In the Geotechnical Analysis add-on, the Hoek-Brown material model is available. The model shows linear-elastic ideal-plastic material behavior. Its nonlinear strength criterion is the most common failure criterion for stone and rocks.
You can enter the material parameters using
Rock parameters directly, or alternatively via
GSI classification.
Detailed information about this material model and the definition of the input in RFEM can be found in the respective chapter Hoek-Brown Model of the online manual for the Geotechnical Analysis add-on.
For calculation diagrams, the "2D | Hinge" is available. These hinge diagrams show the hinge response of load situations for nonlinear hinges.
For calculations with several load situations, such as is the case with pushover analyzes and time history analysis, you can evaluate the state of the hinge in each load step.
The Time History Analysis add-on provides you with accelerograms for the calculation. This extension allows for dynamic structural analysis of the acceleration-time diagrams.
There is an extensive library of earthquake records available for you, but you can also enter or import your own diagrams. The time history analysis is performed using the modal analysis or the linear implicit Newmark analysis.
The "Spring" member type is used to simulate linear and nonlinear spring properties via a linear object. This input function helps you to model the stiffness specifications in the force/displacement unit.
The time history analysis is performed with the modal analysis or the linear implicit Newmark analysis. The time history analysis in this add-on is limited to linear structural systems. Although the modal analysis represents a fast algorithm, it is necessary to use a certain number of eigenvalues to ensure the required accuracy of results.
The implicit Newmark analysis is a very precise method, independent of the number of eigenvalues used, but requires sufficient small time steps for the calculation.
You can simulate the static friction effects between two supporting components along a line using the "Friction" nonlinearity in the Line Release Type.
Did you know? In the Design Supports, you can now define fully threaded screws as transversal compression stiffening elements for the "Compression Perpendicular to Grain" design. In this case, the pressing-in and buckling of the bolts is analyzed.
Moreover, the design shear resistance is checked in the plane of the screw tip. The angle of dispersal can be considered as linear under 45° or nonlinear (according to Bejtka, I. (2005). Verstärkung von Bauteilen aus holz mit vollgewindeschrauben. KIT Scientific Publishing.).
Consideration of nonlinear component behavior using plastic standard hinges for steel (FEMA 356, EN 1998‑3) and nonlinear material behavior (masonry, steel - bilinear, user-defined working curves)
Direct import of masses from load cases or combinations for the application of constant vertical loads
User-defined specifications for the consideration of horizontal loads (standardized to a mode shape or uniformly distributed over the height of the masses)
Determination of a pushover curve with selectable limit criterion of the calculation (a collapse or limit deformation)
Transformation of the pushover curve into the capacity spectrum (ADRS format, single degree of freedom system)
Bilinearization of the capacity spectrum according to EN 1998‑1:2010 + A1:2013
Transformation of the applied response spectrum into the required spectrum (ADRS format)
Determination of target displacement according to EC 8 (the N2 method according to Fajfar 2000)
Graphical comparison of the capacity and required spectrum
Graphical evaluation of the acceptance criteria of predefined plastic hinges
Result display of the values used in the iterative calculation of the target displacement
Access to all results of the structural analysis in the individual load levels
During the calculation, the selected horizontal load is increased in load steps. A static nonlinear analysis is carried out for each load step until reaching the specified limit condition.
The results of the pushover analysis are extensive. On one hand, the structure is analyzed for its deformation behavior. This can be represented by a force-deformation line of the system (a capacity curve). On the other hand, the response spectrum effect can be displayed in the ADRS display (Acceleration-Displacement Response Spectrum). The target displacement is automatically determined in the program based on these two results. The process can be evaluated graphically and in tables.
The individual acceptance criteria can then be graphically evaluated and assessed (for the next load step of the target displacement, but also for all other load steps). The results of the static analysis are also available for the individual load steps.
What are plastic hinges? Very simple – plastic hinges according to FEMA 356 help you to create pushover curves. These are nonlinear hinges with preset yield properties and acceptance criteria for steel members (Chapter 5 of FEMA 356).
You probably already know that node, line, and surface releases are used to define transfer conditions between objects. For example, you can release members, surfaces, and solids from a line. It is also easily possible for the releases to have nonlinear properties, such as "Fixed if positive n", "Fixed if negative n", and so on.
Do you want to model and analyze the behavior of a soil solid? To ensure this, special suitable material models have been implemented in RFEM. You can use the modified Mohr-Coulomb model with a linear-elastic ideal-plastic model or a nonlinear elastic model with an oedometric stress-strain relation. The limit criterion, which describes the transition from the elastic area to that of the plastic flow, is defined according to Mohr-Coulomb.
Did you know that To calculate masonry structures, a nonlinear material model has been implemented in RFEM. It is based on the approach of Lourenco, a composite yield surface according to Rankine and Hill. This model allows you to describe and model the structural behavior of masonry and the different failure mechanisms.
The limit parameters were selected in such a way that the design curves used correspond to a normative design curve.
RFEM allows you to use a special line hinge to model the special properties of the connection between the reinforced concrete slab and masonry wall. This limits the transferable forces of the connection depending on the specified geometry. You guess right: This means that the material cannot be overloaded.
The program develops interaction diagrams that are applied automatically. They represent the various geometric situations and you can use them to determine the correct stiffness.
The calculation of masonry is carried out in compliance with the nonlinear-plastic material law. If the load at any point is higher than the possible load to be resisted, redistribution takes place within the system. This have the simple purpose of restoring the equilibrium of forces. With the successful completion of the calculation, the stability analysis is provided.
Are you familiar with the Tsai-Wu material model? It combines plastic and orthotropic properties, which allows for special modeling of materials with anisotropic characteristics, such as fiber-reinforced plastics or timber.
If the material is plastified, the stresses remain constant. The redistribution is carried out according to the stiffnesses available in the individual directions. The elastic area corresponds to the Orthotropic | Linear Elastic (Solids) material model. For the plastic area, the yielding according to Tsai-Wu applies:
All strengths are defined positively. You can imagine the stress criterion as an elliptical surface within a six-dimensional space of stresses. If one of the three stress components is applied as a constant value, the surface can be projected onto a three-dimensional stress space.
If the value for fy(σ), according to the Tsai-Wu equation, plane stress condition, is smaller than 1, the stresses are in the elastic zone. The plastic area is reached as soon as fy (σ) = 1; values greater than 1 are not allowed. The model behavior is ideal-plastic, which means there is no stiffening.
Did you know? In contrast to other material models, the stress-strain diagram for this material model is not antimetric to the origin. You can use this material model to simulate the behavior of steel fiber-reinforced concrete, for example. Find detailed information about modeling steel fiber-reinforced concrete in the technical article about Determining the material properties of steel-fiber-reinforced concrete.
In this material model, the isotropic stiffness is reduced with a scalar damage parameter. This damage parameter is determined from the stress curve defined in the Diagram. The direction of the principal stresses is not taken into account. Rather, the damage occurs in the direction of the equivalent strain, which also covers the third direction perpendicular to the plane. The tension and compression area of the stress tensor is treated separately. In this case, different damage parameters apply.
The "Reference element size" controls how the strain in the crack area is scaled to the length of the element. With the default value zero, no scaling is performed. Thus, the material behavior of the steel fiber concrete is modeled realistically.
Find more information about the theoretical background of the "Isotropic Damage" material model in the technical article describing the Nonlinear Material Model Damage.
Within a member, you can define the integration width and effective slab width of T-beams (ribs) with different widths. The member is divided into segments. You can either grade or specify the transition between the different flange widths as linearly variable. Furthermore, the program allows you to consider the defined surface reinforcement as a flange reinforcement for the reinforced concrete design of a rib.
Use the new useful structure modification object to modify or deactivate stiffnesses, nonlinearities, and objects in a clear and load case-dependent way.
Building stone on stone has a long tradition in construction. The Masonry Design add-on for RFEM allows you to design masonry using the finite element method. It was developed as part of the research project DDMaS - Digitizing the Design of Masonry Structures. Here, the material model represents the nonlinear behavior of the brick-mortar combination in the form of macro-modeling. Do you want to find out more?
Use the specification of the element types for members, surfaces, solids, and so on, to facilitate your input (such as member nonlinearities, member stiffnesses, design supports, and many others).
Also in this case, RSTAB will certainly convince you. With the powerful calculation kernel, its optimized networking and support of multi-core processor technology, the Dlubal structural analysis program is far ahead. This allows you to calculate more linear load cases and load combinations using several processors in parallel without using additional memory. The stiffness matrix only has to be created once. Thus, it is possible for you to calculate even large systems with the fast and direct solver.
Do you have to calculate multiple load combinations in your models? The program initiates several solvers in parallel (one per core). Each solver then calculates a load combination for you. This leads to better utilization of the cores.
You can systematically follow the development of the deformation displayed in a diagram during the calculation, and thus precisely evaluate the convergence behavior.
Stress determination using an elastic-plastic material model
Design of masonry disc structures for compression and shear on the building model or single model
Automatic determination of stiffness of a wall-slab hinge
An extensive material database for almost all stone-mortar combinations available on the Austrian market (the product range is continuously being expanded, for other countries as well)
Automatic determination of material values according to Eurocode 6 (ÖN EN 1996‑X)
You enter and model the structure directly in RFEM. You can combine the masonry material model with all common RFEM add-ons. This enables you to design the entire building models in connection with masonry.
The program automatically determines for you all parameters required for the calculation by using the material data that you have entered. Then, it finally generates the stress-strain curves for each FE element.
Was your design successful? Then just sit back and relax. You benefit from the numerous functions in RFEM also here. The program gives you the maximum stresses of the masonry surfaces, whereby you can display the results in detail at each FE mesh point.
Moreover, you can insert sections in order to carry out a detailed evaluation of the individual areas. Use the display of the yield areas to estimate the cracks in the masonry.
Have you activated the Time-Dependent Analysis (TDA) add-on? Very well, now you can add time data to load cases. After you have defined the start and end of the load, the influence of creep at the end of the load is taken into account. The program allows you to model creep effects for frame and truss structures made of reinforced concrete.
In this case, the calculation is performed nonlinearly according to the rheological model (Kelvin and Maxwell model).
Was the calculation successful? You can now display the determined internal forces in tables and graphics, and consider them in the design.
Did you know that Equivalent static loads are generated separately for each relevant eigenvalue and excitation direction. These loads are saved in a load case of the Response Spectrum Analysis type and RFEM/RSTAB performs a linear static analysis.