Making concrete slab

By Admin | Building
02 June 2016

according to forum participants ontwerper, monolithic concrete, may make its own efforts and results as an argument - well-known and little-known views on their production.According to him, do overlap with his own hands is beneficial for several reasons:

  1. available technologies and materials;
  2. Convenience and practicality with the architectural and engineering points of view;
  3. Such overlap durable, fireproof and have noise proof qualities;
  4. financial feasibility.

Monolithic works

Before pouring the concrete ontwerper advised to think carefully about the whole process, and above all to order the concrete factory.It is better improvised - there is quality control and the amount of fillers that improve the concrete and did not give him a stratified.Composition should consist of heavy aggregates, have strength class B20-B30 (M250-M400), and frost from F50.

Do not be lazy and check the documents of selling options, class-mark and time before setting concrete.

If you need to submit concrete on th

e second, third floor, or over a long distance is to do this without the concrete pump you do not succeed, and the rolling of the endless shoveling concrete troughs is very heavy and awkward to do.

In winter, the concrete can be ordered with antifreeze additives, given that the additives usually increase during curing, some of them provoke corrosion of reinforcement, but in general, it is permissible, if the additive factory.

ontwerper prefer not to build in the winter, but in any case do not prepare the solution, use concrete factory.

Formwork

The main purpose of the formwork - support the weight of concrete svezhenalitogo and not deformed.To calculate the strength you need to know that the 20 cm layer of concrete weighs per square meter of formwork with a force of 500 kg, must be added to this mixture under the pressure of its fall from a hose, and you will see that the design has to be reliable.

for its manufacturing ontwerper advises using plywood 18-20mm laminated (coated) or simple (but it adheres more strongly).For beams, headers and columns should be used formwork beam thickness of at least 100x100 mm.
After its assembly it is necessary to check the levelness of all structures.Otherwise, in the future, you will lose a lot of time and money to correct mistakes.

Reinforcement

For this ontwerper recommends using a ribbed bar A-III, A400, A500.The slab is always a series of four valves.

Lower - along the span, the lower - across the span, the top - across the span, the top - along the span.

span - the distance between the supporting walls (for rectangular plates on the short side).The lowest number is placed on the plastic crackers, specifically designed for this purpose, their height is 25-30mm.Top row - it across the wire and knit at all intersections.

Next in line - separator grids - part of the reinforcement with a certain pitch, it can be done at will.On dividers - top across - knit it along the top - knit wire in all intersections.Outer carcass point (top of the upper rod) must be below the top edge to form walls 25-30 mm, or the thickness of the concrete above the upper reinforcement 25-30 mm.

After the reinforcement frame should be rigid structure that does not need to shift when pouring the concrete pump.Before filling, check that the pitch and the diameter of the reinforcement project.

Pouring concrete

After all the training you need to take and spread over the entire area of ​​the concrete, provibrirovat it.It is best to fill the whole plate for 1 time if it is not possible to put crosscuts - intermediate walls inside the contour formwork limiting the concrete.They are made of steel mesh with the cell of 8-10 mm, placing it vertically and attached to the carcass reinforcement.In no case do not do crosscuts at mid-span and do not make them out of the board, PPP.

Curing

After pouring plates need to hide it, to prevent the ingress of rain, but it is constantly showering the outer surface, so that it was wet.Approximately a month later the formwork can be removed, and in case of emergency it can be done no earlier than a week and take only shields.To do this, carefully remove the shield plate and back to back bar.Rack support plate to its fully cooked, about a month.

Calculation of strength monolithic slabs

It comes down to a comparison between two factors:

  1. forces acting in the plate;
  2. strong as its reinforced sections.

In this first must be less than the second.

constant load on a monolithic slab

Net weight with safety factor for load 2.5t / m3 x 1.2 = 2.75t / m3.
- For plate 200mm - 550kg / m3
own weight floor 50mm-100mm - for example screed - 2,2t / m 2 x 1.2 = 2,64t / m3
- floor 50mm - 110kg / m3

partitions from120mm bricks bring to the area of ​​the plate.Weight 1st meter of partitions 3m 0.12m h1.2h1.8 t / m3 x 3m = 0,78t / m at step walls, for example, is roughly 4m 0.78 / 4 = 0,2t / m2.Thus, reduced weight partitioning = 300 kg / m2.

payload for the 1st group of limit states (strength) of 150 kg / m3 - housing, taking into account the safety factor 1.3 adopt.Temporary 150h1,3 = 195kg / m2.

full design load on the plate - 550 + 110 + 300 + 195 = 1150kg / m2.So, we will sketch the calculations for load - 1.2t / m2.

Defining moment efforts loaded sections

bending moments determined at 95% of flexural reinforcement plates.Which section loaded?- Mid-flight, in other words - the center of the plate.

bending moments in a square plate in terms of reasonable thickness, hinged - nezaschemlennoy the contour (eg brick walls) for each of the directions X, Y can be roughly defined as Mx = My = ql ^ 2/23.You can get some value for special cases.

  • plate in terms 6h6m - Mx = My = 1.9tm;
  • plate in terms 5h5m - Mx = My = 1.3tm;
  • plate in terms 4h4m - Mx = My = 0,8tm.

This effort, which act both along and across the plate, so you need to check the strength of two mutually perpendicular sections.

Checking the strength of the longitudinal axis

When testing the strength of the longitudinal axis of the cross section of the bending moment (even if the time is positive, ie belly down) it is considered that there is a cross-sectional compressed concrete top and bottom tensile reinforcement.They form a power couple, perceiving her coming Moment effort.

some efforts in this pair

height of the pair can be roughly defined as 0.8h, where h - height section of the plate.Stress in the reinforcement is defined as Nx (y) = Mx (y) / (0.8h).We get in the presentation by 1 m wide section of the plate.

  • plate in terms 6h6m -Nx (y) = 11,9t;
  • plate in terms 5h5m - Mx = My = 8,2t;
  • plate in terms 4h4m - Mx = My = 5t.

Under these efforts pick reinforcement Class A-III (A400) - periodic profile.Design strength of reinforcement rupture equal R = 3600kg / cm2.sectional area of ​​the rebar with a diameter = 0,5sm2 F8, F12 = 1,13sm2, F16 = 2,01sm2, F20 = 3,14sm2.

bearing capacity of the bar is Ast = nst * R = 1.8 T F8, F12 = 4,07t, F16 = 7,24t, F20 = 11,3t.From here you can get the required step valves.Step = nst / Nx (y)

  • plate in terms 6h6m armature F12 = Step 4,07t / 11,9t = 34cm;
  • plate in terms 5h5m - for reinforcement F8 Step = 1.8 / 8.2 = 22 cm;
  • plate in terms 4h4m - Step F8 = 1.8 / 5 = 36 cm.

This reinforcement of the strength of each of the directions X and Y, ie, a square grid of rods in concrete tension zone.

Besides strength necessary to reduce the formation of cracks.For slabs residential span up to 6m thick 200mm, supported on a loop (ie, on four sides) for any ratio as / b, usually can be taken from the lowest working reinforcement rods III A in two directions with a pitch diameter 12mm 200x200, top(design) - the same from F8, thinner and smaller should not be.

All this - the special case of a general approach, demonstrating the specificity of the problem, but to implement it is necessary to consult specialists.


Posted forum participant http://www.forumhouse.ru/forum92/thread25385.html ontwerper

Editor: Roman Adamov