The events of recent years remind us of the importance of earthquake engineering in seismic regions. For you as an engineer, the design of structures in earthquake-prone areas is a constant trade-off between economic efficiency – the financial possibilities – and structural safety. If a collapse is inevitable, engineers must estimate how it will affect the structure. This article aims to provide you with an option on how to perform this estimation.
In addition to the basic combination rules of EN 1990, there are other combination conditions for actions on road bridges specified in EN 1991‑2 that must be taken into account. RFEM and RSTAB provide automatic combinatorics that can be activated in the General Data when selecting the standard EN 1990 + EN 1991‑2. The partial safety factors and combination coefficients depending on the action category are preset when selecting the respective National Annex.
In the H - Roofs category, imposed loads have to be applied. These are usually the technician loads for construction and maintenance. Since there is no maintenance for snow, category H must not include both snow and imposed loads together. You can consider thi in the options for automatic combinations.
As in RFEM, load combinations can be generated automatically in RF‑PIPING. This feature is activated by default and creates the recommended load and result combinations for piping design. It is necessary to assign the relevant action category to load cases in order to generate the correct combinations. To do this, new action categories have been implemented specifically for loads on piping. Pressure temperature conditions are generated as the sets of the first (second, third, and so on) load case of the "Pressure" category and the first (second, third, and so on) load case of the "Temperature" category. The default setting can be reviewed or adjusted in the "Grouping of Thermal and Internal Pressure Load Cases for Operating Combinations" dialog box. You can access this dialog box by clicking the corresponding button in the "Piping Load Combinations" tab of the "Load Cases and Combinations" dialog box. This dialog box is automatically offered to check your entries in the case of any change of the load case from the "Pressure" or "Temperature" category.
If you select the combinatorics according to EN 1990 + EN 1991‑2 and define a load case in action category gr1a, gr2, or gr5, you have to additionally define in the program which load model should be taken as a basis for the load case. This information is crucial for defining combination rules for automatic combinations according EN 1990 + EN 1991-2. In the gr1a category, you can select TS (LM1), UDL (LM1), or pedestrian and cycle track, for example. TS (LM1) is preset by default. In the gr2 category, you can select breaking and acceleration forces or centrifugal forces as a specification.