# USE OF MODAL ANALYSIS AS A METHOD TO ESTIMATE SECOND- ORDER GLOBAL EFFECTS IN REINFORCED CONCRETE STRUCTURES

## Palavras-chave:

Second-order effect, Modal analysis, Structural stability## Resumo

Recent work shows that there is a relationship between the natural vibration period and the

second-order global effects in the reinforced concrete frames, this link occurs because both depend

essentially on the rigidity and mass matrix of the structure. Formulations are developed to demonstrate

and validate that an amplification factor is able to approximate second-order global effects satisfactorily.

Previous studies just consider the additional mass as a load increment. However, the second-order effects

of external loads on the structure not beem take into account to calculate the internal forces in structural

elements and their influence on the dynamic characteristics. Therefore, the second-order effects are

included to analyze the influence of the dynamic characteristics (natural frequencies and vibration

modes) and the amplification of the structure moment. Analyzes will be carried in a regular element of

reinforced concrete. The amplification will be evaluated by means of natural frequencies and modes of

vibration. Thus, this work generally aims at obtaining an alternative parameter of calculation, based on

the natural frequency and mode of vibration of the structure, to be used as an indicator of the necessity

or not of the consideration of the second-order global effects in reinforced concrete structures.