Building Roof Slab Shuttering and Reinforcement Work
While Construction Work, Building Roof Slab Shuttering and Reinforcement Work should be carefully done
Following Quality Points should be kept in mind
1. Formwork is temporary support given to concrete until it gains strength to withstand its self-weight.
2. Always use staging of MS tubes with timber runners.
3. Use planks under the base plate to distribute load.
4. Guardrails should be fitted at not less than 0.9m and not more than 1.15m above the decking. Clear spacing between the guardrails and the boards should not exceed 0.75m.
5. Toe boards should be at least 150mm high above the decking
6. Formwork oil basically serves the purpose of a separation medium. It acts as an intermediary that avoids any damage to the concrete. It also helps keep the formwork clean and ensures easy maintenance. The application of oil should be done with the help of foam or a similar soft medium and should be applied within 48 hours prior to concreting.
7. All spans in excess of 5 meters for beams and slabs should be kept within a pre camber of 2mm per 1 meter. For cantilever, give a camber at the end of span of 4mm per 1 meter.
8. The quality of finished concrete is dependent on the quality of formwork.
9. Striking time for formwork is as follows under normal conditions.
Walls, Columns, Starters etc. – 24 hours
Slab (span< 6mts) – 7 days
Beam (span < 6mts) – 14 days
Slab beam (span > 6mts) – 21 days
Props to cantilever – 28 days
10. For balcony and other rib beams, duct beams support should be continuous for at least 3 floors
11. Obtain the 7th day cube test result before the removal of formwork
12. Check for plumb and parallelism using 1m / 2m spirit level to the formwork at various points, Inner right angles at all 4 corners checked using right angle template.
1. Start reinforcement works with proper “Good for Construction” drawings and general specifications as issued by the consultant.
2. Make a stage-wise BBS (Bar Bending schedule) on the computer before indenting for steel.
3. IS codes such as IS 456, IS 1786, IS 2502, SP 34 should be available at site office at any given time for ready reference.
4. Mild steel bar should comply with IS 432.
5. Cold worked steel high strength deformed bars should comply with IS 1786.
6. Stack steel 300 mm clear of ground on SSM walls
7. Ensure Mill Certificate
(contains specification: IS 1786, BS 4449-2005, Gr-B 500 B, ASTM A615-09a, Grade 40, 60, 75 or 80 or ASTM A706-09a Grade 60 or 80,
Manufacturing Process: Quenched & Self Tempered,
Chemical Composition %: Carbon – 0.30 % maximum, Mn, Si, Sulphur – 0.06% maximum, Phosporous – 0.06% maximum, Sulphur and Phosporous – 0.110% maximum, Cr, Ni, Cu, N, Mo, V, CE,
Mechanical Properties: Cross Section, Unit Weight – Kg/m, Yield Strength – Minimum guaranteed yield strength (0.2% proof stress) for TMT-415 confirming to IS:1786 Fe 415 4250 Kg/cm2or 416.91 MPa or N/mm2 (1N/mm2 = 10.194 kg/cm2) , Minimum guaranteed yield strength (0.2% proof stress) for TMT-500 confirming to IS:1786 Fe 500 5100 Kg/cm2 or 500.29 MPa or N/mm2(1N/mm2 = 10.194 kg/cm2) , But maximum value that should be used as per international code is 3700 kg/cm2 , Tensile Strength – 485 N/mm2 (10% more than the Yield Strength) and more, T.S/Y.S ratio – 1.17, Total Elongation – 14.5% and more) is delivered with each load.
8. Binding wire shall be 16 – gauge soft annealed iron wire or 18 gauge GI annealed wire.
9. Tolerance for cutting of reinforcement = +75 or –25mm,
10. Bending Tolerance = +0 or –10mm
11. Bar spacing = + or – 10mm
12. All laps should be 50d or as specified
13. Give spacer blocks in CM 1:2 and cured for at least 7 days immersed in water.
14. Give spacers as per specifications. Generally 15mm for slab, 25mm for beam and 40mm for the footing is provided. It depends on the maximum size of aggregate, the reinforcement size and the element concreted.
15. Chairs should be placed as last operation before concreting to avoid distortion of top rod due to traffic.
16. Check if dowels for columns, beams and slabs are given correctly and is of required minimum length.
17. For slab reinforcement, the structural consultant should check and certify each work before concreting.