IN SITU VIBRATION EXPERIMENTS ON INTACT AND MODIFIED BUILDINGS INTEREST FOR VULNERABILITY ANALYSIS C. BOUTIN, S. HANS 1.Experiment : structural identification 2.Integrity threshold : first structural damage 3.Interest for vulnerability analysis Experimental program on 7 buildings ( ) before demolition in Lyon suburbs

IN SITU METHODS Ambient noiseHarmonicShock ~10 -5 g~10 -3 g~10 -2 g

MODAL IDENTIFICATION FREQUENCY – SHAPE – DAMPING Autocor. S3S3 SBF Ambient noiseHarmonicShock mm/s² Time (s) Fr equency (Hz) Time (s) Frequency (Hz) HANS S.&al., Journal of Sound and Vibration, 2000

BUILDING C (~1975)

MODAL CHARACTERISTICS OF BUILDING C Ex : Mode L Mode 2 LMode 3 L S3S3

First modal frequency evolution PRECAST FACADE PANELS Measurable decrease of frequency Shear beam model 20 % of story rigidity Progressive modification BOUTIN C., HANS S. & IBRAIM E, Revue Française de Génie Civil, 2000

BUILDINGS D-E-F (~1973) Stories plan D E F

STRUCTURE-STRUCTURE INTERACTION kinematic interactions soil impedance

SUPPRESSION OF MASONRY WALLS Suppressed walls before after Longitudinal direction Transversal direction TORSION

FIRST CONCLUSION STRUCTURAL INFORMATION –quasi-elastic behaviour g –identification with ambient noise g –modal characteristics including participating elements frequency empirical formula (statistic specific) FIRST LEVEL OF USE –retrofitting –recalculation (reliable data for fitting complex numerical modelling) MORE DETAILLED ANALYSIS ?

INTERPRETATION OF MEASUREMENTS FACT –Measurements not sufficient –Need of model as simple as possible BEAM MODEL (SHEAR, TIMOSHENKO …) ? –Plan + simple assumptions on structural behaviour (distribution of rigidity …) FIT –1 parameter E concrete –Fit of the firt frequency : E real CHECK –comparison with higher frequencies

MODELLING OF DYNAMIC BEHAVIOUR BOUTIN C., HANS S., Computer & Geotechnics, 2003 Modelling by homogenisation

BUILDING C ~ SHEAR BEAM MODEL E= 20 GPa => f 1 = 3,6 Hz Fit of the 1 st frequency E concrete ~ 31 GPa –{4,45 Hz, 13,3 Hz, 21,8 Hz} model –{4,45 Hz, 14,1 Hz, 23,5 Hz} experiment Comparison of the Shapes ModelExperimental

BUILDING G (~1975) Story plan

Fit of the 1 st longitudinal frequency E concrete ~ 16,5 GPa –longitudinal frequencies (L) : {2,15 ; 6,6 ; 11,8 ; 16,6 } model {2,15 ; 7,24 ; 14 ; 20,5} experiment –transversal frequencies (T) {1,86 ; 8,7 ; 19,1} model {1,56 ; 6,64 ; 14,4} experiment Fit of the 1 st et 2 nd frequencies : L {2,15 ; 7,24 ; 11,8 ; 20,1} model T {1,56 ; 6,64 ; 14,4} model BUILDING G ~ TIMOSHENKO BEAM MODEL Comparison of the Shapes

LINK WITH VULNERABILITY LIMIT OF ELASTIC DOMAIN UNDER SEISMIC EXCITATION (FRENCH NORMS PS 92) CALCULUS –1 st mode of vibration –Damage criteria : maximal concrete extension ( = ) INTEGRITY THRESHOLD

Extension criteria max ~10 -4 U max Elastic response spectra (norm) U(A sol ) U(A sol ) = U max S max : integrity threshold (S 1, Ia ) A sol = 1 m/s² C8 : S max = 0,45 m/s² C4 : S max = 1,07 m/s² U max (mm) 0,38 0,42 1,8

SECOND CONCLUSION INTEGRITY THRESHOLD –Quantified available value based on structural characteristics and seismic motions INTEREST FOR VULNERABILITY ANALYSIS ? –First indicator on safety –Check for strategic buildings and facilities : stay in service ? First structural damage LIMITATION : first damage vulnerability BEYOND INTEGRITY ?

PLAUSIBLE COLLAPSE SCENARIO S = 0,45 m/s² Brittle failure of panel (1 st -2 nd storey) K st 1, 2 = 0,6 K st no change in 1 st mode shape and frequency S = 0,52 m/s² Brittle failure of lift walls (1 st -2 nd storey) K st 1, 2 = 0,2 K st Strong change in 1 st mode shape and frequency S = 0,41 m/s² Failure of last walls (1 st - 2 nd storey) In this real case: Integrity Collapse

Other situations CONCLUSIONS INTEREST OF IN SITU EXPERIMENTS –Structural informations –Reliable data to fit sophisticated numerical modelling INTEGRITY THRESHOLD –Discrimination of buildings – Presumption of safety Brittle materials (unreinforced concrete, masonry) Wrong design Transparency (even with ductile materials) Good design Ductile materials Building brittle failure Vulnerability indicator Estimated need of ductility Real mode Push-over analysis ? Used carefully, interesting informations can be drived from in-situ low level experiments, complementary to other methods