Initial tension forces in guys of steel industrial chimneys at adjustment phase

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American Journal of Environmental Engineering and Science 04; (5): 04-09 Published online November 30, 04 (http://www.openscienceonline.

1 American Journal of Environmental Engineering and Science 04; (5): Published online November 30, 04 ( Initial tension forces in guys of steel industrial chimneys at adjustment phase Bernard Wichtowski, Janusz Hołowaty Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology Szczecin, Szczecin, Poland address (J. Hołowaty) To cite this article Bernard Wichtowski, Janusz Hołowaty. Initial Tension Forces in Guys of Steel Industrial Chimneys at Adjustment Phase. American Journal of Environmental Engineering and Science. Vol., No. 5, 04, pp Abstract The free standing and guyed industrial chimneys are the most typical steel chimney structures. Structural system of guyed chimneys is very similar to masts, in particular, to tube masts. Sometimes steel chimneys with too loose guys are in risk to collapse. In the paper, the presented results relate to initial tension force adjustments in 0 steel chimneys. The chimneys range is from 5,0 to 60,5 m of height. Two ways of determining the initial tension forces are described. The measured values of initial tension forces are presented. Analyses of performance in service conditions are also carried out. All the presented chimneys required adjustments because they had deviations from verticality and their guys were hanging loosely. The initial forces in guys at adjustment stages were calibrated to receive adequate horizontal rigidity of the chimney shaft in order to avoid high normal force in the shaft and to prevent guy vibration. The method of initial tension force regulation in chimney guys can be adopted for the assessments and adjustments of technical condition in similar structures. Keywords Chimneys, Guys, Tension Forces, Adjustment Phase. Introduction The most popular types of steel chimneys are free-standing chimneys and those with guys. As to the structural scheme and forms of structure, a guyed chimney corresponds, to a significant extent, to calculation requirements defined for masts, in particular, with reference to masts with a tabular shaft [-3]. Sometimes guys insufficiently tensioned are the reason of steel chimney collapses. Usually initial tension forces in guyed chimneys are selected so as to: obtain a proper initial horizontal rigidity of the shaft elastic support, avoid of too large axial forces in the shaft, resulted from vertical components of the tension forces, avoid vibration of guys. In the paper, based on the example of the structure of ten guyed steel chimneys in which adjustments were made, the results of measurement of initial tension values in guy ropes are presented. The analyses of the initial guys tension forces may be useful when evaluating the technical condition of similar structures and at their adjustment [4, 5].. Characteristics of Chimneys and Guy Ropes Examined General construction data of the discussed ten steel chimneys with guys are presented in Fig. and in Table. The chimneys have single flue pipes without thermal insulation of differentiated construction and height, ranging from 5,0 to 60,5 m. In seven cases, they are rigidly attached constructions on a foundation with one level of guys, however, three chimneys with two levels of guys and the height of 46, and 4,0 m ( b, d and d chimneys) based in an articulated way on brick pedestals ( b ), 7, m and 6,0 m high reinforced concrete pedestals ( d and d ). All chimneys have single-flue pipe welded of structural carbon steels St3SY and St3S of diameters ranging from 70 to 50 mm. Former Polish steel grades (St3SY and St3S) are similar to European steel grade S35.

2 05 Bernard Wichtowski and Janusz Hołowaty: Initial Tension Forces in Guys of Steel Industrial Chimneys at Adjustment Phase Chimneys were used in a continued way or in season. Each of them served an independent boiler, using fine coal and the boilers were not operating simultaneously but in turns. This had it that each chimney was turned off and cooled in turns. Chimneys marked with letter and number were of identical structure. Differentiated types of ropes were used for guys in the discussed chimneys. They are steel ropes from tinned wire of identical diameter of six strands with double or three layer construction of strands T6 9 ( b, g, g ) and T6 37 ( a, c ) with organic chord A and ropes 36+A ( d, d, e, f, h ). The parameters of these ropes, according to the Polish standards are given in Table. In all chimneys, three guys were applied on every level, placed every 0. The angles of inclination from the horizontal level of the guy chords υ were differentiated and fluctuated from 3,95 to 77,0 (Fig. ). At the bottom, the guys were attached in reinforced concrete anchorage blocks through bolts (Fig. ) put into the Table. Technical data of the chimney structures ropes. Only in the ropes of a chimney near the anchorage block were the tensioning devices assembled which were adjusted to the connection of a dynamometer. In b, d and d chimneys, the guys of two levels were anchored in one block (Fig. ). In the analyzed ten chimneys, the overhanging sag of guys ropes was clearly visible and in some chimneys, deflection of the shaft axis from the vertical (Fig. 3). For example, the deflection of d and d chimneys tops amounted to 50 and 58 mm, or else was 4,4 and 4,5 times larger than admitted standard assembling deflection δ = H/300, H constitutes the height of the chimney over the foundation. The occurring rope sag was the proof of a too small value of initial tension forces in the guys. This was confirmed by executed field measurements. For example, in the ropes of c chimney, the values of initial tension forces amounted to 5,83 and 4, kn. This means that the stresses in ropes had only the values of 5,5; 5,5 and 6,6 MPa. Chimney Height Level of guys Shaft parameters Length of rope chord [m] (Fig. ) [m] [m] Diameter[mm] Plate thickness [mm] a 60,50 47, ,9 6,3 56,35 b 46,0 38,50;, , 9,8 45,67; 5,97 c 45,00 35, ,8 9,6 43,0 d, d 4,00 36,00; 6, , 9,4; 9,0 9,4 39,3 55,07; 30,4 49,3 e 40,00 5,0 90 9, 0,0 35,8; 35,60; 8,55 ) f 3,00, ,7 7,4,86; 5,59; 30,54 g, g 30,00 9, ,,8 4,3; 7,0; 5,60 ) 5,0, 3,85; 4,00; 4,4 h 5,00 6,30 80; 50 8,7 9,; 7,4 7,8,50 ) guys attached on the roof of a boiler house Fig.. General construction data for ten steel chimneys

3 American Journal of Environmental Engineering and Science 04; (5): Table. Technical parameters of guy ropes Chimney (Fig. ) Height [m] Guy ropes Type φ [mm] Am [mm] Weight [kg] Rm [MPa] Inclination angle υ [o] ,50 T6 37+A 37+A 8 94, υ = 57,45 46,0 T6 9+A 9+A 0 5, υg =6,05 c 45,00 T6 37+A 37+A 5 9,8 600 υ = 54,46 d 4, ,6 600 υg =56,9 4,4 υd =47,85 3,6 d 4, ,6 600 υg =66,3 40,8 υd =58,7 3,95 e 40,00 96, υ = 45,74 4,74 45,74 f 3,00 96, υ = 77,0 46,90 77,0 g 30,00 T6 9+A 9+A 4 7 0, υ = 54,09 35,38 54,09 g 30,00 T6 9+A 9+A 4 7 0, υ = 55,69 54,68 55,69 h 5, ,6 600 υ = 46,4 Number of levels a b υd =45,78 Table 3. Values of introduced forces in guys Level (Fig. ) Height [m] Tension force of rope [kn] Chimney guy I guy II guy III average value Stress [MPa] a 47,5 38,5,9 35,0 36,7 3,6 4,4,0 56,7 3,6 4,4 30, 59,6 3,6 4,4 43,0 5,0 (50,34) 3,6 4,4 3,4 73,5 56,3 6,3 37, 36,0 6,0 36,0 6,0 4,3 8,0 5,5 5, 0,0 7,0 6,8 7,6 3, 7,4 0,9,9 9, 0,8 7,7 8,,4,4 04, 07,0 e 5, 6,4 0,6,8 9,9 0,7 f,3 4,7 0, 3,3,,7 g 9,7 7,8 9,3 0,9 9,3 8,3 g 9,7 8,9,, 0,7 47,6 h 6,3 8,9 9,4 0,5 9,6 (9,47) 5,3 b c d d a) b) Fig.. Guy anchorage systems: a) chimney a, b) chimney b, c) chimney c c)

4 07 Bernard Wichtowski and Janusz Hołowaty: Initial Tension Forces in Guys of Steel Industrial Chimneys at Adjustment Phase a) b) Fig. 3. Guy ropes of chimney b : a) before adjustment, b) after tension adjustmentt 3. Initial Tension Forces of Ropes Guys in the place of connection with chimney shaft make up elastic supports in the horizontal direction. The flexibility of such a support depends upon the diameter, length, inclination angle of the guy, its modulus of elasticity, on the number of guys at a given level and, first of all, the initial rope tension. The forces of the initial tension of guys are selected correspondingly to the required horizontal rigidity (kn/m) of the elastic support whose calculation has been given in [-3, 6]. The range of initial stress in guy ropes of steel chimneys may be assumed in values recommended for ropes of masts with a pipe shaft, i.e. ranging from 00 to 350 MPa. The values in Table 3 relate to forces and initial stresses which were introduced in the ropes during shaft adjustment of the analysed chimneys. In all 39 guys of ten chimneys, the introduced average tension of ropes of a given level, when they are attached, causes in them a stress of values larger than the minimum value recommended in the literature σ o = 00 MPa. Corresponding values of forces in guys were introduced by rope tension caused by the shortening of tensioning bolts with the anchorage blocks. For example, in c chimney, the bolt was shortened by a value of 50, 80 and a 000 mm. Following a very small range of bolts regulation in seven chimneys, at the same time, there was a necessity to shorten the rope by shifting the foundation thimbles. 4. Analysis of Initial Tension Forces In seven chimneys, the value of initial tension forces was determined by the dynamic method by counting the number of vibration amplitudes in a defined time. By a sharp jerking of the rope near its connection with anchoring, a vertical wave was caused and the amplitude of vibrations counted (full deflection) N in time t = 0 or 5 s. The rope initial tension at a half of its spread is calculated according to the Eq. () obtained from the transformation of the formula, defining the circular frequency of vibrations [5, 7-9]: Gl N F G = t F G rope tension in kn, G total rope weight in kn, l rope length in m, N number of amplitudes in time t, t time of measuring N vibration amplitudes in s. The initial tension force determined according to the Eq. () is a force in the centre of guy spread and its value at FA anchor is determined according to the Eq. (): F A = FG G sin υ + υ is the declination angle from the horizontal plane of guy chord. The difference in the value of forces according to the Eq. () and () is insignificant and depends mainly on the weight of the rope. For example, for guys of a and h chimney, this difference amounts to,3 and 0,7% (F G and F A forces in Table 3, col. 7). The initial tension forces determined in Table 3 relate to guys of a cold chimney and are referred to the standard assembling temperature T 0 = +0 C. For the adjustment of the force in another temperature, its correction F G is introduced, which takes into account the current temperature T a, from the following dependence: G T cosυ α T coefficient of linear thermal expansion, is equal 0-6 / C, T difference between the current and assembling temperature, is equal T a T 0, E 0 = 5 (45) elastic modulus for ropes with non-metal core (metal core) in GPa, A m metallic area of guy wires in cm. G 0 m () () F = α T cos υ E A (3)

5 American Journal of Environmental Engineering and Science 04; (5): In three chimneys d, d and e, the guy initial tension was adjusted by a direct method of measurement, related to the value of forces with the use of the dynamometer connected parallel into the rope. The measurement of forces was carried out with dynamometers of bow type of 30 kn range. The dynamometers were assembled in special lock-tension member devices, specially prepared for this purpose. In chimneys d and d these devices were assembled into the ropes of a given fixing level only for the time of measurement (Fig. 4a), and in e chimney they were installed permanently in guy ropes (Fig. 4b). The guy tension of a given level took place at the same time in a continued manner with a permanent land survey control of chimney shaft tilt. The permanent fixing of measuring devices into e chimney rope allowed to conduct the measurement of real forces occurring in various operating conditions. Such an analyses was conducted for a chimney out of operation (cold) and in operation (warm) at external temperatures T ext = +9 and 4 C [8, 9]. The measured values of operating forces ranged from to 9% of the value of initial tension (on average,5% at T ext = +9 C and 3,5% at T ext = 4 C). Theoretically, the operating forces in guys are determined from the following dependence: Ta hp sin υ Fe = + Tinit l αt E0 A l (4) m F e difference in the value of forces in guys at cold and warm chimney, T a change in the temperature of chimney shell (measured or calculated) in relation to the temperature at initial tension, is equal T a T init t, T init change in the temperature of guys in relation to the initial tension temperature, is equal T a T ext, h p length of a working section of chimney shaft (distance between the top of inlet and the level guys are fixed). The equation (4) was used for the determination of initial tension forces in b chimney guys. The adjustment of forces in ropes was carried at T ext = +3 C and measured average temperatures of the shell for the individual sections under the guys: h = 4,8 m T init = 60 C i h = 3,4 m T init = 45 C (compare Fig. ). a) b) Fig. 4. Guy sections close to the foundation with measuring device: a) chimney d and d, b) chimney e 5. Conclusions All chimneys required an adjustment of shafts with the simultaneous adjustment of rope initial tension to the standard value because of significant deflection from the vertical and a significant sag of ropes. As results from the analyses of the guys initial tension in section 4, it is not always necessary to determine the tension, according to the Eq. (). This note relates in particular to guys of a small weight. A significant reduction in stresses found out in chimney guys causes an increase in the natural period and in the coefficient of wind operating and in consequence an increase in the value of bending moments [0]. The assumption of the guys initial tension causing stresses of a value σ >00 MPa has it that in the distribution of horizontal load, the guys from the leeward side also take part. References [] The CICIND Chimney Book. Industrial Chimneys of Concrete or Steel, CICIND, Zurich, 005. [] Smith, BW, Communication Structures, Thomas Telford, London, 007.

6 09 Bernard Wichtowski and Janusz Hołowaty: Initial Tension Forces in Guys of Steel Industrial Chimneys at Adjustment Phase [3] Rykaluk, K, Steel Structures. Chimneys, Towers and Masts, OWPW, Wrocław (in Polish), 005. [4] Włodarczyk, W, On failures and desinging of steel chimneys, Inżynieria i Budownictwo, No. 0, pp (in Polish), 998. [5] Wichtowski, B, Adjustment of steel chimneys with be-level guyed, Inżynieria i Budownictwo, No. 5, pp (in Polish), 03. [6] Pałkowski, Sz, Steel Structures, Selected Problems and Design, PWN, Warszawa (in Polish), 00. [7] Instruction ER-0, Operation of towers and masts, TP SA, Warszawa (in Polish), 995. [8] Wichtowski, B, Forces in guys according thermal analysis of structural shell of a 40 m high steel chimney, Przegląd Budowlany, No. 8-9, pp (in Polish), 994. [9] Wichtowski, B, Hołowaty, J, Steel chimneys at adjustment phase. Initial tension forces in guys, EUROSTEEL 0, 6 th European Conference on Steel and Composite Structures: Research Design Construction, Budapest 0, pp [0] Kozłowski, A, Baran R, Variablility of loads on a guyed chimney in service, Inżynieria i Budownictwo, No. 0, pp (in Polish), 99.

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PES Institute of Technology Bangalore south campus, Bangalore-5460100 Department of Mechanical Engineering Faculty name : Madhu M Date: 29/06/2012 SEM : 3 rd A SEC Subject : MECHANICS OF MATERIALS Subject