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Effective Thickness of Corroded Steel Plates 44 <strong>AMMJ</strong> 4.2 Comparison of Proposed Effective Thickness The experimentally predicted thickness (Eq. 3 and Eq. 4) and the representative thickness which were valued by different methods were examined and compared to understand the effectiveness of the proposed method of estimating the remaining strength capacities of corroded steel plates. The following Figure 8 shows the behavior of representative thickness, valued by different methods and the experimental tensile effective thickness (t e_b ). Figure 8 shows that the strength estimations obtained by the effective thickness values proposed by all Matsumoto et al 1989, Muranaka et al 1998 and Kariya et al 2003 are rather overestimated. So, this could lead the corroded structures to be at risk as their actual remaining capacities are lesser than that of the predicted. But, the “Proposed” method is much closer to the actual conditions. The Table 3 shows the coefficient of correlation values of the available different methods and the proposed method of effective thickness in estimating remaining yield and tensile strengths. It clearly shows that the proposed effective thickness parameter gives more reliable and better prediction with the experimentally analyzed results than other available methods. 5.0 Conclusions The 42 specimens taken out of the scrapped plate girder which had been used for about 100 years with severe corrosion, was used to perform the tensile tests to clarify the relationship between the representative effective thickness (t eff ) to estimate the mechanical properties of corroded plates and their level of corrosion. A representative effective thickness equation derived by using initial thickness and maximum corroded thickness (derived with minimum thickness) to estimate their remaining yield and tensile strengths is discussed from those experimental results. The main conclusions are as follows: 1. The corrosion causes strength reduction of steel plates and minimum thickness ratio ( ) can ( yn be / y ) used ( bn /as b ) a yn y t eff = measure of the level of corrosion and their strength degradation. Therefore, three basic corrosion P categories can be y Pb defined, Minor Corrosion ( > 0.75), ( yn /Moderate y ) ( bn b ) Corrosion yn y t eff = (0.75 t 0 + ≥ (1-) ≥ t min 0.5) ( yn () and / y ) Severe (t bn e _/ y b ) Corrosion yn y t eff = ( t < 0.5) according B to their severity of corrosion. e t _ b 0 + (1-) ( yn / t min y ) ( () bn / b ) t e yn _ y y t y B b B 2. A representative effective thickness (t eff ), based on the initial thickness (t 0 ) and maximum corroded thickness (t c,max ) can be used to estimate the remaining yield and tensile strength of corroded steel plates. In estimation of both remaining yield strength and tensile strength, the proposed relationship revealed a good comparison with the experimental results and the derived equation is as follows: t eff = t 0 - 0.8 t c,max As the proposed effective thickness equation has only a single variable, maximum corroded thickness (t c,max ), which is an easily measurable parameter and the value of initial thickness (t 0 ) is a well known parameter, it will reduce the contribution of errors occurring during the practical investigation of a corroded member. Also it is necessary to note that the t max should be applied for very old bridges in which t 0 may not be known in very rare situations. Further this method is simple and gives more reliable and closer results compared to the other available methods. References Table Table 3: Comparison 3 Comparison of correlation of correlation coefficients coefficients of different of representative different representative thickness prediction methods thickness prediction methods Method Matsumoto et al. 1989 Muranaka et al. 1998 Kariya et al. 2003 Proposed, Equation of thickness t sa t avg – 0.7 st t avg – 1.3 st t 0 - 0.8 t c,max Correlation Yield - - - 0.89 Coefficient Tensile 0.88 0.04 0.81 0.90 [1] A. Kariya, K. Tagaya, T. Kaita and K. Fuji [2003], ‘Basic study on effective thickness of corroded steel plate and material property’, Annual conference of JSCE, pp 967-968. (In Japanese) [2] A. Kariya, K. Tagaya, T. Kaita and K. Fuji [2005], ‘Mechanical properties of corroded steel plate under tensile force’, Proceedings of the 3rd International Structural Engineering and Construction Conference (ISEC-03), Japan, pp 105-110. [3] A. Muranaka, O. Minata and K. Fujii [1998], ‘Estimation of residual strength and surface irregularity of the corroded steel plates’, Journal of Structural Engineering, vol. 44A, pp 1063-1071 (In Japanese). [4] ‘Corrosion Protection of Steel Bridges’, Steel Bridge Design Handbook, Chapter 23, National Steel Bridge Alliance. [5] I. Sugimoto, Y. Kobayashi and A. Ichikawa [2006], ‘Durability Evaluation Based on Buckling Characteristics of Corroded Steel Deck Girders’, QR of RTRI, Vol. 47, No.3, pp 150-155. [6] K. Fuji, T. Kaita, H. Nakamura and M. Okumura [2003], ‘A Model Generating Surface Irregularities of Corroded Steel Plate for Analysis of Remaining Strength in Bridge Maintenance’, The 9th East Asia-Pacific Conference on Structural Engineering and Construction (EASEC-9), Vol. 9, pp 32-38. [7] M. Bruneau and S.M. Zahrai [1997], ‘Effect of Severe Corrosion on Cyclic Ductility of Steel’, Journal of Structural Engineering, Vol. 123, No.11 pp 1478-1486. t eff Vol 24 No 3
<strong>AMMJ</strong> 45 [8] M. Matsumoto, Y. Shirai, I. Nakamura and N. Shiraishi [1989], ‘A Proposal of effective Thickness Estimation Method of Corroded Steel Member’, Bridge Foundation Engineering, Vol. 23, No. 12, pp 19-25. (In Japanese) [9] R. Rahgozar [2009], ‘Remaining Capacity Assessment of Corrosion Damaged Beams using Minimum Curves’, Journal of Constructional Steel Research, Vol. 65, pp 299-307. [10] S.M. Zahrai [2003], ‘Cyclic Strength and Ductility of Rusted Steel Members’, Asian Journal of Civil Engineering, Vol. 4, Nos. 2-4, pp 135-148. [11] T. Kaita, K. Tagaya, K. Fuji, M. Miyashita and M. Uenoya [2005], ‘A simple estimation method of bending strength for corroded plate girder’, Proceedings of the 3rd International Structural Engineering and Construction Conference (ISEC-03), Japan, pp 89-97. Spares Criticality Has Many Dimensions Phillip Slater Materials and Spare Parts Management Specialist (Australia) One of the things that most maintenance and reliability groups struggle with is the issue of spare parts criticality. It seems that criticality is often seen as a single dimension issue, that is, an item either is, or isn’t, critical. But I don’t think that is right. I think spare parts criticality is a multi-dimensional issue. What do I mean by multi-dimensional? Not that criticality exists in some science fiction space-time continuum but rather that it has a number of characteristics that need to be considered before deciding what to hold in inventory. For example, is the item in question machine critical or operationally critical? By machine critical I mean, will failure of the item stop the piece of equipment of which it is a part? By operationally critical, I mean, will failure of the item stop production? These two characteristics are quiet different and have a different impact on what to do next. For example, the globe in a headlight on my car is machine critical to the light. Obviously, the light will not work without the globe. But my car will still operate. In fact, in daylight hours there is no noticeable difference. If the globe fails at night I would notice the difference but would still be able to operate the car until I can get the globe replaced. Yes, safety will be slightly reduced but I think that this is, in this specific case, acceptable for a short period. Compare the globe failure with a fan belt failure. If you break a fan belt you won’t be able to drive for more than a few minutes before the vehicle starts to overheat and be un-drivable. The fan belt is not only machine critical it is also operationally critical. Yet, how many people carry spare fan belts for their cars? Not many. Why: because the failure is rare and the result may be inconvenient but in most cases tolerable (catch a taxi, get the car towed, call the auto club etc.). If you live in a city you are unlikely to carry a fan belt. If you live in or are driving through a remote area you probably would carry a fan belt. The decision (and quantity to hold) is dependent upon the situation. What about brakes. Everyone would agree that brakes are pretty important but who carries spare brake pads? No-one. Why: because inspections will identify pad wear so that you replace the pads before they become dangerous (plus the occasional grinding noise is a bit of a giveaway!) Everyone would argue that brake pads are operationally critical, but no-one would carry brake pads. Here we have three items. Each is machine critical, two are operationally critical, yet none are carried as spares, except in specific (for most of us unusual) circumstance. Spare parts criticality is definitely multi-dimensional and the inventory that we hold should be a function of the situation. For some critical spare parts we can still operate until we get the spare, for some we can wait until the spare arrives, for some we can manage through condition monitoring. Of course there are some items that we just can’t live without. Just don’t think that all items identified as critical will fall into that final category. Phillip Slater is a leading authority on materials and spare parts management and is currently celebrating ten years as an independent consultant, where he has assisted 297 companies, with more than 1,000 storerooms, holding $3.5bn in inventory. He is also the author of four operations management books, including Smart Inventory Solutions, now in its second edition and a recent finalist in the RGVA 2011 book awards. For more information on spare parts management visit Phillip’s website www.PhillipSlater.com. Vol 24 No 3
Page 3 and 4: LogbooksOnline Web-based logbooks a
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Page 17 and 18: Maintenance 2011 Seminars Download
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Page 25 and 26: Take a vibration expert along NEW F
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Page 39 and 40: AMMJ Effective Thickness of Corrode
Page 41 and 42: Frequency, (%) Effective Thickness
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Page 49 and 50: • Features a valuable practical
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