Modal and dynamic analysis of damaged steel column-beam frame structure subjected to seismic vibrations using experimental and finite element analysis approach

Steel alloy frame structures are mainly used in civil and mechanical industries. These structures are susceptible to mechanical vibrations arising from seismic forces. These vibrations can potentially induce critical damage to various structural elements within these frameworks. This comprehensive research endeavour embarks on the modal and dynamic analysis of damaged steel column and frame structure using experimental and finite element analysis methods. The damage induction process involves systematically introducing cracks of varying depths at distinct positions (single crack at a time) within the structures consecutively. The modal analysis is carried out for all the damaged and undamaged structures. The seismic signal is applied as acceleration base motion in all cases, and modal dynamic analysis is carried out to determine the random response of the models. The numerical model is validated by comparing it with the experimental model data. For free vibration analysis, an initial excitation is imparted by striking the upper free end of the structure with a hammer. The structures are placed on a shake table for forced vibration analysis, and the seismic signal is applied to the base as a load signal. The ensuing response is determined using an accelerometer, having an accuracy of 492.2 (mv/g). It detects and converts the vibration signal into a voltage signal, which is further analysed using a data acquisition system. It is found that the existence of a crack decreases the structure's stiffness, leading to a decrease in the natural frequencies. This decrease can be around 15% of the original frequency for more significant cracks. It is established that the maximum response can increase up to 20% of the undamaged structure response as the location and depth of the crack vary. These response changes manifest in cracks at the joints where elevated stresses are generated. Moreover, a change in gravitational acceleration does not affect the lateral response. The response of the damaged structure can be mitigated around 85% by introducing new steel members at the joints. This study helps determine structure health in the case of random vibrations. Timely evaluating damage severity across diverse structural elements is a preemptive measure against potential catastrophic scenarios.