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Frequently Asked Questions (FAQ)
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First, check if the "design of deformation" has been activated in the settings for the calculation of the SLS designs.
Furthermore, check whether a load for the "quasi-permanent" design situation has been specified in the "Serviceability" tab of Window 1.1. By default, the calculation of deformations in RF‑CONCRETE Surfaces (with RF‑CONCRETE Deflect or RF‑CONCRETE NL) requires a quasi-permanent load.
Regarding the analytical calculation of SLS, you should note that the calculation is based on a provided or applied reinforcement for SLS.
The provided reinforcement can result, for example, from the ultimate limit state design, the defined basic reinforcement, or the automatically determined required reinforcement for SLS. The reinforcement applied to the SLS design can be displayed graphically.
If there are too small or no reinforcement results from ULS or the basic reinforcement in some areas and no required reinforcement is determined for SLS at the same time, the serviceability limit state design is performed without or with too small reinforcement. In this context, very high results may occur during the deformation, for example. Also, there may be poor convergence.
It is necessary to ensure that there is a reinforcement in each area of the structural system. For this, you can apply a basic reinforcement or a minimum reinforcement, for example.
AnswerFor building construction, there are no specific limit values specified in the standards for the serviceability limit state design. Therefore, the limit values should be agreed with your client and, if necessary, with the respective authority. Nevertheless, there are various recommendations in technical literature, which we have also adopted as the default values.
AnswerIn the "Edit Load Cases and Combinations" dialog box, you can specify in the bottom right of the "Combination Expressions" tab which method of analysis should be used as the basis for the generated load combinations. By default, the linear calculation according to the geometrically linear analysis is preset for load cases and the nonlinear calculation according to the second-order analysis for load combinations.Thus, you can quickly determine whether the load case or the load combination is calculated according to the geometrically linear, second-order, or large deformation analysis. The postcritical analysis option allows you to carry out the stability analysis according to the large deformation analysis with regard to the post-critical failure of the entire structure.In case the model includes cable members, the calculation according to the large deformation analysis is preset in all cases.
AnswerThe differences resulting from the determination of the deformation in the cracked state can have various causes. In the case of deviations, you should check the following points:
Is the same calculation method applied?
RF-CONCRETE Deflect uses the analytical analysis approach according to EN 1992‑1‑1, 7.4.3.RF-CONCRETE NL uses the physically nonlinear analysis approach.You can find more information about the calculation methods in Chapter 2.7 and Chapter 2.8 of the RF‑CONCRETE Surfaces manual.
Is the same initial structure available?
If considering the underlying structural system as equivalent, the results of the linear calculation can be considered in the best way. The linearly determined deformation of the underlying combination should be approximately equal. Possible differences in the linear deformation may be increased in the cracked state in connection with the deformation analysis.
Are the same effects taken into account?
When comparing, make sure that the same effects, such as creeping and shrinkage, are taken into account (Figure 02).
Are the same initial values available?
In connection with the deformation analysis, you should further check if the same initial values are available. In this case, a special attention has to be paid to the fact whether the applied reinforcement (Figure 03) and the lever arm or the concrete cover are the same.
If you cannot find the cause after the fundamental examination, please contact our hotline.
AnswerYes, the exponent n is applied differently. Design details can help you to understand this. For EN 1992‑1‑1, for example, n=2 is applied (see Figure 01), and for CSA A23.3-14, n=3 is applied (see Figure 02).
The deformation calculated with RF‑CONCRETE Members represents a simplified calculation according to the standard. In this case, the deformation at the point of the maximum loading is only calculated first. This value and the value of the linear deformation of RFEM or RSTAB at this location are used to calculate a factor. The complete deformation distribution from RFEM or RSTAB will then be multiplied by this factor, and then displayed in the results of the add-on module.
Figure 01 shows a comparison of the results of the linear calculation from RFEM and the calculation of the add-on module. In this case, the calculated factor is approximately 2.66.
It is important that the deformation can actually be compared at the location of the maximum deformation only. Only there, the calculation is actually available. Therefore, various deformations may occur for the connected members, as shown in Figure 02.
AnswerThe deduction of the precamber in the serviceability limit state design is actually not regulated in steel structures. After numerous customer requests, we have adopted this in accordance with the TIMBER or CONCRETE add-on module. However, according to the standard specification, this value should only be considered in the quasi-permanent design combination.This does not apply to the characteristic and frequent design situation. Thus, as soon as the design situation in the add-on module is adjusted accordingly (see figure), the applied precamber is also subtracted from the resulting deformation.
No, it is not absolutely necessary to calculate according to the second-order or large deformation analysis when using a nonlinear material model. The material nonlinearity is also considered in the case of the calculation according to the linear static analysis.
The calculation according to the second-order analysis or the large deformation analysis means that the equilibrium is set on a deformed structure. So it is geometric nonlinearity.
The difference between the second-order and large deformation is that large rotation may occur in the case of the large deformation analysis.
Thus, if there is no stability problem or if the stability problem is further analysed, the calculation according to the linear static analysis is sufficient.
When checking the deformation value, for example, as a result of the deformation analysis in STEEL EC3, it is necessary to subtract nodal deformations from the total deformation shown in RSTAB (see Figure 01): the deformation value in the centre of the member represents the total deformation of the component (the deformation of nodes plus the deformation of the component).
If the deformation is set as relative to the 'undeformed system' in Details of the serviceability limit state design in the add-on module (see Figure 02), the maximum deformation including nodal deformations (the deformation value displayed in RFEM/RSTAB) is used.
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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