On the investigation of providing space truss roofs with ductility until failure under monotonically increasing vertical loads

The aim of this paper is to investigate the nonlinear behavior of space truss roofs subject to different load accumulation forms considering the effect of initial imperfection and slenderness ratio of the truss members. For this, a typical space truss roof using MERO-connection type with flat double-layer was selected as a sample. 3D model of the roof was developed and analyzed by using OpenSEES. Nonlinear behavior of each typical bar of the space truss roof, which, was mainly composed of particular sub-elements such as a tubular element, bolts, sleeves and spheres was represented by a single truss bar. Axial load-displacement relationship of each single truss bar was obtained from nonlinear analysis performed under reversal cyclic loading. Besides, three different types of load distribution that simulates accumulation of rainwater or drifted snow were taken into account as an external load acting on upper layer of the roof system. Analyses results showed that load carrying capacity of the space truss roofs was very susceptible to the form of accumulation and reduces abnormally when the accumulation, in particular, occurred locally. Furthermore, failure mode of the system designed with optimal solution was dominated by buckled truss bars and brittle failure occurred. Also initial imperfection had a negative effect on the members in compression.

Uzay kafes çatý sistemlerinin artan düþey yükler altýnda sünekliðinin araþtýrýlmasý

Bu çalýþmada uzay kafes çatý sistemlerinin çeþitli yük birikme senaryolarý altýndaki doðrusal olmayan davranýþý, çubuk eleman baþlangýç kusurlarý ve çubuk eleman narinlikleri de dikkate alýnarak incelenmiþtir. MERO düðüm noktasýna sahip iki adet örnek uzay kafes çatý sistemi OpenSEES yazýlýmý üç boyutlu olarak modellenerek analizler gerçekleþtirilmiþtir. Bulonlar, somunlar ve düðüm noktasý kürelerinden oluþan her bir çubuk elemanýn davranýþý tekil çubuklar üzerinde tanýmlanarak genel sisteme aktarýlmýþtýr. Her bir çubuk elemanýn eksenel yük-yerdeðiþtirme davranýþlarý çevrimsel tekrarlý yükler altýnda analizler gerçekleþtirilerek elde edilmiþtir. Genel sistem analizleri çatýnýn tamamýnda, yarýsýnda ve dörtte birinde yaðmur suyu veya kar yükü yýðýlmalarýný yansýtacak þekilde belirlenen yükleme altýnda gerçekleþtirilmiþtir. Analizler sonucunda uzay kafes çatý sistemlerinin yük yýðýlmalarýna karþý çok hassas olduklarý ve lokal bölgelerde oluþan yük yýðýlmalarýnýn sistemin taþýma kapasitesini düþürdüðü görülmüþtür. Bunun yanýnda, en ekonomik kesitlerle boyutlandýrýlan sistemde göçme basýnç çubuklarýnýn burkulmasý ile gevrek bir þekilde meydana gelmiþtir. Ayrýca, çalýþma kapsamýnda baþlangýç kusurlarýnýn çubuk elemanlarýn basýnç kapasitelerini düþürdüðü görülmüþtür.