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New European document on assessment of existing structures and building stock

Learn about the principles and target reliability of assessing existing structures, including material properties, past performance, and reliability differentiation. Discover different verification methods and the importance of data and probability updating.

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New European document on assessment of existing structures and building stock

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  1. New European document on assessment of existing structures and building stock Milan Holický CTU in Prague, Klokner Institute General principles Target reliability of existing structures Verification of structures Data updating CESB19, Prague, July 2019

  2. General principles Assessment is in many aspects different from designing a new structure The most important aspects to be considered in assessment of existing structures: - actual material property, actions, and geometry; - effect of construction, alterations, misuse; - past performance, deterioration, damage; - reliability differentiation (due to consequences, cost of safety measures, societal, political and cultural aspects). CESB19, Prague, July 2019

  3. The target reliability index β -two terms are to be distinguish The reference period is used to specify characteristic of basic variables and reliability index The remaining working life (design service life) is used to specify required durability of structures Forindependent failures the reliability index t,nrelated to the reference periodof n years may be derived from t,1related to 1 year (t,n) = [(t,1)]n CESB19, Prague, July 2019

  4. Target reliability indexes β in EN 1990 Assuming independence of failures the reliability indexes for reference periods n = 1 and 50 years However, failures are not independent! CESB19, Prague, July 2019

  5. The indices β for dependent failures in subsequent years The reliability index t,n related to a period of n years and the independence period of k years is estimated (t,n) = [(t,1)]n/k For t,1 = 4,7 and k =1 the value t,50 = 3,8 (EN 1990) For t,1 = 4,7 and k =5 the value t,50 = 4,2 For t,1 = 4,7 and k =10 the value t,50 = 4,4 CESB19, Prague, July 2019

  6. Variation of βnk with β1 for the reference period n = 50 and independence intervals k nk k=50 k=10 k=1 1 Variation of βnk= F-1[F(b1)]n/kwith β1for n = 50and k = 1, 10, 50 y CESB19, Prague, July 2019

  7. Verification methods of a givenβt Reliability of a structure g(Xi) > 0 (R  E > 0) maybeverified by: Partial factor method: The requirement g(Xi) > 0 is substituted by g(xai) = g(xa1, xa2 , xa3, ...) > 0, xai (βt)= xki (βt)or xai = xki/  (βt) Assessment (design) value method: The requirement g(Xi) > 0 is substituted by g(xai) = g(xa1, xa2 , xa3, ...) > 0, Xi(xai) = (–i) Probabilistic method: The requirement g(Xi) > 0 is examined by failure probability Pf = P{g(Xi) < 0} < Pf,t (βt) Risk assessment approach: The reliability is verified by expected risk ER ER(βt) = Pf(βt)  C = P{g(Xi) < 0}  C < ERt CESB19, Prague, July 2019

  8. Data and probability updating fX(x|I) = C L(I|x) fX(x) updated=likelihoodprior Reverend Thomas Bayes 1702 - 1761 CESB19, Prague, July 2019

  9. Concluding remarks • Assessment is in many aspects different from designing a new structure • Present codes do not provide clear information about the target reliability for ultimate and serviceability limit states • The optimum reliability level depends on the ratio of consequences of structural failure and safety measures • The target reliability index for new structures may be different from the index for existing structures • A new approximation is proposed for specification of the index βnk= F-1[F(b1)]n/k from β1 • Updating of probabilities, actions and material properties should be applied professionally (expertly) CESB19, Prague, July 2019

  10. Thank you for your attention In some cases the assessment is difficult The Charles Bridge in Prague – 670 years A new assessment and repair were recently completed CESB19, Prague, July 2019

  11. Differences between design and assessment CESB19, Prague, July 2019

  12. Reasons for assessment • performance deficiency, excessive deflection, cracking; • change in use requiring construction and/or operation interventions; • damage of structural members due to accidental actions and time dependent influences; • doubts about actual reliability of the structure. Lateral deflection of a built-in elements CESB19, Prague, July 2019

  13. Targets in EN 1990:2002indicated in prEN 1990: 2018 CESB19, Prague, July 2019

  14. Variation of βnk with n an k βnk 4.7 3.8 10 8 6 4 k 2 n 0 CESB19, Prague, July 2019

  15. Serviceability of existing structures • Serviceability flaws of existing structures are often the main motivations for assessment, • In case of old existing structures serviceability deficiencies reveal significant damage, distress, deterioration or displacement, • Judgment on satisfactory past performance is based on investigation of serviceability aspects, • National (or client) choice may lead to malfunctioning of structures, • Criteria for some serviceability indicators are still vague and should be assessed individually. CESB19, Prague, July 2019

  16. Sustainability seems to be the most significant aspect of assessment Thanks for your attention CESB19, Prague, July 2019

  17. Doubts about actual reliability Often originated from exceeding serviceability limit states • Excessive deformations of structures • Cracking in structural members and plasters • Spalling of materials • Vibration of structures Serviceability limit states exceeded CESB19, Prague, July 2019

  18. Reference period n and target reliability β F(bnk) = F(b1)n/k,βnkorβ1 β1 β50,50 = 4.3 3.8 3.3 3.0 k Variation of β1with independency interval k for selected β50,50 CESB19, Prague, July 2019

  19. Failure costs initial costs marginal costs Probabilistic optimization approach • Annual failure probability p(x) depends on a structural parameter x (e.g. cross section area) considered as the decision parameter 2. Failure probability Pf(x,i) at the year i and Pfn(x) within n years Pfn(x) = 1 – (1 – p(x))nn p(x) Pf(x,i) = p(x)(1 − p(x))i−1 3. The basic objective function as the total cost 4. The discount factor at the year i considered as Q(q,i) = 1/ (1+q)i CESB19, Prague, July 2019

  20. The total cost κtot(x,q,n)and reliability index βoptfor q = 0,03 and n = 50 yeras CESB19, Prague, July 2019

  21. Not always the optimization is possible Temporary stage for the Pope CESB19, Prague, July 2019

  22. Contents of the Final Document of TS European foreword General (Scope, Normative references, Terms and definitions) General requirements (Objectives, Principles, Target reliability, etc.) General framework of assessment (Procedure, Basis of assessment) Basic variables and updating (Material properties, Actions, etc.) Structural analysis (Analysis, Testing and monitoring, etc.) Verification (Partial factors, Probabilistic methods, Risk, etc.) Assessment based on past performance (ULS, SLS) Intervention (Upgrading, Monitoring, Interventions, etc.) Annexes (all informative) A Flowchart of the assessment (adjusted ISO 13822) B Updating procedure (adjusted JCSS) C Target reliability and partial factors (supplementing 2 Requirements) D Heritage structures (adjusted ISO 13822) CESB19, Prague, July 2019

  23. Optimisation and decision making Total costs = Failure costs+ Upgrading costs Reliabilityindex β(d) Costs Total costs Assessment situation(performance deficiency) βopt Upgrading costs Initial costsindependent of d { Present failure costs curve d0 dopt dcrit Decision parameter d Rehabilitation No rehabilitation CESB19, Prague, July 2019

  24. Data updating fX(x|I) = C L(I|x) fX(x) updated=likelihoodprior Reverend Thomas Bayes 1702 - 1761 CESB19, Prague, July 2019

  25. Documents submitted by PT to NEN in April 2018 • Final Document of TS • Accompanying background documents • Reply to NSB comments • Report setting out the relevant NDPs CESB19, Prague, July 2019

  26. Background documents List of documents Extent 1. An example of reliability verification of an existing structure 9 pages 2. Reliability levels related to different reference periods 9 pages 3. Partial factors for the assessment of existing concrete structures based on the assessment value method 7 pages 4.Structural analysis 2 pages 5. Case study for updating basic variables 6 pages 6. Interaction TS “Assessment of Existing Structures” – EN 1990 “Basis of Structural Design” 6 pages CESB19, Prague, July 2019

  27. Review of WG2 and NSB comments TS draft: first final mainly: General comments 1241 accepted Clause1 General 30 28 accepted Clause2 Requirements 27 46 accepted Clause3 General framework of assessment 59 55 considered Clause4 Basic variables, data updating 50 56considered Clause5 Structural analysis 11 5 considered Clause6 Verification 20 27 considered Clause7 Past performance 7 8 considered Clause8 Interventions 4 6 accepted AnnexA Flowchart 6 3accepted AnnexB Updating procedure 2 4 considered AnnexC Target reliability and partial factors 2accepted AnnexD Heritage structures 5 considered Total number of comments 228 276 CESB19, Prague, July 2019

  28. Substantial (multiple) NSB comments • Link TS to EN 1990 (still in progress), accepted, Annex C • Make more recommendations to practical use, accepted, Annex C • Delete reliability and utilization plans, not accepted • Limit serviceability aspects, not accepted • Transfer Clause 2.3 to annex, accepted, moved to Annex C • Transfer Clause 3 to annex, not accepted • Transfer Annex B to background document, not accepted • Transfer Clause 7 to annex or delete it, not accepted • Transfer Clause 8 to annex or delete it, not accepted • Add list of symbols, provided in the revised Annex C CESB19, Prague, July 2019

  29. Why serviceability of existing structures • Serviceability defects and flaws are often the main motivations for assessmentof existing structures. • In case of old existing structures serviceability deficiencies reveal significant damage, distress, deterioration or displacement. • Judgment on satisfactory past performance is based on investigation of serviceability aspects. • Preferences of national authorities (of clients) may not be correct (appropriate) and may cause subsequent defects of a structure. • Serviceability properties (indicators) of existing structures should be assessed individually. • In prEN 1990 (2017) the serviceability is treated in detail indicating a number of purposeful and practical criteria. CESB19, Prague, July 2019

  30. General requirements, Clause 2, Annex C Target reliability level βt in TS is linked to the target reliability for new structures βt,1990 in EN 1990 for reference periods 1 and n years: • left for national choice (as βt,1990for new structures) • related to failure consequences, cost of upgrading, societal, historical, cultural and political aspects • can be specified on the basis of (probabilistic) cost optimization, • can be generally different from (often less than) βt,1990 • annual target βt,1can be transformed to βt,nfor reference periodn. CESB19, Prague, July 2019

  31. Report setting out the NDPs List of clauses indicating NDPs • Clause 1: 1.1; 1.3.10 • Clause 2: 2.1 (4); 2.1 (5); 2.2 (1); 2.3 (1); 2.3 (5); 2.4 (1) • Clause 4: 4.3.6.1 (1); 4.3.6.1 (2); 4.3.10 (2) • Clause 6: 6.1 (1); 6.2 (1); 6.3 (3); 6.3 (4); 6.4 (2); 6.4 (3); 6.5 (1); 6.6 (2) • Clause 7: 7.1 (1) • Annex A, B, C, D CESB19, Prague, July 2019

  32. MembersoftheProject Team WG2.T1 Preparation of CEN Technical Specification Position Name First name E-mail Leader Holicky Milan milan.holicky@cvut.cz Member Tanner Peter tannerp@ietcc.csic.es Member Shave Jon shavej@pbworld.com Member Schnell Jürgen juergen.schnell@bauing.uni-kl.de Member Nuti Camillo camillo.nuti@uniroma3.it Member Steenbergen Raphaël raphael.steenbergen@tno.nl Secretary Pallierova Jana jana.pallierova@cvut.cz Members Lüchinger Paul plu@luechingermeyer.ch ex officio Fischer Jürg juerg.fischer@sia.ch ObserverWeberMichael michael.weber@bauing.uni-kl.de CESB19, Prague, July 2019

  33. Milestones and meetings of PT WG2.T1 Milestones • First draft, April 2016 • Second draft, April 2017 • Final draft, October 2017 • Final document, April 2018 Plenary meetings of PT • Prague, 26.-27. 11. 2015, kick-off meeting • Zurich, 20. - 21. 1. 2016, together with WG2 meeting • Madrid, 31. 3. - 2. 4. 2016, work meeting (before Milestone 1) • Delft, 16. - 17. 6. 2016, work meeting • Rome, 21. - 22. 12. 2016, work meeting • Kaiserslautern, 16. - 17. 3. 2017, work meeting (before Milestone 2) • Bristol, 6.-7. 9. 2017, work meeting (before Milestone 3) • Prague, 15.-16. 3. 2018, closure work meeting (before Milestone 4) Additional ad hoc meetings Prague 12. - 13. 1. 2017, 23. - 24. 2. 2017, 17. - 18.7. 2017 Zurich 12. - 13. 2. 2018 CESB19, Prague, July 2019

  34. Drafts of TS submitted to WG2 Concept of TS presented at WG2 meeting in Zurich, 20.-21.1.2016 1.0 draft submitted to NEN and WG2 in April 2016 1.8 draft distributed to WG 2 in January 2016 1.8 draft discussed at WG 2 meeting in Paris 26.- 27. 1. 2017 2.0 draft submitted to NEN and WG2 in April 2017 2.0 draft discussed at WG2 meeting in Vienna 3.- 4. 7. 2017 Final draft submitted to NEN and WG2, October 2017 Final document submitted to NEN and WG2, April 2018 CESB19, Prague, July 2019

  35. Reference period n and target reliability β F(bnk) = F(b1)n/k,βnkorβ1 β1 β50,50 = 4.3 3.8 3.3 3.0 k Variation of β1with independency interval k for selected β50,50 CESB19, Prague, July 2019

  36. Liaison between PT WG2.T1 and SC10 Issues common to TS and EN 1990 - PT WG2.T1, January 2017 - Verification format for non-linear analysis - Probabilistic models used for calibration - Target reliability levels - Combination of information → EN 1990 Annex D - Adjustment of partial factors - Robustness - Consequence classes - Utilization and reliability plans should be mentioned in EN 1990 Last availableversionofprEN 1990: N188, October 2017 The last meeting of SC10 in March 2018 did not consider WG2.T1 CESB19, Prague, July 2019

  37. Evolutionof TSsinceApril 2017 • Distribution of 2.0 draft to NEN and WG2 by 30. 4. 2017 • WG2 reviews 2.0 draft by 19. 6. 2017 • WG2 Secretariat distributes collation of comments by 26. 6. 2017 • WG2 meeting on 3.- 4. 7. 2017 in Vienna • PT receives conclusions of WG2 meeting by 10. 7. 2017 • Ad hoc meeting in Prague on 17.-18. 7. 2017 • 7th PT meeting in Bristol on 6.-7. 9. 2017 • Editorial work on Final draft (JF, JP) • MH and JP submitted Final draft to NEN by October 2017 • Closing PT meeting in Prague in March 2018 • MH and JP submitted the Final document to NEN in April 2018 CESB19, Prague, July 2019

  38. Partial factor methodfor a specified βt • Actions – design values • Material properties - d. v. • Geometric data – d. v. An example considering total variablesR and E • Insufficiency in case of existing structures - partial factors mostly rather conservative - failure probabilities are usually unknown - failure probabilities are not balanced CESB19, Prague, July 2019

  39. Design valuemethod • Actions – design values Fi(Fai) = (–it) • Material properties - d. v. fi(fai) = (–it) • Geometric data – d. v. An example considering total variablesR and E • Insufficiency in case of existing structures - distributions Xi(xi) are usually approximated - sensitivity factors E and Rmay not be appropriate CESB19, Prague, July 2019

  40. Probabilistic methods • Actions distributions Fi: Fi(Fi) • Material distributions fi: fi(fi) • Geometric data distributions ai:ai(ai) An example considering total variables R and E • Insufficiency in case of existing structures - distributions Xi(xi) are often approximated due to lack of credible data Pf = P{g(Xi) < 0} < Pf,t (βt) Pf = P{R  E< 0} < Pf,t (βt) CESB19, Prague, July 2019

  41. Flow chartof risk assessment ISO, CIB, JCSS, ISO TC98/SC2/WG11: ISO 13824: 2009 General principles on risk assessment of systems involving structures ISO 31000: 2009 Plain English - Risk management dictionary CESB19, Prague, July 2019

  42. Usual splitting of the reliability level tfor existing structures aEand aRmay be different • Reliability index t • Resistance reliability index • R = R t • Action reliability index • E = E t • Main action • E= 0.7t • Accompanying • E = 0.28t • Resistance • R= 0.8t CESB19, Prague, July 2019

  43. Relative frequency Density Plot (Shifted Lognormal) - [A1_792] 0.020 mX = 290.1 Mpa sX = 23.3 Mpa VX = 0.08 aX = 0.96 fyd,001 = 243 MPa fyk,05 = 259 MPa 0.015 0.010 Outliers fyd fyk 0.005 0.000 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 Yield strength [MPa] Yield point, steel S 235–792 measurements CESB19, Prague, July 2019

  44. GEV Distribution of the maximum values Gumbel Weibull Fréchet type III type I type II 0 1,14 a skewness Distribution of the minimum values type II type I type III - 1,14 0 a skewness Distribution of extreme values CESB19, Prague, July 2019

  45. Schiphol, 65 annualextremes1950 - 2014 Gumbel(20.6, 2.7, 1.14) LN3(20.6, 2.7, 0.41) CESB19, Prague, July 2019

  46. Preliminaryobservation - 1 CESB19, Prague, July 2019

  47. Preliminaryobservation - 2 CESB19, Prague, July 2019

  48. Serviceability of existing structures • Serviceability flaws of existing structures are often the main motivations for assessment, • In case of old existing structures serviceability deficiencies reveal significant damage, distress, deterioration or displacement, • Judgment on satisfactory past performance is based on investigation of serviceability aspects, • National (or client) choice may lead to malfunctioning of structures, • Criteria for some serviceability indicators are still vague and should be assessed individually. CESB19, Prague, July 2019

  49. WG2 in Vienna concerning target β • JDS (DK) : The calculation is incorrect, k is not specified. • MH (CZ): The calculation is an approximation and more appropriate procedure is welcome. All members are invited to provide an improved formulation by 14. 7. 2017. • GM (I): Proposal: to improve specification of independence interval k for various practical cases. • MH (CZ): Formulation will be made more precise. • TL (CH) recommends keeping the view used in EN 1990. • Closure from the discussion:RS (NL) will make a proposal for a new relationship between the target reliability and reference period till July 14, 2017. CESB19, Prague, July 2019

  50. Letter from SC 3 on the revision of safety issues in EN 1990, 2018-05-04Prof. Dr.-Ing. Ulrike Kuhlmann • Decisions to be based on much broader platform • Reference period from 50 to 1 year • Change of the partial factors • Originally β = 4,7 (3,8) changed to β = 4,2 (3,2) • Change αR= 0,8 to αR= 0,7 suggested in N234 • Steel structures are handicapped • Mandate for an evolution and not a revolution CESB19, Prague, July 2019

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