In the Members | Basis tab of the 'Ultimate Configuration' or 'Strength Configuration' dialog, you make basic settings for the design of members and member sets.
The 'Design Parameters' are divided into several categories, which differ depending on the design standard. The following sections describe the parameters of these standards:
EN 1995
General
The 'Perform stability analysis' check box controls whether, in addition to the cross-section checks, stability checks such as those for flexural buckling or lateral-torsional buckling are also performed. You should clear the check box if you do not want to perform a stability analysis or if you have already considered the stability effects in the internal force determination (for example, by a calculation according to the second-order analysis with imperfections and/or stiffness reduction).
If the stability analysis is activated, Effective Lengths must be defined and assigned to the respective members or member sets. If this is not the case, no stability analysis is possible. A corresponding message is displayed in the Errors & Warnings result table after the calculation. Tension members are exempt from this, as they can only absorb tensile forces and do not require stability checks.
Design Ratios for Neglecting Internal Forces and Stresses
The design standards, mostly designed for manual calculations, contain design formulas or interaction conditions that are often only designed for specific internal force combinations. In the context of structural analysis on a 3D model, however, very small values for internal forces are usually obtained. From an engineering point of view, they are irrelevant for the ultimate limit state, but if the design standard is strictly observed, they prevent certain designs or force the use of more unfavorable interaction formulas. The design ratios thus offer a simple and transparent way to neglect stresses from very small internal forces in the designs and to circumvent the problems mentioned above.
The limit value η describes the ratio of the existing stress to the design value of the strength, which is determined in a simplified way via the cross-section properties. The limit ratios of the design strengths are derived from the standard specifications and are preset with very small values to enable a simplified design. You should therefore only use high limit values for test purposes.
If an internal force falls below the limit value condition, the design is performed without a warning that the internal force is being neglected. In the Design Check Details, however, you can use the 'Negligible' note for the design internal forces to check which internal forces were neglected due to the limit values and not considered in the design. If all internal forces at a location are negligible, only the check of the negligible internal forces is specified as the design.
Curved and Saddle Beams
With the check boxes, you can control whether the design of stresses perpendicular to the grain direction should also be performed for non-uniform section distributions. This tension perpendicular to grain design often proves to be a weak point in curved members.
'Saddle beams' represent members with a Section Distribution of the 'Saddle' type. For these members, you can also specify whether the tension perpendicular to grain design should be performed.
Taper Angle Limitation
For members with a linear or haunched Section Distribution, the wood fibers are cut through at the beveled edge. According to [1] 6.4.2, the influence of the taper angle α on the stresses at the cut edge must be considered. According to the German National Annex, this angle must not be too large and may be a maximum of 24°. You can adjust the preset limit value if necessary to enable further design.
System Strength According to 6.6
If the continuous load distribution system is capable of transferring loads from one member to adjacent members in similarly spaced similar structural components (e.g., floor beams all equally adjacent), the strength of the structural components may be increased by the factor ksys according to [1] 6.6. In this case, select the check box.
Increase of Crack Factor for Shear
This category is available for design according to the German National Annex. It concerns the influence of cracks on the shear capacity design of bending-stressed structural components. If you activate the option, the factor kcr for the shear design of softwood cross-sections at a distance of more than 1.5 m from the member ends is increased by 30%. It is assumed that the cracks have only small dimensions there.
NDS
General
The 'Perform stability analysis' check box controls whether, in addition to the cross-section checks, stability checks such as those for flexural buckling or lateral-torsional buckling are also performed. You should clear the check box if you do not want to perform a stability analysis or if you have already considered the stability effects in the internal force determination.
Further notes can be found in the General section in the description for the EN 1995 standard.
Design Ratios for Neglecting Internal Forces and Stresses
The design equations of the design standards are often only designed for specific internal force combinations. Usually, the structural analysis on a 3D model also results in very small values for "secondary" internal forces, which are irrelevant for the ultimate limit state from an engineering point of view, but prevent certain designs if the standard is strictly observed. The design ratios make it possible to neglect certain internal forces in the design and thus circumvent the problems mentioned above. The limit value η describes the ratio of the existing stress to the design value of the strength.
Further notes can be found in the Design Ratios section in the description for the EN 1995 standard.
Torsion Calculation
With the check boxes, you can control how torsion should be considered in the designs:
- Check Torsion Limit Only: A further design is permissible if the shear stress caused by torsion does not exceed the design value of the strength according to [2] Chapter 3.4. If it exceeds the limit value, no design is possible.
- According to Timber Construction Manual: The torsional stresses are designed according to the specifications of [3] Chapter 4.6. In the Design Ratios section, you can specify from which limit ratio η torsional stresses are generally relevant for design.
- Ignore: The shear stresses due to torsion are checked during the design, but have no influence on the design. If the design value of the strength is exceeded, the program only outputs an informative note.
Positive or Negative Bending about y-Axis
According to [2] Table 5A and Table 5C, specific design values apply to structural components made of glued-laminated timber that are stressed in bending about the y/x-axis for positive bending (bottom side of the beam under tensile stress) and negative bending (top side of the beam under tensile stress). Specify whether the bottom side of the members to be designed is in the positive direction of the local z/y-axis or in the opposite direction.
In the remaining categories, you can make further settings relevant to design. The description is in progress.
CSA O86
General
The 'Perform stability analysis' check box controls whether, in addition to the cross-section checks, stability checks such as those for flexural buckling or lateral-torsional buckling are also performed. You should clear the check box if you do not want to perform a stability analysis or if you have already considered the stability effects in the internal force determination.
Further notes can be found in the General section in the description for the EN 1995 standard.
Design Ratios for Neglecting Internal Forces and Stresses
The design equations of the design standards are often only designed for specific internal force combinations. Usually, the structural analysis on a 3D model also results in very small values for "secondary" internal forces, which are irrelevant for the ultimate limit state from an engineering point of view, but prevent certain designs if the standard is strictly observed. The design ratios make it possible to neglect certain internal forces in the design and thus circumvent the problems mentioned above. The limit value η describes the ratio of the existing internal force to the design value of the cross-section resistance.
Further notes can be found in the Design Ratios section in the description for the EN 1995 standard.
Positive or Negative Bending about y-Axis
According to [2] Table 5A and Table 5C, specific design values apply to structural components made of glued-laminated timber that are stressed in bending about the y/x-axis for positive bending (bottom side of the beam under tensile stress) and negative bending (top side of the beam under tensile stress). Specify whether the bottom side of the members to be designed is in the positive direction of the local z/y-axis or in the opposite direction.
