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Review An Evaluation of Mechanical Properties with the of Building Structural Members for Reuse by NDT

Masanori Fujita * and Keiichi Kuki

Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan; [email protected] * Correspondence: [email protected]; Tel.: +81-836-85-9727

Academic Editors: João Manuel R. S. Tavares and Victor Hugo C. de Albuquerque Received: 9 June 2016; Accepted: 13 October 2016; Published: 19 October 2016

Abstract: The reuse system proposed by the authors is one method to reduce the environmental burden in the structural field. As for reusable members, we take up building steel structures used for plants and warehouses. These buildings are assumed to be demolished within approximately 30 years or more for physical, architectural, economic, or social reasons in Japan. In this paper, the performance of steel structural members of a gable frame is evaluated with a non-destructive test for reuse. First, the flow to estimate mechanical properties of steel structural members such as tensile strength, strength, and elongation is shown via a non-destructive test. Next, tensile strength, yield strength, and elongation of steel structural members are estimated, with hardness measured with a portable ultrasonic hardness tester. Finally, the mechanical properties of steel structural members for reuse are estimated based on the proposed flow.

Keywords: steel structural member; mechanical properties; elongation; non-destructive test; Vickers hardness; reuse

1. Introduction In Japan, dioxide emissions from construction-related fields account for approximately one-third of total emissions. Hence, establishing a low-carbon society is an urgent issue shared by all fields [1]. Responses to global environmental issues are called for in the architectural field as well. Under these circumstances, the Architectural Institute of Japan (AIJ) has been deploying various efforts [2–4], including the promotion of “Vision 2050: Building-related Measures to Counteract Global Warming”, aiming to achieve carbon neutrality [5]. In tandem with this movement, we have been studying a reuse system [6–11] for building steel structures aiming to reduce the environmental burden. In order for reusable members to circulate as existing and newly manufactured in the existing distribution system, we aim to establish a venous industry, as opposed to an arterial industry, that is responsible for production and product supply. This venous industry would facilitate the disposal, recycling, and reuse of products resulting from the arterial industry. Among these items, the performance evaluation of reusable members entails comprehending their mechanical properties, such as tensile strength, yield point or yield strength, elongation, and charpy value, through destructive or non-destructive testing. This is assuming, however, that the buildings to be demolished are older than 30 years. Diagnosis charts, drawings and specifications, and steel inspection certificates are usually not available. In such cases, it is possible to evaluate the quality of steel structural members by analyzing their mechanical properties and chemical components by means of destructive testing provided that test pieces can be taken from target buildings. It is, however,

Metals 2016, 6, 247; doi:10.3390/met6100247 www.mdpi.com/journal/metals Metals 2016, 6, 247 2 of 13 difficult to remove structural members from buildings currently in use. In addition, this approach involves various problems, including economic efficiency. When building steel structures are constructed, test pieces or steel inspection certificates are used to confirm the quality of their structural members. Partially, Vickers hardness measured with a destructive test or a non-destructive test has been used as a complement to steel inspection certificates. This is the reason that the correlation between Vickers hardness and mechanical properties such as tensile strength, yield point or yield strength, and elongation has not been fully revealed in practical phases. However, Vickers hardness via NDT has a potential performance. It is economical since Vickers hardness measured via NDT with a portable device does not require cutting test pieces from building steel structure. If the correlation between Vickers hardness and mechanical properties are verified, it is useful to estimate the mechanical properties of the steel structural members for reuse. Past studies have reported that the of steel members could be roughly estimated by measuring their surface hardness or chemical composition through non-destructive testing [12,13]. The ultimate strength is assumed by the Diamond pyramid hardness and Meyer’s hardness coefficient [14]. However, these approaches entail some problems. As an example, for materials where it is difficult to determine the steel type, or where more than one type is applicable, such cases are dealt with by setting yield strength, assuming that the materials are of the lowest possible grade. If the mechanical properties, e.g., the yield point or yield strength and the elongation, had already been specified, it would help narrow down the material of steel structural members. This paper proposes a flow to facilitate the estimation of the mechanical properties (tensile strength, yield point or yield strength, and elongation) of steel structural members assumed to be reused. Based on this flow, the material of the structural members of a steel structure completed in the 1970s is estimated. The degradation status of these members is simultaneously examined.

2. Investigation Overview

2.1. Target Building The target building of the investigation is a factory using non-fireproofed rolled wide flanges, a type of steel that has been standardized mainly by steel manufacturers. The factory is a typical mountain shape and is located in an industrial district. The factory building was completed in the 1970s and is still in use; a demolition plan has not yet been determined. Although this factory building has seen a change of owner, there is no record of overload or fire damage according to the survey. Diagnosis charts, steel inspection certificates, and drawings and specifications are not available. The building’s roof plan, the framing elevation, the cross section, and the structural members’ list are shown in Figure1 and Table1 respectively. The building is a one-way rigid frame, a one-way brace structure (3-ton crane is installed) with a span of 20.15 m and an eaves height of 6.5 m. As for external cladding, folded plates are used for the roofing and siding of the walls.

Table 1. The members’ list of the building steel structure.

Location Mark Size G1 H-400 × 200 × 8 × 13 G2 H-350 × 150 × 6.5 × 9 C1 H-350 × 150 × 7 × 11 B1 H-200 × 100 × 5.5 × 8 Sub-beam B2 H-150 × 75 × 5 × 7 Mid-column P1 H-250 × 250 × 9 × 14 Brace V1 1-M20 Purlin – C-100 × 50 × 3.2 Metals 2016, 6, 247 3 of 13 Metals 2016, 6, 247 3 of 12

(a) (b)

(c) (d)

Figure 1. (a) Plan; (b) elevation (x-axis); (c) elevation (y-axis); (d) interior view. Unit: mm. Figure 1. (a) Plan; (b) elevation (x-axis); (c) elevation (y-axis); (d) interior view. Unit: mm. Table 1. The members’ list of the building steel structure. 2.2. Flow for Estimating Mechanical Properties Location Mark Size G1 H-400 × 200 × 8 × 13 The performance evaluationBeam of steel structural members entails material testing, chemical composition testing, dimensional inspection, andG2 degradationH-350 × 150 × testing. 6.5 × 9 In most cases, non-destructive Column C1 H-350 × 150 × 7 × 11 testing is used for dimensional inspection, degradation testing, and destructive testing for material B1 H-200 × 100 × 5.5 × 8 Sub-beam testing and chemical composition testing. AssumingB2 H- that150 × the75 × structural5 × 7 members are to be reused, this paper focuses on non-destructiveMid-column testing P1 and examinesH-250 × 250 the × 9 tensile × 14 strength, yield point or yield strength, and elongation, among otherBrace mechanicalV1 properties.1-M20 Excessive and damage in the steel structural members arePurlin evaluated -- via visualC-100 inspection. × 50 × 3.2 Figure2 shows an estimation flow of the above-mentioned mechanical properties of the steel structural members assumed to be 2.2. Flow for Estimating Mechanical Properties reused. First, the Vickers hardness of the steel structural members is measured using an ultrasonic hardness testerThe to performance calculate the evaluation tensile strength, of steel structural and the yieldmembers point entails or yield material strength, testing, to chemicaleventually find composition testing, dimensional inspection, and degradation testing. In most cases, non-destructive the yield ratio. As mentioned above, an approach to estimating the tensile strength from the Vickers testing is used for dimensional inspection, degradation testing, and destructive testing for material hardnesstesting employs and chemical the correlation composition between testing. Assuming the surface that hardness the structural of a members welded are joint to be and reused, the Vickers hardnessthis [14 paper,15]. focuses Then, usingon non the-destructive yield ratio testing thus and obtained, examines thethe uniformtensile strength, elongation yield point is calculated. or yield Local elongationstrength is calculated, and elongation using, among the plate other thicknessmechanical ofproperties. the structural Excessive members. deformation Uniform and damage elongation in is Metals 2016, 6, 247 4 of 12 consideredthe steel to bestructural independent members of are the evaluated shape via of thevisual test inspection. piece and Figure to have2 shows a strongan estimation correlation flow with of the above-mentioned mechanical properties of the steel structural members assumed to be reused. the yield ratioelongation [16]. is Elongation considered to after be independent is of calculated the shape of by the summing test piece the and uniform to have a elongationstrong and First, the Vickers hardness of the steel structural members is measured using an ultrasonic hardness local elongation.correlation with the yield ratio [16]. Elongation after fracture is calculated by summing the uniform testerelongation to calculate and local the tensileelongation. strength, and the yield point or yield strength, to eventually find the yield ratio. As mentioned above, an approach to estimating the tensile strength from the Vickers hardness employs the correlation between the surface hardness of a welded joint and the Vickers hardness [14,15]. Then, using the yield ratio thus obtained, the uniform elongation is calculated. Local elongation is calculated using the plate thickness of the structural members. Uniform

FigureFigure 2. Estimation 2. Estimation flow flow of mechanical mechanical properties. properties.

2.3. Non-Destructive Testing Equipment Non-destructive tests consist mainly of portable ultrasonic hardness testers and rebound type portable hardness meters. Eventually, the portable ultrasonic hardness tester shown in Figure 3a,c is used for the maintenance of large-scale structures, steel towers, and bridges, and its Vickers hardness can be calculated using the frequency of the vibration rod at the pressing. Instead of measuring the size of the indentation of steel using a microscope, this tester employs a diamond indenter equipped with a vibrating rod that presses on the steel surface at a fixed load, and this tester measures its hardness by applying ultrasonic vibrations and analyzing its damping effect [17– 21]. When the vibration rod is applied to a soft-surfaced steel with identical qualities and at a fixed , it makes a deep indentation and becomes locked into the groove. Because of this, the resonance frequency increases. Conversely, it does not become locked in when it is used on hard steel and the resonance frequency drops. The Vickers hardness can be calculated using the correlation between this deviation and the tested hardness. The measuring indenter is the diamond indenter to the Micro-Vickers facing to the surface angle of 136 degrees. The measuring range for the Vickers hardness is from HV50 to HV999, and its reproducibility is within ±3% rdg HV. Using the ultrasonic thickness gauge shown in Figure 3c, the thickness of the rolled H section-steel was also measured.

Probe Motor Motor control Hook Fixed force Amplifier circuit Frequency Coil used for counter oscillation Computation circuit Piezoelectric Vibrating element rod Motor start switch LCD indicator Diamond indenter (a) (b)

(c)

Figure 3. (a) A portable hardness tester and (b) the measurement principle of the portable hardness tester. (c) Portable thickness gauge.

Metals 2016, 6, 247 4 of 12 elongation is considered to be independent of the shape of the test piece and to have a strong correlation with the yield ratio [16]. Elongation after fracture is calculated by summing the uniform elongation and local elongation.

Figure 2. Estimation flow of mechanical properties.

2.3. NonMetals-D2016estructive, 6, 247 Testing Equipment 4 of 13 Non-destructive tests consist mainly of portable ultrasonic hardness testers and rebound type portable2.3. Non-Destructivehardness meter Testings. Eventually, Equipment the portable ultrasonic hardness tester shown in Figure 3a,c is used forNon-destructive the maintenance tests consistof large mainly-scale of structure portable ultrasonics, steel towers, hardness and testers bridges and, rebound and its type Vickers hardnessportable can hardness be calculated meters. Eventually, using the thefrequency portable ofultrasonic the vibration hardness rod tester at shown the pressing in Figure. 3 Insteada,c is of measuringused for the the size maintenance of the indentation of large-scale of structures, steel using steel a towers, microscope, and bridges, this tester and its employs Vickers hardness a diamond indentercan be equipped calculated with using a the vibrating frequency rod of the that vibration presses rod on at the pressing.steel surface Instead at of a measuring fixed load the, and size this testerof measures the indentation its hardness of steel usingby applying a microscope, ultrasonic this tester vibrations employs and a diamond analyzing indenter its damping equipped effect with [17– 21]. Whena vibrating the vibration rod that presses rod is on applied the steel to surface a soft- atsurfaced a fixed load,steel andwith this identical tester measures qualities its and hardness at a fixed by applying ultrasonic vibrations and analyzing its damping effect [17–21]. When the vibration force, it makes a deep indentation and becomes locked into the groove. Because of this, the rod is applied to a soft-surfaced steel with identical qualities and at a fixed force, it makes a deep resonance frequency increases. Conversely, it does not become locked in when it is used on hard indentation and becomes locked into the groove. Because of this, the resonance frequency increases. steelConversely, and the resonance it does not become frequency locked drops. in when The it isVicker used ons hardhardness steel and can the be resonance calculated frequency using the correlationdrops. Thebetween Vickers this hardness deviation can beand calculated the tested using hardness. the correlation The measuring between thisindenter deviation is the and diamond the indentertested to hardness. the Micro The-Vickers measuring facing indenter to the is surface the diamond angle indenter of 136 todegrees. the Micro-Vickers The measuring facing torange the for the Vicksurfaceers anglehardness of 136 is degrees. from HV50 The measuring to HV999 range, and forits thereproducibility Vickers hardness is within is from ± HV503% rdg to HV999,HV. Using the uandltrasonic its reproducibility thickness isgauge within shown±3% rdg in HV.Figure Using 3c the, the ultrasonic thickness thickness of the gauge rolled shown H section in Figure-steel3c, was also themeasured thickness. of the rolled H section-steel was also measured.

Probe Motor Motor control Hook Fixed force Amplifier circuit Frequency Coil spring used for counter oscillation Computation circuit Piezoelectric Vibrating element rod Motor start switch LCD indicator Diamond indenter (a) (b)

(c)

FigureFigure 3. (a 3.) A(a )p Aortable portable hardness hardness tester tester and and ( (bb)) the measurementmeasurement principle principle of theof the portable portable hardness hardness testertester.. (c) Portable (c) Portable thickness thickness gauge. gauge.

3. Evaluation of Mechanical Properties Table2 lists the test pieces selected for investigating the mechanical properties of the steel structural members assumed to be reused. The tensile test is conducted in the mechanical properties test of JIS Z 2241, whose specifications correspond to ISO 6892-1 [22,23]. The contained in Series 1 are for adjusting the ultrasonic hardness tester used in non-destructive testing. Series 2 is the data of the steels for which the surface hardness is subscribed [24]. Metals 2016, 6, 247 5 of 13

Table 2. List of the test pieces.

Thickness Yield Strength Tensile Strength Uniform Rupture Vickers Strain Number Series Material Type * 2 2 mm N/mm N/mm Elongation εu (%) Elongation εf (%) Hardness Hv Coefficient Specimen 12 313 436 16 31 140 0.249 SS400 1A 12 315 438 18 30 138 0.229 12 323 442 16 30 141 0.236 Series_1 12 310 459 18 29 138 0.246 8 SN400B 1A 12 321 459 18 29 137 0.248 12 327 463 19 28 137 0.232 12 419 559 15 26 189 0.205 SM490A 1A 12 408 557 16 26 191 0.188 12 279 451 – 43 137 – 12 277 449 – 44 136 – 12 288 442 – 37 134 – SN400B 5 12 300 443 – 44 135 – 12 289 445 – 41 133 – 12 301 448 – 42 138 – 12 294 445 – 43 135 – 12 377 550 – 36 168 – 12 378 545 – 38 157 – 12 388 547 – 39 157 – Series_2 21 SN490B 5 12 399 552 – 36 160 – 12 388 550 – 38 163 – 12 378 549 – 36 163 – 12 394 550 – 38 170 – 40 498 657 – 26 190 – 40 502 647 – 25 175 – 40 495 647 – 25 199 – SA440B 1A 40 491 647 – 26 177 – 40 493 651 – 25 183 – 40 496 648 – 24 185 – 40 496 649 – 24 208 – * Type indicated specimens of JIS. Metals 2016, 6, 247 6 of 13

3.1.3.1. TensileTensile StrengthStrength andand YieldYield PointPointor or YieldYield Strength Strength TensileTensile strength and and yield yield point point or oryield yield strength strength are areestimated estimated from from the Vickers the Vickers hardness hardness using usingEquations Equations (1) and (1) (2) and, taking (2), taking into consideration into consideration the Vickers the Vickers hardness hardness set for set each for yield each ratio yield range ratio range[15,25– [1527,]25: –27]: Ts = 2.5·Hv + 100 (1) Ts = 2.5·Hv + 100 (1) Ys = 2.736·Hv − 70.5 (2) s v 2 Y = 2.736·H − 70.5 (2) where Ts = tensile strength (N/mm ); Hv = Vickers hardness; Ys = yield point or yield strength (N/mmwhere T2).s = tensile strength (N/mm2); Hv = Vickers hardness; Ys = yield point or yield strength (N/mmTensile2). strength and yield point or yield strength are estimated from Vickers based on the test pieceTensile list shown strength in Table and2. yield The correlationpoint or yield between strength Vickers are estimated hardness andfrom tensile Vickers strength based on as wellthe test as thatpiece between list shown Vickers in Table hardness 2. The and correlation yield point between or yield Vickers strength hardness is presented and tensile graphically strength in as Figure well 4as. Althoughthat between the Vickers data is nothardness sufficient, and theyield tensile point strengthor yield strength and the yieldis presented point or graphically yield strength in Figure nearly 4. satisfyAlthough Equations the data (1) is and not (2).sufficient, the tensile strength and the yield point or yield strength nearly satisfy Equations (1) and (2).

Tensile strength(Ts)(N/mm2) Yield strength(Ys)(N/mm2) 1000 1000

800 800 Ts=2.5 Hv+100 Ys = 2.736 Hv - 70.5 600 600

400 400

SS400 SS400 200 SN400B 200 SN400B SM490A SM490A SN490B SN490B SA440B SA440B 0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Vickers hardness(Hv) Vickers hardness(Hv) (a) (b)

FigureFigure 4 4.. (a()a Tensile) Tensile strength strength and and Vickers Vickers hardness hardness and and(b) yield (b) yieldpoint pointor yield or strength yield strength and Vickers and Vickershardness. hardness.

3.2.3.2. RuptureRupture ElongationElongation InIn thethe –strainstress–strain curve curve of of a a steel steel structural structural member, member, rupture rupture elongation elongation can can be representedbe represented by uniformby uniform elongation elongation and and local local elongation, elongation, as shown as shown in the in schematic the schematic diagram diagram in Figure in Figure5. The 5 latter. The latter indicates elongation from the point where constriction starts to develop in the parallel part of indicates elongation from the point where constriction starts to develop in the parallel part of the the test piece to the point where the test piece . It is the fusiform elongation that develops test piece to the point where the test piece fractures. It is the fusiform elongation that develops in in part of the sections after being subjected to the maximum load. It is considered that the point part of the sections after being subjected to the maximum load. It is considered that the point where where constriction starts to develop and the point where the maximum load is reached do not constriction starts to develop and the point where the maximum load is reached do not coincide; here, coincide; here, however, rupture elongation is represented by the sum of uniform elongation and however, rupture elongation is represented by the sum of uniform elongation and local elongation, local elongation, as shown in Equation (3): as shown in Equation (3): εf =εf ε=u ε+u +ε nε,n, (3)(3) ε ε ε wherewhere εff == rupture elongation;elongation; εu = u uniformniform elongation; elongation; εnn == local local elongation elongation..

Metals 2016, 6, 247; doi:10.3390/met6100247 www.mdpi.com/journal/metals Metals 2016, 6, 247 7 of 13 Metals 2016, 6, 247 2 of 12 Metals 2016, 6, 247 2 of 12

Stress応応力力 Tensile strength (Ts) Stress Tensile引張引強 張 strengthさ強(さTs () T(Tss )

Yield strength Yield降降伏 strength伏点点(Y(sY s) ) (Ys()Ys) 一様伸び 局部伸び Uniform elongation (εu) Local局 elongation部伸び (εn) Uniform一様 elongation伸び (εu) Local elongation (εn) 破断伸び Rupture破 elongation断伸び (εf) Rupture elongation (εf)

Elongation歪 Elongation歪 FigureFigure 5. 5Schematic. Schematic diagramdiagram of of stress stress-strain-strain correlation. correlation. Figure 5. Schematic diagram of stress-strain correlation. Uniform elongation is directly related to deformation capacity, and there is a correlation Uniform elongation is directly related to plastic deformation capacity, and there is a correlation betweenUniform uniform elongation elongation is directly and yield related ratio; to hence, plastic the deformation following equation capacity, is proposed and there [28 ].is a correlation between uniform elongation and yield ratio; hence, the following equation is proposed [28]. Y between uniform elongation and yield ratio; hence,s the following equation is proposed [28]. εuRk( 1  )  k ( 1  Y ) (4) T Ys Ys εu = k(1 − ) =s k(1 − Y ) (4) εuRk( 1  )  k ( 1  YR ) (4) where YR = yield ratio; k = correction factor (TheT means value of correction factor k is 0.6). Ts The correlation between the uniform elongation of the steel structural members and the yield wherewhereratioY YR Ris= = p yieldyieldresented ratio;ratio; graphicallyk k= = correctioncorrection in Figure factorfactor 6a. (The(The meanmean valuevalue ofof correctioncorrection factorfactork kis is 0.6).0.6). TheThe correlation correlation between between the the uniform uniform elongation elongation ofof the the steel steel structural structural members members and and the the yield yield Local elongation(ε )(%) ratio is presented graphicallyUniform elongation( in Figureε )(%) 6a. 50 n ratio is presented graphically50 in Figureu 6a. ε = 0.7√A / L n 0 0 ε =0.6(1-Y ) u R 40 Local elongation(ε )(%) 40Uniform elongation(ε )(%) n 50 u 50 ε = 0.7√A / L 30 n 0 0 30 ε =0.6(1-Y ) u R 40 40 20 20 30 30 10 10 SS400 SS400 SN400B 20 SN400B 20 SM490A SM490A 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 √A / L Yield ratio(Y ) 10 0 0 10 SS400 R SS400 SN400B (a) (b) SN400B SM490A SM490A 0 0 0 0.2 0.4 0.6 0.8 1 Figure0 6. (0.2a) Uniform0.4 elongation0.6 0.8 and yield1 ratio and (b) local elongation and AL00. √A / L Yield ratio(Y ) 0 0 R The uniform elongation (ofa) the steel structural members decreases(b) with increasing yield ratio according to Equation (4), and uniform elongations of them shown in Table 2 (SS400, SN400B, and √ SM490A) Figureare approximately 6. (a) Uniform plotted elongation indicated and inyield Equation ratio and (4). (b) local elongation and AL00. Figure 6. (a) Uniform elongation and yield ratio and (b) local elongation and A0/L0. Local elongation is independent of the type of steel used for the test pieces. Local elongation is proportionalThe uniform to theelongation square root of ofthe the steel cross structural-sectional areamembers of the paralleldecreases part with of a testincreasing piece, A 0,yield and ratio The uniform elongation of the steel structural members decreases with increasing yield ratio accordingis inversely to Equation proportiona (4)l, toand the uniform gauge length elongation of a tests piece,of the Lm0, asshown shown in in Table Equation 2 (SS400, (5). Moreover, SN400B, and according to Equation (4), and uniform elongations of them shown in Table2 (SS400, SN400B, and SM490A)a formula are toapproximately calculate local plottedelongation indicated using uniform in Equation elongation (4). and area reduction obtained from SM490A) are approximately plotted indicated in Equation (4). testingLocal iselongation proposed basedis independent on the fact ofthat the rupture type of elongation steel used varies for thedepending test pieces. on the Local shape elongation of the is Localtest piece, elongation e.g., gauge is independentlength [25]. Currently, of the type however, of steel it is used difficult for to the measure test pieces. the area Local reduction elongation by is proportional to the square root of the cross-sectional area of the parallel part of a test piece, A0, and proportionalmeans of tonon the-destructive square root testing, of the so Equation cross-sectional (5) is to areabe used of theonly parallel for rectangular part of test a test pieces piece,: A0, and is inversely proportional to the gauge length of a test piece, L0, as shown in Equation (5). Moreover, is inversely proportional to the gauge length of a test piece, L , as shown in Equation (5). Moreover, a formula to calculate local elongation using uniform elongation0 and area reduction obtained from a formula to calculate local elongation using uniform elongation and area reduction obtained from testing is proposed based on the fact that rupture elongation varies depending on the shape of the testing is proposed based on the fact that rupture elongation varies depending on the shape of the test test piece, e.g., gauge length [25]. Currently, however, it is difficult to measure the area reduction by piece, e.g., gauge length [25]. Currently, however, it is difficult to measure the area reduction by means means of non-destructive testing, so Equation (5) is to be used only for rectangular test pieces: of non-destructive testing, so Equation (5) is to be used only for rectangular test pieces:

Metals 2016, 6, 247 8 of 13

√ A0 εn = γ (5) L0 where L0 = gauge length of a test piece; A0 = original cross-sectional area of the parallel part of a test γ γ piece; = coefficient indicating local elongation ( = 0.7). √ The correlation between the local elongation of the steel structural members and A0/L0 is γ presented graphically in Figure6b. Here, indicates the coefficient of local elongation√ by regression analysis. As seen in the figure, local elongation tends to increase in proportion to A0/L0. The local elongations of the steel structural members shown in Table2 (SS400, SN400B, and SM490A) are slightly larger than the line of Equation (5). Based on this fact, the cross-sectional area required for the calculation of local elongation is set by measuring the plate thickness of the target structural member. From the above, rupture elongation is found by calculating the sum of the uniform elongation and local elongation using Equations (4) and (5), as shown in Equation (3).

3.3. Degradation Degradation evaluation of the steel structural members is performed based on dimensional inspection and coating degradation evaluation (JIS K 5600-8-1 to 6), whose certification corresponds to ISO 4628-1-6, ASTM D714-02, and ASTM D610-01 [29–33]. In the dimensional inspection, the plate thickness of the structural members is measured with Vernier calipers or a micrometer. Where the dimensional inspection results indicate that such structural members do not meet the requirements for reuse specified in the current JIS standard (JIS G 3192: Shape, dimensions, mass and allowable error of hot-rolled steel), they are corrected so that they fall within the range of allowable error [33,34]. The degradation of paint coatings is evaluated according to the degree of blistering, rusting, cracking, flaking, and chalking based on JIS K 5600-8-1 (Testing methods for paints—Evaluation of degradation of paint coatings). For example, the degree of rusting is expressed by the magnitude and area of defect scattering (JIS K 5600-8-3: Degree of rusting).

4. Example of Material Estimation Based on the estimation flow of material properties mentioned in the preceding chapter, this chapter examines the mechanical properties and the degradation status of the structural members of the steel structure targeted for investigation by means of non-destructive testing. Among the mechanical properties, this paper focuses on tensile strength, yield point or yield strength, and elongation.

4.1. Mechanical Properties Vickers hardness of the along individual lines by nondestructive testing is measured, and the tensile strength, yield point or yield strength, and uniform elongation are calculated using the above-mentioned Equations (1)–(5). Vickers hardness, tensile strength, yield point or yield strength are shown in Figure7a. The test values and calculated values of rupture elongation are plotted in Figure7b. The test values obtained by destructive test pieces (Series_1) are tensile strength, yield strength, and elongation, and they have average of three specimens. The Vickers hardness is also measured with the same test pieces via nondestructive testing. The measured object was the flange (a plate thickness of 11 mm) of a column (H-350 × 175 × 7 × 11), and its Vickers hardness (Hv) was found to be 125–140. Prior to measurement, surface grinding was performed on the flange. The Vickers hardness (Hv) of the columns (a height of Floor level +1.0 m) at 14 locations along the individual lines shown in Figure1 was measured three times each, and the mean value of the measurements was taken. As a result of calculations, tensile strength is 413–450 N/mm2, yield point or yield strength is 272–313 N/mm2, and the rupture elongation is 19%–21%. The plate thickness of the structural members being 11 mm, rupture elongation of test values is 30%, which is 1.15 times larger than the calculated values. Metals 2016, 6, 247 9 of 13 Metals 2016, 6, 247 4 of 12

2 500 Ts,Ys (N/mm ) 40 Rupture elongation (%) Ts = 2.5 Hv + 100 Uniform elongation 450 35 Local elongation

30 400 16% 25 350 20 Ys = 2.736 Hv - 70.5 19% 300 15

Tensile strength(Calculated) 10 250 Tensile strength(Test) 14% Yield strength(Calculated) 5 7% 200 Yield strength(Test) 100 120 140 160 180 200 0 Test values Calculated values Hv (a) (b)

Figure 7.7. ((a)) TensileTensile strength,strength, yieldyield pointpoint oror yieldyield strength,strength, andand VickersVickers hardnesshardness andand ((bb)) testtest valuesvalues and calculatedcalculated valuesvalues ofof uniformuniform elongationelongation andand locallocal elongation.elongation.

The measured object was the flange (a plate thickness of 11 mm) of a column (H-350 × 175 × 7 × The mechanical properties of 400 and 500 N/mm2 class steels (JIS standard) are tabulated in 11), and its Vickers hardness (Hv) was found to be 125–140. Prior to measurement, surface grinding Table3. As the corresponding value of the tensile strength obtained from the Vickers hardness was performed on the flange. The Vickers hardness (Hv) of the columns (a height of Floor level +1.0 measurements falls within the range of 400 to 510 N/mm2 specified in JIS, all 400 N/mm2 class steels m) at 14 locations along the individual lines shown in Figure 1 was measured three times each, and fulfill the tensile strength requirements specified in JIS. As for the corresponding value of the yield the mean value of the measurements was taken. As a result of calculations, tensile strength is 413– point or yield strength, the lower limit specified in JIS being 225 N/mm2, all 400 N/mm2 class fulfill 450 N/mm2, yield point or yield strength is 272–313 N/mm2, and the rupture elongation is 19%–21%. the JIS requirements, as in the case of tensile strength. However, 500 N/mm2 class steels do not fulfill The plate thickness of the structural members being 11 mm, rupture elongation of test values is 30%, the JIS requirements as they fail to meet the lower limits of tensile strength and yield point or yield which is 1.15 times larger than the calculated values. strength. The calculated average value of elongation is 20%. SS400 and SN400A steels with the lowest The mechanical properties of 400 and 500 N/mm2 class steels (JIS standard) are tabulated in limit of elongation fulfill the JIS requirements, and its deference of elongation of JIS is small. The target Table 3. As the corresponding value of the tensile strength obtained from the Vickers hardness building was constructed in the 1970s, during which time SN steel was not manufactured, so SN steel measurements falls within the range of 400 to 510 N/mm2 specified in JIS, all 400 N/mm2 class steels is excluded from consideration. From this, the material properties of the steel structural members fulfill the tensile strength requirements specified in JIS. As for the corresponding value of the yield correspond to SS400, SM400A, SM400B, and SM400C. Designing these members for reuse is desirable point or yield strength, the lower limit specified in JIS being 225 N/mm2, all 400 N/mm2 class fulfill for SS400 safety. the JIS requirements, as in the case of tensile strength. However, 500 N/mm2 class steels do not fulfill the JIS requirements as they fail to meet the lower limits of tensile strength and yield point or Table 3. Mechanical properties (JIS standard). yield strength. The calculated average value of elongation is 20%. SS400 and SN400A steels with the lowest limit of elongationYield fulfill Strength the (N/mmJIS requirements2), and Tensile its deference Strength (N/mm of 2elongation) Rupture Elongationof JIS is (%)small. Materials The target building wasLower constructed Limit/Upper Limit in the 1970s, during which time SNLower steel Limit was not Grade Lower Limit/Upper Limit manufactured,6 so≤ t SN* < 12 steel 12 is≤ excludedt < 16 t =from 16 consideration. 16 < t ≤ 40 From this, the material 6 ≤ t ≤properties16 16 < t ≤ of50 the steel SS400 structural 245/–members correspond 245/– 245/– to SS400, 235/– SM400A, SM400B, 400/510 and SM400C. 17 Designing 21 these SM400A 245/– 245/– 245/– 235/– 400/510 18 22 membersSM400B for reuse 245/– is desirable245/– for SS400245/– safety. 235/– 400/510 18 22 SM400C 245/– 245/– 245/– 235/– 400/510 18 22 SN400A 235/– 235/–Table 3. Mechanical 235/– 235/–properties (JIS standard).400/510 17 21 SN400B 235/– 235/355 235/355 235/355 400/510 18 22 SN400C – – 235/355 235/355 400/510 18 22 Yield Strength(N/mm2) Tensile Strength SM490A 325/– 325/– 325/– 315/– 490/610 Rupture17 Elongation 21 (%) (N/mm2) MaterialsSM490B 325/– Lower Limit/Upper325/– 325/–Limit 315/– 490/610 17 21 SN490B 325/– 325/445 325/445 325/445 490/610 17 21 Grade Lower Limit SN490C – – 325/445 325/445 Lower Limit/Upper490/610 Limit 17 21 6 ≤ t * < 12 12 ≤ t < 16 t = 16 16 < t ≤ 40 * Thickness of steel plates. 6 ≤ t ≤ 16 16 < t ≤ 50 SS400 245/-- 245/-- 245/-- 235/-- 400/510 17 21 SM400A 245/-- 245/-- 245/-- 235/-- 400/510 18 22 SM400B 245/-- 245/-- 245/-- 235/-- 400/510 18 22 SM400C 245/-- 245/-- 245/-- 235/-- 400/510 18 22 SN400A 235/-- 235/-- 235/-- 235/-- 400/510 17 21 SN400B 235/-- 235/355 235/355 235/355 400/510 18 22

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SN400C -- -- 235/355 235/355 400/510 18 22 SM490A 325/-- 325/-- 325/-- 315/-- 490/610 17 21 SM490B 325/-- 325/-- 325/-- 315/-- 490/610 17 21 SN490B 325/-- 325/445 325/445 325/445 490/610 17 21 MetalsSN490C2016 , 6, 247 -- -- 325/445 325/445 490/610 17 1021 of 13 * Thickness of steel plates. 4.2. Degradation 4.2. Degradation Degradation evaluation of the steel structural members was performed based on dimensional Degradation evaluation of the steel structural members was performed based on dimensional inspection and coating degradation evaluation, as mentioned in Section 3.2. In the visual inspection, inspection and coating degradation evaluation, as mentioned in Section 3.2. In the visual inspection, excessive deformation due to overload and fire damage was not found in the structural members; excessive deformation due to overload and fire damage was not found in the structural members; however, a considerable amount of rust was observed. Typical coating degradation of the column however, a considerable amount of rust was observed. Typical coating degradation of the column flanges is shown in Figure8 and Table4[ 29]. The volume of rust on the structural members in the flanges is shown in Figure 8 and Table 4 [29]. The volume of rust on the structural members in the vicinity of the openings is slightly larger than that on the structural members located away from the vicinity of the openings is slightly larger than that on the structural members located away from the openings. The rust status of the structural members located in the vicinity of the openings along the Y openings. The rust status of the structural members located in the vicinity of the openings along the1 and Y2 lines corresponds to Ri5(S5). The rust status of the structural members at the other locations Y1 and Y2 lines corresponds to Ri5 (S5). The rust status of the structural members at the other is mostly Ri4(S4). The coating film thickness of the structural members along the Y1 line and the locations is mostly Ri4 (S4). The coating film thickness of the structural members along the Y1 line Y2 line is 65–102 µm and 65–99 µm, respectively. The coating film thickness of the columns located and the Y2 line is 65–102 μm and 65–99 μm, respectively. The coating film thickness of the columns away from the openings is slightly larger than that of the columns in the vicinity of the openings. located away from the openings is slightly larger than that of the columns in the vicinity of the The distribution of the plate thickness of the flanges and webs of the columns along individual lines openings. The distribution of the plate thickness of the flanges and webs of the columns along is shown in Figure9. Although both the flanges and webs have a deference of varying degrees of individual lines is shown in Figure 9. Although both the flanges and webs have a deference of coating degradation, with the tolerance of the plate thickness of the former being ±1.0 mm and that varying degrees of coating degradation, with the tolerance of the plate thickness of the former being of the latter being ±0.7 mm, they satisfy the JIS requirements [33–36]. From Sections 4.1 and 4.2, it is ±1.0 mm and that of the latter being ±0.7 mm, they satisfy the JIS requirements [33–36]. From considered that the material of the steel structural members of the target building correspond to SS400 Sections 4.1 and 4.2, it is considered that the material of the steel structural members of the target and that these members can be reused. building correspond to SS400 and that these members can be reused.

(a) (b)

(c) (d)

Figure 8. Coating degradation of column (a) Ri5 (S5), Y1X1 line; (b) Ri4 (S4), Y1X6 line; (c) Ri5 (S5), Figure 8. Coating degradation of column (a) Ri5(S5), Y1X1 line; (b) Ri4(S4), Y1X6 line; (c) Ri5(S5), Y2X1 Y2X1 line; (d) Ri4 (S4), Y2X8 line. line; (d) Ri4(S4), Y2X8 line.

Table 4. Coating degradation evaluation. Table 4. Coating degradation evaluation. Thickness of Painting Thickness of Painting Line Thickness of Mark of Rust Line Thickness of Mark of Rust Line (μm) Mark of Rust Line (μm) Mark of Rust Painting (µm) Painting (µm) Y1X1 74 Ri5(S5) Y2X1 65 Ri5(S5) Y X 74 Ri5(S5) Y X 65 Ri5(S5) Y1X2 1 1 65 Ri5(S5) Y2X2 2 1 74 Ri5(S5) Y1X2 65 Ri5(S5) Y2X2 74 Ri5(S5) Y1X3 67 Ri4(S4) Y2X3 80 Ri4(S4) Y1X3 67 Ri4(S4) Y2X3 80 Ri4(S4) 1 4 2 4 Y X Y1X4 89 89 Ri4(S4) Y YX2X 4 7272 Ri4(S4)Ri4(S4) Y1X6 Y1X6 85 85 Ri4(S4) Y Y2X2X6 6 9595 Ri4(S4)Ri4(S4) Y1X7 Y1X7 102 102 Ri4(S4) Y Y2X2X7 7 9999 Ri4(S4)Ri4(S4) Y1X8 94 Ri4(S4) Y2X8 86 Ri4(S4) Y1X8 94 Ri4(S4) Y2X8 86 Ri4(S4)

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Thickness(mm) 14 Flange Web Flange 12 Upper limit:12 mm

10 Lower limit:10 mm

8 Web Upper limit: 7.7 mm

6 Lower limit: 6.3 mm

4

2

0 X1 X2 X3 X4 X6 X7 X8 X1 X2 X3 X4 X6 X7 X8 Y1 Y2 Line

Figure 9.9. Thickness of the flangeflange and web of the column.

5. Conclusions Conclusions By meansmeans of non-destructivenon-destructive testing, this study examined the mechanical properties, namely, namely, tensiletensile strength,strength, yieldyield point point or or yield yield strength, strength, yield yield ratio, ratio and, and elongation, elongation, and and the the degradation degradation status status of steelof steel structural structural members members assumed assumed to beto reused.be reused. The The test test results results revealed revealed the the following: following: (1) Based on Vickers hardness found via NDT, this paper proposed a flow for estimating the (1) Based on Vickers hardness found via NDT, this paper proposed a flow for estimating the mechanical properties of the steel structural members. Tensile strength and yield point or yield mechanical properties of the steel structural members. Tensile strength and yield point or strength were calculated using Vickers hardness. Uniform elongation and local elongation of yield strength were calculated using Vickers hardness. Uniform elongation and local elongation the steel structural members were calculated using the yield ratio and plate thickness of the of the steel structural members were calculated using the yield ratio and plate thickness of the structural members, respectively. structural members, respectively. (2) The proposed estimation flow of mechanical properties, e.g., tensile strength, yield point or (2) yieldThe proposed strength, estimation and rupture flow of elongation mechanical, was properties, verified e.g., applying tensile strength, to a target yield building point or yield steel structure.strength,and rupture elongation, was verified applying to a target building steel structure. Since thethe datadata ofof thethe correlationcorrelation between between Vickers Vickers hardness hardness via via NDT NDT and and mechanical mechanical properties properties is small,is small, statistical statistical analysis analysis has not has been not conductedbeen conducted yet. By storingyet. By a storing database a ofdatabase mechanical of mechanical properties, suchproperties as tensile, such strength, as tensile yield strength, point or yield yield strength,point or yield and elongation, strength, and measured elongation by test, measured pieces, statistical by test analysispieces, statistical can be conducted analysis can in the be nearconducted future. in the near future.

Acknowledgments:Acknowledgments: TheThe authorsauthors wishwish toto thankthank MamoruMamoru Iwata, at KanagawaKanagawa University, forfor hishis cooperationcooperation in performing this study. performing this study. Author Contributions: The first author (Masanori Fujita) planned out the concept and carried out the survey test. TheAuthor second Contributions: author (Keiichi The Kuki) first carriedauthor out(Masano the surveyri Fujita) test andplanned supported out the the concept first author, and carried and the out corresponding the survey authorstest. The controlled second author the entire (Keiichi project. Kuki) carried out the survey test and supported the first author, and the Conflictscorresponding of Interest: authorsThe controlled authors declarethe entire no project conflict. of interest. Conflicts of Interest: The authors declare no conflict of interest. References

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