Actions on Element Ends
Element End Displacement – load types DGB, DGE, DLB, DLE (formerly VGA, VGE, VLA, VLE)
The load types "Element end displacement" do not prescribe a global displacement value to the point, where it is assigned, but it induces a displacement difference between the specified element end and the nodal point to which it is connected. I.e. a gap or overlapping distance between the element end and the appropriate node is prescribed. The global deformation behavior is calculated as a reaction of the structural system to this prescription.
This load type is for instance typically used for simulating support settlements. In this case, an element end displacement in the vertical direction will be applied on the support element (typically a spring element with one node fixed). The respective node will be moved by the specified amount in relation to the elastic element end. When the node is fixed, the specified movement will result in a movement of the elastic element end in opposite direction.
Example: This example describes a 5 mm downward support settlement (displacement) of a bridge pier. This settlement is simulated by an element end displacement in the global Y direction applied at the element begin of the support element (e.g. spring element 501). By applying a global element end-displacement (DGB) Vy or a local element end-displacement (DLB) Vx of +0.005 m the program will try to move the start node upwards by that amount. But as the start node is restrained the element begin will be moved downwards by 5 mm instead.
If these load types are applied to an element of the superstructure, the resulting deformations will represent an influence line for the respective internal force at the regarded point.
The Element end displacements may be specified at the begin (DGB, DLB) or end (DGE, DLE) of an element, and they may be defined either in the global (DGB, DGE) or in the local (DLB, DLE) coordinate system. In case of eccentric connection, any element end deformations defined in the local direction system are applied at the position of the elastic element end, whereas deformations defined in terms of global direction components are applied in the position of the node. This is analogous to the convention for hinge definition.
Mind the sign conventions: The element end displacements are defined as vectors from the element end to the displaced node in the regarded coordinate system, i.e. the node is moved away from the element end by the specified amount. This convention applies also to rotations, where the node is rotated right hand turning in relation to the original position at the element end.
| Load Type | Description |
|---|---|
| DGB | (VGA) End-displacement (global – at the start node) – Prescribed displacements and/or rotations (right-hand turning) of the start node with respect to the element begin, defined in the global coordinate system. |
| DLB | (VLA) End-displacement (local – at the start node) – Prescribed displacements and/or rotations (right-hand turning) of the start node with respect to the element begin, defined in the local coordinate system. |
| DGE | (VGE) End-displacement (global – at the end node) – Prescribed displacements and/or rotations (right-hand turning) of the end node with respect to the element end, defined in the global coordinate system. |
| DLE | (VLE) End-displacement (local – at the end node) – Prescribed displacements and/or rotations (right-hand turning) of the end node with respect to the element end, defined in the local coordinate system. |
Element End Displacement without Static Effect – load types DSPLA, DSPLE
| Load Type | Description |
|---|---|
| DSPLA | The input for applying a displacement to the beginning of the element is prepared with this load type. |
| DSPLE | The input for applying a displacement to the end of the element is prepared with this load type. |
These load sets cause no internal forces in the structure (no static effects).
The load sets are used for incremental launching method and later for nonlinear calculation.
Element removing – load type DEMO
| Load Type | Description |
|---|---|
| DEMO | Support removal – simulation of removing a previously active support element. This will typically but not necessarily be a spring element. |
- The sum of all the internal forces in the structure resulting from all applied permanent load cases accumulated from all the previous construction stages must be stored in a special load case (e.g.: STG-SUM).
- The accumulated internal forces of the specified element(s) from this specified load case are now automatically applied to the redefined structure and redistributed on the structure in accordance with the normal rules of static analysis. This case must be considered as a normal load case and must be combined with all other previous load cases to get the total result.
Cable end displacement correction – load type DISCOR
Construction state kink correction – load type CSCORB
| Load Type | Description |
|---|---|
| CSCORB | In construction stage analyses there often arises the problem that previous deformations of the end cross-section of the previous construction stage cannot be neglected when the elements of the new stage are connected, i.e. the kink between the deformed position of the previously active element end and the start point of the new element series as placed in the defined position in accordance with the design shape needs to be closed. This load type allows for closing this kink. |
Fabrication shape – load type FSHP
Whenever pre-cast or prefabricated segments are used to assemble bridge superstructures, they usually get a shape, which deviates to some extent from the theoretical design shape in order to achieve the required design shape of the final structure. These deviations must be taken into consideration in structural analyses, at least in the case of geometric non-linearity and in the case of construction stage analyses, where the deformations of the previously active structure have to be taken into account when new elements are activated (erection control analysis). Otherwise, the results will not be accurate and consistent.
Normally, these geometry deviations are tangential deviations of the end cross-sections of the different segments, deviations of the segments length and any torsional rotation difference between start cross-section and end cross-section. These basic values can be prescribed by using the load type FSHP. The data correspond to the data of the load types DLB and DLE, i.e. they are defined in the local coordinate system of the respective elements and specify displacement and rotation differences between element begin and start node, or between element end and end node respectively.
The length changes (dVx) are herewith always defined at the element begin like the parameters of DLB, and the torsional rotations (Rxe) at the element end (Rxe) like the parameters of DLE. The tangential deviations of the end cross-sections (Rya, Rye, Rza, Rze) can be specified for both, the element-begin and the element-end. A curved shape along the element length cannot be specified.