INFLUENCE OF THE SEISMIC EXCITATION FREQUENCIES CONTENT ON THE BEHAVIOR OF A TUNED MASS DAMPER IN LOW-RISE BUILDING CONSIDERING SOIL-STRUCTURE INTERACTION

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GILDA ESPINOZA
FRANCO BENEDETTI
PATRICIO ALVAREZ-MENDOZA
EDUARDO BONILLA

Abstract

THE INFLUENCE OF THE FREQUENCIES CONTENT OF SEISMIC EXCITATIONS ON BEHAVIOR OF AN OPTIMAL TUNED MASS DAMPER (TMD) IS STUDIED IN THE CONTEXT OF A SYSTEM WITH EXPLICIT CONSIDERATION OF SOIL-STRUCTURE INTERACTION. A STOCHASTIC ANALYSIS IS MADE IN THE TIME DOMAIN FOR TWO RANDOM PROCESSES, ONE CONSIDERING A BROAD BANDWIDTH PROCESS (BBP) AND OTHER CONSIDERING A NARROW BANDWIDTH PROCESS (NBP). A STRUCTURE BUILT OVER THREE DIFFERENT TYPES OF SOIL IS CONSIDERED (SOFT, MEDIUM AND HARD). FOR THE TMD'S OPTIMIZATION, THE MINIMIZATION OF THE RATIO BETWEEN THE STANDARD DEVIATION OF THE DISPLACEMENT OF THE MAIN STRUCTURE WITH TMD WITH REGARD TO A STRUCTURE WITHOUT TMD IS USED AS THE TARGET FUNCTION. IT IS FOUND THAT FOR SEISMIC EXCITATIONS WITH HIGH FREQUENCIES CONTENT, THE RATIO OF TMD'S FREQUENCIES COMPARED TO THE STRUCTURE'S FIXED BASE FREQUENCY APPROACHES TO 1 AS THE SOIL BECOMES MORE RIGID. IN THE OTHER HAND IT ALSO OBSERVED THAT IT TUNED WITH THE FLEXIBLE BASE FREQUENCY FOR ALL SOIL TYPES, PRODUCING PERFECT TUNING FOR SMALL MASS RATIOS AND DETUNING DECREASINGLY FOR HIGHER MASS RATIOS. ON THE OTHER HAND, THE TMD OPTIMAL DAMPING RATIO INCREASES AS THE TMD'S MASS RATIO IS HIGHER INDEPENDENTLY OF THE SOIL TYPE. THE TMD IS MORE EFFICIENT FOR HIGHER VALUES OF THE TMD'S MASS RATIOS, ESPECIALLY ON SOFT SOIL. IN STRUCTURES BUILT OVER FLEXIBLE BASE, THAT ARE SUBJECTED TO LOW FREQUENCY CONTENT EXCITATIONS, THE OPTIMAL TMD IS TUNED WITH THE FLEXIBLE BASE, INDEPENDENTLY OF THE TYPE OF SOIL AND THE MAIN STRUCTURE'S FIXED BASE PERIOD. THE TMD'S OPTIMAL DAMPING IS NOT SENSITIVE TO THE FLEXIBLE PERIOD FOR SMALL MASS RATIOS, AND REACHES ITS MINIMUM VALUE WHEN IT MATCHES WITH THE SEISMIC EVENT'S PREDOMINANT PERIOD. ON THE OTHER HAND, THE TMD REACHES ITS MAXIMUM EFFICIENCY WHEN IT IS TUNED WITH THE FLEXIBLE PERIOD OF THE SOIL-STRUCTURE SYSTEM, AND COINCIDES WITH THE PREDOMINANT PERIOD OF THE SEISMIC EXITATION AND IS HIGHER ON SOFT SOIL. A DETERMINISTIC ANALYSIS IS MADE THROUGH THE MODEL'S EXCITATION FOR TWO SEISMIC EVENTS, AN ARTIFICIAL EARTHQUAKE COMPATIBLE WITH THE CHILEAN NORM NCH2745 CHARACTERIZED BY HIGH FREQUENCIES CONTENT AND OTHER SIMILAR TO THE EVENT IN 1985 IN MEXICO, CHARACTERIZED BY LOW FREQUENCIES CONTENT. IT IS SEEN THAT THE OPTIMAL TMD IS EFFICIENT CONTROLLING THE STRUCTURE'S RESPONSE IN ALL TYPES OF SOIL ANALYZED.

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