IN SITU TESTS FOR SEISMIC ASSESSMENT OF R.C. STRUCTURES

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1 Otober -7, 8, Beijing, China IN SITU TESTS FOR SEISMIC ASSESSMENT OF R.C. STRUCTURES S. Biondi, E. Candigliota Assoiate Professor, Department of Design, Rehabilitation and Control of Arhitetural Strutures, Prios, University G. D Annunzio, Chieti-Pesara, Italy Ph.D. in Strutural Engineering, Department of Design, Rehabilitation and Control of Arhitetural Strutures, Prios, University G. D Annunzio, Chieti-Pesara, Italy ABSTRACT: [email protected], [email protected], In Italy a great part of the territory wasn t lassified as seismi up to 3, so that lower intensity earthquakes aused important strutural damages and loss of human life (as for Umbria-Marhe Region Earthquake 997 and Molise Earthquake ). Partiularly relevant buildings (Monumental Buildings as San Franeso Basilia in Assisi in 997, Publi Buildings as San Giuliano Primary Shool in Molise in ) suffered an extreme earthquake fragility. For this reason new Codes were issued by National Government; in all these Codes seismi zoning was improved and existing buildings diagnosis is onsidered as a relevant topi. At same time a wide program of strutural analysis and seismi assessment was finaned by Loal and National Governments. On the basis of these new seismi Codes, in the Abruzzo Region, in Eastern Central part of Italy, four reently built sport domes (Chieti, Laniano, Ortona, asto) were analyzed in order to evaluate their seismi behavior. All of these buildings have been designed without any seismi provision. A wide program of in situ and laboratory tests was arried out regarding RC elements of these buildings. In partiular the atual onrete strength is deteted by means of ombined non-destrutive methods (Rebound index, ultrasoni veloity). Some onrete ores were drilled out for destrutive laboratory tests in order to determine both ompressive harateristis (strength and elasti modulus) and to validate in-situ non destrutive tests. Some literature proposals are disussed for test data evaluation. Proposals for strutural engineer involved in suh ativities are arried out. KEYWORDS: RC existing frames, in-situ non destrutive tests, SonReb method, existing frames seismi assessment. INTRODUCTION From a geotetoni point of view, Italy is learly a seismi prone Nation and a lot of earthquakes have been suffered in many parts of the Country. Some of these earthquakes were very destrutive (suh as Messina Earthquake in 98, Friuli Earthquake in 976, Irpinia Earthquake in 98). Naturally the greater part of earthquakes was low and medium intensity earthquakes; in spite of that situation, a great part of National territory wasn t lassified as seismi (as Molise region involved in earthquake, Mola et al. 3) and these lower intensity earthquakes aused unexpeted failure of relevant buildings (as Umbria-Marhe Region Earthquake, De Sortis et al. ). After the Molise Region Earthquake, the seismi zoning was upgraded and all national territory has been lassified as seismi with 4 seismi input levels (OPCM (3)). This Code wasn t a full Performane Based Code but it provided that an extensive program of seismi analysis ould be arried in order to define a global strategy for seismi risk redution. In partiular strategi existing buildings, as shools, hospitals, fire-stations, had to be analyzed in order to obtain not only a Life Safety Performane Level but also an Operational or Immediate Oupany Level. More reently another Code (D.M. 4..8) onfirmed these objetives and redefined seismi zoning introduing a grid of 75 nodes of seismi spetral parameters for all national territory. In eah node a different value for peak ground aeleration (a g ), loal amplifiation fator (F o ) and ontrol period (T C, upper limit of the period of the onstant spetral aeleration branh) is defined. On the basis of these Codes four sport buildings are analyzed in order to evaluate their seismi behavior; this analysis was promoted by Chieti Provinial Government for 7 Women European Basketball Championships.

2 Otober -7, 8, Beijing, China The buildings are reently built with RC struture without seismi odes and preliminarily to a modeling ativity (that was arried out by another Chieti-Pesara University researh team), a wide program of in situ and laboratory tests was arried out regarding RC elements. This in-situ ampaign onsisted of determination of onrete arbonation degree, reinforement disposal by means of over meter instrumentation and onrete strength determination by ombined non-destrutive methods (rebound index and ultrasoni pulse veloity). Some ylindrial onrete speimens were drilled out in order to arrying out ompressive laboratory tests for in situ data validation. Some results were disussed in Biondi et al. (8). In the present paper the omplete test program will be presented and some operative onlusions will be pointed out, useful for similar strutures.. SEISMIC ZONING AND LOCALIZATION OF TEST SITES In Figure Italian seismi zoning evolution is pointed out, the 984 Code map was in fore at the time of Molise Earthquake beause the 998 National Commission Proposal wasn t issued as Tehnial Code. Aording to this 984 zoning all four sites were seismially unlassified (grey olor in map).in 7 seismi zone in fore was that of OPCM 374 (3): Chieti was nd ategory seismi zone, Laniano, Ortona and asto were 3 rd ategory seismi zones. In Table seismi parameters for different seismi ategories aording to OPCM 374 (3) are shown for C ground type. Today the latter Code is in fore (D.M. 4..8), in Table spetral parameters of this Code are summarized onsidering two returns periods that quit represents respetively Damage Limit State ( T R = years) and Ultimate Limit State ( T R = 475 years) for lass III buildings. The OPCM 374 (3) onsiders an importane fator γ I =. for this lass of buildings: so seismi parameters of two Codes are quite similar. Figure. Italian seismi zoning (Chieti Provine highlighted) after 984 Code (left), 998 National Commission Proposal (enter), OPCM 374 (3) (right) In Figure photos of the Sport domes of this researh are shown (Calzona (98)); every struture is ast in situ reinfored onrete struture. Strutural arrangement is generally haraterized by a entral hall with lateral (ast in sity or partially preast) tiers of seats; under these tiers generally are loated dressing rooms, lavatories, tehnial rooms or, as in Laniano dome, little boxing hall. As shown in Figure RC frames are partially infilled and generally a soft storey portion is deteted on the top of tiers; due to seismi fragility of this onfiguration, a great part of test in situ and ore drilling was at this level. Table. Seismi parameters for different seismi ategories aording to OPCM 374 (3) City 3 OPCM zoning D.M zoning T R = years T R = 475 years Seismi a g /g S T a g /g F o T a g /g F o T Category [-] [-] [s] [-] [-] [s] [-] [-] [s] Chieti Laniano Ortona asto

3 Otober -7, 8, Beijing, China Figure. Sport domes involved in in-situ test ampaign: Chieti, Laniano, Ortona, asto Due to diret ontat of RC elements with atmosphere (often near the sea) and pollution, relevant arbonation effets on onrete were expeted and ontrolled by means of arbonation degree measures. 3. NON DESTRUCTIE METHODS FOR COMPRESSIE STRENGTH EALUATION Aording to OPCM 374 (3) or to Euroode 8 (CEN 5), a knowledge level has to be preliminarily evaluated in order to define material properties for existing buildings and onsequently to define a orret strutural analysis and assessment design proedure. This knowledge level onsiders three different evaluation steps: geometry, details and materials. Regarding materials evaluation OPCM 374 (3) stated that non-destrutive test methods ouldn t be used in plae of destrutive tests. This limit was removed by OPCM 343 (5), (Biondi (8)). Basing on knowledge level definition goal some destrutive tests have to be arried out: in the ase of an RC struture both ompressive tests on ores and tensile tests on rebars obtained by mean a onrete over removal and a mehanial ut of longitudinal or transversal rebars. These proedures are too intrusive for RC strutures, for this reason some loal governments state different approahes: so Tusany Region disourages the rebar extration due to diffiulty in a orret reonstrution (Ferrini Ed. 4) while Basiliata Region, aording to OPCM 343, enourages to substitute destrutive tests with non-destrutive tests (Dole et al. 5) for a maximum of % of tests. In the ase this paper a similar proedure was adopted aording with Publi Owner Government: no tensile tests on existing rebars were arried out (onsidering the industrial origin of steel omponent) while an extensive series of onrete tests was defined. In partiular onrete ores were drilled out (some of them were subdivided in two parts for global 3 onrete ylindrial speimens), 68 rebound test and 78 ultrasoni test sites were defined (some of them were both diret and semi-diret or indiret measurements for a global number of 66 measurements). Before drilling out non destrutive tests were arried out in the test site in the aim to orrelate laboratory to in-situ results. As in pratie ompressive strength values is prinipal objetive of this test series while a few tests for elasti modulus evaluation were arried out in laboratory. In order to arry out eah test phase, expert tehnial people was employed and standard provisions are taken into aount: UNI EN 4-: (ore drilling and testing), UNI EN 4-: (rebound number), UNI EN 4-4:5 (ultrasoni pulse veloity), UNI EN 395:5 (resistane to arbonation). Correlation formulas, basing on literature proposals or pratie, will be disussed in the following paragraphs. 3.. Rebound index Four different Shmidt hammers were used in order to determine rebound index I ; an horizontal position was assumed by the operator and equivalent ube ompressive strength R R (in MPa) has be determined by using two different rebound index I orrelation formulas: R R = α I + βi + ϕ (3.) ( ) 3.7 RR = 9.67 I (3.) Eqn. (3.) parameters are defined on the basis of Shmidt hammer instrutions while Eqn. (3.) is a literature proposal; in Figure 3 the good approximation of this general orrelation formula is pointed out with respet of different produer instrutions in the range I. For this reason it is possible to note that the great differene between rebound index ompressive strength and ore ompressive strength that will be pointed out in the next hapter, doesn t depend on orrelation formulas but is deeply rooted in rebound index method itself.

4 Otober -7, 8, Beijing, China RR = α I + βi + ϕ Instrument α β ϕ I II III I R R ( I ) R R ( I ) Figure 3. Comparison between average values of (3.) [dot line] and (3.) [solid line] equations for I 3.. Ultrasoni veloity Thus for Rebound index, orrelations between the pulse veloity and strength of onrete are physially indiret and ould to be established for the speifi onrete mix (UNI EN 4-4:5). In ase of existing buildings not only onrete mix is unknown but also reinforement and random raking distribution are unknown. If an elasti isotropi medium is assumed, a ompressive strength R (in MPa) an be determined by means of dynami E d, stati elasti modulus E, using ultrasoni pulse veloity (m/s), Poisson ratio ν, onrete mass density γ (kg/m 3 ) as shown in Eqn. (3.3). In Eqn. (3.3) oeffiients in funtional relationship between 6 dynami and stati elasti modulus are δ =.49 and λ =.5953 for 3 m/s. The ompressive ubi strength, R, is obtained from ylindrial ompressive strength, f, aording to Code as R =.83 f : E d ( + ν)( ν) γ = γ = ν η E fk λ fk E = = δ Ed R = = (3.3) R = = R 4 =.73e (3.4) In Eqn. (3.4) three other relationships are shown: the first, R, onsiders only the pulse veloity, the seond, R, is an expliit relationship in term of elasti harateristis of medium and the third was proposed for low 3 R ( η η ) strength onrete. In Figure 4 a omparison for these four formulas is arried out in the range m/s. For R the onventional values γ = 3 kg/m 3 and ν =. are onsidered. It is possible to note that R shows an asymptoti value for = m/s and is negative for higher pulse veloity; similar asymptoti behavior for R 3. As stated R 4 is in the range of other relationships only for lower pulse veloity. I R ( v ) R ( v ) R 3 ( v ) R 4 ( v ) R ( v) R ( v) R 3 ( v) Figure 4. Comparison of different strength provisions (left). ariation of R value on Poisson s ratio (enter, onstant mass density γ = 3 kg/m 3 ) and mass density (right, onstant Poisson s ratio ν =. ) If Eqn. (3.3.) is assumed as unique stable relationships in onrete typial pulse veloity range, it ould be interesting to evaluate the sensitivity of this relationship on Poisson s ratio and mass density. The first ase is shown in Figure 4 (enter) for ν =. (solid line), ν =. (dot line) and ν =. (dashed line). The seond one is shown in Figure 4 (right) for γ = kg/m 3 (solid line), γ = kg/m 3 (dot line) and γ = kg/m 3 (dashed line). It is possible to note that the first parameter is more relevant than seond one.

5 Otober -7, 8, Beijing, China Theoretially Eqn. (3.3)-(3.4) an be used for non diret tests: aording to UNI EN 4-4:5 for semi-diret the path length is the distane measured from entre to entre of the transduer faes while for indiret transmission a series of measurements has to be made with the transduers at different distanes. We will see that these provisions don t guarantee orret ompressive strength evaluation SonReb method The SonReb (Soni & Rebound) method is a well known method that aims to inrease the auray of single methods; two equations of similar mathematial struture are used, based on rebound index and pulse veloity,:,, RS = I (3.5) RS =. I (3.6) The first of these relationships is a Rilem Standard provision while the seond is a literature proposal for low pulse veloity. In Figure 5 sensitivity of theses relationships on rebound index and pulse veloity are shown. The first ase is shown in left side for different pulse veloity: = 3, =, = m/s. The seond one is shown in right side for I = 35, I =, I = 45. Eqn. (3.6) generally overestimates ompressive strength in omparison with Eqn. (3.5). It is to note that both equations disregards theoretial dependene on Poisson s ratio and mass density of Eqn. (3.3). R S ( I, ) R S ( I, ) R S ( I, 3 ) R S ( I, ) R S ( I, ) R S ( I, 3 ) R S ( I, v) R S ( I, v) R S ( I 3, v) R S ( I, v) R S ( I, v) R S ( I 3, v) I Figure 5. Comparison between R S (solid line) and R S (dot line) provisions for three different pulse veloity values (left) and three different rebound index (right) 4. TEST RESULTS ANALYSIS A great number tests were arried out in situ (68 rebound and 78 ultrasoni tests, the latter for 66 different diret, semi-diret or indiret measures) and in laboratory ( drilled ores were used to prepare 3 ylindrial onrete speimens. Eah speimen was used in ompressive and pulse veloity tests). In Figure 6 a preliminary evaluation of semi-diret and indiret pulse veloity measures is arried out.,5,,75,,5, -,5 -, -,75,x olumn,x olumn,x beam,x beam ,,75,,5,,75, Figure 6. Pulse veloity slope in indiret tests for olumns and beams (left), ratios between different pulse veloity proedure (d diret, s semi-diret, i indiret, right) s/d i/d i/s

6 Otober -7, 8, Beijing, China In the left side of Figure 6 average values of pulse veloity slope (adimensional variation for unity length) for 7 olumns and beams are shown both onsidering the sign,,x, and in absolute value,,x, where x i and i are respetively position and pulse veloity at i th point of measure of a series of n points of measure:, x Δi i+ i = = n Δx n x x ( ) n i i n i+ i i, x Δ = = n Δx n x x i i+ i (4.) n i i n ( i+ i) i It is possible to note a onsiderable variation of these parameters ( 46% and 9% in terms of absolute value respetively for olumns and beams). This sattering is onfirmed if the right side of Figure 6 is onsidered. In this diagram results in terms of semi-diret to diret (s/d), indiret to semi-diret (i/s), indiret to diret (i/d) pulse veloity ratios are shown for 3 measure points where at least two kinds of measure were arried out. A great differene an be observed. On the basis of these result the assumption of Tosana Region (Ferrini (Ed.) 4) to avoid non diret ultrasoni measure has to be onsidered orret, above all for olumns, and ould be reommended to strutural engineers when old existing buildings have to be investigated. On the ontrary, if it should be impossible to make diret pulse veloity measures, a measure series has to be arried out for eah test position and a loal orrelation funtion is stritly reommended. In order to evaluate ombined method provisions in Figure 7 a omparison between rebound strength R R, pulse veloity strength R, Eqn. (3.5)-(3.6) SonReb strengths, R S and R S, is arried out. Data regard 39 test stations and onsider only diret pulse veloity test, thereafter data are ordered for inreasing values of R S. It is possible to note a quite regular behavior: the RS value is average of rebound and pulse veloity values. Thereafter for low pulse veloity results the ombined method values are influened by pulse veloity values in spite of rebound index values. These results ould be onsidered as enouraging if it is possible to demonstrate the availability of R S SonReb expression for this kind of onrete. As above said 3 ylindrial onrete speimens have employed for both ompressive and diret pulse veloity test: results are disussed in Figure 8. 7 R R R R S R S Figure 7. Comparison between rebound strength R R, ultrasoni strength R, SonReb strengths, RS- R S Figure 8. Comparison of R - R ompressive strengths with ore ultrasoni strengths, R - R. Data ordered for asending ore strength R (left side) and for asending speimen mass density γ i (right side). R R R R

7 Otober -7, 8, Beijing, China Core speimens where = 75 95mm diameter with various slenderness ratio. l /.36 ; these speimens are preliminarily tested using ultrasoni apparatus and then in ompression; in this ase two orrelations between test ylindrial f and equivalent ubi R ompressive strength were onsidered:. f l f C CrCd =.98 = R R. + l (4.) The first (Biondi et alt. 8) is valid in for l /., in the seond C, C r and C d are orretion oeffiients depended on ore diameter, rebar presene, damage due to drilling out (Dole et al. 6). In Figure 8 together with R and R of Eqn. (4.), Eqn. (3.3) is used in order to obtain both R (with mass density γ = 3 kg/m 3 ) and R with atual mass density for eah ore ( 85 γ i 37, average value γ = kg/m 3 with only two ores with γ i > kg/m 3 ). In the right side of Figure 8 same data are shown in terms of speimen mass densityγ i. It is possible to note a lear dependene of ompressive strength on ore mass density (Biondi et al. 8) and to point out that the use of atual mass density in Eqn. (3.3) redues pulse veloity sattering. In Table average values and standard deviation for eah quantity are summarized (where ρ ij = R i R j R j ). As shown in Figure 4, probably a better fitting of experimental data ould be obtained if atual Poisson s ratio is used in Eqn. (3.3). But unfortunately for strutural engineer this value is quite diffiult to determine than mass density. Table. Average values and standard deviation in laboratory ompressive and pulse veloity tests (3 ores) γ R R R R ρ ρ ρ ρ [kg/m3] [Mpa] [Mpa] [Mpa] [Mpa] [-] [-] [-] [-] average standard deviation R R R R Sd R Si Figure 9. Core failure strengths, R and R, for 8 ores drilled out from 9 in-situ test positions (left side). Comparison of R ( in-situ test, 9 twie ores) with in-situ SonReb results, R Sd diret, R Si indiret In Figure 9 a omparison that regards only those ore speimens that an be orrelated with in-situ tests is arried out. In the left side ore failure strengths, R and R, for 9 double ores (i.e. for 9 drilled out ores, suessively divided in two speimens) are shown. In spite of a great attention in laboratory utting operation, a notable sattering of strength results is shown. The average value of ore ompressive strength R ( R = R i if two ores are drilled out from the same in-situ test position) is shown in Table ( R m = 3.7 MPa) and it is quite similar to SonReb R S values determined in in-situ test position ( R Sm = 8.7 MPa). In the right side of Figure 9 a omparison of average values for different drilling out sites ( R Sm ) distribution with in-situ SonReb results (Eqn. (3.5),

8 Otober -7, 8, Beijing, China R Sd for diret pulse veloity tests, R Si for indiret pulse veloity tests) is shown. It is possible to note a strong sattering of in-situ provisions with diret SonReb tests that overestimate onrete strength (average value R Sdm = 35.5 MPa) and indiret SonReb tests that, on the ontrary, show a quite similar average value of ompressive ( R Sim = 3.95 Mpa) with a disouraging dispersion. 5. CONCLUSIONS In the first part of the paper, orrelation formulas, basing on literature proposals or pratie, to evaluate onrete ompressive strength with non-destrutive methods, have been disussed. It has shown the lear dependene of ompressive strength on ore mass density and the neessity to use the atual mass density in pulse veloity evaluation. In the seond one, non-destrutive and destrutive methods to evaluated onrete failure strength, are been ompared in order to outline some tehnial proposals. In situ tests have shown a great, sometimes disouraging, dispersion of results, also for within the same building, due to several building phases, and the same element, due to environmental onditions and loading. This dispersion are due to raking of strutural elements and to poor mix design and a lak of onrete vibration during ast-in-situ too, both phenomena typial of old existing RC buildings. Partiularly in the ase of buildings with strutural elements of wide dimensions or with large reinforement ratio, the lassifiation of onrete strength has shown notable levels of diffiulty even if ombined (SonReb) non-destrutive method was used and an extreme diffiulty to reah unitary onlusions an be deteted (Biondi 8). Conrete strength determination by means of the ombined non-destrutive method has shown high levels of diffiulty due to diret, indiret and semi-diret ultrasoni pulse veloity dispersion (Biondi et al. 8). On the basis of these results, in order to obtain orret ompressive strength evaluation, it is strongly reommended the assumption of diret ultrasoni measure for ombined method in partiular to old existing buildings that have to be investigated, also for studies of loal orrelation funtion with destrutive tests results. So the prudential statement of Tusany Region (Ferrini (Ed.), 4) to onsider unaeptable indiret and semi-diret ultrasoni pulse veloity measurements ould be onsidered as orret for this lass of existing RC buildings. REFERENCES Biondi, S., Candigliota, E. (8). Non destrutive tests for existing R.C. strutures assessment, Pro. of fib 8 Symposium: Tailor Made Conrete Strutures: New Solutions for Our Soiety, Amsterdam, May 9-, 8, Paper Italia- Biondi, S. (8). The Knowledge Level in existing buildings assessment. Pro of 4 th World Conferene on Earthquake Engineering, Bejing, China, Paper No Calzona, R. (98). Dome for the sports palae at asto (Chieti), L Industria Italiana del Cemento, 98:5, 397-, (in Italian) CEN Comité Européen de Normalisation Ed. (5). Euroode 8: Design of strutures for earthquake resistane - Part 3: Assessment and retrofitting of buildings. En 998-3: 5 E, Brussels D.M (8). Norme tenihe per le ostruzioni. Gazzetta Uffiiale 9: S.O., (in Italian) De Sortis, A., Di Pasquale, G., Orsini, G., Sanò, T., Biondi, S., Nuti, C., anzi, I. (). Hospital behavior during the September 997 earthquake in Umbria and Marhe (Italy). Pro of th World Conferene on Earthquake Engineering, Aukland, New Zealand, Paper No. 54. Dole, M., Masi, A. (5). Linee guida per la valutazione della vulnerabilità sismia degli edifie strategii e rilevanti. CRiS, Regional Seismi Department, Potenza, Italy, (in Italian) Dole, M., Masi, A., Ferrini, M. (6). Estimation of the Atual In-Plae Conrete Strength in Assessing Existing RC Strutures, Pro. of the nd International Fib Congress. Naples, Italy. Paper ID 9-. Ferrini, M. (Ed.) (4). Criteri per lo svolgimento di indagini diagnostihe finalizzate alla valutazione della qualità dei materiali in edifii esistenti in emento armato. Tusany, Regional Seismi Department, Florene, Italy, (in Italian) OPCM 374 (3). Primi elementi in material di riteri generali per la lassifiazione sismia del territorio nazionale e di normative tenihe per le ostruzioni in zona sismia. Gazzetta Uffiiale 5: S.O. 7, (in Italian) OPCM 343 (5). Ulteriori modifihe ed integrazioni all'opcm 374, reante «Primi elementi in materia di riteri generali per la lassifiazione sismia del territorio nazionale e di normative tenihe per le ostruzioni in zona sismia». Gazzetta Uffiiale 7: S.O. 85, (in Italian)