Q.
a) With use of a diagram, label the elements of a brick wall openings. Elaborate the function of each element. (10 marks)
b) Explain the term flush door. Use diagrams to indicate the types of flush doors and give reasons why it should not be used as external door. (15 marks)
(2011 Q4)
A.
For part b) please click here.
a)
The top part of the brick wall opening is "lintel". The sides of the opening is called "abutments"
As the lintel has to support the entire weight of the load above, it is reinforced. Lintel can be made of reinforced concrete or wood or steel. Lintels impose only vertical loads on the adjoining sections of walls and are themselves subjected to bending loads, shear loads and compression loads at their support points. Concrete lintels may be either cast in place or prefabricated and installed as the wall is constructed.
Arches are subjected to the same bending and shear forces but, in addition, there are thrust forces against both the arch and the abutting sections of the wall.
It is not difficult to determine loads and choose a wood or steel lintel to install, or to design the reinforcing for a concrete lintel. However, the design of an arch always involves assumptions, followed by verification of those assumptions.
Lintels made of wood are suitable for light loads and short spans. Timber that has been pressure-treated with a preservative should be used.
Steel angles are suitable for small openings and Table 8.8 presents size, span and load information for several sizes. Larger spans require universal section I-beams and a specific design analysis. Steel lintels should be protected from corrosion with two or more coats of paint.
If an arch is constructed by bricks in place of the lintel, it arches upwards with wedge shaped joints. Such shape of arch would reinforce the strength of support for the bulk of load above. It is also a common design for Churches windows and doors in the past.
Abutment explained:
The solid portion of a structure that supports the lateral pressure of an arch or vault.
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