Abstract

In this article, we will design an Angle section in pure compression, considering its principal axes (u-u & v-v).  

Keywords: Advance Design, Angle, Eurocode 3, EN 1993-1-1

1.Introduction

ke most steel structural members, angle sections are designed not in their geometrical axes (y-y & z-z, parallel to the legs) but in their principal axes (u-u & v-v).

2.    Theory

The Eurocode 3 convention for member axes refers to the axes about which the moment acts.

For most sections, that would be the geometrical axes (y-y & z-z):

• y-y is the cross-section axis parallel to the flanges
• z-z is the cross-section axis perpendicular to the flanges

Yet, this convention is not suitable to angle sections, for which bending occurs about the principal axes (u-u & v-v).

Therefore, the u-u & v-v axes should be used instead:

• u-u major principal axis
• v-v major principal axis

3. Application

Assume a L 90×9 equal leg angle, subjected to a N_Ed = 80 kN compressive axial force.

Steel grade is S275.

The effective slenderness (λ_eff) refers to annex G from EN1993-3-1:

The effective slenderness involves a k parameter, which depends on the type of restraint, as per Table G.2 from EN 1993-3-1.

For buckling about the v-v axis though, the k formula is unchanged.

The angle section under consideration is properly designed.

4.     Conclusion

Angle sections should be designed about their principal axes, especially in pure compression situations, where buckling typically arises about the v-v axis.

The upcoming update of Advance Design (version 2023.1) will enable this option, while letting the user consider the effective slenderness ratio.

Learn more about Advance Design!

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Abstract

In this article, we will compute the shelter factor that applies to a free-standing wall to account for the presence of an upwind wall or fence.  

Keywords: Advance Design, wall, free-standing wall, Eurocode 1, EN1991-1-4, return corner

1.Introduction

In a previous publication, we have covered the determination of wind forces on a free-standing wall at the Eurocode 1:  

https://civil-engineering-design.com/2022/07/19/wind-action-on-free-standing-walls-at-the-eurocode-1/

The present article goes one step further by considering the interaction between several walls, and the sheltering effect they may produce on each other.

In addition to these supports, a user defined nonlinear support mechanism is also possible (“NL-Diagram” option in Figure 2).

2.    Theory

Shelter factor is defined in §7.4.2 from EN1991-1-4.

This coefficient will reduce the pressure coefficients when an upwind wall is able to provide protection to the wall under consideration.

The shelter factor can be determined on Figure 7.20, based on:

• The spacing between the two walls (x)
• The solidity ratio of the sheltering wall (φ)
• The height of the sheltered wall (h)

3. Example

Assume a 15m x 4m wall, with a φ = 0,9 solidity ratio.

The pressure coefficients on this isolated wall would be:

• Zone A: C_p,net = 1,863
• Zone B: C_p,net = 1,375
• Zone C: C_p,net = 1,237

Now, if a similar wall, were to be located at a 40m distance, it would produce a sheltering effect that would be introduced in the calculation through the shelter factor.

Of course, the alternate oblique wind direction should be considered as well:

The climatic generator Advance Design is able to automatically detect the potential upwind walls and to compute the corresponding shelter factor for each wind direction. 

On the picture below, Advance Design detected that the wall under consideration could benefit from the sheltering effect of an upwind wall for the Y+ wind direction, resulting in ψ_s=0,55.

Yet, no such walls were detected in the other directions, resulting in ψ_s=1,0 for the X+, X- and Y- directions.

4.     Conclusion

When designing a wall or a fence for climatic actions, the determination of the shelter factor can be a lengthy and tedious process, yet totally worthy as it can allow for a significant reduction of the wind forces.

Fortunately, in Advance Design, the detection of the potential upwind walls with the shelter factor they produce, is performed instantly during the automatic wind generation.

Learn more about Advance Design!

Visit website – https://graitec.com/advance-design/
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Abstract

In this article, we will apply the procedure from the EN1991-1-4 to estimate the wind forces on a free-standing wall with a return corner.  

Keywords: Advance Design, wall, free-standing wall, Eurocode 1, EN1991-1-4, return corner

1. Introduction

Free-standing walls are covered in §7.4.1 from EN1991-1-4.

This part is intended towards fences as well as buildings with so many openings that they should be designed as per §7.3 (canopy roofs) and §7.4 (free-standing walls).

2. Theory

The Eurocode 1 defines two types of free-standing walls:

• Without return corner
• With return corner

Pressure coefficients for each zone are determined from Table 7.9 and may require up to 3 successive linear interpolations based on:

• The dimensions of the wall (Length/Height ratio)
• The length of the return corner (if any)
• The solidity ratio of the wall (also called opening ratio or porosity)

3. Example – Free-standing wall with return corner

Assume a free-standing wall (Length: 16m and Height: 4) with a 0,9 solidity ratio.

This wall has a 2m-long return corner.

Yet, the values we have just obtained (in red) only stand for a wall without a return corner.

A 2^nd linear interpolation is then required.

3.2            2^nd linear interpolation

We perform a 2^nd linear interpolation based on the length of the return corner (noted L’).

3.3.            3^rd linear interpolation

We perform a 3^rd linear interpolation based the solidity ratio of the wall.

The values we have just obtained (in green) are the ones we should expect for the A, B and C zones (the wall is not long enough to get a D zone).

There are the values the climatic generator from Advance Design 2023 will return:

Of course, Advance Design will consider all required wind directions (perpendicular and oblique winds).

Advance Design will also consider more complex effects, such the potential force reduction that can be benefited from an upwind wall, through the shelter factor (ψ_s) defined in §7.4.2:

4. Conclusion

The estimation of wind forces on free-standing walls sure is a tedious process, with a high risk of errors due to the various linear interpolations needed.

Fortunately, version 2023 of Advance Design now handles these structural elements, generating the corresponding forces on your 3D structures in a single click.

Learn more about Advance Design!

Visit website – https://graitec.com/advance-design/
Visit Advance Design Virtual Stand – https://graitec.com/advance-design-virtual/
Linkedin – https://www.linkedin.com/showcase/advance-design-&-advance-design-connection/
Free trial – https://graitec.com/free-trial/