Shear Walls Systems

As the name implies, shear walls resist lateral load in shear.  Shear walls may be of wood, concrete or masonry.  In the US the most common material for low-rise  apartments is light-weight wood framing with plywood or particle board sheathing. Framing studs, spaced 16 or 24 inches, support gravity load and sheathing resists lateral  shear.  In seismic areas concrete and masonry shear walls must be reinforced with steel  bars to resist lateral shear.

1  Wood shear wall with plywood sheathing
2  Light gauge steel shear wall with plywood sheathing
3  Concrete shear wall with steel reinforcing
4  CMU shear wall with steel reinforcing
5  Un-reinforced brick masonry (not allowed in seismic areas)
8  Two-wythe brick shear wall with steel reinforcing

MOMENT REDUCTION FOR ANCHORED SHEET PILE WALLS.

The design of anchored sheet piling by the free-earth method is based on the assumption that the piling is perfectly rigid and the earth pressure distribution is hydrostatic, obeying classical earth pressure theory. In reality, the sheet piling is rather flexible and the earth pressure differs considerably from the hydrostatic distribution.

As such the bending moments M(max) calculated by the lateral earth pressure theories are higher than the actual values. Rowe (1952) suggested a procedure to reduce the calculated moments obtained by the/ree earth support method.

Anchored Piling in Granular Soils
Rowe (1952) analyzed sheet piling in granular soils and stated that the following significant factors are required to be taken in the design

1. The relative density of the soil
2. The relative flexibility of the piling which is expressed as

Anchored Piling in Cohesive Soils
For anchored piles in cohesive soils, the most significant factors are (Rowe, 1957)

1. The stability number

2. The relative height of piling a

Fig. 20.20 gives charts for computing design moments for pile walls in granular and cohesive soils.

FREE CANTILEVER SHEET PILE WALLS.

When the height of earth to be retained by sheet piling is small, the piling acts as a cantilever. The forces acting on sheet pile walls include:

1. The active earth pressure on the back of the wall which tries to push the wall away from the backfill

2. The passive pressure in front of the wall below the dredge line. The passive pressure resists the movements of the wall
 
The active and passive pressure distributions on the wall are assumed hydrostatic. In the design of the wall, although the Coulomb approach considering wall friction tends to be more realistic, the Rankine approach (with the angle of wall friction δ = 0) is normally used.
The pressure due to water may be neglected if the water levels on both sides of the wall are the same. 

If the difference in level is considerable, the effect of the difference on the pressure will have to be considered. Effective unit weights of soil should be considered in computing the active and passive pressures.

⇒  General Principle of Design of Free Cantilever Sheet Piling

EXTERNAL STABILITY - MSB wall.

The MSB wall system consists of three zones. Thye are

1. The reinforced earth zone.
2. The backfill zone.
3. The foundation soil zone.

The reinforced earth zone is considered as the wall for checking the internal stability whereas all three zones are considered for checking the external stability. The soils of the first two zones are placed in layers and compacted whereas the foundation soil is a normal one. The properties of the soil in each of the zones may be the same or different. However, the soil in the first two zones is normally a free draining material such as sand.

It is necessary to check the reinforced earth wall (width = B) for external stability which includes overturning, sliding and bearing capacity failure. These are illustrated in Fig. 19.17. Active earth pressure of the backfill acting on the internal face AB of the wall is taken in the stability analysis. The resultant earth thrust Pa is assumed to act horizontally at a height H/3 above the base of the wall. The methods of analysis are the same as for concrete retaining walls.

Figure 19.17 External stability considerations for reinforced earth walls

Building Components: Masonry units: walls, columns etc.

Masonry may be defined as the construction of building units bonded together with mortar. These building units, commonly known as masowy units may be stones, bricks or precast blocks. Masonry is used for the construction of foundation walls, columns and other similar structural components. The construction with stone units, bonded with mortar is known as stone masonry, while the construction with brick units, bonded with mortar is known as brick masonry. A composise masonry may use different types of building units for the construction.

Walls are the mosi essential componens of a building. The primary function of the wall is to endose or divide space of the building to make it more functional and useful. Walls provide privacy, afford security and give protection against heat, coid, Sun and ram. Walls may be either load bearing or non-load bearing. Load bearing walls are those which are designed to carry the super-imposed loads (transferred through roofs), in addition to their own (self) weight. Non-load bearing walls carry their own load only. They generally serve a divide walls or partilion walls. Wall may be of several types, such as cavity walls, party walls, partittion walls, dwarf walls, retaining walls

A column is an isolated vertical load bearing member, the width of which is neither less than its thickness nor more than four times its thickness. A pier is a member similar to a column except that it is bonded into load bearing wall at the sides to form integral part and extends to the fuli height of the wall. A pier is used to increase the stiffness of the wall to carry additional load or to carry vertical concentrated load.