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- Monday, 01 September 2014
2. Overview of the design procedure
In order to run the design, it is necessary to create an appropriate ETABS/ Scia Engineer model that must include at least the following :
- Units must be set to KN–m.
RC material properties : Concrete characteristic compressive strength (f’c, range of values 5000-150000 begin_of_the_skype_highlighting 5000-150000 end_of_the_skype_highlighting kPa), longitudinal reinforcement tensile strength(fy, range of values 100000-1000000 kPa) and tensile strength of links (fys, range of values 100000-1000000 kPa).
- Rigid diaphragms may be created at floor levels (required for the torsional checks and to check if the structure qualifies for the joint capacity design omission ).
- The model must be analysed using dynamic spectra analysis, so as to calculate its natural periods and the corresponding diaphragm displacements (required for the torsional checks and to check if the structure qualifies for the joint capacity design omission1).
- Optional input of accidental eccentricity as a torsional moment at the gravity centre of each floor due to earthquake along the x and y axes (in separate static load cases) or input of the eccentricity in the spectrum of each direction.
- Static load cases with predefined names EXSTAT and EYSTAT must be created for the x and y directions respectively, so as to calculate the RC walls contribution per floor (to check if the structure qualifies for the joint capacity design omission1).
- RC walls must be deifned as Piers, comprising of either linear or area elements or a combination of linear and are elements. RC walls design demands that each section is created in the relevant editor of ECtools, since their geometry cannot be directly extracted from ETABS (as is the case for beam and column sections or for Scia Enginner piers).
- The necessary load cases must be created for the design procedure. They can include from the bare minimum DEAD, LIVE, Earthquake X and Earthquake Y load cases to temperature load cases (with automatic relevant combination generation) and even extra user defined combos.
- The necessary RC beam and column sections (rectangular, T-, L-, U- or circular sections). Arbitrary column sections and sections with jackets must be created using ETABS Section Designer.
The various program options are described before the description of the design procedure.
2.1 Project file creation
File -> Open project file : Opens a stored project file (.etp extension) from the hard drive. Also, an .etp file can open in ECtools by double-clicking.
File -> Save project file : Saves the current project (settings, additional information, etc.) in a file of the form .etp. It is noted that the project file does not need to be saved in the same folder with the Input, Output and section files. The following folder structure is recommended for the project folders :
File -> Create compressed project file (zip) : Creates a compressed .zip file that includes all the files in the project folder. The user is initially prompted for the .etp file of the project and then a .zip file is created having the same name in the project folder. This function is particularly useful for easy exchange of all the project files between different users.
2.2.1 General options
The general options window is opened from the menu Options -> General options :
- Full results file : The user can select if a full results file is to be created after the design is complete, and can define the file name. The full results file includes separate results for all the load combinations and not only for the most honerous ones that appear in the design calculations issue.
- Design calculations issue : The user can choose for the language to be used in the design calculations issue between Greek and English.
2.2.2 Design options
The design options window opens from the menu Options -> Design options :
- Exposure conditions : The desirable exposure condition according to EC2 are selected, which corresponds to specific reinforcement cover. There is also the option to select an alterntive reinforcement cover other than the ones listed above, by selecting the relevant option.
- Standard : The design standard is selected. Options are EC2 (for structures without earthquake resisting requirements) and EC8 (for earthquake resisting structures – masonry included).
- Coefficient q : The behaviour coefficient, q, is input, which is used for designs according to EC8.
- Checks : The building checks (design criteria) that are to performed according to EC8 are defined. These include 2nd order effects, joint widths, fill materials, torsional susceptibility and omission of joint capacity design checks. See section 3.3 for additional information.
- Load combinations : The user can choose whether the necessary design load combinations are to be created automatically by ECtools, based on the load cases that have been defined in the ETABS model. Also, the ψ2 coefficient can be defined and whether the eccentricity load cases are to be included in the above-mentioned combinations.
Joint capacity design check along the x and y axes : The user can choose whether the joint capacity checks are performed during the structural design.
- Masonry : The masonry material factor (γm) and the ratio between the compressive and tensile capacity (f¬c / ft) of masonry is entered.
- Common RC wall base : By definition, each RC wall base is assumed as the founding level of the corresponding Pier that has been defined in the ETABS model (the node with the lesser vertical co-ordinate z). Should the user wish to define a common founding level for all the RC walls in the model, the floor name that is to be defined as the common founding level is entered in the field. The common RC wall founding level can be altered latter during the design run (described in more detail in section 2.5.7).
2.2.3 Strengthening options
The strengthening options window is opened from the menu Options -> Strengthening options :
For checking an existing structure according to EC2, the option Activate strengthening must be selected and the load and material safety factors to be input in the relevant fields. These factors will replace the default EC2 factors. During the design run the user is prompted for the existing element reinforcements that are entered in table format, so as to perform the individual structural element capacity checks.
2.2.4 Reinforcing bar diameter sizes
The reinforcing bar diameter sizes window is accessed from the menu Options -> Rebar sizes :
The user can set limits to the bar sizes to be used as bending reinforcement in beams, columns and RC walls and which will be proposed in the design calculations issue.
2.3 Design input
Having entered the Input and Output files in the relevant fields and once the design parameters are set according to the previous sections of this manual (it is recommended at this point to save the project file), the design can be run be clicking on the Run button.
The design begins by reading the Input file, whilst simultaneously information regarding the number of materials, sections, structural elements, etc. contained in that file, are displayed in the adjacent window.
Once the Input file is read, all of the model sections (beam, column and wall) are presented in tabulated form. If the strengthening option has been activated the existing beam and column reinforcement data (for bending and shear) is displayed previous to that:
The user can in these tables alter the model data before the Output file is read and the design is run. The data editing window includes the following tabs :
- Materials : Displays the material names and properties table included in the model. The following editing options are available :
|button : Adds a new material in the table to be assigned to sections. Material properties are entered in the figure shown on the right. For masonry materials, the fvko and flim properties are entered initially at the fy and fys fields respectively, enabling the program to automatically recognise these as masonry materials.|
button or double click : Edits the selected material properties. It is also possible to edit multiple materials from the table either by clicking the particular button or by right-clicking on the multiple selection. For multiple material editing, all the selected materials should be of the same type, i.e. all concrete or all masonry.
- Sections : Displays the section names and characteristics table contained in the model. The following editing options are available :
|button : Adds a new section in the table. Section properties are entered in the window shown on the right. Section type can be rectangular, T-, L-, U- or circular section. Depending on the section type, the relevant data input fields are activated and the section outline is drawn for checking purposes.|
button or double click: Edits the selected section geometry. It is also possible to edit multiple sections from the table either by clicking the particular button or by right-clicking on the multiple selection. For multiple sections editing, all the selected sections should be of the same type.
If the selected section is an RC wall or masonry wall section, then it is opened in the corresponding editor, as described in section 2.3.
button : Opens the selected section fro editing in Nous (see section 2.4). If the section is modified (e.g. by adding a jacket), then it is saved on the hard drive as a .sd file and is entered in the table as a jacketed section by clicking the update button (described latter on). Also, jacketed sections can be edited in Nous by double-clicking.
- Beams / Columns / RC Walls / Masonry Walls : Displays the structural elements names and characteristics contained in the model. Editing of structural elements is performed by clicking on the button or by double-clicking for a single selection or by right-clicking for multiple selection.
|For beams and columns, only the section names can be modified. The section material will be that of the newly applied section.|
|For RC walls the section, material (choice of concrete materials only) and base (founding level) name that is to be used in design can be modified. Initially, the founding level of every RC wall is assumed to be the respective Pier base that has been defined in the ETABS model or the common founding level defined in the design options (see section 2.5.4).|
|For masonry elements, the section and material name (choice of masonry materials only) can be edited.|
The user can select table lines using standard windows keys. The general options of the data editing window, irrespective of the selected tab, are as follows :
button : Updates the jacketed sections in the table from the files contained in the folder where the Input and Output files are stored. Updating is necessary before the design is run, if any additional jacketed sections are created in Nous.
button : Replaces existing sections with jacketed sections (strengthened sections) located in the same folder where the Input and Output files are stored. These strengthened sections are highlighted in green (see figure below) in the column, RC and masonry wall tables. The strengthened section creation process is described in detail in section 2.5.10.
|button : Updates the ETABS data file (file with a .Ε2Κ or .$ET extension) to all the modifications that have been performed in the data editing tables window.|
This new file can be loaded in the ETABS environment from the menu File -> Import -> ETABS .E2K Text File. It is noted that all the jacketed sections created in Nous, are input as ETABS Section Designer sections. Also, all the changes to the correlations between sections and frame elements that have been performed in the data editing window are incorporated in the new data file.
2.4 Design output
Depending on the selected options, the following windows for additional data input are displayed when the design is run :
2.4.1 Design calculations issue
The solution time bar-chart includes the following categories :
buttons : Displays the beam/column/wall.masonry data.
The various colors represent the following :
Elements that are adequate in the cross-section capacity design checks (safety factor larger than unity).
Columns where the maximum ratio (v) of applied axial force to axial capacity as defined in Eurocodes has been exceeded.
Elements where the concrete core shear capacity (VRd2) has been exceeded in design.
Elements that are inadequate in the cross-section capacity design checks (safety factor smaller than unity).
In the cases mentioned above, if the section is a jacketed one (.sd extension) or a masonry wall, then an actual design is not performed but merely a cross-section adequacy check is carried out. Consequently, the only possible states in the bar-chart are (adequate) or (inadequate).
On the solution time bar-chart the following actions can be performed :
- Left click -> Displays the selected element in the design calculations issue.
- Double left click -> Opens the selected element in Nous. This action is useful for creating strengthened sections, as described in the relevan section.
2.4.2 Automatic element relabelling
In many cases, the drawing names of structural elements do not match those of the ETABS/Scia Engineer model (especially when non-latin characters are used in drawings e.g. Δ10, which cannot be entered in ETABS/Scia). For checking purposes, it is possible in ECtools to correlate the structural element names of drawings to those used in the ETABS/Scia Engineer model and display them in the design issue. The user needs only to provide a tab delimited text file named “Relabel.txt” that correlates for each story ETABS/Scia Engineer element names to their drawing counterparts. If the Relabel.txt file is found during the design run, then the drawing name for each element contained in that file is displayed in the following windows :
|Data editing tables
(see section 2.5.7)
|Existing reinforcement tables
(see section 2.5.7)
|Design calculations issue
(see section 2.5.9)
|In Nous when it is run through the design
(see section 2.5.10)