Some useful notes on Pile Cap Design

Definition of Pile Cap: A pile cap refers to a thick concrete mat that is situated on concrete or timber piles driven into soft or unsteady ground to develop a proper & secure foundation. It normally builds up section of the foundation of a building, mostly a multi-story building, structure or support base for heavy equipment.

It is frequently found that one pile can’t bear the entire load enforced on the column. Therefore, the column requires over one pile to bear the load. Here, a pile cap plays an important role to disperse the column load to these piles uniformly.

In this stage of design, precautions should be undertaken to disperse the load to the piles evenly by placing the center of gravity of the column to match up with the center of gravity of the pile cap.

To make sure that the load is transmitted from the column to the pile, the pile steel reinforcement should be expanded inside the pile cap with minimum 600 mm so that the load is transmitted with the bond among concrete and steel.

The pile caps are designed as a rigid foundation and ensure that the piles bear equivalent loads from the column in order that the pile cape thickness should be designed to withstand the punching stresses and the tension in top and bottom.

Shape and Size of Pile Caps:

1. The shape and plan dimensions of the pile cap are based on the number of piles in the group and the gapping among each pile.
2. These pile caps outlines & minimizes the plan area for uniform arrangement of piles about the load.
3. The pile cap should overlap exterior piles by minimum 150mm but should not be too much, usually not in excess of the diameter of the pile diameter.

It reduces the plan area as well as the cost, at the time of arranging adequate length to the followings:

1. Affix the tension reinforcement with a large radius bend
2. Provide sufficient cover to the reinforcement
3. Meet the tolerances of the construction

Depth of Pile Cap - The depth of pile cap is influenced by the following factors :

1. Shear strength of pile cap (beam and punching shear)
2. Shrinkage and swelling of clay

3. Frost attacks
4. Pile anchorage
5. Water table and soluble sulphates
6. Maintain bolt assemblies for steel columns

Shear is considered as most important factor for selection of depth of pile cap.

Normally a pile cap is much deeper as compared to a pad footing having similar dimensions, since it is prone to greater concentrated reactions, and accordingly to much greater bending moments and shear forces.

However, the increased depth assigns greater rigidity to the pile cap that results in spreading the load uniformly to all piles.



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Published By
Rajib Dey
www.constructioncost.co
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Brief overview of adjustable steel columns

Adjustable steel columns alias screw jacks or beam jacks, belong to hollow steel posts. The purpose of these columns is to provide strong support to the structure. A secured adjustable steel column threaded adjustment mechanism is employed to alter the height of the post with the help of a big screw.

They are frequently utilized in basements.

They are constructed as multi-part assembles, often known as telescopic steel columns, or as single-piece columns.

When a column is applied or set up improperly or its condition is damaged, the column becomes insecure. General faults occur due to persistent utilization of temporary columns, inappropriate installations and extreme exfoliating rust, all of which can cause abrupt collapsing of the column as well as the structure it supports. As a result injury and property damage will occur.

The following are possibly faulty conditions:

The diameter of the post remains under 3 inches as per 2006 International Residential Code (IRC), Section R407.3. Poles which remain under 3 inches go against the IRC, although they are not inevitably faulty. A 2½-inch post is sufficient to support the load over it, whereas a 4-inch post can buckle when the load goes beyond the structural strength of the post. Structural engineers normally take decision whether adjustable steel posts contain equivalent size.

Rust-inhibitive paint is not applied to safeguard the post. The IRC Section R407.2 defines:

All surfaces (interior and exterior) of steel columns should be provided with a shop coat of rust-inhibitive paint, exclusive of corrosion-resistant steel and steel treated with coatings to provide corrosion resistance.

Inspectors are unable to recognize paint as rust-inhibitive. In dry climates where rust is not happen, rust-inhibitive paint should not be applied. Visible signs of rust represent a possible deficiency.

The post is not straight. It should be checked that the highest lateral displacement among the top and bottom of the post should not go beyond 1 inch. However, endurable lateral displacement is influenced by several factors, like the height and diameter of the post. The post should not bend at its centre. Bending implies that the column is unable to endure the weight of the house.

The column is not mechanically attached with the floor. An inspector can’t identify whether a connection among the post and the floor subsists if this connection is wrapped with concrete.

The column is not attached with the beam. The post should be mechanically attached with the beam over to add extra resistance capacity against lateral displacement.

In excess of 3 inches of the screw thread are uncovered.

Cracks exist in upstairs walls. This condition may lead to the failure of the columns.

The following types of adjustable steel columns are commonly found - Single Piece Adjustable Columns, Telescoping Adjustable Columns

To learn how set up a adjustable steel column, go through the following link www.thespruce.com



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Published By
Rajib Dey
www.constructioncost.co
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