The previous article, titled Lateral-Torsional Buckling in Timber Construction | Examples 1, explains the practical application for determining the critical bending moment Mcrit or the critical bending stress σcrit for a bending beam's lateral buckling using simple examples. In this article, the critical bending moment is determined by considering an elastic foundation resulting from a stiffening bracing.
When performing structural calculations, the derivation of forces from the roof to the foundations is one of the central tasks of the calculation, in addition to the dimensioning of the cross-sections.
Steel-fiber-reinforced concrete is mainly used nowadays for industrial floors or hall floors, foundation plates with low loads, basement walls, and basement floors. Since the publication in 2010 of the first guideline about steel-fiber-reinforced concrete by the German Committee for Reinforced Concrete (DAfStb), a structural engineer can use standards for the design of the steel fiber-reinforced concrete composite material, which makes the use of fiber-reinforced concrete increasingly popular in construction. This article describes the nonlinear calculation of a foundation plate made of steel fiber-reinforced concrete in the ultimate limit state with the FEA software RFEM.
Steel-fiber-reinforced concrete is mainly used nowadays for industrial floors or hall floors, foundation plates with low loads, basement walls, and basement floors. Since the publication in 2010 of the first guideline about steel-fiber-reinforced concrete by the German Committee for Reinforced Concrete (DAfStb), a structural engineer can use standards for the design of the steel fiber-reinforced concrete composite material, which makes the use of fiber-reinforced concrete increasingly popular in construction. This article explains the individual material parameters of steel-fiber-reinforced concrete and how to deal with these material parameters in the FEM program RFEM.
With RF-FOUNDATION Pro, it is possible to determine the settlements of single foundations and resulting spring stiffnesses of the nodal supports. These spring stiffnesses can be exported into the RFEM model and used for further analyses.
RFEM and RSTAB offer different options to model bored piles. One option is to display bored piles as single-valued supports or hinged columns. Another option is realistic modeling while taking the soil into account by means of applying a member elastic foundation. The two following examples will describe it in detail. However, pile base resistance, skin friction, and soil layers are not considered in this technical article.
The RF-/FOUNDATION Pro add‑on module designs single foundations (foundation plates, bucket and block foundations) for all support forces arising in the RFEM/RSTAB model. The geotechnical designs are performed according to EN 1997-1.
Using RF-/FOUNDATION Pro, it is possible to perform geotechnical design according to EN 1997-1 [1] for single foundations. The following article explains the design of highly eccentric loading in the foundation core according to DIN EN 1997‑1, A 6.6.5 (see [3]).
Using RF-/FOUNDATION Pro, it is possible to perform geotechnical design according to EN 1997‑1 [1] for single foundations. Subsequently, the program displays detailed information about the influence of the ground water level on the selected design according to EN 1997‑1.
The product range of Dlubal Software contains various modules for the design of steel and timber connections. The RF-/JOINTS Steel – Column Base add-on module allows you to analyze footings of hinged or restrained steel column bases. The fastener selection, foundation geometry, and material quality are crucial for the cost-effective and safe design of the column base.
In addition to the reinforced concrete design according to EN 1992‑1‑1, RF-/FOUNDATION Pro allows you to perform geotechnical designs according to EN 1997‑1. In RF-/FOUNDATION Pro, the design of the allowable soil pressure is performed as a ground failure resistance design. If you select CEN as National Annex, you have two options for defining the ground failure resistance. First, you can directly specify the allowable characteristic value of the soil pressure σRk. Second, there is also the option to analytically determine the bearing capacity according to [1], Annex D.
A previous article presented different variants of surface elastic foundations in addition to the traditional subgrade reaction modulus method. The following article describes another method for surface foundation. This method considers the adjacent ground areas by means of a foundation overlap. In this case, foundation parameters refer to the continuing works by Pasternak and Barwaschow.
A structural analysis does not only determine and design internal forces and deformations. It also ensures that the forces and moments in a structure are generated in a reliable way and applied to the foundation. Dlubal Software provides a wide range of products for the structural analysis and design of steel and timber connections. The RF-/JOINTS Steel – Column Base add-on module allows you to design footings of hinged and restrained column bases. The design can be performed for column base plates with or without stiffeners.
For the serviceability limit state design according to Section 6.6 of Eurocode EN 1997‑1, settlement has to be calculated for spread foundations. RF-/FOUNDATION Pro allows you to perform the settlement calculation for a single foundation. For this, you can chose between an elastic and a solid foundation. By defining a soil profile, it is possible to consider several soil layers under the foundation base. The results of the settlement, foundation tilting, and vertical soil contact stress distribution are displayed graphically and in tables to provide a quick and clear overview of the calculation performed. In addition to the design of the foundation settlement in RF-/FOUNDATION Pro, the structural analysis determines the representative spring constants for the support and can be exported to the structural model of RFEM or RSTAB.
The RF‑PUNCH Pro add‑on module allows you to perform the punching shear design of floor slabs and foundation plates according to EN 1992‑1‑1. In the case of a floor slab, the basic control perimeter is applied according to 6.4.2 (1), EN 1992‑1‑1 [1] at a distance of 2d from the loaded area.
A foundation is usually created in RFEM using the subgrade reaction modulus method. The reason for this is the relatively easy and straightforward manageability. Also, no iterative calculations are necessary and the computing time is relatively short. The subgrade reaction means that, for example, a foundation plate is loaded flat elastically.
For structural components consisting of slabs, it is necessary to perform shear design on the locations with concentrated load introduction, applying the punching shear design rules according to Sect. 6.4 of EN 1992‑1‑1 [1]. The concentrated load introduction is present on the individual locations; for example, by columns, concentrated load, or nodal supports. In addition, the end of linear load introduction on slabs is also regarded as concentrated load introduction. For example, this includes wall ends, wall corners, and ends or corners of line loads and line supports. You can perform the punching shear design for floor slabs or foundations, considering the existing available plate topology about the designed node of punching shear. The punching shear design according to EN 1992‑1‑1 checks that the acting shear force vEd does not exceed the resistance vRd.
Nodal supports are usually defined with regard to the global axis system. However, it is sometimes necessary to rotate the nodal support. For example, for a floor slab with a pile foundation. For geological reasons, the piles do not rest in the ground vertically, but in an inclined position. Each end point of the piles has a nodal support that can only absorb forces along the pile foundation direction. Therefore, rotating the nodal support is required. Various options for this are described in previous posts.
As of program version x.06.1103, you can enter a soil profile in RF‑/FOUNDATION Pro. This gives you the advantage of setting several soil layers with different soil parameters above and below the foundation base. To enter the soil layers, there is a library with various soil types that can also be extended with user‑defined soils. The user-defined soil profile is shown in an interactive information graphic. Any change (for example, a soil thickness modification) is reflected in the graphic immediately.
Various optimizations are available with program version x.06.1103. The RF-/FOUNDATION Pro add-on module has also been subjected to further development.
RF‑/FOUNDATION Pro introduced the geotechnical design of single foundations according to EN 1997‑1 in RFEM 5 and RSTAB 8. Depending on the National Annex preset in the add‑on module, you can determine the bearing resistance using Approach 2 or 3 in compliance with EN 1997‑1 up to Version x.04.0108.
The national parameters of EN 1992‑1‑1 for each country can be exported from RF‑/CONCRETE, RF‑/CONCRETE Columns, and RF‑/FOUNDATION Pro. To do this, there are interfaces with MS Excel, OpenOffice, and CSV. By exporting the national parameters, you can edit them in (for example) MS Excel, and display possible differences between the individual National Annexes clearly (see the image).
If a model should contain members with elastic foundations, the contact forces and moments are displayed in numerical form in the result windows. The graphical display of results is specified by the "Members" entry in the Results Navigator.
The updated Results Navigator of RF‑JOINTS allows you to display the results of different module cases simultaneously. Thus, you can display all column base designs at the same time in order to perform collision checks of the foundations, for example.
In RFEM 5 as well as RSTAB 8 in RF-/FOUNDATION Pro, you can save the foundation dimensions for all five foundation types as foundation templates in a user-defined database and use them later in other models.
In RF-/FOUNDATION Pro, the foundation design requires the definition of the corresponding loading (load cases, load combinations, or result combinations) for different design situations (STR, GEO, UPL, or EQU).