Load Identification on an Arch Bridge Based on the Generalized Flexibility Matrix

Health problems of the bridge structure are a hot issue in engineering research currently. Load identification together with damage identification is an important method to diagnose the health status of the bridge. In order to identify different loads on bridges, this paper takes a box arch bridge built with prestressed reinforced concrete in Chongqing as an example and establishes it’s finite element model. The general flexibility matrix is obtained by calculating the response values of each control section separately caused by each unit characteristic load. The maximum bending moment of each control section is acquired by using the time history analysis of Wenchuan Seismic wave, and the equivalent loads are derived from the general flexibility matrix. Results indicate that this method can identify a wide range of basic load types and accurately identify the actual load of the bridge with high precision. Thus the actual operating conditions of bridge can be better reflected and the bridge’s safety condition can be evaluated. Besides, the load evaluation and maintenance of the bridge can be based on this.


Introduction
With the development of national economy and increase of traffic volume and traffic density, damage accumulation of bridge structure will be caused as the bridge is repeatedly affected by traffic and natural causes.Thus, fatigue damage, even the fatigue rapture can be caused, threatening the bridge safety in use and reducing the service life of the bridge.For example, there is some phenomenon of destruction on the deck of many shortly used bridge, such as cracking, material unconsolidation and collapse, which cannot be explained by static theory; meanwhile, cracking emerges on many prestressed concrete bridges which have been designed with crack resistance, and the cracking may become worse due to the repeated action of traffic loads as well as the increase of operation time, consequently, corrosion of steel bar will be caused and the load capacity of the bridge will decrease.Therefore, if detailed research on bridge damage and destruction mechanism that are caused by various loads can be conducted and loads acting on the bridge can be identified and measured, it will be of great theoretical and applicational value in health monitoring, daily maintenance, safety assessment and traffic design of bridge.And it is also of important guiding significance in design, construction and maintenance of bridge structure.
Load identification of bridge structure is one of the most important issues in bridge design, and it is also an import aspect in inverse problem in structural dynamics.The research of identifying the load on bridge deck by means of bridge response has made some progress and the main identifying methods are: Frequency Domain Method, Frequency-Time Domain Method and methods based on neural network, etc.At present, the load identification methods at home and abroad mainly target at certainty load, which mainly include periodic dynamic load and impact load.Many researches show that the bridge response caused by dynamic load is stronger than that of static load, besides, dynamic load will cause more damage than static load does, usually 2-4 times (Cebon, 1987).The research of identification of random load as well as accidental load is still in progress and there is little achievement in this area.
Based on a prestressed reinforced concrete box arch bridge in Chongqing, this paper focuses on the time-history analysis of its finite element models under the effect of Wenchuan Earthquake Load and the actual response time-history of the bending moment of the key measure points of the bridge structure is achieved.According to the princip span of the achieved.high practi when tryin

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Conclusion
This essay, on the background of stress reinforced concrete box arched bridge, set up finite element models, and verifies the effectiveness and pragmatism of substituting actual load with equivalent feature load according to the equivalence principle of internal forces by identifying the actual load during the Wenchuan earthquake by means of generalized flexibility matrix of itself.And this essay draws the following conclusions: (1) The errors of the results inducted from the equivalence principle of internal forces for the Wenchuan earthquake load are all less than 5%, most of which are less than 1%, which fully demonstrates that it is feasible to substitute actual load with equivalent load.The method stated in this essay can be used in various types of basic loads, and various types of information can be measured out.The actual load of the bridge can also be figured out fairly accurately which can reflect the actual operation condition of the bridge so as to evaluate the security condition of the bridge.
(2) As for the bridges which already have structural health-monitoring systems set up, they can take the actual load during the operation as the equivalent feature load which is fast, pragmatic, and accurate in an acceptable scope of engineering projects.
(3) The equivalence principle of internal forces based load identification method of this essay is able to get the equivalent feature response under actual load.When the response is highly representative, the accuracy of load evaluation can be increased pronouncedly, which provides evidence for the maintenance and management of the bridge's regular operation.
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