Abstract

The seismic assessment of unreinforced masonry (URM) buildings with cavity walls is a relevant issue in many countries, such as in Central and Northern Europe, Australia, New Zealand, China and several other countries. A cavity wall consists of two separate parallel masonry walls (called leaves) connected by metal ties: an inner loadbearing wall and an outer veneer having mostly aesthetic and insulating functions. Cavity walls are particularly vulnerable structural elements. If the two leaves of the cavity wall are not properly connected, their out-of-plane strength may be significantly smaller than that of an equivalent solid wall with the same thickness.The research presented in this paper focuses on a mechanical model developed to predict the failure mode and the strength capacity of metal tie connections in masonry cavity walls. The model considers six possible failures, namely tie failure, cone break-out failure, pull-out failure, buckling failure, piercing failure and punching failure. Tie failure is a predictable quantity when the possible failure modes can be captured. The mechanical model for the ties has been validated against the outcomes of an experimental campaign conducted earlier by the authors. The mechanical model is able to capture the mean peak force and the failure mode obtained from the tests. The mechanical model can be easily adopted by practising engineers who aim to model the wall ties accurately in order to assess the strength and behaviour of the structures against earthquakes. Furthermore, the proposed mechanical model is used to extrapolate the experimental results to untested configurations, by performing parametric analyses on key parameters including a higher strength mortar of the calcium silicate brick masonry, a different cavity depth, a different tie embedment depth, and solid versus perforated clay bricks.

Highlights

  • Cavity wall is a construction practice that usually is used for thermal and weather resistance, and provide drainage as well [1,2]

  • In the Netherlands, a cavity wall usually consists of an inner load-bearing wall made of calcium silicate brick masonry and an outer veneer of clay brick masonry separated by a cavity

  • The current study focuses on cavity walls made of calcium silicate brick masonry and perforated clay brick masonry, connected by metal ties with a zigzag-end embedded in calcium silicate brick masonry (CS) and a hooked-end were embedded in perforated clay brick masonry (CB)

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Summary

Introduction

Cavity wall is a construction practice that usually is used for thermal and weather resistance, and provide drainage as well [1,2]. The behaviour of the cavity wall tie needs to be adequately investi­ gated to be properly modelled (either analytically or numerically) For this reason an experimental campaign was conducted at the Delft Uni­ versity of Technology to provide benchmarks for the validation of analytical models for cavity wall ties [4]. Various failure modes were reported for cavity wall tie connections either through tests at component level [5,6,7,8] or on full scale structures [9,10,11,12,13]. Considering the models already described in the literature and the outcomes of the experimental campaign carried out at the Delft Uni­ versity of Technology, a mechanical model which considers six different possible failure modes is proposed in this paper to define the axial behaviour of metal tie connections in masonry cavity walls. The proposed mechanical model has been used to integrate the outcomes of the experimental campaign by performing parametric an­ alyses in order to assess the influence of several key parameters

Possible failure modes of a cavity wall tie under axial loading
The mechanical model for a wall tie connection
Tensile capacity of the connection
Cone break-out failure
Failure modes in compression
Calibration of the proposed model against the tests performed at TU Delft
Extension of the model to untested configurations
Mortar with higher strength class
Reduced cavity width
Solid clay bricks
Summary of the failure modes for all the different configurations studies
Findings
Conclusions

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