Two Dimensional Truss

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1 Tw Dimensinal Truss Intrductin This tutrial was created using ANSYS 7.0 t slve a simple 2D Truss prblem. This is the first f fur intrductry ANSYS tutrials. Prblem Descriptin Determine the ndal deflectins, reactin frces, and stress fr the truss system shwn belw (E = 200GPa, A = 3250mm 2 ). (Mdified frm Chandrupatla & Belegunda, Intrductin t Finite Elements in Engineering, p.123) Preprcessing: Defining the Prblem 1. Give the Simplified Versin a Title (such as 'Bridge Truss Tutrial'). In the Utility menu bar select File > Change Title: The fllwing windw will appear:

2 Enter the title and click 'OK'. This title will appear in the bttm left crner f the 'Graphics' Windw nce yu begin. Nte: t get the title t appear immediately, select Utility Menu > Plt > Replt 2. Enter Keypints The verall gemetry is defined in ANSYS using keypints which specify varius principal crdinates t define the bdy. Fr this example, these keypints are the ends f each truss. We are ging t define 7 keypints fr the simplified structure as given in the fllwing table crdinate keypint x y (these keypints are depicted by numbers in the abve figure) Frm the 'ANSYS Main Menu' select: Preprcessr > Mdeling > Create > Keypints > In Active CS

The fllwing windw will then appear: T define the first keypint which has the crdinates x = 0 and y = 0: Enter keypint number 1 in the apprpriate bx, and enter the x,y

Nte: When entering the final data pint, click n 'OK' t indicate that yu are finished entering keypints.

3 The fllwing windw will then appear: T define the first keypint which has the crdinates x = 0 and y = 0: Enter keypint number 1 in the apprpriate bx, and enter the x,y crdinates: 0, 0 in their apprpriate bxes (as shwn abve). Click 'Apply' t accept what yu have typed. Enter the remaining keypints using the same methd. Nte: When entering the final data pint, click n 'OK' t indicate that yu are finished entering keypints. If yu first press 'Apply' and then 'OK' fr the final keypint, yu will have defined it twice! If yu did press 'Apply' fr the final pint, simply press 'Cancel' t clse this dialg bx. Units Nte the units f measure (ie mm) were nt specified. It is the respnsibility f

4 the user t ensure that a cnsistent set f units are used fr the prblem; thus making any cnversins where necessary. Crrecting Mistakes When defining keypints, lines, areas, vlumes, elements, cnstraints and lads yu are bund t make mistakes. Frtunately these are easily crrected s that yu dn't need t begin frm scratch every time an errr is made! Every 'Create' menu fr generating these varius entities als has a crrespnding 'Delete' menu fr fixing things up. 3. Frm Lines The keypints must nw be cnnected We will use the muse t select the keypints t frm the lines. In the main menu select: Preprcessr > Mdeling > Create > Lines > Lines > In Active Crd. The fllwing windw will then appear: Use the muse t pick keypint #1 (i.e. click n it). It will nw be marked by a small yellw bx. Nw mve the muse tward keypint #2. A line will nw shw n the screen jining these tw pints. Left click and a permanent line will appear.

Cnnect the remaining keypints using the same methd. When yu're dne, click n 'OK' in the 'Lines in Active Crd' windw, minimize the 'Lines' menu and the 'Create' menu.

5 Cnnect the remaining keypints using the same methd. When yu're dne, click n 'OK' in the 'Lines in Active Crd' windw, minimize the 'Lines' menu and the 'Create' menu. Yur ANSYS Graphics windw shuld lk similar t the fllwing figure. Disappearing Lines Please nte that any lines yu have created may 'disappear' thrughut yur analysis. Hwever, they have mst likely NOT been deleted. If this ccurs at any time frm the Utility Menu select: Plt > Lines Define the Type f Element It is nw necessary t create elements. This is called 'meshing'. ANSYS first needs t knw what kind f elements t use fr ur prblem: Frm the Preprcessr Menu, select: Element Type > Add/Edit/Delete. The fllwing windw will then appear:

figure. Select the element shwn and click 'OK'. Yu shuld see 'Type 1 LINK1' in the 'Element Types' windw.

6 Click n the 'Add...' buttn. The fllwing windw will appear: Fr this example, we will use the 2D spar element as selected in the abve figure. Select the element shwn and click 'OK'. Yu shuld see 'Type 1 LINK1' in the 'Element Types' windw. Click n 'Clse' in the 'Element Types' dialg bx. Define Gemetric Prperties We nw need t specify gemetric prperties fr ur elements: In the Preprcessr menu, select Real Cnstants > Add/Edit/Delete

n 'OK'. 'Set 1' nw appears in the dialg bx. Click n 'Clse' in the 'Real Cnstants' windw.

7 Click Add... and select 'Type 1 LINK1' (actually it is already selected). Click n 'OK'. The fllwing windw will appear: As shwn in the windw abve, enter the crss-sectinal area (3250mm): Click n 'OK'. 'Set 1' nw appears in the dialg bx. Click n 'Clse' in the 'Real Cnstants' windw. Element Material Prperties Yu then need t specify material prperties: In the 'Preprcessr' menu select Material Prps > Material Mdels

Nte: Yu may btain the nte 'PRXY will be set t 0.0'.

8 Duble click n Structural > Linear > Elastic > Istrpic We are ging t give the prperties f Steel. Enter the fllwing field: EX Set these prperties and click n 'OK'. Nte: Yu may btain the nte 'PRXY will be set t 0.0'. This is pissn's rati and is nt required fr this element type. Click 'OK' n the windw t cntinue. Clse the "Define Material Mdel Behavir" by clicking n the 'X' bx in the upper right hand crner. Mesh Size

The last step befre meshing is t tell ANSYS what size the elements shuld be. There are a variety f ways t d this but we will just deal with ne methd fr nw.

9 The last step befre meshing is t tell ANSYS what size the elements shuld be. There are a variety f ways t d this but we will just deal with ne methd fr nw. In the Preprcessr menu select Meshing > Size Cntrls > ManualSize > Lines > All Lines In the size 'NDIV' field, enter the desired number f divisins per line. Fr this example we want nly 1 divisin per line, therefre, enter '1' and then click 'OK'. Nte that we have nt yet meshed the gemetry, we have simply defined the element sizes. Mesh Nw the frame can be meshed. In the 'Preprcessr' menu select Meshing > Mesh > Lines and click 'Pick All' in the 'Mesh Lines' Windw Yur mdel shuld nw appear as shwn in the fllwing windw

10 Plt Numbering T shw the line numbers, keypint numbers, nde numbers... Frm the Utility Menu (tp f screen) select PltCtrls > Numbering... Fill in the Windw as shwn belw and click 'OK'

Nw yu can turn numbering n r ff at yur discretin Saving Yur Wrk Save the mdel at this time, s if yu make sme mistakes later n, yu will at least be able t cme back t this pint.

11 Nw yu can turn numbering n r ff at yur discretin Saving Yur Wrk Save the mdel at this time, s if yu make sme mistakes later n, yu will at least be able t cme back t this pint. T d this, n the Utility Menu select File > Save as... Select the name and lcatin where yu want t save yur file. It is a gd idea t save yur jb at different times thrughut the building and analysis f the mdel t backup yur wrk in case f a system crash r what have yu. Slutin Phase: Assigning Lads and Slving Yu have nw defined yur mdel. It is nw time t apply the lad(s) and cnstraint(s) and slve the the resulting system f equatins. Open up the 'Slutin' menu (frm the same 'ANSYS Main Menu'). 1. Define Analysis Type First yu must tell ANSYS hw yu want it t slve this prblem:

Frm the Slutin Menu, select Analysis Type > New Analysis. Ensure that 'Static' is selected; i.e. yu are ging t d a static analysis n the truss as ppsed t a dynamic analysis, fr example. Click 'OK'. 2.

12 Frm the Slutin Menu, select Analysis Type > New Analysis. Ensure that 'Static' is selected; i.e. yu are ging t d a static analysis n the truss as ppsed t a dynamic analysis, fr example. Click 'OK'. 2. Apply Cnstraints It is necessary t apply cnstraints t the mdel therwise the mdel is nt tied dwn r grunded and a singular slutin will result. In mechanical structures, these cnstraints will typically be fixed, pinned and rller-type cnnectins. As shwn abve, the left end f the truss bridge is pinned while the right end has a rller cnnectin. In the Slutin menu, select Define Lads > Apply > Structural > Displacement > On Keypints

Therefre, select 'All DOF' by clicking n it and enter '0' in the Value field and click 'OK'.

13 Select the left end f the bridge (Keypint 1) by clicking n it in the Graphics Windw and click n 'OK' in the 'Apply U,ROT n KPs' windw. This lcatin is fixed which means that all translatinal and rtatinal degrees f freedm (DOFs) are cnstrained. Therefre, select 'All DOF' by clicking n it and enter '0' in the Value field and click 'OK'. Yu will see sme blue triangles in the graphics windw indicating the displacement cntraints. Using the same methd, apply the rller cnnectin t the right end (UY cnstrained). Nte that mre than ne DOF cnstraint can be selected at a

14 time in the "Apply U,ROT n KPs" windw. Therefre, yu may need t 'deselect' the 'All DOF' ptin t select just the 'UY' ptin. 3. Apply Lads As shwn in the diagram, there are fur dwnward lads f 280kN, 210kN, 280kN, and 360kN at keypints 1, 3, 5, and 7 respectively. Select Define Lads > Apply > Structural > Frce/Mment > n Keypints. Select the first Keypint (left end f the truss) and click 'OK' in the 'Apply F/M n KPs' windw. Select FY in the 'Directin f frce/mm'. This indicate that we will be applying the lad in the 'y' directin Enter a value f in the 'Frce/mment value' bx and click 'OK'. Nte that we are using units f N here, this is cnsistent with the previus values input. The frce will appear in the graphics windw as a red arrw. Apply the remaining lads in the same manner. The applied lads and cnstraints shuld nw appear as shwn belw.

15 4. Slving the System We nw tell ANSYS t find the slutin: In the 'Slutin' menu select Slve > Current LS. This indicates that we desire the slutin under the current Lad Step (LS). The abve windws will appear. Ensure that yur slutin ptins are the same as shwn abve and click 'OK'.

16 Once the slutin is dne the fllwing windw will pp up. Click 'Clse' and clse the /STATUS Cmmand Windw.. Pstprcessing: Viewing the Results 1. Hand Calculatins We will first calculate the frces and stress in element 1 (as labeled in the prblem descriptin). 2. Results Using ANSYS Reactin Frces A list f the resulting reactin frces can be btained fr this element frm the Main Menu select General Pstprc > List Results > Reactin Slu.

Select 'All struc frc F' as shwn abve and click 'OK'

Defrmed Shape. The fllwing windw will appear.

17 Select 'All struc frc F' as shwn abve and click 'OK' Defrmatin These values agree with the reactin frces claculated by hand abve. In the General Pstprc menu, select Plt Results > Defrmed Shape. The fllwing windw will appear. Select 'Def + undef edge' and click 'OK' t view bth the defrmed and the undefrmed bject.

18 Observe the value f the maximum deflectin in the upper left hand crner (DMX=7.409). One shuld als bserve that the cnstrained degrees f freedm appear t have a deflectin f 0 (as expected!) Deflectin Fr a mre detailed versin f the deflectin f the beam, Frm the 'General Pstprc' menu select Plt results > Cntur Plt > Ndal Slutin. The fllwing windw will appear.

19 Select 'DOF slutin' and 'USUM' as shwn in the abve windw. Leave the ther selectins as the default values. Click 'OK'.

20 Lking at the scale, yu may want t use mre useful intervals. Frm the Utility Menu select Plt Cntrls > Style > Cnturs > Unifrm Cnturs... Fill in the fllwing windw as shwn and click 'OK'. Yu shuld btain the fllwing.

'List Ndal Slutin' windw and click 'OK'.

21 The deflectin can als be btained as a list as shwn belw. General Pstprc > List Results > Ndal Slutin select 'DOF Slutin' and 'ALL DOFs' frm the lists in the 'List Ndal Slutin' windw and click 'OK'. This means that we want t see a listing f all degrees f freedm frm the slutin. Are these results what yu expected? Nte that all the degrees f freedm were cnstrained t zer at nde 1, while UY was cnstrained t zer at nde 7.

22 If yu wanted t save these results t a file, select 'File' within the results windw (at the upper left-hand crner f this list windw) and select 'Save as'. Axial Stress Fr line elements (ie links, beams, spars, and pipes) yu will ften need t use the Element Table t gain access t derived data (ie stresses, strains). Fr this example we shuld btain axial stress t cmpare with the hand calculatins. The Element Table is different fr each element, therefre, we need t lk at the help file fr LINK1 (Type help link1 int the Input Line). Frm Table 1.2 in the Help file, we can see that SAXL can be btained thrugh the ETABLE, using the item 'LS,1' Frm the General Pstprcessr menu select Element Table > Define Table Click n 'Add...' As shwn abve, enter 'SAXL' in the 'Lab' bx. This specifies the name f the item yu are defining. Next, in the 'Item,Cmp' bxes, select 'By sequence number' and 'LS,'. Then enter 1 after LS, in the selectin bx Click n 'OK' and clse the 'Element Table Data' windw. Plt the Stresses by selecting Element Table > Plt Elem Table The fllwing windw will appear. Ensure that 'SAXL' is selected and click 'OK'

Because yu changed the cntur intervals fr the Displacement plt t "User Specified" - yu need t switch this back t "Aut calculated" t btain new values fr VMIN/VMAX.

23 Because yu changed the cntur intervals fr the Displacement plt t "User Specified" - yu need t switch this back t "Aut calculated" t btain new values fr VMIN/VMAX. Utility Menu > PltCtrls > Style > Cnturs > Unifrm Cnturs... Again, yu may wish t select mre apprpriate intervals fr the cntur plt List the Stresses Frm the 'Element Table' menu, select 'List Elem Table' Frm the 'List Element Table Data' windw which appears ensure 'SAXL' is highlighted Click 'OK'

24 Nte that the axial stress in Element 1 is 82.9MPa as predicted analytically.

Space Frame Example. This tutorial was created using ANSYS 7.0 to solve a simple 3D space frame problem.

Space Frame Example. This tutorial was created using ANSYS 7.0 to solve a simple 3D space frame problem. Space Frame Example Intrductin This tutrial was created using ANSYS 7.0 t slve a simple 3D space frame prblem. Prblem Descriptin The prblem t be slved in this example is the analysis f a bicycle frame.