Study On The Static And Dynamic Mechanisms Of CFRP Cable Suspended Building Structures

We forecast that CFRP is the structural material which plays a very important role in civil engineering in the 21st century. Suspended building structures, in which CFRP cable is used as main reinforcement, will not only reduce self-weight and increase effective load-carrying capacity of themselves, but also completely avoid corrosion and fatigue of the cables and optimize the structural capability and then reduce the maintenance expenditure, so the structures will benefit much from the general perfomance and whole-life-cycle economics.CFRP cable suspended building structures (CSBSs) conforming to the natural principle of transferring loads comprise structural art of nature and consist of profound architectural artistry and structural esthetics, which lead to harmonic unification of structure and architecture, function and art, and strength and esthetics.CFRP CSBSs possess the attributes of new material and new structural system. The mechanical performance and computational methods of this new structure have been studied, which are summarized as follows.Firstly, based upon the natural and social attributes, the general situation of types, application, development and distinguished merits of suspended structures and CFRP cables or tendons are introduced. The concepts of structural form and control of CFRP CSBSs have been established. After reviewing the structural control methods, the idea of suspended control system is brought forward. Additionally, the development foreground of CFRP CSBSs in China is forecast.Secondly, the design principles, mechanical model and some hypotheses are brought up. In CFRP cable core-tube suspended building structure, the core tube is the vertical and horizontal main stem, and also the most important load-carrying structure. The mechanical behaviors of the hexagonal core tube with holes in all the six sides are analyzed with the continuous method, and the analysis results are compared to that analyzed with finite element method, which proves that the continuous method is effective, and much simpler and more timesaving than finite element method, and capable of being used in practical design.Thirdly, the laws of energy transferring and dissipation in CFRP CSBSs (i.e. Super Suspended Tuned Mass Damper, SSTMD) are expatiated on based upon the concept of Suspended Tuned Mass Damper (STMD). According to the two-degree movement equation, the frequency transfer functions of absolute acceleration and displacement are derived under the action of harmonic ground excitation, as well as the transfer function of acceleration under the action of harmonic load on the superstructure of suspended building. The influences of frequency ratio, damping ratio and suspended mass ratio on the dynamic responses of the structures are analyzed detailedly. The optimal parameters of acceleration and displacement responses are derived with Den-Hartog method. The methods of parameter optimum of CSBSs are discussed, and then theconceptions of the maximum value and reasonable value of damping ratios of secondary structures are put forward, innovatorily. Moreover, the acceleration and displacement responses are analyzed in the round by using the reasonable values of damping ratios of secondary structures. The efficiency of shock absorption of CSBSs is analyzed with the combinations of different parameters, and indicates that the CSBSs are of very stable capability of shock absorption. Furthermore, the shock absorption mechanisms of both small suspended mass ratio STMD and SSTMD are studied. The robustness of the shock-absorption capacity of CSBSs is discussed.Fourthly, the dynamic response optimization of the two-degree SSTMD is analyzed, which is under the action of white noise ground excitation, and then the variance responses of acceleration and displacement are derived. When the SSTMD is in the case of non-constraints, the analytical expressions of optimal parameters are obtained without damp of main structure, while the numerical figures of optimal acceleration and displacement parameters are offered with damp of main structure. The dynamic responses of SSTMD in the cases of single or double constraints are discussed with numeric method. When the SSTMD is optimized in the case of double constraints, the stability of dynamic displacement response of main structure could be guaranteed radically and the iteration divergence could be avoided. And, withal, the double-constraint dynamic responses are of very nice robustness and efficiency. To choose the optimal dynamic parameters, four types of objective functions and four types of optimal parameters are summarized, innovatorily, and then some useful conclusions are drawn. Adopting the parameters of optimal acceleration response of main structure will lead to very good dynamic behaviors of main and secondary structures, including acceleration and displacement responses; adopting the parameters of optimal displacement response of main structure will lead to excellent acceleration behaviors of main and secondary structures and excellent displacement behavior of main structure, but the displacement behaviors of secondary structures are not so good.Fifthly, the mechanical model and movement equation of multi-section suspended building structure (MSBS) are constructed. Then the corresponding response functions and optimization method of the Multiple Objective Functions (MOFs) are determined. The method of parameter optimization of shock-absorption MSBS is innovatorily expatiated on with the instance of a three-section suspended building structure. The coefficient of shock-absorption efficiency of the main structure of MSBS is defined. The displacement responses of secondary structures are remarkably correlative with the frequency ratios of themselves, but not remarkable with the other frequency ratios. Based on the analysis, with the method of MOFs, all the responses of main structure and secondary structures are limited in a very low and even level. Moreover, the results are adequately accurate with the optimal parameters of some fixed mass ratio when calculating the responses of other ratios. According to the time-history analysis of MSBS, it is clear that the optimization method of MOFs is much superior to that of the SOF. After parameter optimization, the dynamic displacement responses of the MSBS are clearly better than that of ordinary structure. On the basis of analysis and computation in frequency domain and time domain, it is proved that the optimization method of MOFs is more effective and stable than that of SOF, and with the former, the ideal shock-absorption capability of MSBS could be acquired.Sixthly, the model experiment of a core-tube suspended building structure finished by Dr. Liu Yuxin is introduced. According to the experiment, the excellent dynamic capability of the suspended building structure is testified. And that in some given condition, the shock-absorption capability of the structure will increase with the adjacent stiffness between the main and thesecondary structures decreasing is proved.Seventhly, construction measures are offered to the main structure and the self-adjustment connections between main and secondary structures of CFRP CSBS, respectively. The vibration stiffness of secondary structures is discussed and the more accurate stiffness formula is derived. The couple relationship of P-? effect on core tube and inclined action of box basement is analyzed. The rigid-body movement function of secondary structures is constructed and solved analytically, and then the formula of the maximum displacement is obtained. Based on the current Chinese Code, the nominal height-to-width ratio of hexagonal core-tube suspended building structure under different seismic fortification intensities are listed in the table.Finally, the forms of the CFRP cable suspended transferring beams and hangers are introduced, as well as the elastic design method of the beams. Because the prestresssing technique and the high-strength and high-performance CFRP cable are used in the transferring beams, the deflection of the beam may be limited to a very low level, even to zero, and the relative displacement between suspended secondary structures and main structure is also very little, from which the performances of the suspended building structure will benefit very much. Additionally, with the guidance of Prof. Lu Zhitao, who is the author's supervisor, the colleagues of the research team have developed and manufactured the CFRP cable anchorages. On the basis of our efforts, the 1st CFRP cable-stayed bridge in China has been designed and constructed. Furthermore, the author has proposed to design and build a CFRP cable suspended building structure, which is sustained by his supervisor.