Experimental and theoretical investigation of the behaviour of brickwork cladding panel subjected to lateral loading
Ng, Chee Liang
This thesis deals mainly with the resistance of single leaf brickwork cladding panels subjected to uniform lateral pressure. Such panels when supported on three or four sides bend like thin plates and are subjected to bi-axial bending. A bi-axial failure criterion for brickwork, which shows both strength and stiffness orthotropies, is required to predict the strength of the cladding panels. A systematic investigation was undertaken to establish the failure criterion of brickwork in bi-axial bending using a novel test method. A total number of 33 cross-beams in which both vertical and horizontal moments can be applied simultaneously was tested to define the failure criterion. From the tests, it appears that the strength in the weaker direction is enhanced in biaxial bending. In most cases, the load was shed from the weaker to the stronger direction after cracking. Once the section cracks, it is not capable of carrying any moment, which indicates the brittle nature of masonry. A conventional plate bending finite element program was modified incorporating the bi-axial failure criterion which takes into account the load-shedding observed in the tests. A smeared crack modelling technique was used to model the progressive cracking in bi-axial bending. Once the material properties in bi-axial bending were established and numerical modelling was carried out to predict the behaviour, it was essential to apply the theoretical model to walls subjected to lateral loading. A total number of 15 walls with different aspect ratios and boundary conditions was tested for comparison with the numerical method. Good agreement was obtained between the theoretical model and experimental results. All walls were tested under ideal boundary conditions so that rotational restraint at the supports could be avoided. Similar observations of load shedding from the weaker vertical direction to the stronger horizontal direction were observed also in the wall tests. This was confirmed by measuring the drop and increase in the reactions in the weaker and stronger directions. This was also confirmed from strain measurements in two orthogonal directions before and after cracking. These results also indicate without doubt that a cracked section cannot support any moment. This modified finite element program using the bi-axial failure criterion developed in this thesis was also used to compare the results with the wall test carried out by other researchers. A good agreement between the theoretical and the experimental results of wall with and without openings and subjected to lateral loading was also obtained. Hence, this finite element program using the bi-axial failure criterion can be used for the design of laterally loaded brickwork panels with confidence.