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Title: Performance of Beam-Column Joints in Concrete Filled Steel Tubular Frames
Authors: Kumari, Beena
Supervisor: Kwatra, Naveen
Sharma, Shruti
Keywords: Concrete filled steel tubular columns;End Plate bolted connections;Seat Angle- Connections;FE modelling;corrosion monitoring
Issue Date: 24-Aug-2018
Abstract: The use of concrete filled steel tubes (CFST) in building construction has seen renaissance in recent years due to their numerous advantages, apart from their superior structural performance. Their practice as columns in high-rise buildings, as beams in low-rise industrial buildings and as arch bridges, has become widespread in countries like China in past two decades. But unfortunately, their usage in India is a new concept and has hardly seen the light of the day. The focus of this research is to explore the bounties of CFST sections to investigate potential usage in the building industry; mainly considering the structural behaviour. It is widely recognized that innovative use of two or more different materials in a structure usually lead to more efficient system for resisting seismic forces. The CFST structures make an efficient structural system with the advantage of both steel and reinforced concrete frame. It has numerous advantages in terms of structural performance and construction sequence. The concrete in-fill delays inherent buckling problem of thin-walled steel tubes and confinement effect exerted by the steel tube improves their performance. The steel at the outer perimeter performs most effectively in tension and bending enhancing its structural performance. CFST system has all the merits which bring it into the category of sustainable construction system as it reduces the cost of construction in many ways and this helps to save resources. Main focus of the present study is to investigate the behaviour of beam-column joints in CFST frames. Various parameters influencing the behaviour of these columns have been studied. Numerical study of short columns has been carried out by using the experimental data available in literature and the model has been validated by comparison. From the comparison of the experimental results with the results obtained from finite element (FE) model it can be concluded that the proposed FE model is capable of predicting the column behaviour very accurately. It is observed from the experimental and the numerical investigations that the capacity of the columns is significantly affected by various factors viz; slenderness ratio, thickness, cross section of steel tube, strength of concrete core and the grade of steel. vi The focus of the study is to explore the prospective of CFST beam-column joints as part of CFST frame structures. For this purpose, two types of connections using extended end plate and seat angle, are proposed to investigate the static performance and failure modes of the proposed connections. An experimental program has been conducted involving exterior beam-to-column joints subjected to monotonic loading applied at the free end of beam. The performance is evaluated in terms of load deformation behaviour, moment-rotation curves and failure modes. The test parameters chosen for comparison are the length, diameter and type of bolts. It can be concluded from the experimental investigations that extended end plate connections exhibit higher strength over seat angle connections. Variation in size of end plate, diameter, length and grade of bolts significantly affect the capacity of the joints. The experimental results indicate that the proposed connections perform in a semi-rigid and partial strength mode as per EC3 specification, and their rotational capacity satisfies the ductility requirements. To validate the experimental behaviour of the proposed connections in CFST beam-column joints, finite element analysis (FEA) has been carried out under the static load using software ATENA-3D. Results of the proposed model are compared with the experimental results. The proposed FE model of CFST beam-column connections is found capable of predicting the behaviour of beam-column joints. Subsequently, the behaviour of the composite frame comprising CFST columns and beams using end plate connections has been studied under a lateral monotonically increasing load. The environmental durability of CFST structures is a major issue in context with their performance. The susceptibility of CFST sections to corrosion can severely reduce the strength and durability of these structures. Interfacial debonding caused by corrosion weakens the confinement effect of steel tube and results in the loss of load-carrying capacity. Unfortunately, such damage cannot be visually identified. Hence, it is necessary to develop a non-intrusive technique for early detection of damages in the form of cracks, debonds and corrosion in CFST members. In this study, ultrasonic guided waves are used for monitoring two type of defects i.e. notches and delamination simulating loss of area and debond due to corrosion. Specific guided wave modes are used for investigating varying extents of notches and simulated delamination defects. It is concluded that Pulse Transmission (PT) signatures can relate to the percentage vii notch and delamination very efficiently. The method is further applied to CFST sections undergoing accelerated corrosion. It can successfully relate to the state of steel tube undergoing chloride induced corrosion and can be applied to real time corrosion monitoring of CFST sections.
Description: Doctor of Philosophy- Civil Engineering
Appears in Collections:Doctoral Theses@CED

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