Steel brace overview

Tekla Structural Designer allows you to analyze and design a steel member with pinned end connections for axial compression and tension.

Steel braces can be specified as rolled I-sections, C-sections, T-sections, rectangular, square and circular hollow sections, angles, double angles, and flat sections.

Note: If working to the US head code, a brace specified as a flat section can only be analyzed, but design is beyond scope.

Design is performed using a set of design forces obtained from 3D Analysis. (Grillage Chasedown Analysis and FE Chasedown Analysis results are not required.)

Applied loading

The following points should be noted:

Loads for the brace are derived from the building model.
Element loads cannot be applied directly to the brace itself.
Live and Roof Live load reductions are not applied.
Moments due to self weight loading are ignored.

Design Forces

The design forces for strength checks are obtained from an analysis of the entire structure. Braces can be subject to axial compression or tension, but will not be subject to major and minor axis bending.

Input method for A and V Braces

A and V Braces should be modeled using special tools which can be found on the 'Steel Brace' drop list in the 'Steel' section on the 'Model' tab.

Although it is also possible to model the exact same brace arrangement using individual elements created using the simple 'Steel Brace' command, it is important to note that whilst the Notional Loads \ EHFs (Equivalent Horizontal Forces) calculated for models built using the A or V Brace tools are correct, this is not the case when the A or V braces are built up out of individual brace members. In this latter case, elements of the vertical loads that are supported by the bracing system are 'lost' and are not included in the Notional Load \ EHF calculations with the result that the calculated Notional Loads \ EHFs are not correct.

Steel brace in compression

Effective length factors are defined for each axis of buckling.

Effective length factor y-y
Effective length factor z-z

Note: If designing to British Standards, see Steel brace design to BS 5950 - Axial compression

Steel brace in tension

The net area of the section is required for tension checks. This can be specified either as:

Percentage value
Effective net area

Note: If designing to British Standards, see Steel brace design to BS 5950 - Axial tension

Fire proofing

Ambient temperature utilization (Eurocode only)

The ambient temperature calculations can be included in the design checks by selecting Ambient temperature utilization located under Fire proofing in brace properties.

When this option is enabled the calculation of the ambient temperature utilization at fire limit state is carried out for the relevant phenomena depending on the selected member type and considering:

The load reduction factor prescribed in EN 1993-1-2 Clause 2.4.2 applied to the actions,
The guidance for resistance under fire in EN 1993-1-2 Clause 4.2

The critical ratio is then reported in the design summary table.

Check for fire resistance

While the mechanical resistance of a steel brace in case of fire can not currently be checked, fire protection can still be added by selecting Protected located under Fire proofing in brace properties.

If you choose this, you'll need to specify the fire protection material details. The weight of this protection will then be included in the "Self weight - excluding slabs" load case.

UDAs for fire (Eurocode only)

To assist in the flow of fire data between Tekla Structural Designer and Tekla Structures, the following UDAs can be added to the brace properties by selecting Populate UDAs on the Design ribbon.

Exposure
Nominal fire exposure
Ambient UR (u0)
Load reduction factor (nfi)
Critical temperature
Imposed loading category

Depending on the selections made under 'Fire Proofing' in the brace properties the actual UDA values will also be populated:

If Ambient temperature utilization is selected, Ambient UR (u0), Load reduction factor (nfi) and Imposed loading category UDAs are populated.
Because braces are not currently checked for fire resistance, the Critical temperature UDA is not populated.
Exposure and Nominal fire exposure UDAs are populated with any of the fire proofing options active.