TCVN 9262-1:2012 ISO 7976-1:1989 TOLERANCES FOR BUILDING – METHODS OF MEASUREMENT OF BUILDINGS AND BUILDING PRODUCTS – PART 1: METHODS AND INSTRUMENTS

Foreword

TCVN 9262-1: 2012 is identical to ISO 7976-1 : 1989.

TCVN 9262-1: 2012 is converted from TCXD 193 : 1996 (ISO 7976-1 : 1989) in accordance with the provisions of Clause 1, Article 69 of the Law on Standards and Technical Regulations and Point a), Clause 1, Article 7 of the Government’s Decree No. 127/2007/ND-CP of August 01, 2007 detailing the implementation of some articles of the Law on Standards and Technical Regulations.

TCVN 9262 with the general title “Tolerances for building – Methods of measurement of buildings and building products” consists of the following 2 parts:

– TCVN 9262-1: 2012, Part 1: Methods and instruments

– TCVN 9262-2: 2012, Part 2: Position of measuring points.

TCVN 9262-1 : 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 proclaimed by the Ministry of Science and Technology.

1. Scope

1.1. This standard provides methods for determining the shape, dimensions and dimensional deviations of buildings and prefabricated components which are to be fitted together. These methods may also be used when data on accuracy are collected either in factories or on building sites.

The standard specifies the deviations of components of buildings or prefabricated components determined by the instruments described below.

1.2. These methods of measurement are only applicable to items with planar surfaces and having a modulus of elasticity greater than 35 kPa, for example: concrete, timber, steel, rigid plastics. This standard is not applicable to items made of fiberglass and similar laminated materials.

This standard does not specify rules for quality control inspections at all stages of measurement such as frequency, location, time, etc.

1.3. The positions of measuring points specified in TCVN 9262-2 : 2012 are applied according to the measurement methods described in this standard.

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.

TCVN 9262-2 : 2012, Tolerances for building – Methods of measurement of buildings and building products – Part 2: Position of measuring points.

ISO 4464¹⁾, Tolerances for building – Relationship between the different types of deviations and tolerances used for specification.

ISO 7078, Building construction – Procedures for setting out, measurement and surveying – Vocabulary and guidance notes

ISO 8322²⁾, Building construction – Measuring instruments – Procedures for determining accuracy in use.

3. General provisions

3.1. Methods of measurement

3.1.1. These methods of measurement are applicable to the measurement of the principal dimensions of construction components, the distances between these components and the geometric deviations of the components. However, they may also be applied to parts and smaller segments of construction components.

3.1.2. The components to be measured shall be set up as they will be in actual use. If this is not possible, the conditions of setting up shall be agreed upon in the measuring scheme. If the part is measured while still in the manufacturing jig, this shall be clearly stated. Parts which are easily deformable shall always be fully supported on a plane surface.

3.1.3. In order to carry out measurements and collect data on accuracy, the measuring methods shall be substantially more accurate than the allowable deviations specified in the manufacturing or construction process.

The main purpose is to check the accuracy of the measuring procedure (see ISO 8322).

When recording measurement results, the following conditions and parameters must also be recorded:

– Name of measurer, instrument, time;

– Location and shape of the item being measured;

– Temperature and humidity of the item being measured;

– Other issues related to the measurement.

Usually the inside surface adjacent to the mold can be measured directly. Measurements shall not be made over localized defects such as voids, burns, casting fins and shall not be represented as incorrect dimensions but the presence of such defects shall be recorded. In the case where the surface is rough compared to the allowable deviation, the measurement method may be specified by using an additional sufficiently large locating piece placed on the object to be measured.

At the end from 4.1 to 4.4, there is a table specifying the items for each measuring operation, which records:

– Measuring operation;

– Limit of measuring accuracy, depending on the allowable deviation of the object to be measured;

– Measuring range;

– Selected equipment and instruments.

3.2. Influence of deviations from standard conditions

Differences between environmental conditions and standard conditions can lead to errors in the measured dimensions. Temperature, especially direct sunlight, is the most important environmental condition. Other conditions such as timber moisture and concrete age must also be taken into account.

In practice, it is very difficult to determine the actual temperature of the component to be measured or the measuring instrument, because they have uneven temperatures and there are deviations due to internal temperature of the object or instrument. The most satisfactory solution is to allow the component to be measured and the measuring instrument sufficient time to reach a stable ambient temperature. This temperature can be measured and will be considered when there is a difference from the specified standard temperature.

The most common heat sources for measuring instruments are from handling and from deviations between ambient temperature and standard conditions. The component to be measured is also affected by ambient temperature and may be heated multiple times during manufacturing.

The standard temperature in this example is taken as 20 °C. The symbols are as follows:

– t₁ is the temperature of the object to be measured, in degrees Celsius;

– t₂ is the temperature of the measuring equipment, in degrees Celsius;

– a₁ is the coefficient of thermal expansion of the object to be measured;

– a₂ is the coefficient of thermal expansion of the measuring equipment;

– Δt₁ is the temperature difference of the object to be measured at 20 °C (Δt₁ = t₁-20);

– Δt₂ is the temperature difference of the measuring equipment at 20 °C (Δt₂ = t₂-2;

– L is the length to be measured, in m.

Measurement error ΔL caused by temperature differences Δt1 and Δt2:

ΔL = L(a₁Δt₁ – a₂Δt₂)                    (1)

4. Measuring methods used in the factory

NOTE: Most examples of components may also be applicable to on-site construction elements.

4.1. Component dimensions

4.1.1. This section provides examples of measuring instruments and methods to determine the length, width and thickness of components.

Length is determined by instruments specified in Clause 6 (with or without locating plates), which include instructions on typical errors and conditions to avoid. Special attention must be paid to pulling force and temperature when measuring with a tape measure. A tape tensioning device should be used to create a standard tension force when specified or when the length to be measured exceeds 10 m. It is recommended to have a measuring support to reduce the influence of the temperature of the component to be measured (see Figure 1). When the tape measure rests on a building component or floor, the temperature of the component may differ from the measured ambient air temperature and cause measurement errors (see 3.2). This error can be reduced by supporting the tape measure. The correct temperature of the tape measure can be measured with a contact thermometer.

Figure 1 – Measuring support reduces the influence of the temperature of the component to be measured

4.1.2. Length and width:

On components without clear corner edges, locating plates can be used (see Clause 6) to increase measuring accuracy. The locating plates must be held or fixed to the surface of the component for the duration of the measurement to accurately determine the edge. An example using corner locating plates is shown in Figure 2.

Figure 2 – Use of corner locating plates

Figure 3 – Use of corner locating plates

The measurement result between two opposite points (not corner points) can be used to preliminarily check the result of measuring straightness deviation (see 4.3 and Figure 4).

Figure 4 – Use of measurement result between two opposite points

When measuring along a curved surface, the error is because the curve AB is always larger than the chord AB. The usual accuracy requirement allows the reading to be taken to the nearest millimeter. This means that in practice, a certain amount of curvature may be allowed (See Figure 5).

Figure 5 – Relative curvature allowed

Figure 6 provides a graph for correction when measuring along a curved component.

Figure 6 – Correction graph when measuring along a curved component

4.1.3. Thickness or height:

The thickness (or cross-sectional height) of components is determined by instruments specified in Clause 6 and in principle is carried out as described in 4.1.2.

When necessary, angle plates and/or edge plates should be used.

Instruments with large contact surfaces are used for materials with uneven surfaces.

Thickness shall be measured perpendicular to at least one of the component surfaces (See Figure 7).

Figure 7 – Types of thickness gauges for components

4.1.4. Allowable deviations for component dimensions are specified in Table 1.

Table 1 – Allowable deviations for component dimensions

4.2. Squareness of components

4.2.1. This section describes examples of measuring instruments and methods for determining squareness deviations, but may be applied in principle to any angle.

According to ISO 4464, angular deviation is the difference between the actual angle and the corresponding standard angle. Figure 8 shows angular deviations expressed in grad or degrees (Figure 8a) or by a deviation segment (Figure 8b).

a) Angular deviation expressed in grad	b) Angular deviation expressed by deviation segment

Figure 8 – Angular deviation

If method b) is used, the angular deviation is determined from the shorter edge of the angle and shall be measured perpendicular to the corresponding edge of the standard angle.

Deviations from parallelism, another form of angular deviation, will be described in 4.2.3.

Angular deviations are determined by instruments specified in Clause 6 (with or without locating plates).

Three methods are described for determining squareness deviations in construction products (see Figure 9). The method chosen depends on the size of the object to be measured.

If b and c <1 200 mm, then a square as described in Figure 10 is used. Otherwise, a sighting tube (see 4.2.3) or diagonal measurement method (see 4.2.2) is used. However, the edge measurement method is only used when the allowable deviation of squareness is greater than 5 mm/m.

Figure 9 – Description of squareness deviation determination

The three methods used to determine angular deviation are illustrated by the examples below. Deviation is always measured on the shorter edge of the angle and the final result will be the deviation of point B or point C from the required position.

In Figure 9, the angles to be measured are the angles between the straight lines connecting the corner points.

4.2.2. Angular deviation:

4.2.2.1. Measuring with a square

In Figure 10, a sufficiently large square is placed with the long side along AB so that the short side touches B or C. The angular deviation of vertex B is determined as shown in Figure 10.

Figure 10 – Determination of angular deviation of vertex B

In Figure 11, the method of placing the square for measuring angular deviation is described. The square rests on supports S. To reduce friction, edge L₁ is placed on roller R. In Figure 12, the method described in Figure 11 can also be used to measure the angular deviation of a column.

When using the methods described in Figure 11 and Figure 12, the thickness of the spacers will have to be subtracted from the reading when calculating the angular deviation.

The method described in Figure 13 is only used when there is no straightness deviation, otherwise only the squareness deviation between parts of the surface to be measured will be seen, i.e. angle ABC rather than angle ABD.

4.2.2.2. Diagonal measurement

In Figure 14, the distances AB, BC and AC are determined using a tape measure and corner plates.

The dimensions of the object to be measured shall not exceed the length of the tape measure and the width/length ratio of the object shall not be less than 1 : 2.

The angle at point B can be calculated as follows:

This procedure can be repeated for points A, B and C.

The sum of the angles (α + β + γ + δ) must be 400 grad (gon) or 360°. If they do not close, they must be equally divided among the 4 angles, the angular misclosure error not exceeding 0.12 grad (0.11 degrees = 7 minutes) for components of dimensions about 1 200 mm x 3 000 mm. If the angular misclosure error exceeds this value, re-measurement is required.

The angular deviation calculated as the deviation segment (CC1) can be determined along edge CB as follows:

β = 100 grad

Or:

4.2.2.3. Measurement using a sighting tube (Telescope)

In Figure 15, a measuring telescope is placed at point B and is adjusted to point 0 when sighting at A. It is then rotated by 100 grad (90°) and the deviation at point C is determined, for example, by a millimeter rule placed at that point.

Figure 16 describes a method for determining the angular deviation (at B) using a transit (T) with the sighting axis placed parallel to AB by rotating the instrument so that the readings for the measuring rod (P₁ and P₂) are equal.

The transit is then rotated by 100 grad (90°) and the distances P₃ and P₄ are read in the sighting tube, using the measuring rod. The distances P₁ to P4 must be within the range of 500 mm to 1 000 mm. This means that in most cases an additional lens must be fitted to the transit to observe a shorter range when reading the values P₁ and P₃.

The angular deviation measured as a deviation segment in this case is positive (P₃ – P₄).

4.2.3. Parallelism

Non-parallelism deviation is a form of angular deviation and is the difference between the direction of the straight line passing through A and B and the direction of the standard straight line AB1, passing parallel to DC (See Figure 17). This deviation is measured as the distance between B and B₁, (See ISO 4464).

In Figure 17, the distances AD and BC are measured perpendicular to the length from C and D respectively, practically parallel to the edges BC and AD, using the instruments specified in Clause 6. The difference between AD and BC is the deviation due to non-parallelism between AB and CD.

Figure 17 – Measurement of non-parallelism deviation

4.2.4. Angular and directional deviations are specified in Table 2.

Table 2 – Angular and directional deviations

4.3. Straightness and curvature of components

This section describes examples of measuring instruments for determining deviations from straightness and from design curvature.

4.3.1. Straightness

According to ISO 4464, straightness deviation is described as the variation of the actual shape of a line from a straight line. The deviations a and b are measured as the distances from points on the actual line to the straight line connecting the start and end points A and B of the actual line (See Figure 18).

Figure 18 – Measurement of straightness deviation

Straightness deviation is determined by the instruments specified in Clause 6 (with or without locating plates).

The two ends of a line, usually an edge, along which straightness deviation is to be measured, are connected either by a taut string between two knot points A and B, or by a straight edge resting on locating plates or by the sighting axis of a sighting tube.

4.3.1.1. Measurement using a straight edge

The length of the straight edge shall not exceed 3 m.

Figure 19 describes the measurement method using a straight edge and angle plates along the edge of the object to be measured.

Dimensions are in millimeters

LEGEND e: height of the gauge block; d: straightness deviation.

EXAMPLE: The deviation is calculated as follows: e = 25 mm. Deviation d = e – reading.

Case 1: d = 25 – 15;

Case 2: d = 25 – 32;

d = 10 mm (positive)

d = – 7 mm (negative)

Figure 19 – Description of measurement method using a straight edge and angle plates along the edge of the object to be measured

4.3.1.2. Measurement using a taut stringThe measuring method described in Figure 20 consists of creating a reference line using a taut steel or nylon string, supported at the ends by spacer plates and tensioning plates. The string is placed in a groove 50 mm from the edge.

The purpose of the spacer plates and tensioning plates is to keep the string at a predetermined distance from the corner vertices of the object to be measured and to ensure that the string does not touch the surface.

Figure 20 – Measurement using a taut string

4.3.1.3. Measurement using a sighting tube

The method described in 4.2.2.3 using a sighting tube to measure angular deviation can be used to determine the straightness of components.

4.3.2. Design curvature

The methods described in 4.3.1.1 to 4.3.1.3 can also be used to determine deviations from design curvature.

4.3.3. Allowable deviations for design curvature are specified in Table 3.

Table 3 – Allowable deviations for design curvature

4.4. Flatness and warpage of components

This clause describes examples of instruments, measurement methods and reference planes used to determine flatness.

According to ISO 4464, flatness deviation is described as “the variation between the actual shape of a surface and a plane surface”. In the case of local flatness, these surfaces are respectively replaced by a line and a straight line. When determining flatness deviation, it is necessary to specify which reference plane is used to measure the deviation.

4.4.1. Measurement principles

A reference plane can be defined in one of the following ways:

– The mean plane of 4 corner points;

– The plane determined by the least squares method;

– Through a number of straight lines (local flatness);

– Through a box (box principle);

– The plane passing through 3 corner points (warpage).

4.4.1.1. Mean plane

The flatness deviation on a rectangular surface, according to ISO 4464, can be determined by a mean plane with respect to the 4 corners. This mean plane is placed at S/4 above two opposite corners across the diagonal and at S/4 below the other 2 corners (See Figure 21), where S is the warpage determined as stated.

LEGEND: a, b, c, d: flatness deviations

Figure 21- Measurement of deviation using a mean plane

In Figure 21, the reference plane is the mean plane passing through A + S/4, B – S/4, C + S/4 and D – S/4. The flatness deviations are measured from points across the entire surface, not just at the sections; in Figure 21, the sections are drawn for simplicity. The surface to be measured is scanned against the mean plane. The flatness deviation is expressed by a positive or negative number according to the maximum distance from a point above and below this plane.

4.4.1.2. Least squares method

A more general definition of flatness is that the reference plane is established so that the sum of the deviations of the measured surface from the reference plane is zero; that is, the sum of the positive deviations equals the sum of the negative deviations, and the sum of the squares of these deviations is a minimum (this is the principle of least squares). For a plane, a large number of measuring points is required (about 16 points for a component of dimensions 4 000 mm x 6 000 mm), so it must be calculated by computer.

It should be noted that the calculation using the least squares method should be entrusted to a qualified person.

NOTE: The application of the least squares principle means that the calculation result gives the position and two directions of the reference plane in relation to the measured plane. Only in the case where the surface to be measured is already part of the erected structure can the two methods usually ensure the accuracy requirement.

Figure 22 depicts the reference plane calculated using the least squares principle.

As an example, the measurement of flatness can be specified as follows:

|V positive| + |V negative| ≤ T₁ mm

Where:

– V positive – Maximum positive deviation;

– V negative – Maximum negative deviation;

– T₁ – Specified flatness tolerance.

4.4.1.3. Local flatness

Local flatness deviations can be measured from a number of specific straight lines in specific directions.

(i = 1.1; 1.2; 1.3… 4.4)

Figure 22 – Reference plane calculated using the least squares principle

This method allows direct measurement of local straightness and indirectly of flatness. It is a practical method for checking flatness for many construction purposes.

Figure 23 describes the flatness deviation a1 from the reference plane ABCD or the deviation a2 from the reference line passing through points X and Y on the surface of the component.

Figure 23 – Flatness deviation from reference plane and reference line

4.4.1.4. Box principle

The box principle is used to determine flatness deviation. According to ISO 4464, the box principle is described as follows: “The volume considered is the volume of space between two imaginary homothetic box-shaped surfaces having a common direction, one lying within the other. The distance between corresponding faces of these boxes may or may not be evenly distributed, depending on the width of the specified tolerance. No point on the surface of the component may exceed that volume”.

NOTE: This principle also applies when considering two spatial dimensions. This is the most common case (See Figure 24).

In Figure 24, for two-dimensional components such as beams or plates, the simplified box principle can be used.

Figure 24 – Two-dimensional components using the box principle

The general use of the box principle with a three-dimensional orthogonal coordinate system requires measurement in three planes.

4.4.1.5. Warpage

According to ISO 4464, warpage is a special case of flatness deviation. That is, when a reference plane passes through three corner points of the component to be measured (or points close to the corner points), it is often difficult to determine the corner points. Warpage is described as the absolute value of the deviation of the fourth corner from the reference plane. Deviations from the reference plane of other points on the surface are considered flatness deviations. With warpage, large flatness deviations can be observed.

Flatness deviations are determined by the instruments specified in Clause 6, which also indicates typical sources of error and necessary precautions.

The methods below show different possibilities for measuring the overall shape of the component surface. First, the reference plane to be used and the allowable deviation must be specified. Flatness usually relates to a specific area of a finished surface, to an individual component, to the joint between two components or between two stages to create a “flat” surface. Large areas such as floors are usually checked by elevation error and sometimes by warpage with respect to grid points (see 5.2).

4.4.2. Overall flatness

4.4.2.1. Measuring flatness deviation using a sighting tube (transit)

Measurement can be done using levels or transits. Combined with thickness measurement, these methods provide an example of material applying the box principle.

In practice, the measurement is made from a plane outside the component and parallel to the two principal directions of the component.

This recommendation is implemented for the methods specified in 4.4.2.2. For methods using levels or transits, this recommendation cannot be followed. In that case, it is recommended to level as usual and the measured values are converted relative to the chosen reference plane. For ease of calculation, programmable computers for field conditions can be used.

4.4.2.1.1. Vertically positioned components

A vertical plane is scanned by a transit, a level with a 100 grad (90°) prism or a device that scans the surface to be measured at a distance of about 300 mm. When there is direct sunlight, this distance must be increased to at least 500 mm to avoid distortion due to refraction.

The instrument is aligned in the usual way. The leveling staff or scale in the sighting tube must be attached nearly perpendicular to the object to be observed.

Figure 25 describes an example of determining overall flatness deviation.

If a transit is used, measurements must be taken in both the left and right positions of the telescope. To avoid collimation error, the sighting distance is not less than 10 m.

Figure 25 – Determination of overall flatness deviation

4.4.2.1.2. Horizontally positioned components.

It is recommended to use a level. Alternatively, a transit with a sighting tube locked in the horizontal position can be used. The reading is taken on a leveling staff placed vertically and checked for verticality using a circular level.

In Figure 26, short (300 mm) leveling staffs are used, placed on instrument bases. They have the advantage of requiring only one operator. The disadvantage is that refraction can cause reading errors.

Figure 26 – Measurement of horizontally positioned components

4.4.2.2. Measuring flatness deviation using specially designed instruments

Figure 27 and Figure 28 describe two examples of measuring flatness using short-focus non-compensating devices. With these instruments, it is easier to follow the recommendation of ISO 4464 regarding the measuring plane being from outside the component and parallel to the two principal directions of the component than using two levels or transits placed at some distance from the component. The instruments described in Figure 27 and Figure 28 have the advantage that they can be used to measure components in any position.

The examples described in Figure 27 and Figure 28 have a plane passing through three corners of the component as the reference plane. When choosing the mean plane as the reference plane, the measured values are completely converted to this mean plane.

Figure 27 describes an example of measuring flatness with respect to a reference plane passing through three corner points (B, C, D). In some cases, the instrument at C has a fixed square angle, allowing direct reading of the squareness deviation at vertex B.

NOTE: It should be remembered that the instruments must be checked for collimation error. Compensating instruments are not allowed because this method can be used in any plane, not just in the horizontal plane.

The sighting axis of the sighting tube at point C (See Figure 27) is directed to point 0 on the scale at B and D. These 0 points correspond to the height of the sighting axis above the surface at point C.

The reading is then taken at target X, which can be placed at any point on the surface. (The reading at point A gives the warpage, see 4.4.4). The same principle can be applied to the instrument described in Figure 28, which consists of a surface scanning device D and a measuring instrument M (transit or detector), which is placed exactly on the reference plane defined by device D.

Figure 27 – Example of measuring flatness with a reference plane passing through three corner points

Figure 28 – Example of measuring flatness using a short-focus non-compensating device

The measurement of flatness of opposite surfaces (with the instrument placed in two positions, facing upward and downward), combined with thickness, is an example of applying the box principle.

4.4.3. Local flatness

The methods described above do not give flatness deviations from a certain reference plane, but only deviations from one or more reference lines, each passing through at least two points on the surface of the component to be measured. Such measurement means that sections must be used.

For this simplified method, the following issues must be recorded in the inspection plan:

– According to which method and on which side of the surface the sections were selected;

– How many sections there are and how many points are recorded at each section;

– How the results are recorded;

– Any other important issues.

In the following examples, only three points are used – two reference points and one point to be measured.

4.4.3.1. Measuring local flatness using a string or straight edge

A straight edge (with or without spirit level) or string can be used to measure components in the horizontal, vertical or inclined position (See Figure 29). Using a level, measurement can be combined with verticality checking. The instruments are placed on spacer pieces of known equal thickness Y. The measurement X between the surface and the string or straight edge is measured using a ruler or wedge gauge. Care must be taken not to lift the string with the wedge gauge. The straightness deviation is (X-Y), and this is an indicator of construction flatness.

The string must be tensioned by a force of 100 N.

It should be noted that when measuring with a horizontally tensioned string, the measuring range is limited to about 10 m. A high-strength steel wire with a diameter of 0.5 mm should be used.

Flatness deviations using a string should be avoided in strong wind and rain.

Figure 29 – Measuring local flatness using a string or straight edge

4.4.3.2. Measuring local flatness using a sighting tube

4.4.3.2.1. Vertically positioned components

A vertical plane is scanned by a transit, a level with a 100 grad (90 degree) prism or a surface scanning device (construction laser). The plane must be placed 300 mm from the surface to be measured. When there is direct sunlight, this distance must be increased to not less than 500 mm to avoid distortion due to refraction.

The instrument is aligned in the usual way, the leveling staff or scale in the sighting tube must be placed nearly perpendicular to the sighting axis of the instrument and placed nearly perpendicular to the object to be observed.

Figure 30 describes an example of measuring local flatness. The local flatness deviation d is:

Where, R1, R2, R3 are the readings on the leveling staff placed at positions R1, R2, R3 respectively. If the component is not completely vertical, this must be noted if the deviations are measured at points other than the center.

Figure 30 – Measuring local flatness using a sighting tube

4.4.3.2.2. Horizontally positioned components

It is recommended to use a level or a transit with a sighting tube locked in the horizontal position. The reading is taken on a leveling staff placed vertically and checked for verticality using a circular level.

Figure 31 – Measuring local flatness with a horizontally positioned component

Figure 31 describes an example of measuring local flatness. The local flatness deviation d is:

Where, R₁, R₂, R₃ are the readings on the leveling staff placed at positions R₁, R₂, R₃ respectively. If the component is not completely horizontal, this must be noted if the deviations are measured at points other than the center.

4.4.4. Warpage

4.4.4.1. Measuring warpage using a string or straight edge

Place a straight edge or a high-strength steel string between two opposite corner points on the diagonal of the component to be measured. The distance from the surface of the component to the straight edge or string is measured as d1 for the first diagonal, d₂ for the second diagonal; measured at the center of the surface, i.e. the intersection of the two diagonals. The warpage of the surface a is:

a = 2(d₁ – d₂)                   (6)

Figure 32 describes the method of measuring warpage using a string and wedge gauge. Care must be taken not to lift the string with the wedge gauge.

The string must be tensioned by a force of 100 N. It should be noted that when measuring with a horizontally tensioned string, the measuring range is limited to about 10 m. A high-strength steel wire with a diameter of 0.5 mm should be used. Measuring straightness deviations using a string should be avoided in rain and strong wind.

Figure 32 – Method of measuring warpage using a string and wedge gauge

4.4.4.2. Measuring warpage using a sighting tube

See also 4.4.2.1 and 4.4.3.2.

Measure the distances from the plane of the sighting axis to the four corners and calculate a plane passing through any three corner points. Calculate the distance from the fourth corner to this plane and obtain the warpage deviation (See Figure 32). A parallel-plate micrometer can be attached to the sighting tube if higher accuracy is desired. The warpage d₄ at R₄ is:

a₄ = (R₁ + R₃) – (R₂ + R₄)                         (7)

Where, R₁, R₂, R₃, R₄ are the readings on the measuring rod or staff placed at positions R₁, R₂, R₃, R₄ respectively.

4.4.5. Methods and devices for measuring components according to the box principle

Measurement according to the box principle can be carried out using conventional instruments and methods, i.e. surveying instruments, tape measures, large squares and tensioned strings; but due to the large amount of calculation required to incorporate these deviations into the acceptance standard of the box principle, this method of measurement is rarely used. However, the partial box principle, on 1, 2 or 3 edges of an object, is very commonly used with standard measuring instruments.

Measurement and calculation are simplified in most systems specifically developed for checking concrete components (See Figure 33 and Figure 34). These systems are very effective when used with the simplified box principle.

Static jigs can be used to measure according to the box principle, directly related to a production line. They consist of a steel structure on which the component to be measured rests on three points. Many measuring points are mounted at specific positions on all sides of the jig on the surface of an imaginary box. The distance from the measuring points to the surface of the component to be measured can be measured by extendable scale rules. Checking with jigs is very fast but for each jig, the size range and type of component to be measured is limited.

Figure 33 – Method of measuring components according to the box principle

The instruments described in Figure 34 and Figure 35 are examples of devices used to measure the overall dimensions of components according to the box principle.

a) Measuring frame: elevation	b) Measuring frame: cross section

LEGEND:

1) Movable frame;

2) Vertical graduated guide bars;

3) Horizontal graduated guide bars;

4) Measuring rod;

5) Object to be measured

Figure 34 – Devices used to measure according to the box principle

LEGEND:

– At F₁ in the X, Y and Z directions;

– At F₂ in the Y and Z directions;

– At F₃ in the Y direction.

Figure 35 – Description of the positions of devices used to measure according to the box principle

4.4.6. Allowable deviations for measuring components according to the box principle are specified in Table 4.

Table 4 – Allowable deviations for measuring components according to the box principle

5. Measuring methods carried out on site

This clause describes how to determine deviations of prefabricated or in-situ structures. Common deviations relate to the following parts: (See Figure 36).

– 5.1: Deviations in the horizontal plane, for example a, b, c, d for the facade or e, f, g, h inside the building; – 5.2: Deviations in the vertical plane (elevation) (not shown in Figure 36); – 5.3: Verticality, for example: k or b – a or d – c or h – g or f – e; – 5.4: Eccentricity, for example c – b; – 5.5: Positional deviations relative to other components, for example m and n; – 5.6: Flatness or straightness F1 (See Figure 75); – 5.7: Other important dimensions: bearing length (See Figure 76); joint width; steps at joints (See Figure 77).

Figure 36 – Some common deviations

Figure 36 describes some deviations. For example: verticality (5.3) or eccentricity (5.4) can be deduced from positional deviations measured from vertical reference planes passing through auxiliary lines, outside or inside the building.

Measurement of structures is carried out using measuring instruments (with or without locating plates) as specified in Clause 6, which also gives typical sources of error and precautions such as tension and temperature when using tape measures. To avoid collimation error in sighting tubes, the sighting distance shall not be less than 10 m. If this is not possible, then the sighting tube must be checked for collimation error. Chalk lines should not be used. The thickness of the chalk line can vary along its length. Therefore, the use of chalk lines is limited to assembly and is not suitable for collecting measurement data.

The methods described below generally apply the method of offsets from auxiliary lines. Other surveying methods can be used but accurate calculations must be performed. For both the measurement and the collection of accuracy data, the measuring procedure should be much more accurate than the allowable deviations specified for the accuracy of the manufacturing or construction process. This document assumes that there are suitable reference positions, according to ISO 4464, on the erection site or on the erection structure itself that needs to be measured, such as auxiliary lines or grids or leveling benchmarks. The structural grid lines, centerlines or other lines used in the design are usually not suitable as direct reference lines for measurement, because they are rarely visible after construction of the building parts (See Figure 37), except for measuring the position of bolts before erecting components.

Figure 37 describes the use of lines for measurement and lines intentionally marked parallel to the building’s surveying grid lines identified as auxiliary lines. Before implementing one of the methods below, the accuracy of the auxiliary lines must be known or surveyed.

Figure 37 – Description of measurement methods on site

Figure 38 describes some examples of transferring the auxiliary system to higher floors.

Figure 39 describes an example of two methods of transferring elevations.

Elevations transferred to a higher floor must always be checked by measuring back to the original leveling benchmark (for accuracy requirements, see ISO 4464).

Measurements must be carried out so that deviations measured on different floors can be referred to a reference position, such as auxiliary lines and auxiliary elevations.

5.1. Deviations in the horizontal plane

The measurement procedures described below describe how to measure horizontal distances to determine positional deviations and to calculate directional deviations, for example deviations from verticality.

LEGEND

a) Using an optical plummet;

b) Using the free station method;

c) Plumbing with a transit;

d) Plumbing with a transit and forced centering.

Figure 38 – Transferring the auxiliary system to higher floors

Figure 39 – Two methods of transferring elevation

5.1.1. Measuring deviations from the building’s surveying grid

The position of bolts, groups of bolts or guide bars in column voids can be measured directly from pre-marked centerlines, from auxiliary lines parallel to the centerlines of building parts (using a method similar to 5.1.2), or by the free station method and similar methods depending on the actual situation.

Figure 40 and Figure 41 describe some possibilities for measuring position relative to centerlines and internal positions.

A metal plate or other material with drilled holes for bolt positions should not be used for measurement or collection of accuracy data. This device should only be used specifically in construction to place bolts in their correct positions.

In Figure 40, the position of the bolts relative to the centerline or their internal position can be determined using a transit and a tape measure, measuring rod or leveling staff. The distance L shall not exceed 30 m and in any case shall not exceed the length of the tape measure, measuring rod or staff. The advantage of using a staff is that the measuring crew can be reduced from three people (See Figure 40) to two or even one, because the staff only needs to be placed in the correct position and does not need to be tensioned like a tape measure.

To read or estimate to the millimeter on the tape measure, measuring rod or staff, the distance D shall not exceed 40 m, intermediate instrument stations or suitable sighting targets are required – as specified in Clause 6.

This requirement also applies when measuring from auxiliary lines parallel to the centerline.

NOTE: An optical plummet can be used.

Figure 40 – Measuring position relative to the centerline

Figure 41 describes the determination of the position of guide pieces relative to a column.

Figure 41 – Determination of the position of guide pieces relative to a column

5.1.2. Measuring deviations from auxiliary lines parallel to the structure

The auxiliary lines should be established by the optical axis of the sighting tube.

In Figure 42, positive deviations can be measured at floor level from auxiliary lines parallel to the structural lines, using the offset method. Distances should be measured twice, on the left and right sides.

Positions can also be measured above floor or ground level. A transit must be used for this type of measurement. The transit should have a level with a sensitivity greater than 60.

LEGEND:

L: Known distance;

P₁ to P₄: positions on the auxiliary line;

P₂ – P₁ = directional deviation according to ISO 4464

Figure 42 – Measuring deviations from auxiliary lines parallel to the structure

The transit scans a vertical plane. This plane is about 300 mm from the surface to be measured. When there is direct sunlight, it must be increased to at least 500 mm to avoid distortion due to refraction. Measuring tall or long buildings under direct sunlight should be avoided.

The instrument is aligned in the usual way. The measuring rod or staff must be placed as nearly perpendicular to the sighting axis of the instrument as possible and nearly perpendicular to the object to be observed.

Figure 43 describes the measurement of positional deviations from inside or outside the building at higher elevations. It is important to check the measurement by measuring on both sides and perpendicular to the facade.

NOTE: The measuring rod is also used with a square to ensure the rod is perpendicular to the line of sight (sighting ray, sighting axis).

Figure 43 – Measuring positional deviations at higher elevations

5.1.3. Determining deviations based on auxiliary lines perpendicular to the structure

Figure 44 describes the principle of determining positional deviations relative to the structural grid lines perpendicular to the building. It can be carried out with a steel tape measure, starting from one reference line and ending at another subsequent line for verification.

When measuring positional deviations of components relative to two edges of the grid, always start from A and end at B for checking (See Figure 44).

The result of the measurement from A to B can be checked by starting from B and ending at A.

There may be a reading error when the side of the component has a protruding chamfer on the steel tape measure (See Figure 45).

When the joint is too narrow to use an angle plate, the reading error can be avoided by placing a ruler or the flat surface of a square tightly against the end of the component and perpendicular to the tape measure.

Figure 44 – Measuring positional deviations relative to the structural grid lines perpendicular

Figure 45 – Possible reading error when the component chamfer protrudes on the steel tape measure

Figure 46 describes the use of a vertical plane passing through the auxiliary lines at ground level to measure the position of walls.

Figure 46 – Measuring the position of walls

5.1.4. Allowable deviations based on auxiliary lines perpendicular to the structure are specified in Table 5.

Table 5 – Allowable deviations based on auxiliary lines perpendicular to the structure

5.2. Deviations in the vertical plane

5.2.1. Floors and ceilings are usually measured for elevation at grid points. The inspection outline will specify the grid spacing.

Figure 47 describes an example of measuring the elevation of floors (B) and ceilings (C) at grid points. It is recommended that there should be at least two elevation benchmarks (A) on each floor.

Readings are usually taken in millimeters. The staff must be kept vertical using a circular level. The measuring surface must be clean. After completing all measurements, the sighting axis of the instrument must be checked by taking a second reading on the elevation reference benchmark. If this reading differs from the first reading at the reference benchmark, all measurements from this instrument station must be rechecked.

The distance between the instrument and the staff shall not exceed 40 m.

5.2.2. The measurement results can be used to determine both the elevation and flatness deviations of floors and ceilings.

NOTE:

a) Because the sighting distances are usually not equal, the level must be checked for collimation error;

b) The detailed treatment of the measuring procedure to determine the flatness of floors when the allowable deviations are extremely small will be the subject of another standard on transferring elevations. (See Figure 39 and Figure 47)

Figure 47 – Measuring the elevation of floors B and ceilings C

In Figure 48, the elevation of the top of the component is checked by suspending a leveling staff on it. First, check the deviation of the staff from the vertical before measuring the elevation.

In Figure 49, to measure the elevation of the top of a beam, wall cap or panel from below, a locating rod must be attached to the foot of the staff.

Figure 48 – Measuring the elevation of a component by suspending a leveling staff on it	Figure 49 – Attaching a locating rod when measuring elevation

In Figure 50, a surface scanning laser can also measure elevation.

Figure 50 – Measuring elevation using a laser beam

5.2.3. Allowable deviations in the vertical plane are specified in Table 6.

Table 6 – Allowable deviations in the vertical plane

5.3. Verticality

Verticality is determined using the following instruments:

– Transit;

– Optical plummet;

– Inclinometer;

– Plumb bob.

Deviations from verticality must generally be determined from two mutually perpendicular reference planes. The verticality of multi-story building columns and buildings should be checked using two transits (left and right sides) or optical plummet instruments (two positions). The transit used for this type of checking must have a level with a level tube graduation interval of r ≤ 66″/2mm.

5.3.1. Using a transit combined with an optical plummet

Figure 51 describes the checking of wall verticality using a transit.

When the tilt angle of the telescope is greater than 50 grad (44°), plumbing should be done using an optical plummet instrument (See Figure 52).

Figure 51 – Checking wall verticality using a transit

Figure 52 – Transit combined with an optical plummet

Figure 53 describes how to determine deviations from verticality using an optical plummet instrument.

When checking the verticality of a column, the edge of the column or its centerline is checked. The transit is placed on one of two lines intersecting at right angles with a corner of the column at the base. These lines should be parallel to the lines at the base and coincide with the column edges. The transit is sighted so that the image of the top edge of the column just touches the center of the crosshair. The instrument is then rotated in the vertical plane to the base of the column and the deviation of the column edge from the crosshair is measured with a measuring rod. The transit is then adjusted to another line and the column is checked in the same way. The accuracy of this method is adversely affected by variations in column width and edge irregularities.

Figure 54 describes how to check the verticality of the edges of a multi-story column using a transit.

OF = known distance S1F1 = measured distance a1 = deviation from verticality = OF – S1F1 over height L1
Figure 53 – Determining deviations from verticality using an optical plummet instrument	Figure 54 – Checking the verticality of the edges of a multi-story column using a transit
A more accurate method is to mark the centerline of the column at the top and bottom on two adjacent faces when erecting the column. The transit is placed on two intersecting lines at right angles at the center of the column. If possible, these lines should coincide with the base lines so that position can be checked simultaneously. The column is positioned so that its centerline coincides with the vertical plane of the transit. The centerline may be steel ruler templates on which graduation marks are printed to read off verticality deviations. It is important to check this operation by measuring in both the left and right positions of the transit telescope.
	Figure 55 – Checking the positioning of the actual centerline of a column

Figure 55 describes how to check the position of the actual centerline of a column relative to the marked centerline on the column. If the column center is marked at places other than the top and bottom, straightness deviations can also be determined.

5.3.2. Using an inclinometer

An inclinometer is used to measure deviations from verticality over heights less than or equal to normal room height (See Figure 56).

All such rules must be designed so that they can be inverted to eliminate errors due to the level system and so that the level can be adjusted. The inclinometer must have additional support rods for measuring along curved surfaces (See Figure 57).

In general, there are two main methods for determining vertical deviations using an inclinometer:

a) Indirectly: converting the number of graduations of the level bubble displaced from the center position (See Figure 58) to the vertical angular deviation, expressed as the offset in millimeters per meter.

b) Directly: reading the vertical deviation on a movable scale after the bubble has been centered. (See Figure 58)

Figure 56 – Inclinometer	Figure 57 – Support rod for measuring along curved surfaces

Figure 58 – Graduations of the level bubble displaced from the center position

The accuracy of the instrument must be as follows:

– The level of the inclinometer must have a sensitivity greater than 3″;

– The level must be checked and adjusted before use;

– The inclinometer must be accompanied by staffs;

– After the first measurement, the inclinometer must be inverted and measured again. The average of the two readings gives the actual deviation;

– The flat surface of the inclinometer – i.e. the surface not used for measuring – must be placed vertically (See Figure 59). Usually this is done simply by using a level that is less sensitive than the main level.

NOTE:

1) Mason’s or carpenter’s levels are not suitable for measurement checking and shall not be used;

2) Since the sensitivity of the level may differ from the value given by the manufacturer, it is recommended to select a level with a sensitivity of one half the required sensitivity. For example, for a required or calculated level sensitivity of 60″, use a level with an indicated sensitivity of 30″.

Figure 59 – Position of placing the inclinometer

5.3.3. Using a plumb bob

A plumb bob can cause large errors. However, accuracy can be increased if the plumb bob has a mass of not less than 1 kg and is immersed in an oil tank (water is not sufficient to damp the oscillations of the plumb bob).

Figure 60 describes how to determine verticality deviations (A-B) using a plumb bob. Extreme care must be taken to avoid spilling oil on the floor.

Figure 60 – Determining verticality deviations using a plumb bob

5.3.4. Allowable deviations when using a plumb bob are specified in Table 7.

Table 7 – Allowable deviations when using a plumb bob

5.4. Eccentricity

5.4.1. Eccentricity is the case where a load-bearing component or building part is inadvertently placed in a vertical plane different from the component above or below it, reducing stability.

Figure 61 describes the eccentricity between two load-bearing components.

5.4.2. The concept of eccentricity is also used to indicate the inadvertently asymmetrical position of a component relative to two building surveying grids.

Figure 62 describes how to determine eccentricity relative to two building surveying grids. T1 and T2 show the positional deviations.

Figure 61 – Eccentricity between two load-bearing components

Figure 62 – How to determine eccentricity relative to two building surveying grids

5.4.3. Allowable deviations for eccentricity are specified in Table 8.

Table 8 – Allowable deviations for eccentricity

± 0.5 mm/m< 100 m± 0.8 mm/mα < 50 grad± 1.2 mm/mα = 50 grad – 70 grad± 5 mm< 10 m ± 10 mm± 15 mm

5.5. Positional deviations relative to other components (gaps and distances)

5.5.1. The determination of positional deviations relative to other components – such as deviations in room dimensions or other critical internal dimensions – can be calculated from the values measured using one or more of the above methods.

The distance between walls and between columns can be measured using an extendable measuring rod. Care must be taken to measure perpendicular distances rather than oblique distances. The extendable measuring rod must be placed perpendicular (See Figure 63).

Figure 63 – Measuring the distance between walls and between columns using an extendable measuring rod

When using a tape measure, the distance between walls in an enclosed space is usually determined by measuring at floor level with auxiliary benchmarks placed a short distance from the walls (See Figure 64).

Figure 64 – Measuring the distance between walls at floor level with auxiliary benchmarks

Direct measurement of the distance between walls at ceiling level should be avoided when the height exceeds 3 m; it must be measured indirectly, for example using a level, inclinometer, optical plummet or transit (See Figure 65).

Figure 66 and Figure 67 describe how to measure floor width using a steel tape measure and square, in which the relative position of columns can be determined using the steel tape measure and locating plates.

Figure 65 – Indirect measurement when the ceiling is above 3m

Figure 66 – How to measure floor width using a steel tape measure

Figure 67 – How to measure floor width using a square

Height measurement can be done directly using a pocket rule or extendable measuring rod (See Figure 68). Care must be taken to measure perpendicular distances rather than oblique distances. For a room height of 3 m, the deviation from plumb of the steel tape measure or staff shall not exceed 5 mm.

Figure 68 – Measuring height using a pocket rule or extendable measuring rod

Figure 69 describes indirect measurement using a level. This measurement can be combined with the measurement of floor and ceiling elevations (See Figure 47).

EXAMPLE: The height of the room H = floor side reading plus ceiling side reading (H = r₁ + r₀)

Figure 69 – Indirect measurement using a level

The readings on the staff must be corrected because there may be a zero point error. There is a zero point error because the zero point of the staff does not coincide with the foot of the staff (See Figure 70).

When measuring the height of a void or when transferring elevation using a steel tape measure, the application of standard tension to the tape and correction of the measurement for temperature must be applied when the height exceeds 10 m, for example for an elevator shaft (See Figure 71).

For tall buildings, an EDM (electro-optical distance measurement) instrument can be used as follows: The elevation difference can be measured either directly along the plumb line or indirectly by reducing the slope distance when determining the vertical angle. Figure 73 describes the setup of the instrument to determine the elevation difference between floor elevation benchmarks and the additional measurements that must be made. The total elevation difference between the points is:

ΔH = A_FU – A_FO – A_D + A_K + L – K + K_S + K_BR                     (8)

Where:

F_O, F_U – elevation benchmarks;

ΔH – elevation difference between two elevation benchmarks;

L – large distance (MNQ);

K – small distance (MN);

K_S – elevation constant of the rotation axis of the upper mirror on the tripod;

K_BR – elevation constant of the rotation axis of the reflector;

A_FU, A_FO, A_D, A_K I – readings on the leveling staff.

This method allows the elimination of the instrument constant. Figure 73 describes how to measure height using an EDM.

NOTE: This measurement is complex and should be performed by a qualified person.

In Figure 73, the vertical distance ΔH is derived from the difference of two distance measurements (MNQ – MN). This method eliminates the zero point error of the EDM. For the method described in Figure 75, only one distance measurement is required but now the zero point error (MO) must be known or considered.

Figure 74 describes a more direct measurement method.

Figure 73 – Measuring height using an EDM.

Figure 74 – Description of the EDM measurement method.

5.5.2. Allowable deviations for position relative to other components are specified in Table 9.

Table 9 – Allowable deviations for position relative to other components

5.6. Flatness, straightness, design curvature

5.6.1. The values measured from the measuring methods described in 4.3, 5.2 and 5.3 can also be used to determine construction deviations of flatness, straightness and design curvature according to the principles of 4.3 and 4.4. However, for these cases, the reference plane from which the deviations are calculated must also be agreed upon (See 4.4).

Flatness deviations (overall or local) are determined relative to an agreed reference plane, for example in this simple example it is the plane passing through the points of the main surface at ground and roof level (See Figure 75).

5.6.2. Table of allowable deviations

For information on the accuracy of a measuring method when used to determine flatness, straightness and design curvature, see the tables of allowable deviations in 4.3, 4.4, 5.1, 5.2 and 5.3.

LEGEND:

a, b, c are measured values

H_B is the height of the structure

H_S is the height of the story

F is the surface flatness deviation

${\displaystyle F=(a-<!--\; -\; -->b)-<!--\; -\; -->\frac{H_S}{H_B}(a-<!--\; -\; -->c)}$

Figure 75 – Determination of flatness deviation

5.7. Other important deviations

5.7.1. Width of bearing surface

The width of the bearing surface (See Figure 76) of floor components is mostly difficult to check after the floor component has been placed in position. One method to avoid this difficulty is to create a line parallel to the edge of the floor component at a distance C before erection, and to mark this line at 2 or more places, with a sharp notch, and if permitted, to mark the position of this notch with a paint mark for easy identification. After erection, measure the distance M between the mark on the floor and the supporting component.

LEGEND: b = width of the bearing surface C = constant distance M = measured distance

Figure 76 – Measuring the width of a joint

5.7.2. Width of joint

The width of a joint can be measured using a wedge gauge, inside caliper or enlarging ruler. Go/no-go gauges are sufficient for measurement but not sufficient for collecting accuracy data. If the joint has a chamfer over 10 mm, it is difficult to read from the wedge gauge due to reading error. In this case, an inside caliper or joint gauge can be used.

5.7.3. Step at joint

The step at a joint can be measured while performing one of the mentioned measuring operations (See Figure 42 and Figure 48), or measured separately using a square or ruler and extendable rule (See Figure 77).

Figure 77 – Measuring a step at a joint

5.7.4. Allowable deviations for supports and joints are specified in Table 10.

Table 10 – Allowable deviations for supports and joints

6. Measuring instruments

6.1. General provisions

6.1.1. This clause provides guidance on appropriate measuring methods for construction sites and factories for measuring structures and prefabricated components of structures.

The choice of instrument depends on the measuring task and the specified allowable deviation (see ISO 8322).

6.1.2. It should be noted that conditions on site and in the factory can seriously disrupt the function of measuring instruments. Therefore, measuring instruments must be regularly checked and cleaned immediately after use. Measuring instruments should be checked before first use and after storage and repair.

6.1.3. Measuring instruments not mentioned in this standard – which may be available in some countries – may be used on the condition that they meet the accuracy requirements of the method.

It is assumed that the measuring instruments are regularly calibrated and the users have been trained to properly operate the instruments.

6.1.4. The manual for measuring instruments must be read to familiarize operators with the instruments.

6.2. Calipers and sliding gauges

Calipers and sliding gauges are used to measure dimensions up to 1 000 mm. (See Figure 7)

In practice, calipers with faces that can measure both internally and externally are commonly used. When the above rules have two scales, care must be taken to read the correct scale.

The following points should be noted:

a) Excessive wear and compression can cause gaps and deformation of the jaws;

b) The required pressure can be checked using gauge blocks;

c) Excessive use on concrete products can wear the faces;

d) The caliper must be placed perpendicular to the surface of the object to be measured;

e) A locking device is required to prevent slippage during placement;

f) When measuring externally, the parallelism of the surfaces shall not be affected by tightening the slides;

g) Care must be taken to read the correct scale.

6.3. EDM instruments (electro-optical distance measurement)

EDM instruments are used for direct measurement under the condition that the distances are greater than 30 m. Most EDMs are mounted on transits, but there are also some instruments with distance and angle measurement devices. There are also models that directly convert the measured values into information about horizontal distance and elevation difference. These are commonly referred to as “total stations”. Operation of these types of instruments must be done by highly qualified personnel.

The following points should be noted:

a) Before use, the instruction manual for the equipment must be read. Many errors can occur due to unfamiliarity with the instrument;

b) Regularly check the instrument over known distances;

c) Before measurement, it is recommended to wait a few minutes after switching on the instrument to allow it to warm up and stabilize to body temperature;

d) Atmospheric influence (pressure and temperature) is a source of error;

e) Zero point errors, graduation errors and errors due to frequency changes need to be checked periodically;

f) Instrument centering errors and sighting errors must be considered.

6.4. Go/no-go gauges

Go/no-go gauges are used to measure whether the width range of a joint gap is acceptable. They are made of steel, hard wood or other hard material. (See Figure 78)

If the smallest gauge fits and the largest gauge does not fit, then the joint gap is acceptable. Care must be taken when using many different sizes of gauges.

NOTE: Go/no-go gauges shall not be used to collect accuracy data when measuring.

Figure 78 – Go/no-go gauge

6.5. Inclinometer

An inclinometer is used to measure verticality deviations (plumb line deviations), horizontal deviations or deviations from design inclination for the height and length of a normal building story. The inclinometer can be a simple measuring instrument such as a level placed in a frame (for example: a mason’s level) or a complex one with a micrometer fine adjustment screw.

The following points should be noted:

a) An accuracy check must be carried out to see if this inclinometer meets the requirements;

b) The means of checking the instrument are designed to be invertible to eliminate level errors;

c) The accuracy depends greatly on the sensitivity of the level (See example 5.3.2).

6.6. Laser instruments

Laser instruments are used to determine height/elevation/level. Positional deviations or directional deviations of a laser standard used in construction are referred to as weak lasers (Helium – Neon gas).

The following points should be noted:

a) Before use, the instruction manual for the equipment must be read. Many errors can occur due to unfamiliarity with the instrument;

b) When using lasers, warning signs must be placed in accordance with local and national safety instructions;

c) “Weak laser” means that it does not harm the skin and clothing. People still need to avoid looking directly into the laser beam;

d) Never use a telescope to locate the beam;

e) The laser beam is also affected like any other light beam;

f) Regularly check the direction into the position of the laser and check that the locking function for the inclined plane when rotating the laser horizontally is still operating;

g) Power supply components, for example weak rechargeable batteries, need to be checked regularly;

h) After switching on the instrument, allow 15 minutes for the beam to stabilize;

i) The usual measuring length is limited to below 80 m.

6.7. Spirit level

A spirit level is used to detect small elevation differences over short distances (< 2 m), accompanied by a straight edge (See Figure 79).

The following points should be noted:

a) Two observations must be made: after the first observation, invert the level;

b) Using a level for large distances is inaccurate and laborious;

c) It shall not be used to collect accuracy data when measuring.

Figure 79 – Spirit level

6.8. Water level

Some simple types of water levels can be used when other methods cannot be used, for example to go around obstacles.

The following points should be noted:

a) Air bubbles or cracks can occur in the tube connecting the two reading vessels;

b) There may be a zero point error on the reading scale.

There are many different types of water levels (See Figure 80), for example:

a) Common type;

b) Water level where only the water level in one of the tubes needs to be read.

Figure 80 – Some types of water levels

6.9. Level

A level is the most common instrument for determining the elevation of a point relative to a reference benchmark or for determining deviations from the horizontal or for determining flatness deviations of floors and components and warpage.

There are three main types of levels:

a) Fixed-telescope levels, in which the sighting tube and bubble tube are attached directly to the support base;

b) Tilting levels, in which the sighting tube and bubble tube can be tilted at an angle to the instrument base using a screw;

c) Automatic-compensating levels, in which the sighting axis is automatically brought into the horizontal position after the sighting tube is placed nearly horizontal.

The following points should be noted:

a) The backsight and foresight should have equal lengths and not exceed 40 m;

b) Checking the angle i is particularly important when the sighting lengths differ greatly;

c) The staff should be made of invar steel, wood or other material with a small coefficient of thermal expansion;

d) Keep the staff vertical using a bubble;

e) Check that the staff is sufficiently illuminated for accurate reading;

f) When checking the staff, always place it on a hard surface;

g) Check whether the instrument satisfies the requirements for minimum sighting distance;

h) Elevation work should start and end at points of known elevation (reference elevation points).

6.10. Micrometer measuring rod

A micrometer measuring rod is used to measure in the range up to 1 500 mm, to measure internal dimensions, when high accuracy is required (See Figure 81).

The following points should be noted:

a) Check whether the rod has been heated up by the operator’s hand;

b) Lubricate only one place (micrometer screw) and use only light oil;

c) If possible, use a friction screw to avoid non-standard compression force.

Figure 81 – Micrometer measuring rod

6.11. Caliper

A caliper is used to measure in the range up to 50 mm (See Figure 82).

The following points should be noted:

a) The tip of the micrometer screw must be 1 mm;

b) It must be adjustable to zero;

c) The spindle must have friction to avoid non-standard force that can damage the frame;

d) The frame must be insulated;

e) The caliper must be placed perpendicular to the object to be measured;

f) The screw must be rotated in the same direction until contact;

g) Check the reading against known dimensions;

h) Never store the caliper in a state where the measuring anvils are closed.

6.12. Enlarging measuring glass

An enlarging measuring glass is used to measure narrow joints and cracks (See Figure 83).

The following points should be noted:

a) Adjust to eliminate parallax;

b) Place the graduated surface of the glass close to the object to be measured.

Figure 82 – Caliper	Figure 83 – Enlarging measuring glas

6.13. Measuring rod

Measuring rods are rods made of steel or other suitable material, with one edge graduated to 1 millimeter for surface measurement.

The following points should be noted:

a) The cross-section of the rod shall be such that parallax is minimized, i.e. a chamfered cross-section is better than a square cross-section;

b) If the zero point is at the end of the rod, there may be a zero point error due to wear;

c) If the rod is longer than 1 000 mm, it must be supported at least 3 points during measurement;

d) Care must be taken to keep the rod horizontal.

6.14. Extendable measuring rod

An extendable measuring rod is used to measure horizontally, vertically and diagonally between surfaces or points up to 5 m apart. There are many types of measuring rods.

The following points should be noted:

a) When measuring vertically or horizontally, use a rod with an attached circular level to prevent the rod from being inclined or deviating from the plumb line;

b) Wear on the contact surface can cause inaccuracy. Regularly check the measuring rod by comparing it with a known distance.

6.15. Wedge gauge

A wedge gauge is used to measure the width of a joint at or near the surface (See Figure 84).

It must be agreed where the measurement will be made along the joint.

Figure 84 – Wedge gauge

6.16. Optical plummet

Currently, three types of optical plummets can be found: The type that only plumbs from top to bottom, the type that only plumbs from bottom to top, and the type that can plumb both from top to bottom and from bottom to top.

The following points should be noted:

a) If the instrument does not have an automatic leveling device, it is necessary to project in four mutually perpendicular positions;

b) If the instrument has an automatic leveling device, it should be projected in two mutually perpendicular positions;

c) If the instrument has two automatic leveling devices, it is only necessary to perform the projection in one position, but it is better to perform it in both positions;

d) Plumbing from bottom to top requires extreme caution in terms of safety;

e) An optical plummet shall only be entrusted to a person who has been trained to use it.

6.17. Plumb bob

A plumb bob is used to establish a reference vertical line. The following points should be noted:

a) Air currents can cause large errors, especially for long plumb lines (< 3 m);

b) The plumb bob must have a sufficiently large weight (>1 kg) to keep the line stable;

c) Immersing the plumb bob in oil can reduce oscillations but does not eliminate the influence of air movement and wind. Extreme care must be taken not to spill oil on the floor.

6.18. Locating plates

Locating plates are used to define the corners and edges of products (such as concrete), where the surface construction is distinct or where the corners and edges are easily chipped. There are special locating plates for use on inward-facing corners (See Figure 85).

The following points should be noted:

a) The locating plate needs to be pressed against the component to be measured so that it does not shift during measurement;

b) When necessary to secure tape measures, use anchors for wires, etc.;

c) Be careful to use pins, supports and similar plates of the same size simultaneously.

6.19. Right-angle prism

A right-angle prism is an optical instrument for preliminary adjustment or checking of right angles. The following points should be noted:

a) There is no way to adjust this instrument. Check the accuracy using a verified right angle;

b) Angle mirrors should not be used.

Figure 85 – Use of locating plates

6.20. Square

A square is an L-shaped instrument, preferably made of steel, used to check right angles. The following points should be noted:

a) If necessary, the measuring points must be defined by locating plates;

b) The blade of the square shall not be longer than 1 200 mm;

c) The angle that has been checked once needs to be checked again by inverting the square.

One method of checking a square is to place it on the surface of a plate and draw a thin line on the vertical surface of an object standing on that plate. Then turn the base of the square from left to right or vice versa and draw a second line close to the first line. If there is an angular error between the blade and the base of the square, it is immediately recognized when observing the two lines (See Figure 86).

Figure 86 – Checking a right angle using a square

6.21. Straight edge

A straight edge is used to draw a line to measure straightness deviation. The following points should be noted:

a) At the two ends of the straight edge there must be supports of the same length;

b) The straightness of the straight edge must be regularly checked by inverting or tensioning a metal wire or fiber.

6.22. Pocket steel tape measure

A pocket steel tape measure is used to directly measure dimensions with distances up to 5 m and is graduated in millimeters throughout its length. This type of tape measure is housed in a closed case. The following points should be noted:

a) The movement of the L-shaped end at the zero mark must be checked;

b) It shall not be used to measure distances exceeding the length of the tape measure;

c) It must be cleaned and oiled to prevent the retraction spring from jamming.

6.23. Steel tape measure

Steel tape measures must comply with national standards or OIML recommendations. The tape measure is used for direct measurement of dimensions with distances up to 100 m but preferably within 50 m. Accuracy can be increased by vertical tension force and correction for the influence of slope, sag and thermal expansion (See Appendix A). The following points should be noted:

a) With frequent use, the accuracy decreases, so the tape measure needs to be checked regularly against a standard tape measure or existing reference benchmarks. For steel tape measures used daily, check at least once a month;

b) Tape measures that have been repaired shall not be used for measurement checking or collecting accuracy data unless they have been recalibrated after repair;

c) After each day of use, the tape measure must be cleaned and lightly oiled to prevent rust and for easy reading;

d) The fixing ring at the end of the tape measure must be checked to determine the zero mark of the graduation (varies by manufacturer);

e) Care must be taken when making corrections;

f) The characteristics of the tape measure related to temperature and tension force must be known;

g) The tape measure must be allowed to reach ambient temperature. The temperature of the tape measure needs to be measured with a contact thermometer;

h) The temperature of the tape measure along its entire length depends on the temperature of the material supporting it;

i) Avoid exposing an unused tape measure to strong sunlight.

6.24. Targets

Targets are auxiliary devices to indicate the position of points to be observed (See Figure 87). The following points should be noted:

a) There should be a clear contrast between the target and the background;

b) The target must be observed correctly and observed at its axis of symmetry;

c) To achieve high accuracy, place the target on a tripod or fix it to a fixed benchmark.

LEGEND:

1) Special sighting board on tripod or fixed benchmark, for distances from 5 m to 20 m when high accuracy is required;

2) Small nails or pencil tips can be used as targets for distances up to 30 m;

3) Wall target for distances from 20 m to 1 000 m;

4) Target with movable horizontal screw for distances from 20 m to 500 m. When the distance is greater than 500 m, an additional sighting plate is attached to the target;

5) Star target for distances from 200 m to 1 000 m.

Figure 87 – Points to be observed on various types of targets

6.25. Transit

A transit is used to measure, establish and check horizontal and vertical angles, lines and planes. The instrument may have an additional eyepiece with a broken tube for viewing in the vertical or near vertical direction. The following points should be noted:

a) Always use both the left and right positions of the telescope if it is a traditional transit;

b) Check the operation of the optical centering device;

c) Check the stability of the tripod and protect it from sunlight when measuring;

d) Do not create long lines by extending short lines;

e) Periodically check the collimation error (2c) and the optical conditions of the instrument;

f) When measuring, protect the bubble tube of the transit from sunlight;

g) Each time when switching from a distant target to a near target (or vice versa), consider the error due to the influence of focusing. If possible, keep the focusing distance greater than 10 m.

6.26. Tripod

A tripod is used to support the instrument and target. Basically there are two types, rigid tripods and extendable tripods (i.e. the tripod legs can be extended and retracted). The following points should be noted:

a) The stability of the tripod needs to be checked regularly. Check the tight connection between the tripod head and the extendable legs, they must be tightened sufficiently when measuring and the metal tips at the ends of the legs must not be loose;

b) Tripods with large thermal deformation, especially some lightweight metal tripods, should be avoided for use in direct sunlight.

Appendix A (Normative) Corrections for steel tape measures

A.1. Correction for tape sag

When a tape measure is not supported, it will sag in a catenary curve between the two ends, causing the read distance to be greater than the distance between the two knot points. The sag correction C1, in meters, can be calculated as follows:

C₁ = (L³m²/24t²)cos² α                (A.1)

Where:

L – measured length (of the catenary), in meters;

m – mass of the tape measure, in kilograms;

t – tape tension force, in Newtons;

α – vertical angle between the inclined chord connecting the two ends of the tape measure and the horizontal, in degrees (0)

Tension must be applied with the appropriate tension force. This is done by using a tape tensioning device or spring dynamometer.

A.2. Correction for temperature (to adjust for thermal expansion of the tape measure)

The change in length of the steel tape measure due to temperature can cause significant errors when the temperature of the tape measure differs by 5 °C from the standard temperature, usually taken as 20 °C.

The temperature correction for the steel tape measure Ctemp is calculated as follows:

C_tenmp = LaΔt                              (A.2)

Where:

L – measured length, in meters;

a – coefficient of expansion per degree C (0.000011 or 11 x 10^-6 for steel tape measures);

Δt – difference from the temperature at calibration Δt = (t_m – t_c);

t_m – temperature at measurement, in °C;

t_c – temperature at calibration, in °C

The temperature of the tape measure in the measuring line is always related to the air temperature. When the tape measure is supported on the measured object along its entire length, its temperature depends greatly on the temperature of the supporting material, which means it will be difficult to determine the temperature of the tape measure.

Avoid measuring and storing unused tape measures in strong sunlight, for similar reasons, the actual temperature of the tape measure should be measured with a contact thermometer.

A.3. Correction for the influence of terrain slope (to obtain horizontal length)

With small slopes, the elevation difference between the measuring points can also cause significant errors. Over short distances, this can be corrected by keeping the tape measure nearly horizontal. However, over long distances, accuracy can be increased by measuring along the slope and applying appropriate corrections.

Where:

L – length, measured in meters;

a – vertical angle between the inclined chord connecting the two ends of the tape measure and the horizontal, in degrees (°)

h – elevation difference between the ends of the tape measure, measured in meters.

BIBLIOGRAPHY

ISO 17123, Optics and optical instruments – Field procedures for testing geodetic and surveying instruments;

ISO 1803, Tolerances for building – Expression of dimensional accuracy – Principles and terminology.

1) ISO 4464 has been replaced by ISO 1803

2) ISO 8322 has been replaced by ISO 17123