Foreword

TCVN 9259-1:2012 is completely equivalent to ISO 3443-1:1979.

TCVN 9259-1:2012 is converted from TCXD 247:2001 (ISO 3443-1:1979) in accordance with clause 1, Article 69 of the Law on Standards and point a), Clause 1, Article 7 of the Government’s Decree No. 127/2007/ND-CP dated 01/8/2007 detailing the implementation of some articles of the Law on Standards and Technical Regulations.

TCVN 9259 set under the general title “Tolerances for building” includes the following parts:

• TCVN 9259-1:2012, Part 1: Basic principles for evaluation and specification.
• TCVN 9259-8:2012, Part 8: Dimensional inspection and monitoring of construction works.

The ISO 3443 Tolerances for building set also includes the following parts:

• ISO 3443-2:1979 – Part 2: Statistical basis for predicting fit between components having a normal distribution of sizes
• ISO 3443-3:1987 – Part 3: Procedures for selecting target size and predicting fit
• ISO 3443-4:1986 – Part 4: Method for predicting deviations of assemblies and for allocation of tolerances
• ISO 3443-5:1982 – Part 5: Series of values to be used for specification of tolerances
• ISO 3443-6:1986 – General principles for approval criteria, control of conformity with dimensional tolerance specifications and statistical control – Method 1
• ISO 3443-7:1988 – Part 7: General principles for approval criteria, control of conformity with dimensional tolerance specifications and statistical control – Method 2 (Statistical control method)

TCVN 9259-1:2012 is drafted by the Vietnam Institute for Architecture, Urban and Rural Planning, proposed by the Ministry of Construction, appraised by the Directorate for Standards, Metrology and Quality, and published by the Ministry of Science and Technology.

1. Scope

1.1. This standard describes the nature of dimensional variations in building with the aim of quantifying and determining the factors to be considered when evaluating quality, specifying requirements and checking tolerances in the manufacture of building components and on-site construction.

1.2. This standard applies generally to all components and structures, including modular coordination designed buildings.

1.3. This standard is part of a system of standards on tolerances and fits, used for:

• Evaluating and allowing for dimensional and positional variations in design;
• Specifying tolerances in specifications;
• Measuring and checking the dimensions and shape of components and structures during manufacture and construction.

NOTE: Where it is possible to check the dimensions of the entire structure when the components are arranged in a continuous system (modular grid), deviations in shape, size and position must be self-compensating within that system.

2. Normative references

The following referenced documents are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 2445, Joints in building – Fundamental principles for design.

3. General provisions

3.1. When constructing a building, the assembly technology, construction requirements and construction costs must be checked. Technical issues in the field of tolerances and fits should be considered.

3.2. The assembly of large components with varying dimensions on site by means of measurement and positioning operations can cause significant changes compared to the designed dimensions and shapes (induced deviations). Additionally, dimensional changes due to transportation and inherent dimensional changes of materials caused by internal and external physical and chemical conditions must be considered (inherent deviations).

3.3. The design of joints must take into account tolerances in component manufacture and building construction to provide the required dimensional flexibility (see ISO 2445).

This does not mean that all joints consider tolerances, but only that tolerances are provided for joints between individual components or for special joints at intermediate intervals to ensure permissible deviations at certain points.

In addition, it is necessary to consider tolerances when there is an influence of dimensional changes on structure, aesthetics, legal requirements and function in order to achieve the required overall quality.

3.4. It is necessary to analyze the deviations in joint width when determining the actual dimensions of components in order to apply joint connection techniques with a certain dimensional flexibility. This applies to both standard components and custom-made components. It is also necessary to check the suitability of standard components for use with this or other jointing techniques at specific positions in the building design in order to ensure that in all cases the components can be assembled without “non-fit” problems and the joints meet the exact requirements.

If deviations are analyzed based on statistical principles, then a certain limit of “non-fit” must be accepted in the design. That level depends on the type of component and the technique used to create the joints.

The technical requirements for tolerances are to determine the limits of permissible deviations arising in the design related to measurement methods that can be used to test conformity with technical provisions.

The technical requirements and tolerance checks must refer to standard measurement conditions, to consider the effect of inherent deviations on actual dimensions. Tolerances can be specified in classes, related to the construction method (materials, processes and techniques) and the required level of accuracy to be achieved.

However, it is necessary to check the dimensional compatibility of components used at specific locations even if the tolerance falls within a class due to the complexity and specific factors that govern the distribution of deviations.

4. Origins of dimensional deviations

4.1. Induced deviations

In any measurement process (straightening or positioning), deviations can occur to some extent due to human error and limitations of measuring instruments. These deviations are called “induced deviations” and are divided into the following groups:

a) Manufacturing deviations: dimensional and shape deviations that arise during the manufacture of components;

b) Setting-out deviations: dimensional and positional deviations that arise in the measurement and marking of dimensions on site;

c) Erection deviations: positional and directional deviations that arise in the positioning of components based on setting out and alignment in the vertical and horizontal directions.

In many cases, the values of induced deviations will follow a normal statistical distribution around the mean size or position (Gaussian-shaped random errors). This reflects the variation of systematic deviations, for example progressive dimensional deviations in production or deviations due to inaccuracy of measuring instruments. Large deviations due to measurement errors are usually not taken into account and therefore the results are unacceptable.

Random induced deviations can be treated based on statistical principles, therefore relative probabilities can be calculated, with large and small values, and expressed by standard deviations as a measure of dimensional deviations. Systematic induced deviations must be treated as definite, repetitive values, applicable to components, groups of components or sets of measurements.

4.2. Inherent deviations

In reality, all materials have dimensional deviations due to physical and chemical causes. These deviations are called “inherent deviations”, including permanent and reversible changes due to variations in temperature, humidity, stress and chemical reactions.

Settlement of foundations is one of the origins causing inherent deviations.

5. Consequences of dimensional deviations

Deviations in dimensions and positions must be taken into account in the design of structures, components, joints and their effect on the following issues:

a) Building function:

Deviations in the dimensions and shape of voids or openings, smoothness, flatness, horizontality and verticality of surfaces, including deviations in joint width will directly affect the function of the building.

b) Assembly of components and performance of joints:

Deviations in joint width due to induced and inherent deviations must be taken into account when determining the construction dimensions of components and when selecting jointing techniques appropriate to the joint width.

c) Structural stability:

Deviations in dimensions and position can cause eccentricity of loads and reduce bearing areas. These inherent deviations can induce stresses.

d) External appearance:

Deviations in size, shape, and orientation of components, spacing and deviations in joint width must be checked and sealed to ensure external appearance requirements.

e) Standard dimensions:

Deviations can affect dimensions where maximum and minimum sizes are selected according to regulations and conform to standard dimensions.

6. Selection of tolerance values

It is permissible to use specified tolerances that limit the deviations arising in the design with acceptable actual dimensions. These tolerances are only specified for critical dimensions and positions corresponding to one or more of the consequences of deviations listed in Clause 5 of this standard.

The selection of tolerance values reflects the economic balance between the cost of increasing accuracy and the cost of allowing deviations in the design. The performance of joints and the assembly of joints is the most important consideration in assessing this balance when choosing between small tolerances with simple joints and large tolerances with complex joints.