Research On Damage Identification Of Steel-Concrete Composite Beams Based On Structural Noise

The steel-concrete composite beams are good in load-bearing geometry,short in construction period,economical and aesthetically pleasing,and has broad application prospects in bridge engineering.In operation,steel-concrete composite beams will experience reduced rigidity of shear stiffeners,fatigue damage of steel beams,corrosion of steel,and tensile cracking of concrete,which reduces the bearing capacity and rigidity of composite beams.In worst case scenario,this reduced safety standard even leads to bridge failure.In order to ensure the safety of the structure,regular inspection and evaluations are necessary.This paper presents a damage detection technique for steel-concrete composite beams based on structural noise.The relationship between the vibration characteristics and structural noise of simply supported as well as continuous steel-concrete composite beams after damage were systematically studied.Research work mainly are as follows:(1)Based on the strain energy method,basic vibration equation of the simply supported steel-concrete composite beam considering deteriorated shear stiffener,deteriorated concrete and steel beam was derived.Emphasis was on the free vibration equation of composite beams considering change in shear stiffener stiffness.Natural frequencies and vibration modes of composite beams with different shear stiffness were analyzed.The natural frequency of the composite beam was tested through experiments.Theoretical,experimental and numerically simulated value of natural frequencies were compared.The results showed that the error is within 3%,which verifies the correctness of the theoretical model and the numerical model,requirements of accuracy are met.(2)Simply supported as well as continuous steel-concrete composite beam models were established.Single and coupled working conditions according to the types of shear stiffener damage,steel beam damage,and concrete damage were designed.Changes of structural natural vibration characteristics and equivalent structural stiffness reduction were analyzed.It is found that the change of the structure's natural frequency was extremely insensitive to deteriorated concrete and shear stiffeners,changes in equivalent structural stiffness is small.Changes in damaged steel beam natural frequency is also not obvious,however,changes in equivalent structural stiffness is significant.(3)The geometric model parameters and modal results of the steel-concrete composite beam under various damage conditions are imported into the Vaone software.Structural noise was calculated based on the boundary element method.The results showed that structural noise of the steel-concrete composite beam is very sensitive to damage.It can be seen from the pattern of analyzing various damage conditions in the range of 20 ? 2500 Hz.In the low frequency range,under the condition of 50% reduction in shear stiffeners stiffness,cracked steel beam lower flange plate,and 50% reduction in concrete elastic modulus,the noise sound pressure values of simply supported beam were reduced by 13%,15%,and 2.3%,respectively.The noise sound pressure values of continuous beams under the same conditions were reduced by 22.2%,16%,and 5.0%,respectively.With the increase in structural damage intensity,in the middle and high frequency bands,the changes in the differences between noise sound pressure values caused by shear stiffener damage was obvious,but the change in the case of concrete crack damage of concrete and steel beams was not obvious.This leads to the identification of the type of structural damage through the change in structural noise.