Analysis & Design Using ETABS

ACECOMS, AIT ₁

Analysis and Design of Buildings

Using ETABS 9.5

Dr. Naveed Anwar, Keerati Tunthasuwat, Thuang Htut Aung

Asian Institute of Technology

Users’ Forum

Manila, 2009

About ACECOMS and AIT

„ The Asian Center for Engineering Computations and Software

(ACECOMS) is a part of the Structural Engineering Field in the School of Engineering and Technology (SET) at the Asian Institute of Technology (AIT), Thailand.

„ AIT is a postgraduate international institute established in 1959 with the mission “to develop highly qualified and committed professionals who play leading roles in the region's sustainable development and its integration into the global economy”.

„ The Structural Engineering Field is one of the first programs to be established at AIT and has been as a strong academic and research program for almost fifty years. The program is well known for

excellence in academic, research and industry partnership. „

About ACECOMS and AIT

„

ACECOMS was established in 1995 as one of

the first not-for-profit, self-sustaining outreach

center in then the School of Civil Engineering to

provide and interface between academic and

research activities and the professional practice.

Since its establishment., ACECOMS has been

contributing significantly in the development and

effective applications of computational

technologies in structural and civil engineering

through its activities

ACECOMS

„ Carry-out research and development in engineering

computational technology and software.

„ Carry-out research and provide consultancy for the

applications of computing tools on the real world problems

„ Provide general and specialized consulting services and

support for project design, system development, review and investigation etc.

„ Provide trainings and technical support for development

of knowledge, information and skills

„ Establish networks and associations with regional

academic institutions and professional organizations

„ Disseminate practical information and knowledge

ACECOMS, AIT ₃

Agenda

„

Overview

„

Handling Materials, Sections, Loads

Handling Special Behavior

„

Creating Complex Models

Analysis for various purposes

Interpreting and evaluating results

Specific Questions

„

What is Coming Next?

Discussion

Software Discussed

ETABS

SAP2000

SAFE

CSICOL

GEAR

GRASP

Overall Process

„

Define the Parameters and Properties

Quick Modeling

„

Import, Draw and Edit

Select and Assign

„

Analyze and Understand

Design and Check

Define and Preferences

ACECOMS, AIT ₅

Define Coordinate System/Grids

„ For a regular or general system, the coordinate system is defined using an origin and orientation relative to the Global coordinate system.

„ All coordinate systems follow the right-hand rule. The grid lines for a regular system are defined relative to X and Y (Cartesian) or r and theta (cylindrical). The grid lines for a general system are defined relative to X and Y only.

„ A regular system is any coordinate/grid system having a Cartesian (rectangular) or cylindrical grid system.

„ A general system is a system comprised of arbitrarily defined grid lines.

„ The Global coordinate system always exists, and has its own grid. All other systems are user defined with respect to the Global system.

Define Coordinate System/Grids

„

Configuration of alternate coordinate systems

Define Coordinate System/Grids

„

Configuration of alternate coordinate systems

Define Coordinate System/Grids

„ How to determine regular system or general system

„ To determine if a previously defined system is a regular or general system, access the Coordinate/Grid Systems form and highlight the system name in the Systems display area. If the

Convert to General Grid check box is NOT checked (with the

ACECOMS, AIT ₇

Define Coordinate System/Grids

„ General System

„ In general system, we can draw the arbitrary grid lines which does not need to perpendicular each other.

Define Coordinate System/Grids

„ General System

Functions

„

Response Spectrum

„

Time History

Functions

Response Spectrum Function

For Seismic Analysis

„ From Code (IBC2006, AASHTO, EuroCode 8 …etc.)

„ User Define from File

ACECOMS, AIT ₉

Functions

Time History Function

„ From Built-in (Sine, Cosine, Ramp, Sawtooth…etc.)

„ User Define from File

Time History Function for Sine Function

Quick Modeling

Templates

ACECOMS, AIT ₁₁

Staggered Truss System

Flat Slab with Perimeter Beams

ACECOMS, AIT ₁₃

Ribbed Slab System

Template

„

Add template to existing model

„

Able to add the components from template to

Export, Draw and Edit

Creating Complex Geometry Efficiently

Import & Export

„

Capability to import data from many

structural engineering software to create

the model

„

Export the model to SAFE and other

drawing software

ACECOMS, AIT ₁₅

Export to AutoCAD .dxf File

Drawing and Editing

„

Points

„ Nodes, Supports etc.

„

Lines

Areas

Move

Replicate

Extrude

Edit Points

Divide

Mesh

Replicate

„ Generating a large model from a small model when the

objects and/or joints form a linear or radial pattern or are symmetrical about a plane or story.

„ Different from Cut, Copy and Paste commands.

„ Replicate command replicated the assignments and

loads on the objects but Cut, Copy and Paste commands are NOT capable of copying the assignments or loads.

„ Four types of replication

„ Linear

„ Radial

„ Mirror

ACECOMS, AIT ₁₇

Extrude

„

Sweep selected objects through space to

create new objects of higher dimension

„

Extrude points to lines

„Model circular-shaped beam

„

Extrude lines to areas

„Model the ramp

Extrude

Extrude

Model circular shaped ramp by radial extrusion of line object

Edit Point

„

Merge joints

„ Merge the joints outside the auto merge tolerance.

„ To eliminate the extraneous joints that may occur if

the elements are drawn with snap turned off.

„

Align points

„ If the floor area is manually meshed in irregular

pattern and the different pattern loading is to be assigned, the edge of area elements should be aligned along the border of the pattern loading.

ACECOMS, AIT ₁₉

Edit Point - Merge

Select the points to merge

Merge tolerance must be greater than distance between the points

Edit Point - Align

Live load = 2 kN/m2 Live load = 5 kN/m2

To assign different pattern loading on irregular shaped

meshed floor

Draw the line along the border of pattern

loading. Select the line and the points to

be aligned

The floor elements are aligned along the

border of different pattern loading

Edit Lines

„

Divide frames

Join frames

„

Trim/Extend frames

„

Edit curved frame geometry

Edit cable geometry

„

Edit tendon profile

Edit Lines

„

Divide frames

„ Divide the frame intersect with selected frames.

Select the frame object to bed divided and select the

intersecting objects

„

Join frames

ACECOMS, AIT ₂₁

Edit Areas - Divide

„

Divide into the number of objects specified

using the edit box for each edge.

Edit Areas - Divide

„

Divide area into objects of given maximum

size

Edit Areas - Divide

„ Divide area based on points on area edges

„ Divide based on specified lines and points. Program will not extend the selected line to make it intersect an edge; the selected line must already intersect an edge of the selected area object. The selected point must also intersect an edge of the selected object, not inside the selected object.

Edit Areas - Divide

„ Divide area using cookie cut based on selected straight

line objects

„ The selected line object does not need to intersect with the edge of the selected area object .

ACECOMS, AIT ₂₃

Edit Areas - Divide

„ Divide area into given number of objects

„ The selected point object must lie either on the edge or inside the selected area object. The rotation in degrees of dividing lines can be specified from original local 1 and 2 axes.

Edit Areas - Divide

„ Divide area using general divide tool based on selected

points and lines

„ Divide the area object based on specified maximum dimension. „ The division lines intersect the selected points and concurrent

Edit Areas - Divide

„

Local axes for added points

„

Specify that the local axes definitions for new

points added along the edges of an area

object are the same as an adjacent area

object corner point if the local axes definition

for the adjacent corners are identical.

„

Specify that the local axes definition for the

new points on the face of the area object are

set the same as a corner point of the area

object if the local axes definitions for all of the

corner points of the area object are identical.

Edit Areas - Divide

Added points on the edge of original element have the same local axes with original element. If the second check box is checked, local axes of added points on the face of original element will be same.

ACECOMS, AIT ₂₅

Edit Areas - Divide

„

Restraints and constraints for added points

„ Specify that a restraint degree of freedom (or

constraint) is added to new points on the edges of the area object if both adjacent corners have that degree of freedom restrained (constrained) and the local axes definitions for the adjacent corners and the new point are identical.

„ Specify that a restraint degree of freedom (or

constraint) is added to new points on the face of the area object if all area object corners have that degree of freedom restrained (constrained) and the local axes definitions of all corners and the new points are

identical.

Edit Areas - Divide

Added points on the edge of original element have the same restraints with original element. If the second check box is checked, restraints of added points on the face of original element will be same.

Edit Areas-Merge

„ Selected areas essentially in the same plane and sharing a common edge or with overlapping area edges will be merged.

„ Areas that lie one on top of the other or that share no common or overlapping edges will not be merged.

„ Choose an area that has assignments suitable for the merged area.

Edit Areas-Merge

Area 6

Area 7

Maintain the assignments for Area 7

ACECOMS, AIT ₂₇

Edit Areas

„ Expand/Shrink areas

„ A positive value expands the area and a negative value shrinks the area.

„ The offset distance is measured perpendicular to the area edge.

100 100

100

100

Offset all area edges

Select the edge or whole area

Edit Areas

Offset selected area edges only Select the edge

Edit Areas

Offset selected points of selected areas only 100

Select the point and area The offset for points is measured _{along a bisector angle formed by} the area edges adjacent to the

selected point(s).

Edit Areas

„

Add point to area edge

„ Add points to the edges at the midpoint between the

existing points of the selected object.

„ This procedure can do repeatedly as many times as

ACECOMS, AIT ₂₉

Edit Areas

„

Remove points from area

„ Select the area and the point to be removed.

„ If the point was not colinear with the remaining points,

the area object will be reshaped.

Special Tools

Basic Modeling Techniques

-Behavior

Constraints

Restraints

Springs

Nonlinear Links

Nonlinear Hinges

„

Element End Conditions

Dummy elements

Link/Support Element

„ A Link element is a two-joint connecting link.

„ A Support element is a one-joint element

Support Element Link Element

ACECOMS, AIT ₃₁

Link/Support Element

Type of Link/Support Element available in ETABS

„ Linear „ Damper „ Gap „ Hook „ Plastic1 „ Isolate1 „ Isolate2

Link/Support Element

Damper Element

Gap Element

„ Compression only (for example Spread Footing)

„

Hook Element

Diaphragms

In ETABS: Only diaphragms is available as

constraint option for joint and shell element

Diaphragms

Rigid Option

ACECOMS, AIT ₃₃

Diaphragms

Semi Rigid Option:

„

The in-plane rigidity of the diaphragm comes

from the stiffness of the objects that are part of

the diaphragm

„

Used to calculate the dimension of diaphragm in

application of the wind/static equivalent

earthquake loading

Select and Assign

Select and Assign

„

Many tools to select the drawn objects

Many types of assignments

„

Sections

„

Loads, Temperature, Joint Patters

„

Constraints, Restraints, Releases

„

Special modifications

„

Axis, Insertion Points, Offsets

„

Local material changes

Analyze and Understand

ACECOMS, AIT ₃₅

Analysis Case

„

Static

„

Linear Static

„

Nonlinear Static (Included Push Over)

„

Staged Construction

„

Response Spectrum

Time History

„

Linear Time History

„

Nonlinear Time History

Analysis Case

„

Static

:

„

Linear: The most common type of analysis.

Loads are applied without dynamical effects.

„

Nonlinear: Loads are applied without

dynamical effects. May be used for pushover

analysis, and other types of nonlinear

problems. (Pushover + P-Delta)

„

Nonlinear Staged Construction: The definition

of a nonlinear direct-integration time-history

analysis case for staged construction.

Analysis Case

Analysis Case

Modal:

Calculation of dynamic modes of the structure using the Eigenvector or Ritz-vector method. Loads are not actually applied, although they can be used to generate Ritz vectors.

ACECOMS, AIT ₃₇

Analysis Case

„

Response Spectrum

.

Statistical calculation of the response caused by

acceleration loads. Requires response-spectrum

functions.

Response Spectrum Function

Analysis Case

„

Time History:

„ Linear Time History. Time-varying loads are applied.

Requires time-history functions. All objects behave linearly.

„ Period. Specify a single cycle of the periodic function

and assumes that the specified cycle continues indefinitely. All objects behave linearly.

„ Nonlinear Time History. Time-varying loads are

applied. Requires time-history functions. Nonlinear dynamic properties assigned to link elements are considered.

Pushover Analysis

Pushover Analysis

Available Hinge Properties

„

Axial P

Shear V2

Shear V3

Moment M2

Moment M3

Torsion T

Interaction P-M2-M3

ACECOMS, AIT ₃₉

Pushover Analysis

Hinge Property Data

Displacement Controlled

Pushover Analysis

Pushover Analysis

Pushover Curve

„ ATC-40 Capacity Spectrum ATC-40 Capacity Spectrum

Show Response Spectrum Curve

„

Create from Time History Case at Particular

Joint

„

Frequency or Period

„

Versus

„ Spectral Displacement

„ Spectral Velocity

„ Pseudo Spectral Velocity

„ Spectral Acceleration

ACECOMS, AIT ₄₁

Show Plot Function

„

Energy Function

Input, Kinetic, Potential Modal Damping

Link Damper, Energy Error

„

Base Function

„

Joint Displacement/Forces

Frame Forces

„

Pier Forces

„

Spandrel Forces

Show Plot Function

Displacement Function Base Function

Energy/ Virtual Work Function

Figure "a," that has lateral loads P1 and P2 at the Roof and Second story levels, respectively. Also note the displaced shape, D, associated with this structure and loading, which is shown as a dashed line.

Energy/ Virtual Work Function

Figure "b", with a single load P (typically a unit load) applied to it and a resulting displaced shape, d, shown as a dashed line. Maxwell's Reciprocal Theorem states that:

ACECOMS, AIT ₄₃

Energy/ Virtual Work Function

In this very simple example, the equation above could be reduced to an element level where the elements are illustrated in Figure "c" as:

P _δ= [P1_{δ roof}- P1_{δ second}] + [(P1 + P2)_{δ second}]

Energy/ Virtual Work Function

P _δ= [P1_{δ roof} - P1_{δ second}] + [(P1 + P2)_{δ second}] ETABS show the energy diagram, it reports the equivalent of the values shown in brackets in the above equation of the background information for each element in the structure.

Note the following about the energy values that ETABS reports:

Energy/ Virtual Work Function

P _δ= [P1_{δ roof} - P1_{δ second}] + [(P1 + P2)_{δ second}] They are based on all six degrees of freedom of the element, not just the one degree of freedom described in the Figure and the associated equations in the background information.

They are determined as follows:

„ ETABS determines the energy per unit volume

associated with each element in the structure.

„ ETABS normalizes all of the calculated energy values

such that the largest one has a value of 100.

Energy/ Virtual Work Function

ACECOMS, AIT ₄₅

Time History Traces

Available Functions for Time History Traces

„Input Function

„Energy Function

„Base Function

„Point Displacement/ Forces

„Line Element Forces

„Pier Forces

„Spandrel Forces

Time History Traces

Time History Traces

Energy Function

Time History Traces

ACECOMS, AIT ₄₇

Time History Traces

Base Function = Total Base Reaction Function

Time History Traces

„ Point Displacement/ Forces

„ Line Element Forces

„ Pier Forces

„ Spandrel Forces

Displacement/ Forces at Particular Element and

Location

Time History Traces

„ Point Displacement/ Forces

„ Line Element Forces

„ Pier Forces

„ Spandrel Forces

Displacement/ Forces at Particular Element and

Location Element ID Force Component Location

Outrigger System

ACECOMS, AIT ₄₉

Shear Force in Beams due to Lateral

Load (No Outrigger Wall)

3.14 T 3.25 T 4.24 T

Shear Force in Beams due to Lateral

Load (Outrigger Wall)

Axial Force in Columns due to

Lateral Load (No Outrigger Wall)

623 T 350 T 383 T

Axial Force in Columns due to

Lateral Load (Outrigger Wall)

ACECOMS, AIT ₅₁

Bending Moment due to Lateral Load

(No Outrigger Wall)

8.3 8.6 11.3

40.2 38.3 36.9

Bending Moment due to Lateral Load

(Outrigger Wall)

6.9 6.4 7.9

Top Displacement due to Lateral

Load

Top Displacement = 75 cm Top Displacement = 40 cm

ACECOMS, AIT ₅₃

Construction Sequence Analysis

Deflected Shape due to DL

(Linear Analysis) Deflected Shape due to DL (Construction Sequence Analysis)

Construction Sequence Analysis

Axial Force due to DL at the Base (Linear Analysis)

Axial Force due to DL at the Base (Construction Sequence Analysis)

Construction Sequence Analysis

Bending Moment due to DL (Linear Analysis)

Bending Moment due to DL (Construction Sequence Analysis)

11.3 12.4

Construction Sequence Analysis