Retrofitting Of Reinforced Concrete Coupling Beams By Bolted Side Steel Plates For Strength And Deformability

This dissertation, "Retrofitting of Reinforced Concrete Coupling Beams by Bolted Side Steel Plates for Strength and Deformability" by Yong, Zhu, 朱勇, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled RETROFITTING OF REINFORCED CONCRETE COUPLING BEAMS BY BOLTED SIDE STEEL PLATES FOR STRENGTH AND DEFORMABILITY ZHU YONG For the degree of Doctor of Philosophy at The University of Hong Kong in February 2006 Modern cities like Hong Kong contain numerous old reinforced concrete (RC) buildings which often require substantial strengthening, retrofitting or refurbishment as the materials used in their construction age. Many local RC buildings were built three or four decades ago, and their concrete and reinforcement have already suffered serious deterioration due to carbonation and chloride attack. Major retrofitting is normally required for these buildings. Furthermore, several existing buildings designed according to outdated design standards are deficient in shear reinforcement, and require substantial strengthening to increase their safety margin. A recent seismic hazard study has also revealed that Hong Kong is located in a region of low- to-moderate seismicity, and the latest design standards include increased load specifications. Many existing buildings were designed without any provision for earthquake resistance, and are now considered structurally inadequate. As a result the limited deformability and energy dissipation of existing structures, particularly their coupling beams, have become a major concern for many local structural and seismic engineers. Accordingly, this study provides a theoretical base for the design of retrofitting of RC coupling beams, and also establishes a fundamental framework for further investigations of strengthening of RC structure using bolted steel plate. In the first part of this thesis, a simple procedure based on the displacement-based approach has been derived for the seismic assessment of existing RC buildings. Using this procedure, the maximum seismic inter-storey drift demand of buildings and the maximum chord rotation demand of coupling beams with various span-to- depth ratios can be obtained easily. In the next part, an experimental study on full-scale retrofitting of RC coupling beams using bolted side steel plates is reported. The study revealed that external steel plate attachment by bolted connection could considerably enhance the strength, deformability and energy dissipation of RC coupling beams under reversed cyclic loads provided that appropriate connection details and arrangements were employed. The effects of local slip of mechanical bolt connections and buckling of steel plate could have a significant influence on the load-carrying capacity and the inelastic behavior of the retrofitted coupling beams. Detailed laboratory tests of dynamic set bolts and cast-in bolts were then conducted to investigate the load-slip behavior of the connection. The initial stiffness of dynamic set anchors was found to be much higher than that of cast-in anchors, and therefore dynamic set anchors were considered effective in controlling excessive bolt slips. The measured nonlinear slip relationships of various anchor bolts were used in a subsequent nonlinear finite element analysis and parametric study of the retrofitted beams. A set of guidelines with recommendations was drawn up for the design of anchor bolt arrangements. Two original theoretical models based on the rigid plastic and mixed analyses were also developed to predict the load-carrying ca