The given tolerances set out the overall building tolerance. These are the fi rst order of tolerance for the structure and all elements must fi t within their prescribed envelope or ‘box’. Individual elements of the structure are allowed individual tolerance (location see Cl. 10.4 and 10.5 of NSCS Standard Specifi cation; and size see Cl. 10.6, 10.7 and 10.8 of NSCS Standard Specifi cation) but individual element tolerance may be limited to ensure the element is not taken outside the ‘box’. As the tolerances are dependent on storey height and element size the acceptable values for tolerance are specifi c to the dimensions of the project. The example shown in Figure 10.2.1 illustrates the standard acceptable deviation and application of the ‘box’ principal for a project. The deviation for inclination applies to the plane on both the x and y axis of the intended position. It should be noted that the maximum deviation diagonally of the centre and corner of an element can be √ 2 D, although there is a low probability of both x and y axis deviations being at maximum at the same place. This diagonal deviation is usually limited by hierarchy considerations (see NSCS Standard Specifi cation, Cl. 10.1.1).
Figure 10.2.1 illustrates the ‘box’ principle applicable to column centrelines from foundation to upper fl oors.
Figure 10.2.1
Deviations 2, 3 & 4 are governed by the ‘box’
principle and are less than 50 mm as BS EN 13670: 2009, Cl. 10.1.(5)
Deviation 3 less deviation 2 must be less than 15 mm or h/400 (Cl.10.5.2 of NSCS Standard Specifi cation)
Deviation 4 less deviation 3 must be less than 10 mm or t/30 (Cl. 10.5.3. of NSCS Standard Specifi cation) This is a ‘corrective tolerance’ to ensure that:
Deviation 4 less deviation 2 is less than 10 mm (Cl.10.5.1 of NSCS Standard Specifi cation) Bottom storey – special case
Deviation 2 must be less than 10 mm from the intended Design position (Cl. 10.5.1 of NSCS Standard Specifi cation)
Deviation 1 for the base (substructure), not the superstructure, must be less than 25 mm from the intended design position (Cl. 10.3.1 of NSCS Standard Specifi cation)
In a multi-storey structure the columns can therefore only deviate over 10 mm/storey in complying with Cl.10.5.1 of NSCS Standard Specifi cation, although there is greater verticality tolerance. Any ‘drift’ in one direction will be limited by the need to satisfy the requirements of Cl.10.2.1 of NSCS Standard Specifi cation.
Note
There are two situations where mutually compliant tolerances may cause a problem and they must be defi ned in NSCS Project Specifi cation.
1 Where a combination of column height and thickness allows the tolerance for verticality from Cl. 10.5.2 of NSCS Standard Specifi cation and offset from Cl. 10.5.3 prevents the tolerance for position in Cl. 10.5.1 being achieved.
2 Where a combination of column height and thickness and verticality of adjacent columns have divergent tolerances from Cl. 10.5.2 of NSCS Standard Specifi cation would prevent the distance between columns at the top in Cl. 10.5.6 being achieved.
10.2.1 Inclination
Lift shaft tolerances require careful consideration and agreement between Designer, Contractor and lift supplier. This applies to all buildings, particularly tall buildings where alterations to the lift are more diffi cult.
In NSCS lift shafts inclination tolerance is considered to be covered by Order 1 tolerance (Cl.10.2.1 in NSCS Standard Specifi cation) not exceeding 50 mm. The element tolerance would depend on the construction method adopted – jump form, slip form or fl oor height wall stages. However, guidance on lift shaft construction and tolerances is given in BS 5655–6: 2002: Lifts and service lifts – Code of practice for the selection and installation of new lifts; lift shafts require a minimum plumb dimension and a positive only tolerance. The fi rst issue is therefore to set the nominal dimension for the shaft greater than the required minimum plumb. The tolerance on the lift shaft can then only
be ±25 mm to comply with BS 5655, so if there has been no other agreement, tighter tolerances
10.3 Base support (foundations)
10.3.1 Plan section
The foundations tolerances given are for individual bases and ground beams for concrete and steel framed structures.
Care should be taken with trench fi ll foundations where the centre line is used for determining deviation. When considering section of elements, larger permissible deviations are advisable than those in NSCS Standard Specifi cation Cl. 10.7.
10.3.2 Vertical section
Two values are given for this tolerance as one is fi xed to coordinate with BS 1090. Particular attention is drawn to the need to specify adequate thickness of any grout bed beneath follow-on items such as steel base plates, and also projection lengths of cast-in anchor bolts. This is required as the tolerances in the top level of foundations and bolt projections affect the achieved thickness of grout bed.
10.4
10.5 Elements – columns and walls
10.5.1 Position on plan
The location of the ‘kickers’ is, in practice, the commencement of the execution of a fl oor and the control of deviation at this level is essential. It is recommended that the centre lines are used for control as this will prevent cumulative errors leading to unacceptable deviation. Care should be taken when cladding or other components have to fi t between columns or walls, although tolerances are not cumulative (see NSCS Standard Specifi cation Cl. 10.1), therefore the maximum deviation in the ‘fi t’ dimension is +20 mm, whether caused by position or cross-section deviations.
Figure 10.5.1 Rotational tolerance
Element design position
Acceptable rotation of element
Tolerance box
The tolerance for rotation or twist of an element has not been given as an individual tolerance as it will be limited by the tolerances given for position on plan, squareness, and cross-section of an element. The relevant tolerances depend on the element considered and are given in NSCS Standard Specifi cation Cl. 10.5.1, 10.7.1 and 10.7.2. They provide an envelope or ‘box‘ within which the rotation of an element is acceptable. The effect of this is illustrated in Figure 10.5.1. This rotation