Types of reinforcement or mesh in several footings (foundations)
Different types of Reinforcement in footings or types of mesh used in foundation:-
Several types of reinforcement exist in footings. The reinforcement should be provided in footings for tension requirements. Normally, the percentage of reinforcement in footings should remain among 0.5% to 0.8%. Based on the load analysis, the structural engineer design the type of Mesh in footings. Given below, the details about he types of mesh (reinforcement) implemented at several types of footings or foundations.
Usually, four different types of reinforcement in footings or foundations are found :?
1. Plain Mesh: This type of Mesh is normally implemented at plain or isolated or combined footings. It is specifically useful for low-rise buildings. Prior to use plain mesh to high rise buildings, the load should be analyzed in accordance with this mesh and determine either the type of mesh is balanced with the load or not.
Under this type, bars are arranged as a grid. It may contain bars with various diameter and spacing in either direction. The spacing may or may not vary in both directions.
2. Mesh with hooks (Hook Mesh): It is suitable for both low rise and high rise buildings. The footing is reinforced as grid and the bars are arranged with hook at the ends of the mesh. The perfect anchorage of the reinforcement can be obtained by bending the bars ends. Normally, the standard length of hook is 10D where D stands for the diameter of the bar.
3. Footing Mesh up to the depth of Footing: It has similarity with Plain footing. Under this type of footing, the bars are bent at ends up to a height of footing. The concrete cover of 1" to 4" should be arranged in all the sides of footing.
4. Raft Mesh: This type of Mesh is ideal for raft footing. Raft footing is suitable when the bearing strength of soil is very low. Under this type, mesh is segregated into two parts like top mesh and bottom Mesh.
Initially, the bottom mesh is arranged on covering blocks, ends of a bottom mesh are bent at an angle of 90 degree up to a height of 50D where D stands for Dia of Bar. After that top mesh is attached with the bottom mesh in opposite direction. Besides, the top mesh equivalent to bottom mesh is bent with 90 degrees but an additional bar of 50D is not arranged since it is already equipped on bottom mesh.
The 50D extra bar is arranged either on bottom or top mesh.
Single ring or double rings are attached with top mesh and bottom mesh to retain the proper framework. The rings allow the steel reinforcement not to distort in any direction. Least diameter of bars used for rings should be 6 mm.
In single ring raft mesh, rings are arranged in only one direction either horizontal or vertical, while in double ring system, the rings are arranged in both the direction.
The following points should be taken into consideration :-
1. Concrete cover differs from 1" to 4" depending on the size of the footing.
2. Hook length in Hook mesh is always 9D, where D stands for Dia of bar.
3. Additional bar is arranged either on top or bottom mesh and additional bar length is 50D.