Creating a new construction stage

Procedure to create a new construction stage

Open the Construction stages manager.

Click button [New].

If no suitable load case is available, you are asked to create one.

A new construction stage is added to the list.

Click button [Edit] to open the editing dialogue.

Fill in the parameters (see below).

Confirm with [OK].

Close the Construction stages manager.

Parameters of a construction stage

Name	Defines the name of the stage.
Order of stage	(informative) Gives the sequence number of the stage.
Description	Contains a short description of the construction stage. It is useful to say in a few words what happens in the current construction stage. The comment helps the user to keep clear image of the construction process. The name is also used in the generated names of result classes and generated load case combinations. E.g. for combinations, this description is the only unambiguous identifier of the generated load case combinations. Note: It is highly recommended to use this field.
Last construction stage	Defines, whether the current stage is the last construction stage. If ON, then the next construction stage is the first service stage. The user cannot change the structure from that time, but he can add dead load and variable load (no prestressing!). Therefore no changes in configuration of the structure (changes of cross-section, prestressing, etc.) are possible in service stages. If a variable load is assigned to a construction stage before (including) the last construction stage, it is "consumed" and cannot be used again in another construction stage. If a variable load is assigned to a service stage (i.e. into a stage following after the last construction stage), it can be reused freely in another construction stage.
Load case	Selects the load case that is assigned to the construction stage. Note: Read the comment below the table.
Gamma min, Gamma max	Load factors. Note: Read the comment below the table.
Psi	Factor for variable load. Note: Read the comment below the table.
Variable load cases	Allows for input of a variable load case into the construction stage. Note: Read the comment below the table.

Load case permanent or long-term

A load case of type permanent or self-weight must be defined and assigned to a construction stage. One load case of this type must be exclusively assigned to each stage. The load case may be empty. As mentioned above, the load case applied in a construction (or service) stage can be of two types: permanent or self-weight. The input of a permanent load is done by standard way, but concerning the self-weight, there are two possibilities of the input.

(1) First possibility is via permanent loads. The self-weight of the 1D member is calculated by the user in advance and is specified as a uniform or trapezoidal load distributed along the length of the 1D member. This method can be used in combination with other permanent loads, e.g. the self-weight of diaphragms, surfacing, etc. The self-weight of the 1D member can be applied in any construction stage (at any time) independently from the time of installation of this 1D member. Therefore the input of the permanent load is not tied up with the 1D members or composite parts of 1D members added at the current (active) construction stage.

(2) Second possibility of the input of own weight can be applied only on 1D members added at the current (active) construction stage on added composite parts of 1D members. The appropriate load case must be of "self weight " type. No input of other loads is possible in such a load case. Therefore, if the "self-weight" load case is specified in current construction stage, only an increment of structural own weight is applied. The increment is defined as the self-weight of that part of the structure (structural elements or their composite parts) that is installed in the current construction stage.

The two approaches will be demonstrated on a simple example.

Example: Introduction of self-weight into the model

Let’s assume a beam of a T-cross-section that is made in two phases: (i) core cross-section, (ii) composite slab.

The cross-section consists of two stages: 1 = the "core" beam, 2 = the composite slab.

We’ll describe three model situations, two of which employ the first approach (user-calculated permanent load) and one of which uses the second one.

We do not say which situation is better and which one is worse, we just describe them here to explain the consequences of different approaches. It is up to the user to decide which procedure of modelling best reflects the unique conditions of a particular project.

Situation A (user-calculated self-weight)

Stage	Action	Load case assigned to construction stage
1	casting the beam (phase 1 of the cross-section is introduced into the model)	empty permanent-standard load case
2	casting the composite slab (phase 2 of the cross-section is introduced into the model)	empty permanent-standard load case
3	introduction of the manually calculated self weight	permanent-standard load case with defined load that represents the self-weight of the 1D member

In this situation, the user is fully responsible for the introduction of the self-weight into the model. On the other hand, the process is fully under his/her control. First, the "core" beam is produced. Then, the composite slab is cast. And only at the very end, the self-weight is introduced in its full size. To sum up, until the composite beam is completed, it is not subject to any load.

Situation B (user-calculated self-weight)

Stage	Action	Load case assigned to construction stage
1	casting the beam (phase 1 of the cross-section is introduced into the model)	empty permanent-standard load case
2	introduction of the manually calculated self weight	permanent-standard load case with defined load that represents the self-weight of the 1D member
3	casting the composite slab (phase 2 of the cross-section is introduced into the model)	empty permanent-standard load case

Once again, in this situation, the user is fully responsible for the introduction of the self-weight into the model. First, the "core" beam is made and is subjected to no load. Then the self-weight is introduced in its full size. Finally, the composite slab is cast. To sum up, the "core" beam is subjected to the self-weight of the whole cross-section before the composite slab is made.

Situation C (automatically calculated self-weight)

Stage	Action	Load case assigned to construction stage
1	casting the beam (phase 1 of the cross-section is introduced into the model)	permanent-self-weight load case
2	casting the composite slab (phase 2 of the cross-section is introduced into the model)	permanent-self-weight load case

In this situation, the self-weight is introduced automatically and in parts. First, the core beam is cast and is automatically subjected to the self-weight of the completed part of the cross-section, i.e. of the "core" beam. When the composite slab is made, its self-weight is calculated and added to the existing self-weight of the "core" beam.

Conclusion

It is clearly seen from this very simple example that the calculation stages analysis allows for almost innumerable possibilities. The user must therefore think in advance and must be aware of (i) what he/she wants to model and (ii) what he/she in fact created.

Prestressing

One load case (type permanent - prestress) can be specified and assigned to the current stage. Each of the "permanent – prestress" loadcases is again exclusively assigned to one construction stage.

γ_min, γ_max

Load factors γ_min, γ_max are attached to permanent load cases of both types – load (γG) and prestress (γP). The load factors γGmin(≤ 1), γGmax(≥ 1), γPmin(≤1), γPmax(≥1) are specified (for each load case) in each construction (or service) stage. If a long-term variable load is selected in the combo box Load case permanent or long-term, only maximum factor γQmax is asked, because γQmin is automatically taken as zero (when all variable load is removed). At the same time additional factor γ< 1 appears. Factor γ specifies the long-term part of the load. If a permanent, prestressing or variable LC is applied in a construction stage, it can never be applied again (exclusivity), because the configuration of the structure could be changed in next construction steps and the results would be different.

After the calculation has been performed, both SLS and ULS combinations are generated automatically. For ULS combinations all factors for dead load γG, prestressing γP, quasi-permanent γQ load, and creep γC are applied using both their maximum (≥ 1) and minimum (≤ 1) values.

All combinations required by the codes (for EC2 persistent and transient, accidental, seismic, rare, frequent, quasi-permanent) must be defined manually as "envelope combinations".

Two types of variable load can be applied in service stages: short-term load case and long-term load case (quasi-permanent). This classification has no connection to types of load cases specified elsewhere in SCIA Engineer. Therefore, the long-term variable load case is identified only by specifying the long-term part of the load (using coefficient 0 ≤ γ ≤ 1). The quasi-permanent part (γ) of the load case is assumed to stay on the structure until the end of its service life. The results of long-term load cases are also calculated by standard SCIA Engineerand they are applied (by zero or full value) in all combinations generated for this and following service stages. It means, it is assumed that the quasi-permanent part of variable load can be removed from the structure (or variable load can be applied by its full value) for short time (with no influence on creep). The long-term load cases cannot be applied in construction stages (only in service stages).

Variable load cases

Variable loads (instantaneous and short-term) can be added into current stage. It is possible to add an arbitrary amount of load cases defined in advance. The load defined in this dialog is assumed to be temporary one Once the variable load case is applied in construction stage, it must be copied into new load case before it can be used in some other construction stage. We have to realize, that the results of the same load can be different for different construction stages, because the configuration of the structure changes. Starting from first service stage the short-term load case can be applied repeatedly, because the structure does not change during service, and the response (results) are identical for all service stages. The short-term load cases are calculated by standard SCIA Engineer with no influence of age of concrete, and with all materials at age of 28 days. In fact, the running of variable load-case after some construction stage is kind of analysis after analysis.