simple grill

Upload: ashish-loya

Post on 14-Oct-2015

35 views

Category:

Documents


0 download

DESCRIPTION

Grill

TRANSCRIPT

  • Description

    1

    Example : SimpleGrillageFor software product(s): LUSAS Bridge.With product option(s): None.

    DescriptionA simple grillage is to be analysed. The geometry is as shown below. All membersare made of C50 concrete to BS5400. Section properties of the longitudinal beamsand diaphragms are to be calculated using the Section Property Calculator facility.

    The structure is subjected to four loadcases: Dead load, Superimposed dead load,Lane loads in both lanes (UDL and KEL), and an abnormal load (HB) in the lowernotional lane with a lane load (UDL and KEL) in the upper lane.

    Units of kN, m, and t are used when modelling the grillage. Units of N, mm, and tare used in calculating the section properties of selected components.

    0.75m

    0.5m

    20 m

    Longitudinal section along deck

    Y6 beam with insituconcrete top slabSpan = 20mWidth = 12mSkew = 0o

    6 @ 2 m

    Cross-section through deck

    0.25m

    12 m

    Footway 0.25m ConcreteDensity 2.4t/m3

    Surfacing 0.1m TarmacDensity 2.0t/m3

    3.5m Lane 3.5m Lane2.5m 2.5m

  • Example : Simple Grillage

    2

    ObjectivesThe required output from the analysis consists of:

    q A deformed shape plot showing displacements caused by the imposed loadingq A diagram showing bending moments in the longitudinal members for the

    design load combination

    Keywords2D, Y6 Precast Section, Section Property Calculation, Local Library, Grillage,Basic Load Combination, Smart Load Combination, Enveloping, DeformedMesh, Bending Moment Diagram, Print Results Wizard

    Associated Files

    q grillage_modelling.cmd carries out the modelling of the example.

    Modelling

    Running LUSAS ModellerFor details of how to run LUSAS Modeller see the heading Running LUSASModeller in the Examples Manual Introduction.

    Note. This example is written assuming a new LUSAS Modeller session has beenstarted. If continuing from an existing Modeller session select the menu commandFile>New to start a new model file. Modeller will prompt for any unsaved data anddisplay the New Model Startup form.

    Before creating the grillage model the section properties of the longitudinal beamsand end diaphragms are to be computed using the section property calculator andstored for future use.

    Creating the Longitudinal Beam Model Enter the file name as Y6

    Use the Default working folder.

    Enter the title as Y6 Precast Beam

    Select units of N mm t C s from the drop down list provided.

    Leave the startup template as None

    Precast Section

  • Example : Simple Grillage

    4

    Click the Cancel button to close the form.

    Creating the End Diaphragm Model

    Create a new model and discard the changes to the previous model.

    Enter the file name as diaphragm

    Use the default working folder.

    Enter the title as End diaphragm

    Ensure units of N m kg C s are selected.

    Leave the startup template as None

    Click the OK button.

    Defining Diaphragm Geometry

    Enter coordinates of (0,0), (0.5,0),(0.5,0.5), (1.0,0.5), (1.0,0.75), (0,0.75) todefine a surface representing the enddiaphragm and slab (which is to berepresented by the end beam on thegrillage model) and click OK

    FileNew

    Geometry >Surface >

    Coordinates

  • Modelling

    5

    Calculation of End Diaphragm Section PropertiesThe units of themodel selected in thestartup form, metres(m) in this case, willbe displayed in thedrop down list.

    Select the optionAdd local library

    Click the Applybutton to computethe sectionproperties. Thesewill be displayedin the greyed textboxes on the righthand side of theform and writtento the local library file for future use.

    Click the Cancel button to close the form.

    Creating the Grillage ModelNow that the beam and diaphragm properties have been calculated the grillagemodel can be created.

    Create a new model and discard the changes to the previous model.

    Enter the file name as grillage

    Enter the title as Simple grillage analysis

    Set the units as kN m t C s

    Leave the model template as None

    Click the OK button.

    Note. It is useful to save the model regularly as the example progresses. Thisallows a previously saved model to be re-loaded if a mistake is made that cannot becorrected easily by a new user.

    UtilitiesSection PropertyCalculator>

    Arbitrary Section

    FileNew

    !

  • Example : Simple Grillage

    6

    Using the Grillage WizardIn this example the grillage wizard is used to generate a model of the bridge deck.The grillage wizard defines the grillage geometry, assigns grillage elements to eachof the lines, and assigns supports to the end beams. It also assigns an equivalencedataset to ensure nodes are generated at each of the line intersections and createsGroups to ease member identification and the application of section properties.

    Note. It is difficult to make absolute recommendations as to how individualstructures should be modelled using a grillage. A few basic recommendations arehowever valid for most models:

    a) Longitudinal beams within the grillage should be coincident with theactual beams within the structure.

    b) Transverse beams should have a spacing which is similar or greater than

    that of the longitudinal beams and the total number of transverse beamsshould be odd to ensure a line of nodes occur at mid span.

    Select the Set defaults button

    Ensure Slab deck is selected and click Next

    The grillage is Straight with 0 degrees skew so click Next again

    Enter the grillage width as 10 and the number of internal longitudinal beams as 6and click Next

    Leave the number of spans as 1

    Enter the length of span as 20 and the number of internal transverse beams as 9

    Click Finish to generate the grillage model.

    !

    BridgeGrillage Wizard

  • Modelling

    7

    Caution. The grillage wizard creates nodes at the intersection of each line anduses an equivalence dataset to merge the nodes together. If the grillage geometry ismodified the nodes will not appear at the line intersection and the equivalence willbe unable to merge out the nodes to connect the longitudinal and transversemembers.

    Calculation of Transverse Beam Section PropertiesThe internal transverse beams each represent 2m of slab so the section properties arecomputed for an equivalent solid rectangular section.

    Select the solid rectangular section.

    Enter a depth of D = 0.25

    Enter a width of B = 2

    M

    Longitudinal Section

    Transverse Grillage beamsSlabEnd Diaphragm

    2m1m 2m

    UtilitiesSection PropertyCalculator>

    Standard Section...

  • Example : Simple Grillage

    8

    The section properties will be displayed in the greyed text boxes on the right handside of the form. Note the torsion constant (J) is approximately 0.010. This will berequired later in the example.

    Ensure the Add to local library option is selected, change the section name toSlab D=0.25 B=2 and click OK to add the properties to the local section library.

    Adding Section Library Items to the Treeview Select the User Sections library from the drop down list.

    Select the Local library type.

    Select Y6 Precast Beam from the name in the drop down list.

    Note. Even though the Y6 beam was defined in millimetres the units can beextracted from the library in metres. The units will be set to metres automatically asthese were the units selected on the startup form.

    Ensure the Grillage option is selected

    Click Apply to add the Y6 precast beam section properties to the Treeview.

    Select End diaphragm from the Name drop down list and click Apply to add theEnd diaphragm section properties to the Treeview.

    Select the Slab D=0.25 B=2 entry from the Name drop down list and click OK toadd the properties to the Treeview and cancel the form.

    Note. For grillage analysis it is common practice to assume 50% of the torsioncapacity of the slab is taken by the transverse beams and 50% by the longitudinalbeams. The torsion constant of the Y6 beam thus needs to be reduced by 50% of thetorsion constant for the slab.

    Double click on the Slab D=0.25 B=2 (m) entry in the Treeview and reducethe torsion constant to 0.005 i.e. 50% of the computed value.

    Click OK to make the change and Yes to overwrite the previous value.

    Double click on the Y6 Precast Beam (m) entry in the Treeview and modifythe torsion constant to be 0.022 (The computed value of 0.027 less the 50%allowance of the torsion constant for the slab of 0.005)

    Click OK to make the change and Yes to overwrite the previous value.

    AttributesGeometric >

    Section Library...

    !

    !

  • Modelling

    9

    Assigning Geometric Properties to the Grillage MembersThe Y6 beam section properties are to be assigned to all the longitudinal members.

    In the Treeview select the Y6 Precast Beam (m) entry and click on the copy button.

    In the Treeview select the Edge Beams group and click the paste buttonto assign the Y6 beam section properties to the edge beams.

    Confirmation of the assignment will appear in the text window.

    Select the Longitudinal Beams group and click the paste button again toassign the Y6 beam section properties.

    The diaphragm section properties are assigned to the end diaphragms in a similarfashion.

    In the Treeview select the End diaphragm (m) entry and click on the copy button.

    In the Treeview select the End Diaphragms group and click the pastebutton to assign the slab section properties.

    The slab section properties are assigned to the transverse members in a similarfashion.

    In the Treeview select the Slab D=0.25 B=2 (m) entry and click on the copy button.

    In the Treeview select the Transverse Beams group and click the pastebutton to assign the slab section properties.

    Defining the MaterialNote. In this example a single material property will be used. If deflections androtations are of interest then separate analysis runs with short and long termproperties may be appropriate.

    !

  • Example : Simple Grillage

    10

    Select material ConcreteBS5400 from the drop downlist, and Short Term C50 fromthe grade drop down list.

    Leave the units as kN m t C sand click OK to add thematerial dataset to the Treeview.

    With the whole model selected(Ctrl and A keys together) dragand drop the material datasetConcrete BS5400 Short TermC50 (kN m t C) from the Treeview onto the selectedfeatures and assign to theselected Lines by clicking theOK button.

    LoadingIn this example seven loadcases will be applied to the grillage. These will envelopedand combined together to form the design combination.

    Renaming the Loadcases In the Treeview right click on Loadcase 1 and select the Rename option.

    Rename the loadcase to Dead Load by over-typing the previous name.

    Use the Isometric View button to rotate the model

    Dead LoadDead load is made up of the self weight of the structure which is defined as anacceleration due to gravity.

    Note. When a bridge deck is modelled with a grillage the slab is represented byboth the longitudinal and transverse members. This means that when self weight isapplied the acceleration due to gravity should only be applied to the longitudinalmembers.

    AttributesMaterial >

    Material Library

    !

  • Modelling

    11

    A load dataset called Gravity -ve Z will be added to the Treeview.

    In the Treeview select the Gravity -ve Z entry and click on the copybutton.

    In the Treeview select the Edge Beams group and click the paste button.

    With the Assign to lines option selected click the OK button to assign the gravityloading to the Dead Load loadcase with a factor of 1

    The self weight dead load will be displayed on the edge beams.

    In the Treeview select the Longitudinal Beams group and click the paste button to gravity loading.

    With the Assign to lines option selected click the OK button to assign the gravityloading to the Dead Load loadcase with a factor of 1

    The self weight dead load on the internal longitudinal beams will be added to thedisplay.

    Superimposed Dead LoadSuperimposed dead load consists of the surfacing loads. These represent the selfweight of the footways and the surfacing on the road.

    Specify the surfacing loading for the footway:

    Leave the density as 2.4

    Change the thickness to 0.25

    Set the length to 20 and set the width to 2.5

    Click the Apply button to add the loading to the Treeview.

    Now specify the tarmac highway surfacing load:

    Change the density to 2.0

    Change the thickness to 0.1

    Change the width to 3.5

    Click the OK button to add the loading to the Treeview.

    BridgeBridge Loading >

    Gravity

    BridgeBridge Loading >

    Surfacing

  • Example : Simple Grillage

    12

    Discrete point and patch loads are positioned by assigning them to points which donot have to form part of the model.

    Enter the coordinates of the mid point of each footway and each notional lane(10,0.25), (10,3.25), (10,6.75), (10,9.75) and click OK

    On the toolbar at the bottom of the display, click the Z axis button toreturn to a global Z direction view.

    Select the points at thecentre of each footwayby holding the Shiftkey down to selectpoints after the initialselection.

    Drag and drop thediscrete loadingdataset Surface 20x2.5T=0.25 Density=2.4(Centre) onto theselected points.

    Select Include FullLoad from the dropdown list. This willensure the portion ofthe pavement loadwhich isoverhanging theedge of the grillagemodel is applied tothe edge beams.

    Update the Numberof Divisions in PatchLoad Y direction to4 to ensure sufficientpoint loads areapplied in thetransverse directionto represent theapplied load.

    GeometryPoint >

    Coordinates

    Select thesepoints to assignfootway surfaceloading

  • Modelling

    13

    Enter Superimposed DL as the Loadcase and click OK to assign the loading.

    The loading will be visualised.

    Now the road surfacing is to be assigned:

    Select the two points atthe centre of eachnotional lane.

    Drag and drop thediscrete load datasetSurface 20x3.5 T=0.1Density=2 (Centre)from the Treeviewonto the selected points.

    Leave the loadingoption for loads outside the search area set as Exclude All Load because for thisload type it is irrelevant whether include or exclude is used since the load length,which is positioned centrally, is the same length as the span length

    Update the Number of Divisions in Patch Load Y direction to 4

    Select Superimposed DL from the Loadcase drop down list.

    Click OK to assign the road surfacing load.

    Vehicle Load DefinitionHA loading is to be applied to each notional lane in loadcases 3 and 4. These loadsare defined using the UK vehicle loading definitions supplied with LUSAS Bridge.

    Select the Lane load (HA load) button.

    With the code set to BD 37/88 change the length to 20 and select the OK buttonto add the load dataset to the Treeview.

    Select the Knife edge load (KEL load) button.

    Leave the width as 3.5 and the intensity as 120 and click the OK button to addthe load dataset to the Treeview.

    Select the Abnormal load (HB vehicle) button.

    With the axle spacing set to 6 and 45 units of HB load select the OK button toadd the load dataset to the Treeview.

    Select thesepoints toassign lanesurfaceloading

    BridgeBridge Loading >

    United Kingdom

  • Example : Simple Grillage

    14

    Click the Close button to close the UK bridge loading form.

    Assigning HA Loading Select the point defined at the centre of the upper notional lane.

    Drag and drop the dataset HA BD37/88 20x3.5 Skew=0 (Centre) from the Treeview.

    Enter HA upper as the Loadcase, leave other values as their defaults, and clickOK

    Select the point defined at the centre of the lower notional lane.

    Drag and drop the dataset HA BD37/88 20x3.5 Skew=0 (Centre) from the Treeview.

    Enter HA lower as the Loadcase, leave other values as their defaults, and clickOK

    Assigning KEL Loading Select the point defined at the centre of the upper notional lane.

    Drag and drop the dataset KEL 120kN Width=3.5 Offset=0 Skew=0 (Centre)from the Treeview.

    Enter KEL upper as the Loadcase and click OK

    Select the point defined at the centre of the lower notional lane.

    Drag and drop the dataset KEL 120kN Width=3.5 Offset=0 Skew=0 (Centre)from the Treeview.

    Enter KEL lower as the Loadcase, leave other values as their defaults, and clickOK

    Assigning Abnormal HB Loading Select the point defined at the centre of the lower notional lane.

    Drag and drop the dataset HB 6m spacing 45 units from the Treeview ontothe selected point.

    Enter HB lower as the Loadcase, leave other values as their defaults, and clickOK

  • Running the Analysis

    15

    Save the modelSave the model file.

    Running the AnalysisWith the model loaded:

    A LUSAS data file name of grillage will be automatically entered in the Filename field.

    Ensure that the options Solve now and Load results are selected.

    Click the Save button to finish and click the Yes button to close any currentlyopen results files.

    A LUSAS Datafile will be created from the model information. The LUSAS Solveruses this datafile to perform the analysis.

    If the analysis is successful...The LUSAS results file will be added to the Treeview.

    In addition, 2 files will be created in the directory where the model file resides:

    q grillage.out this output file contains details of model data, assignedattributes and selected statistics of the analysis.

    q grillage.mys this is the LUSAS results file which is loaded automaticallyinto the Treeview to allow results processing to take place.

    If the analysis fails...Use a text editor to view the output file and search for ERROR. Any errors listed inthe output file should be fixed in LUSAS Modeller before saving the model and re-running the analysis.

    Rebuilding the ModelIf errors are listed that for some reason cannot be corrected by the user, a file isprovided to re-create the model information correctly, allowing a subsequent analysisto be run successfully.

    q grillage_modelling.cmd carries out the modelling of the example.

    FileSave

    FileLUSAS Datafile...

    Open...

    UtilitiesVertical Axis

    FileSave

    FileLUSAS Datafile...

  • Viewing the Results

    17

    Use the Isometric Viewbutton to rotate the model.

    Step through each of theloadcases in the Treeview using the SetActive option and checkeach deformed shape lookscorrect.

    Return to the view from the global Z direction.

    Defining Envelopes and CombinationsThe design combination will consist of all dead loads and an envelope of all liveloads factored by the appropriate adverse or relieving factor.

    Loadcase Adverse Factor Relieving Factor

    g fl g f3

    Dead Load 1.15 1.10 1.0

    Super Dead Load 1.75 1.10 1.0

    HA alone 1.5 (*) 1.10 0

    HA with HB 1.3 (*) 1.10 0

    Note. According to BS5400 part 1 two safety factors should be applied to adverseloading. g fl accounts for the uncertainty in the applied loading and g f3 is a safetyfactor to allow for inconsistencies in the material properties.

    Note. (*) When designing to BD 37/88 the HA lane loading factors also includeadditional lane factors. For a two lane structure these are noted in the tables whichfollow.

    Defining a Basic Load Combination 1A basic load combination to investigate HA and Knife Edge loads will be defined.

    !

    !

  • Example : Simple Grillage

    18

    Combination 8 will be created in the Treeview .

    On the Properties dialog:

    Add loadcases (3) HA upper, (4) HA lower, (5) KEL upper, (6) KEL lower

    Note. To add a number of loadcases all together select the first loadcase in the list,hold down the Shift key and select the last loadcase in the list (scrolling down the

    list if necessary) and click the button.

    Each loadcase selected then needs a corresponding lane factor to be specified.

    Select the Grid button and update the factors as shown in Factor column of thefollowing loadcase combination table.

    Loadcase Load Factor LaneFactor

    LaneFactor tobe used

    g fl g f3

    HA upper 1.5 1.10 0.956 1.5774

    HA lower 1.5 1.10 0.956 1.5774

    KEL upper 1.5 1.10 0.956 1.5774

    KEL lower 1.5 1.10 0.956 1.5774

    Click OK to return to the combination properties dialog.

    Change the combination name to HA + KEL both lanes

    Click OK and Yes to overwrite the combination definition.

    Defining a Basic Load Combination 2A basic load combination to investigate HA, HB and Knife Edge loads will also bedefined.

    Combination 9 will be created in the Treeview.

    On the Properties dialog:

    Add loadcases (3) HA upper, (5) KEL upper, (7) HB lower

    UtilitiesCombination >

    Basic

    !

    UtilitiesCombination >

    Basic

  • Viewing the Results

    19

    Each loadcase selected needs the factor to be specified.

    Select the Grid button and update the factors as shown in Factor column of thefollowing loadcase combination table.

    Loadcase Load Factor Lane Factor Lane Factorto be used

    g fl g f3

    HA upper 1.3 1.10 0.956 1.367

    KEL upper 1.3 1.10 0.956 1.367

    HB lower 1.3 1.10 0.956 1.367

    Click OK to return to the combination properties dialog.

    Change the combination name to HB lower, HA + KEL upper

    Click OK and Yes to overwrite the combination definition.

    Enveloping the Basic Live Load CombinationsEnvelope 10 (Max) and Envelope 10 (Min) will be created in the Treeview.

    On the Properties dialog:

    Change from Results file:1 to Model data in the drop down list

    Add combinations (8)HA+KEL both lanes and (9)HB lower, HA+KELupper

    Change the envelope name to Live Load Envelope

    Click OK and Yes to overwrite the envelope definition.

    Note. When either a Max or Min smart combination or envelope is modified thecorresponding Max and Min dataset will be updated automatically.

    Defining a Smart CombinationSmart load combinations take account of adverse and relieving effects for theloadcase being considered. The Self Weight, Superimposed Dead Load, and the LiveLoad Envelope will all be combined using the Smart Load Combination facility togive the design combination.

    UtilitiesEnvelope

    !

  • Example : Simple Grillage

    20

    Combination 12(Max) and Combination 12(Min) will be created in the Treeview.

    On the Properties dialog:

    Add loadcase (1)Dead load and (2)Superimposed DL to the Included panel.

    Change from Results file:1 to Model data in the drop down list

    Add (10)Live Load Envelope (Max) and (11)Live Load Envelope (Min) tothe Included panel.

    Each loadcase/envelope selected needs the permanent and variable factors to bespecified.

    Select the Grid button and update the Permanent Factor for the Live LoadEnvelopes to 0.0 and the Variable Factor for all loadcases to be as shown in thetable.

    Loadcase PermanentFactor

    Variable Factor VariableFactor tobe used

    g fl g f3

    (1)Dead Load 1.0 0.15 0.10 0.265

    (2)Superimposed DL 1.0 0.75 0.10 0.925

    (10)Live Load Envelope (Max) 0.0 1.0 1.0 1.0

    (11)Live Load Envelope (Min) 0.0 1.0 1.0 1.0

    Click OK to return to the combination properties dialog.

    Change the envelope title to Design Combination

    Click OK and Yes to overwrite the combination definition. Both Max and Mincombination datasets will be overwritten.

    Selecting Loadcase results In the Treeview right-click on Design Combination (Max) and select the Set

    Active option.

    UtilitiesCombination >

    Smart

  • Viewing the Results

    21

    Select My from the drop down list to combine and apply the variable factorsbased on the moments about the Y axis and click the OK button.

    Note. When activating a smart combination the selected component is used todecide if the variable factor should be applied. (The variable component is onlyapplied if the resulting effect is more adverse) Viewing results for a component otherthan the selected component will result in display of the associated values(coincident effects). When the results of an envelope or smart combination areprinted the column used to compute the combination or envelope is denoted with anasterisk in the column header.

    Selecting Members for Results ProcessingResults are to be plotted for selected longitudinal members of the grillage only. Thegrillage wizard automatically creates groups which are useful in the resultsprocessing.

    In the Treeview select the Longitudinal Beams with the right hand mousebutton and pick Set as Only Visible

    In the Treeview select Edge Beams with the right hand mouse button andpick Visible

    Delete the Deformed mesh layer from the Treeview.

    In the graphics window, with no features selected, click the right-hand mousebutton and select the Mesh option to add the mesh layer to the Treeview.

    Click Close to accept the default properties.

    Bending Moment DiagramA plot showing the bending moment from the design combination is to be displayedfor the selected members of the grillage.

    With no features selected, click the right-hand mouse button in a blank part ofthe graphics area and select the Diagrams option to add the diagram layer to the

    Treeview.

    The diagram properties will be displayed.

    Select entity Stress results of component bending moment My

    Select the Diagram Display tab

    Select the Label values option.

    !

  • Example : Simple Grillage

    22

    Enter an Angle of 45 degrees

    Set the Number of significant figures to 4

    Set % of element length to 60

    Click the OK button to display the bending moment diagram.

    Note. Results plots which are to be printed are best created in the page layout view.This provides a view which will appear similar to the printed output. Labels howevermay however be difficult to read in the page layout view since they reflect the size ofthe labels on the final printout. When this situation arises the zoom facility may beused to examine labels of interest more closely.

    Switch to page layout view.

    Add a border to the page which contains the title, date and version of the LUSASsoftware in use.

    Ensure the orientation is set to Landscape. Change the page margins to enablethe annotation to be added without obscuring the display. Set the left margin to50, the right margin to 15 and the top and bottom margins to 10. Click OK

    !

    ViewPage Layout Mode

    UtilitiesAnnotation >

    Window border

    FilePage Setup

  • Viewing the Results

    23

    A summary of results will be added to the graphics window showing the loadcasename, diagram component, maximum and minimum diagram values, and elementnumbers in which the maximum and minimum moments occurs.

    Select the annotation by clicking and holding the left-hand mouse button downover the base line of any piece of text and then drag it to an appropriate locationon the plot.

    Note. The location of any model feature, element or node can be found by using theAdvanced Selection facility. This can be used to find the location of the maximumand minimum results values as the element number is output in the windowsummary text.

    As well as creating a results plot, results can be printed for transfer to a spreadsheetusing standard Windows copy and paste.

    Select entity Stress, type Component and location Gauss to obtain a grid of theresults for the active elements in the display.

    This completes the example.

    UtilitiesAnnotation >

    Window summary

    !

    UtilitiesPrint results wizard

  • Example : Simple Grillage

    24

    Return to Index