scope:

General

This Dutch Code of practice provides guidance to assess whether:

a) buildings to be built are sufficiently earthquake-resistant,

b) existing buildings are sufficiently earthquake-resistant, and

c) existing buildings are sufficiently earthquake-resistant after having been strengthened.

This considers both the collapse of the entire building and the failure of individual structural elements, while also taking the foundation into consideration.

NOTE 1 Based on the definition of a building in the Dutch Housing Act (Woningwet), certain transformer houses, gas distribution stations, water distribution stations and sewage treatment plants are not buildings, even though they have four walls and a roof and are therefore perceived as buildings. A structure is not considered to be a building unless the construction forms a covered space, entirely or partially enclosed by walls, that is accessible to people. Because of the importance of infrastructure for the building-related environment, and even though this NPR is not intended to be applied to such structures which are formally defined as a 'structure other than a building', it is recommended that at least situation CC1b from Table 2.1 is adopted accordingly. If it concerns a facility whose failure has a significant impact on society, a higher CC class is to be recommended. This recommendation does not apply to other 'structures other than a building', such as bridges, towers, industrial plants etc.

The NPR is intended to be applied to all load-bearing structures of existing buildings and buildings to be built, regardless of the associated consequence classes. For ease of use, guidelines and instructions for the design of new building structures are included in Annex L. For load-bearing structures where human safety is not at stake, the assessment of seismic actions from the perspective of human safety is not considered necessary. The NPR is suitable for application to load-bearing structures of buildings produced of concrete, steel, composite steel and concrete, timber, masonry or a combination thereof. The principle of equivalence shall be applied to other construction methods.

This NPR distinguishes three levels of reliability, namely:

1) the level applicable to buildings to be built (including complete renovation of an existing building (rebuilt buildings));

2) the level applicable to renovation of existing buildings;

3) the level applicable in order to assess whether an existing load-bearing structure still satisfies a sufficient level of reliability in relation to human safety.

NOTE 2 For the background of these reliability levels, reference is made to the report [1.1], which is complementary to the report [1.2], which is complementary to the report [1.3].

This NPR focuses on the design or assessment of individual buildings. For structural safety, a semi-probabilistic approach is assumed, except for Annex F.

It is also possible to start from a fully probabilistic approach. This can be advantageous, for example, if large numbers of similar structures have to be assessed and also for the assessment of individual buildings.

This NPR exclusively deals with structural aspects. Cracking as a consequence of seismic actions can occur even if this NPR is used. Cracking plays a role when determining resistance to seismic actions.

NOTE 3 This NPR can also be used to test that the seismic resistance of non-structural elements that belong to the building is sufficient in relation to human safety. This can be determined similarly to individual non-seismic structural elements, as given in 4.3.6 of this NPR. The recommendations given for that purpose are not part of the technical building regulations.

NOTE 4 Other building-related (sub-surface) elements, such as gas pipes and data lines or sewers are not covered by the structural safety of the building and are therefore not included, despite potential (environmental) nuisance due to, for example, broken sewer drains or the probability of consequential damage by fire or health hazards due to faulty gas or flue pipes. Flexible passages of these parts with the structure are recommended.

This NPR is not intended for use in order to assess whether a load-bearing structure that was damaged by an earthquake, is able to withstand the legally prescribed loads, the 'disapproval' level according to NEN 8700, with adequate safety during its remaining life span. This NPR only focuses on the structural safety of a load-bearing structure before, during and immediately after an earthquake.

NOTE 5 According to Subclause 2.1.2 of the Dutch 2012 Building Decree (Bouwbesluit 2012), a building shall at least comply with the 'disapproval' level of NEN 8700. This shall also apply if a load-bearing structure is damaged after an earthquake, but the damage is not such that progressive collapse has occurred.

NOTE 6 The aim is that by using this NPR, based on the knowledge at the time of publication, such a reliability of the structure (structural safety) is reached that load-bearing structures assessed and adjusted on the basis of this NPR, in principle will not need to be reassessed and adjusted after a potential incorporation in the building regulations in the future. Future developments are also influenced by increasing knowledge and social developments.

NOTE 7 If ever the extent of the seismic actions becomes greater than the value assumed in this NPR, it will need to be evaluated whether additional provisions for the building are necessary.

This NPR is not sufficiently tailored to assessing monuments within the meaning of the Dutch Heritage Act (Erfgoedwet).

NOTE 8 This NPR exclusively deals with structural aspects. In addition to structural aspects, in some cases restrictions can apply under local requirements of external appearance or other statutory provisions, such as the Dutch Heritage Act [1.4]. Application of this NPR is no guarantee that a particular solution is actually allowed to be applied in any given situation.

NOTE 9 Pursuant to the Dutch Heritage Act, in the interest of preserving cultural heritage and in derogation of the provisions of the Dutch Housing Act, the authorities may issue a permit for altering a monument. The Dutch 2012 Building Decree provides that stipulations of the environmental permit concerning the adaptation of a monument prevail over the provisions of the environmental permit for building.

In principle, when choosing a solution for preserving monuments, any possibility between the following two extremes can be chosen:

a) An intervention where the monument is reversibly strengthened such that the requirement of the individual risk of 10 is fulfilled and furthermore no form of damage whatsoever due to an induced earthquake is accepted. When the period in which ground motions due to earthquakes can be expected has ended, the strengthening options will be undone to restore the original look of the monument.

b) Not implementing any strengthening interventions whatsoever, thus temporarily accepting an increased individual risk as well as possible damage during the period in which seismic ground motions can occur. The damage is repaired after this period.

In order to aid the authorities' decision-making as regards monuments, Annex K contains supporting information that can be consulted when making decisions.

NOTE 10 Given the importance of the management, maintenance and preservation of cultural heritage and of preventing unnecessary strengthening actions, the resistance of structural elements to earthquakes should be determined as accurately as possible, using as few conservative principles as possible. Non-linear analysis methods that have been validated against sufficiently relevant test results should preferably be used here.

When choosing between the various non-linear analysis programs that may be appropriate, it should be taken into consideration that:

- the information available as regards the construction method and the materials used to build the monument is often limited;

- carrying out destructive testing in a monument is generally not desired or not accepted.

More complex analysis methods may possibly lead to more accurate results, but the simpler analysis methods can be more appropriate in order to visualize the resistance to seismic actions using susceptibility analyses.

NOTE 11 Protected cityscapes and townscapes do not have monument status. The regulations that generally apply to buildings also apply to the structural safety of buildings in protected cityscapes and townscapes. However, the permit requirements and the building aesthetics requirements differ. The activities for which no permits are required are described in Article 4(2) of Annex II to the Dutch Environmental Law Decree (Besluit omgevingsrecht). This implies that the authorities (the municipality) can set conditions on the techniques to be used when reinforcing existing buildings, to the extent that they can affect the characteristic values.

The NPR includes an inspection protocol to determine the structural conditions under which, with the help of literature research, in-situ measurements, analysis and sample solutions, recommendations can be made for improvements to the load-bearing structure so that it becomes earthquake-resistant.