Regulation of guyed mast stresses

Abstract

Development of mobile communications and their networks in Lithuania produced an essential influence on high telecommunications structures design activities. In its turn it has stimulates their research and innovations of such structural systems. One of the most efficient systems of telecommunication structures is guyed mast. It should be indicated that the behaviour of prestressed structures systems has been thoroughly examined in many investigations. But recently the increase of economical efficiency of guyed masts becomes undoubtedly actual. The development of such structures in many cases is directed to the selection in the mast elements scheme and their cross-sections. It should be underlined that geometric and physical parameters have a decisive moment on prestressed structures. An exact parameters choice allows to obtain in the mast rational distribution of bending moments, predetermining a project solution closely connected with the mass criteria. The diagram of bending moment’s distribution in guyed mast is considered rational when negative and positive moment values are absolutely equal. In the present research, analytical expressions for rational bending moments determining are presented. Above mentioned non-linear expressions estimate an influence of axial force for the bending moments. When solving the task of rational bending moments in a guyed mast, it is necessary to select suitable (i.e. rational) guyed mast bending spans. In the article is described the calculations of the guys fastening altitudes when guy level number is known. It should be noted that it is necessary to use the way of gradual approximation. The sequence of calculations is interrupted, when the sum of guyed mast spans corresponds to the exactness selected. The decisive part in mast behaviour is played by guys. The main parameters of them are pretension and cross-section area. In the article the equations are presented for determining the above-mentioned parameters. It should be stressed that after making uniform stresses of the guys on the different level of each of them it is possible to minimise some steel quantities. In the article a numerical experiment is presented for determining the technical-economical effectiveness of stress regulation. For the analysis, a standard three edged lattice guyed mast with cross-section parameters was selected in a usual way. By the suggested beam composition methods the design of the shaft was performed, and the results obtained were compared to a standard guyed mast shaft. For determining the stresses of beam elements Robot Millennium software was used; its reliability was demonstrated by earlier investigations. The results of numerical experiment that the maximal bending moment of composed guyed mast is three times less than that of a standard maximal one. An applied regulation of stresses has allowed to lessen much of the cross-section of guy rope. By applying the suggested methods it was possible to diminish the steel expenditure of shaft by more than 30%.

Article in Lithuanian.

Plieninių stiebų įrąžų reguliavimas

Santrauka. Straipsnyje aptariama plieninių stiebų projektavimo metodika, paremta įrąžų reguliavimu. Pateikiamos analitinės išraiškos racionaliems lenkiamiesiems momentams bet kuriame kamieno tarpsnyje nustatyti. Šiose netiesinėse išraiškose vertinama ašinės jėgos, veikiančios kamiene, įtaka racionalių lenkiamųjų momentų reikšmėms. Straipsnyje aptariamas ir atotampų tvirtinimo prie kamieno racionalių koordinačių (altitudžių) apskaičiavimas, taip pat ir pačių atotampų išankstinio įtempimo bei jų skerspjūvio ploto nustatymas. Atliktas skaitinis tipinio tribriaunio spragotinio plieninio stiebo eksperimentas parodė, kad siūloma įrąžų reguliavimo metodika leido ne tik sumažinti atotampų skerspjūvio plotą, bet ir bendrąsias sąnaudas.

Reikšminiai žodžiai: plieninis stiebas, racionalūs lenkiamieji momentai, įrąžų reguliavimas, geometriniai ir fizikiniai parametrai, elgsenos modeliavimas.

First Published Online: 16 May 2013

Keyword : guyed mast, rational bending moments, stress regulation, geometric and physical parameters, behaviour modelling