Study On Critical Preload Of Prestressed Composite Structures Of Large Hydraulic Press

Apart from the structural stiffness and strength, integrity is a crucial issue of theprestressed composite frame and prestressed composite beams on the body design ofheavy hydraulic press, since integrity is closely related to the fatigue life and thegeometric precision of hydraulic press body under loading conditions. Preload is the mainmeasure to guarantee the integrity of composite structures. However, the correspondingpreload parameter calculation of hydraulic press frame is still mired in the preloadcalculation model of the1940s, which is based on simple tension and compressiondeformation of column and rod. The calculation model ignores the bending deformation ofthe beams and columns，which results in large differences with engineering practice. Theresearch work on preload calculation model of composite beam is still in its infancy.Therefore, it’s of important significance to establish preload model to ensure integrity ofthe prestressed composite structures.In the present article, the research objects were respectively prestressed compositeframe and prestressed composite beam of hydraulic press. With the method of simulation,systematically analyzed were influence factors, such as rigidity factor of rod and column,bending factor of upper beam and column, on integrity of prestressed composite frame,and influence factors, such as span-depth ratio, rod position factor, relative width of beam,load ranges factor, support ranges factor, load, on integrity of prestressed composite beam.Revealed was the influence law of each factor on slotted factor and critical preload ofprestressed composite structures.For the prestressed composite frame, based on plane frame deformation, the criticalcriterion was proposed that the compressive stress was equal to zero at the inner edge ofthe contact surface between the upright column and upper beam under loading conditions.Then established and verified respectively were the critical preload calculation formulas ofthe prestressed composite frame under centric loads and eccentric loads, consideringbending deformation of upright column and upper beam.For the prestressed composite beam, the method of equivalent-beam-length wasderived to solve the problem, that the calculation results of Airy stress function can not be a true reflection of stress distribution in the direction of x in cross section of compositebeam. The calculation formula of equivalent-beam-length factor was derived by leastsquares fit, which can improve the calculation accuracy of the stress in the direction of xin the middle section of composite beam. The critical preload calculation model of theprestressed composite beam was established combined with the critical criterion, that thecompressive stress was equal to zero at the lower edge of the contact surface betweencomposite beams.Experimental apparatus were designed and prepared for prestressed composite frameand prestressed composite beam of hydraulic press in the present article. Experimentaltests were carried out on critical preload of the prestressed composite frame underdifferent loads and the prestressed composite beam under different loads and span-depthratios. The maximum error, the minimum error and the average error between calculationand experimental results of critical preload on the prestressed composite frame undercentric loads were4.5%,1.8%and2.9%. The maximum error, the minimum error and theaverage error between calculation and experimental results of critical preload on theprestressed composite frame under eccentric loads were12.6%,10.4%and11.5%. Themaximum error, the minimum error and the average error between calculation andexperimental results of critical preload on the prestressed composite beam were9.4%,5.4%and7.7%. Comparative data showed that the calculated results agree well with theexperimental results. Compared with the traditional method, the calculation accuracy hasbeen improved greatly.