evaluation of forces on steel truss structure using resonance frequency analysis (experimental and numerical study)

Structural decay may be defined as any deviation in a structure�s original geometry or material properties that may cause undesirable stresses, displacements, and vibrations in the structure. This decay may be due to cracks, loose bolts, broken welds, corrosion, or fatigue. In addition, many bridges are decayed due to aging, misuse, lack of repair, and, in some cases, caused by improper design. Conventional inspection remains the most commonly used method for the structural evaluation of bridges. Conventional inspection can be costly and time consuming, especially when disassembly is necessary to provide access to the area being inspected. Nondestructive testing such as resonance frequency analysis provides an alternative solution. Based on literature study carried out on resonance frequency testing for the determination of axial forces, a simple truss structure was modeled. The truss structure has 2 members using equal steel section of L.30.30.3, each acting as a compression and tension members, and then applied load was accomplished by hanging a steel block on the tip of the truss being tested. Finally, transversal frequency measurements were performed on the truss members under various load levels. The collected resonance frequencies were then evaluated using Bernoulli beam theory to estimate member forces and rotational spring parameter at the ends of the member. This research shows that the error of estimation of member forces in compression and tension members using modified natural frequency and rotational spring parameter by linear regression method varies from 0.26% to 1.99% and 0.2% to 2.41% respectively. The value of rotational spring parameters indicates that the members have semi rigid behavior and closer to fixed rather than pinned conditions