7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
1/147
International Seminar on
Computer Aided Analysis and Design
Of Building Structures
Aug 23-24, Kuala Lumpur, Malaysia
Institute of Engineers Malaysia
Computers and Structures Inc., USA
Asian Center for Engineering Computations and Software
Asian Institute of Technology, Thailand
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
2/147
Building Structures
Modeling and Analysis Concepts
Naveed Anwar
Asian Center for Engineering Computations and Software, ACECOMS, AIT
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
3/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Overall Design Process
Conception
Modeling
Analysis
Design
Detailing
Drafting
Costing
Integrated
Design
Process
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
4/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Building Systems
Building is an assemblage of various Systems
Basic Functional System
Structural System
HVAC System
Plumbing and Drainage System
Electrical, Electronic and Communication System Security System
Other specialized systems
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
5/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Beams, Columns, Two-way Slabs, Flat Slabs, Pile caps
Shear Walls, Deep Beams, Isolated Footings, Combined Footings
Sub-structure and Member Design
Frame and Shear WallsLateral Load Resisting System
Floor Slab SystemGravity Load Resisting System
Building Structure
Floor Diaphragm
The Building Structural System - Physical
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
6/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Building Structural System - Conceptual
The Gravity Load Resisting System (GLRS)
The structural system (beams, slab, girders, columns, etc)
that act primarily to support the gravity or vertical loads
The Lateral Load Resisting System (LLRS)
The structural system (columns, shear walls, bracing, etc)that primarily acts to resist the lateral loads
The Floor Diaphragm (FD)
The structural system that transfers lateral loads to the
lateral load resisting system and provides in-plane floorstiffness
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
7/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Building Response
Objective: To determine the load path gravity and lateral loads
For Gravity Loads - How Gravity Loads are Distributed
Analysis of Gravity Load Resisting System for:
Dead Load, Live Live Load, Pattern Loads, temperature, shrinkage
Important Elements: Floor slabs, beams, openings, Joists, etc.
For Lateral LoadsHow Lateral Loads are Distributed
Analysis of Lateral Load Resisting System for:
Wind Loads, Seismic Loads, Structural Un-symmetry Important elements: Columns, shear walls, bracing , beams
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
8/147
Structural Response
To Loads
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
9/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Simpl i f ied Structu ral System
STRUCTURE
pv
EXCITATIONLoads
VibrationsSettlements
Thermal Changes
RESPONSESDisplacements
Strains
Stress
Stress Resultants
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
10/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Analysis of Structures
pv
Real Structure is governed by PartialDifferential Equations of various order
Direct solution is only possible for:
Simple geometry
Simple Boundary Simple Loading.
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
11/147 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Need for Modeling
A - Real Structure cannot be Analyzed:
It can only be Load Tested to determine response
B - We can only analyze aModel of the Structure
C - We therefore need tools to Model the
Structure and to Analyze the Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
12/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Structural
Model
The Need for Structural Model
EXCITATIONLoads
VibrationsSettlements
Thermal Changes
RESPONSESDisplacements
Strains
Stress
Stress Resultants
STRUCTURE
pv
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
13/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
F ini te Element Method: The Analysis Tool
Finite Element Analysis (FEA)A discretized solution to a continuum
problem using FEM
Finite Element Method (FEM)A numerical procedure for solving (partial)
differential equations associated with field
problems, with an accuracy acceptable to
engineers
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
14/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Continuum to Discrete Model
pv
(Governed by partial
differential equations)
CONTINUOUS MODEL
OF STRUCTURE
(Governed by either
partial or total differential
equations)
DISCRETE MODEL
OF STRUCTURE
(Governed by algebraic
equations)
3D-CONTINUM
MODEL
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
15/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
From Classical to FEM Solution
Assumptions
Equilibrium
Compatibility
Stress-Strain Law
(Principle of Virtual Work)
Partial Differential
Equations
Classical
Actual Structure
Algebraic
Equations
K = Stiffness
r = Response
R = Loads
FEM
Structural Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
16/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Simpli f ied Structural System
Loads (F) Deformations (D
Fv
F = K D
F
KD
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
17/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Struc tural Sys tem
EXCITATIONRESPONSES
STRUCTURE
pv
Static
Dynamic
Elastic
Inelastic
Linear
Nonlinear
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
18/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Equil ibr ium Equations
1. Linear-Static Elastic OR Inelastic
2. Linear-Dynamic Elastic
3. Nonlinear - Static Elastic OR Inelastic
4. Nonlinear-Dynamic Elastic OR Inelastic
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
19/147
Di ti ti f C ti
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
20/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
X
Z
Y
Membrane/ PanelIn-Plane, Only Axial
ShellIn-Plane and Bending
Plate/ SlabOut of Plane, Only Bending
General Solid
Regular Solid
Plate/ Shell
( T small compared to Lengths )
( Orthogonal dimensions)
Discretization of Continuums
Beam Elemen
Solid Element
H, B much less than L
Gl b l M d li f St t l G t
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
21/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Global Modeling of Structural Geometry
(f) Grid-Plate
Di i f El t
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
22/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Dimensions of Elements
1 D Elements (Beam type)
Can be used in 1D, 2D and 2D 2-3 Nodes. A, I etc.
2 D Elements (Plate type)
Can be used in 2D and 3D Model
3-9 nodes. Thickness
3 D Elements (Brick type)
Can be used in 3D Model
6-20 Nodes.
DOF f 1D El t
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
23/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
DOF for 1D Elements
Dx
Dy
DxDz
Dy
Dx
Dy
Rz
Dy
RxRz DxDz
Dy
Rx
Rz
Ry
2D Truss 2D Beam3D Truss
2D Frame 2D Grid 3D Frame
Dy
Rz
DOF for 2D Elements
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
24/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
DOF for 2D Elements
Dx
DyDy
Ry ?
RzRx
Dz
Dy
Rx
Rz
Ry ?
Dx
Membrane Plate Shell
DOF for 3D Elements
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
25/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
DOF for 3D Elements
DxDz
Dy
Solid/ Brick
Frame and Grid Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
26/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Frame and Grid Model
The structure represented by rod or
bar type elements Does not model the cross-section
dimensions
Suitable for skeletal structures
Sometimes surface type structures
can also be represented by frame
model
The simplest and easiest model to
construct, analyze and interpret
Can be in 2D or in 3D space
3D Fram
2D Grid
2D Frame
Membrane Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
27/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Membrane Model
Ignore bending stiffness
Tension / Compression
In- plane Shear
For in plane loads
Principle Stresses
suitable for very thin structures/ members
Thin Walled Shells,
Specially Suitable for Ferro
Cement Structure
Plane Stress and Plane
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
28/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Plane Stress and Plane
Plane Stress ProblemPlane Strain Problem
Plate Bending Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
29/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Plate Bending Model
Primarily Bending mode
Moment and Shear arepredominant
Suitable for moderately thick
slabs and plates
For Out-of-plane loads only
Can be used in 3D or 2D models
Suitable for planks and
relatively flat structures
General Plate-Shell Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
30/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
General Plate Shell Model
Combined Membrane and Plate
Suitable for general applicationto surface structures
Suitable for curved structures
Thick shell and thin shellimplementations available
Membrane thickness and platethickness can be specifiedseparately
Numerous results generated.Difficult to design the section for
combined actions
Solid Model
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
31/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Solid Model
Shear Axial deformation mode in 3D
Suitable for micro-models
Suitable for very thick plates / solids
May not be applicable much to
ferocement structures
Use 6 to 20 node
elements
Soil-Structure I nteraction
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
32/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Soil Structure I nteraction
Simple Supports
Fix, Pin, Roller etc.
Support Settlement
Elastic Supports Spring to represent soil
Using Modulus of Sub-grade reaction
Full Structure-Soil Model
Use 2D plane stress elements
Use 3D Solid Elements
Connecting Different Types of Elements
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
33/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Connecting Different Types of Elements
Truss Frame Membrane Plate Shell Solid
TrussOK OK Dz OK OK OK
FrameRx, Ry, Rz OK
Rx, Ry, Rz,
Dz
Rx ?
Dx, DyRx ? Rx, Ry, Rz
MembraneOK OK OK Dx, Dy OK OK
PlateRx, Rz OK Rx, Rz OK OK Rx, Rz
ShellRx, Ry, Rz OK
Rx, Ry, Rz,
DzDx, Dz OK Rx, Rz
SolidOK OK Dz Dx, Dz OK OK
0
Orphan Degrees Of Freedom:
1 2 3 4
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
34/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
What Type of
Analysis should beCarried Out?
Analysis Type
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
35/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Analysis Type
The Type of Excitation (Loads) The Type Structure (Material and Geometry)
The Type Response
The type of Analysis to be carr ied outdepends on the Structural System
Basic Analysis Types
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
36/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
as a ys s yp s
Excitation Structure Response Basic Analysis Type
Static Elastic Linear Linear-Elastic-Static Analysis
Static Elastic Nonlinear Nonlinear-Elastic-Static Analysis
Static Inelastic Linear Linear-Inelastic-Static Analysis
Static Inelastic Nonlinear Nonlinear-Inelastic-Static Analysis
Dynamic Elastic Linear Linear-Elastic-Dynamic Analysis
Dynamic Elastic Nonlinear Nonlinear-Elastic-Dynamic Analysis
Dynamic Inelastic Linear Linear-Inelastic-Dynamic Analysis
Dynamic Inelastic Nonlinear Nonlinear-Inelastic-Dynamic Analysis
Some More Solution Types
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
37/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
yp
Non-linear Analysis
P-Delta Analysis
Buckling Analysis
Static Pushover Analysis
Fast Non-Linear Analysis (FNA)
Large Displacement Analysis
Dynamic Analysis
Free Vibration and Modal Analysis
Response Spectrum Analysis
Steady State Dynamic Analysis
Static Vs Dynamic
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
38/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Static Excitation
When the Excitation (Load) does not vary rapidly with Time When the Load can be assumed to be applied Slowly
Dynamic Excitation
When the Excitation varies rapidly with Time
When the Inertial Force becomes significant
Most Real Excitation are Dynamic but are considered
Quasi Static
Most Dynamic Excitation can be converted to
Equivalent Static Loads
Elastic Vs I nelastic
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
39/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Elastic Material
Follows the same path during loading and unloading and returns to initialstate of deformation, stress, strain etc. after removal of load/ excitation
Inelastic Material
Does not follow the same path during loading and unloading and may not
returns to initial state of deformation, stress, strain etc. after removal of
load/ excitation
Most materials exhibit both, elastic and inelastic behavior
depending upon level of loading.
L inear Vs Nonl inear
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
40/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Linearity
The response is directly proportional to excitation
(Deflection doubles if load is doubled)
Non-Linearity
The response is not directly proportional to excitation
(deflection may become 4 times if load is doubled) Non-linear response may be produced by:
Geometric Effects (Geometric non-linearity)
Material Effects (Material non-linearity)
Both
Elastici ty and L inear ity
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
41/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Action
Deformation
Action
Deformation
Action
Deformation
Action
Deformation
Linear-Elastic Linear-Inelastic
Nonlinear-Elastic Nonlinear-Inelasti
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
42/147
Physical Object Based
Modeling, Analysis and Design
Continuum Vs Structure
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
43/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
A continuum extends in all direction, has infinite
particles, with continuous variation of materialproperties, deformation characteristics and stress state
A Structure is of finite size and is made up of an
assemblage of substructures, components and members
Dicretization process is used to convert Structure to
Finite Element Models for determining response
Physical Categor ization of Structures
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
44/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Structures can be categorized in many ways.
For modeling and analysis purposes, the overall physicalbehavior can be used as basis of categorization
Cable or Tension Structures
Skeletal or Framed Structures Surface or Spatial Structures
Solid Structures
Mixed Structures
Structure Types
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
45/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Cable Structures
Cable Nets
Cable Stayed
Bar Structures
2D/3D Trusses
2D/3D Frames, Grids
Surface Structures
Plate, Shell
In-Plane, Plane Stress
Solid Structures
Structure, Member, Element
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
46/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Structure can considered as an assemblage of Physical
Components called Members
Slabs, Beams, Columns, Footings, etc.
Physical Members can be modeled by using one or more
Conceptual Components called Elements
1D elements, 2D element, 3D elements
Frame element, plate element, shell element, solid element, etc. Modeling in terms Graphical Objects to represent Physical
Components relieves the engineers from intricacies and
idiosyncrasy of finite element discretization
Structural Members
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
47/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Load Transfer Path For Gravity Loads
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
48/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Most loads are basically Volume Loads generated due to
mass contained in a volume
Mechanism and path must be found to transfer these loads to
the Supports through a Medium
All types of Static Loads can be represented as:
Point Loads
Line Loads
Area Loads
Volume Loads
The Load Transfer Path
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
49/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Load is transferred through amedium which may be:
A Point A Line
An Area
A Volume
A system consisting of combination of
several mediums
The supports may be represented as:
Point Supports
Line Supports
Area Supports Volume Supports
Graphic Object Representation
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
50/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Object
Line
Area
Volume
Point LoadConcentrated Load
Beam Load
Wall Load
Slab Load
Slab Load
Wind Load
Seismic Load
Liquid Load
Node
Beam / Truss
Connection Element
Spring Element
Plate ElementShell Element
Panel/ Plane
Solid Element
Point SupportColumn Support
Line Support
Wall Support
Beam Support
Soil Support
Soil Support
Point
LoadGeometry
Medium
Support
Boundary
ETABS uses graphic object modeling concept
Load Transfer Path is diff icul t to Determine
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
51/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Complexity of Load Transfer
Mechanism depend on:
Complexity of Load
Complexity of Medium
Complexity of Boundary
Point Line Area Volume
Line
Area
Vol.
Line
Area
Volume
Load
Mediu
Boundary
Load Transfer Path is diff icul t to Determine
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
52/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Transfer of a Point Load to Point Supports Through Various Mediums
Point Line Area Volume
Objects in ETABS
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
53/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Building Object Specific Classification
PlankOne way slabs
SlabOne way or Two way slabs DeckSpecial one way slabs
WallShear Walls, Deep Beams, In-Fill Panel
FrameColumn, Beam or Brace
Finite Elements Shell
Plate
Membrane
Beam
Node
The Frame Element
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
54/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Actions Corresponding to Six DOF at Both Ends, in
Local Coordinate System
1
3
2
3
2
+P+V2
+V3
+V3
+V2+P
1
3
2
3
2
+T+M2
+M3
+M3
+M2+T
Shell Element
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
55/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
General
Total DOF per Node = 6 (or 5)Total Displacements per Node = 3
Total Rotations per Node = 3
Used for curved surfaces
Application
For Modeling surface elements carryinggeneral loads
Building Specific ApplicationMay be used for modeling of general slabs
systems. But not used generally
Plate Element
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
56/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
General
Total DOF per Node = 3Total Displacements per Node = 1
Total Rotations per Node = 2
Plates are for flat surfaces
Application
For Modeling surface elements carryingout of plane loads
Building Specific ApplicationFor representing floor slabs for Vertical
Load Analysis
Model slabs
Membrane Element
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
57/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
General
Total DOF per Node = 3 (or 2)Total Displacements per Node = 2
Total Rotations per Node = 1 (or 0)
Membranes are modeled for flat surfaces
Application
For Modeling surface elements carryingin-plane loads
Building Specific ApplicationFor representing floor slabs for Lateral
Load Analysis.
Model Shear walls, Floor Diaphragm etc
Meshing Slabs and Walls
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
58/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
In general the mesh in the slab
should match with mesh in the wall
to establish connection
Some software automatically
establishes connectivity by using
constraints or Zipper elements
Zipper
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
59/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Selection Of Structural Systems
Basic Concepts and Considerations
Knowledge Model for System Selection
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
60/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Structural
System Selection
Architecture
Syste
msEng
ineering
Aesth
etics
Value
Engin
eering Econom
ics
Construction
Engineering
Knowledge
Engineering
Artificial Intelligenc
SoftwareEngineering
Build
ing
Serv
ices
Engineering
S
tructural
E
ngineering
Engin
eering
Judgementa
nd
Common
Sens
e
Ergonomic
s
Eng
ineering
Architecture
Building Services
Construction Eng.
Value Eng.
Aesthetics
Ergonomics Eng.
Structural Eng.
Knowledge Eng.
Economics
Artificial Intelligence
System Eng.
Common Sense
Determining System Suitabi l i ty
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
61/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The Analytical Hierarchy Approach
A weighted importance and sui tabil i ty value analysis to
determine the comparative value of a system or option
Value of
an Option
Global
Importance
Weights and
Scores
Sub
Importance
Weights and
Scores
Suitability
Value and
Score
Evaluating System Suitabil i ty
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
62/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Slab Systems Criteria Weights and Scores System
Value(V)
Main Criteria Ai Am
Sub Criteria Bij Sub Criteria B
in B
mn
Item k Item p Item k Item p Item p
Wt Score Wt Score Wt Score Wt Score Score
System1
System l Cijkl Sijkl Cijnl Sijpl Cinkl Sinkl Cinnl Sinpl Smnpl
System - q
The Suitability Equation
Using the Suitability Equation
Assigning Suitabil i ty Values
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
63/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
10 Most important, most suitable, most desirable, essential
8,9 Very important, very suitable, very desirable
6,7 Important, suitable or desirable
5 May be or could be important, suitable or desirable
4,3 May not be important, suitable or desirable
1,2 Not important, not suitable, not desirable
Score or Weight Representation of Suitability
0 Definitely not required, definitely not suitable, ignore
Selection of Structural System
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
64/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Function has considerable effect on the selection
of structural system
Based on Function/Occupancy of Tall Buildings:
Residential Buildings
Apartments
Hotels
Dormitories
Office and Commercial Buildings
Mixed OccupancyCommercial + Residential
Industrial Buildings and Parking Garages
Typical Character istics of Residential Bldg
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
65/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Known location of partitions and their load
Column lines generally matches architectural layout
Typical spans 15-22 ft
Tall buildings economy in achieved using the thinnest slab
One way pre-cast or flat slabpopular
Lateral load resistance provided by frame or shear walls
More or less fixed M/E system layouts
Typical Character istics of Off ice and Commercial Bldg
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
66/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Unknown location of partitions and their load
Typical spans 20-35 ft
Need for flexible M/E layouts Post-tension or ribbed and flat slab with drop panel
popular
Ideal balance between vertical and lateral load resisting
systems: sufficient shear walls to limit the resultanttension under gravity plus wind
Lateral load resistance varies significantly
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
67/147
Vertical Load
Resisting Systems
The Components Needed to
Complete the Load-Transfer Path
for Vertical Gravity Loads
Gravity Load Resisting Systems
P
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
68/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Purpose
To Transfer Gravity Loads Applied at the Floor Levels
down to the Foundation Level
Direct Path Systems
Slab Supported on Load Bearing Walls
Slab Supported on Columns
Indirect Multi Path Systems
Slab Supported on Beams
Beams Supported on Other Beams
Beams Supported on Walls or Columns
Vertical Load Resisting Systems
1 Sl b t d L Ri id S t
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
69/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
1. Slabs supported on Long Rigid Supports
Supported on stiff Beams or Walls
One-way and Two-way Slabs Main consideration is flexural reinforcement
2. Slab-System supported on Small Rigid Supports
Supported on Columns directly
Flat Slab Floor systems
Main consideration is shear transfer, moment distribution in various
parts, lateral load resistance
3. Slabs supported on soil
Slabs on Grade: Light, uniformly distributed loads
Footings, Mat etc. Heavy concentrated loads
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
70/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Vertical Load
Behavior and Response
Popular Gravity Load Resting Systems
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
71/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Direct Load Transfer Systems (Single load transfer path)
Flat Slab and Flat Plate Beam-Slab
Waffle Slab
Wall Joist
Indirect Load Transfer System (Mul ti step load transfer path)
Beam, Slab
Girder, Beam, Slab
Girder, Joist
Conventional Approach
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
72/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
For Wall Supported Slabs
Assume load transfer in One-Way or Two-Way manner Uniform, Triangular or Trapezoidal Load on Walls
For Beam Supported Slabs
Assume beams to support the slabs in similar ways as walls
Design slabs as edge supported on beams
Transfer load to beams and design beams for slab load
For Flat-Slabs or Columns Supported Slabs
Assume load transfer in strips directly to columns
Popular Gravity Load Resting Systems
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
73/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Gravity Load Transfer Paths
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
74/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Single PathSlab On Walls
Single PathSlab on Columns
Dual PathSlab On Beams,
Beams on Columns
Gravity Load Transfer Paths
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
75/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Mixed PathSlab On Walls
Slab On Beams
Beams on Walls
Complex PathSlab on Beams
Slab on Walls
Beams on Beams
Beams on Columns
Three Step PathSlab On Ribs
Ribs On Beams
Beams on Columns
Simpli f ied Load Transfer
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
76/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Transfer of Area Load
To Lines To Points To Lines and Points
Load Transfer Through Slab and Beam
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
77/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Slab Deformation and Beams
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
78/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Slab System Behavior
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
79/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Slab T = 200 mm
Beam Width, B = 300 mm
Beam Depth, D
a) 300 mm
b) 500 mmc) 1000 mm
D
B
Moment Distr ibution in Beam-Slab
Effect of Beam Size on
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
80/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Effect of Beam Size on
Moment Distribution
a) Beam Depth = 300 mm
b) Beam Depth = 500 mmc) Beam Depth = 1000 mm
Moment Distr ibution in Slabs Only
Effect of Beam Size on Moment Distribution
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
81/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
a) Beam Depth = 300 mm b) Beam Depth = 500 mm c) Beam Depth = 1000 mm
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
82/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Modeling and Analysis for
Vertical Loads
Modeling for Gravity Loads
Must be carried out for several load cases/ patterns
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
83/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Does not change much for different floors
1. Use Direct Design Methods Model, analyze and design Floor by Floor, Without columns
Slab analysis and design by using Coefficients
Beam analysis as continuous beams
2. Use Sub-Frame Concept
Model slab/ beam for in-plane loads
Model, analyze and design Floor by Floor, With columns
3. Use Grid, Plate Model for the Floor
Model slab and beams for out-of plane loads
Analyze un-symmetrical loads, geometry, openings etc.4. Use full 3D Modeling
The Design Str ip Concept
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
84/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Column Strip
Middle Strip
DesignStrip
Middle Strip
DesignStrip
Using Equivalent F rame MethodDesign Str ip
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
85/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Column Strip
Middle Strip
Middle Strip
Design Strip
L
L
L1
Longitudinal Beams
Transverse Beams
Drop Panels
L t l L d
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
86/147
Lateral Load
Resisting Systems
The Components Needed toComplete the Load-Transfer Path
for Lateral Loads
Purpose
Lateral Load Bearing Systems
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
87/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
To Transfer Lateral Loads Applied at any location in the
structure down to the Foundation Level
Single System
Moment Resisting Frames
Braced Frames
Shear Walls
Tubular Systems
Dual System
Shear Wall - Frames
Tube + Frame + Shear Wall
Lateral Loads
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
88/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Primary Lateral Loads
Load generated by Wind Pressure
Load generated due to Seismic Excitation
Other Lateral Loads
Load generated due to horizontal component of Gravity
Loads in Inclined Systems and in Un-symmetricalstructures
Load due to lateral soil pressure, liquid and material
retention
Sample Lateral Load Resistance Systems
Bearing wall system
Light frames with shear panels
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
89/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Light frames with shear panels
Load bearing shear walls
Fully Braced System (FBS) Shear Walls (SW)
Diagonal Bracing (DB)
Moment Resisting Frames (MRF)
Special Moment-Resisting Frames (SMRF)
Concrete Intermediate Moment-Resisting Frame (IMRF)
Ordinary Moment-Resisting Frame (OMRF)
Dual Systems (DS)
Shear Walls + Frames (SWF)
Ordinary Braced Frame (OBF)
Special Braced Frame (SBF)
Moment Resisting Frame
The Load is transferred by
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
90/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
shear in columns, that
produces moment in
columns and in beams
The Beam-Column
connection is crucial for the
system to work
The moments and shearfrom later loads must be
added to those from gravity
loads
Shear Wall and Frame
The lateral loads is
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
91/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
primarily resisted by the
shear in the walls, in turn
producing bending moment
The openings in wall
become areas of high stress
concentration and need to
be handled carefully Partial loads is resisted by
the frames
Traditionally 75/25
distribution haws been used
Shear Wall - F rame
The Walls are part of the
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
92/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
frame and act together with
the frame members
The lateral loads is
primarily resisted by the
shear in the walls, in turn
producing bending moment.
Partial loads is resisted bythe frame members in
moment and shear
Braced Frame
The lateral loads is primarily
i d b h A i l F i
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
93/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
resisted by the Axial Force in
the braces, columns and
beams in the braced zone.
The frame away from the
braced zone does not have
significant moments
Bracing does not have to beprovided in every bay, but
should be provided in every
story
Tubular Structure
The system is formed by using
l l d l d d
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
94/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
closely spaced columns and deep
spandrel beams
The lateral loads is primarily
resisted by the entire building
acting as a big cantilever with a
tubular/ box cross-section
There is a shear lag problembetween opposite faces of the tub
due to in-efficiency of column
beam connection
The height to width ratio should
be more than 5
Braced Tube Systems
Diagonal Braces are added to
th b i t b l t t
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
95/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
the basic tubular structure
This modification of theTubular System reduces shear
lag between opposite faces
Lateral Load
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
96/147
ResistingSystem
Behavior, Response
and Modeling
Modeling for Lateral Loads
1 2D Frame Models
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
97/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
1. 2D Frame Models
Convert building in to several 2D frames in each direction
Suitable for symmetrical loads and geometry
2. 3D Frame Model
Make a 3D frame model of entire building structure
Can be open floor model or braced floor model
3. Full 3D Finite Element Model
A full 3D Finite Element Model using plate and beam elements
4. Rigid Diaphragm Model
A special model suitable for buildings that uses the concept of Rigid
Floor Diaphragm
Modeling as 2D F rame(s)
Convert 3D Building to an assemblage of 2D Frames
U i I d d t F
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
98/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Using Independent Frames
Using Linked Frames Using Sub-Structuring Concept
Advantages
Easier to model, analyze and interpret
Fairly accurate for Gravity Load Analysis
Main Problems:
Center of Stiffness and Center of Forces my not coincide
Difficult to consider building torsional effects
Several Frames may need to be modeled in each direction
Difficult to model non-rectangular framing system
Create a Simple 2D Model
2. Select and
isolate Typica
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
99/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
1. Consider the Structure
Plan and 3D View
isolate Typica
2D Structure
4. Obtain results
3. Discretize
the Model,
apply loads
Using Linked Frames
Linked Elements
F1
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
100/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Plan
Modeling
Shear Wall
Typical Frame Elevation
Linked Elements
Link Element can allow only to transmit the shear and
axial force from one end to other end. It has moment
discontinuity at both ends
Link Element act as a member which links the forces of
one frame to another frame, representing the effect ofRigid Floor.
F3
F2
F1 F2 F3
Ful l 3D F ini te Element Model
The columns and beams are modeled by using
beam elements
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
101/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
beam elements
The slabs and shear walls are modeled by usingplate elements
At least 9 or 16 elements in each slab panel must be
used if gravity loads are applied to the slabs
If the model is only for lateral analysis, one element
per slab panel may be sufficient to model the in-plane stiffness
Shear walls may be modeled by plate or panel or
plane stress element. The out of plane bending is
not significant
Ful l 3D F ini te Element Model
Example:
U th 4000
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
102/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Uses more than 4000
beam and plate elements Suitable for analysis for
gravity and lateral loads
Results can be used for
design of columns and
beams Slab reinforcement
difficult to determine
from plate results
Modeling of F loor Diaphragm
U Di l
Use Plate Elements
P l Pl St
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
103/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Use Plate
Elements
Use Diagonal
Bracing Panels, Plane Stress
Use Diagonals In 3D Frame Models
Use Conceptual Rigid
Diaphragm
Link Frames in 2D
Master DOF in 3D
Use Approximately
The Rigid Floor Diaphragm
Combines the simplicity and advantages of the 2D Frame
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
104/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
p y g
models with the accuracy of the 3D models
Basic Concept:
The building structure is represented by vertical units (2D Frames,
3D Frames and Shear Walls), connected by the invisible rigid
diaphragm
The lateral movement of all vertical units are connected to three
master degree of freedom
This takes into account the building rotation and its effect on the
vertical units.
The modeling and analysis is greatly simplified and made efficient
Rigid Floor Diaphragm Concept
Modeled as Rigid Horizontal Plane of infinite
in-plane stiffness (in X-Y plane)
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
105/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
p ( p )
Assumed to have a hinge connection with
frame member or shear wall, so flexural
influence of all floors to lateral stiff ness is
neglected
All column lines of all frames at particular
level can not deform independent of eachother
The floor levels of all frames must be at the
same elevation and base line, but they need
not have same number of stories
How RFD Concept Works
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
106/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
UL
UL1
UL2
UL3
X
Y
F3 , 2
F1 , 1
F3 , 3
Building d.o.f.s
F2 , 1
r x
r qrY
Local Frame DOF
When Single Rigid Floor Cannot be Used
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
107/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
108/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Automatic Floor Meshingand Auto Load Transfer
(In ETABS)
Area Objects: Slab
By default uses two-way load transfer
mechanism
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
109/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Simple RC solid slabCan also be used to model one way slabs
Area Object: Deck
Use one-way load transfer mechanism
lli C i Sl b
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
110/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Metallic Composite Slabs
Includes shear studs
Generally used in association with
composite beams
Deck slabs may be
o Filled Deck
o Unfilled Deck
o Solid Slab Deck
Area Object: Plank
By default use one-way load transfer
mechanism
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
111/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Generally used to model pre-cast slabs
Can also be simple RC solid slab
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
112/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Automatic Floor MeshingFirst step to Auto Load Transfer
Basic F loor M odeling Object
Points
Columns
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
113/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Load Points Boundary Point
Lines
Beams
Areas
Deck: Represents a Steel Metal Deck, One way Load Transfer
Plank : Represents clearly on-way slab portion
Slab: Represents one-way or two-way slab portion
Opening: Represents Openings in Floor
Automatic Meshing
ETABS automatically meshes all line objects with frame
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
114/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
section properties into the analysis model
ETABS meshes all floor type (horizontal) area objects (deck
or slab) into the analysis model
Meshing does not change the number of objects in the
model
To mesh line objects with section properties use Edit menu> Divide Lines
To mesh area objects with section properties use Edit menu
> Mesh Areas
Automatic Meshing
Automatic Meshing of Line Objects
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
115/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Frame elements are meshed at locations where other frame
elements attach to or cross them and at locations where point
objects lie on them.
Line objects assigned link properties are never automatically
meshed into the analysis model by ETABS
ETABS automatically meshes (divides) the braces at the point
where they cross in the analysis model
No end releases are introduced.
Automatic Meshing of Line Objects
Girder A
Piece 1 Piece 2 Piece 3
Beam 1 Beam 2
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
116/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Girder B
Beam1
Beam2
b) Girders A and B As Modeled inthe ETABS Analysis Model
a) Floor Plan
Example showing how beams are automatically divided (meshed) where they
support other beams for the ETABS analysis model
Automatic Meshing of Area Objects
ETABS automatically meshes a floor-type area object up into four-sided (quadrilateral) elements
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
117/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
sided (quadrilateral) elements
Each side of each element of the mesh has a beam (Real or Imaginary)or wall running along it
ETABS treats a wall like two columns and a beam where the columnsare located at the ends of the wall and the beam connects the columns.
Each column is assumed to have four beams connecting to it
The floor is broken up at all walls and all real and imaginary beams tocreate a mesh of four-sided elements
Girder A Girder A
Automatic Meshing of Area Objects
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
118/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Girder B
Beam1
Beam2
Beam3
Girder B
Beam1
Beam2
Beam3
c) ETABS Automatic Floor Meshingb) ETABS Imaginary Beams Shown Dasheda) Floor Plan
Example of ETABS automatically generated mesh for floor-type area objects
Automatic Meshing of Area Objects
Example of ETABS
automatically generated mesh
f fl bj
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
119/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
d) ETABS Automatic Floor Meshing
b) ETABS Imaginary Beams Connecting
Columns Shown Dashed
a) Floor Plan (No Beams)
c) ETABS Imaginary Beams Extended to
Edge of Floor Shown Dashed
for floor-type area objects
Automatic Meshing of Area Objects
For floors that are automatically meshed by ETABS it is
d d h d l b ( l ll li bj )
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
120/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
recommended that model beams (or at least null-type line objects)
are connecting columns rather than no beams (or line objects)
This makes the automatic meshing for the analysis model cleaner,
faster and more predictable
Including beams and/or null-type line objects between all
columns in your model makes automatic floor meshing more
predictable
Automatic Meshing of Area ObjectsC3C4 C3C4 C3C4
Illustration of how ETABS
creates the distribution of
imaginary beams
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
121/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
c)b)a)
f)e)d)
i)h)g)
C1 C2 C1 C2
C1 C2
C3C4
C1 C2
C1 C2
C3C4
C1 C2
C3C4
C1 C2
C3C4
C1 C2
C3C4
C1 C2
C3C4
imaginary beams
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
122/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Automatic Transformation andTransfer of Floor Loads toAppropriate Elements
(Using the Auto Meshed Geometry)
Load Transformation
The main issue:
How point loads line loads and area loads that lie on an area
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
123/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
How point loads, line loads and area loads that lie on an area
object in your object-based ETABS model are represented inthe analysis model
There are four distinct types of load transformation inETABS for out-of-plane load transformation for floor-type
area objects with deck section properties
with slab section properties that have membrane behavior only
all other types of area objects
In-plane load transformation for all types of area objects
Load Transformation
Area Objects
load transformation occurs after anyautomatic meshing into the analysis Edge1 dge
4
12
Edge1d
ge4
12
r
s
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
124/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
automatic meshing into the analysis
model
ETABS normalizes the coordinates ofthe four corner points of the area object
The normalization is the key
assumption in this method
It is a perfectly valid assumption if thequadrilateral is a square, rectangular or
a parallelogram
a) Quadrilateral Element
Ed
4
3
Ed
ge2
Edge3
b) The r and s Axes
Ed
4
3
r
Ed
ge2
Edge3
(1, 1)
(-1, 1)
(1, -1)(-1, -1)
c) Corner Point r-s Coordinates
12
43
r
s
(r, s)
P
(1, 1
(-1, 1)
(1, -1)(-1, -1)
d) Point Load, P
12
43
r
s
Example of transfer of out-of-plane loads
for other area objects
Load Transformation
The load distribution for deck sections is one way, in
contrast to slab sections which are assumed to span in two
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
125/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
contrast to slab sections which are assumed to span in two
directions
ETABS first automatically meshes the deck into
quadrilateral elements
Once the meshing is complete ETABS determines the
meshed shell elements that have real beams along them andthose that have imaginary beams
It also determines which edges of the meshed shell elements
are also edges of the deck.
Load Transformation
Rectangular Interior Meshed Element with Uniform Load
If the supporting membert th d i t f
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
126/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Edge 1
Edge 3
Edge
2
Edge
4
x
Edge 1
Edge 3
Edge
2
Edge
4
x / 2 x / 2
Uniform load = w
Direction of deck span
a) Rectangular Interior Element
of Meshed Floor
b)Distribution of Uniform Load
wx / 2
c) Loading on Edges 2 and 4
Example of rectangular interior meshed
element with a uniform load
at the end point of animaginary beam is itselfimaginary, then the load
from the imaginary beamtributary to that end pointis lost, that is, it isignored by ETABS
Load TransformationRectangular Interior Meshed Element with Point Load
ETABS distributes the point load to the appropriate edge beams
(based on the direction of the deck span)
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
127/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
If the beams along edges are real beams ETABS transfers the load ontoadjacent beams
Edge 1
Edge 3
Edge2
Edge4
x1 x2
Point load, P
Direction of deck span
a) Rectangular Interior Element
of Meshed Floor
b)Distribution of Point Load
x1 x2Edge 4 Edge 2
P
P * x2
x1 + x2
P * x1
x1 + x2
c) Loading on Edge 2
P * x1
x1 + x2
d) Loading on Edge 4
P * x2
x1 + x2
If the supportingmember at the end pointof an imaginary beam is
itself imaginary, then theload from the imaginarybeam tributary to thatend point is lost, that is,it is ignored by ETABS
Load Transformation
Rectangular Interior Meshed Element with Line Load
A line load is transformed in a similar fashion to that for a point load
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
128/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
using a numerical integration technique
The line load is discredited as a series of point loads which are
transformed to surrounding beams
The series of point loads is then converted back to a line load on thesurrounding beams
An area load that does not cover the entire element is also transformed in
a similar fashion to that for a point load using a numerical integration
technique.
General Interior Meshed Element
Edge3
Edge2
Ed
ge4
Uniform load
Di ti f d k
Edge3
Edge2
Ed
ge4
Edge3
Edge2
Ed
ge4 Midpoint
Midpoint
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
129/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
d)
Edge1
Edge3
Edge2
Ed
ge4
Edge1
Edge3
Edge2
Ed
ge4
e) Transformation of Uniform Load
Edge1
Direction of deck span
a) General Interior Element of
Meshed Floor Deck
b)
Edge1 Edge1
c)
g) Loading on Edge 2
f) Loading on Edge 1
h) Loading on Edge 3 i) Loading on Edge 4
Midpoint
Example of general interior meshed element with a
uniform load
a) General Interior Element ofMeshed Floor Deck
Edge1
Edge3
Edge2
Ed
ge4
P1
P2
P3
b)
Edge1
Edge3
Edge2
Ed
ge4
P1
P2
P3
Line 1
Line 2
Line 3
Example of general interior meshed
element with a point load
Exterior Meshed Element
Beam 1a
E FD
Beam 1b Beam 1
Beam2
b
Beam2
bExample of exterior meshed
elements with real beams on all sides
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
130/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
Edge of deck is atcenter of spandrelbeam, typical in thisexample
B CA
a) Floor Plan b) Deck Meshing
Beam2
a
Beam2
a
Beam 3a
B CA
ED
a) Floor Plan b) Deck Meshing
Beam
Beam1
a
Bea
m1
b
Bea
m2
b
Beam 3a Beam 3b
Beam1
a
Bea
m1
b
Beam2
a
Bea
m2
b
Beam 4a Beam
Imag
inaryNo beam at
edge of deck
No beam at
edge of deck
Example of exterior meshed elements
with cantilever beams extending to
edge of deck
Exterior Meshed Element
ED inaryBeam6
b2
b ba
m2
bImagin
aryBeam7
ImaginaryB
eam8
No beam at
d f d k
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
131/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
ImaginaryBe
am8
a) Floor Plan b) Deck Meshing
B CA
ED
ImaginaryBeam5
Im
agi
Beam 3a Beam 3b
Beam1
a
Bea
m1
Beam2
a
Bea
m2
Beam 3a Beam 3b
Beam1
a
Bea
m1
Beam2
a
Bea
E1ImaginaryBeam6
Beam 3b
Beam2
b
E2
c) Condition at Skewed Deck
Edge (Areas D and E)
ImaginaryB
eam7
D
D
Beam 3aBeam1
b
edge of deck
No beam at
edge of deck
Example of exterior
meshed elements
with cantilever
beams extending to
edge of a skewed
deck
Exterior Meshed Element
Beam 1
EDBeam 1
Edge of deck
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
132/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
B CA
a) Floor Plan b) Deck Meshing
Beam2
Beam2
Column 1 Column 1
Example of exterior meshed elements with overhanging slab
Exterior Meshed Element
Beam 1a Beam 1a
E FD
Beam 1b Beam 1b
Beam2
b
Beam2
b
G H I
J
Beam3
b
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
133/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
B CA
a) Floor Plan b) Deck Meshing
Beam2
a
Beam2
aK
Beam3
a
Example of exterior meshed elements with overhanging slab
Effect of Deck Openings
4' 6' 14'Note: Assume floor loading is 100
psf. Opening is either loaded or
unloaded as noted in c, d, e and f
which are loading diagrams for
Beam 1.
Example of effect of openings
on distribution of load over
deck sections
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
134/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
a) Floor Plan with Unframed Opening
Beam 1
6'
4'
2'
b) Floor Plan with Framed Opening(Beams on all Sides)
Beam 1
4' 6' 14'
6'
4'
2'
c) Unframed, unloaded opening
4' 6' 14'
d) Unframed, loaded opening
e) Framed, unloaded opening
f) Framed, loaded opening
0.7k
0.6 klf0.2 klf
0.6 klf 0.6 klf
0.6 klf 0.6 klf
0.1 klf
0.1 klf
0.7k
1.5k 1.5k
Load TransformationVertical Load Transformation for Floors with Membrane
Slab Properties
only applies to floor-type area objects with slab section
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
135/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
properties that have membrane behavior only The load distribution for membrane slab sections is two way
The actual distribution of loads on these elements is quite
complex
ETABS uses the concept of tributary loads as a simplifying
assumption for transforming the loads
Floors with Membrane Slab Properties
1
1
33
34
2
2
4
1 2
12
3
1
1 2
1
3
24
1
3
24
123
1
231
2
3
1
2
3
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
136/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
l) Vertical support
elements at two
adjacent corner point
(no real beams)
j) Vertical support
elements at all corner
points (no real beams)
1
k) Vertical support
elements at three
corner points (no real
beams)
2 1 2 1
m)Vertical supportelements at two
opposite corner points
(no real beams)
1
1
Legend
Real beam at shell edge
No beam at shell edge
Tributary area dividing
Vertical support elemen
n) Vertical supportelements at one
corner point (no
real beams)
1
1
2
2
f) Real beam on one sidee) Real beams on two
opposite sides
d)Real beams on two
adjacent sides
c) Case 2 of real beams onthree sides
b) Case 1 of real beams onthree sides
a) Real beams on all sides
1 1 1
1
2
1
2
1
1
1
1
2
2
i) Real beam on one side
plus two vertical
support elements at
corner points
h) Real beams on two
adjacent sides plus
one vertical support
element at corner point
g)Real beam on one side
plus one vertical
support element at
corner point
11
1
1
1
3
1
3
2
2
2
2midpoint
2
2
3
3
midpoints
Tributary areas for various
conditions of a membrane slab
Floors with Membrane Slab Properties
3
24
3
24
3
24
3
24
Example of load distribution on a
membrane slab
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
137/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
a) Full uniform load
transformation
b) Partial uniform load
transformation
c) Line load transformation d)Point load transformation
1
1
1
1
1
3
24
3
24
1
1
3
24
3
24
1
Type of Slab Systems in SAFE
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
138/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
The 5-Story Walkup F lats
5
6
A CB D E F G
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
139/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
4.0 4.0 5.5 5.5 4.0 4.0
6.0
6.0
2.8
2.8
Column Layout Plan
1
2
3
4
The 5-Story Walkup F lats
5
6
A CB D E F G
C1= 0.3 x 0.8C1C2
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
140/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
4.0 4.0 5.5 5.5 4.0 4.0
6.0
6.0
2.8
2.8
Slab and Beam Layout
1
2
3
4
C2 = 0.3 x 0.4
B1 = 0.25 x 0.4
B2 = 0.25 x 0.5
S1 = 0.15
B1
B2
The 5-Story Walkup F lats
3.0
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
141/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM
12356 4
3.0
3.0
3.0
3.5
2.0
Section
35 Story Off ice Bui lding5
7.0
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
142/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM6.0 6.0 8.0 8.0 6.0 6.0
8.0
8.0
1
2
4
A CB D E F G
3
7.0 Plan
Typical Floor
(B1, B2, 4-35)
35 Story Off ice Bui lding5
7.0
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
143/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM6.0 6.0 8.0 8.0 6.0 6.0
8.0
8.0
1
2
4
A CB D E F G
3
7.0 Plan
Floor 1-2
35 Story Off ice Bui lding
4
5
7.0
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
144/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM6.0 6.0 8.0 8.0 6.0 6.0
8.0
8.0
1
2
4
A CB D E F G
3
7.0 Plan
Floor 3
35 Story Off ice Bui lding
32 @ 3 5
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
145/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM1245 3
2 @ 5.0
2 @ 2.8
32 @ 3.5
Section at
C and D
35 Story Off ice Bui lding
32 @ 3 5
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
146/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM1245 3
2 @ 5.0
2 @ 2.8
32 @ 3.5
Section at
B and E
35 Story Off ice Bui lding
32 @ 3 5
7/28/2019 82273570 International Seminar on Computer Aided Analysis and Design of Building Structures
147/147
Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM1245 3
2 @ 5.0
2 @ 2.8
32 @ 3.5
Section at
A and G
Top Related