ISO/TC 98 - Bases for design of structures

This document establishes the common vocabulary of the principal terms used in the field of reliability of structures and design actions used within ISO TC98 documents on bases for design of structures.

This document specifies general principles of risk assessment for systems involving structures. The focus is on strategic and operational decision-making related to design, assessment, maintenance and decommissioning of structures. This also includes formulation and calibration of related codes and standards. Systems involving structures can expose stakeholders at various levels in society to significant risks. The aim of this document is to facilitate and enhance decision-making with regard to monitoring, reducing and managing risks, and preparing for emergency in an efficient, cost-effective and transparent manner. Within the broader context of risk management, risk assessment provides decision-makers with procedures to determine whether or not, and in what manner, it is appropriate to treat risks. This document provides a general framework as well as a procedure for identifying hazards and estimating, evaluating and treating risks of structures and systems involving structures. This document also provides a basis for code writers as well as designers to set reasonable target-reliability levels, such as stated in ISO 2394, based on the result of risk considerations. For existing structures, it is intended that assessment of the risks associated with the events that were not considered in the original design or with changes in use be implemented according to the principles stated in this document. This document can also be used for risk assessment of exceptional structures upon specific adaptation and detailing, the design of which is not usually within the scope of existing codes.

Accidental actions can be subdivided into accidental actions with a natural cause and accidental actions due to human activities. This document applies to reliability based and risk informed decision making for the design and assessment of structures subject to accidental actions due to human activities. However, fires and human-made earthquakes are not included. The information presented in this document is intended for buildings and civil engineering works, regardless of the nature of their application and the use or combination of materials. The application of this document can require additional elements or elaboration in special cases. This document is intended to serve as a basis for those committees that are responsible for the task of preparing International Standards, national standards or codes of practice in accordance with given objectives and context in a particular country. Where relevant, it can also be applied directly to specific cases. This document describes how the principles of risk and reliability can be utilized to support decisions related to the design and assessment of structures subject to accidental actions and systems involving structures during all the phases of their service life. For the general principles of risk informed design and assessment, it is intended that ISO 2394 be considered. The application of this document necessitates knowledge beyond that which it contains. It is the responsibility of the user to ensure that this knowledge is available and applied.

This document provides the requirements for structural design and procedures following a semi-probabilistic approach that conform to the general principles for structural reliability as stipulated by ISO 2394. The scope of requirements and procedures are accordingly limited to the design of structures for which sufficient knowledge and experience are commonly available on design and construction practice to ensure that target levels of reliability account for the nature and consequences of structural failure. Situations outside these limitations are covered by ISO 2394. The methods that are included in this document are the semi-probabilistic limit states approaches that are proven to achieve sufficient and consistent levels of structural reliability. This document relies on standardized procedures for the characterization of the load bearing performance of the structures within its scope. Sufficient information is needed on uncertainties of design variables and models to be able to derive semi-probabilistic design measures for verification of structural reliability within the scope of this and the related design standards.

ISO 12494:2017 describes the general principles of determining ice load on structures of the types listed in this clause. In cases where a certain structure is not directly covered by this or another standard or recommendation, designers can use the intentions of this document. However, it is the user's responsibility to carefully consider the applicability of this document to the structure in question. The practical use of all data in this document is based upon certain knowledge of the site of the structure. Information about the degree of "normal" icing amounts (= ice classes) for the site in question is used. For many areas, however, no information is available. Even in such cases, this document can be useful because local meteorologists or other experienced persons should be able to, on the safe side, estimate a proper ice class. Using such an estimate in the structural design will result in a much safer structure than designing without any considerations for problems due to ice. CAUTION It is extremely important to design for some ice instead of no ice, and then the question of whether the amount of ice was correct is of less importance. In particular, the action of wind can be increased considerably due to both increased exposed area and increased drag coefficient. ISO 12494:2017 is intended for use in determining ice mass and wind load on the iced structure for the following types of structure: - masts; - towers; - antennas and antenna structures; - cables, stays, guy ropes, etc.; - rope ways (cable railways); - structures for ski-lifts; - buildings or parts of them exposed to potential icing; - towers for special types of construction such as transmission lines, wind turbines, etc. Atmospheric icing on electrical overhead lines is covered by IEC (International Electrotechnical Commission) standards. This document is intended to be used in conjunction with ISO 2394. NOTE Some typical types of structure are mentioned, but other types can also be considered by designers by thinking in terms of which type of structure is sensitive to unforeseen ice, and act thereafter. Also, in many cases, only parts of structures are to be designed for ice loads because they are more vulnerable to unforeseen ice than is the whole structure. Even if electrical overhead lines are covered by IEC standards, designers can use this document for the mast structures to overhead lines (which are not covered by IEC standards) if they so wish.

ISO 3010:2017 (including both the super structure and foundation) and other structures. ISO 3010:2017 is not applicable to certain structures, such as bridges, dams, geotechnical works and tunnels, although some of the principles can be referred to for the seismic design of those structures. ISO 3010:2017 is not applicable to nuclear power plants, since these are dealt with separately in other International Standards. In regions where the seismic hazard is low, methods of design for structural integrity can be used in lieu of methods based on a consideration of seismic actions. ISO 3010:2017 is not a legally binding and enforceable code. It can be viewed as a source document that is utilized in the development of codes of practice by the competent authority responsible for issuing structural design regulations. NOTE 1 This document has been prepared mainly for new engineered structures. The principles are, however, applicable to developing appropriate prescriptive rules for non-engineered structures (see Annex N). The principles could also be applied to evaluating seismic actions on existing structures. NOTE 2 Other structures include self-supporting structures other than buildings that carry gravity loads and are required to resist seismic actions. These structures include seismic force-resisting systems similar to those in buildings, such as a trussed tower or a pipe rack, or systems very different from those in buildings, such as a liquid storage tank or a chimney. Additional examples include structures found at chemical plants, mines, power plants, harbours, amusement parks and civil infrastructure facilities. NOTE 3 The level of seismic hazard that would be considered low depends not only on the seismicity of the region but also on other factors, including types of construction, traditional practices, etc. Methods of design for structural integrity include nominal design horizontal forces (such as an equivalent static loading determined from a simplified equivalent static analysis) which provide a measure of protection against seismic actions.

ISO 2394:2015 constitutes a risk- and reliability-informed foundation for decision making concerning design and assessment of structures both for the purpose of code making and in the context of specific projects.

ISO/TR 12930:2014 provides seismic design examples for geotechnical works based on ISO 23469:2005 in order to demonstrate how to use this ISO standard. The design examples are intended to provide guidance to experienced practicing engineers and code writers. Geotechnical works include buried structures (e.g. buried tunnels, box culverts, pipelines, and underground storage facilities), foundations (e.g. shallow and deep foundations, and underground diaphragm walls), retaining walls (e.g. soil retaining and quay walls), pile-supported wharves and piers, earth structures (e.g. earth and rock fill dams and embankments), gravity dams, tanks, landfill and waste sites.

ISO 4355:2013 specifies methods for the determination of snow load on roofs. It can serve as a basis for the development of national codes for the determination of snow load on roofs. National codes should supply statistical data of the snow load on ground in the form of zone maps, tables, or formulae. The shape coefficients presented in ISO 4355:2013 are prepared for design application, and can thus be directly adopted for use in national codes, unless justification for other values is available. For determining the snow loads on roofs of unusual shapes or shapes not covered by ISO 4355:2013 or in national standards, it is advised that special studies be undertaken. These can include testing of scale models in a wind tunnel or water flume, especially equipped for reproducing accumulation phenomena, and should include methods of accounting for the local meteorological statistics. Examples of numerical methods, scale model studies, and accompanying statistical analysis methods are described in ISO 4355:2013 (Annex G). The annexes of ISO 4355:2013 describing methods for determining the characteristic snow load on the ground, exposure coefficient, thermal coefficient, and loads on snow fences are for information only as a consequence of the limited amount of documentation and available scientific results. In some regions, single winters with unusual weather conditions can cause severe load conditions not taken into account by ISO 4355:2013. Specification of standard procedures and instrumentation for measurements is not dealt with in ISo 4355:2013.

ISO 13033:2013 establishes the means to derive seismic actions on nonstructural components and systems (NSCS) supported by or attached to new or existing buildings. It also provides procedures for the verification of NSCS seismic capacities. NSCS include architectural elements, mechanical and electrical systems, and building contents. ISO 13033:2013 is not a legally binding and enforceable code. It is a source document that is utilized in the development of codes of practice by the competent authority responsible for issuing structural design regulations. It is intended for application by regional and national standards committees when preparing standards for the seismic performance of NSCS. ISO 13033:2013 does not specifically cover industrial facilities, including nuclear power plants, since these are dealt with separately in other International Standards. However, the principles in ISO 13033:2013 can be appropriate for the derivation of seismic actions for NSCS in such facilities.

ISO 3898:2013 covers physical quantities in a general sense. The kernel-index-method enables to form (compound) symbols of physical quantities related to a particular material and/or a particular technical field of design of structures. It also gives the main names, symbols, and units for physical quantities within the field of design of structures.

ISO 13822:2010 provides general requirements and procedures for the assessment of existing structures (buildings, bridges, industrial structures, etc.) based on the principles of structural reliability and consequences of failure. It is based on ISO 2394. ISO 13822:2010 is applicable to the assessment of any type of existing structure that was originally designed, analysed and specified based on accepted engineering principles and/or design rules, as well as structures constructed on the basis of good workmanship, historic experience and accepted professional practice. The assessment can be initiated under the following circumstances: an anticipated change in use or extension of design working life; a reliability check (e.g. for earthquakes, increased traffic actions) as required by authorities, insurance companies, owners, etc.; structural deterioration due to time-dependent actions (e.g. corrosion, fatigue); structural damage by accidental actions (see ISO 2394). ISO 13822:2010 is also applicable to heritage structures provided additional considerations shown in Annex I are taken into account. ISO 13822:2010 is applicable to existing structures of any material, although specific adaptation can be required depending on the type of material, such as concrete, steel, timber, masonry, etc. ISO 13822:2010 provides principles regarding actions and environmental influences. Further detailed considerations are necessary for accidental actions such as fire and earthquake. ISO 13822:2010 is intended to serve as a basis for preparing national standards or codes of practice in accordance with current engineering practice and the economic conditions.

ISO 4354:2008 describes the actions of wind on structures and specifies methods of calculating characteristic values of wind loads for use in designing buildings, towers, chimneys, bridges and other structures, as well as their components and appendages. The loads are suitable for use in conjunction with ISO 2394 and other International Standards concerned with wind loads. In particular, ISO 4354:2008 facilitates the conversion between peak- and mean-wind-speed methodologies and covers the three main storm types, synoptic winds, thunderstorms and tropical cyclones (hurricanes and typhoons). ISO 4354:2008 provides the basic methods from which to determine wind loading analytically through the determination of design pressures or orthogonal along-wind and cross-wind forces and moments for structures of simple shape and wind directionality effects, and through wind tunnel or computational determinations of pressure, forces and moments for structures with complex shapes and wind directionality effects resulting in complex combinations of forces and moments. Two methods of analytical determination of design wind loads are given, one based on a peak velocity and the other on a mean velocity.

ISO 13823:2008 specifies general principles and recommends procedures for the verification of the durability of structures subject to known or foreseeable environmental actions, including mechanical actions, causing material degradation leading to failure of performance. It is necessary to insure reliability of performance throughout the design service life of the structure. Fatigue failure due to cyclic stress is not within the scope of ISO 13823:2008.

ISO 10137:2007 gives recommendations on the evaluation of serviceability against vibrations of buildings, and walkways within buildings or connecting them or outside of buildings. It covers three recipients of vibrations: human occupancy in buildings and on walkways; the contents of the building; the structure of the building. It does not include bridges that carry vehicular traffic, even in conjunction with pedestrian traffic, nor the design of foundations or supporting structures of machinery.

ISO 21650:2007 describes the principles of determining the wave and current actions on structures of the following types in the coastal zone and estuaries: breakwaters: rubble mound breakwaters; vertical and composite breakwaters; wave screens; floating breakwaters; coastal dykes; seawalls; cylindrical structures (jetties, dolphins, lighthouses, pipelines etc.). ISO 21650:2007 does not include breakwater layout for harbours, layout of structures to manage sediment transport, scour and beach stability or the response of flexible dynamic structures, except vortex induced vibrations. Design will be performed at different levels of detail: concepts; feasibility; detailed design. ISO 21650:2007 is aimed at serving the detailed design.

ISO 23469:2005 provides guidelines for specifying seismic actions for designing geotechnical works, including buried structures (e.g. buried tunnels, box culverts, pipelines, and underground storage facilities), foundations (e.g. shallow and deep foundations, and underground diaphragm walls), retaining walls (e.g. soil retaining and quay walls), pile-supported wharves and piers, earth structures (e.g. earth and rockfill dams and embankments), gravity dams, landfill and waste sites. The guidelines provided in ISO 23469:2005 are general enough to be applicable for both new and existing geotechnical works. However, for use in practice, procedures more specific to existing geotechnical works can be needed, such as those described for existing structures in ISO 13822.

Deals with pressure conditions in hoppers, bunkers, bins and silos constructed using normal structural engineering materials. For the purposes of definition, the term silo is used to represent all forms of storage. All parameters given shall be agreed with the client and written into all contract documents. Design of the silo shall be checked if any of the criteria given are changed.

Defines the actions due to the self-weight of structures, non-structural elements and stored materials and gives the numerical values of their densities. These actions are to be determined by multiplying the densities by the gravitational acceleration and by the actual volume. The actions caused by the weight of the earth placed on the structures are similarly calculated.

Fixes the equivalence of the principal terms used in the field of reliability of structures, in different languages (English, French, Russian and German). An annex contains approximate but simple definitions of, and commentary on, the terms listed, gives indications about their use and quotes the corresponding symbols and subscripts.

Indicates the lowest nominal values of loads due to use and occupancy in residential and public buildings. These values are the most unfavourable values for certain conditions of normal use of a building. Gives also the lowest nominal values of uniformly distributed loads, the reduction of uniformly distributed loads, and horizontal loads.

Establishes the basic principles that should be adopted when setting up national standards, regulations and recommendations for the deformation of buildings at the limit states of serviceability. Refers to the deformations at the serviceability limit states of buildings such as dwellings, offices, public buildings, and factories. Does not refer to the deformations of bridges, roads, masts, underground works, non-residential farm buildings, or special-purpose buildings such as atomic power stations or industrial plant.

Specifies methods of determining imposed floor loads to be adopted for certain functions of production buildings and warehouses, for design-calculation purposes. Indicates definitions, establishing of imposed floor loads, minimum imposed floor loads and reduction of imposed floor loads.

ISO 13824:2009 specifies general principles on risk assessment of systems involving structures. The focus is on strategic and operational decision-making related to design, assessment, maintenance and decommissioning of structures. This also includes formulation and calibration of related codes and standards. Systems involving structures can expose stakeholders at various levels in society to significant risks. The aim of ISO 13824:2009 is to facilitate and enhance decision-making with regard to monitoring, reducing and managing risks in an efficient, cost-effective and transparent manner. Within the broader context of risk management, risk assessment provides decision makers with procedures to determine whether or not and in what manner it is appropriate to treat risks. ISO 13824:2009 provides a general framework as well as a procedure for identifying hazards and estimating, evaluating and treating risks of structures and systems involving structures. ISO 13824:2009 also provides a basis for code writers as well as designers to set reasonable target-reliability levels, such as stated in ISO 2394, based on the result of risk considerations. For existing structures, assessment of the risks associated with the events that were not considered in the original design or with changes in use shall be implemented according to the principles stated in ISO 13824:2009. ISO 13824:2009 can also be used for risk assessment of exceptional structures, the design of which is usually beyond the scope of existing codes.

ISO 22111:2007 specifies the general requirements for the structural design of buildings and industrial and civil engineering structures using reliability-based concepts. ISO 22111:2007 is applicable to the design of complete structures, the structural elements making up the structure and the foundation. Information on the assessment of existing structures is given in ISO 13822.

Gives recommendations and covers three recipients of vibrations: a) human occupancy in buildings and on pedestrian bridges, b) the contents of the building, c) the structure of the building. Applies to buildings, pedestrian bridges and walkways found within buildings or connecting them.

Presents basic methods for the determination of seismic actions on structures. Specifies methods of evaluating seismic actions for the earthquake-resistant design of buildings, towers, chimneys, and similar structures. Most of the principles are applicable also to stuctures such as bridges, dams, harbour installations, tunnels, fuel storage tanks, chemical plants, conventional power plants excluding nuclear power plants.

Is intended to be a guideline for code-writers. Can be applied to the determination of unfavourable characteristic values of temperature difference due to temperature climatic actions which are taken into account in static analysis of structures for which the variation of temperature within the cross-section can be treated as linear. Is not applicable to massive structures (dams, retaining walls, tunnels, bridge piers ets.). For condideration of such structures it may be necessary to take into account non-linear distribution ot temperature through the body of the massive structural elements.

The different approaches to the drafting of International Standards resulted in a lack of uniformity in the technical content, and in the layout and sequence of the subject matter, of such documents. This Technical Report has, therefore, been prepared to create guidelines for the presentation of International Standards dealing with the design of structures.

Creates a common basis for the determination of actions for the verification of safety and serviceability of structures. Concers building and civil engineering structures whatever the nature of the material used. Covers terminology, classification and representation of actions, design values and combinations of actions.