ملخص البحث :
Abstract
The concept of semi-rigid connection and steel-concrete composite action has been
extensively researched in the past. However, they are not widely used in practice due to
the lack of detailed information, not only about the advantages of the semi-rigid design
philosophy, but also about the potential risks if its effect is not accounted for. The above
considerations were the motivations in taking up this research.
Firstly, a numerical study to investigate the effect of connection stiffness on the
natural frequency of semi-rigid frame was carried out using ABAQUS software. The
results of this numerical study confirmed the necessity of incorporating this effect to get
safe and economical design. Consequently, an analytical procedure for a beam with
semi-rigid connections under gravity load was developed which overcomes the
limitations of previously published procedures. The frequency of a steel beam was also
calculated using effective length concept. Furthermore, two new analytical “hand’’
calculation methods to estimate the first three frequencies of a semi-rigid frame were
developed. Both methods were developed by modifying or improving for existing
methods in the literature for rigid-jointed plane steel frame to incorporate the effect of
connection stiffness. Fist method is suitable only for a semi-rigid plane steel frame
which has uniform properties along its height so as it can be modelled as equivalent
flexural-shear cantilever beam. The proposed second method is suitable for non-uniform
plane steel frame. Both the above methods can be extended to composite structure using
the equivalent stiffness concept of composite beam. Moreover, examples of steel frame
were used to demonstrate the application of the proposed analytical methods. It was
shown that the proposed methods not only can predict the difference in frequency of
rigid and semi-rigid frames, but they are also simple enough to be used in day-to-day
design practices.
Secondly, as the stiffness of connection is essential in the calculation of natural
frequency of a semi-rigid frame, a new simple mechanical component-based model was
developed to determine the initial rotational stiffness of commonly used flush end-plate
steel or composite connection incorporating the partial interaction effect. The traditional
axial spring of shear connectors was replaced by rotational spring to make the model
suitable to extending further than the linear region. A chart was developed to estimate
the appropriate values of the secant stiffness and strength of a shear stud, since the
empirical equations that researchers have used in the past can lead to unrealistic results
in some cases.
Thirdly, a simplified model, which combined three components of a composite
connection in one “lump’’ component (RCCS), was developed. It can be used in the
finite element modelling of a composite connection to overcome the convergence
problems associated with cracking of concrete and also it will reduce the computational
time significantly with adequate accuracy. A new procedure to determine the number of
“active’’ studs was developed. The relationship between the number of “active’’ shear
studs and the maximum number of shear studs required for a full shear connection was
derived.
Finally, the relationship between connection ductility and frame ductility was
investigated. It was found that the moment resistance and ductility of connection affect
significantly the whole behaviour of a frame. Consequently, a simple flowchart to
predict the failure mode of a flush end-plate composite connection was developed. A
procedure to estimate the moment resistance of a flush end-plate composite connection
by modifying the existing procedures in the literature to incorporate the partial shear
connection effect was proposed. Also, the proposed mechanical model was further
extended using the appropriate post-linear values of its components in order to calculate
the rotational ductility of a connection.
All the suggested procedures have been validated with the numerical results using
ABAQUS, the results from other existing models and experimental tests in the literature
where available.
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سنة النشر : 2013
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تصنيف البحث : theses
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