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Title: Punching shear in heated interior reinforced concrete slab-column connections
Author: Al Hamd, Rwayda
ISNI:       0000 0004 7965 3193
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2018
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Slab-column connections are a very economical type of construction, which ensures their wide use. However, due to the form of such connections, they are potentially subject to an undesirable brittle failure mode that is referred to as punching shear failure. In the thesis, a specific case of slab-column connections is explored often referred to as a 'flab slab' without drop panels. Heating concrete results in a reduction in its mechanical properties, especially its compressive strength, which affects the structural response of the connection, including the failure mechanism. After fire caused a car park to collapse in Gretzenbach, Switzerland, in 2004 several recent sets of experimental results regarding the punching shear behaviour of slab-column connections in situations in which fire has erupted have produced apparently anomalous deflections results in which the slab deflections on heating are in the opposite direction to those expected if they had arisen from free thermal expansion. Therefore, this project was conducted to numerically investigate the punching shear failure mechanism of reinforced concrete slab-column connections at elevated temperatures. The first step in modelling the slab-column connection at elevated temperatures is to conduct a numerical investigation into the punching shear behaviour of concrete slab-column connections at ambient temperatures (where no shear reinforcement is provided). The validation of the numerical models was performed using a set of experimental data that was obtained from the literature in which the punching shear failure mechanism had been explored numerically at ambient temperature. Then, the validated numerical approach was used to develop a model that captures the effect of the elevated temperatures on the connection and explains the unexpected deflection response that has been reported in the literature. Numerical analysis showed that the results are explained by the effect of load-induced thermal strains (LITS). Using two independent modelling approaches, the profound effect of LITS on the deflection behaviour was demonstrated. The same modelling approach was used to conduct a parametric study to examine the effect of different variables on punching shear failure at both ambient and elevated temperatures. The expanded database at ambient temperature was then used to form a comparison of the results with existing design provisions, the results of which suggest that, in some circumstances, current design methods over-predict punching capacity. An exception was the prediction obtained from the Model Code 2010, which is based on the critical shear crack theory. An improvement to the critical shear crack theory is proposed in this thesis to produce design recommendations for punching shear at elevated temperatures. The results obtained from the modified critical shear crack theory at elevated temperatures showed a close agreement with the numerical predictions; however, the approach taken still needs further studies, but there is scope for further refinement of the approach as more experimental results become available. Finally, as a solution for the punching shear problem at elevated temperatures, a new shear reinforcement type (proposed in the author's previous work) called a “shearhead” was embedded into the connection under fire conditions and has shown its reliability in resisting punching shear failure. The results presented in this study showed that the unexpected deflection behaviour of the slab-column connection reported in the literature can be replicated numerically by incorporating the load-induced thermal strain into the concrete constitutive model. However, while the load-induced thermal strain had a significant effect on reversing the deflection response of the slab, it did not have much impact on the failure mechanism of the connection. Furthermore, the same modelling approach was used to conduct a parametric study that explores the implications of the load-induced thermal strain on design recommendations for punching shear at elevated temperatures. Finally, the modelling approach was used to propose a solution to the punching shear problem that showed its efficiency in a fire situation.
Supervisor: Wang, Yong Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available