MASONRY DESIGN: CRACKS ANDDEFORMATIONS IN LOW-RISE BUILDINGS

MS ARIADNE TSAMBALI

ARISTOTLE UNIVERSITY OF GREECE,DEPARTMENT OF CIVIL ENGINEERING,MECHANICS OF MATERIAL, EGNATIA ROAD, POST CODE 54124, THESSALONIKI, GREECE.

a.tsambali@yahoo.gr

EXTENDED ABSTRACT

This paper brings the title “ Crack & Deformations in Low Rise Buildings” with major concern into all cracks, which it happened to developed into the life of the Brickwork. This paper investigates the relationship between the settlement and the crack formation in a low-rise building. Masonry or brick buildings are subject to settlements in real life. Many brick buildings show failures due to settlement and subsidence.

On each stage of design days before the final process to import on site for finally construction stage any type of materials and manufacturer influenced the best and good design process. Costs and qualityare all important on the design process. For a process to be workable/mark able it is, must be supplied at an acceptable costs and be of an acceptable quality. It is difficult to generalise as all factors influenced the construction and finally costs a building considers Human Factors.

Brick strength and durability should be sufficient for the conditions in which a brick is to be used and if it is to be seen as a facing brick, it should be a good appearance. Alternatively a base for decoration,or a keyed brick for renedering on plastering may be required. For purposes of analysis we constructed a malels on various scale to determined analysis further.

1.0 INTRODUCTION

This paper investigates the relationship between the settlement and the crack formation in a low-rise building. Masonry or brick buildings are subject to settlements in real life. Many brick buildings show failures due to settlement and subsidenceIn order to clarify better this paper, a small research on this field took place.In order to investigate the relationship between the settlement of a structure and the amount of developed on it, a 1/10-scale model has been constructed. For the purpose of this paper, it was not possible to investigate and analyse the real behaviourof a structure, and a one tenth scale model of a two-storey building dwelling was used for the purpose our research. Two storey (1/10 scale of the actual structure) building have been constructed and tested. Themodel was tested for sagging moment.

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2.0 DESCRIPTION

We build a model of a modern two-storey brick house on a scale of 1/10. Our model is built from mortar and cement while this experiment take place on laboratory we use for mortar simple flour and for bricks and blocks only plaster brick and blocks on scale of 1/10 of the actual size of the brick which is 215 x 102.5 x 75 in (mm). We used the British Code of Practise BS 5268 for Mansory.

We test our model for vertical and horizontal alignment and as well for deformations and cracks on each side.

Our model was consisting on bases from screw. The purposes of the screw are to playing the role of the pad footing. Each time when we turn one circle the screw this mean that the lower the model for 0.1mm downwards or upwards. On the top of the house we placed weights bars over 100 Kgr and we tested our model for lateral movements and cracks.

To established a good pictured of our result we hang from the roof a thread along the full side of the house. So, for the horizontal side of the house we having 5-threats and for the 2 verticals sides of the house, we hang 3 threads down to the level of the footing. We divide the house on levels and we measured with a ruler, each lateral movement and the cracks while we simultaneously turned the 2 screws on the corner of the house.

On the horizontal side of the model we placed 5 screws of 1-¼ inches and on vertical side we placed 3screws. All of them they represent the pad foundations of a normal house.

Every time we turn the screws simultaneously once each time we transfer movement on our model on the same was, as a real house accept the seismic waves or even more any lateral movement of the ground.We expect to find cracks on buildings where the footings are pad and on such conditions of clayey soil and sand.

On, its traditional construction the model was consisted from a 300 mm cavity wall. The external walls were from brickwork and internal walls were single leaf block- work and wall ties were placed on every block. Timber floor joists were placed at first and second level to provide lateral restraint.The main materials were bricks, blocks and mortar. Bricks used for this model are a mixture of plastersand and water, like the normal bricks but the dimensions were 20 mm x 10 mm x 5 mm. Blocks were constructed with the same mixture of plaster, sand and water with dimensions 40 mm x 20 mm x 5mm. Door frames were from 10mmx10mm softwood with dimensions 90mm in width by 210mm in height.Window frames constructed from 30mmx30mm softwood with dimension 100 mm x 100 mm square windows. Finally the foundation frame had dimension of 1000 mm x 600 mm with foot screws attached to the underside of the frame to accommodate the settlement require to impose damage to the structure.

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3.0 METHODOLOGY

For the purpose of this research, settlement was simulated at different corners of the building by lowering of one corner of the structure. This achieved with the installation of screwed on the base of the structure.Then, settlement was simulated at different corners of the building. This was achieved by lowering of one corner of the structure using the screws. It was expected that the brick would move or deflect as the screws are turned or lowered. Their movements (achieved by the turning of the screws) eventually lead to the development of crack. And, a record was kept. In order to simulate settlement in the building, the foot screw of the model were to be lowered. The foot screw at 1 was lowered by one turn (i.e. 1.5mm movement) in the anti-clockwise direction. A sequential turning at points 2,3,5,6 and 4 followed this. The turning was ¾,½,½,¼ and ¼ turn respectively. The turning mode used in achieving a 1cm movement, which is 6.5 turns. It was observed that as the screws were turned and the model is being lowered, the model was begun to move. As the movement increased, cracks were being formed due to the distortion of the model (bowing). Afterwards, we investigate the stability of the structure.

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4.0 DISCUSSION ON RESULTS

Differences in level profiles (Initial Readings – Final Readings)

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5.0 INITIAL LEVELLING

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6.0FINAL PLAN VIEWS AT DIFFERENT LEVELS OF HEIGHT

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6.0 CONCLUSION

A final reading gave measured settlement around 10mm and a maximum crack width of 1.0mm on side 3 of our model. Settlement was simulated at different corners of the building. Settlement of the building resulted in the formation of cracks within the building.The reason of this was the fact that all our models have existing cracks on sides one, two and three. For example, the measured cracks observed will be directly related to cracks in real life of the structures. These cracks often started at diagonals, joints or any weak point around the brickwork. The most significant cracks occurred near windows, door.

PHOTO 1. A FRONT SIDE OF OUR MODEL-BEFORE TESTING

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7.0 BIBLIOGRAPHY

1. Arya, Design of Structural Elements, edition E & FN Spon2. Timoshenko, Young, Theory of Structures.3. W.G.Curtins, Structural Masonry Designers Manual, edition 1995 by Blackwell4. M.F.Atkinson, Structural Foundation Manual for low-rise buildings, edition 7th,

by Pearson, Prentice Hall5. W.G.Curtins, Structural Foundation Designer’s Manual, edition 1995 by Blackwell6. British Code of Practise, BSI 5268.

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