Re: Temperature all'interno delle torri e comportamento dell'acciaio in generale
Inviato da piedone70 il 20/7/2013 6:30:13
buongiorno!
Allora, come preannunciato ieri sera è buona educazione, prima di andare avanti, quella di commentare e cercare di dare una risposta a tutti gli interventi che si sono sussseguiti all’ultimo mio di ieri pomeriggio (circa una ventina…)
Ritengo che questo sia il modo più corretto di portare avanti un dibattito, altrimenti non si capisce poi più bene il filo logico.
Se qualcuno di voi etichetta questo mio modo di fare come TERGIVERSARE è un problema suo: io ho postato una bella (?) e pesante trattazione, alcuni di voi hanno preso forti posizioni contrastanti e quindi bisogna un attimino fare il punto.
… e naturalmente slitterà di un poco anche la trattazione che le termografie sono esatte E PERFETTAMENTE COMPATIBILI con i 1100 gradi all’interno (ovvero lo spettacolo tanto atteso, cioè LA BATOSTA)
Piccola premessa:
MI SCUSO PUBBLICAMENTE se in un mio post ho fatto una battuta un po’ spiacevole (riguardo certe dimensioni…)
SCUSATEMI ANCORA, nella mia mente pensavo di partecipare ad un qualsiasi dibattito tra maschietti adulti, insomma la classica discussione del dopocena di gruppo, dove anche peraltro molto animatamente (ma senza per questo arrivare alle botte neh…) ognuno butta lì le sue asserzioni. Bene in queste circostanze, solitamente, battute simili sono all’ordine della serata, e ritengo sia normale così, in modo da spezzare ogni tanto il discorso e farsi una sonora risata!
Però è altresì vero che non tutti la pensiamo allo stesso modo, per cui se qualcuno è rimasto diciamo contrariato, CHIEDO UMILMENTE SCUSA ben sicuro che da parte mia non si ripeterà più!!
Andiamo avanti…
@dr house
Hai asserito che uso il metodo cherry picking. Allora andiamo a prendere in esame la pagina del nist per intero e la mettiamo qui:
6.6.1 Visual Inspection of Recovered Structural Components
NIST has developed a novel approach to evaluating the primer paint on the structural components for evidence of exposure to high-temperature excursions (see Appendix D of NIST NCSTAR 1-3C).
This method was found to be relatively easy to implement and robust enough to examine an entire component in the field. Calibration tests in the laboratory showed that, although there was little or no change in color, the primer paint used on the WTC steels that reached temperatures over 250 °C cracked (similar to a “mud cracking” pattern) from the difference in thermal expansion between the paint and the steel.
Since deformation and environmental effects can also cause mud-cracking, the absence of mud-cracking indicates the steel has not exceeded 250 °C, but the presence of mud cracks cannot be assumed to be caused by high temperature. Visual inspection for the fire effects on recovered steel was conducted solely on the perimeter panels and core columns, as these were the only structural elements that had known as-builtlocations. Twenty-one panels were selected with numerous locations on the inner webs, flanges, spandrels, and floor truss connectors for each floor level analyzed, providing that sufficient paint was available for the analysis.
Core columns C-80 and HH from WTC 1 were examined while C-88a and C-88b were tested from WTC 2; these columns resided within the fire floors for their respective buildings. The entire length of each core column was examined, and evaluations of the primer paint were made when sufficient paint was available for inspection.
over 170 areas associated with the 21 exterior panels were analyzed, and the results may be found in Appendix E of NIST NCSTAR 1-3C. These 21 panels represent only 3 percent of the panels on floors involved with fire and cannot be considered representative of other columns on these floors. Only three locations showed evidence of paint mud cracking:
1. Panel K-1, WTC 1, column 210, flange and inner web of 98th floor region. Prior to the collapse of WTC 1, the panel was observed to have experienced varying degrees of fire exposure for a minimum of 31 cumulative minutes in this area. A unique feature of this panel is that the upper portion of the column was crushed while generally maintaining concentric axial alignment with the lower portion of the column, Fig. 6–36. This suggests that deformation occurred at the onset of collapse, while the lower portion of the column was still constrained due to the bolted splice (endplates).
2. Panel K-2, WTC 1, column 236, 93rd floor spandrel. This area was observed to have fire exposure for nine cumulative minutes prior to collapse, Fig. 6–13. A positive reading was made directly below the truss seat while above the seat in the same location a negative result was obtained, Fig. 6–37. This suggests that the concrete floor may have shielded the upper portion of the column from the high-temperature exposure experienced by the lower portion.
3. Panel N-8, WTC 1, column 143, seat and standoff plates of the 99th floor. This seat (Fig. 6–38) was exposed to fire for a minimum of 18 cumulative minutes before collapse. Mud cracking was not observed on the spandrel plate to which the seat was welded.
6.6.2 Core Columns Exposed to Fire
Four of the core columns with known as-built locations were examined for mud cracking of the paint. For columns C-88a and C-88b, sufficient paint for analys is was not available. For columns HH and C-80, few areas of paint were observed (three to five spots per column) with no indication of temperatures over 250 °C. Note that these core columns represent less than1 percent of the core columns on floors involved with fire and cannot be considered representative of any other core columns.
6.6.3 Metallographic Analysis of Elements Exposed to Fire
Some aspects of the thermo-mechanical history of a structural steel element may be revealed through a careful assessment of the component’s microstructure. Identification of phases, whether stable or metastable, and their characteristics (e.g., size, morphology, distribution) can help lead to an understanding of the possible rolling conditions and/or cooling rates used during fabrication.
These factors are directly related to the room temperature mechanical properties of the component. Likewise, high-temperature excursions due to fire can also alter the microstructure and the mechanical properties. Therefore, if knowledge of the as-fabricated microstructure is available, then a review of the “affected” microstructure may give an indication of the level of elevated temperature exposure while in service. Thus, an assessment was made to determine if information could be compiled on the extent and effect of fire exposure through changes in the microstructure. When appropriate, chemical analysis and hardness evaluations were used to supplement the results. A full discussion of these results can be found in NIST NCSTAR 1-3C.
Samples for analysis were chosen based upon the panel exposure to pre-collapse fires. These included floor truss connectors (seats) and the lower portion of spandrels where external flaming was observed in the window directly beneath the location of sample removal.
The microstructural results were compared with the paint mapping analysis, to confirm the apparent dissonance between the results of the paint mapping study and those from the pre-collapse fire exposure results reported in Sec. 1.2.5
The spandrel steels identified as having been exposed to fire prior to the collapse of the building showed no microstructural evidence of change. Similar results indicated that three of the four seats observed to be exposed to severe pre-collapse fire conditions did not experience significant microstructural changes as a result of the exposure.
However, the seat with the melted binder (Fig. 6–38) did show signs of microstructural alteration as a result of elevated temperature exposure, though it was unknown when this exposure occurred.
Finally, in the several columns with known pre-collapse fire exposure, metallographic analysis provided no conclusive evidence that the steel exceeded 625 °C, based on calibrations in furnace exposure studies of WTC steel reported in NIST NCSTAR 1-3E.
ALLORA, il contenuto di quei paragrafi che decalagon continua ad elencarmi è questo, PER INTERO.
Dr House insiste dicendo che io faccio il “giochino” del cherry picking…
Bene… nonostante il mio inglese traballante sono perfettamente in grado di leggerlo, e se volete disponibilissimo a ricopiarlo in italiano.
ALLORA: CI SONO DUE IPOTESI DI INTERPRETAZIONE (mentre il significato è univoco…):
Decalagon (e gli altri) conclude così:
"non sono state trovate prove decisive che gli incendi che hanno preceduto i crolli siano stati abbastanza gravi da avere conseguenze significative che portassero ad un indebolimento della struttura d'acciaio".
INVENTANDOSI PARI PARI la frase “…siano stati abbastanza gravi da avere conseguenze significative…”
MENTRE IO CONCLUDO COSI’:
“nelle diverse colonne con conosciuta esposizione al fuoco prima del collasso, l’analisi metallografica non FORNISCE PROVE SCHIACCIANTI CHE L’ACCIAIO HA SUPERATO I 625°… based on ecc ecc."
ALLORA CHI E’ CHE NON HA LETTO BENE? E DOVE HO FATTO CHERRY PICKING?
CIAO!
Allora, come preannunciato ieri sera è buona educazione, prima di andare avanti, quella di commentare e cercare di dare una risposta a tutti gli interventi che si sono sussseguiti all’ultimo mio di ieri pomeriggio (circa una ventina…)
Ritengo che questo sia il modo più corretto di portare avanti un dibattito, altrimenti non si capisce poi più bene il filo logico.
Se qualcuno di voi etichetta questo mio modo di fare come TERGIVERSARE è un problema suo: io ho postato una bella (?) e pesante trattazione, alcuni di voi hanno preso forti posizioni contrastanti e quindi bisogna un attimino fare il punto.
… e naturalmente slitterà di un poco anche la trattazione che le termografie sono esatte E PERFETTAMENTE COMPATIBILI con i 1100 gradi all’interno (ovvero lo spettacolo tanto atteso, cioè LA BATOSTA)
Piccola premessa:
MI SCUSO PUBBLICAMENTE se in un mio post ho fatto una battuta un po’ spiacevole (riguardo certe dimensioni…)
SCUSATEMI ANCORA, nella mia mente pensavo di partecipare ad un qualsiasi dibattito tra maschietti adulti, insomma la classica discussione del dopocena di gruppo, dove anche peraltro molto animatamente (ma senza per questo arrivare alle botte neh…) ognuno butta lì le sue asserzioni. Bene in queste circostanze, solitamente, battute simili sono all’ordine della serata, e ritengo sia normale così, in modo da spezzare ogni tanto il discorso e farsi una sonora risata!
Però è altresì vero che non tutti la pensiamo allo stesso modo, per cui se qualcuno è rimasto diciamo contrariato, CHIEDO UMILMENTE SCUSA ben sicuro che da parte mia non si ripeterà più!!
Andiamo avanti…
@dr house
Hai asserito che uso il metodo cherry picking. Allora andiamo a prendere in esame la pagina del nist per intero e la mettiamo qui:
6.6.1 Visual Inspection of Recovered Structural Components
NIST has developed a novel approach to evaluating the primer paint on the structural components for evidence of exposure to high-temperature excursions (see Appendix D of NIST NCSTAR 1-3C).
This method was found to be relatively easy to implement and robust enough to examine an entire component in the field. Calibration tests in the laboratory showed that, although there was little or no change in color, the primer paint used on the WTC steels that reached temperatures over 250 °C cracked (similar to a “mud cracking” pattern) from the difference in thermal expansion between the paint and the steel.
Since deformation and environmental effects can also cause mud-cracking, the absence of mud-cracking indicates the steel has not exceeded 250 °C, but the presence of mud cracks cannot be assumed to be caused by high temperature. Visual inspection for the fire effects on recovered steel was conducted solely on the perimeter panels and core columns, as these were the only structural elements that had known as-builtlocations. Twenty-one panels were selected with numerous locations on the inner webs, flanges, spandrels, and floor truss connectors for each floor level analyzed, providing that sufficient paint was available for the analysis.
Core columns C-80 and HH from WTC 1 were examined while C-88a and C-88b were tested from WTC 2; these columns resided within the fire floors for their respective buildings. The entire length of each core column was examined, and evaluations of the primer paint were made when sufficient paint was available for inspection.
over 170 areas associated with the 21 exterior panels were analyzed, and the results may be found in Appendix E of NIST NCSTAR 1-3C. These 21 panels represent only 3 percent of the panels on floors involved with fire and cannot be considered representative of other columns on these floors. Only three locations showed evidence of paint mud cracking:
1. Panel K-1, WTC 1, column 210, flange and inner web of 98th floor region. Prior to the collapse of WTC 1, the panel was observed to have experienced varying degrees of fire exposure for a minimum of 31 cumulative minutes in this area. A unique feature of this panel is that the upper portion of the column was crushed while generally maintaining concentric axial alignment with the lower portion of the column, Fig. 6–36. This suggests that deformation occurred at the onset of collapse, while the lower portion of the column was still constrained due to the bolted splice (endplates).
2. Panel K-2, WTC 1, column 236, 93rd floor spandrel. This area was observed to have fire exposure for nine cumulative minutes prior to collapse, Fig. 6–13. A positive reading was made directly below the truss seat while above the seat in the same location a negative result was obtained, Fig. 6–37. This suggests that the concrete floor may have shielded the upper portion of the column from the high-temperature exposure experienced by the lower portion.
3. Panel N-8, WTC 1, column 143, seat and standoff plates of the 99th floor. This seat (Fig. 6–38) was exposed to fire for a minimum of 18 cumulative minutes before collapse. Mud cracking was not observed on the spandrel plate to which the seat was welded.
6.6.2 Core Columns Exposed to Fire
Four of the core columns with known as-built locations were examined for mud cracking of the paint. For columns C-88a and C-88b, sufficient paint for analys is was not available. For columns HH and C-80, few areas of paint were observed (three to five spots per column) with no indication of temperatures over 250 °C. Note that these core columns represent less than1 percent of the core columns on floors involved with fire and cannot be considered representative of any other core columns.
6.6.3 Metallographic Analysis of Elements Exposed to Fire
Some aspects of the thermo-mechanical history of a structural steel element may be revealed through a careful assessment of the component’s microstructure. Identification of phases, whether stable or metastable, and their characteristics (e.g., size, morphology, distribution) can help lead to an understanding of the possible rolling conditions and/or cooling rates used during fabrication.
These factors are directly related to the room temperature mechanical properties of the component. Likewise, high-temperature excursions due to fire can also alter the microstructure and the mechanical properties. Therefore, if knowledge of the as-fabricated microstructure is available, then a review of the “affected” microstructure may give an indication of the level of elevated temperature exposure while in service. Thus, an assessment was made to determine if information could be compiled on the extent and effect of fire exposure through changes in the microstructure. When appropriate, chemical analysis and hardness evaluations were used to supplement the results. A full discussion of these results can be found in NIST NCSTAR 1-3C.
Samples for analysis were chosen based upon the panel exposure to pre-collapse fires. These included floor truss connectors (seats) and the lower portion of spandrels where external flaming was observed in the window directly beneath the location of sample removal.
The microstructural results were compared with the paint mapping analysis, to confirm the apparent dissonance between the results of the paint mapping study and those from the pre-collapse fire exposure results reported in Sec. 1.2.5
The spandrel steels identified as having been exposed to fire prior to the collapse of the building showed no microstructural evidence of change. Similar results indicated that three of the four seats observed to be exposed to severe pre-collapse fire conditions did not experience significant microstructural changes as a result of the exposure.
However, the seat with the melted binder (Fig. 6–38) did show signs of microstructural alteration as a result of elevated temperature exposure, though it was unknown when this exposure occurred.
Finally, in the several columns with known pre-collapse fire exposure, metallographic analysis provided no conclusive evidence that the steel exceeded 625 °C, based on calibrations in furnace exposure studies of WTC steel reported in NIST NCSTAR 1-3E.
ALLORA, il contenuto di quei paragrafi che decalagon continua ad elencarmi è questo, PER INTERO.
Dr House insiste dicendo che io faccio il “giochino” del cherry picking…
Bene… nonostante il mio inglese traballante sono perfettamente in grado di leggerlo, e se volete disponibilissimo a ricopiarlo in italiano.
ALLORA: CI SONO DUE IPOTESI DI INTERPRETAZIONE (mentre il significato è univoco…):
Decalagon (e gli altri) conclude così:
"non sono state trovate prove decisive che gli incendi che hanno preceduto i crolli siano stati abbastanza gravi da avere conseguenze significative che portassero ad un indebolimento della struttura d'acciaio".
INVENTANDOSI PARI PARI la frase “…siano stati abbastanza gravi da avere conseguenze significative…”
MENTRE IO CONCLUDO COSI’:
“nelle diverse colonne con conosciuta esposizione al fuoco prima del collasso, l’analisi metallografica non FORNISCE PROVE SCHIACCIANTI CHE L’ACCIAIO HA SUPERATO I 625°… based on ecc ecc."
ALLORA CHI E’ CHE NON HA LETTO BENE? E DOVE HO FATTO CHERRY PICKING?
CIAO!
Messaggio orinale: https://old.luogocomune.net/site/newbb/viewtopic.php?forum=4&topic_id=7462&post_id=238063