SEISMIC SAFETY OF BRIDGE CRANE STEEL STRUCTURES OPERATING IN NPP Kalin RADLOV*, Vesko PANOV** *University of Architecture, Civil Engineering and Geodesy Sofia, Bulgaria **Technical University Sofia, Bulgaria Abstract. The seisic stability assessent of systes and equipent operating in Nuclear Power Plants (NPP) is a very iportant preventive precaution for ensuring their eergency safety. The actuality of this case study arises extreely after Fukushia NPP disaster, caused by the earthquake on March 0. Bridge cranes are a significant and integral part of the technological equipent, which affects the odern NPPs safety. The ain ai of the present study is to propose an analytic-siulation approach for analysis of bridge crane steel structures dynaic behavior during earthquake ipact as to evaluate ostly the sliding ability of crane traveling wheels on rail roads. Loads and harful effects acting on the crane bridge steel structure caused by the sliding phenoenon are defined and analysed. Keywords: bridge crane, steel structure, seisic ipact, sliding, safety. Introduction The present days break downs and accidents in NPPs caused by earthquakes becoe ore frequent. Particularly after Fukushia NPP (caused by earthquake in Japan on March 0) engineers and researchers have paid attention to seeking of effective approaches and ethods for assessent of NPP systes and equipent behavior. The seisic stability proof of systes and equipent operating in NPPs is a very iportant preventive precaution for ensuring their eergency safety. In this connection а particular place is taken by the bridge cranes, which are a significant and integral part of the technological equipent, which affects the odern NPPs safety. During the construction of the first Bulgarian NPP in 970, the site located near Kozloduy town was evaluated under VI-th degree of seisic intensity by MSK-64 scale [3] and in a view of that the energy blocks and their equipent inside were not ensured against seisic ipact. During the Vrancha earthquake on 4 March 977 was easured VII-th degree of seisic intensity by MSK-64 scale at Kozloduy NPP site. According to the operative nors [7] for VII-th degree earthquakes confors axiu acceleration for free field a g 0. /s. After the failure in Chernobil's NPP in 986, International Atoic Energy Agency (IAEA), increase again anti-seisic requireents for all the European NPPs. There begins the new seisic re-evaluation and new seisic qualification for energy blocks and equipent inside of NPPs. In view of high degree of hazard for NPPs, have been developed a special group of standards [ and ] by IAEA for seisic qualification, not only for NPPs at all, but also for their equipent. Bridge cranes are one of the ost nuerous group aterial handling equipents, which operate in NPPs. Question with seisic qualification of hoisting achines in accordance with Russian nors and standards is not exactly a new question, but it is regulated in any norative docuents [4, 5, 6, 7, 8]. Even so there is not known a research or norative docuent, in which to be analyzed the specific character of contact between crane bridge traveling wheel and rail. Likewise coplicated dynaic behavior of structure in case of sliding between crane traveling wheel and rail during earthquake. The ain ai of the present developent is to propose an analytic-siulation approach for analysis of bridge crane steel structures dynaic behavior during earthquake ipact as to evaluate ostly the sliding ability of crane traveling wheels on rail roads. Researches have to be pointed to analysis of loads acting on the crane bridge, caused by sliding effect, and also to specific engineering solutions for protection the crane structure against non-allowable loads.. Norative require ents to steel structures of bridge cranes operating in NPPs In accordance with the requireents of the design nors [7], one of the recoended load cobinations for study of bridge crane steel structures in case of earthquake includes loads of noral operation and loads caused by seisic ipact. According to the requireents for construction and safety operation of hoisting cranes in sites of 6
NPP [8], there are adissible dynaic loads of "noral operation" and "non-noral operation" which are not included in operational loads of crane. In accordance with [8], the construction and the calculation of cranes operating in NPPs ust be perfored, so that the strength requireents should not be contravened, in case of crane bridge and crane trolley sliding in longitudinal and transverse direction of the crane railroad direction during seisic ipact (figure ). RECENT, Vol., nr. (3), July, 0 where F C (t, x) is the inertia seisic force, depending on tie t and coordinate x, which is a linear paraeter, indicating the location of crane trolley on the bridge; (x) - luped ass to a point of crane structure (in ost cases for such point is selected the geoetric centre of crane bridge or geoetric centre of front bea); a(t) - seisic acceleration of pointed ass in the corresponding direction. According to the shock theory [3], the seisic force can be calculated by the equation: Figure. Sliding of a crane bridge longitudinal and transverse the crane railroad direction On figure with and are designated the corresponding distances between the rail top and the wheel flanges, for which is in force the equality: + = BХК С Р () where B XК is the distance between wheel flanges; C P width of rail top. According to [0], recoended values of B XК and C P are selected depending on the traveling wheel diaeter D XК, as for one diaeter of travelling wheel are possible several values of distance between wheel flanges. The final selection of B XК has to be perfored, as nuerous additional factors are taken into account, such as crane span (distance between rails), technological and functional requireents etc. Sliding effect of crane bridge on the rail is ostly a result of: - seisic force, which is acting on crane bridge in horizontal plane, and - friction forces between travelling wheels and rail. Inertia seisic force, acting on a pointed ass of bridge crane construction (figure ), in each of the three directions X, Y and Z, is calculated by the known equation []: F C ( t, x) = ( x) a( t) () 3 4 FC = ( + k) 3 + 4 r. MAX, (3) τ where τ is durability of the ipact - fro practice it is known, that τ = (0 3 0 6 ) s [3]; k - coefficient of restitution by ipact between two steel bodies; 3 - the part of building construction ass, which is taken into account by ipact (on the basis of ethodology in [4], for the purpose of present developent, it can be assued that 3 000 kg); 4 - the part of bridge crane ass, which is taken into account by ipact; y & r. MAX - axiu sliding velocity of the traveling wheel on rail, which is calculated according to ethodology presented in point 3.. 3. Sliding in longitudinal direction 3.. Matheatical odel The study of crane bridge sliding along railroad is perfored with following siplifications: - crane is without load, as it decreases the friction forces between travelling wheel and rail and causes sliding effect; - ass of crane bridge is luped into two asses and (figure ), located in geoetric centers of the two front beas, which are calculated by the following equations: + [ L L ( x)] M D ( x) = + TR, (4) + ( x) M D = + TR, (5) L L ( x) where M is the ass of crane bridge; D - ass of additional equipent installed on bridge crane (electrical cabinets, gears, onitoring and guiding equipent etc.); TR - ass of crane trolley; L - distance fro crane trolley to the centre line of the railroad; L - crane span. - crane bridge reaction along the crane railroad is represented by elasticity coefficient c and daping coefficient β. L 6
Figure. Matheatical odel for research of crane bridge sliding along crane railroad With help of the above defined siplifications is created echanical-atheatical odel (figure ) for study of crane bridge sliding along crane railroad. On figure are used the following denotations: ζ Y (t) and ζ Y (t) are longitudinal displaceents of corresponding railroad beas regarding to the origin of iovable coordinate syste XYZ; y r (t) and y r (t) - respectively relative oveent (sliding) of front crane bea regarding to rail; G and G - weight, which is transferred fro crane bridge to corresponding rails; R and R - friction forces in travelling wheels; c - elasticity coefficient of crane bridge along axis Y; β - daping coefficient of crane bridge along crane railroad. Differential equations of crane bridge oveent are worked out by d Alabert principle. They represent crane sliding on corresponding rail []: & r = β ( r r) c yr µ g sgn && ζ r RECENT, Vol., nr. (3), July, 0 y Y, r (6) 3.. Practical exaple for crane sliding along crane railroad It is analyzed a double girder crane of type КМ 300 with hoisting capacity Q = 30 t, and crane trolley located at the end of crane bridge. In this condition the ore loaded front bea should have at least possible sliding in coparison to all the other cases. If seisic loads in this case are bigger than the allowable values, this would ean also potential hazard for all the other cases of crane trolley location. Аs the building bearing structure is not an object of the present study, to help on siplifications of calculations, it is assued that both of the railroad beas have the sae dynaic behavior: ζ Y (t) = ζ Y (t) = ζ Y (t), as it is included coefficient of aplification of free site seisic acceleration transferred to level of crane railroad. According to [5] this aplification is a product of the coefficient of loading intensivity (with axial value ) and the coefficient, which indicates height of equipent installation (with value 3 for H = 40 ). Maxiu acceleration value of input seisic ipact is selected g. For the present study it is generated a rando seisogra and its accelerogra, presented on figure 3. & r = β r r µ g sgn c yr ζ&& r Y y, r (7) where µ is friction coefficient between travelling wheel and rail. The friction coefficient depends on nuerous factors such as type of aterial, condition and wearing of rubbing surfaces, pressure distribution in contact area, rotation (skewing) of crane bridge in horizontal plane and particularly of type of contact between travelling wheel and rail, which question is in detail analyzed in [9]. For crane which work in roofed workshops it can be assued [0] µ 0.. Figure 3. Input seisogra and accelerogra 63
After substitution of paraeters values with real data for analyzed double girder crane ( T = 30,000 kg, L =.5, L =.6, D XК =0.7, B XК = 0., C P = 0.07, M =,67 kg, D = 0,973 kg, TR = 0,530 kg) in equations (3) and (4) are obtained the following values for luped asses: = 6,39.8 kg and = 7,367.6 kg. In accordance with ethods given in [4] are deterined values of coefficient c and β : c = 6,453 N/ and β =,3 N s/. Equation syste (6) and (7) is solved by software product MATLAB [], as the input seisic ipact is haronic expanded with ethods given in [4]. Graphics for relative oveent (sliding) of crane bridge along the crane railroad, at the side of ore loaded front bea are obtained. The results are presented on figures 4, 5 and 6. Analysis of shown graphics leads to several ore iportant deductions. Maxial displaceent of ore loaded front bea is 0.38, in case of input seisic ipact duration 0 s. This eans that during earthquake event, as a result of sliding effect, there is a potential danger that the crane bridge would reach the railroad buffer support. RECENT, Vol., nr. (3), July, 0 Figure 6. Relative acceleration (sliding acceleration) Maxiu value of relative velocity (sliding velocity) is 0.395 /s, fro which by equation (3) can be calculated seisic force F C = 59. kn. The axiu value of sliding acceleration in ore loaded front bea is 6.85 /s, fro which by equation () can be calculated the inertia seisic force, acting on the crane bridge - F C = 80.8 kn. It is obvious, that the seisic force calculated according to shock theory is ore than three ties bigger than seisic force calculated as a noral inertia force. The calculated value of seisic force acting on ore loaded front bea is significant and its ignoring is inadissible. For the particular crane seisic force is fro 4% to 38% than bridge crane own weight. Figure 4. Relative oveent (sliding) 4. Sliding in direction across the railroad 4.. Matheatical odel For study of crane bridge sliding transverse the crane railroad is created echanical-atheatical odel shown on figure 7, likewise are adopted the sae siplifications as these in point 3.. On figure 7 are used the following denotations: c 3 is the elasticity coefficient of crane bridge along axis X; β 3 - daping coefficient of both crane ain beas along axis X. The rest denotations are the sae as these fro figure. Differential equations of crane bridge oveent are worked out again by d Alabert principle as follows (8) and (9): Figure 5. Relative velocity (sliding velocity) x&& r && x r = β3 x& r x& r) c3 xr µ g sgnx& ζ && r r x X = β3 x& r x& r) c3 xr µ g sgnx& ζ &&, X r x. r (8) (9) 64
RECENT, Vol., nr. (3), July, 0 graphic shown on figure 8, is obvious that axiu displaceent is 0.043. This displaceent value shows that there is a potential hazard to have a contact between wheel flange and rail top. Maxiu value of relative velocity in tie. s is 0.43 /s, fro which in accordance with shock theory (by equation (3)) is obtained value of seisic force F C = 644.48 kn. Figure 7. Matheatical odel for research of crane bridge sliding across crane railroad 4.. Practical exaple for crane sliding transverse the crane railroad As an input seisic ipact is used again in the seisogra fro figure 3. There is assued siilar dynaic behavior of the both railroad beas, and also crane trolley located at the end of crane bridge, because of considerations given in point 3.. In accordance with ethods given in [4] are deterined values of coefficient c 3 and β 3 : c 3 = 9,374,737 N/; β 3 = 5,836 N s/. It is ade a substitution in equations (8) and (9) with real data paraeters for analyzed double girder crane type КМ 300, as in point 3. and the equation syste is solved by software product MATLAB []. On figures 8, 9 and 0 are shown graphics for relative oveent (sliding) of crane bridge transverse the crane railroad, at the side of ore loaded front bea. Fro the presented graphics it is obvious that, the axiu displaceent of ore loaded front bea is 0.059, which is uch bigger than axiu distance (gap) between travelling wheel flange and rail top, calculated with substitution of the particular nuerical data in equation (): + = 0.04. Fro the graphic shown on figure 0, can be deterined, that acceleration with value 9. /s is reached in tie. s since the earthquake event beginning, for which tie after coparison with Figure 8. Relative oveent (sliding) Figure 9. Relative velocity (sliding velocity) Figure 0. Relative acceleration (sliding acceleration) 65
For the calculated acceleration value, which is considered that can be realized in practice 9. /s, can be calculated inertia seisic force by equation (), which for the particular exaple is F C = 40.8 kn. The obtained seisic force, which is acting on the wheel flange, again reaches significant values regarding to bridge crane own weight (fro 56% to 49%). This force has a considerable value and by its action causes significance shear (tangential) stresses in wheel flanges, which ust be taken into accounted by echanical engineers. It can be entioned, that seisic force, calculated in accordance with shock theory, is ore than.5 ties bigger than this calculated in equation (). 5. Constructive easures for safety of bridge crane steel structure 5.. Safety in direction transverse the crane railroad Constructive solutions for ensuring the safety of bridge crane steel structure in direction transverse the crane railroad are connected with averting an eventual crane slipping out the railroad. These decisions can be considered in two levels: first level protection ensured by traveling wheels flanges; second level protection ensured by additional ounted safeguards. The additional ounted safeguards can be ipleented as shown on figure. RECENT, Vol., nr. (3), July, 0 where δ and δ are distances (gaps) between the safeguard and rail; and - distances (gaps) between wheel flanges and ra il. By deterining the values of distances (gaps) δ and δ, the ain requireent, which ust be observed, is to decrease the value of dynaic ipact forces, calculated by ethod given in point 4, to allowable leve ls. By strength calculations of travelling wheel flanges and additiona l safeguards, the ain strength check ust be ade with seisic loads, calculated in accordance with point 4. 5.. Safety in direction along the crane railroad For averting crane bridge sliding a long the crane railroad is provided teporary engaged locking echaniss, fro type shown on figure, which are engaged only in crane parking position or in exact operation points located along the crane railroad. On figure are used the following denotations: position driving echanis; position locking bar; position 3 frae, welded to the crane steel structure; position 4 frae, welded to the crane railroad; γ and γ - distances between the locking bar and the frae, welded to the crane railroad in transverse direction; γ 3 and γ 4 - distances between the locking bar and the frae in longitudina l direction. Figure. Safeguards against crane slipping out the rail in direction transverse the crane railroad On figure with position is designated the peranent engaged safeguard against crane slipping out of the rail, for which ust be observed the following constructive requireent: δ + δ > +, (0) Figure. Locking echanis s of crane bridge Such type of locking echanis restrict ostly crane bridge sliding a long the crane railroad, but also transverse the crane railroad, in crane nonworking condition. By deterining the values of distances γ 3 and γ 4 ust be observed not only the requireent for 66
necessary braking distance for crane bridge positioning along the railroad, but also the requireent for decreasing the values of dynaic forces, calculated by the approach given in point 3, to allowable levels. For γ and γ is ostly necessary to be observed the requireent for decreasing the values of dynaic forces, calculated by approach given in point 4, to allowable levels. The ain strength check, which is necessary to be perfored by designing the locking echaniss, should be ipleented with seisic loads, calculated in accordance with point 3 and 4. 6. Conclusions On the basis of the perfored study, analysis and generalizations of the obtained results the following ore iportant conclusions can be ephasized: 6.. An analytic-siulation approach for study of bridge crane steel structure dynaic behavior during earthquake event is proposed. The approach assists engineers to estiate the probability for sliding between bridge travelling wheels and rail in direction along and transverse the crane railroad. 6.. Through created echanical-atheatical odels are obtained graphics for relative oveent (sliding) of real double girder crane in direction transverse and along the crane railroad. 6.3. It is calculated the value of realized seisic force in accordance with two ethods: by shock theory and as a noral inertia seisic force. On the basis of calculated values can be concluded that the shock theory gives uch bigger values (fro three to five ties). 6.4. Loads and harful effects acting on the crane bridge steel structure caused by the sliding phenoenon are defined and analyzed 6.5. Specific engineering solutions for protection crane structures against non-allowable loads in direction transverse and along the crane railroad are proposed. RECENT, Vol., nr. (3), July, 0 In conclusion, it should be noticed that the present study can be used as an effective engineer tool in design practice in cases of enhanced safety requireents for bridge crane steel structures, as it is, beyond all questions, bridge crane operating in NPPs. References. IAEA-50-SG-D5: Seisic Design and Qualification for Nuclear Power Plants. 99. IAEA Safety Guide No.50-SG-S: Seisic Analysis and Testing of Nuclear Power Plants 3. Tsenov, L.: Basis of the seisic engineering. Ed. Marin Drinov, Sofia, Bulgaria, 00 (in Bulgarian) 4. СNiP II- 7-8: Building in seisic areas. Ed. "М.:Minstroy", Russia, 995 (in Russian) 5. ISO 658 International Standard: NPP Earthquake resistance design. 6. RTM 08.00.37-8: Nuclear power plants equipent. Strength calculations in case of earthquake. Ed. "M.: Minenergoash" (NPO CKTI), 986 (in Russian) 7. NP-03-0: Nors for seisic resistance NPP designing. (in Russian) 8. NP-043-03: Requireents for construction and safety operating of hoisting cranes for NPPs. (in Russian) 9. БДС EN 300-3-3:007: Cranes. General design. Part 3-3: Liit states and safety check of travelling wheels and other parts in contact with rails. 00 (in Bulgarian) 0. Kolarov, I., Prodanov, M., Karaivanov, P.: Hoisting achines designing. Ed. Technica, Sofia, Bulgaria, 986 (in Bulgarian). Ivanov, A.: Basis of seisic echanic. Ed. "ARTE NOVO", Sofia, Bulgaria, 003 (in Bulgarian). Tonchev, Y.: MATLAB - Transforations, Calculations, Visualisation. Part. Ed. "Technica", Sofia, Bulgaria, 006 (in Bulgarian) 3. Pisarev, A., Paraskov, C., Bachvarov, С.: Course in theoretical echanic. Part II: Dynaic. Ed. Technica, Sofia, 988 (in Bulgarian) 4. Radlov, K.: Coon syste "girder crane- building" bearing structure experiental research in case of earthquake. Mechanic of achines, TU Varna, 85, year XVIII, book, 00 (in Bulgarian), ISSN 086-977 5. RI/D-30-3: Guide for seisic re-estiation and designing of equipents operating in NPPs. 00 (in Bulgarian) Received in June 0 67