Construction tolerances are like the flexibility given to a builder, allowing slight variations in the dimensions of cast-in-place reinforced concrete elements within a building. These tolerances are crucial in maintaining the vertical alignment, size, length, and placement of various concrete components. The reason? Buildings aren’t always constructed perfectly straight, level, or plumb, and aiming for such perfection is unnecessary. However, careful establishment of tolerances is essential to avoid compromising the strength of the concrete members.
The American Concrete Institute’s ACI 117M-10 provides valuable guidance on construction tolerances for cast-in-place concrete members in buildings. This guidance aids contractors in constructing concrete buildings that meet safety standards without the burden of unnecessary perfection.
One critical aspect is the deviation from the plumb, which refers to the vertical alignment of various concrete elements. Table outlines the acceptable deviations for different elements based on their height, ensuring that they remain within specified limits.
| Building Element | Height Limit, m | Tolerances |
|---|---|---|
| Lines, surfaces, corners, arrises, and elements | ≤ 25.4 | Lesser of 0.003 times the height or ±25 mm |
| Outside corner of exposed corner columns | ≤ 25.4 | Lesser of 0.002 times the height or ±13 mm |
| Lines, surfaces, corners, arrises, and elements | 25.4-152.4 | Lesser of 0.001 times the height or ±150 mm |
| Outside corner of an exposed corner | 25.4-152.4 | Lesser of 0.0005 times the height or 75 mm |
| Vertical edges of openings | > 0.3 | ±13 mm |
Horizontal deviations, or departures from a designated point measured horizontally, are crucial. Table provides tolerances for different concrete elements, ensuring they maintain their intended positions within the building.
| Building Elements | Tolerances, mm | Notes |
|---|---|---|
| Vertical elements | ±25 | Measured at the top of the element foundation |
| Other elements | ±25 | |
| Edge location of all openings | ±13 | |
| Sawcuts, joints, and weakened plane embedments in slabs | ±20 |
Vertical deviations, or departures from a designated point measured vertically, are equally crucial. Table provides tolerances for different elements within the building.
| Elements in Building | Tolerances for Vertical Deviations |
|---|---|
| Elements | ±25 |
| Edge location of all openings | ±13 |
Maintaining the right elevation for various elements is vital. Table outlines tolerances for deviation from elevation for different elements.
| Concrete Element | Tolerances for Deviations from Elevation, mm |
|---|---|
| Top surface of slabs-on-ground, formed suspended slabs | ±20 |
| Lintels, sills, parapets, horizontal grooves in exposed concrete | ±13 |
| Top of walls | ±20 |
| Fine grade of soil immediately below slabs-on-ground | ±20 |
Table provides tolerances for deviations from cross-sectional dimensions for different concrete members.
| Concrete Element | Cross-sectional Dimensions, mm | Tolerances, mm |
|---|---|---|
| Thickness of elements except for slabs | ≤ 300 | +10-6 |
| Thickness of elements except for slabs | 300-900 | +13-10 |
| Thickness of elements except for slabs | > 900 | +25-20 |
| Horizontal deviation of unformed beams and walls cast against soil from plan dimension | < 600 | +75-13 |
| Horizontal deviation of unformed beams and walls cast against soil from plan dimension | > 600 | +150-13 |
Deviation from formed opening width or height is maintained within the range of -13 mm to +25 mm.