In IDEA StatiCa Connection, there are two strategies of weld sizing available to all users:

- to full-strength
- with over-strength

For Eurocode users, there are two more:

- to capacity estimation
- to minimum ductility

Weld sizing method is specified in Operations dialogue.

When running Weld sizing, every fillet weld in the model is modified according to weld sizing method. Generally, the size of welds will increase in this order:

- To capacity estimation
- To minimum ductility
- Full strength
- With over-strength

The methods are described in detail below.

### To capacity estimation

Weld sizing to capacity estimation automatically provides weld sizes that are strong just enough to transfer set loads.

Weld capacity estimation is the first use of machine learning in IDEA StatiCa. At the moment, it is implemented only in Eurocode. Weld resistance is determined according to the most stressed weld element. Therefore, weld utilization is highly nonlinear. The resistance of the whole length is estimated by a machine-learning algorithm based on the stress distribution along the weld length.

Weld sizing to capacity estimation requires results. Size of fillet welds is adjusted according to the following formula:

\[ a_{new} = a \cdot Ut_c / Ut_{target} \]

where:

- \(a_{new}\) – adjusted fillet weld size
- \(a\) – previously set fillet weld size
- \(Ut_c\) – capacity estimation based on machine learning algorithm visible at Weld check
- \(Ut_{target}\) – target utilization in Settings → Design → Autodesign → Weld sizing

Resulting \(a_{new}\) is rounded up according to Preferences → Application units → New entity rounding → Weld size.

Note that weld sizes are limited by detailing rules, e.g. weld size cannot be smaller than 3 mm (EN 1993-1-8 – 4.5.2). These detailing rules are adhered to. Also, keep in mind that multiple welds in IDEA StatiCa are often set by one value. In these cases, the size is set according to the most utilized one.

Also, a calculation loop is available. When weld sizing method is set to capacity estimation, it:

- Sizes the fillet welds to full strength
- Calculates the model
- Sizes the fillet welds to capacity estimation
- Calculates the model

Welds are then set at or below target utilization with just one click.

### To minimum ductility

Weld sizing to minimum ductility automatically provides welded connections that are strong enough to prevent brittle failures. The weld strength allows for the initial yielding of the plate, but ultimately, the weld ruptures.

The requirement for minimum ductility of welded joints in FprEN 1993-1-8:2023 – 6.9(4). It originates from Dutch national annex of EN 1993-1-8, where the fixed ratio of weld strength to plate strength is 0.8. It is also included in widely-used Green books from the UK, namely in Chapters C2 and C3. However, the fixed ratio is suitable only for steel grade S355. In the second generation Eurocode, this is expanded for all steel grades.

This requirement is checked for double-sided fillet welds by:

\[a/t=\frac{\beta_w\gamma_{M2} f_y}{\sqrt{2} f_u \gamma_{M0} } \cdot \min \left \{1.0, 1.1\frac{f_y}{f_u} \right \}\]

where:

- \(a\) – weld throat thickness
- \(t\) – thickness of the plate connected by edge
- \(\beta_w\) – weld correlation factor
- \(\gamma_{M2}\) – safety factor for bolts and welds; editable in Code setup
- \(f_y\) – plate yield strength
- \(f_u\) – weld ultimate strength
- \(\gamma_{M0}\) – safety factor for plates; editable in Code setup

The weld throat thickness for single-sided fillet weld is twice larger than that for double-sided fillet weld.

Note that the method is useful for transversely loaded welds and works if the plate is connected by its full width.

### To full strength

Weld sizing to full strength automatically provides welds that are stronger than the connected plate. In the calculation, it is assumed that the plates are loaded in tension and welds transversely as the worst case for weld strength and ductility. This design is useful to avoid brittle failures of welds for static loading.

This approach is also included in widely-used Green books from the UK, namely in Chapter C1.

This requirement is checked for double-sided fillet welds by:

\[a/t=\frac{\beta_w\gamma_{M2} f_y}{\sqrt{2} f_u \gamma_{M0} }\]

where:

- \(a\) – weld throat thickness
- \(t\) – thickness of the plate connected by edge
- \(\beta_w\) – weld correlation factor
- \(\gamma_{M2}\) – safety factor for bolts and welds; editable in Code setup
- \(f_y\) – plate yield strength
- \(f_u\) – weld ultimate strength
- \(\gamma_{M0}\) – safety factor for plates; editable in Code setup

Note that the method is useful for transversely loaded welds and works if the plate is connected by its full width.

### With overstrength

Weld sizing with overstrength automatically provides welds that are much stronger than the connected plate. Overstrength factor is specified Settings → Design → Autodesign → Weld sizing. The default value of 1.4 is taken from EN 1993-1-8 – 6.2.3 (5) to form a plastic hinge.

In the calculation, it is assumed that the plates are loaded in tension and welds transversely as the worst case for weld strength and ductility. This design is useful to avoid brittle failures of welds for plastic design or cyclic loading. Note that the large weld size automatically does not guarantee high ductility. On the opposite, it may lead to excessive residual stresses and deformations caused by weld shrinkage.

This requirement is checked for double-sided fillet welds by:

\[a/t=\frac{\beta_w\gamma_{M2} f_y}{\sqrt{2} f_u \gamma_{M0} } \cdot f_{overstrength}\]

where:

- \(a\) – weld throat thickness
- \(t\) – thickness of the plate connected by edge
- \(\beta_w\) – weld correlation factor
- \(\gamma_{M2}\) – safety factor for bolts and welds; editable in Code setup
- \(f_y\) – plate yield strength
- \(f_u\) – weld ultimate strength
- \(\gamma_{M0}\) – safety factor for plates; editable in Code setup
- \(f_{overstrength}\) – overstrength factor specified in Settings → Design → Autodesign → Weld sizing

Note that the method is useful for transversely loaded welds and works if the plate is connected by its full width.