a selection of features in more detail - … nordic...2016 / 5 prestress prestressing applications...

A Selection of Features in more

Detail

Prestressing

Example - Precast Pre-tensioned Beam

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Prestressing

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Prestressing

Different types of pre-stressing

• Internal / external tendons.

• Bonded / unbonded tendons

• Pre- and post-tensioning.

• For beam- & shell –elements

• In haunched beam/plate

Definition

• 3D Geometry (spline, polyline, etc.)

• Free-shape modelling in AutoCAD

• Graphical editor

• Eccentric duct position.

• Integrated in CABD (= axis-based)

Modelling/Analysis

• Detailed loss calculation, including friction, wedge slip,

time-dependent effects etc.

• Construction sequence

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Prestressing

Applications for Bridges/Buildings:

• Longitudinal post-tensioning

• Transversal post-tensioning

• Post-tensioned slabs

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Prestressing


• Local and global

• Tension band for arches

• Free cantilever with many stages

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Prestressing


• Precast post-tensioned beams

• Precast pre-tensioned beams

• Simple or composite section?

• Construction stages?

• Short and long term losses?

• Force transfer length?

Example – Precast Pre-tensioned Beam

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Simple or composite section?

Composite: After the beam is erected to its final position, it will be completed with

an in-situ deck. The cross section report from Module Aqua will look like this:

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Construction Stages?

• Yes: We will use construction stages so that we can differentiate between

the precast section and the end section including the slab portion of the

beam, as different loads act on different stages.

• It is important to define the construction sequence before starting with

modelling. The construction sequence might be something like this:

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Short term (immediate) losses?

• Elastic shortening of concrete Must be taken into account by using a factor

• Slip at anchorages immediately after prestressing Only for post-tensioning

• Friction between tendon and tendon duct, and wobble effect Only for post-tensioning

Long term (time dependent) losses?

• Creep and Shrinkage of concrete Will be calculated automatically in CSM

“creep steps”

• Relaxation of prestressing steel Will be calculated automatically in CSM

“creep steps”

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Force transfer length?

• The transfer length of prestressing

force is the length of cable measured

from the end of the prestressed

element along which the effective

stress due to prestressing is

transferred to the concrete. The force

of pre-tensioning in the concrete

linearly increases along the transfer

length from a value of 0 at the end of

the element to the effective value of

prestressing stress on the length L

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Workflow:

1- Open new project

2- Define required materials

3- Define the prestressing system

4- Open SOFiPLUS for model creation

5- Create a new cross section in the “Cross Section Editor”

6- Create structural lines

7- Create support conditions

8- Create tendons


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Workflow:

9- Define and assign loads

10- Export model to SSD

11- Control the prestressing forces and immediate losses

12- Define the construction stages with task CSM

13- Calculate other required tasks

14- Control results


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Workflow: Special considerations

1- Open new project







8- Create tendons


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When working with composite sections, different material should be used for the

different cross section parts.

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1- Open new project







8- Create tendons


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Insert a new used defined prestressing system. In the Construction tab, set all values

which are relevant for the calculation of immediate losses in post-tensioning to zero.

Set the inner and outer diameters of the duct to the same value as “real” the tendon

diameter.

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1- Open new project







8- Create tendons


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Define a new solid section. Make sure you define two construction stages, according to our

stage definition: CS10 for the prefabricated part and CS40 for the cast in place portion

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1- Open new project







8- Create tendons


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Draw a structural line with group 10 and the defined t-beam as an eccentric cross

section.

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1- Open new project







8- Create tendons



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To create the support conditions, define a rigid link from the insertion point of the

structural line, to the actual support point at the bottom of the beam. Define structural

points with spring elements within group 10.

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1- Open new project







8- Create tendons



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In SOFiPLUS, any AutoCAD line can be converted into a tendon. Furthermore, already

created tendons can be copied as often as wanted.


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In the tendon properties wizard, set the

prestressing load case to 11 and choose

the prestressing system. It is important to

set the Stage No. of Stressing and the

Stage No. of Grouting to 11. This way, the

tendon will always be bonded to the

concrete. Select the method to “According

Stresses”. For the jacking procedure,

select “Tensioning”.


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Change the default option Enable

additional data from no to yes, and

choose the force transition length

(no anchor) to e.g. 2.0 m.

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14- Control results



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If immediate losses due to elastic shortening are to be considered, please take them into

consideration by using a factor while defining the prestressing system or when performing

the design combinations.

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14- Control results



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Choose the following Stages definition and Groups definition. The superimposed dead loads

and long term creep effects will act on the composite cross section. All other loads will act

on the precast section.


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In reality CS10 and 11 happen at the same time, meaning that when the prestressing

tendons are cut and force is transferred to the cross section, a camber will occur. At this

same moment, the beam self-weight will create a deformation in opposite direction until an

equilibrium is reached

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14- Control results



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Check results: Animator, Result Viewer, Wingraf

LC 4000 Accumulated forces from the construction stage calculation

LC 5000 Individual results from the construction stage calculation (differences)

LC 6000 Creep and shrinkage results

LC 7000 General stress results


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LC 4010: Activation of precast segment

(no loads applied yet!)

LC 4011: Prestressing + segment self weight;

deformed geometry


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LC 4020: Self weight of wet concrete LC 4040: Hardening of in situ concrete

(no change in stresses!)


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LC 7011: Prestressing + activation of precast segment self weight ; stress distribution on

the cross sections


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LC 5011: Forces along the beam (Nx, My)


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LC 6015: Long term prestressing losses along the beam (Nx, My)

a selection of features in more detail - … nordic...2016 / 5 prestress prestressing applications...

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