显示纵向钢筋抗拉包络图或者抵抗弯矩包络图

技术文章

出于经济目的当按照计算所得出的钢筋面积较大时,可以考虑在沿受弯梁的纵向长度方向进行钢筋截断,即按照阶梯形实际配置纵向钢筋。梁纵向的阶梯形配筋将按照弯矩包络图形进行配置。使用附加模块 RF-CONCRETE Members 与 CONCRETE 可以按照计算所需的纵向钢筋面积自动设置钢筋沿纵向的阶梯形分布。为了计算此钢筋的配置必须要求实配钢筋的抵抗弯矩图包络在实际弯矩包络图之外(欧洲规范称之为拉力包络图)。

Curtailment of Longitudinal Tension Reinforcement

The design of the curtailment of the longitudinal tension reinforcement ensures that the envelope of the acting tensile force FSd can be absorbed by the provided reinforcement. 9.2.1.3(2) of EN 1992‑1‑1 [1] requires to also consider the additional tensile force ΔFtd due to the shear force. For structural components with shear reinforcement, this additional tensile force ΔFtd can be calculated according to 6.2.3 (7) of EN 1992‑1‑1 [1]. The tensile force FSd is calculated from the following equation:

$\begin{array}{l}{\mathrm F}_\mathrm{sd}\;\;=\;\;\left(\frac{{\mathrm M}_\mathrm{Eds}}{\mathrm z}\;+\;{\mathrm N}_\mathrm{Ed}\right)\;+\;{\mathrm{ΔF}}_\mathrm{td}\\\mathrm{where}\\{\mathrm{ΔF}}_\mathrm{td}\;=\;0.5\;\cdot\;{\mathrm V}_\mathrm{Ed}\;\;\cdot\;(\cot\;\mathrm\theta\;–\;\cot\;\mathrm\alpha)\end{array}$

For structural components without shear reinforcement, the tensile force ΔFtd may be taken into account by shifting the tensile force curve from $\left(\frac{{\mathrm M}_\mathrm{Eds}}{\mathrm z}\;+\;{\mathrm N}_\mathrm{Ed}\right)$ about a distance of al = d in the unfavourable direction. This approach may also be used as an alternative to the approach for structural components with shear reinforcement mentioned above. In this case, this 'shift rule' is determined according to the formula ${\mathrm a}_\mathrm l\;=\;0.5\;\cdot\;\mathrm z\;\cdot\;(\cot\;\mathrm\Phi\;-\;\cot\;\mathrm\alpha)$.

Figure 01 - Curtailment of Longitudinal Reinforcement from [1]

The resistant tensile force FRs of the provided reinforcement is determined within the anchorage lengths lbd.

Graphical Display of Reinforcement Covering Line / Curtailment of Longitudinal Reinforcement

If the tensile force of the curtailment of longitudinal reinforcement is divided by the design stiffness fyd of the reinforcing steel, a reinforcement covering line is obtained. In RF-CONCRETE Members and CONCRETE, the distribution of the required tension reinforcement As (the first result diagram in Figure 02) is shifted by the shift rule a1 in order to obtain the envelope of the required reinforcement (the second result diagram in Figure 02). You can display these shifted required reinforcement envelopes graphically by selecting 'Detailed results' under 'Provided Reinforcement' in the result navigator (see Figure 02).

If the envelope of the required reinforcement (red), the shifted envelope of the required reinforcement (green), and the provided reinforcement (blue) are shown graphically together, a reinforcement covering line is obtained (the third result diagram in Figure 02). This diagram corresponds to the curtailment of longitudinal reinforcement in Figure 9.2 of EN 1992‑1‑1.

Figure 02 - Reinforcement Covering Line / Curtailment of Longitudinal Reinforcement

Reference

[1]  Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings; EN 1992‑1‑1:2011‑01

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结构设计与有限元­分析软件(FEA)可以用于建立平面与空间结构模型,适用于由杆件、面、板、墙、折板、膜、壳、实体以及接触单元等的建模与分析计算。

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