howto do analysis and design

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How to do Analysis & Design - practical examples


Description This document provides practical examples on how to do Analysis & Design with Tekla Structures.

This document can be used as reference manual, as the items in the table on contents are linked to the corresponding headings in the document.

Contents If you want to review a certain subject, please select the subject in the table of contents, which is linked to the corresponding heading in the document.

How to do Analysis & Design - practical examples........................................................................1 Create analysis model.......................................................................................................................3 Set member analysis properties ......................................................................................................5 Setting load properties......................................................................................................................7 Add intermediate nodes to a member ...........................................................................................10 Analysing composite beams ..........................................................................................................11 Analysis of haunch connection......................................................................................................18 Analysis of plate girders.................................................................................................................19 Support displacement loading .......................................................................................................20 Temperature difference load for the whole building ....................................................................21 Check which members are loaded.................................................................................................23 Setting optimisation section groups .............................................................................................24 Draw analysis model in Tekla Structures......................................................................................27 Enable or disable rigid links...........................................................................................................29 Find STAAD.Pro element in TS model...........................................................................................31 Find STAAD.Pro node in TS model................................................................................................34 Find TS member in STAAD.Pro model ..........................................................................................36 Modelling curved beams.................................................................................................................38 Setting beam unsupported length for design check ....................................................................40 Setting column buckling length for design check........................................................................42 Rigid diaphragms (rigid floors) ......................................................................................................44 Creating a report in STAAD.Pro .....................................................................................................48 Checking calculated displacements in STAAD.Pro......................................................................49 Viewing calculated member forces in STAAD.Pro .......................................................................52

2006-02-10 Copyright © Tekla 2006

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Viewing STAAD.Pro output file in STAAD.Pro ..............................................................................54 Beam not connected because of gap ............................................................................................57 Bracing members modelled incorrectly ........................................................................................59 Bracing members are not connected to beam..............................................................................60 Column skewed in the analysis model ..........................................................................................61 Duplicate members .........................................................................................................................64 Analysis run failed...........................................................................................................................65 Material error in analysis ................................................................................................................66 Analysis takes a long time, extra members included...................................................................67 Design tab is empty.........................................................................................................................68 No design check is done.................................................................................................................69 How to check instability problems.................................................................................................70 Basic modelling errors causing instability....................................................................................71 Invalid load spanning direction......................................................................................................74 Load is missing because bounding box is too small...................................................................75 Self weight load of model members ..............................................................................................76 Wind loads created at incorrect height .........................................................................................77 Member results are in member local coordinate system.............................................................78 Stability problems may cause completely incorrect results........................................................80 Slab/wall not connected to beam ...................................................................................................81 Wall not connected to columns......................................................................................................83 Dense element mesh created for slab or wall ...............................................................................85 Supports for wall or slab.................................................................................................................88 Beam should not be connected to slab.........................................................................................89


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Create analysis model Menu command Analysis->New model... Some notes related to the basic analysis models: Select either Full model or By selected parts and loads:

Full model: All parts of the model will be included, except those which the analysis type has been set as Ignore (on the analysis tab of part dialog). Any existing select filter may also be connected to filter out parts. Parts created by macros will not be included in the full model (exceptions where parts are created by the truss and concrete slab macros, as these macros set the analysis properties for the parts they create). By selected parts and loads: Selected parts and loads will only be included. Any connection part may also be included. Parts and loads may later be added or removed by Analysis->Add members, Analysis->Remove members. Select either Force to centric connection or Use rigid links:

Extended clash check should be used, for more accurate analysis model creation. Option Use rigid links is used if more accurate modelling of eccentricities in the model is required: Force to centric connection:


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Use rigid links:

See also case “Enable or disable rigid links in specific places”. Both of the following are possible:

• Analysis model is set to Force to centric connection. Generally rigid links are not used, but it is possible to force rigid link at a specific place.

• Analysis model is set to Use rigid links. Generally rigid links are used, but it is possible to disable rigid link at a specific location.


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Set member analysis properties These are some notes regarding the analysis properties of beams and columns in standard cases:

Member analysis type:

• Truss for braced members • Otherwise Normal.

Member axis location

• Columns: Typically Neutral axis, or alternatively Reference axis • Beams and bracings: Typically Reference axis, or alternatively Neutral axis

Analysis offsets: These are used to introduce longitudinal offsets, to model the conditions more accurately. One example is the connection between a precast concrete beam and column where the load from the beam is eccentric on the column:


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Setting load properties

To make sure the correct members are loaded use the Part names filter. To guarantee that the load will be applied to the required members, ensure that the bounding box is large enough. Generally, it should be no problem if the bounding box is over-sized. Load panel properties Set spanning to single/double and primary spanning direction. If double spanning and Automatic primary axis weight is set to Yes it makes no difference as to which of the two spanning directions is selected as the primary direction.

Only in double spanning case, automatic primary axis weight and the weight value affect the proportions of the load which is applied to the primary axis and to the perpendicular axis. If automatic primary axis weight is set to Yes, the proportions will be in shared to the third power of the span lengths in these two directions, i.e. the shorter the span, the larger the proportion of the load. The weight value does not matter. If automatic primary axis weight is set to No, the given factor is used to divide the load, see diagrams below. The settings are applicable to point load, line load and uniform/area load (although this issue is not relevant to uniform/area load if they cover the whole panel area).


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Setting create fixed support conditions automatically is related to load distribution on continuous structures (setting is actually renamed to Use continuous structure load distribution in version 11.1). When uniform load Q is applied on a continuous beam with span lengths L, the load on the leftmost span is not divided equally to the supports, but instead the support loads will be 0.375QL and 0.625QL. Enabling this setting means that this effect is included in the load distribution.


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Add intermediate nodes to a member Sometimes intermediate nodes are required along a member. This is often required for frequency analysis. There are user defined attributes and specify the number of split nodes and distances to create the additional nodes.


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Analysing composite beams Composite construction consists of beams, studs and concrete slabs on top of the beams.

To model composite beam the user can either give composite beam properties directly to the beam or use the Automatic Composite Beam option. On the later condition Tekla Structures recognizes the concrete deck above the beam and takes composite properties directly from the deck properties.

Decks can be modelled as flat slab or as a composite deck. Concrete thickness material is taken from the deck and also rib height and width if the composite deck used. Deck properties are defined in the profile catalog.

If beam has shear studs defined the analysis uses information directly from them.


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If deck or shear studs are not modelled these design properties are defined on the beams composite and design tab pages.

Beam settings To analyse beams as composite beams, then modify the beam properties on the Analysis tab.

1. Select:

• Composite beam: modify composite beam properties manually

• Automatic composite beam: Tekla Structures automatically recognizes

the composite beams, and calculates the effective slab width.

2. When you have modified the properties, run analysis and Tekla Structures calculates the effective slab width.

• 1/8 of beam span, center-to-center, of support

• Effective width may not be more than half of the distance to the nearest composite beam.

• The effective width may not be more than the maximum distance to the next beam:

With Composite beam option, the slab width is zero if there is no beam on the left or right.


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With Automatic composite beam Tekla Structures can calculate the width even if there is no beam on either side.

Design tab:

The track attribute affects to level of detail for composite design. Set that to 2 – Print the output at the maximum level.

Design tab page contains composite beam properties if deck or shear studs are not modelled.

Inquiring effective width

When analysis model is active inquire function displays composite beam properties

.

Using slab generation macro for deck creation 1) Select slab generation macro.


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2) Define deck properties

3) Select deck area.

Metal deck profiles Metal deck profiles are defined in the profile catalog.

Interface to STAAD.Pro These values are taken to account when designing the beam and number of studs required. STAAD.Pro takes following arguments into account during the design.

Composite Beam Design as per AISC-ASD

Description

STAAD.Pro now supports composite flexural member design in accordance with the AISC-ASD code. Full composite action and uniformly distributed loading are assumed. Shear connectors are to be continued in the negative moment area. Formed steel deck is assumed to be perpendicular to the member. If it is parallel to the member, the number of shear connectors must be adjusted.

The following additional parameters have been introduced to support the composite member design


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STAAD.Pro Output STAAD.PRO.PRO CODE CHECKING - (AISC 9TH EDITION)

********************************************

------------------------------------------------------------------------

| MEM= 7 Section = CM W27X84 Ratio = 0.054 Status : Pass |

| Section Loc. = 1.00 Load = 103 Moment = 0.4422E+3 kip-inch |

| Critical Condition : Steel stress after concrete hardens: I2 |

| UNITS - POUN FEET |

| Actual Steel Stress before Concrete Hardens = 0.1214E+6 |


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| Allowable Steel Stress before Concrete Hardens = 0.3421E+7 |

| Actual Concrete Stress before Hardening = 0.0000E+0 |

| Allowable Concrete Stress before Hardening = 0.2350E+6 |

| Actual Steel Stress after Concrete Hardens = 0.2524E+6 |

| Allowable Steel Stress after Concrete Hardens = 0.4666E+7 |

| Actual Concrete Stress after Hardening = 0.1037E+5 |

| Allowable Concrete Stress after Hardening = 0.2350E+6 |

| Number of shear connectors required : 51 |

| Diameter of shear connectors : 5/8-inch |

------------------------------------------------------------------------


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Improvements in version 11.1 Tekla Structures 11.1 contains the following improvements

Automatic rigid diaphragm If the deck is created with slab generation macro, the user can select if the slab forms a rigid diaphragm.

Automatic deck's weight load The deck's weight can be included in the analysis model as a load even if it is not otherwise included.

Number of shear studs The number of shear stud transferred back to Tekla Structures as a beam property. The beam information can be used for stud modelling and included in the drawings and reports.


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Analysis of haunch connection Haunch connections can be approximated by inserting a modified section on the haunch area. The section adopted and the length of the section have to specified by the user. In practice, tapered I and H sections will be used.

STAAD.PRO model:


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Analysis of plate girders How should a plate girder be modelled in TS if the user is intending to analyse it using the A&D module? Two ways are possible: Use equivalent profiles i.e. from User Defined Attributes dialog define the profile to be considered in the analysis.

If the plate girder is modelled using custom parts, then the values can be filled in automatically. Optimisation recommends the new equivalent profile. The user can also define a special optimisation group for the plate profile with optimization group UDA. See case “Define optimisation groups”.


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Support displacement loading Support displacement loading is not directly handled. The workaround is to have a stiff spring support which does not yield under existing loads and then apply a strong load at the spring location to create the appropriate displacement.


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Temperature difference load for the whole building In version 11.1: It is possible just to insert one temperature load with "temperature difference for axial elongation", and making the bounding box large enough to contain all the structures elements.


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In versions 10.2 and 11.0: Separate temperature load has to be inserted at each floor level, for beams, i.e. using part name filter BEAM etc. Then, for columns, the work plane has to be changed so that X is vertical. One temperature load is then inserted at each grid line of the building with the part name filter set to COLUMN etc.


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Check which members are loaded After running the analysis, use Inquire->Load to see which members are loaded by a particular load.


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Setting optimisation section groups In optimisation, the lightest safe section (i.e. passes the design check) will be searched for. By default the group of alternatives is based on the grouping in the profile catalog. HEA300 for example:

So, for HEA300 the default choices are HEA100, HEA120, ..., HEA1000, and the optimisation result could be:


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However, in this case the alternatives to HEA300 maybe required to be: HEA100, HEA200, HEA300, HEAA300, HEA400, HEA500, HEA600, HEA700. This group is named A1 and can be defined by modifying each of these profiles in the profile catalog:

NOTE: After modifying the profile catalog, the analysis must be rerun, before optimisation can be performed according to the modified settings.

In addition, as this group contains one section (HEAA300) from another profile tree branch, the advanced option needs to be modified:

After this change, optimisation result is (HEA450 is no longer available):


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Draw analysis model in Tekla Structures The (wire-frame) analysis model can be drawn into TS window by Select objects on the analysis&design models dialog:

Beams are drawn in red, rigid links in dark blue and slab/wall edges in light blue. Also nodes will be drawn. Model parts maybe hidden through the display properties:


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The analysis model cannot be drawn until the analysis has been run, or Analysis->Create model has been used. Create model is useful especially when the STAAD.Pro analysis takes a considerable time, as only the analysis model and STAAD.Pro model are created and no actual analysis is made. Analysis model can then be checked in TS, and also using STAAD.Pro post-processor.


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Enable or disable rigid links Rigid links can be either enabled or disabled in the analysis model (see case “Create analysis model”). This setting can be overridden in specific places. In other words both of the following options are possible:

• Analysis model is Force to centric connection. Generally rigid links are not used, but it is possible to force rigid link at a specific place.

• Analysis model is Use rigid links. Generally rigid links are used, but it is possible to disable rigid link at a specific place.

User defined attribute Rigid link is used to control rigid links at a specific location. The value of the attribute is a three-digit number of 1 or 0, 1 = rigid link enabled and 0 = rigid link disabled. The first digit is the setting for the beam start point, the second digit is the setting for all intermediate points between start and end point, and the third digit is the setting for the beam end point. Rigid link is created at a connection between two members if

• There is an eccentricity • Rigid link is enabled for both parts, either as analysis model attribute or beam attribute

Example 1. Analysis model is Force to centric connection. If Rigid link attribute is not set, there will be no rigid link. Rigid links can be created with the following attribute values:


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Example 2. Analysis model is Use rigid links. If Rigid link attribute is not set, there will be rigid link. To disable the rigid link, it is enough to set the attribute for only one beam:


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Find STAAD.Pro element in TS model Each STAAD.Pro member has a corresponding TS member, except for rigid link members. Several STAAD.Pro elements may be created from one TS member. There is no dedicated tool available to find the TS model member by STAAD.Pro element number. Therefore the element can be found in the following ways:

• If the STAAD.Pro element reference is in TS analysis log file, simply click on the row and the TS member is highlighted (selected). If it is hard to locate the selected member, use View->Fit by parts.

• Highlight the element in STAAD.Pro. Select “beam” mode on the left side of STAAD.Pro post

processor. The location in TS model may then be found visually, and Inquire->Part may be used to check the STAAD.Pro elements of a given TS member.


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• Open STAAD.Pro input file (.std), locate GROUP section. The ID of the TS member can be found there.


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Find STAAD.Pro node in TS model There is no dedicated tool available to locate a STAAD.Pro node in the TS model. Therefore the following options can be used:

• If the STAAD.Pro node reference is in TS analysis log file, simply click on the row and the TS member is highlighted (selected). If it is hard to locate the selected member(s), use View->Fit by parts.

• Highlight the node in STAAD.Pro. Select “node” mode on the left side of STAAD.Pro post

processor. Select node in table, check which member is connected to this node and then use guide “Find STAAD.Pro element in TS model”.


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Find TS member in STAAD.Pro model There is no dedicated tool to find the TS member in the STAAD.Pro model. Apart from locating visually, the following method can be used: Use Inquire->Part in TS to get the element ID(s):

In STAAD.Pro, switch to “beam” mode, click the element in the table and the element is highlighted.


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Modelling curved beams If true curved members are used in the STAAD.Pro model, there may be following problems:

• STAAD.Pro does not support releases for curved members (error message **ERROR-CURVED MEMBER HAS TRUSS, CABLE, TENSION/COMPRESSION OR RELEASES SPECIFIED)

• Load is not applied on curved member • The desired results are not available (forces or displacements along curved beam) • STAAD.Pro model is incorrect

To avoid these problems, curved beams should be modelled using straight segments. In version 11.0, a user defined attribute is used:

• Curved beam by straight segments is set to Yes • No of split nodes is set if additional nodes are required (with larger curvature)

In version 10.2, in certain cases even setting these attribute values is not enough, the curvature must be removed and curved beams split manually into several straight beams. In version 11.1, curved beams are modelled using straight segments by default, using approximation accuracy of 25 mm. In special cases these settings may be changed using the advanced options:


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Setting beam unsupported length for design check Different cases of beam unsupported length for the design check:

• No intermediate supports (the default case). Length is specified as factor UNF = 1.0, which is applied to the physical member length, i.e. this works correctly even if the physical member is split into several analytical (STAAD.Pro) members. UNL = 0.

• Intermediate support at half-span. Factor UNF = 0.5, UNL = 0.

• Intermediate supports at every 1200 mm. UNF is now 0, UNL = 1200 mm.


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NOTE: To control the level of detail reported by STAAD.Pro in the design check, use design parameter TRACK, either in analysis model properties (Design-Steel, Design-Concrete) or part properties.


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Setting column buckling length for design check The possibilities in versions 10.x, 11.0 and 11.1 are limited. Buckling length can be specified either by using a factor (related to the physical or analytical member) or directly by length. It is recommended to specify buckling length directly as length. In these versions it is not possible to define several buckling lengths for a single column, therefore the length must be selected conservatively. Note: The default values of buckling length are factor K = 1.0, length L = 0, in which case the actual length in the design check is 1.0 * column length. This is generally much too conservative.

In above diagram indicates a three storey condition each with a 5 metre. The buckling length could be specified as 1.2 * 5m = 6 m, in the case of a non-sway building condition.


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Tekla Structures 11.2 also allows you to define buckling lengths for column segments, which represent the building levels. Tekla Structures automatically divides columns into segments at the point where there is a support in the buckling direction, or where the column profile changes. NOTE: To control the level of detail reported by STAAD.Pro in the design check, use design parameter TRACK, either in analysis model properties (Design-Steel, Design-Concrete) or part properties.


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Rigid diaphragms (rigid floors) Rigid diaphragms can be used to model rigid floors in a simpler way, without the usage of plate elements, which can complicate the model and increase the analysis time greatly. Consider the following case, slab supported by columns, one lateral point load.

By default, the slab is modelled using plate elements.

To use rigid diaphragm instead, the type of the slab is changed to rigid diaphragm.


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All nodes within the rigid diaphragm are tied laterally, meaning their distances in XY-plane remain unchanged, but the whole rigid diaphragm may rotate. The displacements of the nodes in Z direction remain independent.

Rigid diaphragm can also be visualised in STAAD.Pro (right click on graphics window, select Labels..., enable Show Master/Slave on Labels tab).


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Following issues exist with rigid diaphragms:

• Adjacent rigid diaphragms are merged since version 11.1. In previous versions, there could only be one rigid diaphragm at each level of the building. If the floor was divided into several slabs, they had to be ignored in the analysis and a separate slab, which covered the whole floor, had to be inserted as a rigid diaphragm.

• Version 11.1 includes a new Rigid diaphragm filter. Only nodes which belong to a part matching the filter will be connected. For example, you can use column_filter to only connect column nodes to rigid diaphragms. Before version 11.1 there was no filter to select which nodes are tied and which not.

• In very large models rigid diaphragms may increase the analysis time considerably (compared to the case with no slabs or rigid diaphragms at all). In this case the rigid diaphragm effect can be modelled using truss beam members, which tie all relevant nodes laterally, see the diagram on the next page below.


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Creating a report in STAAD.Pro To create a report, use File->Report setup in STAAD.Pro. Select contents of the report using tabs Items, Steel Design etc. If only certain members are to be included, set filter on Ranges tab.

To create the report file, use File->Export Report->Text file.


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Checking calculated displacements in STAAD.Pro To view calculated displacements, switch to Node mode.

In case the node displacements table is not visible, use View->Tables to make it visible.


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To change the displacement scale, right-click on the graphics area and select Labels...


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Viewing calculated member forces in STAAD.Pro To view calculated member forces, switch to Beam mode.

In case tables Beam End Forces/Beam Force Detail are not visible, use View->Tables to make them visible.


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To change the displacement scale, right-click on the graphics area and select Labels...


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Viewing STAAD.Pro output file in STAAD.Pro STAAD.Pro output file should be checked for

• Possible warnings and errors • Check total applied load and calculated reaction load for each load case

In addition, steel/concrete design check results can be viewed. To open the output file, use File->View->Output File->STAAD.Pro Output or use the tool button.

If there are warnings or errors, these are visible first:


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Beam not connected because of gap Problem: Beam is not connected to another beam because of a gap between members.

There are two ways to solve this:

• Change the tolerance which is used in the member clash check. The default is 1 mm, this could be changed to 30 mm for example, with no probable side-effects.

• Force connection at this specific location, using user defined attribute. The ID of the smaller beam is inquired, and this ID is set as the value of Connect to for the larger beam. Several IDs may be entered, separated by spaces.


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Bracing members modelled incorrectly Problem: Bracing members are modelled incorrectly or strangely in the STAAD.Pro model. To solve this: As a general principle, bracing members should have analysis type Truss. Truss members are handled differently in the creation of the analysis model, usually producing better results.


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Bracing members are not connected to beam This may be caused by having the beam defined as truss. Truss members will not be split. To solve the problem, set type as beam.


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Column skewed in the analysis model Problem: Elements/nodes are not correct in the STAAD.Pro model:

• Column is skewed • There are short duplicate elements


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Duplicate members Problem: Error message about duplicate members (in TS analysis log WARNING- MEMBERS MEMBER 5(Id: 151) AND MEMBER 4(Id: 146) BETWEEN SAME JOINTS) The reason for this can be one of the following:

• There really are overlapping members in the TS model (check by clash check) • There are twin profiles which are not supported by STAAD.Pro. In this case the warning

should just be ignored.

• There is a problem in the analysis model creation, which results in short overlapping members (see case “Column skewed”)


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Analysis run failed

This might be caused by an installation problem, especially if STAAD.Pro analysis dialog is not displayed at all:

The cause of the problem may be found in the log files:

• Tools->Display log file->Log file... • Tools->Display log file->Analysis log file... • If possible, open STAAD.Pro (View results), and check the STAAD.Pro output file


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Material error in analysis The analysis fails if essential material properties are missing. The Material catalog must be modified.


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Analysis takes a long time, extra members included It should be ensured that no unnecessary secondary members are included in the analysis, as these may greatly increase the size of the analysis model and the required analysis time. An example of this are contour plates in stairs. If they are (unexploded) macro parts they are not included in full model, but can accidentally be included in a model by selected parts and loads.


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Design tab is empty

How to solve problem: Activate the analysis model. If no analysis model exists, one must be created and made active.


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No design check is done Problem: No steel or concrete design check is done in STAAD.Pro. To solve this problem: Make sure design check is enabled for steel and concrete respectively.


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How to check instability problems Open the analysis log file in TS (Tools->Display->Analysis log) to check for possible instability warnings or errors. Click on the warning/error row to locate the problem in the model (temporary symbol will be drawn, and all members connected to the node will be highlighted).

NOTE: Instability problems must always be fixed, as they can cause completely erroneous calculation results. Instability problems can also be checked in the STAAD.Pro output file (see “STAAD.Pro, view output file”).


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Basic modelling errors causing instability

• Cantilever beam must not have pinned end, where it connects to other members

• If a member with pinned end conditions is split, there must not be any releases at the split

location for either split member.


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• If member with pinned end conditions is split, torsional rotation must be suppressed at either end, because suppression is not done automatically (it will be automatically done in case of single member).

• Rotation at column bottom cannot be done if there is no corresponding lateral support at column top.


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Invalid load spanning direction The primary axis direction must be valid for the load distribution to succeed, if

• Load is single spanning • Load is double spanning and automatic primary axis weight is off


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Load is missing because bounding box is too small The bounding box of the load must contain both the actual model part and the analytical elements which are to be loaded.


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Self weight load of model members Even if self weight load group is included in the analysis, the self weight of any TS member which is not included in the STAAD.Pro model will be ignored. Typically this affects concrete slabs which often are not included as plate elements in the STAAD.Pro model. In other words, they are not included in the analysis model at all, or their analysis type is Ignore or Rigid diaphragm. In this case the self weight of the slab must be inserted manually as area load.

Update for version 11.1: There is an option to generate self weight loads automatically, whether the slab is included in the analysis model or not.


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Wind loads created at incorrect height The wind load polygon must be inserted at level Z = 0, otherwise loads are placed at incorrect vertical position.


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Member results are in member local coordinate system In STAAD.Pro, member forces are reported in member local coordinate system, where X is in the member axis direction and Y is the ”up direction” of the TS section.

The orientation of members can be displayed in STAAD.Pro, by right clicking on the graphics window and selecting Labels...


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Stability problems may cause completely incorrect results Stability problems must always be checked and fixed, because they can cause completely erroneous calculation results may be produced.


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Slab/wall not connected to beam For slabs and walls, in versions 10.2.x and 11.0 it must be ensured that the analysis plane is correctly set, otherwise slab and beam are not connected. Note: In version 11.1 this can be handled, rigid links are inserted automatically if needed.


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In case none of the options top/middle/bottom plane is suitable, analysis offset user defined attributes can be used to modify the position of the slab in the analysis model.


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Wall not connected to columns In versions 10.2.x and 11.0, connections of walls to columns and beams cannot always be created automatically. Note: In version 11.1 this can be handled, rigid links are inserted automatically if needed.

The situation can be corrected by applying analysis offsets to the wall, using the user defined attributes of the wall.


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Note: Analysis offset user defined attributes can also be used for beams, to modify the position of the beam in the analysis model.


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Dense element mesh created for slab or wall In slab/wall analysis, sometimes very dense element meshes are created. The analysis may take a very long time or the mesh may be corrupted and the analysis fails.

• Forced nodes (from beams/columns/other slabs) too close to each other

o Workaround 1: Move other beam/column so that locations match (analysis offset in user defined attributes).


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o Workaround 2: Consider if all beams/columns must be connected to the slab, if not

see …

• Extra nodes created by loads

o Workaround: Reposition load positions exactly at slab corner points

• Short cantilever


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o Workaround 1: Move beam to slab edge position (use analysis offset UDAs of beam) o Workaround 2: Ignore slab in the analysis, replace with a smaller slab just for the

analysis. This problem has been addressed in version 11.1: Default cantilever length is now set to 300 mm, cantilevers shorter than this are removed from the analysis model. To change this limit, use the user-defined attribute:

attribute("AD_plate_min_cant", "j_AD_plate_min_cant", dimension,"%. 3f", no, none, "0.0", "0.0") { value("", 0) }

Other workarounds:

• Possibly slabs could be replaced by rigid diaphragms? (see “How to use rigid diaphragms”) • Sometimes meshing at the connection between two slabs/walls is improved if the element

sizes are slightly modified either increased or decreased (100 mm steps for example).


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Supports for wall or slab It is currently not possible to define supports for slabs and walls. The workaround is to insert, for example short columns, with a suitable spacing.


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Beam should not be connected to slab It is possible to disable the connection between slab and beam, so that the slab will not impose loads on the beam.

Connection can be disabled using the user defined attributes of the beam.


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Beam and slab will be disconnected

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howto do analysis and design

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allowable

allowable

actual concrete

actual steel

slab generation

disable rigid

user defined

pinned end