الفهرس 
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Abstract
This research presents an experimental and numerical investigation of cold formed section bolted truss connections subjected to tension force. Thirty experimental specimens and eighty finite element models of CFS bolted truss connections were examined to determine the single shear connections bearing strength and behavior without bent edges on both sides of the connected sheets. A total of three distinct bolted connection configurations for CFS are covered in this research. In the first configuration, CFS back-to-back C (fully flanged) sections are used as a horizontal chord of truss members and a single C section is used as a web member connected by two bolts, with different end distances. In the other configurations, the CFS profile has a reduced flanged section C’ and an unstiffened section L, whereas webs are kept the same.
The experimental results of the truss connection are compared to the those computed using the AISI specification design standards. It has connections nominal capacities that are significantly lower than the actual nominal capacities obtained from tests. A finite element model is used to analyze such connection. The chord, web, and the bolt with its head and nut are modeled. ABAQUS, the 2017 release of the finite element software, is used to implement the model. Comparing the finite element results to the experimental results has been done to verify the finite element model.
As a result, the estimated capacities should only be used as a guide and not as reliable indicators of the real capacities. In addition, the following recommendations can be made after carefully examining the results of this study. A new method was proposed for calculating the resistance of truss joint connections based on bearing failure, using the modification bearing factor (α) derived by the classic probability approach AISI 100 [1].
Conclusions
For the investigated truss connections, a new bearing factor and a new modification factor are suggested and calibrated based on experimental and numerical results, the following conclusions are deducted:
Loss of local stability in sections and bolt hole elongation are two common failure modes in cold-formed steel structures (bolt bearing failure).
The type C (full flange) profile section truss connection has a significantly higher capacity in tension test than that of type C’ (reduced flange) in relatively small thickness specimens (1.17 mm). However, the comparison between both types was almost the same in the case of normal thickness sections (1.95 mm) because of the difficulty of rotating the bolt at 1.95 mm compared to 1.17 mm sheet thickness.
The type C profile section truss connection has a significantly greater tension test capacity than type L with a thinner wall thickness (1.17 mm). In the case of a thickness of 1.95 mm, the comparison between the two types was nearly identical. It happened when (d⁄t) reduced up to 60%. Except for the specimen with a 15 mm end distance, the absence of the upper flange resulted in a notable decrease in bearing capacity at (e⁄d)<2.
Bolts with an integral washer have a higher bearing capacity than bolts with conventional washers by 11% to 25%.
All specimens have a bearing failure with curled out-of-plane edges-and with a rotation in the bolt-which increases the amount of elongation of the holes.
The upper flange served as a protective barrier for the occurrence of tearing despite the small end distance of some specimens.
Three new design equations which consider the effects of the flange stiffening, edge distance, and bearing factor C based on the d/t and e/d ratios were presented. The proposed equations show good agreement with the experimental and numerical results and can help designers benefit from the extra connection capacity gained from having a stiffening flange near the edge of the sheet.
Recommendations for Further Research
Some suggestions for potential research extensions have been proposed from the numerical analysis provided in the present thesis to explore the following:
Several models are used to study the effect of varying the flange’s dimensions by a percentage of its thickness.
To reduce the rotation in all test specimens by using a single long bolt instead of two bolts that pass through both back-to-back sections.
Different truss joint connections configuration can be studied such as multiple shear truss joint connections.
Expanding on the concept of CFS profiles by introducing new profiles such the sigma section, omega section, and Z section.
To test sheets made by corrugations in the web of profile sections both before and after the bolt holes.