Robustness is the ability of a structure to withstand events like fire, explosions, impact or the consequences of
human error
Human error refers to something having been done that was " not intended by the actor; not desired by a set of rules or an external observer; or that led the task or system outside its acceptable limits".Senders, J.W. and Moray, N.P. (1991) Human ...
, without being damaged to an extent disproportionate to the original causeas defined in EN 1991-1-7 of the Accidental Actions
Eurocode.
A structure
designed and
constructed to be robust should not suffer from
disproportionate collapse (progressive collapse) under accidental loading.
Buildings of some kinds, especially
large-panel systems and
precast concrete
Precast concrete is a construction product produced by casting concrete in a reusable molding (process), mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples i ...
buildings, are disproportionately more susceptible to collapse; others, such as
in situ cast concrete structures, are disproportionately less susceptible. The method employed in making a structure robust will typically depend on and be tailored to the kind of structure it is, as in
steel frame
Steel frame is a building technique with a "skeleton frame" of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame. The developm ...
d building structural robustness is typically achieved through appropriately designing the system of connections between the frame's constituents.
Design considerations
Three alternative measures are used, sometimes jointly, to achieve structural robustness and reduce the risk of disproportionate collapse.
These are:
* Reducing the possibility of occurrence of accidental loading.
* Preventing the propagation of a possible initial failure and increasing redundancy. Which includes the indirect method and the alternative load path method.
* Designing the structure to withstand accidental loading. Sometimes referred to as specific load resistance method.
Robustness requirements in Eurocodes
The requirements for structures in consequence classes 2 and 3 can be found in
EN 1991-1-7 Eurocode 1 - Actions on structures - Part 1-7: General actions - Accidental actions. Additional requirements and requirements for structures in consequence class 1 can be found in the material specific Eurocode parts,
EN 1992
In the Eurocode series of European standards (EN) related to construction, '' Eurocode 2: Design of concrete structures'' (abbreviated EN 1992 or, informally, EC 2) specifies technical rules for the design of concrete, reinforced concrete and pre ...
for concrete structures,
EN 1993
En or EN may refer to:
Businesses
* Bouygues (stock symbol EN)
* Esquimalt and Nanaimo Railway (reporting mark EN, but now known as Southern Railway of Vancouver Island)
* Euronews, a news television and internet channel
Language and writing
* E ...
for steel structures and so on.
In EN 1991-1-7 buildings are categorised in consequences classes, considering the building type, occupancy and size.
Consequence class 1, low consequences of failure:
*Single occupancy houses not exceeding 4 storeys.
*Agricultural buildings.
*Buildings into which people rarely go, provided no part of the building is closer to another building, or area where people do go, than a distance of 1.5 times the building height.
Consequence class 2a, lower risk group - medium consequences of failure:
*5 storey single occupancy houses.
*Hotels not exceeding 4 storeys.
*Flats, apartments and other residential buildings not exceeding 4 storeys.
*Offices not exceeding 4 storeys.
*Industrial buildings not exceeding 3 storeys.
*Retail premises not exceeding 3 storeys of less than 1000 m² floor area in each storey.
*Single storey educational buildings.
*All buildings not exceeding two storeys to which the public are admitted and which contain floor areas not exceeding 2000 m² at each storey.
Consequence class 2b, upper risk group - medium consequences of failure:
*Hotels, flats, apartments and other residential buildings greater than 4 storeys but not exceeding 15 storeys.
*Educational buildings greater than single storey but not exceeding 15 storeys.
*Retail premises greater than 3 storeys but not exceeding 15 storeys.
*Hospitals not exceeding 3 storeys.
*Offices greater than 4 storeys but not exceeding 15 storeys.
*All buildings to which the public are admitted and which contain floor areas exceeding 2000 m² but not exceeding 5000 m² at each storey.
*Car parking not exceeding 6 storeys.
Consequence class 3, high consequences of failure:
*All buildings defined above as Class 2 Lower and Upper Consequences Class that exceed the limits on area and number of storeys.
*All buildings to which members of the public are admitted in significant numbers.
*Stadia accommodating more than 5000 spectators.
*Buildings containing hazardous substances and / or processes.
For buildings intended for more than one type of use, the consequences class should be that of the most onerous type.
Buildings in consequence class 1 should be designed and constructed in accordance with EN 1990 - 1999 for satisfying stability in normal use, no specific consideration (required by EN 1991-1-7) is necessary with regard to accidental actions from unidentified causes.
Buildings in consequence class 2a (in addition to what is recommended for consequence class 1) should be provided with effective horizontal ties, or effective anchorage of suspended floors to walls.
Buildings in consequence class 2b (in addition to what is recommended for consequence class 1 and 2a) should be provided with effective vertical ties in all supporting columns and walls, or alternatively the building should be checked to ensure that upon the notional removal of each supporting column and each beam supporting a column, or any nominal section of load-bearing wall (one at a time in each storey of the building) the building remains stable and the local damage does not exceed a certain limit. Where the removal of such columns and sections of walls would result in an extent of damage in excess of the agreed limit, such elements should be designed as a key element.
For buildings in consequence class 3 a systematic risk assessment of the building taking into account both foreseeable and unforeseeable hazards, is required.
See also
*
Extreme Loading for Structures
Extreme Loading for Structures (ELS) is commercial structural-analysis software based on the applied element method (AEM) for the automatic tracking and propagation of cracks, separation of elements, element collision, and collapse of structure ...
*
List of structural failures and collapses
This is a list of structural failures and collapses, including bridges, dams, and radio masts/towers.
Buildings and other fixed human-made structures
Antiquity to the Middle Ages
17th–19th centuries
1900–1949
1950-1979
1980–2000 ...
*
Structural failure
Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load (weight, force, etc.) without breaking and includes the study of past structural failures in order to ...
References
External links
EN 1991-1-7 Eurocode 1 - Actions on structures - Part 1-7: General actions - Accidental actionsSCI P391 Structural Robustness of Steel Framed BuildingsPractical guide to structural robustness and disproportionate collapse in buildingsDesign of precast concrete structures with regard to accidental loading Ir. Arnold Van AckerHow to design concrete buildings to satisfy disproportionate collapse requirements O Brooker BEng, CEng, MICE, MIStructEPortland Cement Association Structural Integrity Requirements for Concrete BuildingsReview of international research on structural robustness and disproportionate collapseStructural-Safety Incorporating CROSS and SCOSS
{{Authority control
Structural engineering
Safety engineering
Structural steel
Concrete
Infrastructure
Civil engineering