ASSESSMENT OF MATERIAL BEHAVIOUR AND STRUCTURAL INTEGRITY OF ENGINEERING STRUCTURES BASED ON R6 PROCEDURE

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1 DOI: /adms P. G. ossakowski ielce Univesit of Technolog, Facult of Civil Engineeing and Achitectue, Chai of Stength of Mateials and Concete Stuctues, Tsiąclecia Państwa Polskiego 7, ielce, Poland; ASSESSMENT OF MATERIAL BEHAVIOUR AND STRUCTURAL INTEGRITY OF ENGINEERING STRUCTURES BASED ON R6 PROCEDURE ABSTRACT The R6 pocedue is one of the most advanced, innovative and effective method developed and ecommended fo use in poblems of mateial behaviou and stuctual integit of engineeing stuctues with defects. The idea and basic assumptions of R6 pocedue ae descibed in the pape as well as example of its pactical application in analsis of damaged bidge stuctual element. As a esult of the eseach, the highl consevative appoach of R6 pocedue was obseved, which estimated the level of hazadous loads as the elastic limit load fo analsed element. ewods: R6 pocedue, Failue Assessment Diagam (FAD), stuctual integit, mateial behaviou INTRODUCTION Popel designed and manufactued stuctual elements should meet a numbe of conditions and equiements, in paticula in tems of thei duabilit and eliabilit, with a diect impact on safet. The safet analsis is elativel simple in the case of the elements opeating in the elastic ange and without defects. The situation is much moe complex when the elements ae damaged and opeate in the plastic ange. The assessment of the stuctue safet is extemel impotant in the event of the emegenc state, when the components ae defomed and contain cacks. Unfotunatel, the design standads do not povide specific pocedues o even the geneal ules in such cases. The analsis of stuctual elements opeating in a plastic ange and containing cacks is caied out based on assumptions of factue mechanics. Unfotunatel, a lot of pocedues ae developed onl fo small elements and sample design pieces. The eseach focused on the development of detailed pocedues fo the hazad assessment of the opeation of stuctues containing damages has been conducted fo man eas. Fom developed methods the most useful ae the R6 [1] SINTAP [2, 3] and FITNET [4, 5] pocedues. Due to the pactical impotance and the lack of design standad pocedues, this pape attempts to pesent and discuss one of the mentioned method, i.e. R6 pocedue, which allows to analse the mateial behaviou and test and pedict the stuctual integit of the damaged components. The idea and assumptions of R6 method is descibed in detail as well as example

2 26 ADVANCES IN MATERIALS SCIENCE, Vol. 13, No. 4 (38), Decembe 2013 of its pactical application. Basing on the R6 pocedue this analsis includes the assessment of mateial behaviou and the stuctual integit of the suppot membe containing a defect in the fom of cack. ASSUMPTIONS OF R6 PROCEDURE The R6 pocedue is one of the most poweful tools used in the stength analsis of stuctual elements containing defects. It enables analsis of the hazads of failue at one of thee levels, fom the fist, the simplest and the most consevative, up to the most advanced, but giving the most accuate esults. The safet analsis of damaged component in the R6 method is geneall based on the Failue Assessment Diagam, denoted as FAD. It is a basic gaph that allows us to detemine whethe the flawed section woks safel, the damage is possible o isk of damage is high. R6 pocedue in Failue Assessment Diagam combines two main factue citeia: limit load citeion and stess intensit facto citeion. Consequentl, in R6 pocedue two main paametes ae used, L and. The ae dependent on load, geomet and mateial popeties. The paamete L connected to the limit load citeion is defined as: L = P σ ef P ( a, σ ) = σ L (1) whee: P is applied pima loading, P L (a, σ ) is the coesponding limit load fo the component with a cack size a and ield stess σ, σ ef is pima efeence stess, σ is ield stess equal 0.2% poof stess. The second paametes,which is linked to the stess intensit facto citeion, is defined as: = (2) mat whee: is stess intensit facto, mat is factue toughness of the mateial. The Failue Assessment Diagam in R6 method is constucted on the basis of above paametes, L and, failue assessment cuve f(l ) and the plastic collapse limit L = L max. Assessment of the pobabilit of the element failue is based on the compaison of the assessment point ( L, ) with the failue assessment cuve = f(l ) and the plastic collapse limit L = L max. If the point is located within the aea bounded b failue assessment cuve f(l ) and the plastic collapse limit L = L max, which is shown schematicall in Figue 1, the element will opeate safel (point A). When the assessment point is out of this aea (point C), the pobabilit of the component failue is high.

3 P. G. ossakowski: Assessment of mateial behaviou and stuctual integit Fig. 1. Failue Assessment Diagam (FAD) accoding to R6 pocedue As mentioned befoe, the R6 pocedue enables to assess the stuctue integit on one of thee levels of the analsis, depending on the available input data and expected consevatism and accuac of the esults. The fist level is the easiest and indisciminate in tems of the necessa infomation on the mechanical popeties of the mateial. Hence, the esults ae the most consevative, but also the least accuate. Accuac, complexit of analsis and equiements fo the necessa mateial data incease on subsequent levels, so that failue citeia ae less stingent in compaison to the fist level. The levels of analsis used in the R6 method ae descibed below, basing on the infomation given in [6]. The fist level of R6 analsis is based on FAD. This level is used fo mateials which do not exhibit a stong stain initial hadening. This level is also used in situations whee thee is no specific data on the complete stess-stain cuve, and onl ield stess σ and ultimate tensile stength σ m ae known. When the mateial has a discontinuit at the level of ield stess analsis is caied out onl in the ange fo L < 1. This is the simplest level, which equies onl basic knowledge on mechanical popeties of the mateial. As a esult, the fist level is consevative, that ensues the high degee of safet. It is suggested that the analsis should stat fom this level, because when it is detemined that the component woks safel, automaticall thee is no need to pefom moe sophisticated analsis at highe levels. Fo the second level of analsis it is necessa to know moe on the mateial stength paametes, in compaison to the fist level. It concens the full cuve eal stess eal stain, ield stess σ and ultimate tensile stength σ m. This level is used fo mateials with stong hadening. The use of the second level of R6 pocedue enables the analsis of mateial behaviou and stuctual integit of elements opeating in the ange above the maximum load. It ma be necessa in cetain situations, when the fist-level analsis shows that the assessment point is placed on the FAD in a hazadous aea but close to the limit cuve L max fo the low values of. The thid level of analsis allows us to detemine the most accuate esults fom these levels and is chaacteized b lowe consevatism. Unfotunatel, moe stength paametes, including in paticula the J integal and the full stess-stain cuve is needed fo the analzed mateial. The thid level is ecommended when mixed loading modes ae subjected to the consideed element.

4 28 ADVANCES IN MATERIALS SCIENCE, Vol. 13, No. 4 (38), Decembe 2013 ASSESSMENT OF MATERIAL BEHAVIOUR AND STRUCTURAL INTEGRITY OF STRUCTURAL BRIDGE ELEMENT USING R6 PROCEDURE The analsis pesented below concens the full R6-based assessment of mateial behaviou and stuctual integit of damaged stuctual element, which models the bidge gide with defect, basing on the esults pesented in [7]. The analzed element was made of S235JR steel, which is one of the most common steel gade used in engineeing. The defect in the element was modelled as a cack. The eseach included detemination of stength and factue toughness paametes of S235JR steel, expeimental test of consideed element and essential R6 analsis, which is descibed in detail in subsequent sections. Stength and factue toughness paametes of S235JR steel The stength paametes of S235JR steel wee detemined duing standad tensile test accoding to [8]. The samples of ectangula coss-section b h = mm wee used with initial length base l 0 = 140 mm and pima coss-sectional aea S 0 = 120 mm 2. The mean stength paametes of tested mateial wee: ield stess σ = 290 MPa, ultimate tensile stength σ m = 443 MPa and pecentage elongation A t = 22.7 %. The next pat of the stength tests included detemination of factue toughness fo S235JR steel, defined b citical values of J Ic integal, which is applied fo ductile mateials. The expeiments wee pefomed using SEN (B) tpe specimens. The citical values of J Ic integals wee estimated basing on the factue toughness J Q detemined using specimens of dimensions coesponding to the geomet of coss-section of analzed bidge element. The multiple specimen and electical potential changes methods wee applied in ode to detemine factue toughness J Q accoding to [9]. Basing on the esults obtained, it was noticed, that factue toughness detemined using the electical potential changes method was lowe than those detemined using multiple specimen method. Taking into consideation highe eliabilit of factue toughness detemined using the electical potential changes method it was applied in ode to assess factue toughness J Q and coesponding citical values of J Ic integal fo S235JR steel. The lowest value of citical J Ic integal was assumed as factue toughness paamete, J Ic = 135 kn/m, to appl in factue analsis of consideed element. Then the citical value of stess intensit facto was estimated using the fomula: I c = J Ic E (3) As a esult, fo S235JR steel, citical value of stess intensit facto was detemined as Ic = 166 MPa m 0.5. Expeimental test Expeimental test was pefomed using a T-section beam element made of steel S235JR, modelling the lowe bidge span. Damage was modelled in the lowe pat of the web in the fom of a vetical cack (Fig. 2).

5 P. G. ossakowski: Assessment of mateial behaviou and stuctual integit Fig. 2. Geomet of tested element [7] The element had smmetical and fee suppots. The test was pefomed unde displacement contol incease with a constant speed of tavese equal 2 mm/min. The loading P was applied at two points aanged smmeticall to obtain a constant bending moment and zeo shea foce zone. Duing the test the displacement of tavese l, i.e. deflection of loading points, the load P and suface cack opening displacement δ M, detemined with the use of an extensomete fo measuing base of 5 mm, wee measued. The test was conducted up to the total failue of the element. R6 analsis of damaged stuctual bidge element In the fist ange of this pat of the analsis the citical value of cack opening displacement δ Tc and limit load P L coesponding to the mateial ielding wee detemined. These values wee detemined assuming the citical stess intensit facto Ic = 166 MPa m 0.5, i.e. factue mateial toughness, using the fomula [6]: δ Tc 2 4 I c = (4) π σ E whee: ield stess σ = 290 MPa, Young modulus E = 205GPa Citical values of cack opening displacement was estimated as δ Tc = mm. The value of limit load P L was detemined basing on the citical values of suface cack displacement opening δ Mc accoding to the fomula [6]: whee: a = 40 mm, W = 120 mm, = [ ( W a) + a] Tc δ Mc = δ (5) ( W a)

6 30 ADVANCES IN MATERIALS SCIENCE, Vol. 13, No. 4 (38), Decembe 2013 Fo detemined values of δ Mc = mm and basing on the foce cack suface displacement cuve P δ M, the limit load coesponding to the mateial ielding was estimated as P L = 39.2 kn In ode to assess stuctue integit of tested element, the function (S ) was detemined. The paamete was defined as follows: I = (6) mat whee: I is stess intensit facto, mat is mateial factue toughness. Factue toughness of tested mateial mat was identified on the basis of estimated values of Ic, i.e. mat = Ic = 166 MPa m 0.5. Cuent value of stess intensit facto I was detemined as a function of values of cack opening displacement δ T accoding to the fomula: I δ T πσ E = (7) 2 Accoding to [6] the paamete L = P/P L connected to the limit load citeion was expessed b paamete S, defined as: S = L 2σ σ + σ m = P L 2Pσ ( σ + σ ) m (8) whee: P is applied pima loading, P L is the coesponding limit load fo the component with a cack size a and ield stess σ, σ is mateial ield stess, σ m is ultimate tensile stength. The paamete S was established basing on the limit load P L = 39.2 kn and mateial stength paametes σ = 290 MPa and σ m = 443 MPa. The failue assessment cuve f(l ) was defined as (S ) accoding to [6]: S + 0.1S = S = 0 4 fo fo S S < 1 1 (9) As a esult, the final Failue Assessment Diagam was detemined fo tested element accoding to R6 pocedue, as shown in Figue 3.

7 P. G. ossakowski: Assessment of mateial behaviou and stuctual integit Fig. 3. FAD accoding to R6 pocedue fo tested element [7] As can be seen, the failue assessment cuve f = (S ) defines the safe aea fo whole ange of mateial defomation. The citical point is noticed when analsed cuve meets the failue assessment cuve. It coespond to the values of S = and = In the next diagam shown in Figue 4, the load suface cack opening displacement cuve P δ M is shown, whee the point coesponding to the expected moment of element failue accoding to R6 pocedue is denoted. Fig. 4. Load suface cack opening displacement cuve P δ M [7] It coesponds to the end of the mateial elastic ange and the beginning of the mateial ielding in the case of tested element. In can be concluded that in such case the R6 pocedue is quite consevative method which povide high level of safet.

8 32 ADVANCES IN MATERIALS SCIENCE, Vol. 13, No. 4 (38), Decembe 2013 CONCLUSIONS In this pape, R6 pocedue, which is applied in stength analsis of defected stuctual elements, is pesented. It seems that in the case of lack of pecise standad guidance, R6 pocedue can be successfull used in poblems of mateial behaviou and stuctual integit of damaged elements used in engineeing. A good example of this ae the esults of the pesented analsis, which concens the stuctual integit and mateial behaviou of beam element containing the damage in the fom of cack. The esults obtained showed that citical load accoding to the R6 pocedue was equalled to 0.57 of S paamete, which coespond to the end of the elastic limit of the mateial. As a esult, the R6 is consevative and estictive method, which povides a high safet level fo tested elements. It seems that futhe eseach should be focused on adaptation and development of the methodolog of stuctual analsis using R6 pocedues so that the esults obtained ma be useful in the analsis and expetise in the field of load-beaing capacit of vaious damaged stuctual elements, especiall opeating in the emegenc states. REFERENCES 1. R6: Assessment of the integit of stuctues containing defects. Bitish Eneg Geneation Repot R/H/R6, Revision 4, SINTAP: Stuctual integit assessment pocedues fo Euopean indust. Bite-Euam Poject No. BE , Contact No. BRPR-CT , Final Repot, Ranatowski E.: Relation Stuctue - Factue Resistance in Pocess of Estimate the Weldabilit of Low Allo Steels: Pat II, Advances in Mateials Science, 10, 2010, oçak M., Hadle I., Szavai S., Tkach Y., Talo N.: FITNET Fitness-fo-Sevice (FFS) Pocedue Volume 1, Revision M8. Joint Reseach Cente, GSS Reseach Cente Geesthacht, oçak M., Hadle I., Szavai S., Tkach Y., Talo N.: FITNET Fitness-fo-Sevice (FFS) Annex Volume 2, Revision M8. Joint Reseach Cente, GSS Reseach Cente Geesthacht, Neimitz A., Factue Mechanics [in Polish], PWN, Waszawa, ossakowski P.: The Evaluation of Load-Caing Capacit of Elements of Steel Stuctues Using R-6 And FITNET Methods [in Polish], Poceedings of 56th Annual Confeence of ILiW PAN i N PZITB on Scientific Poblems of Civil Engineeing, ielce Septembe 2010, ielce-nica, PN-EN :2004 Metallic Mateials Tensile Testing Pat 1: Method of Test at Ambient Tempeatue. 9. PN-88/H Metals Test method of factue toughness b measuement citic value J integal.