BBS Preparation
- 2. Bar Bending Schedule: Reinforcement Steel cost is around 20% – 25% of Cost of RCC Structure. Wastage of Reinforcement steel is generally noticed only at the end of works, and the cost implication is huge. IS code – “Code of practice for bending and fixing of bars for concrete reinforcement” – IS 2502 – 1963 (reaffirmed 2004) Particular care needed for higher diameter bars while bending. Size of Mandrel to be as per code else the bars crack at bend location. We typically use Mild Steel bars…….. HYSD Bars………? HYSD bars can be CT or TMT? Available strength – 415 / 500 / 550 / 600 …. With “D”? 1 ADGP
- 3. Bar Bending Schedule: Bar Bending is a process of cutting and bending reinforcement steel into desired shape as per structural drawing. Bar Bending Schedule (BBS) is a detailed list of reinforcement bars containing bar mark (for identification), diameter, numbers, shape with size, and cut length of each. BBS helps in estimating required quantities of the various diameter of bars, which helps in Procurement and Stock Management of various diameter of rebar. BBS assists in checking the work executed vis-à-vis requirement as per drawing and the same can be used in billing. BBS can be given to factory to get cut & bent steel at site, saving working space, better wastage control, reducing labour cost and thereby reduction in overall cost. 2 ADGP
- 4. Bar Bending Schedule: Preparation of BBS: i. Identification (Bar Mark) Tag different types of bars in the drawing with a unique id and list it out in a sheet. Consider the location (Column, Beam, Slab) for tagging. ii. Diameter Mention the diameter of steel bar against each Bar Mark. iii. Numbers required For Columns and Beam Main Steel, the numbers are usually provided, however for the Links of Column, Rings of Beam and Slab Main as well as distribution bars, numbers need to be calculated. Numbers = (Length – 2xCover / Spacing) + 1 iv. Shape with Sizes Refer the drawing for making out the correct shape of each type of rebar and the size of each of the element in shape. For Links and Rings mostly inner dimension is considered, for others it’s end to end v. Cut Length Depend on the diameter, angle & number of bends, laps, type of hooks, type of steel / concrete and type of stresses. 3 ADGP
- 5. Bar Bending Schedule: Important points while preparing BBS: i. Unit weight of various diameter bars ii. Development Length End of Column / Beam Bars iii. Lap Length Depends on type of steel / concrete / stress and diameter Staggering of lap - Minimum distance between C/C of Lap = 1.3 X Lap iv. Lap Location Columns – Beams – Slabs - v. Bends Angles of 30, 45, 60 vi. End Hooks 90 degree hooks, 180 degree hooks 4 ADGP
- 6. Bar Bending Schedule: Imp. Points i. Unit weight of various diameter bars: Use the weight against each diameter as given in the table. The weight is given in 3 digits beyond decimal for accuracy. We mostly use rebars of dia 10, 12, 16 and 20. In these; weight is 0.15% to 0.5% extra considering only 2 digits beyond decimal. We deal in 1000’s of metric tonnes of steel in each project. For every 1000MT, we may loose 1.5 MT to 5 MT. 5 Dia. (mm) Unit weight (Kg/m) 8 0.395 10 0.617 12 0.888 16 1.578 20 2.466 25 3.853 32 6.313 45 12.485 ADGP
- 7. Bar Bending Schedule: Imp. Points ii. Development Length: Extra length of bar provided beyond the required section to 1. Transfer the stresses from steel to concrete 2. Transfer the stresses from one element to other (From Beams to Columns / Slabs to Beams etc.) 3. Develop sufficient bond strength between rebar surface and concrete (To avoid failure due to slippage in ultimate load conditions) In case of bundled bars, development length is increased by 10/20/33 % for 2/3/4 bars in contact This is also called as an anchorage length in case of axial tension or axial compression In case we don’t provide the sufficient Development Length. The failure of junctions / joints will happen Prior to reaching even the safe load limits. Development length, normally is more for HYSD bars And lessor for high strength concrete. 6 ADGP
- 8. iii. Lap Length: Lap length is the overlap of two bars to transfer load For installing the reinforcement steel, when the length of it is not sufficient to cover the entire stretch, or it is not feasible to transport / lift / install / keep it in position then the steel is provided with a lap. Lap is also required, when the diameter of bar has to be changed as per design requirement. While providing laps following to be kept in mind: 1. Use proper splicing technique (Lapping / Welding / Mechanical or Threaded splicing) 2. Location of lap to be away from section of high flexural / shear stresses 3. stagger the location of lap for individual bars of a group (Column / Beam / Slab) If staggering is unavoidable than increase the length of Lap / use spiral rebar over lap 1.3 x Lap Length Lap Length - Flexural Tension – Ld or 30 Dia Direct Tension – 2Ld or 30 Dia Compression – Ld or 24 Dia In case of 2 different dia – Lap should be calculated for smaller dia bar. Stagger the lap in bundled bars as well 7 Bar Bending Schedule: Imp. Points ADGP
- 9. iv. Lap Location Columns – Normally bottom L/4 and Top L/4 are the high stress zones, hence the lap should be provided in the middle L/2 zone. However follow, design guideline if specified. Beams – Normally the bending moment is high in centre and ends in a fixed / continuous beams. Avoid Laps in bars in tension zone, and provide laps in compression zone in such locations. Shear Stress is high in L/3 from support on both sides of beam thus avoid laps in shear reinforcement, however provide laps for Flexural tension zone bars as the bending moment is less. Follow otherwise design guidelines if specified. Slabs – Avoid laps in locations of high bending moment and high shear stress, which is normally at the mid span and ends, provide at 1/3 from the ends. Follow design guidelines otherwise, if provided 8 Bar Bending Schedule: Imp. Points ADGP
- 10. iv. Lap Location 9 Bar Bending Schedule: Imp. Points ADGP
- 11. v. Bends: Normally the requirement of Main reinforcement in Beam is at the bottom for Mid Span and at the top for End span considering the Bending Moment Diagram in Fixed & Continuous beams. In such case the Main reinforcement is bent and taken up as shown in figure. This takes care of the Shear Force Requirement 1/3 span as well. Refer the sketch – the extra length (i.e. l1-l2) to be considered for cutting length calculations. Refer the table beside the sketch for considering the extra length based on angle of bend. 10 Bar Bending Schedule: Imp. Points Angle @ D / Sin@ D / Tan@ la = l1-l2 30 D/0.5 D/0.5733 0.27D 45 D/0.707 D/1 0.42D 60 D/0.866 D/1.732 0.58D ADGP
- 12. v. End Anchorage – Hooks & Bends : (in HYSD Steel Bars) 11 Bar Bending Schedule: Imp. Points Nominal Dia ‘d’ 10 12 16 20 25 32 Hook Allowance ‘H’ 130 155 210 260 325 415-545 Bend Allowance ‘B’ 75 75 95 120 150 190-225 Radius ‘kd’ 40 48 64 80 100 128-192 ADGP End Anchorage Cut Length = l + B B=6d Semi-circular hook Cut Length = l + H H=13d
- 13. The reinforcement bar shape is prepared based on: a. Development Length (As per end conditions) b. Lap Length (As per requirement of Laps) c. Bends (As per details given in the drawings) d. End Anchors / Hooks (As per the requirements specified in drawings) The Cut length is calculated as per various norms given in earlier slides and / or based on various combination of the above. As explained earlier about rebar unit weight to be considered up to 3rd digit after decimal, in case of cutting length also one must consider the reduction due to bends. Though it’s small value in each bar; the overall impact is huge considering the huge quantum of work. 12 Bar Bending Schedule: Imp. Points ADGP
- 14. 13 Bar Bending Schedule: Imp. Points ADGP
- 15. 14 Bar Bending Schedule: Imp. Points Ultimate Tensile Strength Yield stress 0.2% proof stress ADGP
- 16. 15 Bar Bending Schedule: Splicing / Threading ADGP
- 17. Laps are not always appropriate joint for reinforcement steel. Space Constraints – specially large dia bars in Columns and Beams Depend on the strength from concrete / lack structural integrity Time consuming / Costly for higher diameter bars Couplers (Crimping / Threading) are the options fro splicing. Connect quickly at site locations Reduced congestion of rebars due to splicing Independent of concrete – integral reinforcement Cost effective – specially 20mm dia and above. Coupler should meet 125% of yield strength of rebar. 16 Bar Bending Schedule: Couplers Rebar Dia. (MM) Coupler Details Pitch (MM)External Dia. (MM) Internal Dia. (MM) Length (MM) 16 25 13.5 40 2.5 20 32 17.5 48 2.5 25 40 22 60 3.0 32 50 29 72 3.0 40 60 37 90 3.0 ADGP
- 18. 17 Bar Bending Schedule: Splicing / Threading ADGP