Handout.6-21-18.rubenzer.2perpagegrayscale.pdf

6/18/2018

How to Verify SE Software

SAM RUBENZER, PE, SE •

Founded FORSE Consulting in 2010

•

Assists structural engineers on a wide variety of designs with an assortment of structural engineering design software

FORSE •

Many years of experience as licensed engineers

•

FORSE has worked hard to learn each of the software programs used by SEs and have created many presentations comparing the attributes of different software tools.

•

Worked as consultants with software companies teaching others about SE software

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Abstract •

Structural Engineers are relying more and more on structural engineering software for analysis and design. Understanding the different options available for modeling is paramount in ensuring the best model is created to imitate reality and give engineers the best possible design

•

This presentation reviews various methods for verifying the loads defined on models, verifying the analysis results, and finally, verifying the design check made for members within the model

•

It is easy to make the assumption that all structural engineering software solves engineering problems correctly; however, unfortunately there are errors. Sometimes the error is in programming, and sometimes it is user error. Engineers must have a good understanding apart from software to spot these errors

A Word About Software •

Structural engineers rely on finite elements models for analysis and design

•

Understanding the different options available for modeling is paramount

•

Best model is created to imitate reality and give engineers the best possible design

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Is your software model a good representation of reality?

Structural engineering software • Software is continuously changing our ability to do many things in our lives, personal and professional • This is no different with structural engineering. Software will make you a better engineer as long as you use the software as a tool, and don't become an "operator" • Never let the software think for you, only let it think faster • Never let the software decide for you. Period.

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Structural engineering software • Never assume the software is doing anything correctly • Never assume the software is making the same decisions you would make • Software programs are tools, you are the engineer, never forget that

Structural engineering software • Never assume the software is correct, or as you would have done it “by hand” • Examples certain programs will distribute load one-way

o

▪

regardless of the span aspect ratio, even 100:1 SR1

automatic features are by far the most dangerous

o

▪

settings aren't apparent when using software, in the manual

default settings are dangerous

o

▪

create a false sense of a “standard“

4

Slide 8 SR1 Please provide a couple of examples of such automatic features Sam Rubenzer, 6/15/2018

6/18/2018

Structural engineering software: ”do you agree with the programmer?" • Structural engineers also rely on: • Education, experience, and guidance from the code • Your good engineering judgment is still invaluable

• When programmers develop software for us to use, they are relying on codes and their own judgment • You will find that your judgment isn't always in agreement with another structural engineer's • Don’t use a feature you don’t agree with SR2

• Don’t assume other users agree … …so it must be OK?

need to know what we don't know…

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Slide 9 SR2 Provide examples of controversial features Sam Rubenzer, 6/15/2018

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Stated Learning Objectives •

Verify loads applied to models

•

Verify analysis results

•

Verify design checks

IN ORDER TO VERIFY, YOU NEED TO KNOW WHAT THE PROGRAM IS DOING

Let’s start with philosophy “Those that wish to succeed must ask the right preliminary questions” - Aristotle “Good and [bad] both increase at compound interest. That is why the little decisions you and I make every day are of such infinite importance.” - C.S. Lewis

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Verify loads applied to models •

Manually determine loads on structure

•

Approximate distribution

•

Know software load generator capabilities

•

Review applied loads after load generator application

Verify loads applied to models

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Verify loads applied to models •

Manually determine loads on structure

•

Approximate distribution

•

HAND CALCS or SPREADSHEETS

Verify loads applied to models Approximate load and distribution

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Verify loads applied to models Approximate load and distribution

Verify loads - Gravity Load Generators? •

Several programs distribute load without checking span •

•

•

•

•

How far can load be distributed?

Dead Self weight based on members modeled - don’t forget about the elements not modeled, often referred to as super imposed dead load

Live •

Live load keyed to ASCE table based on floor usage

•

reducible of not reducible is not the software’s decision to make

Snow or Roof Live load •

No automated snow drift generators or ponding load generators on the market

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Verify loads - General •

when using a structural analysis and design software package, there is a tendency to assume that the program is correctly generating the loads

•

software programmers are very good at interpreting and implementing the codes •

•

can’t automate every condition that exists in our complex architectural world

to understand this completely as it pertains to your projects •

best to know where software programmers get the loads for the load generators.

•

specifically, what sections of the code are used for load generators in common software packages.

Verify loads - Questions •

•

When an engineer chooses to generate wind loads, what sections of the code are considered? For example: •

How many directions is the load applied?

•

Can enclosed, partially enclosed, and open structures be considered?

When generating seismic loads what code provisions are considered? For example: •

Using approximate building period or calculated period?

•

Is accidental torsion checked and provisions applied?

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Wind based on ASCE 7 •

ENVELOPE PROCEDURE

•

DIRECTIONAL PROCEDURE portions of this procedure are generally used by software to generate wind loads

•

•

WIND TUNNEL PROCEDURE

•

Versions •

7-02

•

7-05

•

7-10 (major change)

•

7-16

Verify loads - Quick Facts •

ASCE 7-10 •

pages dedicated to Wind •

•

pages used for most wind load generators •

•

130

Estimate 10-20, varies depending on software

so when a software indicates ASCE 7-10 is implemented, be sure you know what that means, what’s included, and perhaps more importantly, what’s excluded!

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Seismic based on ASCE 7 •

EQUIVALENT LATERAL FORCE

•

TIME HISTORY ANALYSIS

•

RESPONSE SPECTRUM ANALYSIS

•

Versions •

7-02

•

7-05

•

7-10

•

7-16

Software options and examples

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Software options and examples •

•

Auto exposure edges? •

Determined from defined deck/slab edges

•

Allow Modifications?

User defined exposure areas? •

Can user manually define wind exposure areas and distribution?

•

Combine with user defined loads?

•

Parapets?

Verify loads - User defined load options •

What do you do when the load generator is close, but needs supplemental loads to be added • Can supplemental loads be added to generated loads?

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Wind

Auto exposure edges? Allow Modifications?

RISA 3D

yes | no

RSS (FRAME) RAM Elements

yes | yes

ETABS

yes | yes

User defined exposure areas

Combine with user defined loads?

Parapets

yes yes lateral walls

yes

yes

SCIA

load panels

yes

yes

TEKLA Structural Designer

wall panels

yes

yes

IES VisualAnalysis

areas

yes

yes

Seismic

Equivalent Lateral Force Procedure

Load Eccentricities

Distributed “area” load for Semi-Rigid Diaphragm (SRD) and/or point load for Rigid Diaphragm (RD)

RISA 3D

yes

yes

manual “area” load for SRD or generated point load for RD

RSS (FRAME) RAM Elements

yes

yes

generated “area” load for SRD or generated point load for RD

ETABS

yes

yes

manual “area” load for SRD or generated point load for RD

SCIA

yes

yes

manual “area” load for SRD or generated point load for RD

TEKLA Structural Designer

yes

yes

manual “area” load for SRD or generated point load for RD

IES VisualAnalysis

manual

manual

manual “area” load

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Understanding Dynamic Analysis

Types of Dynamic Loads •

Every structure is subject to dynamic loading

•

Dynamic analysis can be used to find: •

Natural frequency

•

Dynamic displacements

•

Time history results

•

Modal analysis

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Terminology Mass is defined by:

•

•

mass equals force divided by acceleration, m=f/a

•

mass is also equal to its weight divided by gravity

•

Stiffness of a body is a measure of the resistance offered by an elastic body to deformation.

•

Damping is the resistance to the motion of a vibrating body.

Ref. Anil K. Chopra: Dynamics of Structures, Theory and Applications to Earthquake Engineering, Second Ed.

Lateral Dynamic Analysis How is Mass Determined? •

How to calculate Some programs store mass separate from building loads • Some use one load case or combination as mass Members and plates • Masses get lumped at nodes • Split elements and plates to more evenly distribute Floors • Mass gets lumped at a single location per floor for a rigid diaphragm • Limits dof (simplifies the model) Additional applied mass on member or nodes • Good idea for perimeter wall Dynamic analysis is sensitive to the discretization of you model (how many members, nodes, dof) •

•

•

• •

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Natural Frequency •

Every system has a set of frequencies in which it "wants" to vibrate when set in motion •

Based on the system’s mass and stiffness characteristics.

•

Shortest frequency = natural frequency

•

Inverse of frequency = period of the system •

inverse of the natural frequency = fundamental period

Multiple Degree of Freedom Systems (Multi-story) •

Generally, the first mode of vibration is the one of primary interest. •

Usually has the largest contribution to the structure's motion

•

Period of this mode is the longest •

Shortest natural frequency (inverse of period) and first eigenvector

Ref. Anil K. Chopra: Dynamics of Structures, Theory and Applications to Earthquake Engineering, Second Ed.

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Natural Frequency for Wind •

Longer fundamental periods are indicative of buildings that are more susceptible to dynamic amplification effects •

Sustained wind gusts

•

Result in higher design forces.

Natural Frequency for Seismic •

The closer the frequency of an earthquake is to the natural frequency of a building, the more energy is introduced into the building structure

•

Buildings with shorter fundamental periods attract higher seismic forces •

Code-based design spectrum exhibits higher accelerations at shorter periods.

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First Step in Dynamic Analysis In order to investigate the magnitudes of: •

Wind

•

Seismic

…the fundamental periods of the area affected must first be determined

Period Determination from “Properly Substantiated Analysis” •

ASCE allows a "properly substantiated analysis"

•

Most programs quickly and easily perform an eigenvalue analysis •

•

periods can be significantly longer than from approximate equations: •

“non-structural” infill and cladding?

•

stiffening effect of "gravity-only" elements

Approximate equations are skewed to provide shorter periods

Ref. William P. Jacobs, V, P.E.: STRUCTURE Magazine (June 2008); Building Periods: Moving Forward (and Backward)

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Seismic Period Determination from “Properly Substantiated Analysis" •

FORCE - ASCE 7 limits the maximum building period for design loads •

Approximate building period, Ta, multiplied by up to 1.4 factor

•

Cap is intended to prevent possible errors •

In other words, un-conservative building periods for seismic load determination

•

Should make you question… •

•

IS the extra 40% (1.4 factor) JUSTIFIED?

DRIFT, ASCE 7 removes the maximum altogether Use the building period resulting from analysis

•

Seismic Period Determination from “Properly Substantiated Analysis" •

Most programs will quickly and easily perform an eigenvalue analysis •

•

Is that good enough?

Will the building period be too long? •

Did you consider the stiffening effect of the non-structural infill

•

Did you consider the stiffening effect of "gravity-only" columns, beams and slabs

•

Did you consider the gravity W36x150 with 10 rows of 1" dia bolts as more than a pinned connection

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implementation using commercial building software •

TRUE mass not always the same as dead load

•

many times we are conservative with dead loads (+)

•

remember, more mass (+) leads to longer periods and less seismic load

remember sustained live load and 20% of snow

• •

•

TRUE stiffness •

Member partial fixity?

•

Wall cracking?

•

Etc

implementation using commercial building software •

wind load dynamic modeling •

•

seismic load dynamic modeling •

•

longer periods yield higher loads shorter periods yield higher loads

different methods/models needed to be conservative!

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Same Dynamic Analysis Model?

Same Dynamic Analysis Model? Same building - different dynamic results

TABLE: Modal Periods Program 1 Program 2 Program 3 Program 4

different “participation” from columns/slabs

sec

sec

sec

sec

Mode 1

4.26

4.305

2.76

3.33

Mode 2

2.652

2.87

1.87

2.5

•

different crack factors assumed

Mode 3

2.186

2.40

1.46

2.5

Mode 4

0.843

1.47

0.61

0.77

•

one model had localized mode

Mode 5

0.701

1.30

0.56

0.71

Mode 6

0.644

0.99

0.4

0.56

•

Mode

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Program 1 Program 4

Same Dynamic Analysis Model? Program 2 Program 3

How to Avoid Potential Problems with Dynamic Analysis and Loads

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dynamics modeling tips •

•

Some compromise must be made in your finite element model •

in general, the mass in your model will be lumped at nodes (automatically in some programs)

•

shear buildings, where the mass is considered lumped at the stories are much easier to successfully model than other structures

Distributed mass. It is often helpful to define a load combination just for your dynamic mass case, separate from your “Dead Load” static dynamic mass load combination will often be modeled very differently

• •

You want to lump the mass at fewer points to help the solution converge faster, however you have to be careful to still capture the essence of the dynamic behavior of the structure

Models that don’t work well •

Multiple separate frames •

be careful of semi-isolated areas •

hard to get required mass participation

•

Models that have lateral support above the base

•

Models that are poorly discretized •

too few dof – not a true representation, overly simplified (rigid diaphragms for models that aren’t close enough to being truly rigid)

•

too many dof – too complex of a model, hard to get mass participation with reasonable amount of modes

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Avoiding problems with Dynamic Analysis •

Look closely at: •

deflected shape

•

mode-shapes

•

building story shear output for each analysis run

•

Any undesirable behavior could easily be detected by these outputs

•

Also investigate if boundary conditions such as foundation nodes have been properly applied on the model

•

Only when you are satisfied with the general behavior and response of your numerical model, move to design of members

Avoiding problems with dynamic analysis - localized modes •

Modes where only a small part of the model is vibrating and the rest of the model is not

•

May not be obvious from looking at the numeric mode shape results •

•

•

can usually be spotted by animating the mode shape

Make it difficult to get enough mass participation in the response spectra analysis •

local modes don’t usually have much mass associated with them

•

solving for a substantial number of modes but getting very little or no mass participation would indicate that the modes being found are localized modes

Sometimes, localized modes are due to modeling errors (erroneous boundary conditions, members not attached to plates correctly, etc.)

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front view

isometric view

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Implementation using commercial building software •

First and foremost •

Get the TRUE mass modeled •

• •

many times we are conservative with dead loads (+)

•

remember, more mass (+) leads to longer periods and less seismic load

remember sustained live load (code requires this for storage) and 20% of snow when greater than 30psf

Get the TRUE stiffness modeled •

•

not always the same as dead load •

ignoring partial fixity in joints (beam ends, column splices, column base plates, etc. etc.) for example may lead to conservative positive moments for beam design, but also reduces stiffness and leads to less seismic load

For modal analysis, do your best to consider the most likely damping percentages (remember elastic vs inelastic response)

QA/QC for Loading

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QA/QC •

Peer review of model is essential

•

Loads in = Loads out Does resulting base shear = applied lateral load?

•

Wind Load Code Check:

• •

If factored wind loads are applied per ASCE 7-10, confirm LRFD design is applied

QA/QC Torsion considered for Wind and Seismic

• •

Uplift

•

•

Columns, walls, plate elements

•

Confirm % of DL and SDL assumed in uplift force determination

•

Check for uplift effects to tension members, base plates, holddown / anchor connections, and foundations Is P-delta considered?

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Moving Away From Simplicity •

No longer need to run individual load cases and superimpose results… ….run load combinations

Verify analysis results •

Start with simple models to approximate results •

Simple micro models

•

Simple macro models

•

Work in complex elements to overall model

•

Verify final model matches behavior of simple model

•

Understand software capability/limitations of analysis

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Estimate behavior before hitting analyze •

Estimate load

•

Determine Shear for group

•

Determine corner up/down reactions as estimate

Estimate behavior before hitting analyze •

Simple to complex •

•

Lose the ability to do this when we import complex models from BIM models

Counter intuitive behavior? •

Real or not real???

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What happens at first floor? •

Can load really reverse in towers? •

•

created by rigid diaphragms

More realistic with Semi-rigid •

still need to check ability to get load out of wall groups, into diaphragm, then into new walls at foundation

Estimate load distribution 3x

3x 3x

2x

3x 1x

1x

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Before we take on this… 3x

3x 3x 3x 1x

1x

Work on understanding individual area

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Utilize all elements Sample Project Structural System •

3 story structure

•

•

Masonry stair and elevator shaft walls

Semi-rigid diaphragms at Level 1 and 2

•

Flexible diaphragm at roof

•

Steel floor framing and columns

Utilize all elements Steel Lateral System •

Steel beams, roof joists, and columns

•

11 Moment Frames in the N-S direction

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Utilize all elements Utilizing Masonry Walls Forgotten Lateral System Masonry System •

Stairs: 8” masonry walls with #5@24” o.c. vertical reinf

•

Elevators: 12” walls with #5@24” o.c. vertical reinforcement

•

Capable of carrying all lateral load without steel moment frames

Moving Away From Simplicity •

Previously with limited software, slower computers, or no software and computers, we simplified reality with conservative “approximations”

•

Large difference between all "lateral" and "gravity/lateral" member modeling •

How can members be ignored from lateral system?

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Understand software capability/limitations of analysis •

Beam, Column, and Wall Properties

•

Diaphragm Properties

•

Diaphragm connection to lateral support system

Beams and Columns

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Beams and Columns •

Member properties - boundary conditions •

Strong axis - pinned or moment connected •

Maybe semi-rigid?

•

Weak axis and torsion being checked?

•

Concrete •

Does FEA consider cracked sections?

Beams and Columns •

Member properties - boundary conditions •

End zone

•

Rigid end offsets

•

Pinned, fixed or spring support?

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Beams and Columns •

Member properties - type of finite element •

Wide concrete beam •

•

When should it be considered a plate instead of line element (4 node instead of 2)?

Large “deep column” or ‘short wall” •

Remember, “columns” are 1-D finite elements that connect to plates at a single point

Beams and Columns concrete cracked sections stiffness?

weak axis and strong axis commonly fixed, do connections and member check for weak axis?

compressible or fixed?

torsion fixed? is torsion being designed?

concrete cracked sections stiffness?

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Beams and Columns

rigid end zones, and offsets can make a big difference - rigid link between the end of the member and end node

Beams and Columns Software Examples

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TEKLA Structural Designer

RAM Structural System Concrete Beam Crack Factor

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SCIA Engineer Member Property Modifiers

Member End Releases

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Member End Support

Walls

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Walls •

Wall properties, boundary conditions •

Is there weak axis bending? torsional?

•

Horizontal and vertical bending? both being checked?

•

Does FEA consider cracked sections

•

Wall node releases

Walls •

Wall modeling •

Masonry wall stiffness based on partial or full grout

•

“True” long walls vs. short segments •

•

Gap or no gap

Openings

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Walls compressible or fixed?

out-of-plane connected?

plate torsion fixed? in-plane concrete cracked sections stiffness?

do connections and wall check for out of plane moment (vertical bending)?

horizontal bending? is torsion and horizontal bending being designed?

out-of-plane concrete cracked sections stiffness?

Interconnected Walls vs Isolated Panels •

Boxed wall groups

(stair towers | elevator shafts) •

Have approximately double the lateral load stiffness/capacity over individual walls

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Walls Software Examples

RISA 3D wall properties

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Scia Engineer Stiffness Factors 2D

TEKLA Structural Designer

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RAM Structural System

Effective Stiffness for Modeling Reinforced Concrete Structures By John-Michael Wong, Ph.D., S.E., Angie Sommer, S.E., Katy Briggs, S.E. and Cenk Ergin, P.E. STRUCTURE MAGAZINE in Articles, Structural Analysis, January 2017

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Mixing Materials … in the same frame

Steel Frames Connected to Perforated Masonry Shear Walls

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Post-Tensioned Concrete Frame with Masonry Walls

Multiple Material Lateral: Wood - Masonry - Steel

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Diaphragms HALFTIME

More on Semi-Rigid Diaphragm Boundary Conditions •

•

Membrane or plates? •

Membrane - load transfer through “axial/tension/compression” stiffness in 2D element

•

Plates - full axial/tension/compression stiffness in addition to element inplane bending

Diaphragm cracked sections

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in-plane concrete cracked sections stiffness?

out-of-plane concrete cracked sections stiffness?

Semi-Rigid Diaphragm Properties

Software Examples

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Scia Engineer Stiffness Factors 2D

RAM Structural System

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Load Transfer •

Load transfer from diaphragm to vertical element •

Is there flexibility in the connection? •

•

Partition wall or shear wall, does your model know the difference

Can the connection handle the load into (or out of) vertical wall, frames, etc?

Collectors in Diaphragms •

Rigid diaphragms can dump a infinite amount of load into a single node (point) in the model?

•

How can an engineer ensure load can get from diaphragm to lateral frame?

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Openings in Diaphragms •

Exterior wall groups with wall opening, how does lateral load get to outer walls •

•

Rigid diaphragms have way of “sharing” load through open areas (btw, not possible)

Location and size of openings can have minimal or significant effect on diaphragm

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“Redistribution” of Force •

Classic example is podium slab or another example is any building with basement level(s)

•

Redistribution from: •

Rigid diaphragm: easy and often wrong

•

Semi rigid: MUCH more realistic diaphragm

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Verify loads - Load Distribution •

Flexible Diaphragm

•

Semi-Rigid Diaphragm

•

Rigid Diaphragm

•

Something to ponder... • Which would you rather have, software automatically determine forces on a building, or software that can distribute the forces to lateral resisting elements based on one of the appropriate diaphragm types?

LOAD APPLICATION

Flexible diaphragms

Semi-Rigid diaphragms

Rigid diaphragms

Lumped lateral load

Not sure this makes sense

NOT OK - analysis will be flawed

OK

Actual load applied - wind at perimeter - seismic at center of mass

Acceptable

OK, actually, this should be a requirement!

Unnecessary, but OK

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Load Distribution

Flexible diaphragms

Semi-Rigid diaphragms

Rigid diaphragms

RISA 3D

yes

with manual plate elements

yes

RAM Structural System (FRAME) RAM Elements

no, in RSS “flexible means none”

with auto plate elements

yes

ETABS

yes

with manual plate elements

yes

SCIA

by modifying othotropic properties

with manual plate elements

by modifying othotropic properties

with diaphragm braces

yes

with manual plate elements

yes

TEKLA IES VisualAnalysis

yes, areas or plates membrane only

Stepped Diaphragms •

Is the step modeled?

•

Is there a real ability to transfer forces across the step? •

Small step with a shared beam/girder/truss

•

Large step: truss, bracing, wall element needed

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Sloped Diaphragms •

How sloped is too sloped to be considered a rigid diaphragm?

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QA/QC for Member Results

QA/QC •

What are residual forces/stresses? •

Examples •

Torsional load in wide flange?

•

Horizontal bending in walls?

•

Axial forces in connections?

•

Diaphragm forces in floors?

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QA/QC •

Do you have a way to check for unaccounted for residual forces/stresses?

•

Or do you have a means to make sure the magnitude of the load is below a certain threshold to ignore?

QA/QC Detailing Check load path from superstructure to soil

• •

Are drag struts modeled as detailed?

•

Are transfer forces from steel frames to adjacent framing considered in connection design and/or forces shown?

•

How is shear transferred from base plates to foundations - anchors, shear lugs, etc.?

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QA/QC Detailing Base boundary conditions for drift & strength

• •

Confirm simulation to actual foundation stiffness - model bases as springs, pinned, or fixed Expansion Joints

• •

Confirm model properly considers independent diaphragms at expansion joints

•

Check drift of 2 independent structures at an expansion joint is compatible with gap shown on drawings

QA/QC

VIEW THE DEFLECTED SHAPE - ANIMATE

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QA/QC •

Check drift - inter-story and overall drifts

•

Check the animated shapes as well •

tells a story of the buildings response

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RAM Frame

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Verify design checks Never go from analysis to design check without validating results first •

Understand software capability/limitations of design checks •

•

start with simple models to understand design checks •

•

Note: (obvious) not all programs run the same checks Note: (obvious) reading the manual is imperative

be sure design check is comparing the right analysis results against member capabilities

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seismic provisions Program 1

Program 2

Program 3

Program 4

Program 5

separate mass calculation

separate mass calculation

combination of modeled loads

separate mass assignment

separate mass assignment

fundamental period calculation or approx

fundamental period calculation or approx

approx fundamental period

fundamental period calculation or approx

fundamental period calculation

ELF ELF ELF seismic load generation seismic load generation seismic load generation checks based on frame checks based on frame checks based on frame type type type

checks based on frame type

composite steel beam and concrete slab Program 3

Program 1

Program 2

simple or continuous composite design

composite design

composite design

uniform or segmented layout

uniform or segmented layout

uniform or segmented layout

customizable deck profile and properties

customizable deck profile and properties

min/max % composite action

min/max % composite action

automatic tributary width and customizable

automatic tributary width

deflection checks

deflection checks

vibration checks in program, based on AISC DG #11

vibration checks export to FloorVibe, based on AISC DG #11

customizable deck profile and properties abs min/advisory min/max % composite action automatic tributary width and customizable

deflection checks include long term effect of concrete vibration checks in program, based on AISC DG #11

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Examples: Floor Vibration •

structural steel software review •

all these programs do floor vibration checks

•

do they agree with your hand calcs

•

what to do when things get more complicated

dynamic analysis for steel floor vibrations simple software solution

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dynamic analysis for steel floor vibrations simple software solution

dynamic analysis for steel floor vibrations

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dynamic analysis for steel floor vibrations Floorvibe

can be used as a stand-alone program, or can be used from RAM Steel

dynamic analysis for steel floor vibrations RISA Floor

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stability – comparison table Program 3

Program 1

Program 2

Program 4

DA Method

DA Method

DA Method

DA Method

P-delta

P-delta

P-delta

P-delta

option for stiffness reduction

option for stiffness reduction

option for stiffness reduction

option for stiffness reduction

tb=1 for all members

calcs tb tb=1

tb=1 or custom value

calcs tb

uses notional load of 0.3 %

uses notional load of 0.2% or 0.3 %

uses notional load of 0.2% or 0.3 %

automatically determines % (generally 0.2%)

dynamic analysis loading Program 1

Program 2

Program 4

Program 5

mass at nodes or rigid diaphragms calculation

mass at rigid diaphragms

mass at nodes or rigid diaphragms calculation

mass at nodes or rigid diaphragms calculation

determine mode shapes

determine mode shapes

determine mode shapes

determine mode shapes

response spectrum analysis

response spectrum analysis

response spectrum analysis

response spectrum analysis

time history analysis

time history analysis

time history analysis

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steel connections – comparison table ETABS Steel SDS/2 STI HSS CONNEX Connection Engineering ONLINE Design

DESCON

RAM Conn / RAM Conn Standalone

RISA Conn

LIMCON

Skewed connections an option?

no

Yes - follows AISC, skew must not be no more than 15 deg

no

no

yes

no

yes

limited to 15degrees

Can adjust T/Beam elevation?

yes

yes

no

yes

yes

n/a

yes

n/a

no

Yes, but not in a col-beam-brace conn

yes

no

yes

yes

no

no

LIMIT STATE / SOFTWARE

Sloped connections an option?

VAConnect

Develop your checklist Design features vary between programs, know what the differences are.

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Software Expert - key to success Software expert • Teaches • Tests • Benchmarks • QC reviews

What should you do? •

Develop a Software Expert program immediately

•

Software Expert is NOT:

• Is not just the most proficient "operator" • Is not lacking experience • Is not only defining capabilities • also clearly understands limitations • Probably is not only looking at one program

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What should you do? •

Develop a Software Expert program immediately

•

Software Expert is:

• Leading staff trainings • Helping team maximize proficiency and efficiency

• Clearly defining Do’s and Don’ts • Part of team deciding best tool for project (before project starts)

• Part of every project software QC

In Conclusion •

Get to know your software, develop Software Experts

•

Get to know the code, and how it's been implemented in each software you use

•

Always know capabilities, and more importantly limitations

•

Always have your loads in a software model reviewed by a peer

•

Always, always check total load on model with hand calc

AND Always remember, software is a tool, you’re the engineer...

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Who? SR3

•

Young engineers - you’re the one building FEMs

•

Senior engineers - you’re the one checking FEMs

•

Design firms - these models are your responsibility, even though no one will ever likely “check your FEMs” even if they check your calc

•

Remember….

“It is not your business to succeed, but to do right.” - C.S. Lewis

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Slide 147 SR3 What recommendations do you suggest, modeling courses? Sam Rubenzer, 6/15/2018

6/18/2018

Questions? [email protected] [email protected] sam@FORSE consulting.com [email protected] [email protected]

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SR4

questions?

[email protected]

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Slide 151 SR4 COULD YOU PROVIDE A SHORT EXAMPLE OF DRASTICALLY DIFFERENT NUMERICAL OUTPUTS AS A RESULT OF 2 DIFFERENT MODELING SCENARIOS (CONNECTION OR DIAPHRAGM DESIGN FOR INSTANCE)? THIS WOULD HELP ILLUSTRATE SOME OF THE MOST IMPORTANT CHECKS TO MAKE WHEN BUILDING COMPUTER MODELS Sam Rubenzer, 6/15/2018