ABSTRACT

This is a proposal for a nonlinear analytical model that was developed to predict the structural response of post-tensioned beam with unbonded tendon. The structural response includes deflections under the service load before or after cracking, as well as the ultimate load capacity. A comprehensive procedure for the deflection calculation was implemented, considering the additional shear deformation and tension stiffening effect. The shear deformation calculation is based on the Timoshenko beam theory, considering the shear modulus reduction upon cracking. Furthermore, a modification of the tension stiffening model from CEB–FIP Model Code 1990 is proposed to account for the significant strain concentration in the post-yielding region. A fixed-point iterative procedure is introduced in the prediction model to compute the incremental strain in the unbonded tendon. Each iteration brings the estimated strain increase in the tendon closer to the actual value until it is reasonably accurate. Predictive accuracy of the proposed model in both load–deflection relationships and strain rates, as a function of deflections, is successfully validated against experimental beam tests and a nonlinear finite element analysis considering concrete plasticity, respectively.

摘要

这是一个非线性分析模型的提议，该模型被开发用于预测具有未粘合肌腱的后张拉梁的结构响应。结构响应包括开裂之前或之后在使用载荷下的挠度，以及极限承载能力。考虑到额外的剪切变形和拉伸硬化效应，实施了一个综合的挠度计算程序。剪切变形计算基于 Timoshenko 梁理论，考虑到开裂时的剪切模量减少。此外，建议对 CEB-FIP 模型代码 1990 中的拉伸硬化模型进行修改，以解释屈服后区域的显着应变集中。在预测模型中引入了一个定点迭代程序来计算未粘合肌腱中的增量应变。每次迭代都会使肌腱中的估计应变增加更接近实际值，直到它相当准确。所提出的模型在载荷-挠度关系和应变率中的预测精度，作为挠度的函数，分别通过实验梁试验和考虑混凝土塑性的非线性有限元分析成功验证。