Sunday, January 29, 2017

FOUNDATION & BRICK MASONRY

FOUNDATION & BRICK MASONRY


TYPES OF BONDS IN BRICK MASONRY

1.   Stretcher bond
2.   Header bond
3.   English bond and
4.   Flemish bond

1. STRETCHER BOND
A stretcher is the longer face of the brick as seen in the elevation. In the brick of size 190 mm × 90 mm × 90 mm, 190 mm × 90 mm face is the stretcher. In stretcher bond masonry all the bricks are arranged in stretcher courses as shown in Fig-1. However care should be taken to break vertical joints. This type of construction is useful for the construction half brick thick partition wall.

2. HEADER BOND
A header is the shorter face of the brick as seen in the elevation. In a standard brick it is 90 mm × 90 mm face. In header bond brick masonry all the bricks are arranged in the header courses as shown in Fig-2. This type of bond is useful for the construction of one brick thick walls.

3. ENGLISH BOND
In this alternate courses consist of headers and stretchers. This is considered to be the strongest bond. Hence it is commonly used bond for the walls of all thicknesses. To break continuity of vertical joints a brick is cut lengthwise into two halves and used in the beginning and end of a wall after first header. This is called queen closer. (Refer Fig-3). Fig-3 shows typical one brick and one and half brick thick wall with English bond.

4. FLEMISH BOND
In this type of bond each course comprises of alternate header and stretcher [Fig-4]. Alternate courses start with stretcher and header. To break the vertical joints queen closers are required, if a course starts with header. Every header is centrally supported on the stretcher below it.
Flemish bonds may be further classified as

  • Double Flemish Bond
  • Single Flemish Bond.
Building elements: 
The building materials used in the construction of the following elements are the foundation for classification, be they wood, steel, or masonry.
  • Structural frame
  • Exterior bearing walls
  • Interior bearing walls
  • Exterior nonbearing walls and partitions
  • Interior non-bearing walls and partitions
  • Floor construction, including supporting beams and joists
Fire-resistance rating:
This is the other factor in determining construction class. The building materials used in the construction of the building elements above will have a fire-resistance rating. Fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time (ex. 0 hours, 1 hour, or 2 hours), or it may entail a host of other criteria involving other evidence of functionality or fitness for purpose.
  • “Minimum” rule: It is important to remember when selecting the construction class that the building is only as strong as its weakest element. For example, a masonry building may have an unprotected wood roof. The wood roof is the weakest member such that it has no fire-resistance. Thus, the construction class would be Joisted Masonry (see below). Now imagine this same building with a metal deck roof. So long as the supporting members of the building do not contain wood then this building would be Masonry Noncombustible (see below).


Foundation
In this article we will discuss the common types of foundations in buildings. Broadly speaking, all foundations are divided into two categories: shallow foundations and deep foundations. The words shallow and deep refer to the depth of soil in which the foundation is made. Shallow foundations can be made in depths of as little as 3ft (1m), while deep foundations can be made at depths of 60 - 200ft (20 - 65m). Shallow foundations are used for small, light buildings, while deep ones are for large, heavy buildings.

 Shallow Foundations
Shallow foundations are also called spread footings or open footings. The 'open' refers to the fact that the foundations are made by first excavating all the earth till the bottom of the footing, and then constructing the footing. During the early stages of work, the entire footing is visible to the eye, and is therefore called an open foundation. The idea is that each footing takes the concentrated load of the column and spreads it out over a large area, so that the actual weight on the soil does not exceed the safe bearing capacity of the soil.There are several kinds of shallow footings: individual footings, strip footings and raft foundations. In cold climates, shallow foundations must be protected from freezing. This is because water in the soil around the foundation can freeze and expand, thereby damaging the foundation. These foundations should be built below the frost line, which is the level in the ground above which freezing occurs. If they cannot be built below the frost line, they should be protected by insulation: normally a little heat from the building will permeate into the soil and prevent freezing.

Individual Footings
Individual footings are one of the most simple and common types of foundations.  These are used when the load of the building is carried by columns. Usually, each column will have its own footing. The footing is just a square or rectangular pad of concrete on which the column sits. To get a very rough idea of the size of the footing, the engineer will take the total load on the column and divide it by the safe bearing capacity (SBC) of the soil. For example, if a column has a vertical load of 10T, and the SBC of the soil is 10T/m2, then the area of the footing will be 1m2. In practice, the designer will look at many other factors before preparing a construction design for the footing.

STRIP FOOTINGS
Strip footings are commonly found in load-bearing masonry construction, and act as a long strip that supports the weight of an entire wall.  These are used where the building loads are carried by entire walls rather than isolated columns, such as in older buildings made of masonry.

RAFT OR MAT FOUNDATIONS
Raft Foundations, also called Mat Foundations, are most often used when basements are to be constructed. In a raft, the entire basement floor slab acts as the foundation; the weight of the building is spread evenly over the entire footprint of the building. It is called a raft because the building is like a vessel that 'floats' in a sea of soil.Mat Foundations are used where the soil is week, and therefore building loads have to be spread over a large area, or where columns are closely spaced, which means that if individual footings were used, they would touch each other.

PILE FOUNDATIONS
A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground so that structures can be supported on top of it.
Pile foundations are used in the following situations:
1.When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer.
2.When a building has very heavy, concentrated loads, such as in a high rise structure.

End Bearing Piles
In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.

Friction Piles
Friction piles work on a different principle. The pile transfers the load of the building to the soil across the full height of the pile, by friction. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil. To visualise how this works, imagine you are pushing a solid metal rod of say 4mm diameter into a tub of frozen ice cream. Once you have pushed it in, it is strong enough to support some load. The greater the embedment depth in the ice cream, the more load it can support. This is very similar to how a friction pile works. In a friction pile, the amount of load a pile can support is directly proportionate to its length.

Construction methods – what’s available?
Most buildings (both residential and commercial) are built around a frame that provides the structure and support for the building. Framing typically falls into two categories – heavy framing and light framing – with light framing used in the majority of residential buildings.

Heavy framing includes construction methods such as post-and-beam construction, also known as timber framing, where large, heavy timber beams are used instead of dimensional lumber (wood cut to standardized dimensions such as 2×4, 2×6, etc.), and heavy steel framing that is normally seen in skyscrapers and other large commercial buildings. Light framing is typically done using dimensional lumber or light-gauge steel, with the building’s structural skeleton of wood or steel components assembled piece by piece.

Other construction methods such as masonry (building with individual stones or bricks held together by mortar), reinforced or unreinforced concrete (a material made from a mixture of gravel, sand, cement and water), rammed-earth blocks (building blocks made of compressed earth), and Structural insulated panels (SIPs) (sandwich panels with engineered wood on two sides and insulation in between) can be used independently or in conjunction with frames to build homes, but most of these methods are used in tandem with a frame in the US and Canada.