Temperature Effect Analysis On Bridge Natural Frequency And Monitoring System Construction Of Forces In Hangers In Chill Region

The natural frequencies are the most common parameters in bridge design, detection,monitoring and damage identification. The bridge natural frequencies measured can alter asthe changes in external environmental factors. Related data show that the changes in naturalfrequencies aroused by external environmental factors can cover those caused by damage.Temperature is the main factor leading to the changes in the natural frequencies. At present,the scholars at home and abroad set about the researches in this respect, however, until nowthere is no conclusion about the mechanism, influencing laws and the excluding methods oftemperature affection on the bridge natural frequencies. Therefore, it’s necessary to form theeffective method in excluding temperature effects from the measured natural frequencies.To the concrete bridge structure, the mechanical property of the concrete material directlydetermines the structural dynamic performance. So the variability of the concrete materialmechanical property under different temperatures may lead to the changes in the bridgenatural frequencies. The scholars at home and abroad conducted some basic researches onthe mechanical property changes caused by the temperature. Research results concentrate onthe changes in the concrete material mechanical property in the extreme high temperature orthe extreme low temperature. But the bridges are structures affected by the outdoorenvironment temperature. On the other hand, the influencing laws of different concretematerials on the mechanical properties are not the same.In bridge structures, simply-supported and continuous beams are the most commonstructure styles. Under the nonlinear temperature gradient, simply-supported beam may havethe thermal self-restraint stress, and continuous beams may have the thermal self-restraintstress and secondary temperature stress, which change the structure vibration initial state.And how the changes in vibration initial state lead to the changes in the natural frequenciesshould be researched further.The values and distribution of the cable forces of tied arch bridge has significant effects onthe mechanical property of the whole bridge. It’s believed that the cable force statedetermines the operational safety and the comfort in use of this kind of bridge. So it’snecessary to accurately master the cable force bridge. In order to timely grasp the cable forcestate, the most effective method is to build the monitoring system of cable force to conduct real-time monitoring of the whole cable forces. To the data transmission module, there aretwo kinds of transmission methods. They are wired and wireless methods. No matter whichmethod, the data transmitted are giant, which may easily lead to system breakdown and thedisability to acquire effective information from the giant data. Therefore, it’s necessary toeffectively screen and control the data transmitted, which is one of the problems with urgentneed to be solved. The cable force condition evaluation module analyzes the cable forcesfrom the collected dynamic responses, and then evaluates the cable forces. The evaluationsinclude the single cable force state evaluation and the whole bridge cable force stateevaluation. Related data show that the external environmental temperature has someinfluences on the cable forces measured. Sometimes, the changes caused by the temperaturecan drown the real changes of the cable forces. In chill regions, the temperature range greatlyin a year and in a single day. Therefore, the problem is especially obvious in the cable forcetests in the chill regions. So no matter which kind of cable force evaluation, the temperatureshould be taken into consideration.In the testing process of the natural frequencies of the bridge, especially the large-spanflexible bridge, the environmental temperature, moisture, traffic and the wind load maycause the changes in the natural frequencies. Related data show that each factor influencedifferent frequency modes and vibration styles in different extent. And each factor influencesthe natural frequencies in a non-linear process. In order to analyze the measured thermaleffect, the natural frequency modes of the bridge which are mainly affected by thetemperature should be picked out from the multiple frequency modes. After determining thefrequency mode mainly affected by the temperature, the next assignment more important isto establish the relationship between the environmental temperature and the bridge naturalfrequencies based on the measured data. Then form the excluding algorithm of the effectiveenvironmental temperature, so as to analyze the temperature effects from the naturalfrequencies measured. Because different factors have a coupling effects on the naturalfrequencies, it’s difficult to find out the frequency mode mainly affected by the temperature.The effects of temperature on natural frequencies are a complex nonlinear process, it’s achallenge to establish the method excluding temperature effects.Relying on the National High Technology Research and Development Program ofChina(863Program)“Research on the System for Monitoring, Identification andEarly-warning of Wide Range Road Hazards in Seasonal Frozen Soil” and the SpecializedResearch Fund for the Doctoral Program of Higher Education Project “Study on the Bridge Modal Frequency Updating Technique Based on the Multiple Temperature Fields(20090061110036)”,and this paper conducts the following researches to analyze thetemperature effects on bridge natural frequency and monitoring system construction offorces in hangers in chill region:1. The cube compressive strength, axial compressive strength, modulus of elasticity, tensilesplitting strength and Poisson’s ratio are measured under the temperature of-20℃-60℃. Thegeneralized least squares method is applied to conduct statistical analysis on the measureddata and conclude the influencing law of temperature on each mechanical parameter.2. The natural frequency calculation method of simply-supported beam is formed underthe solar radiation, and the natural frequency analysis method for continuous box girderbridge is present based on the SSI.3. Grey relational analysis theory is used to form the screening method for the massivedata and effectively control the data transmission, then establish a cable force monitoringsystem. Neural network method is applied to analyze and assess the single cable force. Andthe analysis and assessment for all the cable forces are formed based on the grey relationaltheory and the support vector machine arithmetic. Both the single cable bridge stateassessment method and the whole bridge cable force assessment method can effectively getrid of the effects of external environment.4. Based on the project of a three-span tied arch bridge, reduction of dimensionality isconducted to the influencing factors by means of nonlinear principal component analyticalmethod, and the frequency mode mainly affected by the temperature is picked out from themultiple natural frequencies combined correlation analysis. Then the measured data areanalyzed by means of the grey particle swarm optimization neural network algorithm toestablish the relationship between temperature and the natural frequencies, and then form themethod to get rid of the temperature.