Chapter 4Modular Coordination, Architectural Treatment and Finishes

NBC 2016 (SP 7:2016) Volume 1

2016 · PDF page 1097

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4.1 Modular Coordination

The basic module shall be adopted. After adopting this, further work is necessary to outline suitable range of multimodules with greater increments, often referred to as preferred increments. A set of rules as detailed below would be adequate for meeting the requirements of conventional and prefabricated construction.

These rules relate to the following basic elements:

a) The planning grid in both directions of the horizontal plan shall be:

$15M$ for industrial buildings, and
$3M$ for other buildings.

The centre lines of load bearing walls should preferably coincide with the gridlines.

b) The planning module in the vertical direction shall be $2M$ for industrial buildings and $1M$ for other buildings.

c) Preferred increments for sill heights, doors, windows and other fenestration shall be $1M$ .

d) In the case of internal columns, the grid lines shall coincide with the centre lines of columns. In case of external columns and columns near the lift and stair wells, the grid lines shall coincide with centre lines of the column in the topmost storey.

4.2 Architectural Treatment and Finishes

In general, prefabricated systems provide better opportunity to achieve superior finishes leading to an array of aesthetically pleasing options. The architectural elevational treatments, form and features can also be effectively incorporated in the structures with careful advanced planning. In addition, detailed coordination between the architectural and structural design team during the planning stage for panel joints and false joints is necessary. The purpose of finishes and architectural treatment is not only to give prefabricated buildings an individual character but also to effect better performance and greater user satisfaction.

Treatment and finishes have to be specified keeping in view the requirements of protection, function and aesthetics of internal and external spaces and surfaces.

While deciding the type of architectural treatment and finishes for prefabricated buildings, the following points should be kept in view:

a) Suitability for mass production techniques;

b) Recognition of the constraints imposed by the level of workmanship available;

c) Possibility of using different types of finishes;

d) Use of finishes and architectural treatment for the creation of a particular architectural character in individual buildings and in groups of buildings by the use of colour, texture, projections and recesses on surfaces, etc;

e) Incorporation of structural elements like joists, columns, beams, etc, as architectural features and the treatment of these for better overall performance and appearance;

f) Satisfactory finishing of surfaces; and

g) Use of light weight materials to effect economy in the structural system.

Some of the acceptable methods of finishes integral with the precasting are:

Concrete surface moulded to design/shape;
Laid-on finishing tiles fixed during casting;
Finishes obtained by washing, tooling, grinding, grooving of hardened concrete;
Exposed aggregates; and
Other integral finishes.

5 COMPONENTS

5.1 The dimensions of precast elements shall meet the design requirements. However, the actual dimensions shall be the preferred dimensions as follows:

a) Flooring and roofing scheme — Precast slabs or other precast structural flooring units:

Length — Nominal length shall be in multiples of 1 M;
Width — Nominal width shall be in multiples of 0.5 M; and
Overall Thickness — Overall thickness shall be in multiples of 0.1 M.

b) Beams:

Length — Nominal length shall be in multiples of 1 M;
Width — Nominal width shall be in multiples of 0.1 M; and
Overall Depth — Overall depth of the floor zone shall be in multiples of 0.1 M.

c) Columns:

Height — Height of columns for industrial building and other buildings shall be in multiples of 1 M; and
Lateral Dimensions — Overall lateral dimension or diameter of columns shall be in multiples of 0.1 M.

d) Walls:

Thickness — The nominal thickness of walls shall be in multiples of 0.1 M.

e) Staircase:

Width — Nominal width shall be in multiples of 1 M.

f) Lintels:

Length — Nominal length shall be in multiples of 1 M;
Width — Nominal width shall be in multiples of 0.1 M; and
Depth — Nominal depth shall be in multiples of 0.1 M.

g) Sunshades/Chajja Projections:

Length — Nominal length shall be in multiples of 1 M.
Projection — Nominal length shall be in multiples of 0.5 M.

PART 6 STRUCTURAL DESIGN — SECTION 7 PREFABRICATION, SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION: 7A PREFABRICATED CONCRETE

5.2 Casting Tolerances of Precast Components

Sl Product Tolerances Product (see Key No.)
No.
(1) (2) (3)
i) Length:
a) ± 5 mm 1, 7
b) ± 5 mm or ± 0.1 percent, whichever is greater 2, 3, 8
c) ± 0.1 percent subject to maximum of +5 -10 mm 4
d) 1) ± 2 mm for length below and up to 500 mm 5
1. ± 5 mm for length over 500 mm
e) ±10 mm 6, 9,10
ii) Thickness/cross-sectional dimensions:
a) ± 3 mm 1
b) ± 3 mm or 0.1 percent, whichever is greater 2, 8
c) 1) ± 2 mm up to 300 mm wide 4, 5
1. ± 3 mm greater than 300 mm wide
d) ± 2 mm 3, 7
e) ± 4 mm 6, 9, 10
iii) Straightness/Bow:
a) ± 5 mm or 1/750 of length, whichever is greater 2, 4, 8
b) ± 3 mm 1, 5
c) ± 2 mm 7
iv) Squareness — When considering the squareness of the corner, the longer of two adjacent sides being checked shall be taken as the base line, and the following tolerances shall apply:
a) The longer side shall not vary in length from the perpendicular by more than 5 mm 2, 5, 8
b) The shorter side shall not vary in length from the perpendicular by more than 3 mm 1, 7
c) The shorter side shall not be out of square line for more than +2 -5 mm 4
v) Twist — Any corner shall not be more than the tolerance given below from the plane containing the other three corners:
a) 1) Up to 600 mm in width and up to 6 m in length 5 mm 2, 8
1. Over 600 mm in width and for any length 10 mm
b) ± 1/1 500 of dimension or ± 5 mm. whichever is less 4
c) ± 3 mm 1
d) ± 1 mm 7
vi) Flatness — The maximum deviation from 1.5 m straight edge placed in any position on a nominal plane surface shall not exceed:
a) ± 5 mm 2, 8
b) ± 3 mm 4
c) ± 2 mm 1, 7
d) ± 4 mm or maximum of 0.1 percent length 5
Key No. for product reference:
1 Channel unit.
2 Ribbed slab unit/hollow slab.
3 Waffle unit.
4 Large panel prefabrication.
5 Cellular concrete floor/roof slabs.
6 Prefabricated brick panel.
7 Precast planks.
8 Ribbed/plain wall panel.