scope:

Scope and applicability

General

This Dutch Code of practice provides guidance to assess whether:

a) new to be build buildings that are 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 reinforced.

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 new to be built buildings, regardless of the associated consequence classes. 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 new to be build buildings (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 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 reinforced 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 reinforcement options will be undone to restore the original look of the monument.

b) Not implementing any reinforcement 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 reinforcement actions, the resistance of structural elements to earthquakes should be determined as accurately as possible, using as few conservative principles as possible. Nonlinear analysis methods that have been validated against sufficiently relevant test results should preferably be used here.

When choosing between the various nonlinear 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 city or townscapes do not have monument status. The regulations that generally apply to buildings also apply to the structural safety of buildings in protected city 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.

Starting points of the NPR

General

This NPR establishes the principles, rules of application and assessment methods for assessing reliability under seismic actions.

This NPR is designed to be used to determine and to demonstrate the structural reliability for:

a) buildings (new to be build and buildings that are to be completely renovated, in conjunction with the standards NEN-EN 1990 to NEN-EN 1999);

b) the partial renovation of an existing building (in conjunction with the standards NEN 8700 and NEN 8701), and

c) the determination of the disapproval level of existing load bearing structures (in conjunction with the standards NEN 8700 and NEN 8701).

The scope of this NPR is limited to the northern part of the Netherlands as far as induced earthquakes arise there due to gas extraction from the Groningen gas field.

Safety philosophy

The safety philosophy is the core of any discussion regarding the reliability of structures, also in relation to seismic resistance. Within the context of this NPR, it has been established what economic and social impact may be considered as acceptable and which reliability indices and safety parameters and factors belong to it, differentiated between new to be build buildings, reconstruction and disapproval.

The safety philosophy behind this NPR, in terms of procedure and choices, is consistent with the principles that have been used in NEN 8700 for existing load bearing structures and in NEN-EN 1990 for new load bearing structures. Where the nature of the seismic actions requires specific choices to be made, this has been indicated. The basic premise is a maximum acceptable individual risk of 10^-5 per year.

NOTE 1 The Dutch 2012 Building Decree refers to the above standards.

NOTE 2 If the assessment of the resistance of a building against seismic actions demonstrates that the maximum acceptable individual risk of 10^-5 per year has not been met, it cannot be concluded that the building will immediately collapse during the next earthquake. For the background of the safety philosophy (including probability theory), reference is made to the report [1.1], which complements [1.2], which complements the report [1.3].

NEN-EN 1998 series of standards (Eurocode 8)

This NPR introduces the first steps towards the National Annexes to Eurocode 8.

NOTE The NEN-EN 1998 series has been developed for the design and assessment of load bearing structures under seismic actions by the joint national standardization bodies, united in the European Committee for Standardization (CEN). This series of standards includes National Annexes which enable the nationally desired reliability level to be established by establishing 'Nationally Determined Parameters' (NDPs) and possibly adding national Non-Contradictory Complementary Information (NCCI). These National Annexes have not been established for the Netherlands.

NEN 8700

NEN 8700 is not yet tailored towards the assessment of buildings against seismic actions. This NPR can be seen as a first step towards the necessary adaptations of NEN 8700 related to seismic actions.

NOTE NEN 8700 is intended to be applied to the assessment of existing buildings, both the state of an unchanged building and the reconstruction thereof (i.e.: partial renewal, modification or extension). NEN 8700 is consistent with the Eurocodes that apply to new to be build buildings and to the complete renewal of buildings. Based on the Dutch 2012 Building Decree, reconstruction projects where structural interventions are implemented, are assessed by assessing bodies according to NEN 8700.

Legal unit

When assessing a building for seismic actions, the legal unit shall have been established unambiguously.

Pursuant to the Dutch 2012 Building Decree, houses or holiday homes not situated in a residential building or a guest accommodation building may rely on each other for stability.

NOTE 1 See the Dutch 2012 Building Decree, 2.4(3) and 2.8(2).

NOTE 2 For existing buildings, it should be derived from the permit that was originally issued, what the legal unit is for the assessment of structural safety.

NOTE 3 As a rule, if the legal unit has several owners, there will be a homeowners' association.

Building phase

A safe work environment should be ensured during the building phase. Therefore the structural safety should have been considered at an individual risk level during the building phase, related to the structures functioning in that phase.

NOTE 1 During the building phase, the client and the employer are under the obligation to ensure a safe working environment pursuant to the Dutch Civil Code on the one hand and Dutch Occupational Safety and Health legislation on the other. Although this risk is not quantified in legislation, it is generally taken to be higher than that stipulated in building regulations, but not lower than 10^-4 a year. That is why a seismic action with a return period of 475 years may be assumed for the building stage or the reconstruction stage. When viewed from the Dutch Heritage Act (Erfgoedwet), a return period longer than 475 years may be needed for the building stage or the reconstruction stage. Temporary reinforcement structures may be needed in order to achieve the minimum safety required during the building phase.

NOTE 2 The provisions of NOTE 1 also apply in case of Article 8.2 of the Dutch 2012 Building Decree.