EUROPEAN PRESTANDARD ENV 1991-2-7 - ULisboaweb.ist.utl.pt/guilherme.f.silva/EC/EC1 - Actions on...

EUROPEAN PRESTANDARD ENV 1991-2-7PRÉNORME EUROPÉENNEEUROPÄISCHE VORNORM

______________________________________________

English version

EUROCODE 1 : Basis of designand actions on structures

Part 2-7 : Accidental actions due to impact and explosions

Final Draft June 1998

CEN

European Committee for StandardizationComité Européen de NormalisationEuropäisches Komitee für Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels_____________________________________________________________© CEN 1998 Copyright reserved to all CEN membersRef.No ENV 1991-2-7:1998

ENV 1991-2-7:1998

Contents Page

FOREWORD............................................................................................................................ 4

1 GENERAL ............................................................................................................................ 7

1.1 SCOPE .................................................................................................................................................7

1.2 NORMATIVE REFERENCES ..................................................................................................................8

1.3 DISTINCTION BETWEEN PRINCIPLES AND APPLICATION RULES ........................................................10

1.4 DEFINITIONS .....................................................................................................................................10

1.5 SYMBOLS ..........................................................................................................................................11

2 CLASSIFICATION OF ACTIONS.................................................................................. 12

3 DESIGN SITUATIONS..................................................................................................... 13

3.1 DEFINITION OF ACCIDENTAL DESIGN SITUATIONS AND ACCIDENTAL ACTIONS................................13

3.2 DESIGN FOR ACCIDENTAL SITUATIONS.............................................................................................13

4 IMPACT.............................................................................................................................. 16

4.1 FIELD OF APPLICATION .....................................................................................................................16

4.2 REPRESENTATION OF ACTIONS .........................................................................................................16

4.3 ACCIDENTAL ACTIONS CAUSED BY VEHICLES ..................................................................................17

4.4 ACCIDENTAL ACTIONS CAUSED BY RAIL TRAFFIC UNDER BRIDGES OR NEAR OTHER STRUCTURES .21

4.5 ACCIDENTAL ACTIONS CAUSED BY SHIPS.........................................................................................22

4.6 ACCIDENTAL ACTIONS CAUSED BY HELICOPTERS ............................................................................25

5 EXPLOSIONS ..................................................................................................................... 26

5.1 FIELD OF APPLICATION .....................................................................................................................26

5.2 REPRESENTATION OF ACTIONS .........................................................................................................26

5.3 EXPLOSIONS IN ROOMS WITH VENTING PANELS ...............................................................................26

ANNEX A (INFORMATIVE) ADVANCED IMPACT DESIGN...................................... 28

A.1 GENERAL ........................................................................................................................................28

A.2 IMPACT DYNAMICS .........................................................................................................................28

A.3 IMPACT FROM TRUCKS AND LORRIES..............................................................................................29

A.4 IMPACT BY TRAINS...........................................................................................................................32

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ANNEX B (INFORMATIVE) EXPLOSIONS .................................................................... 34

B.1 GENERAL..........................................................................................................................................34

B.2 STRUCTURES IN CATEGORY 3 .........................................................................................................34

B.3 DUST EXPLOSIONS ..........................................................................................................................34

B.4 EXPLOSIONS IN TUNNELS.................................................................................................................36

ANNEX C (INFORMATIVE) ADDITIONAL GUIDANCE FOR DESIGN ................... 38

C.1 ACCEPTABLE LOCALISED DAMAGE IN BUILDINGS ...........................................................................38

C.2 SIMPLIFIED ANALYSIS FOR CATEGORY 2 STRUCTURES IN BUILDINGS .............................................38

C.3 PREVENTIVE AND PROTECTIVE MEASURES AGAINST RAIL TRAFFIC UNDER BRIDGES........................ 38

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Foreword

Objectives of the Eurocodes

(1) The "Structural Eurocodes" comprise a group of standards for the structural andgeotechnical design of buildings and civil engineering works.

(2) They cover execution and control only to the extent that is necessary to indicate the qualityof the construction products and the standard of the workmanship needed to comply with theassumptions of the design rules.

(3) Until the necessary set of harmonised technical specifications for products and formethods of testing their performance are available, some of the Structural Eurocodes coversome of these aspects in informative annexes.

Background to the Eurocode programme

(4) The Commission of the European Communities (CEC) initiated the work of establishing aset of harmonised technical rules for the design of buildings and civil engineering workswhich would initially serve as an alternative to the different rules in force in the variousmember states and would ultimately replace them. These technical rules became known as the"Structural Eurocodes".

(5) In 1990, after consulting their respective member states, the CEC transferred the work offurther development, issue and updating of the Structural Eurocodes to CEN, and the EFTASecretariat agreed to support the CEN work.

(6) CEN Technical Committee CEN/TC250 is responsible for all Structural Eurocodes.

Eurocode programme

(7) Work is in hand on the following Structural Eurocodes, each generally consisting of anumber of parts:

EN 1991 Eurocode 1 Basis of design and actions on structures

EN 1992 Eurocode 2 Design of concrete structures

EN 1993 Eurocode 3 Design of steel structures

EN 1994 Eurocode 4 Design of composite steel and concrete structures

EN 1995 Eurocode 5 Design of timber structures

EN 1996 Eurocode 6 Design of masonry structures

EN 1997 Eurocode 7 Geotechnical design

EN 1998 Eurocode 8 Design of structures for earthquake resistance

EN 1999 Eurocode 9 Design of aluminium alloy structures

(8) Separate Sub-Committees have been formed by CEN/TC250 for the various Eurocodeslisted above.

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(9) This Part of Eurocode 1 is being published as a European Prestandard (ENV) with aninitial life of three years.

(10) This Prestandard is intended for experimental application and for the submission ofcomments.

(11) After approximately two years CEN members will be invited to submit formal commentsto be taken into account in determining future actions.

(12) Meanwhile feedback and comments on this Prestandard should be sent to the Secretariatof CEN/TC250/SC1 at the following address:

SIS / BSTBox 490 44S- 100 28 StockholmSWEDEN

or to your National Standards Organisation.

National Application Documents (NADs)

(13) In view of the responsibilities of authorities in member countries for safety, health andother matters covered by the essential requirements of the Construction Products Directive(CPD), certain safety elements in this ENV have been assigned indicative values which areidentified by or [ ] (“boxed values”). The authorities in each member country areexpected to review the "boxed values" and may substitute alternative definitive values forthese safety elements for use in national application.

(14) Some of the supporting European or international standards may not be available by thetime this Prestandard is issued. It is therefore anticipated that a National ApplicationDocument (NAD) giving any substitute definitive values for safety elements, referencingcompatible supporting standards and providing guidance on the national application of thisPrestandard, will be issued by each member country or its Standards Organisation.

(15) It is intended that this Prestandard is used in conjunction with the NAD valid in thecountry where the building or civil engineering works is located.

Matters specific to this Prestandard

(16) The scope of Eurocode 1 is defined in clause 1.1.1 and the scope of this Part of Eurocode1 is defined in clause 1.1.2. Additional Parts of Eurocode 1 which are planned are indicated inclause 1.1.3.

(17) This Part is complemented by three informative annexes.

(18) Accidental actions are described in different parts of Eurocode 1. In particular, ENV1991-3 includes accidental actions due to impact on structural elements of bridges. In therelevant sections of ENV 1991-3 design values are listed, which have to be taken into accountfor the design situations of impact.

This Part and ENV 1991-3 are consistent with regard to the design values.

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(19) Design situations endangered by accidental actions may be categorised. Thecategorisation may follow national traditions and preferences. The categorisation will be amatter for relevant authorities.

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Section 1 General

1.1 Scope

1.1.1 Scope of ENV 1991 - Eurocode 1

(1)P ENV 1991 provides general principles and actions for the structural design of buildingsand civil engineering works including some geotechnical aspects and shall be used inconjunction with ENVs 1992-1999.

(2) It may also be used as a basis for the design of structures not covered in ENVs 1992-1999and where either other materials or other structural design actions are involved.

(3) ENV 1991 also covers structural design during execution and structural design fortemporary structures. It relates to all circumstances in which a structure is required to giveadequate performance.

(4) ENV 1991 is not directly intended for the structural appraisal of existing construction, indeveloping the design of repairs and alterations or for assessing changes of use.

(5) ENV 1991 does not completely cover special design situations which require unusualreliability considerations, such as nuclear structures, for which specified design proceduresshould be used.

1.1.2 Scope of ENV 1991-2-7 Accidental actions due to impact and explosions

(1)P This Part describes the possible safety strategies in case of general accidental situationsand it covers in detail the accidental actions due to impact and internal explosions.Consideration of accidental actions described in this Part includes actions caused by humanactivities but excludes actions arising from external explosions, warfare and sabotage. Also,this Part does not refer to some events, which are generally considered as accidents, but whichdo not result in structural damage (e.g. persons falling through roof claddings).

(2) Accidental actions arising from the natural phenomena such as tornadoes, extreme erosionor falling rocks are not included. However, they may be incorporated in design usingprinciples similar to those contained in this Part.

(3)P Structures exposed to fire shall be designed in accordance with ENV 1991-2-2 "Actionson structures exposed to fire" in conjunction with the relevant fire design Parts of ENVs 1992to 1996 and ENV 1999.

(4)P Structures exposed to seismic events shall be designed according to ENV 1998"Earthquake resistant design of structures".

(5)P This Part defines the general principles that can be used in the analysis of accidentaldesign situations and describes:

– the procedure for a risk analysis to identify extreme events, the causes and consequencesof undesired events;

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– the safety precautions required to maintain a safety level which complies with theacceptance criteria, by using adequate measures to reduce the probability or theconsequences of the extreme events.

(6) In particular this Part specifies:

– recommended design models for the most common cases of accidental actions arisingfrom impact and explosions;

– detailing provisions which may be used as alternatives to design verifications.

(7) Accidental actions given in Section 4 are related to impacts and collisions from thefollowing sources:

– vehicles;

– derailed trains;

– ships;

– the hard landing of helicopters on roofs.

(8) Three informative annexes are included :

– Annex A describes an advanced impact design concept;

– Annex B includes an advanced explosion design concept;

– Annex C gives additional guidance for design.

1.1.3 Further Parts of ENV 1991

(1) Further Parts of ENV 1991 which, at present, either are being prepared or are planned, aregiven in clause 1.2.

1.2 Normative references

(1) This European Prestandard incorporates by either dated or undated reference, provisionsfrom other standards. These normative references are cited in the appropriate places in the textand are listed below.

ISO 3898 1987 Basis of design for structures Notations.General symbols.

ISO DP 10252 Accidental actions due to human activities.

ISO 6184-a Explosion protection systems - Part 1: Determination of explosion indices of combustible dusts in air.

UIC SC 7J Report 777/2R (May 1996): Structures built over railway lines.

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NOTE: The following European Prestandards which either are published or are inpreparation are cited at the appropriate places in the text and are listed below.

ENV 1991-1 Eurocode 1 : Basis of design and actions on structuresPart 1 : Basis of design

ENV 1991-2-1 Eurocode 1 : Basis of design and actions on structuresPart 2.1 : Densities, self-weight and imposed loads

ENV 1991-2-2 Eurocode1 : Basis of design and actions on structuresPart 2.2 : Actions on structures exposed to fire

ENV 1991-2-3 Eurocode 1 : Basis of design and actions on structuresPart 2.3 : Snow loads

ENV 1991-2-4 Eurocode 1 : Basis of design and actions on structuresPart 2.4 : Wind loads

ENV 1991-2-5 Eurocode 1 : Basis of design and actions on structuresPart 2.5 : Thermal actions

ENV 1991-2-6 Eurocode 1 : Basis of design and actions on structuresPart 2.6 : Actions during execution

ENV 1991-3 Eurocode 1 : Basis of design and actions on structuresPart 3 : Traffic loads on bridges

ENV 1991-4 Eurocode 1 : Basis of design and actions on structuresPart 4 : Actions in silos and tanks

ENV 1991-5 Eurocode 1 : Basis of design and actions on structuresPart 5 : Actions induced by cranes and machinery

ENV 1992 Eurocode 2 : Design of concrete structures

ENV 1993 Eurocode 3 : Design of steel structures

ENV 1994 Eurocode 4 : Design of composite steel and concrete structures

ENV 1995 Eurocode 5 : Design of timber structures

ENV 1996 Eurocode 6 : Design of masonry structures

ENV 1997 Eurocode 7 : Geotechnical design

ENV 1998 Eurocode 8 : Earthquake resistant design of structures

ENV 1999 Eurocode 9 : Design of aluminium alloy structures

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1.3 Distinction between principles and application rules

(1) Depending upon the character of the individual clauses, distinction is made in this Part 2-7of ENV 1991 between principles and application rules.

(2) The principles comprise:

– general statements and definitions for which there is no alternative, as well as;

– requirements and analytical models for which no alternative is permitted unlessspecifically stated.

(3) The principles are identified by the letter P following the paragraph number.

(4) The application rules are generally recognised rules which follow the principles and satisfytheir requirements.

(5) It is permissible to use alternative rules different from the application rules given in thisEurocode, provided it is shown that the alternative rules accord with the relevant principlesand have at least the same reliability.

(6) In this Part 2-7 of ENV 1991 the application rules are identified by a number in brackets,e.g. as this clause.

1.4 Definitions

For the purposes of this Prestandard, a basic list of definitions is provided in ENV 1991-1;and the additional definitions given below are specific to this Part of ENV 1991.

1.4.1 Accidental actions: Action, usually of short duration, which is unlikely to occur witha significant magnitude over a period of time under consideration during the design workinglife.

1.4.2 Explosion: Rapid chemical reaction of dust or gas in air. It results in hightemperatures and high overpressures. Explosion pressures propagate as pressure waves.

1.4.3 Deflagration: Explosion where the continuation of the chemical reaction is caused bythe transport of heat. The flame front travels through the mixture at a subsonic speed, in theorder of 100 m/s. The pressure waves travel with the local speed of sound. Peak pressurevalues may vary from 10 to 1 500kN/m2.

1.4.4 Detonation: Explosion where the continuation of the chemical reaction is caused by apressure shock wave travelling at a supersonic speed generally more than 1 000 m/s. Atypical value for the pressure is 2 000 kN/m2 but the peak duration is very short (10 ms).

1.4.5 Key element: An element of the structure, essential for the overall stability of thestructure, the failure of which would cause disproportionate damage and/or collapse of thestructure.

1.4.6 Risk: Risk is expressed in terms of possible consequences of the event and theassociated probability.

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1.4.7 Risk reducing measures: Risk reducing measures consist of measures to reduce theprobability of the accident and measures to reduce the consequence, including contingencyplans, of an accident.

1.4.8 Hazard scenarios: Events caused by natural phenomena or human activities whichmay endanger the structural safety. A hazard scenario is characterised by one predominantaction.

1.5 Symbols

(1) For the purpose of this Prestandard, the following symbols apply.

NOTE: The notation used is based on ISO 3898:1987.

(2) A basic list of notations is provided in ENV 1991-1, ”Basis of design” and the additionalnotations below are specific to this Part.

Latin upper case letters

Av the area of venting components

F impact or collision force

Fd,x horizontal static equivalent impact load in direction of normal travel

Fd,y horizontal static equivalent impact load perpendicular to the direction of normal travel

V Volume of room

W weight of a loaded truck

Latin lower case letters

d diameter or equivalent diameter

f friction coefficient

h height

l length

m mass

p probability

pd nominal equivalent static pressure

pv uniformly distributed static pressure

r a multiplication factor

s distance

Greek lower case letters

αQ adjustment factor

θ angle of hit

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Section 2 Classification of actions

(1)P According to ENV 1991-1 "Basis of design" actions arising from impact and explosionsshall be classified as accidental actions.

(2) For these accidental actions the representative value is generally a design value. Thespecifications of the models for determining the design values are given in Section 4 forimpacts and Section 5 for explosions respectively.

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Section 3 Design situations

3.1 Definition of accidental design situations and accidental actions

(1)P In the accidental design situation, as defined in ENV 1991-1, the occurrence ofexceptional events and corresponding accidental actions shall be considered, in combinationwith permanent and variable loads. Additionally, in some cases it may be necessary toconsider also the period of time shortly after the occurrence of the exceptional event.

(2) The actions in the case of accidental design situations are usually actions with a lowprobability of occurrence, which have severe consequences and are usually of short duration.

(3)P The selected design situations shall be sufficiently severe and varied as to encompass allconditions which can be reasonably foreseen to occur during the execution and use of thestructure. In this case "which can be reasonably foreseen" shall be interpreted as "which havea low but reasonable probability of occurrence.

(4) A severe possible consequence requires the consideration of extensive hazard scenarios,while less severe consequences allow less extensive hazard scenarios. Consequences may beassessed in terms of injury and death to people, unacceptable change to the environment, largeeconomic losses for the society, and so on.

NOTE 1: ISO DP 10252 "Accidental Actions due to Human Activities" specifies thatthe representative value of an accidental action should be chosen in such a way thatthere is an assessed probability less than p = 10-4 per year for one structure that this or ahigher impact energy will occur. However, only in some cases can the probability ofoccurrence of an accidental action and the probability distribution of its magnitude bedetermined from statistics and risk analysis procedures. Design values in practice areoften nominal values.

NOTE 2: In some cases accidental actions and variable actions may originate from thesame sources of action. For instance, this may be the case for impact from ships, wherea ship out of control may be the source of an accidental action, whereas actions fromfendering and mooring of ships are variable actions. Similar examples may be found forcars in garages.

(5) Sequences of accidental events are not within the scope of this Part.

3.2 Design for accidental situations

(1)P Accidental actions shall be accounted for, when specified, in the design of a structuredepending on:

– the possible consequences of damage to the structure;

– the probability of occurrence of the initiating event;

– the provisions taken for preventing or reducing the dangers involved and the exposure ofthe structure;

– the level of acceptable risk.

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(2)P No structure can be expected to resist all actions that could arise due to an extreme cause,but there shall be a reasonable probability that it will not be damaged to an extentdisproportionate to the original cause.

NOTE: In practice, the occurrence and consequences of accidental actions can beassociated with a certain risk level. If this level cannot be accepted, additional measuresare necessary. A zero risk level, however, will only seldom be reached and in most casesit is necessary to accept a certain level of residual risk. This final risk level will bedetermined by the cost of safety measures weighed against the perceived public reactionafter an accident. The risk should also be based on a comparison with risks generallyaccepted by society in comparable situations. In defining the acceptable risk levels theRelevant and National Authorities play an important role.

(3) Localised damage due to accidental actions may be acceptable, provided that it will notendanger the whole structure or that the loadbearing capacity is maintained during anappropriate length of time for necessary emergency measures to be taken, for instanceevacuation of the building and its surroundings.

(4) Measures to control the risk in the case of accidental actions may pursue as appropriateone or more of the following strategies:

– preventing the action from occurring or reducing to a reasonable level the probabilityand/or magnitude of the action;

– protecting the structure against the effects of an action by reducing the actual loads on thestructure (e.g. protective bollards);

– designing in such a way that neither the whole structure nor a significant part of it willcollapse if a local failure (e.g. single element failure) occurs;

– designing key elements, on which the structure is particularly reliant, with special care,and for appropriate accidental actions;

– applying minimum prescriptive design/detailing rules which in normal circumstancesprovide an acceptably robust structure (e.g. three-dimensional tying for additionalresistance, or minimum level of ductility of structural elements subject to impact);

– providing additional prescriptive design/detailing rules in order to obtain the residualstability requisite for a safe evacuation of the occupants;

– applying the principles of capacity design (examples: limiting strength of parapets onbridges to avoid damage to the main structural system or installing venting componentswith a low mass and strength to reduce the effect of explosions);

– providing measures to mitigate the consequences of structural failure.

In the structural design the presence of preventive and protective measures should be regardedas design assumptions (see ENV 1991-1, ”Basis of design”, clause 1.3).

NOTE 1: Strategies may be mixed in the same design procedure. Prescriptive rules areprovided in the relevant ENVs 1991 to 1999.

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NOTE 2: The limited effect of preventing actions must be recognised; it is dependentupon factors which, over the life span of the structure, are commonly outside the controlof the structural design process. The responsibility of the maintenance of the preventivemeasures is often a matter for the relevant authority.

(5) Accidental design situations may be categorized as follows:

– Category 1 Limited consequences;

– Category 2 Medium consequences;

– Category 3 Large consequences.

For facilitating the design of certain types of structures it might be appropriate to treat someparts of the structure as belonging to a different category from the overall structure. Thismight be the case for parts that are structurally separated and differ in exposure andconsequences.

NOTE: The categorization may follow national traditions and preferences, and theactual categorization will be a matter for the relevant authorities.

(6) The different categories may be considered in the following manner:

– Category 1 : no specific consideration is necessary with regard to accidental actions;

– Category 2 : depending upon the specific circumstances of the structure in question: asimplified analysis by static equivalent action models may be adopted or prescriptivedesign/detailing rules may be applied;

– Category 3 : a more extensive study recommended, using dynamic analyses, non-linearmodels and load structure interaction if considered appropriate.

NOTE: The effect of preventive and/or protective measures is that the probability ofdamage to the structure is reduced. For design purposes this can sometimes be takeninto consideration by assigning the structure to a lower category class. In other areduction of forces on the structure may be more appropriate.

(7) In this standard, Section 4 includes values which may be used in analyses for accidentalimpacts, and Section 5 deals with gas explosions.

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Section 4 Impact

4.1 Field of application

(1) The actions presented in this section should be applied to those structural elements or, ifappropriate, to their protection systems where the consequences of failure in thecorresponding design situations are considered to be in the categories 2 and 3 as defined inSection 3.

NOTE: The design of structures in Category 3 may also consider the use of other morerigorous types of analysis as described in Annex A. These analyses may be expected togive different results.

(2) This section defines actions due to impact for:

– collisions from vehicles;

– collisions from trains;

– collisions from ships;

– the hard landing of helicopters on roofs.

(3) Buildings to be considered are parking garages, buildings in which vehicles are driven,warehouses in which forklift trucks are driven and buildings that are located in the vicinity ofeither road or railway traffic.

(4) For bridges the actions due to impact to be considered depends upon the type of trafficunder and over the bridge.

(5) Actions due to impact from helicopters need to be considered only for those buildingswhere the roof contains a designated landing pad.

4.2 Representation of actions

(1)P The impact process is determined by the mass distribution, deformation behaviour,damping characteristics and initial velocities of both the impacting body and the structure. Tofind the forces at the interface, the object and the structure shall be considered as oneintegrated system.

(2)P When defining the material properties of the impacting body and of the structure, upperor lower characteristic values shall be used, when appropriate; additionally, strain rate effectsshall be taken into account, when appropriate.

(3)P Actions due to impact shall be considered as free actions. The areas where actions due toimpact need to be considered shall be specified individually depending on the cause.

(4) For structural design purposes the actions due to impact may be represented by anequivalent static force giving the equivalent action effects in the structure. This simplifiedmodel may be used for the verification of static equilibrium or for strength verifications,depending on the protection aim.

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(5) For structures which are designed to absorb impact energy by elastic-plastic deformationsof members, the equivalent static loads may be determined by considering both plasticstrength and deformation capacity of such members.

(6) For structures for which the energy is mainly dissipated by the impacting body, equivalentstatic forces may be taken from clauses 4.3 to 4.6.

4.3 Accidental actions caused by vehicles1

4.3.1 Actions from vehicle traffic under bridges or other structures

(1) In the case of hard impact, design values for the horizontal actions due to impact onvertical structural elements (e.g. columns, walls) in the vicinity of various types of roads maybe obtained from Table 4.1.

Table 4.1: Horizontal static equivalent design forces due to impact on supportingsubstructures of bridges or other structures over roadways

Type of road Type of vehicle Force Fd,x

(kN)

Force Fd,y

(kN)

motorway

urban area

courtyards

parking garages

truck

truck

passenger cars only

trucks

passenger cars only

[1 000]

[500]

[50]

[150]

[40]

[500]

[250]

[25]

[75]

[25]

NOTE 1: x = direction of normal travel, y = perpendicular to the direction of normaltravel.

NOTE 2: The values in the table are applicable to normally exposed structuralelements; in special cases for category 3 types of structures a more advancedanalysis as indicated in Annex A might be more appropriate. In particular Annex Agives information on design velocities, duration of the loads and the effect of thedistance from the road to the structural element.

(2) The forces Fd,x and Fd,y need not be considered simultaneously.

(3) For car impact on vertical members the resulting collision force F on the structure shouldbe applied at 0,5 m above the level of the driving surface (see Figure 4.1). The forceapplication area may be taken as 0,25 m (height) by 1,50 m (width) or the member width,whichever is the smaller.

1 The statements in this clause are compatible to those in ENV 1991-3, clause 4.7. It is envisaged that the clausesrelating to impact in ENV 1991-3 will be deleted when it is converted to an EN.

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(4) For impact from trucks and lorries on vertical members the resulting collision force F onthe structure should be applied at 1,25 m above the level of the driving surface (see Figure4.1). The force application area is 0,5 m (height) by 1,50 m (width) or the member width,whichever is the smaller.

(5) Actions due to impact loads from trucks and lorries on horizontal structural elementsabove traffic lanes need only be considered, when minimum values for clearances or othersuitable protection measures to avoid impact are not provided.

(6) In case where verifications of static equilibrium or strength or deformation capacity arerequired for impact loads from trucks on horizontal structural elements above traffic lanes, thefollowing rules may be applied (see Figure 4.2):

– on vertical surfaces the design impact loads are equal to those given in Table 4.1,multiplied by a factor r (see Figure 4.3);

– on the under side surfaces the same impact loads as above with an upward inclination of10o should be considered.

NOTE 1: The values may depend upon national legal limits and/or other localcircumstances such as other bridges above the same road.

NOTE 2: Information on the effect of the distance s can be found in Annex A.

The force application area may be taken as 0,25 m (height) by 0,25 m (width).

(7) For buildings where fork lift trucks are present on a regular basis, a horizontal staticequivalent design force F = 5W, where W is the weight of a loaded truck, should be taken intoaccount at a height of 0,75 m above floor level.

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Figure 4.1: Collision force on structural elements near traffic lanes

Fh

h

d riving d ire c tio n

F

10 10

Figure 4.2: Collision force on horizontal structural elements above traffic lanes

1.50 m or member width whichever is the smallest

Direction of travel

ds

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r

h

h

F

0,5

6,0 m

0,0

5,0 m

Figure 4.3: Value of the factor r for collision forces on horizontal structural elementsabove traffic lanes, depending on the free height h

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4.3.2 Actions from vehicles on the bridge

4.3.2.1 Collision forces on safety barriers2

(1) For structural design, a horizontal vehicle collision force transferred to the bridge deck byrigid safety barriers 100 kN should be applied acting transversely and horizontally 100 mmbelow the top of the barrier or 1,0 m above the level of the carriageway or footway, whicheveris lower.

This force should be applied on a line 0,5 m long. The vertical traffic load actingsimultaneously with the collision force should be taken as 50 % of the characteristic axle load,including the adjustment factor αQ, as specified in ENV 1991-3.

4.3.2.2 Collision forces on structural members

(1) The vehicle collision forces on vertical structural end members above carriageway levelsare the same as specified in 4.3.1.(1) and are given in Table 4.1.

4.4 Accidental actions caused by rail traffic under bridges or near other structures

(1) Design values for the horizontal static equivalent forces due to impact on verticalstructural elements (e.g. columns, walls) for various design situations are given in Table 4.2.

Table 4.2 : Horizontal static equivalent design forces due to impact on supportingsubstructures of bridges or other structures over railways

Distance s from structural elementsto the centreline of the nearest track

(m)

Force Fd,x

(kN)

Force Fd,y

(kN)

continuous walls s < 3 m [0] [1500]

non-continuous walls s < 3 m first element: [10 000]other elements [4 000]

first element : [3 500]other elements: [1 500]

3 m ≤ s ≤ 5 m [4 000] [1 500]

s > 5 m [0) [0]

NOTE : x = track direction, y = perpendicular to track direction

2 See also, when available, technical approvals or standards established by CEN/TC 226.

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(2) The horizontal static equivalent design forces, given in Table 4.2 are applicable forsituations where the maximum permitted line speed is less or equal to 120 km/h. For speedsabove 120 km/h, the values of the horizontal static equivalent design forces together withadditional preventative and/or protective measures should be determined.

(3) If the maximum permitted line speed is lower or equal to 50 km/h, the forces in Table 4.2may be multiplied by 0,5.

(4) The forces Fd,x and Fd,y should be applied at a level of 1,8 m above track level and neednot be considered simultaneously. The impact area should be taken as 1 m high by 2 m wide.

(5) For supports which are situated within solid platforms or surrounded by a solid plinth atleast 0,55 m above top of the rail, the equivalent loads allocated may be reduced by half.

(6) For end walls a design force of Fdx = 5 000 kN for passenger trains and Fd,x= 10 000 kN for shunting and marshalling trains should be taken into account. These forces should beapplied at a level of 1,0 m above track level.

(7) Impact on the superstructure (deck structure) due to rail traffic under a bridge need not beconsidered. Rail traffic under a bridge may be assumed to impact the substructure only.

4.5 Accidental actions caused by ships

(1) The characteristics to be considered for collisions from ships depend upon the type ofwaterway, the type of vessels and their impact behaviour and the type of the structures andtheir energy dissipation characteristics. The types of vessels that can be expected should beclassified according to standard ship characteristics, see Tables 4.3 and 4.4.

(2) In case more accurate calculations are not carried out and the energy dissipation of thestructure can be neglected, the static equivalent forces according to Tables 4.3 and 4.4 may beapplied.

NOTE: Information on the duration of the load can be found in Annex A.

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Table 4.3: Ship characteristics and corresponding nominal horizontal static equivalent design forces for inland waterways

CEMT1)

classLength l

(m)

Mass m

(ton)

Reference Massof freight m

(ton)

Force Fd

(kN)I 30-50 200-400 300 [4 000]II 50-60 400-650 500 [5 000]III 60-80 650-1 000 800 [6 000]IV 80-90 1 000-1 500 1 300 [7 000]Va 90-110 1 500-3 000 2 300 [11 000]Vb 110-180 3 000-6 000 4 600 [15 000]VIa 110-180 3 000-6 000 2 300 [11 000]VIb 110-190 6 000-12 000 4 600 [15 000]VIc 190-280 10 000-18 000 6 900 [22 000]VII 300 14 000-27 000 6 900 [22 000]1) CEMT : European Conference of Ministers of Transport, classificationproposed 19 June 1992, approved by the Council of European Union 29October 1993.

Table 4.4: Ship characteristics and corresponding nominal horizontalstatic equivalent design forces for sea waterways

Class of ship Length l(m)

Mass m(ton)

Force Fd

(kN)small 50 3 000 [15 000]medium 100 10 000 [25 000]large 200 40 000 [40 000]very large 300 100 000 [80 000]

NOTE : The forces given correspond to a velocity of about 2,0 m/s.

(3) In harbours the forces given in Tables 4.3 and 4.4 may be reduced by a factor of 0,5.

(4) Bow, stern and broad side impact should be considered where relevant; for side and sternimpact the forces given in Tables 4.3 and 4.4 may be multiplied by a factor of 0,3 .

(5) Bow impact should be considered for the main sailing direction with a maximum deviationof 30o.

(6) If a wall structure is hit at an angle θ, the following forces should be considered:

– perpendicular to the wall: Fd,y = Fd sin θ (4.1)

– in wall direction: Fd,x = f Fd sin θ (4.2)

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where:F is the collision force at θ = 90°;

f is the friction coefficient, f = 0,4.

(7) The point of impact depends upon the geometry of the structure and the size of the vessel.As a guideline the most unfavourable impact point may be taken as ranging from 0,05l belowto 0,05l above the design water levels (see Figure 4.4). The impact area is 0,05l high and 0,1lbroad, unless the structural element is smaller (l = ship length).

(8) The forces on a structure depend upon the height of the structure and the type of ship to beexpected. In general the force on the superstructure of the bridge will be limited by the yieldstrength of the ships’ superstructure. A maximum of 10 percent of the bow impact force maybe considered as a guideline.

Figure 4.4 : Possible impact areas for ship collision

(9) Under certain conditions it might be necessary to consider the possibility that the ship islifted by an abutment or foundation block and collides with columns on top of them.

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4.6 Accidental actions caused by helicopters

(1) If the roof of a building has been designated as a landing pad for helicopters, a heavyemergency landing force should be considered, the vertical static equivalent design forcebeing equal to:

F A md = (4.3)

where:

A is 100 kN·ton-0.5;

m is the mass, in tons.

(2) The force due to impact should be considered to act on any part of the landing pad as wellas on the roof structure within a maximum distance of 7 m from the edge of the landing pad.The area of impact may be taken as 2 × 2 m2.

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Section 5 Explosions

5.1 Field of application

(1)P Design situations classified as Category 1 : No specific consideration of the effects of anexplosion is necessary other than complying with the rules for connections and interactionbetween components provided in ENV 1992 to ENV 1999.

(2)P Design situations classified as Category 2 or 3 : key elements of the structure shall bedesigned to resist actions either using analysis based upon equivalent static load models or byapplying prescriptive design/detailing rules.

(3) For structures in Category 3 it is recommended to consider the use of dynamic analysis asdescribed in Annex B.

5.2 Representation of actions

(1) In this context an explosion is defined as a rapid chemical reaction of dust or gas in air. Itresults in high temperatures and high overpressures. Explosion pressures propagate aspressure waves.

(2) The pressure generated by an internal explosion depends primarily on the type of gas ordust, the percentage of gas or dust in the air and the uniformity of gas or dust air mixture, thesize and shape of the enclosure in which the explosion occurs, and the amount of venting orpressure release that may be available.

NOTE: In completely closed rooms with infinitely strong walls, gas explosions may leadto pressures up to 1 500 kN/m² and dust explosions up to 1 000 kN/m², depending onthe type of gas or dust. In practice, pressures generated are much lower due to imperfectmixing and the venting which occurs due to failure of doors, windows, etc.

(3) To reduce confined explosion pressures and to limit the consequences of explosions thefollowing guidelines may be applied :

– use of venting panels with defined venting pressures;

– separation of sections of the structure with explosion risks from other sections;

– limiting the area of sections with explosion risks;

– dedicated protective measures between sections with explosion risks from other sectionsto avoid explosion and pressure propagation.

5.3 Explosions in rooms with venting panels

(1) Generally, there are many variable or unknown parameters, some outside the designer’scontrol, making the effective estimating and modeling of the effects of an explosion complexand inexact.

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(2) In Category 2, for a single room event, an equivalent static load model analysis of keyelements of a structure may be carried out using either the procedures described in 5.3(3) or5.3(4).

(3) Each key element and its connections should be designed to withstand a notionalaccidental static pressure of design value pd= 20 kN/m², applied from any direction,together with any reaction which could be expected to be directly transmitted to the memberby an attached building component which is also subjected to the same pressure.

(4) Key elements are designed to withstand the effects of an internal natural gas explosionusing a nominal equivalent static pressure given by:

pd= 3 + pv (5.1)

or

pd = 3 + pv/2+0,04/(Av/V)² (5.2)

whichever is the greater,

where:

pv is the uniformly distributed static pressure at which venting components will fail, in (kN/m²);

Av is the area of venting components, in square metres;

V is the volume of room, in cubic metres.

The ratio of the area of venting components and the volume are valid as in (5.3):

0,05 (1/m) ≤ Av/V ≤ 0,15 (1/m) (5.3)

The expressions (5.1) and (5.2) are valid in a room up to 1 000 m³ total volume.

The explosive pressure acts effectively simultaneously on all of the bounding surfaces of theroom.

NOTE 1: Where building components with different pv values contribute to the ventingarea, the largest value of pv is to be used.

(5) Paragraphs 5.3.(3) and 5.3.(4) apply to buildings which have provision of natural gas orwhich may have this provision in future, on the basis of which a natural gas explosion may beconsidered the normative design accidental situation. For design of buildings where provisionof natural gas is totally impossible, a reduced value of the equivalent static pressure pd may beappropriate. Key elements should have adequate robustness to resist other design accidentalsituations, see Section 3.

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Annex A (Informative)

Advanced impact design

A.1 General

(1) Advanced design for accidental actions due to impact may include one or several of thefollowing aspects:

– dynamic effects;

– non-linear material behaviour;

– probabilistic aspects;

– analysis of consequences;

– economic optimisation of mitigating measures.

(2) In the absence of quantification of consequences and economical optimisation, a failureprobability of 10-4 per year seems to be appropriate for accidental actions.

NOTE: For variable actions the exceedance probability, according to ENV 1991-1 isΦ(-αβ) = Φ(-0,7 × 3,8) = Φ(-2,7) = 0,003 for a reference period of 50 years. Thiscorresponds to a probability of 0,6×10-4 per year.

A.2 Impact dynamics

(1) Impact is an interaction phenomenon between the object and the structure. To find theforces at the interface, object and structure should be considered as one integrated system.

(2) Approximations, of course, are possible, for instance by assuming that the structure is rigidand immovable and the colliding object can be modelled as a equivalent elastic continuousrod (see figure A.1). In that case the maximum resulting interaction force and the duration ofthe loading are given by:

F v k mr= (A.1)

∆t m k= / (A.2)

where:

vr is the object velocity at impact;

k is the equivalent elastic stiffness of the object = EA/l;

m is the mass of colliding object = ρAl;

l is the length of the rod;

A is the cross sectional area;

E is the module of elasticity;

ρ is the mass density of the rod.

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The shape of the force due to impact is a block function; if relevant a rise time can be applied(see Figure A.1).

(3) Expression (A.1) gives the maximum force value on the outer surface of the structure.Inside the structure these forces may give rise to dynamic effects. An upperbound for theseeffects can be found if the structure is assumed to behave elastically and the load is conceivedas a step function. In that case the dynamic amplification factor ϕdyn is 2,0. If the pulse natureof the load is taken into account, calculations will lead to amplification factors ϕdyn rangingfrom below 1,0 up to 1,8, depending on the dynamic characteristics of the structure and theobject. However, in general, it is recommended to use non-linear dynamic analysis todetermine with the loads specified in this annex.

Figure A.1 : Impact model

A.3 Impact from trucks and lorries

(1) In the absence of a detailed analysis the probability of a structural element beingapproached by a truck or lorry which has left its lane may be assumed to be 0,01 per year. Thetarget failure probability for a structural element, given a truck or lorry approaching in itsdirection, therefore is 10-4/10-2 = 0,01.

(2) Given a truck or lorry approaching a structural element and the target failure probabilityaccording to A.3.(1) the design force Fd may be derived from:

( )( )P mk v as Fr d2 2 0 01− >

= , (A.3)

where:

a is the deceleration of the truck after leaving the track;

s is the distance from the point where the truck leaves its track to the structural element, see Figure 4.1.

For the other variables, see (A.1) and (A.2).

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Notional probabilistic information for the basic variables partly based on statistical data andpartly on engineering judgement is given in Table A.1.

(3) Based on the data and targets in this section the following design value for the force due toimpact can be determined:

F F s sd 0 br= −1 / (A.4)

where:

F0 is the collision force

sbr is the braking distance.

Values are presented in Table A.2. This table also presents the design values for m and v. Adeviation from the lane direction of 30 degrees may be adopted for the truck or lorry afterbraking.

(4) In the absence of a dynamic analysis the dynamic amplification for the elastic responsemay be put equal to 1,4.

Table A.1 : Notional data for probabilistic collision force calculation

variable designation probabilitydistribution

mean value standarddeviation

v vehicle velocity-highway-urban area-courtyard-parking house

lognormallognormallognormallognormal

80 (km/h)40 (km/h)15 (km/h) 5 (km/h)

10 (km/h) 8 (km/h) 5 (km/h) 5 (km/h)

a deceleration lognormal 4 (m2/s) 1,3 (m/s2)m vehicle mass truck normal 20 (ton) 12 (ton)m vehicle mass car - 1 500 (kg) -k vehicle stiffness deterministic 300 (kN/m) -

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Table A.2 : Design values for mass, velocity and collision force F0

type of road massm

velocityv

decelerationa

collision forcebased on (A.1)

F0

brakingdistance

sbr

(kg) (km/h) (m/s2) (kN) (m)

motorway 30 000 90 3 2 400 90

urban area 30 000 50 3 1 300 40

courtyards– only passengercars– also trucks

1 50030 000

2015

33

120 400

5 5

parking garages– only passengercars

1 500 10 3 90 4

NOTE: The values in this table are significantly higher than the values in Table 4.1 ofthe main text; if, however, the structure is analysed using non-linear dynamic models,the required structural dimensions will often be of the same order.

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A.4 Impact by trains

(1) Reference is made to UIC SC 7J report 777/2 R (May 1996) with title : STRUCTURESBUILT OVER RAILWAY LINES (Construction requirements in the track zone)

A.5 Impact by ships

(1) If data about types of ships, traffic intensities, error probability rates and sailing velocitiesare known, a design force Fd may be found from (see Figure A.2):

P F F nT p x P v x y k m F f y x y( ) = (1- ) ( ) [ ( , ) ( ) > ] ( )d dd s> d a r∫ ∫ = −λ 10 4 Erreur! Les arguments du com

where:

vr(x,y) is the impact velocity of the ship, given error or mechanical failure at point (x,y);

k is the equivalent stiffness of the ship;

m is the mass of the ship;

n is the number of ships per time unit (traffic intensity);

T is the reference period (1 year);

pa is the probability that a collision is avoided by human intervention;

λ is the probability of a failure per unit travelling distance;

fs(y) is the distribution of initial ship position in y direction.

(2) As an approximation for expression (A.5) Fd may be derived from expression (A.1). Inelaborating expression (A.1) it is recommended to use the medium mass value for the relevantship class defined in Table 4.3 of the main text, a design velocity vrd equal to 3 m/s increasedby the water velocity and k = 15 MN/m for sea going vessels and k = 5 MN/m for inland ships.In harbours the velocity may be assumed as 1,5 m/s and at full sea 5 m/s is recommended.

(3) The load duration may be derived from expression (A.2). For cases where the rise time isrelevant this may be assumed as ue/vrd, where ue is the elastic deformation for which a value of0,1 m may be taken.

(4) In the absence of a dynamic analysis, a frontal impact factor of 1,3 and a lateral impactfactor of 1,7 is recommended.

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y

B

Figure A.2 : Ship collision scenario

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Annex B (informative)

Explosions

B.1 General

(1) Advanced design for explosions may include one or several of the following aspects:

– explosion pressure calculations, including the effects of confinements and breakingpanels;

– dynamic non linear structural calculations;

– probabilistic aspects and analysis of consequences;

– economic optimisation of mitigating measures.

(2) In the absence of quantification of consequences and economical optimisation, a failureprobability of 10-4 per year seems to be appropriate for accidental actions.

NOTE: For variable actions the exceedance probability, according to ENV 1991-1, isΦ(-αβ) = Φ(-0,7 × 3,8) = Φ(-2,7) = 0,003 for a reference period of 50 years. Thiscorresponds to a probability of 0,6×10-4 per year.

B.2 Structures in category 3

(1) Critical locations where explosions might be initiated should be considered. Explosionpressures on the structural elements should be estimated taking into account, as appropriate,reactions transmitted to the structural elements by non-structural elements. Due allowanceshould be made for probable dissipation of gas throughout the building, for venting effects, forthe geometry of the room or group of rooms under consideration etc. Elements which are notkey elements may fail; key elements may be damaged so long as they retain their structuralintegrity. It is recommended that propane gas be considered for design purposes unless theprobability is acceptably low that such gas could ever be present within the building.

(2) The estimated peak pressures may be higher than the values presented in the main text ofthis Part, but these can be considered in the context of a maximum load duration of 0,2 s andplastic ductile material behaviour (assuming appropriate detailing of connections to ensureductile behaviour).

B.3 Dust explosions

(1) The type of dust under normal circumstances may be considered by a material parameterKSt, which characterises the confined explosion behaviour. KSt may be experimentallydetermined by standard methods for each type of dust. A higher value for KSt lead to higherpressures and shorter rise times for internal explosion pressures. The value of KSt depends onfactors such as changes in the chemical composition, particle size and moisture content. Thevalues for KSt given in Table B.1 are examples.

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NOTE: See ISO 6184-a Explosion Protection systems - Part 1: Determination ofexplosion indices of combustible dusts in air.

(2) The venting area and the design pressure for dust explosions within a single silo may befound from the following set of expressions:

AV = 4,5 × 10-5 × KSt × Kh/d × V0,77 / pd0,57 (B.1)

Kh d p p

ph d/

ln( / )( , ln( ))=

+ − ≤ ≤

≤ ≤

1 4 0 8 20 150

1 150 200

d2

d2

2d

2

for kN/m kN/m

for kN/m kN/m(B.2)

where:ln(..) is the natural logarithm of (..);AV is the venting area, in square metres;KSt see Table B.1, (kN/m2 × m/s);V is the volume, in cubic metres;pd is the design pressure, in kilonewton per square metres;h is the height of the silo cell, in metres;d is the diameter or equivalent diameter of silo cell, in metres.

Expressions (B.1) and (B.2) can be solved directly to determine the venting area, but onlyiteratively to determine the design pressure.

Expressions (B.1) and (B.2) are valid for:

– h/d ≤ 12;

– static activation pressure of rupture disk pa ≤ 0,10 kN/m2;

– rupture disks and panels with a low mass which respond almost with no inertia.

(3) In dust explosions, pressures reach their maximum value within a time span in the order of100 10-6 s. Their decline to normal values strongly depends on the venting device and thegeometry of the enclosure.

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Table B.1 : KSt values for dusts

Type of dust KSt

(kN/m2 × m/s)brown coal 18 000

cellulose 27 000

coffee 9 000

corn, corn crush 12 000

corn starch 21 000

grain 13 000

milk powder 16 000

mineral coal 13 000

mixed provender 4 000

paper 6 000

pea flour 14 000

pigment 29 000

rubber 14 000

rye flour, wheat flour 10 000

soya meal 12 000

sugar 15 000

washing powder 27 000

wood, wood flour 22 000

B.4 Explosions in tunnels

(1) In case of detonation, the following pressure time function should be taken into account,see Figure B.1(a):

p x t p tx

ct

x

ct

x

c

x

c

p x t px

c

x

ct

x

c

x

ct

x

c

p x t

( , ) exp{ ( ) / }

( , ) exp{ ( ) / }

( , )

= − − ≤ ≤ −

= − − − ≤ ≤

=

o o

o o

for

for

for all other conditions

1 1 2 1

1 2 2 1 2

2

0

( . )

( . )

)

B

B

(B.

3

4

5

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where:

po is the peak pressure (= 2 000 kN/m2);

c1 is the propagation velocity of the shock wave (~ 1 800 m/s);

c2 is the acoustic propagation velocity in hot gasses (~ 800 m/s);

to is the time constant (= 0,01 s);

|x| is the distance to the heart of the explosion;

t is the time.

(2) In case of deflagration the following pressure time characteristic should be taken intoaccount, see Figure B.1(b):

p(t) = 4po(t/to)(1-t/to) for 0 < t < to (B.4)

where:

po is the peak pressure (= 100 kN/m2 );

to is the time constant (= 0,1 s);

t is the time.

This pressure holds for the entire interior surface of the tunnel.

(a)p

t toxc1 2

xc1

xc2

-xc

0

(b)p

t0

p

p

Figure B.1: Pressure as a function of time for (a) detonationand (b) deflagration

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Annex C (informative)

Additional guidance for design

C.1 Acceptable localised damage in buildings

(1) To facilitate the design of certain buildings, a small part of the building may have to be leftwithout any provision against the effect of an accident or it may have to remain vulnerable tothe risk of collapse; e.g. a part of the building with openings with removable covers or a partof a load bearing masonry building structure. Such parts of the building should be limited towithin the storeys where an accident may occur and within the immediate adjacent storeys.

C.2 Simplified analysis for category 2 structures in buildings

(1) Depending on the specific circumstances of the structure, simplified analysis by staticequivalent models should be carried out. The measures applied may be determined by therelevant authority, see also ENV 1991-1, 2.1.(4)P.

C.3 Preventive and protective measures against rail traffic under bridges

(1) Unless otherwise specified, priority should be given to reducing the probability andconsequences of an impact by preventative and protective measures. The strategy should bedetermined by the relevant authority.

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