Example 9: Check of user-defined reinforcement pattern in a composite cross section of a column

Data for Cross Section Analysis & Design application

In this example we are going to create the geometry of a composite cross section, define rebars and check their capacity according to Eurocode 2.

Geometry of composite cross section with encased steel section

Regulation: Eurocode 2

Concrete (cylinder) strength: 20 MPa

Yield stress of reinforcement steel: 500 MPa

Reinforcement cover to rebar center: 4 cm

Steel grade: Fe 360

Tensile concrete strength is ignored.

Stirrup type: Tied

All remaining data (safety factors, other coefficients etc.) to be taken according to Eurocode 2.

Load cases
lc 1 N = -1000 kN My = 550 kNm Mz = 123 kNm
lc 2 N = -770 kN My = 140 kNm Mz = -365 kNm
Solution with Cross Section Analysis & Design

First of all define the corresponding Reinforced Concrete Code, by clicking on the Project -> Reinforced Concrete Code menu item.

Selection of Reinforced Concrete Code

Reinforced concrete regulation

Selection of Eurocode 2 regulation

The reinforcement ratio limits are to be calculated according to Eurocode 2, so we keep the default option checked.

Concrete materials form (only default concrete is specified)

Definition of material properties

Next, we are going to specify the material properties.

Concrete can be specified by selecting Materials -> Concrete

Definition of a new concrete grade C20

The Default Concrete material can be overridden by changing its properties, as shown in the form below.

Definition of a new reinforcement grade S500

Value “Concrete strength” has been set equal to 20 MPa. The concrete is not assumed confined and the elasticity modulus is to be calculated according to Eurocode 2, so we do not need to change anything else. The concrete defined here is now accessible through the name “C20”. Alternatively we could click the “Add new” button in order to define a new concrete material.

The reinforcement can respectively be defined from the Material -> Reinforcement menu item.

Importing a European hot rolled steel grade from library

We modify the Default Reinforcement material by specifying a new name (S500) and a yield stress of 500 MPa.

Finally we need to define the grade of the steel Fe 360. This steel grade can be imported from the library of the program by clicking on the Materials -> Import from Library menu item. From the top list we select “Hot Rolled Steel – European (no hardening)” in order to view the materials belonging to this collection.

Fe360 steel grade is available

Then, we can select the first row (Fe 360) and click on “Insert selected only” button to use this material in our project.

Fe 360 steel has been imported in our project. We can view/change its properties by clicking on it from the list of the main form, as shown in the picture below.

Properties of Fe260 steel grade including stress/strain curve, elasticity moduli, etc.

Alternatively, as Fe 360 steel is as bilinear material, it can be edited from the Materials -> Bilinear Materials menu item.

Properties of concrete section part

In this form, the stress/strain curve of Fe 360 hot rolled steel is represented. We do not need to change anything and click OK.

Drawing the geometry

We are now ready to draw the geometry of the cross section, by clicking the Draw -> Circle (2Points).

First of all we make sure that material “C20” has been selected in the shown form.

Then, we can specify the center point of the circle by entering its coordinates (0,0) and then clicking the Button to use current value button, or just by clicking on the point (0,0) with the mouse.

After that we need to define one point on the circle. This can be done by clicking at the point (0.30,0).

Drawing concrete circular section part

So, the circle is now defined and we can see it in the drawing area.

Concrete section part has been inserted

We can modify its properties by moving the mouse over it, right clicking and selecting “Properties” from the corresponding menu.

Showing properties of circular concrete section part

In this way, the “Circle” form is shown and we can view/change its data.

Properties of concrete section part (center point, point on circle, material)

Afterwards, we can insert a hot rolled section from the library by clicking the Draw -> Standard Section menu item.

Importing a European wide flange steel section from library

In this form, the collections of all sections of the library are represented. In order to insert a HEA-400 cross section, we select “European steel shapes” from the top list and then we choose the “HE400A” shape from the list below.

Specifying a HE400A section from library and its insertion point

The insertion point of the shape is selected to coincide with its centroid.

We should not forget to change the material for this section to Fe 360, as illustrated below.

Assigning Fe360 steel grade to the section imported from library

We click OK and see that the steel shape is shown in the main drawing area.

The imported steel section is placed at the specified insertion point

Furthermore, we need to draw the rebars, which will have a circular pattern.

But first let’s see if rebar sizes are defined. We select Project -> Available Rebars.

Available reinforcement bars in project

The rebars shown above are available in the project. This means that we can draw rebars of these diameters and additionally the program will only choose from these rebar sizes when performing a reinforcement design.

Now we are ready to draw the reinforcement bars by clicking on the Draw -> Rebar Circle menu item.

We can enter a value (0.05 m) for the reinforcement cover to the rebar center in the field, which becomes active when inserting reinforcement bars, as shown below. The program automatically draws help points at the specified distance from the concrete edges and enables mouse snapping.

Inserting a rebar circle taking advantage of the snap at specified cover distance

To draw the rebars, we click on (0,0) point and then on one of the available green points.

Properties of rebar circle

We change the rebar count to 8 and also check that the reinforcement material is “S500” and choose a rebar size, ø20.

After clicking the “OK” button, the lower rebars are shown in the drawing area.

Geometry of composite cross section (encased wide steel section in reinforced circular concrete part)

Review of Analysis Parameters

We need to specify the corresponding Analysis Parameters set by clicking Analysis -> Analysis Parameters. We will use the default “ULS” set. All parameters related to Eurocode can be found in this form. The concrete stress block is rectangular according to Eurocode 2 parameters, the tensile resistance of concrete is ignored and all remaining data have the default values. You can override these values by modifying any of the field of the form.

Setting analysis parameters for Ultimate Limit State

Definition of load cases

The load cases can be selected by clicking on the Analysis -> Reinforcement check -> Load cases menu item. The 2 load cases can be entered in the corresponding table. A new load case can be inserted by clicking the Add new load case button button. We make sure that the assigned Analysis Parameters set to each load case is ULS.

Specifying load cases for reinforcement check

Reinforcement check

We just click Analysis -> Reinforcement check -> Analyze, to perform the reinforcement design procedure.

Results

The results can be obtained from the Analysis -> Reinforcement check -> Show results menu item.

As we can see, the cross section is adequate for both load cases. This form reports the placed reinforcement ratio (9.42 ‰) which lies between the allowable limits (2‰ – 4%) calculated according to Eurocode 2 specifications.

Reinforcement check results (capacity ratio, required reinforcement ratio, etc.)

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