混凝土箱形截面考虑二阶效应的配筋图算法

Graphic Algorithm for Concrete Box Section Reinforcement Under Second-order Effect

箱形和工字形截面是工程中常用的截面形式,但按《混凝土结构设计规范》计算此类截面的配筋公式繁多,还需事先判断,然后选择相应的计算公式,比如拉弯时,要判断拉力合力点是否在大小两侧钢筋之间,区分小偏拉或大偏拉;压弯时,要判断大小偏心,除此之外,还需判断中性轴是否在翼缘或在腹板内等。为了方便快速计算,本文不采用规范中的等效矩形应力换算,直接由混凝土和钢筋的应变求应力,进而计算内力。确定其可能的应变范围,由此应变可变成已知量,并将最终的计算结果绘制成了计算配筋的诺模图,该图为无量纲形式,可用于任意宽度和高度的截面尺寸和C50及以下混凝土强度等级。

Box and I-shaped sections are commonly used in engineering,however,there are many formulas for calculating such sections according to the Code for Design of Concrete Structures,so it is necessary to judge in advance and then choose the corresponding formula.For example,when bending,it is necessary to judge whether tension force point is between size on both sides of the reinforcing steel bar,distinguish small slant pull or large deflection.When bending,it is necessary to determine the size of eccentric,in addition,also to determine whether the neutral axis in the flange or in the web,etc.In order to facilitate the rapid calculation,the equivalent rectangular stress conversion in the code is not adopted in this paper,but the stress is calculated directly from the strain of concrete and reinforcement,and then the internal force is calculated.The possible strain ranges are determined,from which the strain can be turned into a known quantity,and the final calculation results are drawn into a norm diagram for calculating reinforcement,which is dimensionless and can be used for section sizes of arbitrary width and height and concrete strength classes up to C50.