Test Method Of Steeve Stretching Force Basis On Natural Frequency Of Steeve Arch

At present,the methods of testing steeve cable force are reading method of number with oil pressure gauge,demarcating method with sensors and frequency method.The precision of reading method of number with oil pressure gauge is very low.While the precision of demarcating method with sensors is somewhat increased,but the test implementation is limited by construction conditions,and also takes much time and vigour.The two methods mentioned above are suitable for the cable force test of the steeve being tensioned. The cable force test of the steeve having been tensioned almost can use frequency method.The existing frequency method mainling learns from string vibration which formula commonly used in cable force test of cable-stayed bridges.That is that by means of vibration signal theory,starting with dynamic equilibrium differential equation,the relationship between steeve cable force and steeve natural frequency is derived.Basis on this,steeve cable force can be obtained by steeve natural frequency.But at actual engineering,there is some error between frequency method and reality.Main reason of the problem is that the influence of steeve stiffness,boundary conditions and effective calculating length on steeve natural frequency is neglected. In cable-stayed bridges,stayed cable is usually long type.The error caused by this influence can meet the demand of engineering precision.But the cables of steeve arch bridges are much shorter than that of cable-stayed bridges.The cables of steeve arch bridges are tens meters,some of them are even several meters,so the influence of steeve stiffness,boundary conditions and effective calculating length on natural frequency of this short cables is very large.Traditional.Error-difference of the frequency method is large when it's used in testing the cable force of short cables,and the relationship between short cable frequency and cable force can not be real reflected.Therefore,it's necessary to study how to testing cable force of short cables exactly.And it's a signality to construction and usage monitoring of steeve arch bridges.In the aspect of short cable force of the arch bridges,basis on analysis of forced state of bar system arch bridges,Xiao Yu-de worked on the calculation of steeve cable force of different length. The influence of boundary conditions is taken into consideration in this calculation,and the method has certain practicality.While under two different conditions,Meng Shao-hua,etc.from the view of considerating steeve flexural rigidity,the relationship between cable force, flexural rigidity and steeve frequency by using energe method,and summarized accurate calculation of cable force by first 2-order natural frequency.Yin Shuang-qing.etc proposed that in the steeve cable force test of arch bridges,the method of testing frequency response function is used to determine natural frequency of short cables.And basis on actual boundary conditions and modal form,the reasonable effective calculating length of cable force is obtained.So short cable force can be calculated accurately.This method depends on improving the accurate of frequency test to improving that of cable force test.Zhou Xiao-ye comparing with several kinds of calculation models of steeve cable force which is used in tie bar arch bridges test basis on frequency method,analyzed the influence law of steeve slenderness on model calculation accuracy,and cable force calculation model corresponding to steeve slenderness is obtained.Li Ting-bo,Li Hong-xiang did application research on frequency method according to concrete bridge type.All of the research on calculation of short cable force obtain some achievements,but the calculation that each influence factor is taken into consideration systematicly and comprehensively isn't formed.Therefore,it is still needed to do systematic research on theory of frequency method test of short cable force.Firstly,theoretical analysis of steeve transverse vibration and theoretical derivation of stretching force calculation of many kinds of steeve vibration models are carried out.The steeve stretching force calculation basis on modified stiffness is formed,and basis theory and calculation course of the method are made clear.Technical problems during the course of steeve natural vibration frequency test are analyzed deeply,and the test course of steeve natural vibration frequency is discussed.Finally, Steeve stretching test of one steeve arch bridge which located in Chang Chun light rail third phase project and has been completed bridge is taken as example. Steeve stretching test and calculation formed in this paper are used in practical engineering and verified.Main research work is carried out in this paper as follows: 1.Steeves are assumed as tension ropes,level straight beams with two sides hinged support and level straight beams with two sides clamped support,repectively.Basis on the basic theory of structural dynamics,transverse vibration equations are established,respectively,and the relationship between natural frequency and stretching is obtained.Transverse vibration of the steeves with additional damper is also analyzed.Based on vibration models of level straight beams,correction method of cable flexural rigidity is proposed in this paper. Calculation of steeve stretching based on modified rigidity is proposed,and basic theory and calculation course of the method is made clear.2. Theoretical analysis of the course of steeve natural frequency test is carried out,and a series technical problems such as exciting method,selection principle of measuring instrument,installation method and position of vibration pickup and setting of sampling frequency are made clear.Based on fully understanding about the basic theory of digital filter,according to the theory of low pass butterworth filter,digital filters are designed.Calculation of adaptive power spectral density of measuring point dynamic response is given,and then calculation of obtaining steeve natural frequency is formed. Finally,obtaining course of steeve natural frequency is concluded,and program block diagram of steeve natural frequency test and extraction is formed.3.Steeve stretching test of one steeve arch bridge which located in Chang Chun light rail third phase project and has been completed bridge is taken as example.Steeve stretching test and calculation formed in this paper are used in practical engineering and verified.Steeve effective vibration lengh and correction flexural rigidity are calculated by using the method of steeve stretching holding when being adjusted.And on basis of the calculated effective vibration lengh and correction flexural rigidity, steeve stretching is tested when the bridge is compeleted.From the result of stretching,it can be considered that, steeve stretching test and calculation formed in this paper has high accuracy;The test course of steeve stretching is easy,and it can be carried out without any auxiliary equipment.Therefore,the steeve stretching test method formed in this paper is reliable and effective.