ISO/TR 6116:1981

TECHNICAL REPORT 6116
Published 1981-07-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION l MEXA’YHAPOAHAlI OPrAHM3AUMfi I-IO CTAHAAPTM3AWM l ORGANIZATION INTERNATIONALE DE NORMALISATION
Actions on structures
Actions sur /es structures
Technical Report 6116 was drawn up by Technical Committee ISO/TC 98, Bases for design of structures, and approved by the
majority of its members. The reason which led to the decision to publish this document in the form of a Technical Report rather than
an International Standard is the impact of the revision of IS0 2394, Generalprincl;oles for the verification of structures, undertaken by
TC 98. The future International Standard will be based partly on this Technical Report which will probably form an integral part of the
revised text of IS0 2394.
0 Introduction
This document which has been prepared as a contribution towards the revision of IS0 2394-1973, Genera/principles for the verifica-
tion of the safety of structures, is based on principles worked out by the Joint Committee on Structural Safety (JCSS), taking into ac-
count other relevant documents such as the CEB Model Code, CMEA Standards, etc. This document is published as a Technical
Report because it covers only some of the problems which enter into the content of IS0 2394, and because the rules for establishing
design values and combination values of actions given in this document are closely related to the principles of verification of structural
safety currently under review. The document points out the existence of divergences in approach between regional organizations on
standardization.
It is hoped to review and possibly transform this document into a standard after the agreement or the new version of IS0 2394 has
been reached.
During the preparation of this document care was taken to weigh off the physical and theoreti cal soundness versus clarity and
simplicity. The flexibility of the document which ensures its acceptability to all member bodies, is achieved by the introduction of a
large number of decision parameters. These are :
-
the reference period T and the probability of non-exceedance p for the characteristic values;
-
the partial safety coefficient vfU for the ultimate limit states;
-
the coefficients w0 and yfU for combination values;
-
the number rl of variable actions for fundamental combinations;
-
the fraction cl and the coefficient yfs for frequent values;
-
the fraction c2 and the coefficients yfU and yfs for quasi-permanent values;
-
the number r2 of variable actions for long-term combinations.
The adoption of these parameters and their numerical values are left to the discretion of national code committees. A proper calibra-
tion of decision parameters should be carried out for those rare situations which - for the sake of simplicity - do not appear explicity
in this document (service value and some rare combinations of actions for the serviceability limit states).
UQC 624.042 Ref. No. ISO/TR 6116-1981 (E)
Descriptors : civil engineering, buildings, sfrucfures, safety, mechanical strength.
@ international Organization for Standardization, 1981 @
Printed in Switzerland
Price based on 14 pages
lSO/TR 6116-1981 (E)
1 Scope and field of application
The aim of th is to create a common basis for the determination of actions for the verification of safety and serviceability
of structures.
The document concerns building and civil engineering structures whatever the nature of the material used.
2 Terminology
An action F is :
a) an assembly of concentrated or distributed forces acting on the structure (direct actions), or
the cause of imposed or constrained deformations in the structure (indirect actions).
b)
An action is considered to be one single action if it can be assumed as being stochastically independent, in time and space of any
other action acting on the structure.
NOTE - Actions, however, often occur simultaneously and they may be stochastically dependent to some extent. For the sake of calculation, it is
more convenient to treat them as single actions. The problem of stochastic dependence may be treated as a special case. To facilitate the calculation
of the action effects, it may be convenient to regroup several analogous elementary actions into one composite action or to resolve certain actions into
a sum or difference of several components.
Actions and their random variations should normally be established on the basis of reliable observations, tests, or from data supplied
of material, equipment, etc.
by manufacturers
Other sources of information, for example, judgement on the type of use, legal or physical constraints, may also be taken into
account.1).
3 Qualitative classification of actions
3.1 General considerations
Actions be classified according to the variation of their ma gnitude with time and/or space, or according to the effects of the ac-
may
tions on the structure (static or dynamic).
NOTE - Actions may be further classified according to other criteria.
Classification of actions according to the variation of their magnitude with time
3.2
according to their variation in time - into :
Actions are divided -
3.2.4 Permanent actions, G, which are likely to act throughout a given design situation2) and for which variation in magnitude
with time are negligible in relation to the mean value; or those for which the variation is in one sense and the actions attain some
limiting values.
The permanent actions include :
the weight of structures themselves (except possibly certain parts of this weight during certain phases of construction);
a)
the weight of superstructures when appropriate;
b)
C) the forces applied by earth pressure, resulting from the weight of soil;
the deformations imposed by the mode of construction of the structure;
d)
1) In existing documents, values obtained within this group of information are described as “nominal values”.
cture i is generally necessary to consider seve It-al distinct design si tuations, for example consecutive stages of construction, normal
2) For any s tru
is required for each design si tuation.
use, changes in use, a C cidents etc. Separate safety checking
lSO/TR 61164981 (E)
e) the actions resulting from shrinkage of concrete, and distortions due to welding;
the forces resulting from water pressure when appropriate;
f)
the actions resulting from support settlements and mining subsidence;
9)
h) prestressing forces.
3.2.2 v tions, Q, which are unlikely to act throughout a given design situation or for variations in magnitude
‘ariable ac
time a re not negiigi bie in relation to the mean value.
The variable actions include :
loads due to use and occupancy;
a)
certain parts of the weight of structures themselves during certain phases of construction;
b)
cl erection loads;
ail moving loads and their effects;
wind loads;
e)
f) snow loads;
ice formation;
9)
earthquakes’);
h)
the effects of variable level of water surface, when appropriate;
k) temperature changes;
wave loads.
ml
materials it is usefu I to disting uish between actions of long and short duration, depending upon the behaviour of the
For some
structure on which they are acting.
which, in any given structure and with a significant
3.2.3 Act idental actions, &, the occurence of value, is unlikely for a period of
time under conside ration.
in the total population of structures only a limited number of structures will be exposed to an accidental action,
The accidental actions include :
collisions;
a)
explosions;
b)
subsidence of su bsoii;
cl
tornados in regions not normally exposed to them;
d)
e) earthquakesI);
f) fire;
extreme erosion.
9)
1) Earthquakes may be considered either as a variable action or as an accidental action.

lSO/TR 6116-1981 (E)
3.3 Classification of actions according to their variation in space
Actions are divided - according to their variation in space - into two groups :
magnitude of the action is unambiguously
fixed ac tions, which have a fixed, spatial distribution over the structure, so that the
a)
point;
de termined for the whole structure if it is given for one
free actions, which may have arbitrary spatial distribution over the structure within given limits.
b)
Actions cannot be defined as belonging to either of these two groups may be considered as consisting of a fixed part and a free
part.
is determined
The treatme nt of free ac tions consideration of different cases. A load case by fixing the configuration of
each of the free actions.
NOTE - In some cases it is necessary to distinguish fixed actions and actions which are movable or act in a probabilistic way at certain points or on
certain parts of structures. In such cases and in the absence of a more detailed study, it is generally agreed that such actions are separated into dif-
ferent elementary actions; those applied to points or parts recognized, a priori, as the most unfavourable, and those applied to other parts.
3.4 Classification of actions according to the structural response
According to the way in which the structure responds to an action it is distinguished between :
to the structure without causing significant acceleration of the structure or structural
a) static actions, which are applied
member;
dynamic actions, which cause significant acceleration of the structure.
b)
Whether or not the action is regarded as a dynamic one is thus dependent on the structure.
dynamic effects which depend on the behaviour of the structure,
NOTE - For simplification, dynamic actions may be often treated as static actions,
nto account by an appropriate increase in the magnitude of actions.
being taken i
Quantitative representation of actions
4.1 Representative values
An action is specified by its representative value. Each action may have several representative values. The main representative value is
the characteristic value of an action. Representative values may also be used to study the effects resulting from frequent or long-term
application of an action (frequent and quasi-permanent values). Other representative values may be values for a combination of ac-
tions (combination values). it is also possible, in the alternative approach, instead of using these combination values, to modify the
safety factors (see 4.3.4).
The characte ristic value E;( of an ac tion is a value with an accepted probability p of not being exceeded towards unfa
vourabie values
during some reference per ,iod, havi ar .d to the in ten ded life of the structure and to the duration of the design situation
w w
action may have two teristic ower. In
in some cases an charac values : upper and I cases where the effect of a reduction in the action is
for the the mor *e unfavourabie.
more da ngerous structure, the lower values should be taken as
4.2 Representative values of permanent action, G
Ail representative values of permanent actions, G, are in general assumed to be equal to the characteristic values.
structures themselves is re prese nted, in general, by a unique value calculated from the drawings of the pro-
a) The weight, G,, of
ject and the mean unit weight of the materials;
represented, where a riate, by two values, upper and lower,
The weight of non -structural elements may be assessed
b) PProP bY
unt ail variations which are reason ably foreseeable.
tak ing in to acco
ts are
NOTE - For many structu res, on ly the maximum values of weight of non-structural elemen relevant for design.
The minimum value of the weight of certain non-structural elements is l often taken as zero.
ISO/TR 61164981 (E)
cl The actions of earth pressure are in the present state of knowledge represented in the same manner, as in b) above.
NOTE - For many structures, only the maximum value of the active earth pressure, and the minimum value of the passive earth pressure, are
relevant for design.
d) The actions of pre-stress may be represented by two characteristic values, an upper and a lower; both values depend on the
time elapsed since pre-stressing .
The deformations imposed by the mode of construction of the structure and by shrinkage, are normally represented by unique
e)
values.
NOTE - However, the shrinkage varies with time, and the action of shrinkage during a certain interval of time may be represented by taking into
account the values calculated at the beginning and the end of this interval of time.
The actions due to settlement and mining subsidence are represented by two values, an upper and a lower which is often zero.
f)
NOTE - Support settlement is generally a composite action representing the global effect of the settlements of various supports. Mining sub
sidence is generally a succession, sometimes complex, of several forces or imposed deformations. Consideration should be given to possible dif-
ferential settlement which may be positive or negative.
Representative values of the variable actions
4.3
Representative values of the variable actions may be, in general, ail those given in 4.1.
4.3.1 Characteristic values, Qk, of variable actions are determined by the general definition given in 4.1.
If an action satisfies certain conditions of stability, the probability p of non-exceedance during the reference period (see 4.1) may be alter-
NOTE -
natively expressed by the corresponding return period (mean return period).
Various statistical procedures for determination of characteristic values may be used. One example of such a procedure is given in annex A.
For certain actions dependent on use, the characteristic values may be taken as those values which the users are expected not to ex-
4.3.2 The representative frequenty value
The frequenty value cyl Fk of a variable action may be determined so that the total duration T1 of its exceedance constitutes a small
1) of the reference period T;
portion cl
A value of an action, which has a significant number of occurences but a value of cl below the specified one, should nevertheless be
taken as the frequenty value. The same applies for a value which is exceeded frequently, regardless of numerical value of the coeffi-
cient c’~.
4.3.3 The representative quasi-permanent value
The quasi-permanent value ly2 F’k of a variable action may be determined so that the total duration T2 of its exceedance constitutes a
large portion c2 2) of the reference period T :
T2 = c2 T
For many types of actions where the relevant data are available (for example, stationary normal processes), this is equivalent to the condition :
I)
w1 Fk = 4m + k, $-J
instanta neous of the action, k, is a coefficient dependin g on the chosen of C’,
where q,,., a nd sq are the mean a nd standard deviation of the
. The value of c, may be taken, for example, as 0,05.
(see annex B)
For many types of actions this is equivalent to the condition :
2)
w2 p;k = 4m + k, 3’q
> 05 the coefficient k, is in most cases negative.
Usually, the value of c2 will be taken as equal to or greater than 0,5. For c’~

ISO/TR 6116-1981 (E)
4.3.4 The representative combination value
< 1) takes account of the reduced probability of simultaneous appearance o
...