BEAM DETAILING

Number of bar in one layer

Beam width divided by 75mm, 125 of 150, 175, 200 use 2, 225 use 2, 300 use 4, etc. Normal beam use is 125mm (internal)/150mm(external), 230mm, 300mm, 450mm, 600mm, 750mm, 900mm, 1200mm, 1500mm, etc. Do not use 200mm under normal circumstances, as it is too wide for 2 bar and too thin for 3 bar.

Number of layer (top or bottom) maximum 1 for 300mm beam depth, 2 for 450mm depth, 3 for 600mm depth to 750mm depth. Beam width to adjust to reduce number of layers.

For beam with cover of 40mm (exposed to weather or underground), 150mm width can only accommodate to 2 No. of 16mm. For upper floor external beam, with one size 20mm and their other size 40mm, Y25 can be used. In some case we may need to use 175 or 200mm.

Try to make optimize bar length of 12m (12m, 6m, 4m, 3m, 2,4m, 2m, 1.5m, etc.). If possible use whole number and not 5.75m but use 5.8m if not 6 m.

Use symmetrical arrangement.

Support Bar

• Allow for 5-10% more.
• Minimum 50% (try to use 60%) to go to 0.3 span and the rest 0.15 span.
• Mark as _Y25 (4m) + _Y20 format.
• Mid span top bar.
• Normally use nominal bar to tie link unless there is compression bars or tension due to heavy support moment.
• Normally the first interior span mid span top bar will be slight more.

Span Bar

Follow the curtainment rule as follow:-

• Simply support end : minimum 50% go thought, the rest 50% reach 0.08 from support.
• Interior span : minimum 40% go thought, the rest go to 0.15 from support.

For end span allow 15% more.

For first interior span add 40% more.

For interior span add 30% more.

Try to allow some bar go throughout the span. Normally this is possible except the end span in which case use different bar size. Use marking a _Y25 thought + _Y20 (5m).

Shear

Allowance for at 10% more. In term of Asv/Sv.

Rebar choice.

To curtain steel bar, we should choose steel bar sizes properly. Preference should be given for single layer and bigger bar size with the same equivalent area. Eg. 3Y20 of 4m (first layer) + 2Y12 of 2m (second layer) is not as good as 2Y20(4m) + 1Y25(2.4m) all in one layer.

• Y10 only should be grouped with Y12, not Y16 and above.
• Y12 should be grouped with Y10 and Y16, not Y20 and above.
• Y16 should be grouped with Y20 and Y25, not Y32 and above.

Tags : engineer, engineering, civil, design, beam, beams, shear, rebar, detail, details, detailing

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