According to ACI 318-19, Section 11.10.3, side skin reinforcement is required in beams and joists with a height greater than 900 mm (36 in.). The side skin reinforcement must be uniformly distributed along both side faces of the member and extend for a distance h/2 from the tension face. The minimum area of side skin reinforcement is equal to 0.002 times the beam or joist cross-sectional area.
The purpose of side skin reinforcement is to prevent the sides of the beam or joist from buckling under compression. The reinforcement helps to distribute the compressive stresses more evenly throughout the member and prevents the formation of local buckles.
The side skin reinforcement can be made of either steel bars or welded wire fabric. The bars or wire fabric should be placed in the same plane as the main reinforcement in the beam or joist.
Here is an example of the side skin reinforcement requirements in ACI 318-19:
- A beam with a height of 1200 mm (48 in.) would require side skin reinforcement with a minimum area of 0.002 * 1200 * 1200 = 2880 mm^2.
- The side skin reinforcement could be made of two No. 5 bars (each with an area of 100 mm^2) spaced 150 mm (6 in.) on center.
It is important to note that the side skin reinforcement requirements in ACI 318-19 are just the minimum. In some cases, it may be necessary to provide more side skin reinforcement to ensure the stability of the beam or joist.
Here are some factors that may affect the need for additional side skin reinforcement:
- The height of the beam or joist
- The span of the beam or joist
- The type of loading on the beam or joist
- The concrete strength
- The steel reinforcement ratio
If you are unsure whether or not your beam or joist needs side skin reinforcement, it is always best to consult with a structural engineer.
Footnotes
- ACI 318-08 Section 10.6.7
- ACI 318-11:2011 Section 10.6.7
- ACI 318-14 Section 9.7.2.3
- ACI 318-19 Section 9.7.2.3