Specifics of determining the tension forces of the cable-stayed bridge elements

Abstract

Objective: to improve the method of determining the force in the cable stays by frequencies of natural transverse oscillations. Methods: synthesis and analysis of theoretical and experimental data, experimental methods for studying the structures. Results: in the paper, the problems of determining the tension forces of the cable stays by the frequencies of their natural oscillations are considered taking into account various factors (the design of anchor fastenings, the angle of inclination and sagging of the cable stay, the change of temperature). The estimation of possible errors in calculations is given. The degree of coincidence of the actual and design stress-strain state of the cable stays depends on the correctness of accounting the influence of the factors considered. The effect of the temperature change and the anchor fastening structure on the frequency of the natural oscillations of the cable stays has been experimentally tested. The recommendations on the determination of the forces in the cable stays by dynamic parameters are given. A method for controlling the tension forces of the cable stays and specialized software “Vant” (“Cable”) for automation of the measurement process are developed. The method has been tested on several bridge structures that have cable-stayed elements. Practical significance: the ability to use the developed method for controlling the tension forces of cable-stayed elements during the operation of artificial structures.

Specifics of determining the tension forces of the cable-stayed bridge elements

“…The method for determining the tension force of the cable-stayed element [16] was developed on the basis of the results of control of the forces in cable-stayed suspensions of the Bugrinsky Bridge across the river Ob in Novosibirsk in the process of construction and the initial period of operation [10,15]. Approbation and verification of the method [16] was carried out in the process of monitoring the forces in the cable stays of the bridge across the river Irtysh on the bypass of Pavlodar [14,15], Vinogradovsky Bridge across the Tatyshev channel in Krasnoyarsk [17], Ugra Bridge across the river Ob near the city of Surgut [13].…”

“…To measure the response of structures to external influences, sensitive vibration sensors-accelerometers (measuring range from -610 • 10 -3 to + 610 • 10 -3 m/s 2 , sampling frequency -100 Hz) and strain gauges (measuring range from -1000 • 10 -9 to + 1000 • 10 -9 m, the inaccuracy of deformation measurements is ± 1.5%) were used. The vibration records were processed using specialized software "Tensor MS" [19] and "Vant" ("Cable stay") [20], in which the algorithm for fast Fourier transform with Welch window transformation is implemented.…”

“…According to our own research and the results given in [2], the magnitude of the abrupt temperature change can reach up to 15 °C. The effect of the change in the force in the cable stay with the temperature changes ΔT and with allowance for Hooke's law can be obtained from the formula [10]…”

“…When measuring the natural oscillations of the cable stays, a large number of forms can appear (for example, when determining the frequency of natural oscillations in the cable stays on a road bridge across the Ob River in the city of Surgut, up to 20 forms of oscillations were observed [3,13], at the Bugrinsky Bridge across the Ob River in Novosibirsk -up to 15 forms. [10] This causes the shortcomings of most methods for determining frequencies -to record all forms of oscillations, it is necessary to install a large number of accelerometer sensors along the length of the cable stay and use special equipment (for example, portable telescopic tower) [1]; special load cells for determining the tension forces of the cable stays are quite expensive, and, besides this, the rearrangement of the equipment is a complex and time-consuming process. However, all these shortcomings can be mitigated if a sensitive sensor (for example, vibration sensoraccelerometer "Tensor MS") is set in one of the fixing points, where all forms of oscillations of the cable stay occur and are recorded.…”

“…A large number of cable-stayed elements themselves and their natural oscillation frequencies require considerable time in the processing of measurement results in the nonautomatic mode. To automate these processes, specialized software "Vant" ("Cable stay") was developed [20]. The "Vant" program implements specially designed filters for the forced oscillation frequencies of the cable stays, algorithms for determining the frequencies of the natural oscillations of the cable stay and calculating the characteristics of damping and dissipation of energy, etc.…”