Research On The Free Suspension Arrangement Line Of Prestressed Tendons And Its Effect On Concrete Slab

At present,quadratic parabola is always uesd as the curve of prestressing tendons in the design of prestressing concrete slabs.But in order to save time,the builders always control only two highest points and one lowest point to allow the prestressing tendons to hang freely in the actual construction of concrete slabs.In this paper,the influence of the linear difference on the performance of concrete slabs is studied.Firstly,the linear theory formulas of prestressing tendons considering bending stiffness are analyzed,and the expression of free-hanging curve in practical construction is deduced by numerical method.The expression is verified by experiments,and the calculation formulas with better fitting effect with the actual line shape of prestressing tendons are obtained.Secondly,the equivalent loads of concrete slabs subjected to two kinds of prestressing tendons are calculated by using load balance method and direct internal load method.The results are compared and the effect of the two kinds of alignments on concrete slabs is preliminarily judged.Then,the finite element software is used to analysis the two plates with the same spacing and quantity of prestressing tendons.The two plates have different prestressing cables,one with the quadratic parabola used in the design and the other with the free-hanging curve used in the actual construction.The results show that the two alignments have little influence on the ultimate bearing capacity of the plate.That is to say,it is feasible to arrange free-hanging curved prestressing tendons instead of quadratic parabolic prestressing tendons in concrete slabs in the case of plate thickness and prestressing girder heights in the paper.Finally,the influence trend of concrete strength grade,effective tension stress,ratio of rise to span of prestressing tendons and boundary conditions of plates on ultimate bearing capacity of prestressing concrete slabs under two kinds of prestressing tendons alignment is studied.The results show that the two kinds of alignments have little influence on the performance of concrete slabs.The reason is that the height of prestressing tendons in slabs is too small relative to the span,and the vertical variation of prestressing tendons is almost negligible.In practical engineering,the ratio of rise to span of prestressing concrete slabs is smaller,so it can be considered that it is feasible to arrange free-hanging curved prestressing tendons instead of quadratic parabolic prestressing tendons in concrete slabs.