Structural Performance During Prestressing And Theory On Servo Construction Process Of Beam String Structure

Beam String Structure (BSS), composed of cable, rigid beam and struts, obtains its overall rigidity by prestressing the cable. With light self-weight, strong overall rigidity upon completion, stable configuration and extensive shape applicability, BSS has been widely used in many large-span space structures. As a non-rigidity structure, the geometric configuration and structural behavior of BSS are highly related to the process of construction. To build a more economical and rational BSS, comprehensive understanding of the structural performance during prestressing is essential, in addition to the advanced construction technology required.In this dissertation, research work has been focused on structural behavior during prestressing and servo construction process of BSS. Utilizing both theoretical analysis and experimental study, numerical method for structural analysis and the structural behavior during prestressing were addressed. Parametric analysis during prestressing and simulation of the realization of the servo construction process were also performed.Firstly, according to the mechanical characteristics of BSS members, C. Oran column-beam element was chosen for rigid beam and struts and catenary element for the cables. Pre-tension of the cable was simulated by changing its original length. Nonlinear analysis algorithm, which is one of basic parts of the numerical algorithm for prestressing analysis, is proposed and validated by solving a benchmark problem.Secondly, based on data collected from a number of practical projects, construction parameters of BSS including construction sequence, prestressing method, temporary supports and times of prestressing were recommended. Numerical method taking the displacement of the reference point as the prestressing target with also consideration of construction parameters has been proposed for analyzing the prestressing process of BSS. Algorithm suitable for BSS form finding was also developed based on the proposed analytical method.Experimental study has been carried out to investigate comprehensively thebehavior of BSS during prestressing. Based on the theory of orthogonal test, twelve BSS specimens were designed and tested. Experimental results show that the structural performance of BSS during prestressing can be described in terms of the deflection, inner forces, configuration and stability of structure: (1) the critical pre-tension force at the completion of prestressing, i.e., the structure getting its overall rigidity, is about k/0.125;(2) when the displacement caused by the pre-tension force is large enough, the relationship between the pre-tension force and structural displacement becomes non-linear;(3) the stresses resulted in members during prestressing is different from that in service stage, which should be considered in structural design;(4) the development of the BSS configuration under prestressing can be described as 'the span shortened, the whole bended upward and the struts inclined';(5) the whole structure moves out of plane when BSS loses its stability, and the cable will greatly increase the stability of BSS by preventing the rigid beam from turning over. Sensitivity of various parameters on structural performance of BSS during prestressing has been obtained from the analysis of orthogonal test. However, further numerical analysis is required to complement the parametric analysis of BSS. It is shown from error analysis that the gap between the nut and the anchor may enlarge structural displacement while loading;the friction of the hole may induce different tension force in the cable and the pump;and the friction of the supports will decrease the structure displacement while the same pre-tension force is added.Parametric analysis has been performed next using the numerical method studied above. The relation between the structural behavior of BSS during prestressing and the parameters of sectional properties, geometric configuration and construction has been found to be: (1) the critical pre-tension depends mainly on the rise and self-weight;(2) the prestressing rigidity is affected significantly by the rigidity ratio of beam to cable, the area ratio of beam to cable, the ratio of rise to span, the ratio of sag to height and the temporary supports;(3) the member force at the completion of prestressing is affected mainly by the geometric configuration;(4) both the sectional properties and the geometric configuration parameters have significant influence to the horizontal displacement of the support at the completion of prestressing;(5) construction parameters may affect the member forces and the structuralconfiguration. Based on the result of parametric analysis during prestressing, reasonable range of parameters of BSS was then recommended, and the formulas for calculating member forces of BSS during prestressing have also been deduced.Finally, a new concept of servo construction of BSS is proposed by analogy with electro hydraulic servo loading system. Parameter identification and construction control are critical to realize a servo construction of BSS. A dynamic Back Propagation artificial network was adopted to identify structural parameters. A scientific construction control method of BSS based on systematic structural analysis, that is, modify prestressing target -*? prefigure structural performance — calculate reference pre-tension -*? adjust construction scheme, is proposed. Parameters identification, construction control and construction operation are integrated to form a servo construction process of BSS, whose superiority is proved when compared with the ordinary construction method.