详情

BBT2014-014 Dynamiskt beteende av brolager - en f�rberedande studie och labf�rs�k

项目名称：	BBT2014-014 Dynamiskt beteende av brolager - en f�rberedande studie och labf�rs�k
摘要：	Previous studies at KTH have shown that the dynamic properties of certain bridges, i.e. the natural frequencies and modal damping ratios have a certain amplitude dependency. Apparently, the main source of this non-linear effect is the frictional behaviour of the bridge bearings. At very small amplitudes of vibration, the frictional resistance in the bearings is not overcome and hence, assumed simple supports then behave as fixed bearings. As the amplitude of vibration increases, the frictional resistance is overcome and at some amplitude of vibration, the bearings behave as free bearings. However, due to the mechanism known as "micro-slip" (for sliding friction) and "pre-rolling resistance" (for rolling friction), there is a transition between the fixed and free state of these frictional devices. During this transition, the natural frequency of the mode of vibration decreases monotonically whilst the damping ratio increases in a uni-modal manner. This behaviour appears to lead to rather large variations in the dynamic properties of bridges, depending on the bridge type and parameters such as construction height and support stiffness. For example, for certain railway bridges, the decreasing natural frequency may lead to underestimated dynamic effects caused by train-bridge resonance while for others; it may lead to overestimated dynamic effects. Therefore, it is highly desirable to improve our understanding of the mechanical behaviour of bridges equipped with sliding bearings or roller bearings. This knowledge is essential in assessments of existing bridges, where measurements can be performed and to define guidelines for design of new bridges so that the properties of the bearings are taken into account in an appropriate manner. If it can be shown that certain existing bridges should be ascribed a higher damping ratio than that specified by the design codes or estimated from measurements at very small amplitudes of vibration, this could lead to substantial savings for society when for example existing railway lines are upgraded to higher speeds and/or higher axle loads.
资金：	0.00
资助组织：	Trafikverket, Sweden
项目负责人：	Mika, Frank
执行机构：	Kungliga Tekniska H�gskolan, KTH
开始时间：	20150301
预计完成日期：	20161231
实际结束时间：	0