Birleşim düzlemi içinde dışmerkez yük etkisindeki bulonlu birleşimler
Bolted connections under in-plane eccentric shear
Yazar: EMİNE KARGI
Danışman: DR. ÖĞR. ÜYESİ CÜNEYT VATANSEVER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Doğrusal olmayan analiz = Nonlinear analysis ; Kiriş-kolon birleşimi = Beam-column collection ; Yapı çeliği = Structural steel ; Çelik kirişler = Steel beams ; Çelik kolonlar = Steel columns ; İnşaat mühendisliği = Civil engineering

Özet:
Uygulanan yükün bulon gruplarının ağırlık merkezinden geçmediği birleşimler, dışmerkez yük etkisindeki bulonlu birleşimler olarak tanımlanmaktadır. Bağlantının bir simetri düzlemine sahip olması durumunda, bulonların kayma alanlarının geometric merkezi (ağırlık merkezi) referans noktası olarak kabul edilmektedir. Birleşime uygulanan yükün tesir çizgisinden bu referans noktasına olan dik uzaklık dışmerkezlik olarak tanımlanmaktadır. Bağlantıların çoğunluğu dışmerkez yük etkisinde olsa da, çoğu durumda dışmerkezlik küçük bir değer olmakta ve ihmal edilmektedir.
Dışmerkez yük etkisindeki bağlantıların analizi ve boyutlandırılmasında uygulanan iki yaklaşım mevcuttur. Bu yaklaşımlardan ilki geleneksel elastik analiz yöntemidir. Diğer yöntem ise dönme merkezi esaslı plastik analiz yöntemidir. Çalışmada dönme merkezi esaslı plastik analiz yöntemi dikkate alınmaktadır. Yükleme durumu, birleşim düzlemi içinde dışmerkez olarak etkiyen tekil düşey yükten oluşmaktadır.
Çalışma esas olarak, metrik bulonlarla teşkil edilen birleşimlerin boyutlandırılmasında, dönme merkezi esaslı (instantaneous center of rotation) analiz yönteminin kullanılabilmesi için gerekli parametrelerin elde edilmesini amaçlamaktadır. Bunun için doğrusal olmayan sonlu eleman analizleri ile regresyon analizlerinden yararlanılmaktadır.
Çalışmanın yürütülmesinde Crawford-Kulak tarafından gerçekleştirilen bir deneysel araştırma esas alınmaktadır [2]. Bu araştırma kapsamındaki deneysel sonuçlar, geliştirilen sonlu eleman modellerinin doğrulanması amacıyla kullanılmıştır. Geliştirilen sonlu eleman modelleri, tek bulonlu birleşimlerden oluşmaktadır.
Tez çalışması kapsamında geliştirilen sonlu eleman modeli, esas alınan deneysel çalışmaya ait yük-yer değiştirme eğrisi kullanılarak doğrulanmaktadır. Buna göre, sonlu eleman modelinin oluşturulmasında esas alınan ön çekme kuvveti mertebesi ile bulon gövdesi-delik kenarı arasındaki boşluk miktarı için en uygun değerler belirlenmiştir.
Doğrulanan sonlu eleman modeli oluşturma esasları, her bir tipik çelik malzeme sınıfı ile tipik bulon sınıfı için, metrik bulonların kullanıldığı tek bulonlu sonlu eleman modellerine uygulanarak yük-yer değiştirme eğrileri elde edilmiştir.
Ayrıca, dönme merkezi esaslı plastik analiz yönteminin, birleşim düzlemi içinde dışmerkez yük etkisindeki bulonlu birleşimlerin tasarımında kullanılmasını sağlamak amacıyla, bir C katsayısı tanımlanmıştır (AISC Steel Construction Manual 15).

Tanımlanan C katsayısı kullanılarak elde edilen iki adet tipik birleşimin dayanımları, sonlu eleman analizleri sonunda elde edilen dayanımlarla karşılaştırılmış ve C katsayısı yardımıyla hesaplanan dayanımların yeterli bir güvenlikle elde edildiği görülmüştür.

Abstract:
An eccentric connection is one in which the resultant of the applied loads does not pass through the center of gravity of the fasteners. If the connection has a plane of symmetry, the centroid of the shear area of the fasteners may be used as the reference point, and the perpendicular distance from the line of action of the load to the centroid is called the eccentricity.
Although a majority of connections are probably loaded eccentrically, in many cases the eccentricity is small and may be neglected.
Two approaches exist for the solution of this problem. The first is the traditional elastic analysis. This method used for the design of eccentrically loaded fastener groups is based on the assumption that the fasteners do behave elastically, that is, the resistance of each fastener is assumed to be proportional to its distance from the centre of rotation.
However, it has been shown that the load - deformation relationship of an individual fasteneris not elastic and that individual fasteners do not have a well-defined shear yield stress.This method provides a conservative solution in the absence of a more realistic approach.This approach is also relatively easy to apply but is innacurate on the conservative side. The major flaw in the analysis is the implied assumption that the fastener load-deformation relationship is linear and that the yield stress is not exceeded.
The second approach is the method of instantaneous center of rotation based on the ultimate strength analysis. In this study, this method analysis method is taken into consideration. The loading condition consists of a single vertical load.
The aim of this study is to modify the required parameters in order to use the instantaneous center of rotation analysis method in designing the joints made by metric bolts. For this purpose, nonlinear finite element analysis and regression analysis are used.
The study is based on an experimental research conducted by Crawford and Kulak. The experimental results in this research were used to verify the finite element models developed. The finite element models developed consist of single bolt connections.
The samples tested in Crawford and Kulak's experiments were prepared as finite element model. A single bolt specimen model was created using Abaqus. Dimensions and material values of bolts and plates were determined in accordance with the report.
In the analysis of the study, the pretension force value in the bolts was estimated. The value in the experiment is not known exactly, several analyzes were performed using pretension strength ranges between 10% and 100%. Another difference in modeling was the amount of gap between the hole in the plates and the bolt body. The values of the gap values were determined as 0.5, 0.7, 0.75, 0.8, and 1 millimeter. Separate analyzes were performed for each pretension force and gap value.
The finite element model developed within the scope of the thesis is verified by using the load-displacement curve of the experimental study. Accordingly, the optimum values for the amount of tensile force level and space between the bolt body-hole edge, which are taken as a basis in the development of the finite element model, were determined.
The amount of the pretension and the gap, defined as the parameters for each analysis, were confirmed based on the curve in the report prepared by Crawford and Kulak. At the end of the evaluation, the amount the pretension and the gap were determined, respectively, as 75% of the minimum tensile strength of the bolt and as 0.4mm, which is the tolerance between the hole edge and bolt body surface. 
The load-displacement curves are obtained by applying the verified principles of finite element modeling to single bolted finite element models using metric bolts for each typical steel material class and typical bolt class.
A total of 42 analyses including the same number of models were performed with the consideration of  plates materials of S 235, S 275 and S 355 and bolt grades of 8.8 and 10.9. In the analysis models, plate dimensions were arranged in the same manner as in the previous verification experiment.
With these analyzes, it is aimed to integrate the equation used in the calculation of the ultimate strength in the joints into the SI unit system in accordance with the metric bolt dimensions. The load deformation curve obtained from each analysis was used to revise the regression coefficients in the equation. The equation obtained by the revised coefficients can be used for ultimate strength calculations in combinations where metric bulons are used.
When the results of numerical analyzes carried out in this study are evaluated, the coefficients of the function defining the behavior model are found;  = 0.40 and                = 0.70.
A coefficient C is defined in order to use the rotation center based analysis method in the design of bolted connections under in-plane eccentric shear (AISC Steel Construction Manual 15). In this analysis method, when determining the coefficient C, it is assumed that the bolt groups rotate around a point outside the center of gravity. The coordinates of each of the bolts are determined by the center of gravity and by this center of rotation. With the help of formulas, it was checked whether the balance was achieved in the system. If equilibrium is achieved, the position of the center of rotation is considered correctly and the coefficient C is determined accordingly. If there is no balance, a new coordinate of the rotation center is determined. Since these operations required iterative analysis, they are performed with the support of computer programs.
The strengths of the two typical combinations obtained using the defined C coefficient were compared with those obtained at the end of the finite element analysis.
It was seen that the strengths calculated with the help of C coefficient were obtained with sufficient safety.
In the last part of the study, bolted joints in the column beam joining area were examined. Using finite element analysis program, single and double bolt row connections in vertical direction were analyzed. M20 8.8 bolt and 20 millimeter thick S355 plates were used for the modeling of the connections. The eccentricity is considered to be 200 millimeters. As obtained from the previous analyzes, the pretension strength range is 75% and the space value is 0.8 millimeters. The analysis was conducted in two ways with and without spaces.
As a result of the analysis, the capacity of the connection was determined. The load-rotation curves were obtained and these curves were used to compare the results.
In this study, only two types of bolt joints are taken as basis for eccentric load effect. The sufficiency of the method can be strengthened by diversifying the types of connections. The results of this study, which is conducted only numerically, are also supported experimentally and can be compared with the results of numerical analysis.