Tuesday, January 21, 2014

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Detailing of Beam Reinforcement in Seismic Zone

Placing beam reinforcement isn't difficult. But it needs some technical knowledge. In a seismic zone, it needs extra care. Structural designers provide every detailing in the structural drawing specially for seismic zone (earthquake zone). As a construction professional you should have clear concept about that. In this article you will see typical beam reinforcement detailing for earthquake zone.
Beam reinforcement detailing for earthquake

Types of reinforcing bar used in beam

A beam can have following types of bar -

Top bar

Bottom bar

Extra top bar

Extra bottom bar


Face bar

Top bar:
 Top bar is placed in the compression zone of beam. It is placed 2 inches below (typical) from the beam's top outer face for maintaining clear cover. It should have 90 degree hook in the both end where beam ends. Hook length should be minimum 12 times of bar dia. If you need to provide lap than place the lap in the middle of beam. Lap length should be minimum 48 times of bar dia.

Bottom bar: Bottom bar is placed in the tension zone of beam. Beam bottom bar placement is same as top bar. But lap of bottom bar should be on the beam support.

Extra top bar: Extra top should be provided on the beam support at top of beam and extent up to one-third of beam's clear span both side of support.

Extra bottom bar: provide extra bottom bar in the middle of beam's bottom portion.

Stirrup: Stirrup often called ring in the construction sector. It is the share reinforcement. Typical Stirrup size is 3 inches less than beam size in both direction for maintaining clear cover. Hook of beam stirrup should be 135 degree angle and hook length not below 3 inches. Place the hooks on both sides of beam top alternatively. Stirrups spacing of beam are always specified in the structural drawing by designers. If not specified than follow the rules showed in the image above.

shear reinforcement for earthquake zone

Face bar: It is also called middle bar or additional bar. Face bar is provided when beam height exceeds 2'-6" feet. It is placed on the middle portion of beam.

Always keep in mind that there should be minimum one inch gap between reinforcing bars. So, use 25 mm steel bar as a spacer if you have to place two layer reinforcement in the beam.

Placing reinforcement in beam I described here is typical details for earthquake zone not in depth details. I will describe reinforcement detail for every type of beam here in "ACE".


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