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NONDESTRUCTIVE TEST FOR STRUCTURAL REHABILITATION. THE CASES OF DEVIL'S AND S. DONATO'S MASONRY BRIDGES IN VENICE S. Russo 1 , G. Boscato 1 , and L. Massaria 1 1 IUAV University of Study, Venice, Italy Abstract: As much known the use of nondestructive test as a methodology to better understand the technical choices more opportune in the field of structural reinforcement and restoration, represents by now a good way for monument and historical manufactured. This research shows the first results on non destructive tests carried out on two masonry bridges in venetian islands Torcello and Murano, named respectively Devil's bridge and realised approximately in XII century, and S. Donato bridge's, in the XVII century. For both bridges nondestructive test (NDT) connected to destructive test (DT) to evaluate the compressive strength of the brick and the homogeneity/compactness of the masonry has been realised. Introduction: The aim of this research regards the evaluation of mechanical characteristics of masonry (brick and mortar) and its homogeneity in the cases of two historical masonry bridge situated in venetian islands Torcello and Murano. For both type of structures named respectively Devil's (in Torcello) and S. Donato's (in Murano) bridge this study shows the first results on non destructive test carried out to evaluate the structural behaviour. In both case we have the arch static scheme, the test has been ordered from venetian municipality in view of the structural restoration with appropriate reinforcement or employment of the new material with the same mechanical characteristics. For NDT the penetrometer to measure the energy released per each hole in the masonry and the Fourier analysis setup were employed; the first instrument gives results on mechanical performance of mortar and brick (also with DT to deduce the curve of calibration between DT and NDT results); with Fourier setup (sonic test type) the information on the homogeneity of the masonry and on the possible presence of empty inside were expected. Also the endoscopy has been utilised in critical cross sections of masonry vaults, to understand the effective stratigraphy of structure. For a structural view point, the study also give prominence to the interaction between the geometry of the structure and the mechanical characteristics of masonry, especially in the case which the structure is very old and the materials (masonry and brick) show low values of mechanical performance. The type of test employed - sonic test - is by now one of more reliable choice to understand in situ the effective performance of structure without destructive test, (1), (2), especially in presence of historical monument/structure, (3), (4), this not only for global performance of masonry but also for the mechanical characteristics of the materials, (5), (6). Besides many works already available in literature give some information of this non destructive procedure, (7), (8). For each bridge the research shows also the crack pattern, the presence of local damage and the general situation for static view point, with the evaluation of effective stiffness degree of boundary condition. The research shows the first results with Fourier analysis device sonic test. Figure 1, 2 shows the dimensions, geometry, material and one view for S. Donato Bridge; figure 3, 4 shows the same thing for Devil bridge. Figure 5 and 6 illustrate for both bridges the crack pattern with presence of local damage. 2512 2371 3 9 1632 3 8 A 418 B A B 9 7 1 4 1 3 4 0 5 4 1 1 4 8 9 5 7 5 9 6 9 9 2 7 420 0 3 9 4 1 2472 2503 Plan LEGEND 458 1032 1019 2510 1550 Trachyte 06 1014 Istria stone 36 UNIT OF MEASURE = cm. 3 6 Brick Campo San Donato 1635 93 1 0 7 1570 Fondamenta A. Maschio 56 56 410 41 86 38 40 42 Prospect1 207 1 4 6 4 79 54 10 80 63 14 3 8 9 0 494 34 491 1240 1034 Fondamenta A. Maschio 234 Section A-A 510 781 791 Section B-B Figure 1 - plan, sections, prospect 1 Figure 2 - view SOUTH 1234 364 453 LEGEND Brick herring-bone pattern Grass 417 B B A 296 29 29 29 5 1 3 4 6 6 Brick 4 6 5 28 8 289 29 private street 29 5 1 A 900 Istria stone 1242 940 1 Unit of measure = cm. Plan 459 361 1183363 52 2 2 5 5 2 4 Prospect 1 49 290 46 601 149 146 141 52 5238 5 31 2 1 30 1 25 0 240 284 464 Section A-A Section B-B Figure 3 - plan, sections, prospect 1 Figure 4 - view WEST Figure 5 - Detail of local damage of Devil bridge Figure 6 - Detail of local damage of S. Donato bridge Results: The Fourier analysis device gives many information on velocity of sonic wave induced by hammer and measured through the masonry by accelerometer. In this way by Fourier's series and fast Fourier transform algoritm the is also possible to determine the frequency and thus the energy dissipated, see respectively equation (1) and (2), (3). F( t ) = a 0 + Σ (n=1 to inf.) [ a n cos n ω t + b n sin n ω t ] (1) with, F( t ) = periodic function ω = 2π /T = frequency T= period of function a 0 ,a n ,b n = Fourier coefficients and for fast Fourier transform we have A(k) = Σ (n=0 to N-1) D(n) e -j2πnk/N (2) with the associated inverse equal to D(n) = Σ (k=0 to N-1) A(k) e +j2πnk/N (3) with, n,k = dimensionless indices, 'n' refers to time increments, 'k' to frequency increments In the case of Devil's bridge the dynamic identification is very interesting because there is not the parapets (see Figure 4) and consequently the evaluation of static and homogeneity of the masonry vault deck is not influenced by the presence of the other structural elements. Figures 7 and 8 show respectively the distance-velocity and the energy dissipated-velocity diagrams for Devil's bridge. Tables 1 and 2 show in both axis x-y the velocity of sonic wave and the percentage of energy released. Distance (cm) Time to wave sonic transit (µs) Velocity (m/sec) Energy retained (%) Energy Released (%) 860 19360 440 0.041 99.96 860 14120 610 0.098 99.90 Table 1- Devil's Bridge. Sonic test on the total longitudinal axis (y) Point Transversal dimension of bridge (cm) Time to wave sonic transit (µs) Velocity (m/sec) Energy retained (%) Energy Released(%) 1 200 6697,5 300 0.35 99.6 2 / 6717,5 300 0.26 99.7 3 / 6277,0 320 0.35 99.6 4 / 6017,4 330 0.35 99.6 5 / 4717,7 420 0.34 99.7 6 / 6700,0 300 0.74 99.2 7 / 6777,0 300 0.37 99.6 8 / 5797,6 340 0.41 99.6 9 / 5582,5 360 0.47 99.5 10 / 5017,5 400 0.64 99.3 11 / 3597,5 550 0.35 99.6 12 / 5057,0 400 0.31 99.7 13 / 5217,5 380 0.36 99.6 Table 2- Devil's Bridge. Sonic test on the longitudinal axis (x) X Y Figure 7 - Devil's Bridge Sonic test - x axis X Y Figure 8 - Devil's Bridge Sonic test - y axis Conclusions: The main findings of this study, for the Devil's bridge, are summarized as follows: a) the level of velocity sonic wave came approximately from 400 to 600 m/sec and is strongly lower than the average value for a good quality masonry (even if old) that came from 1800 to 2000 m/sec.; b) the sonic wave velocity shows also that in the x direction the homogeneity of deck vault is lower than the y axis. This aspect is obviously influenced by the position of the brick and by the presence of cracks; c) if we consider the very low value of thickness of the vault and the low level of homogeneity of the masonry, we can conclude that even if in presence of very old bridges and of the global deterioration of mechanical performance of masonry, the arch static scheme plays a very important rule for structural view point; d) The results showed in Table 1 give prominence that along the total longitudinal length of the bridge the level of energy retained is almost null; e) The results in Table 2 show the good quality of results (for statistically view point) in term of value of wave velocity, even if this value is strongly influenced by the presence of longitudinal cracks present in the vault. f) Generally speaking, this research is still in progress, the next step will consider the calibration between NDT and DT for both bridges. References: (1) NOLAND J.L., ATKINSON R.H., BAUR J.C. - "An investigation into Methods of nondestructive evaluation of masonry structures", Report National Science Founfation, National Technical information service report N° PB 82218074, Springfield, Virginia, 1982. (2) KOMEYLI F., FORDE M.C., WHITTINGTON H.W. - "Sonic invetsigation of shear failed reinforced brick masonry", Masonry Industry, November 1989. (3) RUSSO S., CELEBRIN M., MASSARIA L., - "Indagine non distruttiva su volte e paramenti murari del Palazzo di Diocleziano di Spalato", La tutela del patrimonio architettonico nel bacino del Mediterraneo, pp. 179-186, Mario Adda Editore, Bari, 2002 (4) RUSSO S., "Problemi connessi al rilievo della compattezza di paramenti murari mediante indagini soniche. Il caso dell'Edificio Foscari a Venezia", Atti del Dipartimento di Costruzione dell'Architettura dello IUAV, 1998. (5) BERRA M., BINDA L., ANTI L., FATTICCIONI A.- "Utilization of sonic tests to evaulate daamged and repaired masonry", Proc. Conf. On Non destructive evaluation of Civil Structures and materials, Colorado, 1992. (6) MENDITTO G., GIACCHETTI R.- "Indagini dinamiche non distruttive per l'individuazione delle caratteristiche meccaniche delle strutture", Quaderno CIAS , Italy, 1992. (7) MS-D.1 - "Measurement of mechanical pulse velocity for masonry", Materials and Strcutures, Vol. 29, October 1996. (8) recommendation of RILEM TC 127-MS - "Test for masonry materials and structures", Materials and Structures, Vol.29, October 1996.

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