基于挠度的体外与体内无粘结预应力筋应力增量

研究了体外预应力以及体内无粘结预应力梁力筋变形与跨中挠度的关系,提出了一种基于挠度的预应力筋应力增量计算的新方法.首先建立了体外预应力梁和体内无粘结预应力梁的变形相容方程,推导了用跨中挠度表达的力筋应力增量计算公式,提出了适用于体内外预应力筋应力增量的统一计算公式,能够计算正常使用和承载能力极限状态下预应力筋的应力.最后运用该公式计算了国内外大量试验梁(包括6根体外预应力梁和22根体内无粘结预应力梁),计算出应力增量与试验结果之比的均值在0.99～1.02之间,标准差为0.1左右.表明该式计算值与试验实测吻合良好,公式形式简单,能够反映结构的受力机理.

Stress increment of prestressing tendons based on deflection for unbonded or external prestressed beams

The relationship between the strain of prestressing tendons and the mid-span deflection for unbounded externally or internally PC(prestressed concrete) beams is investigated.A new method to compute the stress increment of unbonded prestrssing tendons is presented based on the deflection.Firstly,the deformation compatibility equations are established.Then a simple formula is derived from the equations which can describe the relationship between the stress increment and the deflection.Lastly,a unified method applicable to the external tendon and internal tendon is presented.The stress of tendons under the service and ultimate limit state can be computed by this method.The proposed method was used to compute many specimens tested by researchers in China and other countries,in which 28 beams(including 6 externally PC beams and 22 internally unbonded PC beams) were analyzed.It shows that the ratios of compute results to test results are all between 0.99 and 1.02,and the standard deviations less than 0.1.It is concluded that the calculated results using the proposed unified method can well agree with the test results,and more significantly it can reflect the structural mechanism clearly.