Theoretical And Experimental Study On Internal Force Identification Of Short Suspender Based On Multi Modal Information

With the vigorous development of China’s economic level,various forms of bridges and long-span spatial structures have gradually become the landmark buildings of various cities.Because of its clear force,convenient installation,beautiful appearance and other characteristics,rod structure is more and more popular with designers.For example,the hollow pole in the space truss structure gymnasium,the suspender in the concrete filled steel tube bridge,etc.In these important building structures,members are the main force bearing components,and most of them bear the axial force.The accurate detection of the axial force of these key members is very important for the overall safety of the structure.In recent years,through the research of many scholars,many axial force identification methods have emerged,and the frequency method is the most widely used.However,a large number of studies show that the frequency method has high recognition accuracy for long and thin members,but low recognition accuracy for short and thick members.At the same time,the recognition accuracy will also be affected when the boundary constraints of members are uncertain.Based on the classical Timoshenko beam theory,some scholars proposed a method to identify the axial force of short bar under unknown boundary by using frequency and mode shape.However,the bending stiffness of members is usually regarded as a known quantity of the product of material elastic modulus and geometric moment of inertia.Many studies show that the elastic modulus of members in practical work will change due to the environmental effect,and the moment of inertia of some members is also different from the theoretical moment of inertia due to the incomplete connection of steel strands,So the bending stiffness is no longer a fixed value.Therefore,on the basis of previous studies,this paper further studies Timoshenko beam theory,and studies the internal force identification method of short suspender under unknown boundary constraints and unknown bending stiffness.In this paper,through the derivation of the classical Timoshenko beam theory formula,it is found that in the partial differential vibration equation of the classical Timoshenko beam theory,when some of its own parameters（area,length,etc.）and modal information are determined,there is a linear relationship between bending stiffness and axial force in any order of modal.Combined with the previous research,the linear equation of bending stiffness axial force of Timoshenko beam under any mode with unknown boundary constraints is constructed.Because the axial force and bending stiffness are the same in different modes,a method is proposed to identify the internal force and bending stiffness of the short suspender under unknown boundary constraints by using the linear relationship between the bending stiffness and axial force under multi-modal information.Then,through the numerical simulation of a simply supported beam model by ANSYS software,the first three order modal information of the simply supported beam is extracted,and the bending stiffness axial force linear relationship of the first three orders of the simply supported beam is constructed.The axial force and bending stiffness of the simply supported beam are identified by any linear relationship of the two order modes,which verifies the correctness of the proposed method.Then,the axial force and bending stiffness of simply supported beam under different conditions（different length,axial force）are identified by numerical simulation,and the identification accuracy is good.Then,the axial force tests of three different cross-section bars（solid round bar,hollow round bar and hollow square bar）are carried out in the laboratory.It is found that there is a certain deviation between the actual elastic modulus and the theoretical elastic modulus.According to the previous axial force identification method,it is necessary to measure the elastic modulus again before the experiment to obtain the accurate bending stiffness.The experimental results show that the proposed method does not need to measure the elastic modulus in advance,and has good recognition accuracy for the axial force and bending stiffness of three different cross-section members.By comparing this method with several common axial force identification methods,the advantages of this method for the identification of axial force under uncertain bending stiffness are verified.Then,through the study of MATLAB software,it is found that the GUI man-machine interface in MATLAB has a unique application value for the identification of the axial force of members.Based on this,the GUI interface of various axial force identification methods is compiled.Finally,the modal test and analysis of the short suspender on a concrete-filled steel tube through arch bridge in Shantou are carried out by using laser vibration meter and highspeed camera.The obtained modal information is substituted into the GUI interface to identify the internal force of suspender.It is found that using GUI to identify internal force of suspender is simple and accurate.