21. Caution and consideration of construction carry-out

1) A man-dayThe amount of reinforcement that a skilled worker can place a day is, in case of slabs,

0.26acre ~ 0.33acre in area, about 500kg~700kg if converted in weight.

※ Daily work capacity(varies with working environment)

2) Weight of concrete① Specific weight of plain concrete(without reinforcement) is 2,300kg/1m3

② Specific weight of concrete with reinforcement in it is 2,400kg/1m3

③ Specific gravity of lightweight concrete with perlite or gas-foaming agent is only

0.6~1.2

3) Load and external forceIn construction, load and external force are critically important factors to be

considered.

Load is classified as fixed load and occupied load, where the former is the weight of

building itself and the later is the weight of people, furniture, equipment, etc..

Occupied load is classified again as long-term load and short-term load.

① The weight that 1m2 (square meter) sustains in long-term loading is

ⓐ Human or furniture 200kg/1m2

ⓑ Snow load 50kg/1m2

Classification

factory, school

apartment, house

<processing separately>

Q’ty(kg)

over 700

below 700

KR 130,000 per worker’s labor cost in 2006 year.

Classification

D10 stirrup, tie hoop

D13 stirrup

bending

<cutting separately>

Q’ty(kg)

600

800

5ton/1 person

② If weak at the long-term load : There might be a crack in walls or beams.

③ If weak at the short-term load : There might be not a crack but part breakage due

to external impact.

4) Crack and shrinkage① Crack of concrete is not simple problem to catch with several symptom such as

crack direction, etc but it is required to the inspection of professional.

Regularly, the crack under 0.3mm will be happened by dry shrinkage for

beginning vulcanization.

② Shrinkage of the building

If the length of the building is longer than 50,000mm, there is expansion or

shrinkage of the building, 10mm ~ 20mm, within temperature range from -18°C

~36°C.

(temperature difference×10-5×the length of building = difference length by

temperature gap(expansion or shrinkage))

③ In case of Korea, temperature difference is 54°C, from -18°C in winter to 36°C in

summer, According to the formula above, expansion in Korea is 27mm maximum

from 54°C×( ×50,000mm) = 27mm, hence there should be expansion

splice in some parts on high building & walls to prevent crack of the building.

5) Caution if construction work does① Distance of main bars against girder(beam)

ⓐ Beam plays an important part in a building, receiving the load from slabs and

passing it out to pillar.

Therefore the reinforcement in beams should be seriously taken into

consideration and accuracy.

Top bars, bottom bars, reinforcement bars, bent bars and middle bars are placed

in beams and distance of reinforcement should be more than 25mm or 1.25

times of the largest aggregate that is in the mixed concrete, over 1.5times

distance of rebar diameter.

ⓑ Splice length of top bar in beams should be required fixed length if it extends to

the center of column and therefore sustains tensile force.

Splice of the bottom bars in beams should be within from the end of beams,

where load is almost 0, and the top bars should avoid the end span of

beams.(min. rebar cost will be over 0.35%)

② Pillar

ⓐ Pillar also has important role to divide total weight and compression power of

building.

Distance of main bar also arrange bar fairly, distance per rebar and rebar will be

over 40mm or over 1.5times of rebar using.

ⓑ The minimum size of column is more than 200mm and cross sectional area

should be more than 600cm2

ⓒ Splice length applies B class splice length.

6) Reinforcement to prevent shrinkage of wallThe building might get shrinkage on building by the expansion of temperature in day

or the down of temperature in night.

Rebar concrete has expansion or shrinkage, and so there are possibility of unexpected

rebar.

Therefore, the point of crack possibility must reinforce outer wall without open part.

Arrangement direction of correct reinforced bar, it can be checked crack correctly, it is

principle to arrange bars vertically against crack direction.

If there are crack on both edges of wall by the expansion of roof, reinforced bar is

principle to arrange bars vertically against crack direction and you reinforce the

reinforced bar of highest wall to outer top pillar & retaining wall of building.

The expansion ratio of roof will be bigger toward outside and very small roof on

center of building.

Also, 1st floor contacts ground do not effected of the influence of temperature.

Therefore , the part of highest influence by expansion & shrinkage of roof is outside

wall and there are expecting many cracks.

Without marking on shop drawing, you must arrange construction with your sincerity

with our experiences.

7) CleaningIt is better to install concrete after cleaning always before installing concrete.

When you checking construction site, there are many other materials to decline the

quality of concrete such as soil, sawdust, trash.

You must delete it inevitably.

After concrete job, you must break concrete of ground and brush concrete on rebar

with hammer drill, wire brush , hammer on next floor splice part, wall, pillar.

8) Problem if oxy-acetylene cutting does

① Don't use the oxygen arc cutter near the pile of unused bars.

If you use the oxygen arc cutter near the piled bars, high heat from cutting rod will

be transferred to unused bars causing thermal deformation or unexpected failure.

Automated cutting machine and bending machine are recommended.

② Oxygen arc cutter will drop tensile strength of the bar, which is critically important

to the reinforcement of the structure, and there might be problems in structural

safety.

③ Manual bar cutters have been normally used in the construction sites so far.

However, in order to increase the effectiveness and ensure perfectness, automated

cutting machines and bending machines are highly recommended.

<Reference>

Rebar arrangement should arranged by the shop drawing.

Technicians must increase the ability to see shop drawing if it is the recent drawing by

limit strength plan method.