In best engineering practice the engineer will produce complete bar-bending¬†schedules for use by the contractor. The engineer may not guarantee that such¬†schedules are error free and may call upon the contractor to check them. But,¬†as often as not, the contractor will fail to do this, so it is advisable for the resident¬†engineer to check the schedules so that he can forewarn the contractor of¬†any error present. In practice, few errors will be found because the advantage¬†of producing bar-bending schedules is that it applies a detailed check on the¬†validity of the reinforcement drawings supplied to the contractor.
In some contracts the contractor is required to produce bar-bending schedules¬†himself from the reinforcement drawings supplied under the contract.
This is not such good practice; the engineer foregoes an opportunity to check¬†the reinforcement drawings, and the contractor (or his reinforcement supplier)¬†who produces the bending schedules will not necessarily be sufficiently¬†acquainted with the design to notice some discrepancy which indicates a possible¬†design error.
Reinforcement is now seldom bent on site, except on sites overseas.
Deliveries of reinforcement should be supervised by the leading steelfixer,¬†who should check the steel against the bar schedules and direct where bars¬†should be stocked. Bars should be delivered with identifying tags on them,¬†but sometimes these get torn off. The leading steelfixer should not allow with ¬†drawals from stock without his permission. If the contractor does not pay¬†sufficient attention to this and, for example, lets various steelfixers pick what¬†steel they think is right, the resident engineer should forewarn the contractor¬†this is a recipe for ultimate chaos and delay.
Properly designed and bent bars can, in the hands of a good steelfixer, be as¬†accurately placed as formwork. Crossings of reinforcement have to be wired¬†together so that a rigid cage is built, able to withstand concrete placing without¬†displacement. To ensure that the correct cover is given to bars, the contractor¬†will need to prepare many small spacer blocks of concrete of the¬†requisite cover thickness and about 25 mm square, which are wired onto the¬†outside of reinforcement, keeping it the required distance from the formwork¬†to give the specified cover. All wire ties should be snipped off close to the reinforcement¬†so that their ends do not penetrate the concrete cover and form a¬†path for corrosion of the reinforcement. The steelfixer will need to make and¬†position spacer bars, generally U-shaped, which keep reinforcement layers¬†the correct distance apart in slabs and walls. He may need many of these.
They are not included in the bar-bending schedules and the cost to the contractor¬†of supplying and fixing them is usually included in the price for
steelfixing. Fig. 19.5 shows some points to watch when formwork and reinforcement¬†is being erected.
Steel reinforcement stored on site rusts, but provided the rust is not so¬†advanced that rust scales are formed, the rust does not appear to affect the¬†bonding of the reinforcement to the concrete. A problem more likely to arise¬†is the contamination of steel reinforcement with oil, grease, or bitumen. If the¬†contractor wishes to oil or grease formwork to prevent it sticking to concrete,¬†he should do so before the formwork is erected and not after it has been put in¬†place. If the latter is attempted it will be almost impossible to prevent some oil¬†or grease getting onto the reinforcement. Similarly, if contraction joints are to¬†be bitumen painted, care must be taken not to get bitumen on bars passing¬†through such a joint.
The proper design and detailing of reinforcement makes a major contribution¬†to the quality and durability of reinforced concrete. The designer must¬†choose diameters, spacings and lengths of bars which not only meet the theoretical¬†design requirements but which make a practical system for erection¬†and concreting. Reinforcement to slabs must either be strong enough for the¬†steel fixer to stand on, or spaced far enough apart for him to get a foot¬†between bars onto the formwork below. Wall and column reinforcement must¬†be large enough diameter that it does not tend to sag under its own weight.
Beam reinforcement should not be so congested that it will be difficult to get¬†concrete to surround the bars without using a mix with too high a water content.
The designer should consider options of design available to avoid heavy¬†congestion of bars. An experienced designer who understands site erection¬†problems will make as much use as possible of the four most commonly used¬†bar diameters ‚Äď 10, 12, 20 and 25 mm. He will appreciate that a 5 m long bar¬†25 mm diameter weighs about 20 kg, so that larger diameter or longer bars can¬†be difficult for a steel fixer to handle on his own. For ease of handling, bars¬†should not exceed 6‚Äď8 m length.
Bond laps have to be allowed for and should be at places which are convenient¬†for the erection of formwork and for concreting. Starter bars in floor¬†slabs are nearly always necessary for bonding to the reinforcement in walls.
The length of their vertical arm should not be longer than is necessary to provide¬†adequate bond length and support the wall reinforcement so they present¬†minimum impedance for slab concreting. If the designer wishes to use ¬†¬†hooked bars, he should make sure that the thickness of slab or wall in which¬†they are to be placed is sufficient to accommodate such hooks.