Farklı geometrik ön kusur şekillerinin ahşap kirişlerin yanal burulmalı burkulma davranışları üzerindeki etkileri
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Tarih
2024
Yazarlar
Dergi Başlığı
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Cilt Başlığı
Yayıncı
Kırıkkale Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Salt eğilme etkisi altındaki elemanlarda basınç bölgesinin zayıf eksen etrafında (yanal doğrultuda) burkulma eğilimi ile çekme bölgesinin stabil kalma eğiliminin neden olduğu ilave eleman burulması, yanal burulmalı burkulma adı verilen özel bir burkulma davranışını ortaya çıkarır. Homojen ve izotropik doğası gereği yapısal çelik kirişlerde yanal burulmalı burkulma hesapları malzeme davranışından asgari düzeyde etkilenir. Yapısal çelik ve diğer metal malzemelerin aksine ahşap, lif doğrultusu ve liflere dik doğrultularda farklı mekanik ve malzeme özelliklerine sahip bir yapı malzemesidir. Bu davranış ortotropik olarak ifade edilmektedir. Ahşap malzemenin bu karmaşık davranışı nedeniyle, ahşap kirişlerin yanal burulmalı burkulma davranışı incelenip analiz edilirken malzemenin doğru bir şekilde tanımlanabilmesi ve modellenmesi çok önemlidir. Kendi alanında bir ilk olma özelliği taşıyan bu çalışma kapsamında sonlu elemanlar paket programı kullanılarak farklı ön-kusur düzenlerine (şekillerine sahip) dikdörtgen kesitli ahşap kirişlerin yanal stabilite analizleri gerçekleştirilmiştir. Kirişlerin yapı malzemesi olarak literatürde fiziksel ve mekanik özellikleri deneysel olarak ortaya konulmuş olan masif kayın ağacı kullanılmıştır. Ön-kusursuz (referans) kirişlerin yanı sıra; tam parabolik, yarım sinüs ve iki farklı genlik değerli tam sinüs ön-kusur eğrilerine sahip ahşap kirişlerin yanal stabilite davranışları analitik olarak incelenmiştir. Açıklık boyunca ön-kusur yayılımının (ön-kusur eğrisinin) kiriş davranış ve dayanımına etkilerini ortaya koymak amacıyla, aynı geometrik ölçülere (boyutlara) sahip kirişler birbirleri ile karşılaştırılmıştır. Yapılan analizler, ahşap kirişlerin burkulma yüklerinin geometrik düzenle yakından ilişkili olduğunu göstermiştir. Tam sinüs dalgası geometrik eğrisi, kirişin birinci burkulma modunu atlayarak ikinci burkulma moduna göre yanal stabilite kaybına uğramasına neden olduğu için, tam sinüs eğrisi şeklindeki ön-kusur bulunduran kirişlerin burkulma yüklerinin ön-kusursuz referans kirişlere oldukça yakın olduğu belirlenmiştir. Yarım sinüs ve parabolik eğrilerle nitelenen ön-kusur düzenli kirişlerin burkulma yüklerinin ise ön-kusursuz kirişlerden %70'e varan oranlarda daha düşük olduğu görülmüştür. Ön-kusur eğrisinden bağımsız olarak bütün kirişlerde kiriş yüksekliği ve serbest uzunluğu arttıkça burkulma yükünün azaldığı ve ön-kusursuz kirişin burkulma yüküne göre azalma miktarının arttığı görülmüştür. Son olarak, tam sinüs ön-kusurlu kirişlerde yanal sehimlerin burkulma anına kadar sınırlı düzeyde kaldığı, ancak parabolik ve yarım sinüs eğrili ön-kusur düzenlerinde burkulma gerçekleşene kadar büyük yanal şekil değiştirmelerin ortaya çıktığı gözlemlenmiştir.
In members under pure bending, the additional twist related to the tendency of the compression zone of the beam to buckle about the weak axis (in the lateral direction) and the tendency of the tension zone to remain stable triggers a special buckling behavior called lateral torsional buckling. Due to the homogeneous and isotropic nature of structural steel, lateral torsional buckling calculations in structural steel beams are minimally affected by the material characteristics and behavior. Unlike structural steel and other metallic structural materials, wood (timber) is a structural material with different mechanical and material properties in the fiber direction and in the directions perpendicular to the fibers. This differential behavior is referred to as orthotropic. Due to this complex behavior of timber, accurate description and modelling of the material behavior is rather crucial when examining and analyzing the lateral torsional buckling behavior of wooden beams. Within the scope of this study, which is a pioneering work on this very topic, lateral stability analyses of timber beams with rectangular cross-section and with different geometrical imperfection patterns (shapes) were carried out using the finite element analysis software. The analyzed beams were made of solid beech wood, whose physical and mechanical properties have been experimentally unfolded in the literature. In addition to perfect (reference) beams; the lateral stability behavior of beams with full parabolic, half sine and full sine geometrical imperfection patterns were examined analytically. In order to reveal the effects of imperfection pattern (initial curve) along the span on beam behavior and strength, the analysis results of the beams with the same geometric dimensions were compared to each other. Analyses depicted that the buckling loads of timber beams are closely related to the geometry of the initial imperfection. Since the full-sine wave imperfection curve causes the beam to bypass the first buckling mode and to lose its lateral stability in the second buckling mode, the buckling loads of the beams with full-sine curve were determined to be rather close to the respective values of the reference perfect beams. The buckling loads of the imperfect beams with half-sine and parabolic imperfection patterns, on the other hand, were established to remain up to 70% below the respective values of the respective perfect beams. The buckling load of a beam was found to decrease as the beam height and unbraced span length increases in all imperfect and perfect beam groups, regardless of the imperfection pattern. What's more, the amount of decrease in the strength as compared to the perfect beam was shown to increase with increasing beam slenderness (beam height and length). Finally, in the case of full-sine imperfection curve, lateral deflections remained limited until the instant of buckling, while in the cases of parabolic and half-sine curves, large lateral deformations occurred until buckling.
In members under pure bending, the additional twist related to the tendency of the compression zone of the beam to buckle about the weak axis (in the lateral direction) and the tendency of the tension zone to remain stable triggers a special buckling behavior called lateral torsional buckling. Due to the homogeneous and isotropic nature of structural steel, lateral torsional buckling calculations in structural steel beams are minimally affected by the material characteristics and behavior. Unlike structural steel and other metallic structural materials, wood (timber) is a structural material with different mechanical and material properties in the fiber direction and in the directions perpendicular to the fibers. This differential behavior is referred to as orthotropic. Due to this complex behavior of timber, accurate description and modelling of the material behavior is rather crucial when examining and analyzing the lateral torsional buckling behavior of wooden beams. Within the scope of this study, which is a pioneering work on this very topic, lateral stability analyses of timber beams with rectangular cross-section and with different geometrical imperfection patterns (shapes) were carried out using the finite element analysis software. The analyzed beams were made of solid beech wood, whose physical and mechanical properties have been experimentally unfolded in the literature. In addition to perfect (reference) beams; the lateral stability behavior of beams with full parabolic, half sine and full sine geometrical imperfection patterns were examined analytically. In order to reveal the effects of imperfection pattern (initial curve) along the span on beam behavior and strength, the analysis results of the beams with the same geometric dimensions were compared to each other. Analyses depicted that the buckling loads of timber beams are closely related to the geometry of the initial imperfection. Since the full-sine wave imperfection curve causes the beam to bypass the first buckling mode and to lose its lateral stability in the second buckling mode, the buckling loads of the beams with full-sine curve were determined to be rather close to the respective values of the reference perfect beams. The buckling loads of the imperfect beams with half-sine and parabolic imperfection patterns, on the other hand, were established to remain up to 70% below the respective values of the respective perfect beams. The buckling load of a beam was found to decrease as the beam height and unbraced span length increases in all imperfect and perfect beam groups, regardless of the imperfection pattern. What's more, the amount of decrease in the strength as compared to the perfect beam was shown to increase with increasing beam slenderness (beam height and length). Finally, in the case of full-sine imperfection curve, lateral deflections remained limited until the instant of buckling, while in the cases of parabolic and half-sine curves, large lateral deformations occurred until buckling.
Açıklama
Fen Bilimleri Enstitüsü, İnşaat Ana Bilim Dalı, İnşaat Mühendisliği Bilim Dalı
Anahtar Kelimeler
İnşaat Mühendisliği, Civil Engineering