Embed Size px x x x x The procedures in this document are based on standard practice in Dubai. However, for specific projects, some parameters or procedures need to be revised. This shall be done in accordance with the design statement and in conjunction with the project lead engineer.
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File Menu 1. Material properties 2. Supports 4. Loading: 5. Load Combinations 6. Analysis Options: 7. Eigenvector 7. Post-Analysis Checks: , Reinforced Concrete Design Module 9. These templates incorporate as many of the requirements as possible, however it should be noted that many of the local authorities requirements may only be implemented while a 3D These units are used in the templates.
Select the layer names to be imported by highlighting them. Make sure that appropriate layers are selected to be imported. Note 3: The following procedure may be used to create a. Since 3-D representation is not used for typical floor plan and elevation in Atkins Dubai, this option will not be covered in this manual. Material Properties Use of other grades may be justified based on project's specific requirements.
Use that form to add, modify, or delete material properties. This value is the same for bending and shear reinforcement. According to local authorities' requirements, the seismic design of reinforced concrete elements shall be based on ACI provisions.
As per ACI provisions Section 3. Definition and Sizing of Elements 3. The user may also import the sections from a user- defined database with". Complex, unsymmetrical shapes may be modelled using the built-in section designer module.
The following general tips may be useful for defining frame sections. It is generally recommended that the material properties are defined first. This assures correct material assignment to the member and allows defining similar sections with different material property. This feature is particularly useful for tall buildings where grade of concrete For reinforce concrete rectangular and circular sections, the user may specify one of the design types, e.
The column design option allows the provided reinforcement to be checked or designed, whereas the beam design option is limited to just designing the required reinforcement value. Section property modifiers may be assigned to each section at this stage or later. However it should be noted that property modifiers for all frame types may be revised anytime by selecting the appropriate member beam, column or brace and there is no need to define them separately for each section.
This will be discussed more in this chapter. A deck option may be used to model one way joist and slab, one way slab or metal deck systems. Plank and slab options may be used to model one-way or two way slabs with or without one- way special load distribution.
Appropriate shell, membrane or plate property shall be assigned to floor members based on their actual behaviour. A membrane element may be used to include only in-plane stiffness properties for the member e. Shell type behaviour considers both in-plane and out-of-plane stiffness properties are considered.
This type is generally recommended unless the user is confident about the realistic behaviour of the member. For membrane and shell type elements, different membrane or bending thickness may be defined based on the actual behaviour of the slab system as shown in the following example.
This option is recommended when modelling thick floor such as rafts and transfer slabs. The section property modifiers may be assigned to each section at this stage or later. However it should be noted that property modifiers for all floor objects may be revised anytime by selecting the appropriate member floor, ramp or wall and there is no need to define them separately for each section.
Define Wall Objects Walls may be defined as shell or membrane elements. Other modelling features are similar to what has been discussed for slabs except for section modifiers which will be discussed more in this chapter. When using a frame element beam to model a shear wall spandrel, keep in mind that the analysis results obtained are dependent on the fixity provided by the shell element that the beam connects to.
Different sized shell elements provide different fixities and thus, different analysis results. In general, for models where the spandrels are modelled using frame elements, better analysis results are obtained when a coarser shell element mesh is used; that is, when the shell elements that the beam connects to are larger.
If the shell element mesh is refined, consider extending the beam into the wall at least one shell element to model proper fixity. If the depth of the shell element approaches the depth of the beam, consider either extending the beam into the wall as mentioned above, or modelling the spandrel with shell elements instead of a frame element.
Note that these modification factors only affect the analysis properties. They do not affect the design properties. Member design will be based on end-face moments not centre-point.
This analysis will be used in arriving at the following results; Slabs and beams section modifiers are as per ultimate limit state provisions as mentioned above. If the stress in any member exceeds the allowable tensile stress value, appropriate section modifiers corresponding to the cracked section properties shall be assigned to that member.
The drift and accelerations shall be checked accordingly. To ensure that the stiffness modifiers are assigned to all the elements, it is generally recommended to assign the stiffness modifiers after completion of the model and prior to the analysis using the "Select by Object Type" option in ETABS. This not only relieves the laborious task of defining the stiffness modifiers separately for each frame section, but also provides a quick, yet reliable way to change these modifiers in no time.
Here you can specify Stiffness Modifiers for the following shell analysis section stiffness in your model. D Membrane f11 Modifier D Membrane f22 Modifier D Membrane f12 Modifier D Bending m11 Modifier D Bending m22 Modifier D bending m12 Modifier The stiffness for each of the items calculated based on the section properties specified for a shell element are multiplied by the specified modifiers to obtain the final stiffness used for the shell element in the analysis.
They do not affect any design properties. The f11, f22 and f12 modifiers are essentially equivalent to modification factors on the thickness t of the shell element. The m11, m22 and m12 modifiers are essentially equivalent to modification factors on the t 3 of the shell element.
The section modifiers for Ultimate limit state analysis for Area Objects are shown in the following table based on UBC 97, clause Refer to the discussion below for further clarification. The gross section area based on UBC 97 Clause This may be easily accounted for frame elements by just revising the section modifier for moment of inertia.
However, the axial and bending stiffness for shell elements can not be de-coupled, i. This may cause displacement incompatibility with adjacent frame column which in turn may require revising the axial stiffness for vertical frame elements, as opposed to code explicit provisions.
Special care shall be taken when defining these labels to ensure realistic values. A wall pier can consist of a combination of both area objects shell elements and line objects frame elements.
If you want to get output forces reported for wall piers, or if you want to design wall piers, you must first define them. If a wall pier is made up of both line and area objects, assign the pier label to the line and area objects separately.
A wall spandrel can consist of a combination of both area objects shell elements and line objects frame elements. If you want to get output forces reported for wall spandrels, or if you want to design wall spandrels, you must first define them.
If a wall spandrel is made up of both line and area objects, assign the spandrel label to the line and area objects separately. The smaller areas are three-sided or four-sided and must have beams on all sides. Select one or multiple lines. If the selected line passes through more than one area, all of the areas will be meshed. Note that this and the Auto Mesh Area option only work in plan view. The angle will be measured in the counter clockwise direction for the x and y-axis.
If the point lies in the overlapping region of two areas, both of the areas will be meshed at the given angle. For example, specifying a meshing of 2 by 8 means that the selected area will be meshed into 2 areas along the x-axis. The size of the meshed areas will be uniform along a given direction.
Only quads and triangles can be meshed using this option. One more points can be selected for this type of meshing. More than one line can be selected to mesh a desired area.
Note the following about Meshing Area Objects: OThe property assignments to meshed area objects are the same as the original area object. OLoad and mass assignments on the original area object are appropriately broken up onto the meshed area objects. If clicked again for the same selected area, they will be divided in half again, and so on.
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