Engineering Structures and Technologies (Dec 2009)
Design and analysis of combined plane steel guyed tower-mast
Abstract
One of the most effective and widely used high-rise telecommunication structures are steel towers and guyed masts. The behaviour, analysis and application fields are exhaustively discussed in a number of scientific publications. The main advantages of tower structures are low building area, however, from the point of view of steel consumptions, such structures are not effective enough. For technical-economic efficiency not only the rational types of cross sections for typical mast elements are selected, but also various combined structural systems are developed and implemented. Flat tower-masts are also known. They are combined from a single plain truss supported out of its plane by guys. In this case, such mixed system is able to carry acting loads and actions in one direction like a tower and in other direction – like a mast. From a technicaleconomic point of view, such system stands in the intermediate position between the guyed mast and the tower. The major weakness of such framework is relatively great depth and the cross sectional area of the chords of the tower truss which is caused by the relatively high values of the bending moment in the chord acting in the plane of guys and the large buckling length of the chord out of truss plane. It must be stressed that wind action on the investigated structure directly depends on the dimensions of the chord cross section. This paper deals with the new combined plain tower-mast structure the chords of which out of plane are stiffened by and inserted between the guys connecting joints and the double-sided strut members. These members are pre-stressed to avoid compression induced by transverse loading. The analysis of the behavior of a separate strut system under transversal loading is performed and analytical expressions for determining internal forces and displacements in its members with and without pre-stressing are provided. The minimum values of the required pre-stressing in ties of the strut system are described. It is proved that a proper choice of the parameters of structural components gives a possibility of obtaining a favorable distribution of bending moments in the chord. On the basis of numerical experiments, a comparison between the results defined analytically and ones determined by the means of the Autodesk Robot Structural Analysis program is performed. The accuracy of the proposed analytical method is discussed. For defining the behaviour peculiarities of the new combined structural system and for estimating its technical-economic efficiency, the numerical experiment by the means of FEM program (Autodesk Robot Structural Analysis) was carried out. Analysis was performed using 98 meter high ordinary and new guyed tower-mast structures with guys fixed at four levels. The member sections of the analyzed structures designed according to the values of the defined acting internal forces are presented. It is estimated that using strut members helps in considerably reducing (about 4,8 times) the maximum values of bending moments in the chords of tower truss. It was estimated that depth between the chords in a new combined system was 2 times lesser than that in the ordinary tower – mast system. It is shown that in case of the same cross section and value of the pre-stressing force, the value of the vertical reaction of the new strutted tower-mast system on foundation was 1,65 time lesser than that in the ordinary system. Conclusions and recommendations are provided. Kombinuoto plieninio plokščiojo bokšto-stiebo konstravimas ir skaičiavimas Santrauka Straipsnyje aptariama nauja kombinuota plokščiojo bokšto-stiebo konstrukcijų sistema, kurios juostos sustandintos iš bokšto santvaros plokštumos dvipusiais paspyriniais iš anksto įtemptais elementais, išdėstytais tarp atotampų tvirtinimo mazgų. Analizuojama atskiros paspyrinės sistemos dalies elgsena veikiant skersinei apkrovai, pateikiama inžinerinė metodika jos elementų įrąžoms ir poslinkiams apskaičiuoti. Atlikto skaitinio eksperimento pagrindu nustatytas parengtos inžinerinės skaičiavimo metodikos tikslumas. Pasitelkus baigtinių elementų programą aptarti naujos kombinuotos konstrukcinės sistemos elgsenos ypatumai. Parodyta, kad paspyrinių elementų naudojimas leidžia gerokai sumažinti maksimalius lenkiamuosius momentus bokšto-stiebo santvaros juostose. Parodyta, kad siūloma nauja kombinuota paspyrinė bokšto-stiebo sistema pagal masės kriterijų yra kur kas efektyvesnė už analogišką tradicinę bokšto-stiebo sistemą. First Published Online: 16 May 2013 Reikšminiai žodžiai: plieninis bokštas-stiebas, paspyrinė sistema, išankstinis įtempimas, elgsenos modeliavimas
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