Hi All

Here in Denmark Seismic loading is merely defined as a percentage of the applied vertical load. In the past i've used NOTIONAL LOADS to create this and it worked fine. But only for Y axis as global vertical axis. I now use SET Z UP since it corresponds to the axis definitions all our clients use.

However, notional loads doesn't seem to Work properly when the command SET Z UP command is used. Can anyone explain this?

The alternative is to manually copy all vertical loads and change direction in the STAAD.Editor. But this is a very time consuming task and it also rather frustrating since loads tend to change a lot during the design phase.

Can anyone help me to explain this or alternatively give me a tip to avoid the manual re-entry of loads? Perhaps someone has created a macro for a similar task?

Thank You.

Kind regards

Morten

Where can I find the ISM Log files?

The ISM applications keep a running log of activity on the local hard drive. These log files can be helpful in debugging application crashes in particular.

On a Windows 7 (or Vista) machine, the logs are located here:

C:\ProgramData\Bentley\Logs

On Windows XP the location is:

C:\Documents and Settings\All Users\Application Data\Bentley\Logs

These locations may be hidden from the user unless the Explorer option to "Show hidden files and folders" is selected.

When working with Technical Support on ISM related issues it's always helpful to include these log files.

Also See

Integrated Structural Modeling Home

Problem

The ISM Viewer application crashes when started reporting a problem with the Bentley Updater Component.

Solution

Update to SELECTseries 5 release 8.11.11.50 manually

Also See

[[How can I find the ISM installer?]]

[[Integrated Structural Modeling Home]]

Hello again.

I was adding some user shear reinforcement to a model recently (hurray for this being a feature now), and had some things happened that piqued my interest.  I started digging around in the audit report to better understand how Concept is calculating the required shear reinforcement.  So far, I have everything worked out except for the 'Available Vn'.  I cannot seem to resolve how this value is being calculated. I have a feeling it still has to do with Eqn 11-18, but have not been able to quite work out what is being used for that value.

Also, in the attached model and auditor screen shot, you can see that the calculated value for 'Minimum additional design Av/s' (0.03765 per ACI eqn 11-23) is greater than the Av/s calculated for torsion (0.03337).  However, the final design Av/s used is the (shear Av/s) + (the torsion Av/s), which is less than the (shear Av/s) + (minimum torsion Av/s).  Is this done for a certain reason?

Finally, on a totally unrelated note, I was hoping that I could get some assistance in the forum with this post:

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/16105.ram-concept-tabular-input-etabs-link.aspx

Is there a working version of the spreadsheet mentioned in this post that could be shared before the examples in that post are finalized?  Having the ability to use tabular input in Concept will be extremely helpful for a project that I have coming up in the near future.  If the VBA spreadsheet isn't near completion yet, would it be possible for one of you to send me a GCFF example file that I could use to begin making my own version of this spreadsheet (not really interested in converting STAAD to Concept...more in creating input files from scratch and importing to concept).  If you could send me a GCFF file that represents the attached Concept model...I feel like that would be more than enough for me to get moving with this tool on my own.

Thanks for the help

Phil

Hi,

I'm getting shear reinforcement in the slab where there shouldn't be any shear reo. According to AS3600 there shouldn't be any shear reo if V*<phiVuc 8.2.5).

Why RAM Concept constantly provides shear reo? In the report it specifies: transverse bar found, but there's no mentioning where it's coming from (see part of report below, where V*=64<phiVuc=272)

Starting 8.2 Shear Check
Considering Effect of Torsion on Shear:
No torsion to consider
No torsion reinforcement required
General Shear Design Parameters
bv = 1828 mm
do = 219.1 mm
bvd = 400500 mm²
Ac = 457100 mm²
Ast = 2632 mm²
Apt = 0 mm²
Ac = 457100 mm²
fc = 40 N/mm²
fsyf = 500 N/mm²
V* = 64.12 kN (absolute value)
M* = 20.26 kN-m
Setting Vo to zero for RC cross section
Setting Pv and Apt to zero for RC cross section
Calculating Web-Shear Cracking Vuc (8.2.7.2(b))
Precompression Stress = -0.0002275 N/mm² (at centroid)
Failure Tensile Stress = 2.277 N/mm²
Shear Stress Limit = 2.277 N/mm² (at centroid)
I = 2380000000 mm⁴
Q = 14280000 mm³
Vt = 693.7 kN [(limit stress) * bv * (I/Q)]
Vuc (web cracking) = 693.7 kN (Vt + Pv)
Calculating Flexure-Shear Cracking Vuc (8.2.7.2(a))
Beta1 = 1.519
Beta2 = 1
Beta3 = 1
Shear Stress Term = 0.6406 N/mm² ([..]¹´³)
Vuc (flexure-shear) = 389.7 kN
Vuc = 389.7 kN
Vu,max = 3204 kN
Less than minimum ligatures required, using large shear lig spacing (0.75D or 500 mm)
Maximum lig spacing = 187.5 mm (considers torsion lig spacing also)
Calculating Compression Strut Angle
Using 0.6062 instead of 0.6 for compatibility of 8.2.8, 8.2.9 and 8.2.10
Asv,min = 260.2 mm² (at max spacing)
Vu,min = 653 kN
Vu,max = 3204 kN
V*/phi = 91.6 kN
Theta-v = 30 degrees
Adjusted Vu,max = 3204 kN (after considering 8.3.3)
Transverse Bar Found:
As = 260.2 mm²
Fy = 500 N/mm²
Spacing = 187.5 mm
Vus = 263.3 kN
Total Vus = 263.3 kN
Vu = 653 kN
phi Vu = 457.1 kN

Why do I get a Report Viewer error?

Problem, when running the framing tables in the Steel Beam module I get the following warning:

This error typically happens when the user switches to another application while the steel beam design is being performed. To reproduce the problem, open RAM Steel beam and click the option to design all after framing. Then switch to another application while the framing tables are running.

The user has to click OK to the message to proceed.

The error can also happen if the report viewer control is registered in the wrong location,

To reregister the report viewer control, follow these steps.

1. Locate the file VPECTRL3.ocx, it is most likely here:

C:\Program Files (x86)\Common Files\Bentley\Engineering\VPEControl\VPECTRL.OCX

2. Go to the Windows Start button or pearl any type "run" without the quotes and hit enter

3. On the command prompt that appear type

regsvr32 "C:\Program Files (x86)\Common Files\Bentley\Engineering\VPEControl\VPECTRL.OCX"

or change the path if the file is in another location

4. you should get a message that the registration succeeded.

Note, if more than one copy of the file is located first unregister all other copies using a similar command but with /u after regsvr32, before registering the good copy like so:

regsvr32 /u "C:\Path to other copy\VPECTRL.OCX"

In at least one case repairing the installation also solved the problem. It's worth noting that with RAM Structural System, only one version can be installed at a time. Users who try to install both the 32 and 64 bit versions might also encounter this (and other) problems.

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Hello,

I am analying this simple model. Here the vertical post is made of plate element. Flanges of web is made of beam and web is made of plate element. I have connected the cantilever to post by pin connection ( element of cantilever is free in rotation. Is it okay ??). A beam is connecting top of the post and cantilever with pin connection. I have released the rotation of the beam MZ ). 

Now, but the element of the post where beam is pinned is showing very high stresses. (It is not practical). Beam element is pinned to only single node of the element. 

Please help. How to model is better ??? I don't know much about master slave connection.

Instability in Finite Element Analysis

A typical 3-dimensional Finite Element analysis of a structure requires that every node must be stable in all 6 degrees of freedom (TX, TY, TX, RX, RY,RZ). This is achieved by specifying fixity conditions for the columns, beams and braces spanning to a given node or through nodal restraint. While many programs can analyze a structure using fewer degrees of freedom, for this discussion all 6 are assumed to be active.

There are many discussions related to FEA online and whole courses devoted to the topic, but the purpose of this article is merely to show by example a few of the most common causes of instabilities in structural models. The rules apply to RAM Elements (aka RAM Advanse), RAM Frame, RAM Concrete or STAAD.pro as well as other FEA applications. The images and examples below are taken from RAM Elements where a light blue circle indicates a hinge, or member release, at the end of a member. A translational restraint is depicted as a triangle on rollers and a rotational restraint is a "T".

Pinning the free end of a cantilever.

Take the case of a single member fixed at the base for all 6 DOF similar to a flagpole. This structure is stable, except that the free end of member away from the support is hinged or released for major axis bending. As a result, node 2 can spin about the global z axis.

For some applications, this type of "nodal instability" will terminate the analysis. For other applications, a small stiffness may be automatically assigned to the z axis rotational stiffness of the node and you may only get a warning, so long as a moment about the z axis is not applied directly to node 2. This would cause infinite rotation of the node and should terminate any analysis.

The same situation often occurs for a beam with a cantilever, where the cantilever beam is the only member connected to the node at the tip. In short, the free end of any member, where that member is the only member in the model connected to a particular node should never be released. 
 

Beam, column and brace intersections.

When multiple members frame to a single node, it is acceptable to release some, but not all of those members. If the beam, column and brace are all released at the same node, then the problem is the same as case 1 above. At least one of those members should be fixed ended. In most situations, it is the column top that should remain fixed to the node.

Releasing the tops of columns.

In this case we have a fixed ended beam setting on two columns, both of which are released at the top node. This case differs slightly from Case 2 because the nodes are fixed to the beam and not themselves instable. The problem is that the beam along with both top nodes can spin as a group on top of the columns similar to a log on water. This is an example of why it is usually better to keep the tops of the columns fixed and release the beams.

Torsional releases

It's hard to envision a realistic connection that allows a member to spin or swivel, but most FEA application do allow member torsional releases. A general rule is to leave the member torsion fixed except in a situation where member rotation really is free. The most common problem occurs in a chevron brace configuration where the beam is two finite elements. If each beam half is released in torsion, then the node at the top of the braces is instable.

2-dimensional frame in a 3-dimensional analysis

Often it is desirable to analyze a 2-dimensional frame using a 3-dimensional analysis. In some applications there is plane frame option that can be used to ignore the deflection out of plane (e.g. z axis) or rotation about the other axes, but if not, the frame can generally be stabilized one of two ways.

• An out of plane, z axis restraint can be applied to some or all of the nodes to effectively keep the frame from falling over, or
• Rotation about the in-plane axes can be restrained at the base nodes (e.g. rotation about the X axis).

The same situation often occurs in RAM frame when no rigid diaphragm is used. This can leave the model with several, isolated, 2D frames in space with no connection between them. If the frames are pinned at the base then they can fall over and an instability results. Fixing the base of the frames against out-of-plane rotation is generally the solution to this problem, though connecting the frames together with lateral members or some other simulation of a diaphragm is also possible.

Other Global stability issues

A certain number of nodal restraints are always required to keep the structure as a whole from moving. Another common case is one where a shell or mat foundation is supported by a series of vertical springs. While that is stable in relation to vertical loads, some mechanism must be provided to keep the mat as a whole from sliding around like a skateboard. This is generally achieved through the use of horizontal springs in addition to the vertical springs, or by restraining the translation of a node (or line of nodes) along the edge of the structure.

This is a common problem in Ram Concept if a vertical resistance area spring is the only support for the structure. When there are no lateral loads, you might get away with providing an area spring with only vertical stiffness, but when there is any external load applied in the plan directions, some resistance to sliding must be incorporated into the model.

Diaphragm stability

In most building type structures there is a horizontal diaphragm that ties the frames together and prevents in-plane deformation of the plan. This is typically modeled using a rigid floor diaphragm. The diaphragm constraint forces the nodes of the floor to move together preventing the plan from racking for example.
In space frame models where no rigid diaphragm is modeled (perhaps because the roof is sloped), there must be some other mechanism to keep the plan from racking. This is generally achieved by providing diagonal members in that plane. Fixing the minor axis of the beams in the plan is another approach. Think of this like creating a Vierendeel truss in plan. Using shell elements is another option, though the interaction between the shells and the members is not always desirable.

Using tension-only members or compression-only springs

When a model utilizes non-linear members or springs most FEA applications iteratively solve for each load case and load combination. On each iteration, if a tension-only member is found to go into compression, that member is thrown out of the analysis and a new iteration is started. If too many of the members go into compression, the frame or structure as a whole can become instable.

There are a couple of ways to effectively deal with such a situation

• Apply a pre-tensioning force to the braces. By putting the member into an initial tension state it is less likely to go into compression and fall out of the analysis.
• Assign some of the members to be tension and compression members. For X braced frames or other symmetric structures it is typically acceptable to analyze the structure with a single tension + compression brace rather than a pair of tension-only braces. This does affect the load path through the columns somewhat, however, and may require two versions of the model to capture the worst condition. A similar option is to leave both braces in the model, but then check the braces or twice the determined force.
• Applying self weight to tension only braces will cause bending moments in the members which usually is not the intent for tension-only braces. in those cases, a zero density material is suggested.
• Additionally, for X braced frames in Ram Elements, the program may be introducing a node at the intersection of the braces. This can be prevented using Process - analyze - FE Model tab - by turning off the option to "Add intermediate nodes at member intersections".

P-Delta effects and model instabilities

There are cases where a structure might be perfectly stable under a first-order analysis, but as the analysis incorporates P-Delta effects the deflection is amplified and instability can result. Different applications handle P-Delta analysis in different ways, but there are usually controls for the tolerance required for P-Delta convergence. Increasing the tolerance often leads to a solution, but some structures may have to be stiffened in order to complete a P-Delta analysis on all load cases.

See Also

RAMSS Eigenvalue Error

RAM Frame P-Delta [TN]

Structural Product TechNotes And FAQs

STAAD.Pro Instability And Zero Stiffness

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!   

I have a building that is partially below-grade.  I'd like to apply the lateral force from the soil against the basement wall to the floor diaphragm.  How do you apply this load case and incorporate it into the appropriate equations?  

How can apply earth pressure in one direction?

There is no direct way to model earth pressures in RAM SS. Lateral loads of the type "Other" are limited to User Defined Nodal Loads, or User Defined Story forces (i.e. diaphragm forces).

If your concern is the design of the frames to take this extra force, then you can enter the total lateral force as a User Defined Story Force in RAM Frame. This works with Rigid or Semi-rigid diaphragms. Note, the positive X direction towards plan right is 0 degrees and angles are measured counter-clockwise from there. You will have to use custom combinations to have these "Other" type loads combined with gravity, wind and seismic effects. Take care not to use negative load factors on other type cases, assuming the lateral pressures are in one direction only.

If you are more concerned with effects on a single frame, then nodal loads (with a flexible diaphragm) might be best. These are applied in the Modeler - Elevation View to the nodes of the lateral members. 

What the program cannot do at this time is design a foundation wall for the earth pressures applied to it out-of-plane. Ram Elements and the retaining wall module might help there.

See Also

Structural Product TechNotes And FAQs

RAM SS - Rigid Diaphragm Constraints and Frame Shear [TN]

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

The following TechNotes and FAQs are provided by Bentley's Technical Support Group. Additional content is available through search at the top or the Table of contents on the left.

STAAD.pro  -  Ram Structural System  -  Ram Elements  -  Ram Connection  -  Ram Concept

Licensing & Installation

• Configuring Structural Products For SELECT Server
• Accessing SELECTservices Online And Downloading Files
• Manually Removing Bentley IEG Licensing Software
• Viewing And Checking In Licenses Using The Site Administration Page
• [[Using Bentley Structural Products Offline]]
• [[Structural Products Compatibility With 64 Bit Operating Systems]]
• [[Non-Interactive Installation Of Structural Products]]
• [[Performing A Clean Installation]]
• [[Structural Products Licensing FAQ]]
• [[Recommended Computer Specifications For Structural Products]]
• [["Another installation is already in progress, you must complete the installation first"]]
• Why do RAM Structural System modules open in trial mode?

 

STAAD.Pro

• STAAD.Pro TechNotes and FAQs 

 

STAAD.Offshore

• STAAD.Offshore Technotes And FAQs

 

STAAD(X)

• STAAD(X) TechNotes and FAQs

 

STAAD(X) Tower

• STAAD(X) Tower TechNotes and FAQs

 

STAAD Foundation Advanced

• STAAD.Foundation Technotes and FAQs

 

RAM Structural System

Release Notes and New Issues

• RAM Structural System Release Notes
• Known Issues in RAM SS v14.06.00

TechNotes and FAQs

General

• [[RAM SS - Modules Overview]]
• RAMSS Installation FAQ
• RAM Defaults Guide
• RAMSS Files FAQ
• RAM SS File-Open Troubleshooting [TN]
• RAM Table Editing
• RAM SS 3D Viewer FAQ
• RAMSS Polygon Intersection Error
• RAM SS Analysis Types
• RAMSS Two Way Decks
• RAMSS Common Framing Table Errors
• New Workflow for tables in RAM Structural System Version 14.06

RAM Modeler

• RAMSS Modeling FAQ
• RAM SS Walls FAQ
• Importing DXF Files into RAM SS

RAM Steel

• RAMSS Gravity Loads FAQ
• RAMSS Beams FAQ
• RAMSS Joists FAQ
• RAMSS Columns FAQ
• RAMSS FloorVibe FAQ

RAM Frame

• RAM Frame Troubleshooting
• RAMSS Eigenvalue Error
• RAM Frame Meshing and Segmentation
• RAM Instability In Finite Element Analysis
• RAM Frame P-Delta
• RAM SS Semirigid Diaphragms
• RAMSS Pseudo Flexible Diaphragms FAQ
• [[RAM Frame - Building and Frame Story Shear]]
• RAMSS Truss Modeling And Design
• RAMSS Wind Loads FAQ
• RAMSS Seismic Loads FAQ
• RAMSS Dynamic Modal Analysis FAQ
• RAMSS Tension Only FAQ
• Star Seismic Buckling Restrained Braces
• CoreBrace™ Buckling Restrained Braces
• RAM Frame AISC 360 Stability Analysis and Design

RAM Concrete

• RAM Concrete Beam [FAQ]
• Wall Boundary Element Design in RAM Structural System [TN]
• RAM Concrete Shear Wall Verification - Planar Wall Using ACI 318

RAM Foundation

• RAM SS - Foundation [FAQ]

Revit Link

• RAM Structural System Revit Link

RAM DataAccess

• What is RAM DataAccess?

 

RAM Elements

NOTE: RAM Advanse is now RAM Elements

Release Notes

• RAM Elements Release Notes

TechNotes and FAQs

• Installation - Ram Elements
• RAM Elements Importing from RAM SS FAQ
• RAM Elements - View Control FAQ
• [[Ram Elements - Modeling FAQ]]
• RAM Instability In Finite Element Analysis
• Creating custom elements in RAM Elements
• RAM Elements Load Combos FAQ
• [[Ram Elements - Distributed Load errors]]
• Ram Elements Shells FAQ
• RAM Elements Masonry Wall FAQ
• RAM Elements Unbraced Lengths
• RAM Elements Effective Length Factors
• RAM Elements AISC Stability
• RAM Elements Dynamic Modal Analysis FAQ

 

RAM Connection

Release Notes

• RAM Connection Release Notes

TechNotes and FAQs

• [[RAM Connection is installed, but the Connection button fails to appear in RAM Elements]]
• RAM Connection Capabilities and Modeling FAQ
• Troubleshooting Errors when Assigning Connections
• RAM Connection Stalls When Assigning Base Plate Connection
• Catastrophic Failure Error when Using Customized Anchor Position
• RAM Connection Extended End-Plate Moment Connections (MEP)
• RAM Connection Base Plate FAQ
• Tips for Using RAM Connection within STAAD.Pro [TN].
• How to Customize a RAM Connection Template in STAAD.Pro
• What Connection Types are available in RAM Connection to the design code BS 5950?

 

RAM Concept

Release Notes

• RAM Concept Release Notes

TechNotes and FAQs

• RAM Concept-RAM Structural System Integration TN
• Modeling Podium Slabs TN
• RAM Concept T-Beams and Axial Force TN
• RAM Concept Lateral Self Equilibrium Analysis TN
• RAM Concept Design Strips TN
• RAM Concept Punching Shear Checks [FAQ]
• RAM Concept Load History Calc Options TN
• [[RAM ConceptCapabilities and ModelingFAQ|RAM Concept Capabilities and Modeling FAQ]]
• RAM Concept Files FAQ
• RAM Concept Plans And Perspectives FAQ
• RAM Concept Structure FAQ
• RAM Concept Tendons FAQ
• RAM Concept Reinforcement [FAQ]
• RAM Concept Loading FAQ
• RAM Concept Shear Reinforcement FAQ

Multiframe

• General FAQS

Problem Description

IMPORTANT- Ram Connection V8i release 09.02.00.117 was released on October 23, 2014 and that installer should be used if possible. The following content is ONLY for Non-SELECT users who have version 9.1.0.94.

Ram Connection builds are occasionally created to fix problems and disseminated via links on this page before full installers can be posted to My SELECT CD. This page is for Ram Connection in English or Spanish, but users should only download one or the other.

Solution

1. Install the latest release build of the software: Ram Connection 9.1.0.94 

2. Download the following file and save it to the hard drive. We suggest you save it in the same location as the main installer, (e.g. C:\BentleyDownloads).

3. Close Ram Connection, Ram Elements, and Ram Structural System if they are running.

4. Extract the files using to the following directories, 

IMPORTANT - use only 7-zip to extract these files, not Windows or WinZip. If 7-zip is not an option, then contact support with a service request. Otherwise the extracted files may have an altered time stamp and the upgrade will fail, giving an error like this:

Details about this unzipping time stamp problem here. 

* These are the default or typical paths for an English language operating system. For other language OS, or when the install path was changed from "Typical", the folder should match the path to the file RAMConnection.exe. On x32 bit machines eliminate the (x86) from the folder path. 

Overwrite existing copies in all cases:

Also merge the contents of any subfolders:

5. Confirm success by checking Help (?) - About for the updated release 9.1.0.101:

See Also

[[Ram Elements - Installing Updated Executables]] 

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Problem Description

IMPORTANT - Ram Elements V8i release 13.03.00.117 was released on October 23, 2014 and that installer should be used if possible. The following content is ONLY for Non-SELECT users who have version 13.02.00.99.

Ram Elements builds are occasionally created to fix problems and disseminated via links on this page before full installers can be posted to My SELECT CD. This page is for Ram Elements in English or Spanish. A set of two files is provided for each version, but users should only download the set that applies to the version that is currently installed.

Solution

1. Install the latest release build of the software: Ram Elements 13.2.0.99 

2. Download either the set of two English version files or set of two Spanish version files and save it to the hard drive. We suggest you save it in the same location as the main installer, (e.g. C:\BentleyDownloads).

3. Close Ram Elements, Ram Connection and Ram Structural System if they are running.

4. Extract the files using to the following directories, 

IMPORTANT - use only 7-zip to extract these files, not Windows or WinZip. When using 7-zip, make sure the program is run as an administrator. You can do this by right-clicking on the 7-zip shortcut, choosing Properties from the menu, clicking on the Compatibility tab, and checking the appropriate box. If 7-zip is not an option, then contact support with a service request. Otherwise the extracted files may have an altered time stamp and the upgrade will fail, giving an error like this:

Details about this unzipping time stamp problem here. 

* These are the default or typical paths for an English language operating system. For other language OS, or when the install path was changed from "Typical", the folder should match the path to the file RAMElements.exe and RAMInteractionDiagrams.exe respectively. On x32 bit machines eliminate the (x86) from the folder path. 

Overwrite existing copies in all cases:

Also merge the contents of any subfolders:

5. Confirm success by checking Ram Elements - Help (?) - About.

6. If you also use Ram Connection, then follow the [[Ram Connection - Installing Updated Executables]] instructions similarly. 

See Also

[[Ram Connection - Installing Updated Executables]] 

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

How do I get RAM Elements to perform a Response Spectra Dynamic Analysis?

1. After the geometry of the model is defined, place nodal masses using the Nodes>Masses spreadsheet input,

2. Define a dynamic load case for each X and Z direction,

3. On the Gen>Earthquake acceleration spreadsheet input, enter a scale factor, direction and damping percentage,

4. On the Gen>Response spectrum spreadsheet, enter some response spectrum,

5. Run the analysis and choose the desired combination method (e.g. CQC),

6. Click the View menu>Finite elements toggle,

7. Use the View>Modal deflection results to see the mode shapes or Output>Analysis> Dynamic analysis to get periods and modes info.

For more details, refer to Help>RAM Elements Manual>Chapter 10: Dynamic Seismic Analysis. 

to see example files go to;

C:\ProgramData\Bentley\Engineering\RAM Elements\Data\Samples

and open Dynamic1.etz or Dynamic2.etz.

How can I change the number of modes used in the dynamic analysis?

Click the Process menu>Analyze model toggle, and under Dynamic and Response Spectra change the number of modal shapes to calcualte.

What scale factor should I apply to the response spectrum?

See RAMSS Dynamic Modal Analysis FAQ

Can RAM Elements perform an Eigenvalue solution to determine mode shapes without the response spectrum data?

RAM Elements will perform an Eigen solution without the response spectrum curve data. The program only requires that the Mass is entered in the Node>Masses spread sheet. Once the mass is defined the program will perform the Eigen solution and the View>Model shapes options and the Output >Analysis >Dynamic Analysis results will be available for viewing.

How do I generate the data for the response spectrum curve?

The data can be generated using ASCE7-05/10 section 11.4.5.  Sample curve data can be loaded using the "Open response spectrum file" toggle.  The following spread sheet shows how to generate this data given a site specific S_DS and S_D1.

http://communities.bentley.com/products/structural/structural_analysis___design/m/structural_analysis_and_design_gallery/255161.aspx

What loads are included in the automatic mass generation and how does the program determine which members or shells to include per rigid floors?

Here’s what’s included in the automatic mass generation (from selected dead and live loads with their percentage):

•             Point loads in nodes

•             Members self-weight

•             Members distributed loads

•             Pressure in members

•             Shell self-weight

•             Shell pressures

The requirements to consider a member in a specific rigid floor are:

•             Both nodes have the same floor number

•             One node belongs to the floor and the other one is below it

The condition to consider a shell in a specific rigid floor is:

•             All its nodes have the same floor number

See Also

RAMSS Dynamic Modal Analysis FAQ

STAAD.Pro Response Spectrum FAQ

External Links

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

How does a dynamic analysis using response spectra for seismic loads differ from a static analysis using equilivalent lateral forces?

Dynamic load cases are not story forces in the same sense as the static load cases. When a dynamic load case with a code selected or user-generated response spectrum is analyzed, the program finds the Eigen solution and determines the modal response for each of the modes included in the analysis. The modal response is based on the response spectra assigned to the dynamic load case, which defines the acceleration vs. period spectrum curve. The modal responses are then combined in some fashion to determine the total response of the structure.

How can I change the number of modes used in the dynamic analysis?

Create an Eigen solution dynamic load case and enter the number of modes to consider. The number of modes can be changed at any point by changing this load case in RAM Frame (Loads > Load cases).

How many modes should I consider?

Generally, building codes require that the dynamic analysis include a sufficient number of modes to obtain a combined modal mass participation of 90% of the total building mass in each of the two orthogonal directions (see ASCE 7-05 12.9.1). The mass participation can be found in the Period & Modes Report under the section titled “Modal Effective Mass Factors” The “%Mass” values represent the mass participation for one particular mode; the “%SumM” values represent the cumulative mass participation. The X and Y modes with the highest mass participation represent the fundamental modes; the program will use the period and frequency associated with these modes in the calculation of the static seismic and wind loads when these values are chosen to be calculated by the program.

There is not a fixed number of modes that need to be specified in order to obtain the 90% mass participation. Rigid diaphragms have 3 degrees of freedom for each diaphragm (x-translation, y-translation, and z-rotation). If you need to include more modes than 3*number of diaphragms to obtain 90% mass participation, then you may need to increase the stiffness or look for instabilities in the model.

Note that when semirigid or pseudo- flexible diaphragms are used, there are 2 mass degrees of freedom for each node (x-translation and y-translation). As a result, default number of modes used by the program may be very large when no Eigen solution dynamic load case is created. In such cases, the number of modes can be changed as noted above.

When I look at the Period & Modes Report, I see that the cumulative mass participation for rotation is always 0% no matter how many modes are included in the analysis?

If a diaphragm includes a two-way deck or it is defined as a semirigid diaphragm, it is meshed and represented with finite (shell) elements. Each node of the finite elements has a nodal (point) mass associated with it. In other words, the diaphragm mass is represented with a network of spatially distributed nodal masses. Note each node includes point mass defined in the global X and Y-directions but not include rotational mass moment of inertia. Because the array of masses does not include rotation, the mass participation for this degree of freedom will always be 0. For the same reason, the mass participation for the rotational degree of freedom will also be 0 when pseudo-flexible diaphragms are used.

It should be known that this type of modeling still suffices for capturing all essential dynamic properties. In other words, the proposed solution accurately captures any dynamic actions related to rotational inertias or any twisting modes due to having center of rigidity and mass center at different locations.

What scale factor should I apply to the response spectrum?

The response spectrum analysis should be factored by the quantity I/R for both forces and drifts. Some codes require the dynamic forces (but not drifts) to be scaled so that the dynamic base shear is at least a specified percentage of the base shear calculated from the equivalent lateral force procedure (see ASCE 7-05 12.9.4, for example). The total base shear is reported in the Building Story Shear Report (Report > Building Story Shear). When the ground level is set to a level other than the base of the model, it is best to use the value reported for the level immediately above the specified ground level.

If you are not considering sign in the analysis, then the perpendicular dynamic base shear value is not really relevant to the X direction scale factor (it could be a result of torsion on the structure only), so we usually recommend scaling the Dynamic load based on the base shear parallel to the load angle.

Should I use SRSS or CQC modal combination?

The CQC method is recommended as the SRSS method can give inaccurate results for 3D structures. When 2D structures are analyzed, the methods will produce similar results.

Does the dynamic analysis consider accidental torsion?

Most building codes require the inclusion of accidental torsion for both the equivalent static load procedure and dynamic analysis. The code requirements for evaluating accidental torsion for dynamic load cases are implemented in RAM Frame when rigid diaphragms are used. To include eccentricity, set the eccentricity to “+ and –" for the x and y directions in the Response Spectra dialog when the dynamic load case is created. The % eccentricity is defined in the Mass dialog in RAM Frame (Loads > Masses). It should be noted that accidental torsion effects can be included in analysis for only rigid diaphragms. For pseudo-flexible diaphragm, it is assumed that a flexible diaphragm is not able transmit diaphragm torsional moments, and hence accidental torsion effect is ignored for flexible diaphragms. In RAM Structural System v14.0.4, accidental torsional effects are also not considered for semirigid diaphragms. These effects are included in v14.2.2.

Why do the analysis results for all members in the model have positive values?

The modal response (nodal deflections, member forces, reactions) determined from a response spectra analysis have signs associated with them. However, once the analysis results are determined by combining the modal results using either the SRSS or CQC method, each response has only a positive value. Because the sign of the result is important for member design, there is an option in the RAM Frame (General > Criteria) to consider the sign in the results. When this option is selected, the sign of the analysis result will match the sign from the predominant modal result. You should not design continuous footings, gusset plate connections, or other elements based on the forces from multiple members using dynamic results unless the sign of the analysis result has been considered.

Why don’t the values reported for the building story shear correspond to the values reported for the change in story shear?

The combination of modal results can affect interpretation of the results, especially building story shear and change in story shear. The program calculates a total story shear and a change in shear for each mode in the analysis. The results are each combined using either the SRSS or CQC combination. As a result, the reported change in shear is not linearly related to the reported building shear. For the same reason, the reported building story shears should not be expected to match the sum of the reported frame story shears. If one is trying to determine equivalent static forces to apply to the diaphragms to match the total base shear, the reported shear from one level should be manually subtracted from the shear reported in the adjacent level rather than using the change in shear values reported in the Building Story Shear Report.

How do I generate load combinations with dynamic loads cases?

Dynamic loads cases are included in the default load combination installed with the program. This was a feature enhancement in v14.05.03. See following web page for release notes: RAM SS v14.05.03 Release Notes

In previous versions of programs, dynamic load cases were not included in the load combination templates. In these versions, you can create load combinations with dynamic load cases using the custom load combinations dialog. You may find it helpful to first generate load combinations with the templates using equivalent lateral force seismic load cases (E) and then modify the load combinations to use the dynamic load case (Dyn) by changing E to Dyn. You can also copy and paste load combinations from another load combination dialog or text document into the custom load combination dialog or create a custom load combination template to include the dynamic load cases.

How can I account for 100/30 orthogonal load effects when using dynamic load cases?

Experts have recommended using a SRSS combination of two orthogonal response spectra analyses to determine the critical forces in a dynamic analysis (see reference below). This method is not implemented in the current version of RAM Structural System. You will need to use load combinations to account for this code requirement.

“A Clarification of the Orthogonal Effects in a Three-Dimensional Seismic Analysis,” E.L. Wilson, I. Suharwardy, and A. Habibullah, EERI Earthquake Spectra, Vol. 11, No. 4, Nov. 1995.

I ran my model with a Response Spectrum analysis using a custom .rsp file, but the results are all zero, what's wrong?

The program interpolates acceleration values from the user provided table, but it does not extrapolate acceleration values past the last data point. It's critical that the last period value in the table is longer than the first mode shape to get accurate results.

For further details see the Ram manager manual section titled, "RAM Frame Response Spectra Tables".

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

RAMSS Eigenvalue Error

STAAD.Pro Response Spectrum FAQ

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

Hi All

Here in Denmark Seismic loading is merely defined as a percentage of the applied vertical load. In the past i've used NOTIONAL LOADS to create this and it worked fine. But only for Y axis as global vertical axis. I now use SET Z UP since it corresponds to the axis definitions all our clients use.

However, notional loads doesn't seem to Work properly when the command SET Z UP command is used. Can anyone explain this?

The alternative is to manually copy all vertical loads and change direction in the STAAD.Editor. But this is a very time consuming task and it also rather frustrating since loads tend to change a lot during the design phase.

Can anyone help me to explain this or alternatively give me a tip to avoid the manual re-entry of loads? Perhaps someone has created a macro for a similar task?

Thank You.

Kind regards

Morten

Hi,

I'm getting shear reinforcement in the slab where there shouldn't be any shear reo. According to AS3600 there shouldn't be any shear reo if V*<phiVuc 8.2.5).

Why RAM Concept constantly provides shear reo? In the report it specifies: transverse bar found, but there's no mentioning where it's coming from (see part of report below, where V*=64<phiVuc=272)

Starting 8.2 Shear Check
Considering Effect of Torsion on Shear:
No torsion to consider
No torsion reinforcement required
General Shear Design Parameters
bv = 1828 mm
do = 219.1 mm
bvd = 400500 mm²
Ac = 457100 mm²
Ast = 2632 mm²
Apt = 0 mm²
Ac = 457100 mm²
fc = 40 N/mm²
fsyf = 500 N/mm²
V* = 64.12 kN (absolute value)
M* = 20.26 kN-m
Setting Vo to zero for RC cross section
Setting Pv and Apt to zero for RC cross section
Calculating Web-Shear Cracking Vuc (8.2.7.2(b))
Precompression Stress = -0.0002275 N/mm² (at centroid)
Failure Tensile Stress = 2.277 N/mm²
Shear Stress Limit = 2.277 N/mm² (at centroid)
I = 2380000000 mm⁴
Q = 14280000 mm³
Vt = 693.7 kN [(limit stress) * bv * (I/Q)]
Vuc (web cracking) = 693.7 kN (Vt + Pv)
Calculating Flexure-Shear Cracking Vuc (8.2.7.2(a))
Beta1 = 1.519
Beta2 = 1
Beta3 = 1
Shear Stress Term = 0.6406 N/mm² ([..]¹´³)
Vuc (flexure-shear) = 389.7 kN
Vuc = 389.7 kN
Vu,max = 3204 kN
Less than minimum ligatures required, using large shear lig spacing (0.75D or 500 mm)
Maximum lig spacing = 187.5 mm (considers torsion lig spacing also)
Calculating Compression Strut Angle
Using 0.6062 instead of 0.6 for compatibility of 8.2.8, 8.2.9 and 8.2.10
Asv,min = 260.2 mm² (at max spacing)
Vu,min = 653 kN
Vu,max = 3204 kN
V*/phi = 91.6 kN
Theta-v = 30 degrees
Adjusted Vu,max = 3204 kN (after considering 8.3.3)
Transverse Bar Found:
As = 260.2 mm²
Fy = 500 N/mm²
Spacing = 187.5 mm
Vus = 263.3 kN
Total Vus = 263.3 kN
Vu = 653 kN
phi Vu = 457.1 kN

Why do I get a Report Viewer error?

Problem, when running the framing tables in the Steel Beam module I get the following warning:

This error typically happens when the user switches to another application while the steel beam design is being performed. To reproduce the problem, open RAM Steel beam and click the option to design all after framing. Then switch to another application while the framing tables are running.

The user has to click OK to the message to proceed.

The error can also happen if the report viewer control is registered in the wrong location,

To reregister the report viewer control, follow these steps.

1. Locate the file VPECTRL3.ocx, it is most likely here:

C:\Program Files (x86)\Common Files\Bentley\Engineering\VPEControl\VPECTRL.OCX

2. Go to the Windows Start button or pearl any type "run" without the quotes and hit enter

3. On the command prompt that appear type

regsvr32 "C:\Program Files (x86)\Common Files\Bentley\Engineering\VPEControl\VPECTRL.OCX"

or change the path if the file is in another location

4. you should get a message that the registration succeeded.

Note, if more than one copy of the file is located first unregister all other copies using a similar command but with /u after regsvr32, before registering the good copy like so:

regsvr32 /u "C:\Path to other copy\VPECTRL.OCX"

In at least one case repairing the installation also solved the problem. It's worth noting that with RAM Structural System, only one version can be installed at a time. Users who try to install both the 32 and 64 bit versions might also encounter this (and other) problems.

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Hello,

I am analying this simple model. Here the vertical post is made of plate element. Flanges of web is made of beam and web is made of plate element. I have connected the cantilever to post by pin connection ( element of cantilever is free in rotation. Is it okay ??). A beam is connecting top of the post and cantilever with pin connection. I have released the rotation of the beam MZ ). 

Now, but the element of the post where beam is pinned is showing very high stresses. (It is not practical). Beam element is pinned to only single node of the element. 

Please help. How to model is better ??? I don't know much about master slave connection.

Instability in Finite Element Analysis

A typical 3-dimensional Finite Element analysis of a structure requires that every node must be stable in all 6 degrees of freedom (TX, TY, TX, RX, RY,RZ). This is achieved by specifying fixity conditions for the columns, beams and braces spanning to a given node or through nodal restraint. While many programs can analyze a structure using fewer degrees of freedom, for this discussion all 6 are assumed to be active.

There are many discussions related to FEA online and whole courses devoted to the topic, but the purpose of this article is merely to show by example a few of the most common causes of instabilities in structural models. The rules apply to RAM Elements (aka RAM Advanse), RAM Frame, RAM Concrete or STAAD.pro as well as other FEA applications. The images and examples below are taken from RAM Elements where a light blue circle indicates a hinge, or member release, at the end of a member. A translational restraint is depicted as a triangle on rollers and a rotational restraint is a "T".

Pinning the free end of a cantilever.

Take the case of a single member fixed at the base for all 6 DOF similar to a flagpole. This structure is stable, except that the free end of member away from the support is hinged or released for major axis bending. As a result, node 2 can spin about the global z axis.

For some applications, this type of "nodal instability" will terminate the analysis. For other applications, a small stiffness may be automatically assigned to the z axis rotational stiffness of the node and you may only get a warning, so long as a moment about the z axis is not applied directly to node 2. This would cause infinite rotation of the node and should terminate any analysis.

The same situation often occurs for a beam with a cantilever, where the cantilever beam is the only member connected to the node at the tip. In short, the free end of any member, where that member is the only member in the model connected to a particular node should never be released. 
 

Beam, column and brace intersections.

When multiple members frame to a single node, it is acceptable to release some, but not all of those members. If the beam, column and brace are all released at the same node, then the problem is the same as case 1 above. At least one of those members should be fixed ended. In most situations, it is the column top that should remain fixed to the node.

Releasing the tops of columns.

In this case we have a fixed ended beam setting on two columns, both of which are released at the top node. This case differs slightly from Case 2 because the nodes are fixed to the beam and not themselves instable. The problem is that the beam along with both top nodes can spin as a group on top of the columns similar to a log on water. This is an example of why it is usually better to keep the tops of the columns fixed and release the beams.

Torsional releases

It's hard to envision a realistic connection that allows a member to spin or swivel, but most FEA application do allow member torsional releases. A general rule is to leave the member torsion fixed except in a situation where member rotation really is free. The most common problem occurs in a chevron brace configuration where the beam is two finite elements. If each beam half is released in torsion, then the node at the top of the braces is instable.

2-dimensional frame in a 3-dimensional analysis

Often it is desirable to analyze a 2-dimensional frame using a 3-dimensional analysis. In some applications there is plane frame option that can be used to ignore the deflection out of plane (e.g. z axis) or rotation about the other axes, but if not, the frame can generally be stabilized one of two ways.

• An out of plane, z axis restraint can be applied to some or all of the nodes to effectively keep the frame from falling over, or
• Rotation about the in-plane axes can be restrained at the base nodes (e.g. rotation about the X axis).

The same situation often occurs in RAM frame when no rigid diaphragm is used. This can leave the model with several, isolated, 2D frames in space with no connection between them. If the frames are pinned at the base then they can fall over and an instability results. Fixing the base of the frames against out-of-plane rotation is generally the solution to this problem, though connecting the frames together with lateral members or some other simulation of a diaphragm is also possible.

Other Global stability issues

A certain number of nodal restraints are always required to keep the structure as a whole from moving. Another common case is one where a shell or mat foundation is supported by a series of vertical springs. While that is stable in relation to vertical loads, some mechanism must be provided to keep the mat as a whole from sliding around like a skateboard. This is generally achieved through the use of horizontal springs in addition to the vertical springs, or by restraining the translation of a node (or line of nodes) along the edge of the structure.

This is a common problem in Ram Concept if a vertical resistance area spring is the only support for the structure. When there are no lateral loads, you might get away with providing an area spring with only vertical stiffness, but when there is any external load applied in the plan directions, some resistance to sliding must be incorporated into the model.

Diaphragm stability

In most building type structures there is a horizontal diaphragm that ties the frames together and prevents in-plane deformation of the plan. This is typically modeled using a rigid floor diaphragm. The diaphragm constraint forces the nodes of the floor to move together preventing the plan from racking for example.
In space frame models where no rigid diaphragm is modeled (perhaps because the roof is sloped), there must be some other mechanism to keep the plan from racking. This is generally achieved by providing diagonal members in that plane. Fixing the minor axis of the beams in the plan is another approach. Think of this like creating a Vierendeel truss in plan. Using shell elements is another option, though the interaction between the shells and the members is not always desirable.

Using tension-only members or compression-only springs

When a model utilizes non-linear members or springs most FEA applications iteratively solve for each load case and load combination. On each iteration, if a tension-only member is found to go into compression, that member is thrown out of the analysis and a new iteration is started. If too many of the members go into compression, the frame or structure as a whole can become instable.

There are a couple of ways to effectively deal with such a situation

• Apply a pre-tensioning force to the braces. By putting the member into an initial tension state it is less likely to go into compression and fall out of the analysis.
• Assign some of the members to be tension and compression members. For X braced frames or other symmetric structures it is typically acceptable to analyze the structure with a single tension + compression brace rather than a pair of tension-only braces. This does affect the load path through the columns somewhat, however, and may require two versions of the model to capture the worst condition. A similar option is to leave both braces in the model, but then check the braces or twice the determined force.
• Applying self weight to tension only braces will cause bending moments in the members which usually is not the intent for tension-only braces. in those cases, a zero density material is suggested.
• Additionally, for X braced frames in Ram Elements, the program may be introducing a node at the intersection of the braces. This can be prevented using Process - analyze - FE Model tab - by turning off the option to "Add intermediate nodes at member intersections".

P-Delta effects and model instabilities

There are cases where a structure might be perfectly stable under a first-order analysis, but as the analysis incorporates P-Delta effects the deflection is amplified and instability can result. Different applications handle P-Delta analysis in different ways, but there are usually controls for the tolerance required for P-Delta convergence. Increasing the tolerance often leads to a solution, but some structures may have to be stiffened in order to complete a P-Delta analysis on all load cases.

See Also

RAMSS Eigenvalue Error

RAM Frame P-Delta [TN]

Structural Product TechNotes And FAQs

STAAD.Pro Instability And Zero Stiffness

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!