Various design parameters of the cross-sections can be adjusted in the serviceability limit state configuration. The applied cross-section condition for the deformation and crack width analysis can be controlled there.
For this, the following settings can be activated:
Crack state calculated from associated load
Crack state determined as an envelope from all SLS design situations
Cracked state of cross-section - independent of load
The design of cold-formed steel members according to the AISI S100-16 / CSA S136-16 is available in RFEM 6. Design can be accessed by selecting “AISC 360” or “CSA S16” as the standard in the Steel Design Add-on. “AISI S100” or “CSA S136” is then automatically selected for the cold-formed design.
RFEM applies the Direct Strength Method (DSM) to calculate the elastic buckling load of the member. The Direct Strength Method offers two types of solutions, numerical (Finite Strip Method) and analytical (Specification). The FSM signature curve and buckling shapes can be viewed under Sections.
Did you use the eigenvalue solver of the add-on to determine the critical load factor within the stability analysis? In this case, you can then display the governing mode shape of the object to be designed as a result.
The Aluminum Design add-on provides you with further options. Here you can also design general cross-sections that are not predefined in the cross-section library. For example, create a cross-section in the RSECTION program and then import it into RFEM/RSTAB. Depending on the design standard used, you can select from various design formats. This includes, for example, the equivalent stress analysis.
With a license for RSECTION and Effective Sections, you can also perform the design checks while taking into account the effective cross-section properties according to EN 1993‑1‑5.
Design of foundation torsion and limitation of gaping joint
Sliding design
Settlement calculation
Bending failure design of the plate and bucket
Punching shear design
Foundation and bucket dimensions can be user-defined or determined by the module. You can edit the determined reinforcement manually. In this case, the designs are updated automatically.
In the "Shear Reinforcement" tab, you can select the option "Cross-ties over free rebars with active selection in graphic". It allows you to arrange additional cross-ties on free rebars of the longitudinal reinforcement.
You can activate or deactivate the position of the cross-ties in the Info Graphic. The cross-ties are applied for the ultimate limit state design and the structural design checks. They are available for the design according to EN 1992‑1‑1.
The Concrete Design add-on allows you to design fiber-reinforced concrete components according to the guideline "DAfStb Steel Fiber-Reinforced Concrete".
You can use this option for the design according to EN 1992‑1‑1. The design according to the DAfStb guideline is carried out once the concrete of the "Fiber Concrete" type has been assigned to the reinforced structural component.
Foundations are assigned graphically by selecting supports using the [Select] function in the graphical user interface of RFEM/RSTAB and by specifying the load cases to be designed. You can define all other foundation details quickly and easily in clearly arranged input windows.
In addition to all support forces from RFEM/RSTAB, you can specify further loads to be considered when dimensioning the foundations. The following additional loadings are available:
Pemanent surface load due to earth covering
Negative surface load; for example, due to traffic
Ground water level for uplift consideration
Concentrated loads in any position on the foundation plate
Line loads with any distribution over the foundation plate
The Concrete Design add-on allows you to perform the seismic design of reinforced concrete members according to EC 8. This includes, among other things, the following functionalities:
Seismic design configurations
Differentiation of the ductility classes DCL, DCM, DCH
Option to transfer the behavior factor from a dynamic analysis
Check of the limit value for the behavior factor
Capacity design checks of "Strong column - weak beam"
Detailing and particular rules for curvature ductility factor
Detailing and particular rules for local ductility
The program creates a reinforcement proposal for the top and the bottom plate reinforcement. The program searches automatically for the most favorable reinforcement combination, with a mat and added rebars. If required, the rebars are distributed across two reinforcement areas by curtailment. It is possible to modify the reinforcement proposal individually by:
Application of another mat type
Individual control of diameter and spacing of added rebars
Free selection of reinforcement area widths
Individual curtailment of reinforcements
You can display the foundation in excellent rendering quality, including reinforcement. In the rendering, as well as in up to seven different dimensioned reinforcement drawings ready for construction, the module provides a solution proposal for bucket design. It is possible to modify the number, position, diameter, and spacing of used rebars here as well. You can also determine the shape of the applied links.
The dimensions of the foundation plate and bucket can be determined by the add-on module, or can be user-defined. Clearly arranged windows display the results of each performed design, including all intermediate values. They are covered in a reduced printout report providing a verifiable structural analysis.
Determination of longitudinal, shear, and torsional reinforcement
Representation of minimum and compression reinforcement
Determination of neutral axis depth, concrete and steel strains
Design of member sections affected by bending about two axes
Design of tapered members
Determination of deformation in state II, for example according to EN 1992-1-1, 7.4.3
Considering tension stiffening
Considering creep and shrinkage
Precise breakdown of reasons for failed design
Design details of all design locations for better traceability of reinforcement determination
Options to optimize cross‑sections
Visualization of concrete section with reinforcement in 3D rendering
Output of complete steel schedule
Fire resistance design according to the simplified method (zone method) according to EN 1992‑1‑2 for rectangular and circular cross‑sections
Optional extension of the RF‑CONCRETE Members add‑on module with a nonlinear calculation of frameworks for the ultimate and serviceability limit states. The extension enables the design of potentially unstable structural components by means of a nonlinear calculation, or a nonlinear deformation analysis of 3D frameworks. Find more information under the product description of the RF-CONCRETE NL add‑on module.
Before the calculation starts, you should check the input data using the program function. Then, the CONCRETE add‑on module searches the results of relevant load cases, load as well as result combinations. If these cannot be found, RSTAB starts the calculation to determine the required internal forces.
Considering the selected design standard, the required reinforcement areas of the longitudinal and the shear reinforcement as well as the corresponding intermediate results are calculated. If the longitudinal reinforcement determined by the ultimate limit state design is not sufficient for the design of the maximum crack width, it is possible to increase the reinforcement automatically until the defined limit value is reached.
The design of potentially unstable structural components is possible using a nonlinear calculation. According to a respective standard, different approaches are available.
The fire resistance design is performed according to a simplified calculation method in compliance with EN 1992‑1‑2, 4.2. The module uses the zone method mentioned in Annex B2. Furthermore, you can consider the thermal strains in the longitudinal direction and the thermal precamber additionally arising from asymmetrical effects of fire.
Stability analyses for flexural buckling, torsional buckling, and flexural-torsional buckling under compression
Lateral-torsional buckling analysis of the structural components subjected to moment loading
Import of the effective lengths from the calculation using the Structure Stability add-on
Graphical input and check of the defined nodal supports and effective lengths for stability analysis
Depending on the standard, a choice between user-defined input of Mcr, analytical method from the standard, and use of internal eigenvalue solver
Consideration of a shear panel and a rotational restraint when using the eigenvalue solver
Graphical display of a mode shape if the eigenvalue solver was used
Stability analysis of structural components with the combined compression and bending stress, depending on the design standard
Comprehensible calculation of all necessary coefficients, such as interaction factors
Alternative consideration of all effects for the stability analysis when determining internal forces in RFEM/RSTAB (second-order analysis, imperfections, stiffness reduction, possibly in combination with the Torsional Warping (7 DOF) add-on)
The deformation analysis according to the approximation method defined in standards (for example, deformation analysis according to EN 1992‑1‑1, 7.4.3) applies to the calculation of "effective stiffnesses" in the finite elements in accordance with the existing limit state of the concrete with or without cracks. These stiffnesses are used to determine the surface deformation by repeated FEM calculation.
The effective stiffness calculation of finite elements takes into account a reinforced concrete cross-section. Based on the internal forces determined for the serviceability limit state in RFEM, the program classifies the reinforced concrete cross-section as 'cracked' or 'uncracked'. If the tension stiffening at a section should be considered as well, a distribution coefficient (according to EN 1992-1-1, Eq. 7.19, for example) is used. The material behavior for the concrete is assumed to be linear-elastic in the compression and tension zone until the concrete tensile strength is reached. This is reached exactly in the serviceability limit state.
When determining the effective stiffnesses, creep and shrinkage are taken into account at the "cross-section level". The influence of shrinkage and creep in statically indeterminate systems is not taken into account in this approximation method (for example, tensile forces from shrinkage strain in systems restrained on all sides are not determined and must be considered separately). In summary, RF-CONCRETE Deflect calculates deformations in two steps:
Calculation of effective stiffnesses of the reinforced concrete cross-section assuming linear-elastic conditions
Calculation of the deformation using the effective stiffnesses with FEM
For the bending failure design, the governing locations of the column are analyzed for axial force and moments. In addition, locations with extreme values of shear forces are considered for the shear resistance design. During the calculation, it is determined whether a standard design is sufficient or whether the column with the moments has to be designed according to the second-order theory. These moments are then determined based on the previously entered specifications. The calculation has four parts:
Load-independent calculation steps
Iterative determination of governing loading taking into account a varying required reinforcement
Determination of the designed reinforcement for governing internal forces
Safety determination of all acting internal forces, including the designed reinforcement
In this way, RF-/CONCRETE Columns provides a complete solution of an optimized reinforcement concept and the resulting load actions.
All results can be evaluated and visualized in an appealing numerical and graphical form. Selection functions facilitate the targeted evaluation.
The printout report corresponds to the high standards of RFEM and -rstab RSTAB. Modifications are updated automatically. Furthermore, you can print the reduced report in a short form, including all relevant data and a user-defined cross-section graphic.
After the design, the punching checks are presented clearly and with all result details, so that traceability is guaranteed at all times. The provided and allowable shear stresses for the shear resistance design of a slab as well as various perimeters and reinforcement ratios are represented in detail. If necessary, a clarifying note is displayed.
The next result window lists the required longitudinal or punching reinforcement of each analyzed node. An explanatory graphic is also available. The design results can be clearly displayed with values in the work window. Furthermore, you can add all result tables and graphics into the global printout report of RFEM, which guarantees coherent documentation.
After the calculation, the module shows clearly arranged tables listing the required reinforcement and the results of the serviceability limit state design. All intermediate values are included in a comprehensible manner.
The results of RF‑CONCRETE Members are displayed as result diagrams of each member. The reinforcement proposals of the longitudinal and the shear reinforcement, including sketches, are documented in accordance with current practice. It is possible to edit the reinforcement proposal and to adjust, for example, the number of members and the anchorage. The modifications will be updated automatically. A concrete cross‑section, including reinforcement, can be visualized in a 3D rendering. This way, the program provides an optimal documentation option to create reinforcement drawings, including steel schedule.
The results of RF-CONCRETE Surfaces can be displayed graphically as isolines, isosurfaces, or numeric values. It is possible to sort the longitudinal reinforcement display by required reinforcement, required additional reinforcement, provided basic or additional reinforcement, and provided total reinforcement. The isolines of the longitudinal reinforcement can be exported as a DXF file for further use in CAD programs as a basis for reinforcement drawings.
With the Concrete Design add-on, you can perform the fatigue design of members and surfaces according to EN 1992‑1‑1, Chapter 6.8.
For the fatigue design, you can optionally select two methods or design levels in the design configurations:
Design Level 1: Simplified design according to 6.8.6 and 6.8.7(2): The simplified design is performed for frequent action combinations according to EN 1992‑1‑1, Chapter 6.8.6 (2), and EN 1990, Eq. (6.15b) with the traffic loads relevant in the serviceability state. A maximum stress range according to 6.8.6 is designed for the reinforcing steel. The concrete compressive stress is determined by means of the upper and lower allowable stress according to 6.8.7(2).
Design Level 2: Design of damage equivalent stress acc. to 6.8.5 and 6.8.7(1) (simplified fatigue design): The design using damage equivalent stress ranges is performed for the fatigue combination according to EN 1992‑1‑1, Chapter 6.8.3, Eq. (6.69) with the specifically defined cyclic action Qfat.
The nonlinear deformation analysis is performed by an iterative process considering the stiffness in cracked and non-cracked sections. The nonlinear reinforced concrete modeling requires definition of material properties varying across the surface thickness. Therefore, a finite element is divided into a certain number of steel and concrete layers in order to determine the cross-section depth.
The mean steel strengths used in the calculation are based on the 'Probabilistic Model Code' published by the JCSS technical committee. It is up to the user whether the steel strength is applied up to the ultimate tensile strength (increasing branch in the plastic area). Regarding material properties, it is possible to control the stress-strain diagram of the compressive and tensile strength. For the concrete compressive strength, you can select a parabolic or a parabolic-rectangular stress-strain diagram. On the tension side of the concrete, it is possible to deactivate the tensile strength as well as to apply a linear-elastic diagram, a diagram according to the CEB-FIB model code 90:1993, and concrete residual tensile strength considering the tension stiffening between the cracks.
Furthermore, you can specify which result values should be displayed after the nonlinear calculation at the serviceability limit state:
Deformations (global, local based on non-/deformed system)
Crack widths, depths, and spacing of the top and bottom sides in principal directions I and II
Stresses of the concrete (stress and strain in principal direction I and II) and of the reinforcement (strain, area, profile, cover, and direction in each reinforcement direction)
RF-CONCRETE Members:
The nonlinear deformation analysis of beam structures is performed by an iterative process considering the stiffness in cracked and non-cracked sections. The material properties of concrete and reinforcing steel used in the nonlinear calculation are selected according to a limit state. The contribution of the concrete tensile strength between the cracks (tension stiffening) can be applied either by means of a modified stress-strain diagram of the reinforcing steel, or by applying a residual concrete tensile strength.
The nonlinear calculation is activated by selecting the design method of the serviceability limit state. You can individually select the analyses to be performed as well as the stress-strain diagrams for concrete and reinforcing steel. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, arrangement of layers over cross-section depth, and damping factor.
You can set the limit values in the serviceability limit state individually for each surface or surface group. Allowable limit values are defined by the maximum deformation, the maximum stresses, or the maximum crack widths. The definition of the maximum deformation requires additional specification as to whether the non-deformed or the deformed system should be used for the design.
RF-CONCRETE Members
The nonlinear calculation can be applied to the ultimate and the serviceability limit state designs. In addition, you can specify the concrete tensile strength or the tension stiffening between the cracks. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, and damping factor.
Free definition of two or three reinforcement layers in the ultimate limit state
Vectorial representation of the main stress directions of internal forces allowing optimal orientation adjustment of the third reinforcement layer to the actions
Design alternatives to avoid compression or shear reinforcement
Design of surfaces as deep beams (theory of membranes)
Option to define basic reinforcements for top and bottom reinforcement layers
Definition of designed reinforcement for serviceability limit state design
Result output in points of any selected grid
Optional extension of the module with nonlinear deformation analysis. The calculation is performed in RF‑CONCRETE Deflect by reducing the stiffness according to the standard, or in RF‑CONCRETE NL by the general nonlinear calculation determining the stiffness reduction in an iterative process.
Design with design moments at column edges
Precise breakdown of reasons for failed design
Design details of all design locations for better traceability of reinforcement determination
Export of isolines for the longitudinal reinforcement in a DXF file for further use in CAD programs as a basis for reinforcement drawings