9.5 Geometry

In Window 1.5 Geometry, you can define the steel plate and fastener parameters.

This window is divided into two parts: On the left, the input parameters of the connection node are displayed; on the right, they are illustrated by graphics. The upper graphic shows a system sketch of the current parameter, the lower graphic shows a 3D visualization of the node.

The graphic buttons are explained in Table 3.1.

In this section, you can define the properties of the steel plates. Please note the following.

• A maximum Number of five slotted plates is possible.
• The Thickness of steel plate must be between 1 mm (for nails) and 40 mm (for SFS: 3 mm).
• The Distance from fasteners to plate edge must meet the standard requirements so that the hole bearing designs can be fulfilled (see [1] Table 3.3 and 3.4).
• The Width of slot is usually the same as the plate thickness. If the connection is made with tolerances, the slot width can be increased by a maximum of 1 mm. When using the SFS intec system, the limit value of 2 mm must be observed. However, this setting makes no difference for the calculation, as only geometry constraints are queried here.
• The plates can also be designed as Side plates. For this purpose, at least two slotted plates must be provided.

Modified slotted plate designs are dynamically visualized in the graphic.

If more than one slotted steel sheet is used, there may be a problem in the generation of the predominant failure modes according to [2] Section 8.2.3, Figure 8.3. The predominant (governing) failure mode of the fasteners in the corresponding joint must be compatible with every other one. The combination of failure modes (c), (f), and (j/l) with other failure modes is thus not allowed.

RF-/JOINTS always checks the hole bearing in the inner and outer shear of a multishear connection. For the cuts at the outer edge of the plates, the failure modes (f), (g), and (h) are checked - both for thick and thin steel plates. The modes according to [2] Equation (8.9) and (8.10) are identical to them.

In the middle part, the failure cases are analyzed according to [2] Equations (8.12) and (8.13). Here too, a distinction is made between thick steel plates with the cases (l), (m) and thin steel plates with the cases (j), (k).

RF-/JOINTS always determines the governing failure mode in the respective joint. If, for a thin sheet, the failure mode (j) is governing at the inner (purple) shear planes and the mode (g) in the outer (green) shear planes, the calculation is not possible. However, if the mode (f) were governing, the calculation could be performed.

This section describes the fastener layout using parameters. The specifications must be made separately for each member. You can use the list or the buttons to switch between the individual members. Different diameters and distances are possible for the respective categories (dowels, bolts, nails, screws).

• The Pattern of the fastener group can be defined as a rectangle or a circle.
• The Diameter of the fasteners can be selected within the respective allowable limits. For dowels, the minimum diameter is 6 mm, for screws it is 1.8 mm. If the SFS intec fastening system has been specified in Window 1.1, 7 mm is set. Combinations with different diameters are also possible.
• If you want the length of the dowel to be shorter than the cross-section width (e.g. for fire protection), you have to enter the Plug length. This automatically reduces the length of the dowel. For nails and screws, the nail or screw length is shortened on one side.

The design of dowel, bolt, screw, and nail connections can be circular or rectangular.

In the case of a circular arrangement, the Number of circles is limited by the cross-section height. In the input lines, you can specify the Number of fasteners in circle.

For circular arrangements, the condition according to [7] that the radius of the circle must be six times larger than the fastener diameter also applies. In the program, this criterion is checked using the height of the fastener that is furthest from the center.

$d_{\text{core,max}} = \frac{{\displaystyle \frac{h}{6}}·sin60}{1+sin60}$

For a rectangular arrangement of the dowels, specify the Number of fasteners in x-direction and in z-direction.

It is also possible to arrange Staggered rows in order to improve the crack behavior of the joint.

The Method of placement can aim for the smallest possible distance of the fasteners to each other or the minimum edge distance. User-defined distances are also possible.

The following options are available for the Orientation of fastener columns and rows:

• Basic - orientation on local member coordinate system
• Rotated - orientation on global coordinate system
• Slanting - orientation on edges with staggered rows
• User-defined - free definition of inclination and rotation

If the Dowel group is reinforced by screws to prevent cracking, the effective number of fasteners does not need to be reduced. The parameters of the reinforcement must then be defined separately (see Figure 9.30).

For the connected web members of a beam, you can define a Member eccentricity that geometrically determines the outlines of the members. The local member coordinate system is shown in the graphic.

With the Avoid bending of side members option (see Figure 9.28), you can prevent additional bending moments due to eccentric load introduction. For this purpose, the program applies a reduced tension resistance for the connecting members. You can find more information about connections subjected to tension in the following article:
https://www.dlubal.com/en-US/support-and-learning/support/knowledge-base/001299

The general parameters for reducing the tensile strength can be found in the Timber tab of the Details dialog box (see Figure 9.38).

The [Details] button below the section (see image 9.28) opens the Details dialog box. In this window, you can deactivate fasteners and adjust the diameters individually.

In the figure above, the Activity of dowel No. 1 is suspended.

In order to calculate with n_ef = n, you can define user-defined reinforcements with screws. The screw reinforcement is identical for all dowel-type fasteners.

When defining Automatically, you have to specify the ultimate tensile strength of the screw.

For the design of the reinforcement, you can arrange the screws between each dowel-type fastener Equally or only on the edges of the fastener group.

The Number of reinforcing screws per dowel column is defined in pairs by default. This corresponds to two screws for a steel plate, three screws for two plates, and so on.

The Screw length is specified up to the axis of the fastener that is furthest from the screw-in point. A Screw extension to the edge of the cross-section with the value l_ext is also possible. The screw length will be calculated automatically.

The Nominal diameter of the screw can be selected from the list or entered directly.

The design of the screws is performed in the direction of the screw axis according to [2] Section 8.7.2.

When automatically defining the screw reinforcement, you have to specify whether the Withdrawal strength determination is carried out according to [2] Section 8.7.2(4) or 8.7.2(5).

The calculation of the pull-out resistance is thus performed either according to

Equation (8.38)

$F_{\mathrm{ax},\mathrm{\alpha },\mathrm{Rk}} =\frac{n_{\mathrm{ef}} f_{\mathrm{ax},\mathrm{k}} d {\mathcal{l}}_{\mathrm{ef}} k_{\mathrm{d}}}{1.2 {\cos }^2 \alpha +{\sin }^2 \alpha }$

or Equation (8.40a)

$F_{\mathrm{ax},\mathrm{\alpha },\mathrm{Rk}}=\frac{n_{\mathrm{ef}} f_{\mathrm{ax},\mathrm{k}} d {\mathcal{l}}_{\mathrm{ef}}}{1.2 {\cos }^2 \alpha + {\sin }^2 \alpha }{\left(\frac{{\rho }_{\mathrm{k}}}{{\rho }_a}\right)}^{0.8}$

Since there is no information about the Ultimate strength of fastener in [2], the value f_u,b must be user-defined. The screw's tensile strength is calculated with the Core diameter of the screw.

$f_{\text{tens,k}} = f_{\text{u,k}}{\left(\frac{d_{\text{core}}}{2}\right)}^2\pi$

The screw action is assumed to be acting separately. Therefore, n = n_ef and thus F_t,Rk = n_ef f_tens,k. This design of the tensile strength is performed with the number 6201 in the module.

The screw's pull-out resistance from the wood is determined in design 6200 when automatically defining with Equation (8.38) or (8.40) (see above).

In the manual screw design, you can freely specify the withdrawal capacity and the tensile strength of the screw.

When determining the screw load, the resulting force F_res in each screw is calculated using the force F_res in each fastener. The force is displayed in design 6010 (see Figure 9.33). The screw design uses the maximum force in vertical direction F_res,z of the member.

For a slotted steel plate, the force of each dowel is respectively absorbed by one screw on the left and right of the plate. The force is therefore divided by two and multiplied by 0.3 according to [8]. This gives F_res,0.3.

F_res (already divided by two) is again divided by 4 for the force F_notch (example of a slotted plate with two screws per dowel), which is why this division only works for the Equally arrangement, as shown (see Figure 9.31).

The force used to design the screws is therefore:

$F_{\text{k,split}}=F_{\text{res,0.3}} + F_{\mathrm{notch}}$