在模块 RF-PUNCH Pro 中计算墙端和墙角的冲切荷载

技术文章

使用附加模块 RF-PUNCH Pro 可以对墙端和墙角位置的楼板和基础板进行冲切设计。

在钢筋混凝土板上选择节点支座或者支座连接时,冲切荷载可以直接由支座反力或者支座中的内力得出。如果选择墙角或者墙端的节点进行设计,冲切荷载不能直接从支座反力或者面上的内力得出。

图 01 - Absorbed Shear Force on Wall End and Wall Corner

Determination of Punching Load on Wall End

Generally, the punching load cannot be determined from the support force or surface internal forces of the connected walls, but from the surface internal forces of the slab for which the punching shear design is to be performed. This approach has the advantage of avoiding the influence of singular results directly on the node to the greatest possible extent. Furthermore, this way of determining loads also allows you to consider the punching shear of a pure line load (pure load from the connected wall surface).

图 02 - Wall Replaced by Line Load

When selecting a point of punching shear, RF‑PUNCH Pro generates the basic control perimeter already at a distance of 2.0 d according to [1], Chap. 6.4.2.

To determine the punching load, a section is created in the module so the surface internal forces from RFEM can be measured out at the control perimeter. For the determination of the punching load, the surface internal force vmax,b from RFEM is used. The definition of the surface internal force vmax,b is described in [2], Chapter 8.15 Surfaces - Principal Internal Forces.

As a default setting for determining the punching load on wall ends and corners, the option ‘Unsmoothed shear force over the critical perimeter’ is preset in RF‑PUNCH Pro. This means that for the applied shear force determination, the maximum value is assigned along the control perimeter.

Figure 03 - Shear Force at Critical Perimeter

The applied shear force VEd results from:

$$\begin{array}{l}{\mathrm V}_\mathrm{Ed}\;=\;\mathrm{basic}\;\mathrm{control}\;\mathrm{perimeter}\;\mathrm{length}\;\cdot\;\mathrm{maximum}\;\mathrm{shear}\;\mathrm{force}\;\mathrm{at}\;\mathrm{the}\;\mathrm{critical}\;\mathrm{perimeter}\\{\mathrm V}_\mathrm{Ed}\;=\;{\mathrm u}_1\;\cdot\;{\mathrm v}_{\max,\mathrm b}\\{\mathrm V}_\mathrm{Ed}\;=\;2.289\;\mathrm m\;\cdot\;156.11\;\mathrm{kN}/\mathrm m\;=\;357.34\;\mathrm{kN}\end{array}$$

Figure 04 - Resulting Shear Force VEd

Verification of Determined Punching Load

The punching load VEd determined in the add‑on module can be verified by creating a line in the basic control perimeter where a new section is defined. In this way, you can visualise the shear force distribution along the perimeter in the RFEM graphic window or in the result diagram of the section.

The following graphic displays the result diagram of the shear force vmax,b determined in RFEM. The result diagram can help you retrace the applied shear force VEd calculated in RF‑PUNCH Pro.

Figure 05 - Result Diagram in Section: Principal Internal Force vmax,b

As already mentioned, the unsmoothed shear force over the critical perimeter is applied by default for the determination of the punching load in RF‑PUNCH Pro. Since the maximum value of the shear force is already applied along the control perimeter, the load increment factor β is set to 1.00 for further design.

Consideration of Load Increment Factor β

As an alternative, you can also select the option of smoothed shear force distribution over the critical perimeter in RF‑PUNCH Pro in order to determine the applied shear force VEd. Thus, the applied shear force is determined by using the ‘smoothed’ shear force vmax,b,average.

In this case, the load increment factor β will be considered in the further design process. You can determine the load increment factor by using the fully plastic shear stress distribution according to 6.4.3 (3), or the constant coefficients according to 6.4.3 (6). In addition to these options for the determination of the load increment factor β, RF‑PUNCH Pro also provides the alternative user‑defined load increment factor.

Reference

[1]   European Committee for Standardization. (2011) Eurocode 2: Design of concrete structures - Part 1‑1: General rules and rules for buildings. EN 1992‑1‑1:2011‑01. Brussels: CEN.
[2]   Manual RFEM 5. (2013). Tiefenbach: Dlubal Software. Download.

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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。

RFEM 混凝土结构
RF-PUNCH Pro 5.xx

附加模块

节点支座和线支座的基础和板的抗冲切计算