Actions
Activation
Each construction stage is related to a certain active system, which may contain all elements of the model or just a part of them. The activation of new elements is done in . Elements, which already have been activated in previous construction stages, remain active until they are explicitly deactivated, and must not be specified. An appropriate indication is given by the program in the case that a previously activated element is again specified. If the user then selects the option Overwrite, the element will be removed from the previous construction stage and added in the current stage.
The elements with changed activation settings are shown in the activation table in ascending order, without considering the input sequence. As far as possible, consecutive elements with same parameters are presented in one line with a from/to/step specification. Attention must be paid to the fact, that it is not possible to remove elements from the table by using the Modify button, because the From/To/Step entries of the modify function are not directly related to the respective line in the activation table. Deleting by mistake specified elements must be done with using the Delete button.
Age and ts are start values of the current elements for creep and shrinkage calculation, where age is the element concrete age at activation time (time of first load application to the elements) and ts is the concrete age when shrinkage starts. The activation time is normally the point in time when the prestressing occurs. This corresponds to the assumption that the self-weight is automatically activated with prestressing. With respect to shrinkage it is usually assumed, that shrinkage starts immediately after the first hardening phase (few hours after the pouring process), i.e. ts is zero. This implies that a certain amount of the total shrinkage strain has already occurred before activation, and does therefore not give stresses.
The values Age and ts are directly cross-linked to the values in the table of Structure |Elements |Time for automatic mutual update. Changes in the element table are considered in the activation table, and vice versa. Attention must be paid to the fact, that the correct values must essentially be entered in the activation input window, because the values of the element table are not taken as default values. On the contrary, the values in the element table are overwritten by the specified values in the activation input. The parameter Action of the activation table is ACT for elements being activated, and DACT for elements being deactivated in this construction stage.
The activation of elements may be checked visually by using the function ?Schedule ?Stage Simulation.
Creep and shrinkage models, imported or user defined (ñPropertiesðVariables), are required. Alternatively, creep and shrinkage may be calculated by using the models directly embedded in the RM Bridge Advanced program code, bypassing the variable definitions (ñFile ðOpti-mization Settings). This option leads to shorter calculation times for large projects. Further-more, the specified load case must have been created as an empty load case in the load definition menu.
Each time step is calculated as an internal load case. The differences of the time step load cases are summed up to the resulting creep and shrinkage load case and may be viewed in the load case pool (7.2.4). The time is split into either linear or logarithmic steps.
Taking into account prestressing steel relaxation requires the definition and assignment of the appropriate relaxation law, as well as specifying the relevant stress state as summation load case LcSum in the ñRecalc pad.
The definition of load cases is required (ñScheduleðLoad Definition). The load case is calculated and the results are listed and stored in the database (accessed in the load case pool. If a load manager definition is assigned to the load case, the load manager will be processed for automatic superposition after calculation.
Details of the applied calculation method depend on the options set in the ñRecalc pad.
In all other cases, when no element is given, the load positions are always calculated to obtain extreme MIN and MAX results for each element
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Table 7-10 Load train positions used for different inputs Result |
Load train position used, if the result point position P1 is specified |
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Requirement for the calculation of influence lines is the definition of traffic lanes (ñSchedule ðLoad Definition òTraffic Lanes). A reference load case may be optionally defined in order to take into account the stress state of the structure prior to the occurrence of the traffic loading. This is only used in non-linear calculations for calculating current tangential stiffness matrix. Mostly this reference load case will be the summation load case SumLC accumulated in the construction stage analysis.
Results are a list file, giving a protocol of the used unit loads, and a set of influence lines (stored in binary files *.inf) used for the influence line evaluation with the LiveL action, and for calculating the most unfavorable position of the load train in the action LiveSet.
| Setting | Description |
|---|---|
| SupInit | Initialise a new superposition file with zero results or with factored results of an existing superposition file. |
| SupAddLc | Superimpose load case results to a superposition file by unconditionally adding the results. |
| SupAddSup | Superimpose envelope results to a superposition file by unconditionally adding the results. |
| SupAndLc | Superimpose load case results to a superposition file by conditionally adding the results. New result values are added to existing minimum envelope values if they are negative and existing maximum envelope values if they are positive |
| SupAndSup | Superimpose envelope results to a superposition file by conditionally adding the results. New result values are added to existing minimum envelope values if they are negative and existing maximum envelope values if they are positive. |
| SupAndXLc | Superimpose load case results to a superposition file by adding the results with the appropriate positive or negative sign to get the most unfavorable results. |
| SupAndXSup | Superimpose envelope results to a superposition file by adding the results with the appropriate positive or negative sign to get the most unfavorable results. |
| SupOrLc | Conditional replacement of the superposition file results by given load case results. Load case results replace existing minimum envelope values if they are smaller and existing maximum envelope values if they are greater. |
| SupOrSup | Conditional replacement of the superposition file results by given load case results. Load case results replace existing minimum envelope values if they are smaller and existing maximum envelope values if they are greater. |
| SupOrXLc | Conditional replacement of the superposition file results by given load case results with positive or negative sign. The superposition rule SupOr is applied twice with given load case results of both signs. |
| SupOrXSup | Conditional replacement of the superposition file results by given envelope results with positive or negative sign. The superposition rule SupOr is applied twice with given envelope results of both signs. |
| SupSqr | The squares of all values in the given envelope are calculated and stored to a given superposition file or rewritten to the source envelope if no superposition file is given. A factor may be applied. |
| SupSqrt | The square roots of all values in the given envelope are calculated and stored to a given superposition file or rewritten to the source envelope if no superposition file is given. A factor may be applied. |
| SupComb | Apply a combination table to calculate an envelope as combination of factored load cases. The resulting envelope is often used for fiber stress checks (Action FibChk). |
| SupImp | Calculate a dynamic impact factor by comparison of envelopes from a dynamic and a static calculation. |
| Sup2D | Reduce given superposition file results to 2D with values Qz, Mx and My set to zero. This is intended to be used for design checks in vertical plane only. |
This action performs a modal analysis with evaluating a given response spectrum.
In this method, the relevant natural modes are multiplied by so-called mass participation factors and superimposed in a suitable manner. Thus, calculating the relevant natural modes is a prerequisite for performing this action.
Input-1 denotes the number of the calculated earthquake event of the respective table defined in ñSchedule ðLoad definition òEarthquake Load . The relevant parameters are there defined. These are the modal file (*.mod) containing the natural modes and participation factors, the superposition rule to be used and the response spectrum, which has to be defined before RespS can be started.
The defined response spectrum is valid for a certain damping ratio (e.g. standard spectrum for 5% damping in most design codes). As the effective damping is dependent on the material and structural details, it can therefore be different for different natural modes. Therefore, RM Bridge Advanced allows for working with different response spectra valid for different damping ratios. This is done by assigning several response spectra with the corresponding damping ratios in ñSchedule ðLoad definition òEarthquake load, and defining a damping table in ñProp-erties ðVariables, where the dependency of the structural damping from the natural mode or natural frequency is described.This table can be assigned in Input-3 to the calculation function. If no table is assigned, the program assumes that the first defined response spectrum is unconditionally valid.
The results of this action are stored to the given superposition file and are extreme forces and displacements. As the superposition rules are statistic, only leading values may be obtained. With the use of a special algorithm, called "TDV-Superposition method" (set in the ñRecalc-option as given in TDV mode superposition method), it is possible to obtain affiliated results in the superposition file.
The list file holds the complete spectrum definition and the response factors of the individual eigenmodes.
The action Eigen iteratively calculates the required number of eigenvalues and eigenvectors of the structure, starting with the lowest mode. The reference load case must include all mass definitions. In Eigen, the reference load case is at first calculated as a static load case. If the option Linear calculation is set in ñRecalc, the results of this reference load case are used as the initial state; otherwise, the results stored in SumLc are additionally taken into account for calculating any geometrically non-linear tangent stiffness matrix. Any mass definitions of load cases stored in SumLc are additionally considered, if the option Accumulate permanent loads is set.
RM Bridge Advanced uses a subspace iteration algorithm for detecting the eigenvalues and eigenvectors in a very efficient way. The size of the subspace matrix (number of iteration vectors), and the initial iteration vectors, are automatically chosen in the program in accordance with suggestions found in literature. These default settings will mostly allow for calculating all required eigenvalues in a very efficient way. However, special conditions of the mathematical model may occur, where not all required eigenvalues are found. In order to overcome such a problem, the user may increase the default number of subspace iteration vectors by a given value (Input3 (Subspace)), accepting a higher computation time (e.g. 10).
Eigenmodes are stored in the given output-file (*.mod) and results are listed in the specified list file. The list file contains the load definitions (masses), the results of the static calculation of the reference load case, the calculated eigenvalues (frequencies in Hertz) with the related participation factors, and a list with the diagonal terms of the mass matrix (nodal masses).
An alpha-numeric printout of the eigenvectors may be created with the action ListMod (see List/plot actions). This list also contains the eigenvalues in rad/sec (Omega) and in Hertz, together with the reference DOF (Node, DOF) being maximally excited (maximum value of the eigenvector being normalized the value 1.0). Further presented data are the parameters used in the modal analysis.
After the calculation, the eigenvectors are stored like static load cases, and the calculated number of load cases (n) can be accessed from the load case pool (named Outputfilename#n, with n being the eigenmode, e.g. Eigen01#3.mod). The load cases contain normalized eigenvectors as displacements and can be used later on for graphical presentations.