Vertex Engineering Loads
General about Loads
Vertex Engineering loads are generated automatically according to the design code of the market area. Australian and European design codes for cold-formed steel structures are supported.
Loads are divided into permanent (G) and variable action (Q) loads. Variable action loads are not effecting permanently to the structure.
Load are also divided by load source, depending how the load is build up. Typically used load types are
- Dead load
- Imposed (live) load
- Wind load
- Snow load
The dead load contains typically the weight of the structure itself. Imposed loads include all the forces that are variable within the object's normal operation cycle.
Loads can be also divided to the fixed action and free action loads, depending is the load moving over the structure or is it effecting always in the same position.
| Variation in Time | Load Duration | Load Source | Movability | |
|---|---|---|---|---|
| Self weight of the roof structure | Permanent | Permanent | Dead | Fixed action |
| Wind load | Variable action | Short term | Wind | Fixed action |
| Weight of the people | Variable action | Medium term | Imposed | Free action |
| Storage load | Variable action | Long/medium term | Imposed | Free action |
| Snow load | Variable action | Medium/short term | Snow | Fixed/free action |
Wind Loads
There are multiple parameters which are effecting to the amount of the wind speed, such as the geological location of the building, the terrain and interfering obstacles. Wind loads are defined according to the wind speed and the loading is not constant over the roof. The roof is divided into different wind pressure areas, depending the location in the building, e.g. wind speed is constant but wind pressure is higher at ridge,eave or corners compared to middle area of the roof.
The wind is generating the internal pressure loads also to roof trusses bottom chords connected to ceiling, if ceiling is not permeable. If there is no ceiling exist or the ceiling is not air-tight, the internal pressure affects to the top chords of the roof truss.
In Vertex BD, wind loads and internal pressure loads are generated into the model. Internal pressure areas are defined by user before generating wind loads.
Load Combinations, Patterns and Cases
Building codes specify a variety of load combinations together with load factors (safety factors) for each load type in order to ensure the safety of the structure under different maximum expected loading scenarios. All combinations are checked in the design process and the worst case scenario rules in capacity results.
Live loads can effect to the structure at the same time or individually and the position of the load can be varied. The worst case scenario may appear when only some of the live loads are effecting to the structure. Load patterns contains typical live load combinations.
Load cases are created using load combinations in setup with typical load patterns. Members are designed using the most critical load case. Load case is similar with Design situation term, which is used in many design codes.
Limit state design
Limit state design is a method for structura design and it is divided into two main states:
- Ultimate limit state (ULS)
- Serviceability limit state (SLS)
Ultimate limit is a physical limit when the capacity of the member is fully used before the failure point. Serviceability limit is based for usage of the building when it's limiting deflections, vibrations and other harmful things for the normal usage of the building. Both limit states are used to check the structure in Vertex BD.