A FREQUENCY IDENTIFICATION METHOD SUITABLE FOR ALL-PHASE SPECTRAL REFINEMENT OF ARCHITECTURAL STRUCTURES

Abstract

SHORT-TIME FOURIER TRANSFORMATION (STFT) HAS BEEN WIDELY RECOGNIZED AS AN INTUITIVE TIME-FREQUENCY ANALYSIS METHOD. HOWEVER, ITS APPLICATION IN BUILDING STRUCTURES IS CONSTRAINED BY ITS LOW ACCURACY OF LOW-FREQUENCY RECOGNITION IN THE SHORT DATA. ACCORDINGLY, THIS STUDY PROPOSES AN ALL-PHASE CHIRP-Z TRANSFORMATION (AP-CZT) FOR FREQUENCY RECOGNITION IN THE BUILDING STRUCTURES BASED ON CHARACTERISTICS OF DYNAMIC TIME HISTORY DATA OF BUILDING STRUCTURES. SPECIFICALLY, THE AR MODEL, WHICH HAS A PROPOSED ORDER DETERMINATION ALGORITHM (ENERGY CONCENTRATION CRITERION,ECC), IS USED TO EXTEND THE DATA LENGTH TO EFFECTIVELY SOLVE THE ISSUE CONCERNING DATA LENGTH LIMITATION IN THE ALL-PHASE DATA PROCESSING TECHNIQUE. SUBSEQUENTLY, ACCORDING TO FREQUENCY CORRECTION THEORY USING SYMMETRIC FUNCTIONS, AN ALGORITHM BASED ON THE ABSOLUTE VALUE OF INVERSE PROPORTIONAL FUNCTION (AIP) IS DEVELOPED FOR POST-REFINEMENT FREQUENCY CORRECTION. TO VERIFY ITS ACTUAL APPLICATION, THE AP-CZT METHOD IS USED TO ANALYZE FREELY ATTENUATING SIMULATING FINITE ELEMENT MODEL SWING DATA AND WHITE NOISE FEEDBACK DATA FROM THE ACTUAL SHAKE TABLE MODEL. THE AP-CZT METHOD IS PROVEN TO BE CAPABLE OF CORRECTLY FINDING HIGH-ORDER FREQUENCIES OUT OF FREE-ATTENUATING VIBRATION DOMINATED BY THE FIRST-ORDER MODE OF VIBRATION, WITH AN ERROR WITHIN 5%. MOREOVER, IT CAN ACCURATELY IDENTIFY FREQUENCIES OUT OF SIGNALS WITH SERIOUS NOISE POLLUTION IN THE SHORT DATA. THEREFORE, THE AP-CZT METHOD PRESENTED IN THIS PAPER CAN BE APPLIED AS A FREQUENCY IDENTIFICATION METHOD IN STFT IN THE FIELD OF BUILDING STRUCTURES.