Field survey and numerical modelling of cracking in masonry walls due to thermal movements of an overlying slab

Concrete slabs exposed to direct sunlight experience temperature related horizontal movements. In addition, temperatures on the top surface will be higher than those on the underside of the slab, causing an upward deflection of the slab during heating. In a typical building, masonry and concrete elements are connected to each other at their respective interfaces. Therefore, significant movements may be generated on the masonry walls due to the movement of the roof slab. These movements can result in overstressing and cracking in masonry. These cracks may not be structurally serious, but may lead to ingress of moisture and in any case are not acceptable especially where good finish is desired.

In this study, the behaviour of these cracks was predicted based on surveys of buildings where cracks have formed. Also, typical structural arrangements were mathematically modelled using 3D brick finite element models, with link elements between the masonry and concrete elements in order to model interfaces. The objective of the study was to investigate the stresses developing on the wall due to the movement of the roof slab. Locations and directions where cracking would occur were identified using the principal stresses developed in the finite element model and a failure criterion developed based on the modified Von-Mises theory. Also, using these numerical models, the effect of wall length and structural form of the wall (i.e. load bearing walls and reinforced concrete framed walls) on the formation of these cracks was studied. These results were compared with the information obtained from the survey.

Keywords: Masonry concrete interface, masonry walls, numerical modelling, thermal cracking, thermal movements  

doi:10.4038/jnsfsr.v36i3.156  

Journal of the National Science Foundation of Sri Lanka 36 (3) 205-213