Etabs Notes

June 14, 2018 | Author: Naveen Revanna | Category: Framing (Construction), Beam (Structure), Bending, Engineering, Mechanical Engineering
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[email protected] 9036098037 Slab in ETABS, shell or membrane Regardless of the software you use, the issue is that there is a wide difference between shell behavior and a membrane one. Structural engineer should know that a shell has six components of stresses possible within it, 4 in the plane of the shell and two in the perpendicular direction to that plane. The shell has a flexural stiffness that allows creating such perpendicular stresses to its plane. Meanwhile a membrane shall have only four components within the plane of the membrane. There is no perpendicular stress to the membrane because there is no flexural stiffness in that direction. Hence a concrete plate is similar to shell in design in light of the presence of flexural stiffness in both. FAIR ENOUGH? For the case of modeling your problem if it is a flat slab there is no hustle. Represent it by a shell with the same thickness as the slab. If there are beams involved, you should draw your shell all-over the beams, then ask the software to subdivide the whole plane model by choosing beams and the slab at the same time. Do I get a like on this illustration?

Shell Vs membrane is a very commonly debated topic among Etabs users.I am sharing response I got from E-tabs tech support Please bear with long description: The rigid diaphragm assumes infinite in-plane stiffness of floors and therefore reduce the stiffness matrix. The semi-rigid diaphragm uses the inplane stiffness of slab and does not condense the stiffness matrix. For most of the concrete structure where slab is sufficiently thick and we do not expect any deformation, results for semi-rigid diaphragm will be same as rigid diaphragm. Can use membrane definition. However, if you are expecting the slab deformations then modeling a semi--rigid diaphragm will be the correct way to handle such cases. A semi-rigid diaphragm is same as assigning no diaphragm except it allows you to assign the accidental ECC due to Wind or Seismic load cases. At the same time , wind loads can be applied at the center of masses and you do not need to use Area Exposure method to define Wind load case for semi-rigid diaphragm cases.Need to use shell definition. There are three levels of modeling for floors in ETABS. 1. The simplest level is that the floor is modeled as one big polygon and is used only to define the extent of the floor. It is assigned meshing type - "For Defining Rigid Diaphragm and Mass only (No stiffness - No vertical load transfer)" . It is assigned a rigid diaphragm so it connects all elements falling within laterally but is unable to transfer any vertical load. This model can be used for a quick

study of the lateral load resisting system. 2. The second level is a step higher in that the floor is meshed coarsely and given only membrane or deck properties. One could assign a rigid diaphragm if needed, otherwise connectivity is still provided through the coarse mesh. The vertical load is transferred to edges of coarse mesh and is either supported directly by columns or by beams and walls on the edges. This is commonly used with composite floors and can be used for thinner concrete floors where beams are designed for full gravity loads and slab bending stiffness is not important to the lateral analysis. 3. The third level is to have a decent mesh of the floor either done externally or internally that connects the major structural elements and also models the correct bending stiffness of the floor for frame action with columns. This obviously is the correct model and the reason to go to the previous two levels is to avoid getting a huge model that takes too much time solving or cannot even be solved on current hardware. Depend on the length of span and thickness of the slab itself. The rule of thumb is if ratio span/thickness >40 we can use membrane but if the ratio between 10 and 40 shell can help you much better.thx You should use a Plate or Shell Element for correct slab behaviour. In LUSAS you have a choice of surface elements and if your model is just 2D slab then plates give the best results for a given number of elements. Always do a mesh sensitivity check however. For a concrete slab I would use a thick plate or a thick shell which models shear deformation (thin ones do not). you can of course model beams under the slab where appropriate using correct eccentricities.

when you use software you must define your slab as shell because in reality you structure work with the six component, but when you design you only use the three component if it's slab use only your bending Mx, My and Mxy you can neglect the normal forces Fx, Fy and Fxy

If the engineer is concerened with seismic load and distribution of seismic loads to the lateral load resisting system, then the memberane action would be enough to represent the slab behavior (as a diaphgram subjected to in-plane load). The lose of accuracy due to not considering the flexural behavior of the slab is minimal in this case. However, if the purpose is to design the slab itself due to gravity loads (transverse loads to slab plane), then shell action (memberane+flexural) must be used, meaning using shell elements with 6 DOF's. If the slab is too thick, then shell element with shear deformation shall be considered.

Great discussion, now I enjoy using ETABS 2013. To crosscheck with manual calculations, the distribution of loads on Frame objects can be viewed from

Display Menu. How can we look at the load transferred from the slab to beams : Show Frame/Line Loads Click the Display menu > Show Loads > Frame/Line command to access the Show Frame/Line Loads form, which has the following options: Load Case Choose the static load case whose frame/line loads you want to display from the drop-down box. Note that static load cases are defined using the Define menu > Static Load Cases command and assigned using the Assign menu > Frame/Line Loads command. Load Type Choose the type of load that you want to display. Note that you can only display one of these types of loads at a time. Also, if a load type is unavailable (grayed out), that type of load has not been assigned (see the Assign menu > Frame/Line Loads commands). The choices are: Span Loading Applied Directly to the Line Object (Forces): Includes all of the point, uniform and trapezoidal force loads (not moment loads) applied to the line object. Span Loading Applied Directly to the Line Object (Moments): Includes all of the point, uniform and trapezoidal moment loads applied to the line object. All Loading that is Tributary to the Line Object (Forces): Displays the calculated point, uniform and trapezoidal loads tributary to the line object. All Loading that is Tributary to the Line Object (moments): Displays the calculated point, uniform and trapezoidal moment loads tributary to the line object. among above four option the last two option will be highlighted after getting analyse the model once.

with all what our enabled Engineers have elaborated with in depth knowledge, can we make the assumptions below; Membrane: used for conventional slab with beam. Shell: is used for flat slab and wall. Plate thin: is used for raft foundation where bending is predominant. Plate thick: is used where shear is predominant.

Membrane is simply like a truss member in line member analogy where as plate is like a beam and shell is an arch. The behavior between these analogy are same. I hope every one is okay with the knowledge of truss member, beam and an arch member. ETABS-2013-Video Training

Chapter-1 Introduction/Kick-Start 

Introduction



Advanced capabilities of ETABS 2013



Brief history



ETABS 2013 Levels



Modeling Process



Modeling Features



Analysis Features



Design Feature



Detailing Feature



Modeling Terminology & details



Load case



Load Combinations



Design Settings and scope



Output and Display settings



Model Initialization



New model quick template



GUI after setting template

Chapter-2

Foundation Concept startup 

The ETABS graphical user interface



File Operations & Different Extn



Time Saving Options



Templates and Defaults



Basic Process



Standard Tool bars for Doc Managing



Standard Tool bars for Doc Zoom



Standard Tool bars for Doc View



Standard Tool bars for Graphics & Load Display



Model Explorer



Draw Tools



Draw beam-Plan/Elev/3D



Draw Column-Plan/Elev/3D



Draw Brace-Plan/Elev/3D



Quick Draw beam-Plan/Elev/3D



Quick Draw Column-Plan/Elev/3D



Quick Draw Secondary Beam-Plan/3D



Quick Draw Braces-Plan/Elev/3D



Draw Floor/Wall-Plan/Elev/3D



Draw Rectangular Floor/Wall-Plan/Elev



Quick Draw Floor/Wall-Plan/Elev



Draw Wall-Plan



Quick Draw Wall-Plan



Draw Wall opening-Plan/Elev/3D



Draw Links--Plan/Elev/3D



Draw Wall stacks-Plan/Elev/3D



Wall Meshing techniques



How to apply conditioning to walls/slabs/floor for EQ Analysis



Understanding of Edge constraints for Shear wall/slabs



Example Case study mesh



Units



Display Units



Units Setting



Project-1



Project-2



Project-3



Exercise-1



Exercise-2



Exercise-3

Chapter-3 Modeling & Properties Options 

Quick Template settings and Structural Objects



Properties of Steel deck



Properties of Staggered truss



Properties of Flat Slab



Properties of Flat Slab with Perimeter Beams



Properties of Waffle Slab



Properties of 2 Way or Ribbed Slab



Grid System



Uniform Grid Spec



Custom Grid Spec



Properties Add



Properties Delete



Properties Modify



Frame section Reinforcement-Rebar



Story Dimension



Story data



Modify/Show Story Data



Project-1



Project-2



Project-3



Project-4



Exercise-1



Exercise-2

Chapter-4 Advanced Modeling Options 

Replicate Options



Extrude Joints & Frames



Add model from Template-2D Frame



Add model from Template-2D Truss



Add model from Template-2D Wall



Add model from Template-3D-Steel Deck



Add model from Template-3D-Staggered Truss



Add model from Template-3D-Flat Slab



Add model from Template-3D-Flat Slab with Perimeter Beams



Add model from Template-3D-Waffle Slab



Add model from Template-3D-2 Way or Ribbed Slab



Move Joints/Frames/Shell



Define Material



Material Property Data



Frame Properties



Snap Options



Cladding non-structural member for wind load



Project-1



Project-2



Project-3



Project-4



Project-5



Project-6

Chapter-5 Advanced Boundary Conditions 

Joint Loads-Force Parameters



Load Pattern & options



Joint Loads-Ground Displacement Parameters



Joint Loads-Temperature



Frame Loads-Point based load Parameters



Frame Loads-Distributed load Parameters



Frame Loads-Temperature



Frame Loads-Structure Wind Parameters



Shell Loads-Uniform Load Sets Parameters



Shell Loads-Uniform Parameters



Joint Restraints



DOF-For Pin,Roller,Fixed & free etc



How to reconfigure Supports



IS 875- Part 1-Dead Loads & ETABS



IS 875- Part 2-Imposed Load & ETABS



IS 875- Part 3-Wind Loads & ETABS



IS.15498.2004



Explanation about EQ Load and Basic Orientation on Project



International Other country Load cases i.e ASCE,AS,EURO,Italian,NBCC,Turkish,AS/NZS,UBC



Project-1



Project-2



Project-3



Project-4



Exercise-1



Exercise-2



Exercise-3

Chapter-6 Detailing–ETABS-2013 

Detailing scope



Detailing Preference



Concrete Detailing Preference-Slab/Beam/Col/Wall



Steel Detailing Preference



Rebar Section Rules



Drawing Sheet Setup



Start Detailing



Show Detailing



Detailing Reports and configuration/Visualization



Prepare component and Elements detailing



Export Drawings



Project-1



Exercise-1



Exercise-2

Chapter-7 Concrete Frame Design-RCC Design 

RCC Design Overview



Capability RCC Design



What To do check list before running RCC Analysis



RCC Design Preference



IS 456:2000 & Design Guide Lines



International RCC Design codes for other countries & Implementation



RCC Design Member



Start Design/Check



Display Design info



Display Design Results



Rebar % and other important Output discussion



Project-1



Exercise-1



Exercise-2



Exercise-3

Chapter-8 Shear Wall Design 

Shear Wall Design Preference



IS 456:2000 & Design Guide Lines



Shear Wall Design –PIERS & SPANDRELS



Shear Wall Optimization for Thickness & Target Drift



Supported Codes



Design Combination



Start Design/Check



Display Design info



Display Design Results



Shear Wall pier summary



Shear wall Design Details



Design Output Complete detail discussion



Longitudinal reinforcement and other important Output discussion



Project-1

Chapter-9

Modal Frequency Analysis 

What is modal Analysis?



The Natural Frequency of a Building



Structural Matrix & System Response



Benefits of modal analysis



How Natural Frequency emanates?



Resonance



Case study-1



Case Study-2& Examples



Modal case Data config



Modal Result Table config



Modal Periods & Frequencies



Modal Participation Mass Ratio



Modal Participation Factors



Load Participation Ratio



Modal Direction Factors



Modal Report Export to Excel



Mode Shapes Settings



Project-1

Chapter-10 Import/Export-Concept 

Importing Fundamentals and Unit systems



Importing from Old ETABS Versions



Importing from STAAD.Pro



Importing from Revit Structure



Importing DWG



Importing DXF



Importing Architectural Options setting



Layer control



ARCH Layer Auto create wall/column/beam/area options



Properties configuration while auto create



Exporting DWG/DXF



Project-1-dxf



Project-2-dwg



Project-3-STAAD

Chapter-11 Selection Quick Tricks 

Pointer/Window Selection



Poly selection



Intersection poly



Interesting Line



Co-ordinate specification



Object type selection i.e. column/beam/wall etc.



Properties selection types



Material properties selection



Frame sections



Slab sections



Deck sections



Wall sections



Link/support properties



Point spring



Line spring



Area spring



Panel zones



Labels



Group



Stories



All



Deselect strata in detail



Invert selection



Clear selection

- See more at: http://store.smartlearningindia.com/Single-Software-Training-DVD/ETABS-2013-VideoTutorials-Training-DVD-id-274196.html#sthash.9stD8H0e.dpuf SIZE OF RCC BEAM FROM CENTERING POINT OF VIEW The posting on the size of beams and columns as pointed out by you should be a practical as well as economical point of view. While designing the depth of beam 1" per one foot span is a thumb rule used while in the good old days when the working stress is adopted that is span/12 but now it can be span/15 to span/20 depending on span, loading and other considerations and make use of LIMIT STATE METHOD OF DESIGNING R.C.C. MEMBERS. The idea of span/12 can be taken as a preliminary calculation and design but practically it can be reduced. The other point is if you need to reduce the steel to some extend the depth may be taken as span/12 as the cost of steel/Kg is more than a few centimeter increase in depth of beam concrete. Wise decision has to be exercised while designing considering the practical aspect and avoiding the material wastage. In this respect use of 13" will be good enough for the use of timber shuttering rather than having odd sizes to match with the available timer sizes which will avoid wastage and lead not only economy but also save time.

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