Eksperimentalna in numerična ocena modalnih parametrov enostavne jeklene konstrukcije : magistrsko delo št.: 276/II. GR

Đukić, Đorđe (author), Brank, Boštjan (mentor), Kosič, Mirko (co-mentor)

V magistrski nalogi smo opravili eksperimentalno in numerično oceno modalnih parametrov enostavne jeklene konstrukcije. Obravnavana konstrukcija je bila postavljena v Laboratoriju za konstrukcije Zavoda za gradbeništvo Slovenije in je sestavljena iz štirih varjenih stebrov ter horizontalnih povezav iz vroče valjanih profilov. Za potrebe meritev smo na konstrukcijo postavili več pospeškomerov. Eksperimentalni del naloge je obsegal meritev odziva zaradi: i) ambientalnih vibracij in ii) vsiljenih vibracij s pomočjo elektromehanskega vzbujevalnika v frekvenčnem območju od 1 – 200 Hz. Za modalno identifikacijo šestih globalnih horizontalnih nihajnih oblik in pripadajočih lastnih frekvenc smo uporabili dve metodi modalne identifikacije, in sicer klasično metodo z upoštevanjem koherence med signali, in metodo razcepa v frekvenčni domeni, ki je vgrajena v komercialni program ARTeMIS Modal Pro. Primerjavo nihajnih oblik smo izvedli na podlagi kriterija modalne gotovosti. Za bolj učinkovito se je izkazala meritev vsiljenih vibracij, na podlagi katere smo zaznali vseh šest globalnih horizontalnih oblik, medtem ko z meritvijo ambientalnih vibracij nismo zaznali dveh globalnih torzijskih oblik. Dodatno smo preučili tudi vpliv dispozicije in občutljivosti senzorjev ter vpliv temperature na rezultate modalne identifikacije. Poleg eksperimentalnega dela smo za konstrukcijo izvedli tudi numerično modalno analizo s programom SAP2000 z modelom iz lupinastih končnih elementov. Iz primerjave izmerjenih in izračunanih lastnih frekvenc smo ugotovili, da izdelani numerični model dobro napove nihajne oblike, slabše pa lastne frekvence. Le-te so bile precenjene, kar kaže na potrebo po posodobitvi preliminarnega numeričnega modela na podlagi izmerjenih modalnih parametrov konstrukcije.

• Language: Slovenian
• Keywords: gradbeništvo, magistrska dela, GR, obratovalna modalna analiza, ambientalne vibracije, vsiljene vibracije, kriterij modalne gotovosti, lastne frekvence, nihajne oblike, koeficienti dušenja
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [Đ. Đukić]
• Year: 2023
• Number of pages: XVII, 70 str., [3] pril.
• PID: 20.500.12556/RUL-148368-5394ebc0-2286-e8ee-27fe-8417810a3cdc
• UDC: 531:624.014.2(043.3)
• COBISS.SI-ID: 168775939
• Publication date in RUL: 19.08.2023

Secondary language

• Language: English
• Title: Experimental and numerical evaluation of modal parameters of a simple steel structure : master thesis no.: 276/II. GR

Abstract

The master thesis presents an experimental and numerical evaluation of the modal parameters of a simple steel structure. The examined structure was set up in the Laboratory for Structures of the Slovenian National Building and Civil Engineering Institute. It consists of four welded columns with horizontal connections made of hot-rolled profiles. For measurement purposes, several accelerometers were installed on the structure. The experimental part of the thesis involved measuring the response of the structure due to: i) ambient vibrations and ii) forced vibrations generated by using an electromechanical shaker with harmonic excitations in the frequency range from 1 to 200 Hz. For modal identification of six global horizontal vibration modes, and their corresponding natural frequencies, we employed two modal identification methods: a classical method considering coherence between signals and the Frequency Domain Decomposition method implemented into the commercial program ARTeMIS Modal Pro. The comparison of the results indicates that both methods yielded comparable estimates of natural frequencies and mode shapes. The mode shapes were compared by the modal assurance criterion. The forced-vibration test proved better as it allowed identification of all six global horizontal modes, while with the ambient vibrations it was not possible to identify the two global torsional modes. Additionally, we examined the influence of sensors disposition and sensitivity, as well as the temperature, on the results of modal identification. Apart from the experimental work, we also performed numerical modal analysis of the structure using the SAP2000 program and shell finite elements. Comparing the measured and computed natural frequencies, it was found that the numerical model predicted well the mode shapes but overestimated the natural frequencies. This indicates the need for updating the numerical model based on the measured modal parameters of the structure.

• Keywords: civil engineering, master thesis, operational modal analysis, ambient vibrations, forced vibrations, modal assurance criterion, natural frequencies, mode shapes, damping coefficients