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To see the model pictures of the cracks and the suggested solutions click on the following url.
http://www.geofreeze.com/residential.html
Walls get cracks mainly as a result of ground movement. It is rare for modern buildings to undergo bad settlement due to foundation overload. On the other hand older buildings were quite often built on soft soils, their builders being unaware of the future consequences. But all categories of structures may suffer settlement through ground movement independent of the foundation loading. Such movements are typically caused by mining, tunneling, earthquakes, changes to groundwater levels, adjacent excavation and soil awelling or shrinkage. Differential settlements are one of the major causes of cracks in walls. Differential settlements must be considered inevitable for every foundation is supported in solid rock. The effect of differential settlement on the building depends to a large extent on the type of construction. Consequently it is necessary to find out by careful inspection of the buildings of known settlement records how much different types of construction can withstand without harm.
Damage is assessed almost exclusively by reference to the crack size and not by some settlement parameter. In practice, when something goes wrong, a geotechnical engineer is called in to identify a foundation/subsoil cause. Elimination of this cause by means of a foundation repair permits simple cosmetic treatment of the masonry cracks without considering the behaviour of the masonry itself. It overlooks the true effect of the soil/structure interaction; and the concern is that engineers seldom ask themselves , namely, whether the damage resulted solely from inadequate foundation support. Where foundation movement is gross, sudden or ongoing then foundation repair may well be the only solution. However, foundation movement that has accumulated over a period of time might be predicted to continue at the same or a reduced rate, or in some cases, reverse itself. In these cases, increasing the flexibility of the walls by reinforcing may offer a more economical solution that provides an adequate extension to the life expectancy of the structure. Rarely is underpinning likely to reduce foundation movement to zero and masonry reinforcement, particularly of stiff walls, may well be a useful additional treatment in this case also.
Physical strengthening of the spandrels to delay cracking could delay the manifestation of damage and create a facade able to withstand greater settlement. Alternatively, increasing the ductility of the wall, through extending the limit of tensile bending strain at the corner points, would also delay the onset of cracking. Where the purpose is restoration/repair, reinforcement should increase ductility in order to limit cracking, not enhance strength. This latter option is preferred as all masonry is inherently weak and forces involved are large. The ideal repair should be able to contain the initial corner cracking, caused by bending, until the limit of diagonal tension due to shear is reached.
In practical terms if a masonry structure develops cracks around a window or door lintel, then a minimum bed reinforcement repair can contain a significant amount of further movement, atleast equal to that causing the damage in the first place. This offers possibility to extend the life of the building such that its further life matches its life to the present. This does not deny the progressive settlement movement caused by landslip, or some other major change in the ground conditions, may require the normal process of repair to the foundations. However, where movement of masonry is likely to be limitedand quantifiable there is the scope to contain existing damage by simply introducing reinforcement.
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