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Deteção e localização de dano estrutural numa estrutura de três andares sujeita a diferentes severidades de dano
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A deteção precoce de danos estruturais é um desafio no âmbito da monitorização estrutural,
uma vez que pequenas alterações nas propriedades dinâmicas podem comprometer o desem-
penho e a segurança das estruturas. Os métodos baseados em vibrações, particularmente as
Funções de Resposta em Frequência (FRFs), têm sido cada vez mais estudados e têm-se mos-
trado eficazes na identificação de danos estruturais.
Esta dissertação tem como objetivo avaliar o desempenho de uma metodologia de identifica-
ção de dano baseada em vibrações, aplicada à deteção, localização e quantificação relativa de
dano numa estrutura experimental de três andares. A metodologia em estudo utiliza o Indi-
cador Razão (Ratio Indicator, RI), um indicador sensível ao efeito acumulado das pequenas
alterações introduzidas nas Funções de Resposta em Frequência (FRFs) da estrutura, resultan-
tes da presença de dano. A aplicação e validação experimental da metodologia foram realiza-
das numa estrutura desenvolvida e construída no Laboratório de Mecânica Estrutural da
NOVA FCT.
A estrutura utilizada é composta por 12 vigas e 4 placas de alumínio, instrumentada com 9
acelerómetros e excitada através de um martelo de impacto. Foram aplicados 19 cenários di-
ferentes de dano, consistindo na remoção de massas em diferentes posições das vigas e placas,
com severidades que variaram entre 0,07% e 9,77% da massa total da estrutura.
A identificação do dano foi realizada pelo cálculo doRI entre as FRFs da estrutura de refe-
rência (sem dano) e as da estrutura com dano. A presença de dano foi confirmada através do
Damage Indicator (DI), com valores superiores a 1 em todos os casos.
A localização do dano, determinada a partir do índice Force-Averaged Ratio Indicator (FARI),
revelou-se precisa para severidades de dano nas vigas até 0,12%. A quantificação relativa do
dano foi obtida para os casos analisados, observando-se um aumento do valor do índice de
dano (DI) com o incremento da severidade do dano.
Os resultados obtidos demonstram o sucesso da metodologia para os danos aplicados nas vi-
gas, e uma eficácia mais reduzida para danos aplicados nas placas.
The early detection of structural damage is a challenge within the scope of structural health monitoring, since small changes in dynamic properties can compromise the performance and safety of structures. Vibration-based methods, particularly Frequency Response Functions (FRFs), have been increasingly studied and shown to be effective in identifying structural damage. This dissertation aims to evaluate the performance of a vibration-based damage identification methodology applied to the detection, localization, and relative quantification of damage in a three-storey experimental structure. The methodology under study employs the Ratio Indica- tor (RI), a damage indicator sensitive to the cumulative effect of small changes introduced in the structure’s Frequency Response Functions (FRFs) as a result of damage. The experimental application and validation of the methodology were carried out on a structure developed and built at the Structural Mechanics Laboratory of NOVA FCT. The structure consists of 12 beams and 4 aluminum plates, instrumented with 9 accelerometers and excited by an impact hammer. Nineteen different damage scenarios were applied, con- sisting of the removal of masses in different positions of the beams and plates, with severities ranging from 0.07% to 9.77% of the total mass of the structure. Damage identification was performed by calculating theRI between the FRFs of the reference structure (undamaged) and those of the damaged structure. The presence of damage was con- firmed through the Damage Indicator (DI), with values greater than 1 in all cases. The damage localization, determined from the Force-Averaged Ratio Indicator (FARI), showed accurate results for damage severities in the beams up to 0.12%. The relative quantification of damage was obtained for the cases analyzed, with an observed increase in the value of the Damage Index (DI) as the damage severity increased. The results demonstrate the success of the methodology in detecting damage in the beams, while showing reduced effectiveness in the plates.
The early detection of structural damage is a challenge within the scope of structural health monitoring, since small changes in dynamic properties can compromise the performance and safety of structures. Vibration-based methods, particularly Frequency Response Functions (FRFs), have been increasingly studied and shown to be effective in identifying structural damage. This dissertation aims to evaluate the performance of a vibration-based damage identification methodology applied to the detection, localization, and relative quantification of damage in a three-storey experimental structure. The methodology under study employs the Ratio Indica- tor (RI), a damage indicator sensitive to the cumulative effect of small changes introduced in the structure’s Frequency Response Functions (FRFs) as a result of damage. The experimental application and validation of the methodology were carried out on a structure developed and built at the Structural Mechanics Laboratory of NOVA FCT. The structure consists of 12 beams and 4 aluminum plates, instrumented with 9 accelerometers and excited by an impact hammer. Nineteen different damage scenarios were applied, con- sisting of the removal of masses in different positions of the beams and plates, with severities ranging from 0.07% to 9.77% of the total mass of the structure. Damage identification was performed by calculating theRI between the FRFs of the reference structure (undamaged) and those of the damaged structure. The presence of damage was con- firmed through the Damage Indicator (DI), with values greater than 1 in all cases. The damage localization, determined from the Force-Averaged Ratio Indicator (FARI), showed accurate results for damage severities in the beams up to 0.12%. The relative quantification of damage was obtained for the cases analyzed, with an observed increase in the value of the Damage Index (DI) as the damage severity increased. The results demonstrate the success of the methodology in detecting damage in the beams, while showing reduced effectiveness in the plates.
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Palavras-chave
Funções de Resposta em Frequência Deteção de dano Localização de dano Quantificação Relativa de dano