Building blocks and materials

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Overview

A model in Optum Concrete Solution comprise a total of seven different types of building blocks. A building block is a family of e.g. walls, and each instance of a building block are a part of that family. Changing a building block will affect all instances of that particular block, which makes it easy and fast to update the size of windows, change concrete strength, change rebar diameter and so on.

When creating a new model, a standard set of blocks is created. These can be modified, copied, and deleted to suit any project.

All blocks can be name, given a description and a colour, which can be used to easily identify instances of different families within the model. All blocks have an auto-generated name, which can be overwritten.

Materials

In OPTUM CS the basic materials are defined separately from the building blocks, and the building blocks then refer to the materials. Two materials are used, namely concrete and steel.

The materials are described by as few parameters as possible. The concrete is defined by a compression strength, a tension strength, and a Young’s modulus used for the elastoplastic analysis. An internal angle of friction of 37 degrees is assumed for the concrete material.

The steel is defined by a yield strength and a Young’s modulus. Generally, it is assumed that the steel only carries tension.

Walls

Walls are the primary building block of OPTUM CS. The block itself is defined by:

  • Thickness (given in mm)
  • Concrete (chosen from the list of concrete materials)
  • Steel (chosen from the list of steel materials)
  • Weight (given in kN/m³)

In addition to that, horizontal and vertical reinforcement meshes can be defined:

The reinforcement mesh is defined by diameter, number of layers, spacing, and anchorage. The anchorage defines how far from an edge, the full strength of the reinforcement mesh can be utilized.

If the reinforcement is fully anchored, e.g. using U-bar loops or similar, the anchorage length can be set to zero. When running an analysis, it can be selected as an option whether or not the anchorage should be included or not.

 Decks

Decks in OPTUM CS serve two purpoes:

  • They distribute load to supporting walls according to their span direction
  • They automatically create horizontal joints in intersecting walls

The block itself contains very little information. Besides the name, description, and colour, the only available field is the height of the deck. The height is used for the automatic creating of horizontal joints.

Holes

In OPTUM CS there are two different types of hole blocks: The freely sized hole block, where no width or height is given, and the sized hole, where the width and height is specified on the block.

The freely sized hole allow you to create holes of any size, since the width and height of the hole is not a part of the block. This also means that the width and height of the hole cannot be controlled by simply updating the block.

In many structures, several holes will have the same dimensions, and in those cases it makes sense to create a sized hole block. Doing so means that updating the size of the block affects all instances of the block, thus, making it easier to handle changes.

Reinforcement

The reinforcement block is used for stirrups as well as beam and column reinforcement. A reinforcement block contains two sets of bars and stirrups:

The reinforcement block will overwrite any reinforcement in the wall, i.e. the mesh reinforcement of the wall will be replaced by stirrups and bars of the reinforcement block.

The bars are modelled as discrete bars using bar elements, while the stirrups are modelled as smeared reinforcement. The coverage of the reinforcement block indicates the cover layer of the bars. The stirrups are placed from edge to edge of the defined area. OPTUM CS automatically sets the orientation of bars and stirrups in a defined area, however, this can be overwritten manually if needed.

For stirrups, a layer is given as well. This layer indicates how many (single) bars are in a cross section, and the typical stirrup will correspond to two layers. For wide beams, more stirrups might be needed, and the layers can be increased accordingly. Modelling-wise, doubling the layers is equivalent to halving the spacing.

Below the properties are a small sketch which shows the bars and stirrups of the reinforcement block. The diameter of the bars are relative, hence, the Ø16 bars above appear larger than the Ø10 bars in the sketch.

Rebars

The rebar block represents stringer reinforcement and other discrete rebars, which should not be modelled as smeared reinforcement. Reinforcement defined by the rebar block is modelled as discrete bar elements for the calculations.

The block itself is defined by

  • Steel (chosen from the list of steel materials)
  • Diameter of the rebar
  • Number of bars
  • Anchorage force at the ends of the rebar

In some cases, it can be convenient to use e.g. two Ø20 bars instead of one Ø32, which can be done by adjusting the number of bars.

Per default, the normal force at an free end of a bar element is zero, which corresponds to a bar without any U-bars or similar for anchorage. If necessary, an anchorage force can be specified for either end of the block, which means that the force at the end no longer is required to be zero, and the rebar can be utilised at the very end.

Vertical joints

Vertical joints are used to divide walls into precast elements. The block comprises an interface as well as reinforcement. The behaviour of the interface is defined by the cohesion, the coefficient of friction and the tensile strength.

The reinforcement in the joint is given by a steel material, diameter, layers, and a spacing. Two layers corresponds to a typical loop reinforcement (U-bar).

Horizontal joints

Whenever a wall intersects a deck, a horizontal joint is automatically added. Unlike the rest of the blocks, horizontal joints cannot be added manually, and the button in the ribbon is a “mode” rather than a creation tool.

The horizontal joint comprises three parts: Two interfaces and a concrete core. The upper interface, i.e. between the concrete core and the wall above, cannot be reinforced, and only cohesion, tensile strength, and friction coefficient can be specified.

For the lower interface, on the other hand, it is possible to define reinforcement. For the interface itself cohesion, tensile strength and friction coefficient can be specified, and for the reinforcement a steel material, diameter, layers, and a spacing can be specified.

The concrete core requires a concrete material and a self-weight. In addition to the concrete, horizontal stringer reinforcement can be specified via a steel material, diameter and layers (or number of bars). The extruding reinforcement from the lower interface is used as the vertical reinforcement in the concrete core.

Supports

In OPTUM CS supports are implemented as a building block. Two types of supports are available in the block, which can be selected from a drop-down:

Simple supports

For the simple support, the movement in the tangential and normal directions can be either fixed for free. The tangential and normal directions refer to the local directions of the support, and for e.g. a vertical edge will the normal direction be horizontal.

Friction supports

The friction support type adds conditions to the reactions. Using the friction coefficient, cohesion, tension capacity and (if needed) compression capacity the behaviour of the supports can be specified easily.

The friction supports have the following properties:

  • Friction type:
    • Specified if the friction criterion is given in terms of tractions or principal stresses (the difference is discussed below).
  • Cohesion parameter set:
    • A: Simply specify the cohesion in kN/m
    • B: Specify the cohesion according to the Eurocode 2, using a c-value, the concrete tensile strength and the width of the support. OPTUM CS then calculates the equivalent cohesion in kN/m.
  • Friction coefficient:
    • Usually between 0.5 (smooth) and 0.9 (indented, keyed).
  • Tension capacity:
    • Specifies the amount of tension given in kN/m, which can be anchored in the support.
    • If the limit is reached, the wall can separate from the support.
  • Compression capacity:
    • Specified the amount of compression given in kN/m, which the support can carry.
    • If the limit is reached, the wall can be pushed through the support.

Per default, the compression limit is turned off, but it can easily be activated by changing the drop down for “Compression limit?” to “Yes”. Finally, below the properties a dynamic diagram for the resulting support condition is shown.

Friction type:

The friction supports offers two models for the interaction between shear and normal forces in the support.

Left: Tractions, right: Principal stresses

Choosing Tractions means that the condition for the support is given solely in terms of the shear and normal forces.

Choosing Principal stresses, on the other hand, means that the principal stresses must obey the tension and compression limits. Using this condition means that for a tension capacity of zero, no shear can be transferred without compression.

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