Dynamic Performance Analysis And Design Of Aluminum Alloy Truss Pedestrian Bridge

In recent years,the application of aluminum alloy has been widely appreciated.It has developed rapidly especially in the application of bridge engineering,and has also attracted people’s attention.Its advantages include small density of materials,light weight,high strength,nice corrosion resistance,good durability,convenient construction,easy maintenance and processing,etc,and its unique metal luster and advantages of materials combine well with modern buildings promote the mutual cooperation and integration of construction engineering and architectural art.The first application of aluminum alloy materials used in bridge engineering is Smithfield Street Bridge in Pittsburgh,USA,which was built in 1933.The original deck of the whole bridge was replaced by aluminum structure.After that,aluminum structure bridges developed rapidly in various countries.China has gradually begun to pay attention to the application of aluminum alloy in bridges.This paper mainly introduces the development and research states of aluminum alloy bridge at home and abroad,Based on the phenomenon of lateral "locking" caused by Millennium Bridge,this paper studies the lateral "locking" phenomenon of aluminum alloy pedestrian bridge when it is close to the safety factor of natural frequency.And takes an aluminum alloy truss pedestrian overpass as the object.Firstly,we design the basic size of the overpass,and then check the bridge stability by Midas software.The maximum deflection in the middle of the span is 38.7 mm,which meets the requirements of the design code for pedestrian overpass in China for the vertical deflection L / 600(66.7 mm).Under the most unfavorable load,the maximum tensile stress appears at the lower part of the middle of the overpass,the maximum tensile stress is 33.4 MPa,and the maximum compressive stress appears at the upper part of the middle of the span,the maximum compressive stress is 36.9MPa.The first-order natural vibration frequency is 3.13 hz,the second-order natural vibration mode is vertical upward instability,the frequency is 5.32 hz,the third-order natural vibration mode is out of plane instability with an inflection point,the natural vibration frequency is6.87 hz,it can be obtained through another software after meeting the requirements In the dynamic time history analysis of 17.0 software,11 working conditions are used for calculation and analysis respectively.The results show that the maximum vertical acceleration is 1.20 M / S2 and the maximum lateral acceleration is 0.27 M / S2 in the most unfavorable working condition.The lateral comfort degree of pedestrian bridge vibration is evaluated by EN03(2007).Through comparison,it is found that the lateral acceleration is close to the lower acceleration value of 0.30m/s2 of discomfort(Level 3),which is in the "critical" state,and there is a risk of "locking".After the Millennium Bridge event,the resonance phenomenon of aluminum alloy bridge is an important problem that can not be ignored.This paper discusses the reasons for the "locking".On the one hand,the first-order natural frequency of the bridge is 3.13 hz,which isclose to the maximum safety frequency,on the other hand,the density of the crowd excited by the external is large and the pedestrian speed is large.The natural frequency can be increased at the beginning of bridge design,the density of external crowd can be controlled,and the damper can be added later.In this paper,through the in-depth study of the resonance problem of aluminum alloy bridge,we hope to provide reference for our country’s aluminum alloy humanoid overpass.