Experimental and numerical investigation of masonry infilled reinforced concrete frames with rubber joints

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16335
Person Identifier (Local)
  • 201874039
Qualification Level
Qualification Name
Department, School or Faculty
  • Masonry infill walls are among the most vulnerable components of reinforced concrete (RC) frame structures. Numerous models have been developed in the last decades to describe the seismic response of masonry-infilled RC frames, by focusing on the description of the interaction between the infill and the frame and/or the global seismic response of the composite frame-infill system. More recently, some techniques for enhancing the performance of the infills have been proposed, with the aim to improve the capacity of the infills and/or the performance of infilled frames. Recent experimental and numerical studies have investigated innovative solutions for protecting these walls by reducing their interaction with the RC frame. Among the most promising ones, there are those that aim to decouple or reduce the infill-frame interaction by means of flexible or sliding joints at the interface between horizontal subpanels or between the panels and the frame. Rubber joints have emerged as a very efficient technical solution with the possibility to tailor the properties through the selection of suitable compounds and geometries. The present thesis aims to improve current knowledge of the mechanical behaviour of rubber joints and of the seismic performance of infilled frames equipped with them. For this purpose, both numerical and experimental studies have been carried out. With regards to the numerical work, a novel computational modelling strategy has been developed using ABAQUS to investigate the in-plane behaviour of RC frames with infill walls and rubber joints. The proposed approach employs three-dimensional solid finite elements to simulate the concrete components, 3D beam elements for the reinforcing bars, and a meso-scale approach for the infill wall with rubber joint. The results of the application of the numerical strategy shed light on the effectiveness of the rubber in minimizing the in-plane seismic damage to the bricks, by localizing the deformation mostly in the rubber joints and reducing the overall stiffness of the infilled system. They also provide some insight into the effect of the rubber joints' layout and stiffness on the behaviour and capacity of the system and its components. In particular, it is shown that, using vertical rubber joints with low stiffness in addition to the horizontal ones further improves the behaviour in terms of reduction of compressive stresses and cracking in the masonry at large displacements. Even the plastic deformations in the frame can be reduced by using vertical joints with low stiffness. Detailed numerical analyses involving micro and meso-scale descriptions of masonry can accurately simulate the behaviour of the system at hand, but they can be computationally expensive and unsuitable for the analysis of large-scale structures. On the other hand, the use of simplified macro-models, characterised by a reduced number of degrees of freedom and parameters that are required to define them, would enable the analysis of larger scale structural systems. In this thesis, a novel two-dimensional macro-element model has been proposed for describing the in-plane behaviour of RC infilled frames with flexible or sliding joints, which is an extension of a discrete 2-D macro-element previously developed for the case of traditional infill panels. The proposed modelling approach, implemented in OpenSees, is calibrated and validated against quasi-static tests from the previous literature, carried out on masonry-infilled RC frames with sliding and rubber joints. The study results show the capabilities of the proposed modelling approach to evaluate the benefits of using flexible joints in terms of minimising the negative effects of the interaction between infill and RC frame. The addition of the sliding/flexible joints enhances the energy dissipation capabilities with more stable and larger hysteresis loops under cyclic loading. However, it has been observed that for a given level of drift demand, the internal forces in the columns of the RC frame with infill and rubber joints have similar maximum values, if not inferior to those of the bare frame, with the exception of the axial and shear force in the windward column. The maximum absolute values of the internal forces in the case of infill with rubber joints are lower than the corresponding values obtained in the system with traditional infill. Although past tests have characterised the behaviour of multi-layer flexible joints, no in-depth investigation has been carried out to date on the hysteretic and dissipative behaviour of mortar-rubber joints. In order to fill this gap, a series of experimental tests were conducted at the University of Strathclyde to characterise the mechanical behaviour of the various components of the rubber-masonry triplets as well as the behaviour of the composite system, with particular focus on the cyclic shear response and the bond strength. The hysteretic responses of the triplets obtained from the experiments are simulated using a finite element micro-modelling strategy using Abaqus. The mortar-rubber joints exhibit an equivalent damping ratio value of the order of 20% or more which is much higher than that of the rubber compound (of the order of 6%). This is due to the frictional mechanism activated at the interface between the rubber joints and the mortar, enhanced by the presence of pins in the surface of the rubber joints. The bond between the rubber layers and the mortar layers was found to be the weakest component of the composite system. While the failure of this bond reduces the stiffening effect of the infills and increases even further the damping capabilities of the joints due to the activation of the frictional mechanism, it may be not desirable because it may result in residual deformations and a weakening of the infill panel in the out-of-plane direction. The study results are useful for informing the development of future models for the design and analysis of rubber joints, and for the selection of the most suitable rubber compound and layer geometrical properties.
Advisor / supervisor
  • Yang, Shangtong
  • Tubaldi, Enrico
Resource Type