Transfer matrisi formülasyonları kullanılarak Pasternak zemini üzerine oturan kademeli Timoshenko kirişlerinin serbest titreşim analizi

Abstract

Bu çalışmanın amacı, iki parametreli elastik zemin üzerine oturan kademeli Timoshenko kirişlerinin serbest titreşim analizinin transfer matrisi yöntemi (TMM) kullanılarak yapılmasıdır. Winkler yaylarına eklenmiş, sıkıştırılamaz dikey elemanlardan oluşan bir kayma tabakasına sahip olan Pasternak zemin modeli dikkate alınmıştır. Pasternak zemini üzerine oturan Timoshenko kirişlerinin hareket denklemlerinin kapalı çözümlerine dayanan transfer matrisi formülasyonları elde edilmiştir. Doğal frekanslar, sınır şartlarına göre indirgeme yapılması sonrası yapının global transfer matrisinin determinantının sıfıra eşitlenmesiyle hesaplanmıştır. Mod şekilleri, uçlardaki durum vektörleri normalize edilerek çizilmiştir. İlk olarak, her iki ucu basit mesnetli bir kiriş için, önerilen yaklaşım kullanılarak elde edilen doğal frekanslar literatürdeki verilerle doğrulanmıştır ve çok iyi bir uyum gözlemlenmiştir. Daha sonra, sayısal analiz için basit-basit (S-S), basit-ankastre (S-F), ankastre-basit (F-S) ve ankastre-ankastre (F-F) sınır koşullarına sahip üç kademeli bir kiriş modelleri dikkate alınmıştır. Kademeli kiriş modeli için TMM kullanılarak hesaplanan doğal frekanslar, elastik zeminin kayma tabakasının etkileri ihmal edilerek SAP2000'in sonlu elemanlar yöntemi (FEM) sonuçlarıyla karşılaştırılmıştır. Winkler yaylarının rijitliğinin ve kayma tabakasının kademeli kiriş modelinin doğal frekansları üzerindeki etkileri sırasıyla S-S, S-F, F-S ve F-F sınır koşulları için ortaya çıkarılmıştır. Kademeli kiriş modelinin mod şekilleri sunulmuştur. Sonuçlar, TMM'nin Pasternak zemini üzerine oturan çok kademeli Timoshenko kirişlerinin serbest titreşim analizi için etkili bir araç olarak kullanılabileceğini göstermektedir.

Keywords

• Mod şekli
• Doğal frekans
• Pasternak zemini
• Kademeli Timoshenko kirişi
• Transfer matrisi

Free vibration analysis of segmented Timoshenko beams on Pasternak foundation by using transfer matrix

Abstract

The aim of this study is performing free vibration analysis of segmented Timoshenko beams on two parameter elastic foundation by using the transfer matrix method (TMM). The Pasternak foundation model which has an incompressible shear layer of vertical elements attached to the Winkler springs was considered. The transfer matrix formulations which are based on closed-form solutions of equations of motion of Timoshenko beams on Pasternak foundation were obtained. The natural frequencies were calculated by equating the determinant of global transfer matrix of structure to zero after the reduction according to boundary conditions. The mode shapes were plotted by normalising the state vectors at the ends. Firstly, the natural frequencies that obtained by using the proposed approach were validated by data in literature for a simply supported beam where a very good agreement was observed. Then, three-segmented beam models having various boundary conditions namely simple-simple (S-S), simple-fixed (S-F), fixed-simple (F-S) and fixed-fixed (F-F) were considered for numerical analysis. For the segmented beam models, the natural frequencies that calculated by using the TMM were compared to the results of finite element method (FEM) from SAP2000 by ignoring effects of shear layer of elastic foundation. The effects of shear layer as well as stiffness of Winkler springs on the natural frequencies of the segmented beam model were revealed for S-S, S-F, F-S and F-F boundary conditions, respectively. The mode shapes of the segmented beam model were presented. The results show that TMM can be used as an effective tool for free vibration analysis of multi-segmented Timoshenko beams on Pasternak foundation.

Keywords

• Mode shape
• Natural frequency
• Pasternak foundation
• Segmented Timoshenko beam
• Transfer matrix

References

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