Investigatin f the seismic sil-structure interactin n a cncrete instrumented building First Eurpean Cnference n Earthquake Engineering and Seismlgy Geneve, 7 sep 26 Teresa Crespellani, Jhann Facciruss, Claudia Madiai jhannf@dicea.unifi.it
Intrductin Sil-Structure Interactin (SSI) effects can lead either t seismic actins lwer than the free field nes, r t mre cnservative nes Cnsidering SSI may be essential fr: assuring safety and reliability r reducing repair csts mainly fr histrical mnuments, public buildings and critical facilities perfrming a safe design A precise predictin f SSI during earthquakes is generally difficult due t several uncertainties affecting: free-field mtin (btained by a site respnse analysis as input t SSI) sil behaviur (f the depsit underlying the structure) numerical cde (adpted t perfrm SSI analysis) 2/
Intrductin A true validatin f a cmputer prgram must be aimed t test the reliability f the numerical results (by cmparing them t real recrded mtins during earthquakes) and the capability f the adpted cde t mdel the mst imprtant aspects f the SSI at the site. The first and crucial step cnsists f chsing the test sites, which must be characterised by: buildings equipped with several seismic recrding instruments a gd knwledge f the prperties f sil underlying the structure (behaviur in static and dynamic cnditins, depth and thickness f layers, bedrck lcatin, etc.) a gd knwledge f the structure and its dynamical behaviur (mdal analysis) a site seismicity cngruent with prgram capability (i.e. linear r linear equivalent mdel lw-t-medium seismicity) Mrever the test site must be representative f many ther sites in the regin 3/
SASSI 2 SASSI 2 is a System which perfrms the Analysis f Sil-Structure Interactin by applying a FINITE ELEMENT METHOD based n SUBSTRUCTURE METHODS The substructure methds divide the sil-structure system int substructures discretised by finite elements, each f them is slved separately and cmbined t btain the cmplete slutin by emplying the principle f superpsitin (hence these methds can handle nly linear r equivalent linear prperties). The slutins are btained in the frequency dmain fr a certain number f frequencies (5-2) frm which the intermediate slutins can be btained by interplatin The basic substructure methds adpted by SASSI 2 are: the Flexible Vlume Methd the Subtractin Methd 4/
Bundary ndes Flexible Vlume Methd SASSI 2 Ndes at the bundary f the near field zne Ndes at the interface between the structure and the grund Ndes within the excavated sil External frces Q b Near field zne Interactin ndes ( structure+fundatin+sil) = - + Q b Free field site Excavated sil (replaced with embedded fundatin) Structure (superstructure+fundatin) 5/
Bundary ndes Subtractin Methd SASSI 2 Ndes at the bundary f the near field zne Ndes at the interface between the structure and the grund External frces Q b Near field zne Interactin ndes ( structure+fundatin+sil) = - + Q b Free field site Excavated sil (replaced with embedded fundatin) Structure (superstructure+fundatin) 6/
SASSI 2 The remaining site (far field) cnsists f hrizntal sil layers verlying a unifrm halfspace simulated by the variable depth methd and viscus dashpts. The sil behaviur is assumed t be elastic r viscelastic and a linear equivalent mdel is adpted t slve the site respnse analysis (cupling SASSI 2 t Prshake). The input mtin (r cntrl mtin) cnsists f an arbitrary 3-D superpsitin f inclined bdy waves and surface waves and is expressed by a time histry acceleratin assigned t ne f the three directins at a cntrl pint Near field zne bundary H i, γ i, V Si, V Pi, D Si, D Pi Cntrl pint HALFSPACE 7/
Site selectin TEST SITE test site quite representative f many ther sites in the regin gd knwledge f the sil prperties and f the dynamical behaviur f the structure lw t medium seismicity cngruent with prgram capability (limited t linear dmain) 8 9 6 6 4 2 8 4 3 2 8 3 SEISMIC OBSERVATORY OF STRUCTURES O wrking systems ( st tranche) O wrking systems (2 nd tranche) O systems under realisatin (3 rd t.) 8 N f systems in a Regin 2 Italy: 5 build.s bridges in ttal 8/
Sil characterisatin Selected building wells brehles 9/
Sil characterisatin and mdelling V S (m/s) Debris sil UNIT A Alluvial depsit UNIT B UNIT C UNIT A and B : clay and silt with fine sand UNIT C : gravel and gravel with sand and silt Marine clays Halfspace Viscus dampers /
Sil characterisatin and mdelling G/G.9.8.7.6.5.4.3.2. Unit A and B (experimental data) UNIT A and B (regressin data) UNIT C (Rllins et al., 998)... γ (%) D (%) 5 4 3 2 Unit A and B (experimental data) UNIT A and B (regressin data) UNIT C (Rllins et al., 998)... γ (%) /
Structure characterisatin and mdelling The building examined has a regular cmpact shape with a rectangular hrizntal sectin. The structure is cmpsed f a cncrete frame with tw masnry cement flrs respectively at 4.25 m and 8.35 m frm grund level with a ttal thickness f 55 cm. 28 m m m The fundatin system, made up f a system f transversal and lngitudinal grund beams, is placed at a depth f 8 cm belw grund level and lies n sils belnging t Unit A. 2/
3 96 36 329 298 267 245 4 97 36 33 299 268 246 5 98 79 8 8 54 55 56 32 33 34 94 95 96 362 33 3 269 247 363 332 3 27 6 99 82 57 63 64 65 66 32 33 2 34 3 97 35 4 364 333 32 27 7 2 83 58 98 67 36 5 365 334 33 272 248 366 335 34 273 249 367 336 35 274 25 368 337 36 275 25 55 84 85 86 87 369 37 338 37 276 339 38 277 37 34 39 278 279 372 373 34 3 342 3 28 76 374 343 32 28 375 344 33 282 252 253 254 255 256 257 258 376 345 34 283 377 346 35 284 378 379 347 36 285 348 37 286 38 349 38 287 259 38 382 35 39 288 35 32 289 383 352 384 353 385 354 386 355 3 322 323 324 325 326 327 29 29 292 293 26 26 262 263 264 265 8 9 22 2 222 223 224 225 226 227 228 229 23 23 232 233 234 235 236 22 23 24 59 35 99 68 37 6 6 36 6 37 62 38 2 69 7 7 38 7 39 8 4 9 3 72 4 4 73 42 63 39 5 74 64 4 6 75 65 4 7 66 42 8 77 43 44 45 46 2 3 4 5 9 78 47 6 79 48 7 67 43 8 49 8 68 44 2 8 5 9 69 7 45 3 46 4 82 83 5 2 52 5 84 53 22 6 85 54 23 238 25 88 7 47 239 26 89 72 48 24 27 9 73 49 24 28 9 74 5 25 26 27 28 29 3 3 7 86 55 24 8 87 56 25 9 2 88 57 26 89 58 27 356 294 29 92 75 9 59 28 357 295 242 93 76 5 22 9 6 29 358 296 243 94 77 52 23 92 6 3 359 328 297 266 244 237 2 95 78 53 24 93 62 3 UNIVERSITA DEGLI STUDI DI FIRENZE Structure characterisatin and mdelling The fundatin system is mdelled with (3-D) 8 ndes prismatic elements (slid) 276 277 278 279 28 28 282 283 284 285 286 287 288 289 29 29 292 293 294 295 296 297 298 299 3 3 246 6 247 7 248 8 249 25 9 22 25 252 253 2 222 223 254 255 224 225 256 257 258 259 26 226 227 228 229 23 26 262 23 232 263 264 233 234 265 235 266 236 267 237 268 238 269 27 27 272 239 24 24 242 243 273 274 275 244 245 2 22 23 24 25 26 27 28 29 2 3 4 5 95 96 97 98 99 79 8 8 82 83 84 85 86 87 88 89 9 9 92 93 94 64 65 66 67 49 5 5 52 53 54 56 28 29 3 3 68 32 69 33 7 34 7 35 36 37 38 39 4 4 72 73 74 75 57 58 59 6 6 62 63 42 43 44 45 76 46 77 47 78 48 2 3 4 5 6 7 8 9 2 22 23 24 25 26 27 y 9 92 93 94 95 96 97 98 99 7 8 9 2 3 4 5 6 Unit = cm 6 62 63 64 65 66 67 68 69 7 7 72 73 74 75 76 77 78 79 8 8 82 83 84 85 86 87 88 89 9 3 32 33 34 35 36 37 38 39 4 4 42 43 44 45 46 47 48 49 5 5 52 53 54 55 56 57 58 59 6 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 22 23 24 25 26 27 28 29 3 x m 2 m 423 elements 4 ndes 3/
Structure characterisatin and mdelling Type flr system The whle superstructure (beams, clumns, infill systems) was (beams, mdelled clumns by means and f 3-D infill beam elements systems) is mdelled by means f 3-D beam elements. Nde influence area t assign the flr system masses Type vertical frame Diagnal infinitely rigid weightless rds t riprduce a plane cnstraint Diagnal weightless rds simulating infill systems Beam influence area t assign infill system weight 4/
Mnitring system and seismic input The whle superstructure (beams, clumns, infill Channel systems) (X-axis) was.8 6 mdelled by means f 3-D beam elements.6 7 9 8 3 5 2 4 2 3 Acceleratin (g).4.2 -.2 -.4 -.6 -.8 5 5 2 Time (s) y PGA (g) PGV (mm/s) PGD (mm) Arias Intensity (mm/s) Trifunac duratin (s) Predminant perid (s) Max spectral acceleratin (g) z x Channel Channel 2.756.388 27.98 4.36.86 2. 4. 7.92 7.48.3.273.2467.87.34 Acceleratin (g) Channel 2 (Y-axis).8.6.4.2 -.2 -.4 -.6 -.8 5 5 2 Time (s) 5/
Acceleratin (g).5..5 -.5 -. -.5 7 9 y UNIVERSITA DEGLI STUDI DI FIRENZE 8 z x 3 5 6 2 4 2 3 Instrumental recrdings Numerical analyses.5..5 -.5 3 6 9 2 5 8 Time (s) -.5 -. Arias intyensity (%) Acceleratin (g) Acceleratin (g) Experimental data and numerical results.5..5 -.5 -. -.5 3 6 9 2 5 8.5..5 -.5 -. -.5 3 6 9 2 5 8 75 5 25 3 6 9 2 5 8 Time (s) 3 6 9 2 5 8 Arias intyensity (%) Time (s) 75 5 25 3 6 9 2 5 8 Time (s) 6/
7 9 y Spectral acceleratin (g) UNIVERSITA DEGLI STUDI DI FIRENZE 8.4.3.2. z x 3 5 6 2 4 2 3 Instrumental recrdings Numerical analyses Experimental data and numerical results Arias Furier intyensity amplitude (%) (g*s) Time (s).5.5 2 2.5 Perid (s). 5 5 2 Frequency (Hz) Spectral acceleratin (g) Furier amplitude (g*s).4.3.2..4.3.2...4.3.2..5.5 2 2.5 5 5 2 Arias intyensity (%) Perid (s) Frequency (Hz) 7/
X (%) = 7 9 y UNIVERSITA DEGLI STUDI DI FIRENZE 8 [X(exp)-X(num)] z X(exp) x 3 5 6 2 4 2 3 I A (%) PGA(%) Experimental data and numerical results 4 3 2 - -2 5-5 - CH 4 CH 4 CH 5 CH 5 CH 7 CH 7 CH 8 CH 8 CH CH CH CH CH 2 CH 2 CH 3 CH 3 DS(%) 8 6 4 2 CH 4 CH 5 CH 7 CH 8 CH CH CH 2 CH 3 S A (%) 3 2 - -2 CH 4 CH 5 CH 7 CH 8 CH CH CH 2 CH 3 8/
3 96 36 329 298 267 245 246 299 6 2 79 4 64 97 5 65 79 8 8 28 29 2 9 3 33 36 33 268 246 98 54 55 56 32 33 3 34 92 94 95 96 6 62 32 34 2 247 8 362 33 3 7 269 247 278 248 8 66 3 63 33 3 363 332 3 27 6 99 82 57 63 64 65 66 32 2 3 97 35 4 279 249 67 3 64 34 4 364 333 32 27 7 2 83 58 98 67 36 5 365 366 367 28 28 282 25 68 32 65 35 5 334 33 272 248 335 25 22 252 34 35 36 2 222 223 273 249 8 23 82 368 283 253 24 83 284 254 369 37 285 286 255 256 39 3 227 372 373 288 25 84 36 3 228 26 85 37 76 259 32 229 27 86 38 26 26 262 34 23 232 377 378 379 38 292 293 294 295 263 264 36 37 233 234 285 286 28 29 265 38 235 287 296 266 236 38 382 297 267 237 298 268 238 384 385 299 3 386 3 269 27 27 272 356 357 358 359 273 274 275 3 322 323 324 325 326 327 328 8 9 22 2 222 223 224 225 226 227 228 229 23 23 232 233 234 235 236 75 69 7 7 72 73 74 76 77 55 84 85 86 87 33 34 35 4 93 66 36 38 6 336 274 25 5 94 67 37 39 7 337 275 6 95 25 22 23 24 59 35 99 68 37 6 6 36 6 37 62 38 2 68 69 7 7 7 8 38 4 8 9 69 39 9 338 37 276 3 72 4 7 4 339 38 277 4 73 42 7 4 37 34 34 278 279 7 96 6 72 42 8 97 7 73 43 342 28 374 343 28 252 253 254 255 256 257 258 63 39 5 74 9 98 8 74 44 43 44 45 46 3 2 64 4 75 3 65 4 4 66 42 77 5 75 76 45 46 47 5 375 344 33 282 9 78 47 6 376 345 283 79 48 7 77 346 35 284 67 43 8 49 8 347 87 39 68 88 4 89 4 2 22 44 99 2 78 8 48 5 8 9 3 79 49 348 5 9 349 259 69 7 45 46 4 8 82 83 5 2 52 2 8 5 35 39 288 5 84 53 22 82 52 22 35 32 289 6 85 54 23 83 53 23 383 352 29 353 239 24 24 29 95 2 96 3 97 9 9 92 244 245 26 27 28 29 2 57 58 59 6 6 62 63 89 9 9 92 93 94 95 42 43 44 45 46 47 48 72 73 74 75 76 77 78 23 24 25 7 8 9 2 8 84 54 56 24 354 292 3 4 9 2 85 86 55 57 25 355 293 26 26 262 263 264 265 238 25 88 7 47 239 48 24 49 24 5 56 58 26 87 57 27 294 88 58 28 295 242 5 296 4 98 26 5 5 99 237 78 27 25 26 27 28 29 3 3 7 86 55 24 87 25 88 26 89 27 9 59 28 22 9 6 29 23 89 59 243 52 92 6 29 3 297 266 244 53 6 24 9 6 93 62 3 3 UNIVERSITA DEGLI STUDI DI FIRENZE Sil-structure interactin effects Once validated the sftware, SSI effects at the fundatin basement are examined fr the selected seismic input...5 Nde n 3 276 277 9 22 224 225 287 289 257 258 226 23 29 29 242 243. 93 94 -.5 49 5 5 52 53 54 56 -. 6 2 8 y..5 Nde n 78. -.5 -. 6 2 8 x m 2 m 2 4 6 7 Instrumental recrding at the free field (X-directin) Numerical results at the selected ndes..5 Nde n 92..5 Free field statin.. -.5 -.5 -. 6 2 8 -. 6 2 8 9/
Sil-structure interactin effects Spectral acceleratin (g).3.2. Free-field nd 3 nd 92 nd 78.5.5 2 2.5 K X = X(nde) X(free-field) Perid (s) PGA [g] I A [m/s] T d [s] K PGA K Ia K Td Nde 92-X.65. 4.88.87.76.65 Nde 78-X.68.93 4.53.82.7.6 Nde 3-X.633.95 4.62.85.72.62 Nde 92-Y.328.46 7.84.88.63.78 Nde 78-Y.325.43 7.84.84.59.78 Nde 3-Y.35.42 7.84.85.58.78 2/
The SSI analysis results shw that: CONCLUDING REMARKS there is a generally gd agreement between numerical results and recrded data bth in time and in frequency dmain SASSI 2 seems t be reliable t perfrm SSI analyses n the selected building when subjected t lw-t medium intensity seismic events the presence f the structure has a slightly damping effect SSI des nt seem t have a significant rle in the selected site The analysis results culd be reasnably extended t ther Italian sites with similar prperties (tw-strey cncrete buildings lying n sft sils with deep bedrck in lw-t-medium seismicity area) /