Structural Behaviour of Masonry Elements with Chases
A research project on the structural behaviour of unreinforced masonry elements with chases subjected to compression is underway at the Institute of Structural Engineering. The main goal of the research project is to investigate the influence of cutting out chases for electrical wiring in masonry walls on masonry compressive strength.
Load tests on the first two series of masonry elements with chases have been completed. Each series consisted of seven clay block masonry elements with dimensions of 1200x1200 mm. The thickness of the elements was 150 mm and 175 mm. A standard cement mortar was used to produce 10 mm thick bed and head joints. Twenty-eight days after preparation 50 mm deep and 35 mm wide chases were cut in six elements of each series while the seventh one was left intact and served as a control specimen. Three different types of chases (horizontal, vertical and inclined), two each per series, were cut only on one side of the masonry elements. After placing the installation ducts, the chases were filled with gypsum or cement mortar. The compressive load was applied in a deformation-controlled manner up to the failure of the specimen.
The results of tests on the first two series of elements were analysed and allow a number of conclusions to be drawn:
- Chases can reduce the masonry compressive strength considerably.
- In general, a reduction of the masonry strength proportional to the reduction of the cross-section area seems to be a reasonable approach in analysing the influence of chases on masonry compressive strength.
- The type of the mortar material of chase infill had relatively small influence on the reduction of masonry compressive strength. It seems that an infill that is as stiff as the masonry unit has to be applied in order to reduce the loss in masonry strength.
- In order to complete the research project additional tests will be carried out and an analytical investigation based on a strut-and-tie model will be performed.
This research project is supported by Ziegelei Schumacher, Körblingen and by Maxit AG. Their support is gratefully acknowledged.
For more details see the following publication:
N. Mojsilovic, S. Notz, B. Wäfler and J. Yu: "Load Test on Masonry Elements with Chases", Proceedings, 11th Canadian Masonry Symposium, Toronto, May 31 - June 3, 2009.
In the second phase of the research project a load tests on one additional series of masonry elements with chases have been completed. The series consisted of seven clay block masonry elements of dimensions 1200x1200 mm. The thickness of the elements was 150 mm. A standard cement mortar was used to produce 10 mm thick bed and head joints. Twenty eight days after preparation 50 mm deep and 35 mm wide chases were cut in six elements while the seventh was left intact and served as a control specimen. Three different types of chases (horizontal, vertical and inclined) were cut on one side only of the masonry elements, except for one specimen that had horizontal chases on both element faces. After placing the ducts, the horizontal and inclined chases, one each per chase type, were filled with high-strength mending cement mortar. The remaining chases were left unfilled. The compressive load was applied in a deformation-controlled manner up to the failure of the specimen.
The results of tests on this series were analyzed and allow a confirmation of conclusions given above. Moreover it could be concluded that, choosing the right type of material for chase infill can have crucial influence on restoring the masonry compressive strength loss caused by cutting the chases. It has been shown that an infill that is as stiff as the masonry unit (in this case high-strength mending mortar) has to be applied in order to reduce the loss in masonry strength.
This phase of research project is supported by Keller Ziegeleien, Pfungen and by Sika Schweiz AG. Their support is gratefully acknowledged.
For more details about the tests performed in this project phase see the following publication:
N. Mojsilovic, D. Geisseler: "An Experimental Study of Masonry Elements with Chases", Proceedings, 11th North American Masonry Conference, Minneapolis, June 5-8, 2011, pp. 995-1004.
In the last phase of the project the obtained experimental results were discussed in respect to the chase orientation and depth as well as in respect to the chase infill. Finally, in order to get a deeper insight into the structural behaviour of masonry elements with chases an analytical investigation based on a simple truss model has been performed. It was shown that such a model can predict the masonry strength of elements with horizontal and inclined chases. As a governing material parameter the tensile strength of the clay block unit was selected.
The abovementioned discussion and analytical solution are summarized in the following publication:
N. Mojsilovic: "external page Masonry elements with chases: Behaviour under compression", Construction and Building Materials, 25 (12), 2011, pp. 4415-4425.
This project has been completed.