Concrete Floor Slab is a structural element that comes in many forms. The most common ones are the slab-on-grade and suspended slab. Slab on grade or commonly called S.O.G is a concrete floor slab on top of thoroughly compacted earth materials.
Suspended slabs, on the other hand, are elevated slabs that form the stories on each building and roof deck. Proper elevations and leveling must be done on casting concrete floor slab. Thus, settlement due to self-weight loads and other external forces induced by the structure must be considered before the actual casting of the slabs, especially for suspended slabs.
1. How would you prepare estimate steel bar to deliver on-site?
Preparing an estimate to deliver on-site has to be strategized depending on the need on-site. Project engineers base the estimate to deliver on a list pre-arranged by the quantity surveyors. Some project engineers prefer to have their respective site engineers check the estimates of the quantity surveyors and compare it to the actual number of steel bars needed on-site. Most of the time, the data given by the site engineers prevail and is used by the procurement team on procuring the total number of steel bars.
Furthermore, project engineers consider adding at least 10% of the actual estimates as a wastage factor.
Additionally, the delivery of needed materials to the site plays an important role to attain the timeline set for any construction projects. Materials on-site have to be on a manageable number.
Work force’s productivity correlated with this. Once the project engineer sees that productivity is increasing, he or she has to anticipate that the steel bars’ supply would not run low by ensuring enough steel bars.
As a practice on-site, project engineers and managers have several steel bar suppliers contacts should one supplier run low, he or she has the second supplier to approach.
Having too many steel bars on-site is not also healthy. Too many materials would mean little space on site making the site crowded. Thus, little space to maneuver dump trucks or other heavy equipment vehicles causes poor day-to-day productivity.
2. How would you prepare a steel bar cutting list?
The Designer with respect to their plan initially prepares a cutting list for steel bars. The Quantity Surveyor then presumes lengths to create bill of quantity needed for monetary proposals. Normally, Quantity Surveyors or estimators have a set of lengths including the number of total lengths prepared. It is the call of the on-site engineers on which he or she will use or should he create his own cutting list.
Cutting list is needed so steel men will be able to properly bend steel intended to prepare all the steel bars ready for installation. Cutting list is a guide of all the cut steel bars with respective degrees of the angle the bars will be bent with corresponding lengths, so with the number of stirrups or ties a column, say, has.
To prepare a cutting list, on-site engineers need the approved construction plan. For concrete floor slab, here is the step-by-step guide to preparing a cutting list.
• Start with the bottom bars. Check all the bars lengths be it transverse bars or longitudinal bars that are used on the slab and write it all down. Create a diagram representation of each bar length or cut including the lengths of the bends or hooks.
• Proceed with the top bars. Do the same as instructed on the bottom bars.
• Check the plan should there be any additional bars for dowels in preparation for masonry walls.
3. How would you ensure the quality of the installation of steel bars?
The actual installation of the steel bars is not the only thing engineers have to inspect to ensure its quality, but also the bars’ grade. Quality assurance engineers are the ones responsible to make sure that prior to the reinforcing steel bars installation, the grade required as per design is the one installed on site.
A quality engineer shall make sure that steel bars are laid as per the approved shop drawing, the dimensions and spacings are the most important including sizes of the bars.
4. What is the good way to attain quality of works for formworks or shuttering, steel bar reinforcement and concrete pouring?
Prior to any concrete pouring, it is relevant that the engineer has thoroughly checked and approved the grades, lines, diameter of bars, and spacing, including dimensions as shown on the plan.
Normally, the formwork engineer checks the credibility of the formwork used as per formwork and shoring installation plan. He or she ensures that the formworks and its accessories are all in good working conditions to prevent any structural failure. Formworks, especially concrete floor slab, has to be free from any laitance. Any uncleaned formwork would cause bulging or cavities on the output which would be unpleasant aesthetically.
The concrete to be used must be as per the approved mix design. You should not merely use concrete that has not undergone trial mixes or tested from the previously completed project.
When pouring you shall make sure that concrete vibrators are fully operational and with sufficient numbers.
5. How would you clean rust of steel?
On cleaning rust of steel, engineers should be able to know the proper ways of doing it, including the ways of preventing the bars from forming so.
Preventing rust from forming in the steel bars may be done by not overbuying steel bars. Reinforcing bars are best with their respective manufacturers, as manufacturers know how to properly store them.
Nevertheless, when situations call it, certain ways should be followed. First, wear personal protective gear like thick gloves, facemask, and eyeglass to keep you safe from shards. Use an appropriate steel brush and scrub it all over until cleaned. Some use air blower to keep the dust blemishes away and then apply rust remover. After that, rust should then be removed when wiped with rags or towels.
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As conclusion, concreting floor slab must be done carefully and in their proper engineering way. From the actual designing to the delivery of materials and the number of materials on site. All shoring and formworks must be in its utmost functional conditions as the settlement may occur during concrete casting. Stripping of formworks must commence once the designed strength of the slab has been attained and should stay to be anchored until 28 days. Precautions like these must be followed to prevent engineers from committing costly future mistakes.