by lack of a differential are much higher and obviously would lead to higher rates of tread wear.