SIST EN ISO 18674-8:2024
(Main)Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 8: Measurement of loads: Load cells (ISO 18674-8:2023)
Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 8: Measurement of loads: Load cells (ISO 18674-8:2023)
This document specifies the measurement of forces by means of load cells carried out for geotechnical monitoring. General rules of performance monitoring of the ground, of structures interacting with the ground, of geotechnical fills and of geotechnical works are presented in ISO 18674-1.
This document is applicable to:
— performance monitoring of geotechnical structures such as anchors, tiebacks, piles, struts, props and steel linings;
— checking geotechnical designs and adjustment of construction in connection with the observational method;
— evaluating stability during or after construction.
This document is not applicable to devices where the load is purposely applied to geotechnical structures in the wake of geotechnical field tests such as calibrated hydraulic jacks for pull-out tests of anchors or load tests of piles.
NOTE 1 This document fulfils the requirements for the performance monitoring of the ground, of structures interacting with the ground and of geotechnical works by the means of load cells as part of the geotechnical investigation and testing in accordance with References [2] and [3].
NOTE 2 ISO 18674-7 is intended to define the measurement of forces by means of strain or displacement gauges.
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 8: Messung von Kräften: Kraftmessdosen (ISO 18674-8:2023)
Dieses Dokument legt Merkmale für Kraftmessungen mittels Kraftmessdosen, die zur geotechnischen Messung durchgeführt werden, fest. Allgemeine Regeln für die messtechnische Überwachung von Baugrund, von Bauwerken, die mit dem Baugrund in Wechselwirkung stehen, von geotechnischen Auffüllungen und von geotechnischen Arbeiten sind in ISO 18674 1 festgelegt.
Dieses Dokument ist anzuwenden für:
messtechnische Überwachung von geotechnischen Bauwerken wie Anker, Zuganker, Pfähle, Steifen, Stützen und Stahlauskleidungen;
Überprüfung geotechnischer Entwürfe und Konstruktionsanpassung in Verbindung mit der Beobachtungsmethode;
Bewertung der Stabilität während oder nach dem Bau.
Dieses Dokument ist nicht anwendbar für Vorrichtungen, bei denen die Last im Verlauf geotechnischer Feldprüfungen absichtlich auf geotechnische Bauwerke aufgebracht wird, beispielsweise kalibrierte Hydraulikzylinder für Auszugsprüfungen von Ankern oder Belastungsprüfungen von Pfählen.
ANMERKUNG 1 Dieses Dokument erfüllt die Anforderungen an die messtechnische Überwachung von Baugrund, von Bauwerken, die mit dem Baugrund in Wechselwirkung stehen, und von geotechnischen Arbeiten mittels Kraftmessdosen als Teil geotechnischer Erkundung und Untersuchung nach Literaturhinweisen [2] und [3].
ANMERKUNG 2 ISO 18674 7 ist zur Festlegung der Kraftmessung mittels Dehnungsmessstreifen oder Verschiebungsmessgeräten vorgesehen.
WICHTIG — Die elektronische Datei dieses Dokuments enthält Farben, die für das richtige Verständnis des Dokuments als zweckmäßig erachtet werden. Die Benutzer sollten daher in Erwägung ziehen, dieses Dokument mit einem Farbdrucker auszudrucken.
Reconnaissance et essais géotechniques - Surveillance géotechnique par instrumentation in situ - Partie 8: Mesure de charges : cellules de charge (ISO 18674-8:2023)
Le présent document spécifie la mesure des forces au moyen de cellules de charge en vue de réaliser une surveillance géotechnique. Les règles générales de surveillance des performances du terrain, des structures en interaction avec le terrain, des remblais et des travaux géotechniques sont présentées dans l’ISO 18674-1.
Le présent document s’applique:
— à la surveillance des performances des structures géotechniques telles que les ancrages, les boulons d’ancrage, les tirants d’ancrage, les pieux, les butons, les étais et les soutènements en acier;
— au contrôle des calculs géotechniques et à l’ajustement d’une construction en lien avec la procédure observationnelle;
— à l’évaluation de la stabilité durant ou après la construction.
Ce document n'est pas applicable aux dispositifs où la charge est appliquée à dessein aux structures géotechniques à la suite d’essais géotechniques sur le terrain, tels que les vérins hydrauliques étalonnés pour les essais d’arrachement des ancrages ou les essais de charge des pieux.
NOTE 1 Le présent document satisfait aux exigences relatives à la surveillance des performances du terrain, des structures en interaction avec le terrain et des ouvrages géotechniques au moyen de cellules de charge mises en œuvre dans le cadre des études et essais géotechniques conformément aux Références [2] et [3].
NOTE 2 L'ISO 18674-7 a pour objet de définir la mesure des forces au moyen de jauges de déformation ou de déplacement.
Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 8. del: Merjenje sil: obremenilne celice (ISO 18674-8:2023)
Ta standard je 8. del skupine standardov ISO 18674, kot je opisano v standardu ISO 18674-1: 1. del.
Podana so splošna pravila za metode in pravila za merjenje običajnih sil oziroma obremenitev sidrnih sistemov, vezi, opornikov in drugih elementov (npr. pilotov) v geotehničnem inženiringu ali splošneje v inženirstvu temeljev.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2024
Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 8. del: Merjenje
sil: obremenilne celice (ISO 18674-8:2023)
Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation
- Part 8: Measurement of loads: Load cells (ISO 18674-8:2023)
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 8:
Messung von Kräften: Kraftmessdosen (ISO 18674-8:2023)
Reconnaissance et essais géotechniques - Surveillance géotechnique par
instrumentation in situ - Partie 8: Mesure de charges : cellules de charge (ISO 18674-
8:2023)
Ta slovenski standard je istoveten z: EN ISO 18674-8:2023
ICS:
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 18674-8
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2023
EUROPÄISCHE NORM
ICS 93.020
English Version
Geotechnical investigation and testing - Geotechnical
monitoring by field instrumentation - Part 8: Measurement
of loads: Load cells (ISO 18674-8:2023)
Reconnaissance et essais géotechniques - Surveillance Geotechnische Erkundung und Untersuchung -
géotechnique par instrumentation in situ - Partie 8: Geotechnische Messungen - Teil 8: Messung von
Mesure de charges : cellules de charge (ISO 18674- Kräften: Kraftmessdosen (ISO 18674-8:2023)
8:2023)
This European Standard was approved by CEN on 19 August 2023.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18674-8:2023 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 18674-8:2023) has been prepared by Technical Committee ISO/TC 182
"Geotechnics" in collaboration with Technical Committee CEN/TC 341 “Geotechnical Investigation and
Testing” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2024, and conflicting national standards shall
be withdrawn at the latest by March 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 18674-8:2023 has been approved by CEN as EN ISO 18674-8:2023 without any
modification.
INTERNATIONAL ISO
STANDARD 18674-8
First edition
2023-09
Geotechnical investigation and
testing — Geotechnical monitoring by
field instrumentation —
Part 8:
Measurement of loads: Load cells
Reconnaissance et essais géotechniques — Surveillance géotechnique
par instrumentation in situ —
Partie 8: Mesure de charges: Cellules de charge
Reference number
ISO 18674-8:2023(E)
ISO 18674-8:2023(E)
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 18674-8:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.3
5 Instruments. 3
5.1 General . 3
5.2 Electric load cells . 4
5.3 Hydraulic load cells . 5
5.4 Instruments for specific applications . 6
5.4.1 Anchor load cells. 6
5.4.2 Load cell for cast-in-place concrete piles . 7
5.5 Measurement accuracy . 9
6 Installation and measuring procedure . 9
6.1 Installation . 9
6.1.1 General . 9
6.1.2 Anchor load cells. 10
6.1.3 Load cells at the base of cast-in-place concrete piles . 10
6.1.4 Load cells for struts across excavations . 11
6.2 Carrying out the measurement . . . 11
6.2.1 Instrumentation check and calibration . 11
6.2.2 Measurement .12
7 Data processing and evaluation .12
8 Reporting .13
8.1 Installation report . 13
8.2 Monitoring report . 13
Annex A (informative) Geotechnical applications .14
Annex B (informative) Measuring examples .15
Bibliography .33
iii
ISO 18674-8:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 182, Geotechnics, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 341, Geotechnical
Investigation and Testing, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
A list of all parts in the ISO 18674 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 18674-8:2023(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 8:
Measurement of loads: Load cells
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing
this document using a colour printer.
1 Scope
This document specifies the measurement of forces by means of load cells carried out for geotechnical
monitoring. General rules of performance monitoring of the ground, of structures interacting with the
ground, of geotechnical fills and of geotechnical works are presented in ISO 18674-1.
This document is applicable to:
— performance monitoring of geotechnical structures such as anchors, tiebacks, piles, struts, props
and steel linings;
— checking geotechnical designs and adjustment of construction in connection with the observational
method;
— evaluating stability during or after construction.
This document is not applicable to devices where the load is purposely applied to geotechnical
structures in the wake of geotechnical field tests such as calibrated hydraulic jacks for pull-out tests of
anchors or load tests of piles.
NOTE 1 This document fulfils the requirements for the performance monitoring of the ground, of structures
interacting with the ground and of geotechnical works by the means of load cells as part of the geotechnical
investigation and testing in accordance with References [2] and [3].
NOTE 2 ISO 18674-7 is intended to define the measurement of forces by means of strain or displacement
gauges.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 18674-1:2015, Geotechnical investigation and testing — Geotechnical monitoring by field
instrumentation — Part 1: General rules
3 Terms and definitions
For the purposes of this document the terms and definitions given in ISO 18674-1 and the following
apply.
ISO 18674-8:2023(E)
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
load cell
field instrument for monitoring forces acting in geotechnical structures
Note 1 to entry: Load cells are commonly placed at an end of a structural member where forces are transmitted
from one member to another.
EXAMPLE Load cell at the anchor head where the force acting in the anchor tendon is transmitted to a
retaining wall.
Note 2 to entry: Common load cells are electric (see 3.2) and hydraulic (see 3.3) measuring principles.
Note 3 to entry: Indispensable components of load cells are a load bearing element and load distribution plates
for transmitting forces between structural members.
Note 4 to entry: Load cells are not useful for fully grouted rock bolts.
3.2
electric load cell
instrument with an elastically-behaving body which deforms under the applied force, where the
resulting deformation is measured by electric sensors
Note 1 to entry: An example of such body is a steel cylinder (see Figure 2).
Note 2 to entry: For typical electric sensors, see 5.2.4.
3.3
hydraulic load cell
instrument with a flat liquid-filled compartment where the force to be monitored acts normal to the
flat distribution plates on the sides of the compartment and where the pressure in the liquid of the
compartment is measured by a pressure measuring device
Note 1 to entry: See Figure 3.
Note 2 to entry: The compartment is formed by two steel plates, welded together around their peripheries, where
the intervening cavity is filled with a liquid (de-gassed fluid).
3.4
anchor load cell
purpose-designed load cell with a centric passage to accommodate the anchor tendon
Note 1 to entry: See Figure 4.
Note 2 to entry: The tendon typically comprises a bar, strands or wires.
3.5
nominal range
range over which the load cell is calibrated
Note 1 to entry: Other terms which are used in practice are, for example, load range, nominal load, capacity, full-
scale capacity or measuring range.
Note 2 to entry: Outside of the nominal range, the load cell is not calibrated and therefore the measurements are
not reliable.
ISO 18674-8:2023(E)
3.6
over range
maximum load that can be applied on the load cell, without damaging the load cell
Note 1 to entry: Other terms which are used in practice are, for example, “overrange capacity” or “overload”.
4 Symbols and abbreviated terms
Symbol Name Unit
B smallest dimension in cross section of structural member m
D outer diameter m
o
F axial force acting in a member N
FS full scale -
H height m
P installation load N
a
P effective axial load N
e
F reaction force in the anchor head N
R
P axial load N
R pile toe resistance N
T
T temperature °C
t elapsed time s, min, h, d
z depth m
α angle between the tendon at the anchor head and the anchor axis degree
5 Instruments
5.1 General
5.1.1 A load cell can be either electric (see 5.2) or hydraulic (see 5.3).
NOTE Other types of load cells, such as mechanical or photo-elastic are not considered in this document.
5.1.2 The maximum load anticipated in the lifetime of the monitoring project plus a margin of 10 %
to 30 % shall not exceed the nominal range of the load cell after installation (see 6.1.1.7).
NOTE 1 Too large a margin reduces the accuracy of the measurements.
NOTE 2 The measurement in the lower end (5 % to 10 %) of the nominal range is often less accurate.
5.1.3 At the measuring location, the force acting in a structural member shall be transmitted through
the load cell via load distribution plates. Spherical distribution plates may be used to improve an aligned
load distribution.
NOTE See Figure 1 for an example of a spherical distribution plate.
ISO 18674-8:2023(E)
Key
1 concave plate
2 convex plate
3 PTFE fabric
Figure 1 — Spherical load distribution plate (example)
5.1.4 The load cell shall have a specified load bearing element.
EXAMPLE See 1 in Figure 2 and 2 to 4 in Figure 3.
5.1.5 The material of the load bearing element (e.g. 1 in Figure 2) of the cell should be mechanically
stable.
EXAMPLE Heat-treated steel grade S355J2+N according to Reference [4].
5.1.6 The influence of temperature on the load measurement shall be considered and documented.
Exposure of the load cell to direct sunlight or other heat sources should be avoided or minimised. The
load cells should be designed to minimize temperature errors.
NOTE 1 The readings of load cells are affected by temperature changes. The use of temperature-compensated
sensors decreases the influence of temperature changes on the measurements. Information for temperature
correction of the load cell are commonly provided by the manufacturer.
NOTE 2 Independent temperature measurements in the vicinity of the load cell assist in the evaluation of the
load measuring results.
NOTE 3 Temperature changes can also affect the loads within the structural members, see ISO 18674-1:2015,
5.3.1.
5.2 Electric load cells
5.2.1 Electric load cells should have features as shown in Figure 2.
NOTE The load bearing element is usually either a solid cylinder or a hollow cylinder, see 1 in Figure 2.
5.2.2 Cylindrical load bearing elements should have a height H to outer diameter D ratio within the
o
range of 0,1 ≤ H/D ≤ 2.
o
NOTE 1 H/D > 2 tends to decrease the stability of the load cell assembly.
o
NOTE 2 The quality of the measurements of load cells with low ratios of H/D can be more sensitive to
o
imperfections on alignment, placement and load distribution plates.
ISO 18674-8:2023(E)
a) Top view b) Side view
Key
D outer diameter of load bearing element (1) 3 O-ring
o
P load 4 electric sensor (here: full-bridge strain gauges)
H height of load bearing element (1) 5 electric cable
1 load bearing element (here: hollow cylinder) 6 control and readout unit
2 protective cylindrical cover 7 upper load distribution plate
8 lower load distribution plate
Figure 2 — Features of an electric load cell (example, see Reference [5])
5.2.3 The deformation of the load bearing element shall be measured by electrical sensors.
5.2.4 The sensor can be based on either strain gauge, piezo-electric, vibrating wire or capacitive
measuring principles, configured in such a way that the influence of eccentric loading is minimised.
NOTE 1 The influence of eccentric loading can be typically minimised by using multiple sensors spaced evenly
around the cylinder and at equal distance from the axis.
NOTE 2 The output signal of an electrical strain gauge load cell can depend on the power supply of the logging
device, when not properly designed.
5.3 Hydraulic load cells
5.3.1 Hydraulic load cells should have features as shown in Figure 3.
NOTE Elements 2, 3 and 4 of Figure 3 form a liquid-filled compartment. Any change in the magnitude of the
load P results in a change of the pressure of the liquid in the compartment (4 in Figure 3).
ISO 18674-8:2023(E)
Key
P load 4 liquid-filled compartment
1 upper load distribution plate 5 lower load distribution plate/bearing plate
2/3 load cell plates 6 pressure measuring unit (here: electric pressure
transducer)
Figure 3 — Features of a hydraulic load cell
5.3.2 The pressure measuring unit (6 in Figure 3) should be positioned as close as practically feasible
to the liquid-filled compartment.
NOTE An increased spacing between the liquid-filled compartment (4) and the pressure measuring unit (6)
results in a decreased stiffness of the load measuring system influencing the measurement.
5.3.3 The pressure measuring unit can be either a Bourdon gauge or an electric pressure transducer.
5.4 Instruments for specific applications
NOTE See Annex A.
5.4.1 Anchor load cells
5.4.1.1 Anchor load cells shall have an axial centric passage to accommodate the anchor tendon.
NOTE See Figures 1 and 4.
5.4.1.2 Anchor load cells can be of an electric (see 5.2) or hydraulic type (see 5.3).
5.4.1.3 At the measuring location, the anchor load shall be transmitted through the load cell via load
distribution plates. The load distribution plates shall be designed to withstand yielding at capacity load
and to limit distortions when distributing the load to the structure.
NOTE 1 See 7 and 8 in Figure 2 and 1 and 5 in Figure 3.
NOTE 2 Common are heat-treated steel load distribution plates of a H/D -ratio of about 0,22 to 0,30.
o
NOTE 3 The plate between the bearing element and the load cell (8 in Figure 2 and 5 in Figure 3) is commonly
referred to as bearing plate.
ISO 18674-8:2023(E)
5.4.1.4 The hole for feeding the anchor tendon through a load distribution plate shall be in the centre
of the plate.
5.4.1.5 For anchor tendons, spherical seats or wedges may be used to improve aligned load
distribution.
NOTE 1 See Figures 4 a) and b).
NOTE 2 Deviations from the perpendicular alignment between the load distribution plates and the anchor
tendon generate a force component which acts in transverse direction of the load cell. This effect, which affects
the accuracy of the anchor load measurement, cannot be avoided by a spherical nut or wedges, see 6.1.1.4 to
6.1.1.6.
a) Spherical seat for a bar tendon b) Wedges for two strand tendons
Key
1a nut 5 load bearing element 10 bearing plate
1b wedge 6 protection sleeve 11 ground surface
2a spherical seat 7 potting 12a bar tendon
2b head plate 8 electric sensor 12b strand tendon
3 upper load distribution plate 9 electric cable to readout 13 borehole wall
4 lower load distribution plate
Figure 4 — Schematic layout of anchor head devices for aligning different types of tendons
5.4.2 Load cell for cast-in-place concrete piles
5.4.2.1 When monitoring the performance of a cast-in-place concrete pile, a load cell may be located
at the toe of the pile. In this case, the layout of the load cell should be as in Figure 5.
NOTE 1 The load at the top of the pile is commonly measured by means of strain gauges, see Reference [1].
ISO 18674-8:2023(E)
NOTE 2 A load cell at the head or at another location between toe and head is commonly associated with
pile testing procedures where a load is actively applied and systematically varied and where the deformational
response of the pile is considered in dependency of the applied load.
NOTE 3 Outside of pile testing, the use of a load cell at the head of the pile is limited to situations where only
axial loads are expected during the lifetime of the pile, as the presence of the load cell can influence the load
transfer to the pile.
Key
1 hydraulic load cell embedded in (5)
2 weld ring
3 reinforcement cage
4 ring of compressible material
(e.g. synthetic rubber)
5 conical plug (e.g. mortar)
6 concrete/mortar bed
7 borehole wall
8 bottom of borehole
9 casing inner wall (where applicable)
Figure 5 — Schematic layout of a hydraulic load cell at the base of a cast-in-place concrete pile
(example, see Reference [6])
5.4.2.2 In case of a pile diameter greater than 1,00 m, an array of at least three load cells can be used.
Number and position (layout/geometry) of the load cells shall be designed to minimize eccentricity.
Distribution plates shall be designed to equally distribute the load into the load cells.
ISO 18674-8:2023(E)
5.5 Measurement accuracy
5.5.1 The measurement accuracy is predominately controlled by the design of the mounting devices,
the quality of the installation of these devices with regard to axiality (see 6.1.1.5) and eccentricity (see
6.1.1.6) and changes of the ambient temperature at the measuring location.
NOTE For strand tendons, the angle formed by the cables at the anchor head with respect to the anchor
axis produces a transverse effect that is absorbed by the (upper) distribution plate. The measured axial load
component is smaller than the actual strand load (see 7.4).
5.5.2 For anchor load cells, the central hole of the cell shall be large enough to avoid a contact of
the cell with the anchor tendon and, thus, the development of transverse loads to the cell resulting in
reduced overall accuracy and possible damage to the cell.
6 Installation and measuring procedure
6.1 Installation
6.1.1 General
6.1.1.1 Load cells should be installed concurrently with the structural member.
NOTE This simplifies the placement and alignment of the cells and the associated load distribution plates. It
also ensures a full record of the load history.
6.1.1.2 The forces shall be transmitted from the structural mem
...
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