GSA Training Notes Raft and Piled-raft Analysis

Transcription

1 GSA Tranng Notes Rat and Pled-rat Analyss 1 Introdcton Rat analyss n GSA provdes a means o lnkng GSA statc analyss and sol settlement analyss, so the sol-strctre nteractons can be consdered n the analyss. In ths analyss, the typcal strctre model s a rat or a pled-rat that s connected to the sol beneath by rat nteracton nodes or ple nteracton nodes. Sol settlement analyss s condcted sng Oasys Pdsp program whch s seamlessly embedded n GSA, so explct se o Pdsp program s not reqred when dong rat or pled-rat analyss n GSA. Rat analyss s an teratve process whch, when converged, gves compatble settlements between sol and rat or pled-rat at the nteracton ponts. As mentoned above, Pdsp s a program that calclates sol settlements (and stresses Bossnesq analyss method s sed) wthn a non-lnear elastc sol mass arsng rom vertcal and/or horzontal norm pressre loads appled to rectanglar and/or crclar areas. Pdsp can be sed to predct sol settlements arsng rom the actons o more than one sol pressre loads to gve sers an nderstandng o the lkely settlement pattern both beneath and beyond the bldng beng analysed. It eectvely replaces the need or the engneers to se Newmark charts and other smlar devces. Becase Pdsp has been embedded and sed n GSA, the GSA data relatng to Pdsp can be mported rom or exported to Pdsp as well as edted drectly wthn GSA. 2 Data Reqrements Snce sol nteractons need to be consdered n rat or pled-rat analyss, categorcally, the data reqred or rat or pled-rat analyss are more than those reqred or an ordnary strctre analyss. Bascally, there are three derent types o data are reqred to do a rat or pled-rat analyss and they are: 2.1 Rat or pled-rat model data To bld p a rat or pled-rat model s the same as bldng p other types o strctre models, e.g. the rat can be modelled by grllage o beam elements or 2D elements and ples can be modelled by beam or bar elements. Snce rat wll nteract wth sol n vertcal drecton (not n horzontal drecton) and ples wll nteracton wth sols n all three drectons, explct nodal constrants or these nodes n the relevant drecton are not necessary. I explct nodal constrants are speced to any o those nodes, the sol nteracton o those nodes wll be gnored. 2.2 Sol data These data are exactly the same as those n Pdsp program when sed as a standalone program. For detaled descrpton o these data, reer to the Pdsp ser manal. The data tables or npttng or edtng these data n GSA can be opened ether rom men tem `Data Rat Pdsp Data or rom Gateway tab `Rat Pdsp Data. There are two optons or sol settlement analyss, Mndln and Bossnesq. Ths can be set when gong throgh analyss wzard or rat analyss, the dealt analyss opton can also be set on Rat Speccaton. The derences between these two methods are broadly as ollows: Mndln: No stress reslts are calclated. The analyss reslts are not senstve to the nmber o ntermedate dsplacement levels n sol prole denton, so ewer ntermedate dsplacement levels can be sed to GSA Tranng Notes Rat and Pled-rat Analyss 1 o 6

2 enhance the analyss speed. I the thckness o the sol layer s relatvely small, zero ntermedate dsplacement levels can be sed. Can take both vertcal and horzontal loads and calclate both vertcal and horzontal sol dsplacements. Bossnesq: Do prodce stress reslts n the sol The analyss reslts are senstve to the nmber o ntermedate levels n sol prole denton. More ntermedate dsplacement levels wll prodce more accrate reslts. Slow, especally when the nmber o ntermedate dsplacements nterval s large Cannot take horzontal loads and do not calclate horzontal sol dsplacements. Generally, stresses wthn sol are nterested, Bossnesq analyss method shold be sed, otherwse sng Mndln method s recommended. Snce Bossnesq method does not calclate horzontal dsplacements o sol, t cannot be sed when dong pled-rat analyss. The loads on sol rom rat or ples are generated atomatcally drng rat or pled-rat analyss and they shold not be nclded n the Pdsp load data. Only addtonal loads to those rom rat or ples shold be dened n Pdsp load data table. The sol layers and zones can also be dsplayed on graphc vew and the dsplay can be trned on and o rom Dsplay Methods page o Labels and Dsplay Methods settngs. 2.3 Sol-Rat and sol-ple nteracton data Ater rat or pled-rat model and sol data have been dened, we also need to tell GSA whch parts o the rat and ples wll nteract wth sol. These can be dened on Rat Interacton table and Ple Interacton table. Rat Interacton table denes the nodes on rat that nteract wth sol n vertcal drecton snce rat does not nteract wth sol n horzontal drecton. Ple Interacton table denes the nodes on ples that nteract wth sol n all three drectons. The two tables can be opened rom men tem `Data Rat Rat (or Ple) Interacton or rom Gateway nder Rat tab. The sol-rat and sol-ple contact area at each node as well as the elevaton o nteracton pont can also be dened n these two tables and normally Atomatc s sed. Note that the horzontal postons o the nteracton area are generated atomatcally by GSA based on the coordnates o the nodes on rat and ples as well as sol zone denton, so they do not need to be dened. The dsplay o sol nteracton areas and reerence nmbers on graphc vew can be trned on or o rom On Nodes page o Labels and Dsplay Methods settngs. 3 GsRat Solton Method The rat and pled-rat analyss solton s an teratve process lnkng the lnear analyss solver (GSS) o strctre analyss and the sol settlement analyss solver (Pdsp). The process terates ntl rat, ples and sol have compatble dsplacements wthn speced convergence crtera,.e. the derence o dsplacements between rat and sol at the same pont shold be wthn the speced tolerance and the derence o dsplacements between ple and sol shold generate the correct reacton orces rom sol to the ples based on the Ple Sol Interacton Coecent crves (See GSA manal or detals o Ple Sol Interacton Coecent crves). I t s a pre rat analyss, the rst stage n the analyss s a lnear statc (GSS) analyss or the rat model only wth spport sprngs representng sol spports. The sol nder each rat nteracton node s represented by a spport stness. I ntal spport stness o the nodes has not been speced, the dealt ntal spport stness wll be sed. The dealt spport stness can be changed on rat analyss wzards. Ater the GSS analyss, the pressre loads on the sol at the nteracton pont are calclated sng the sprng orces and the nteracton areas, then Pdsp analyss s carred ot to determne the sol settlements at the nteracton ponts. From the sol settlements and the sprng orces, new spport GSA Tranng Notes Rat and Pled-rat Analyss 2 o 6

3 stness are calclated or the Rat model. Ths teraton contnes ntl the convergence crtera are satsed. I spport stness has been dened or the nteracton nodes n the rat model beore rat analyss, they wll be restored to ther orgnal vales ater rat analyss. I lag save sol stness s set rom the analyss wzard, the spport stness o the nteracton nodes at the last teraton wll be saved and the orgnal GSA model wll be moded. I t s a pled-rat model, the teraton process or the rat nteracton nodes wll be the same as rat model as explaned above and the ple sol teraton procedres are as ollows. Sol maxmm stress dened n Ple-Sol Interacton Propertes table s sed to lmt the contact pressre between ples and sol. The actal contact pressre between sol and ple s determned based on: (1) the relatve dsplacements between sol and ple at the same pont; (2) the Ple-Sol Interacton Coecent crve, the vertcal axs o ths crve s a percentage and the maxmm s 100%, the horzontal axs o ths crve s the normalsed relatve dsplacement between sol and ple at the same pont. Ths crve s sed to determne the crrent ple sol contact pressre whch s a percentage o the maxmm sol stress; (3) the maxmm sol stress at the nteracton pont. Once ple sol contact pressre s known, the reacton orces rom sol to ple n the relevant drecton can be determned whch, n the converged state, shold make the ple n eqlbrm. The teraton o the analyss wll stop when all the ples are n eqlbrm and the sol reacton orces to all the ples are compatble wth the relevant Ple-Sol Interacton Coecent crves. 3.1 Iteraton scheme or rat nteracton nodes The program terates throgh the ollowng steps ntl convergence s reached: 1. For each nteracton node that, generate a vertcal sprng spport wth the stness beng dened as ollows: the ntal spport stnesses have been dened or the node, these wll be sed, otherwse, the dealt ntal spport stness dened n the Analyss Wzard wll be sed. 2. Rn GSS lnear statc analyss to get dsplacements rat and sprng-spport orces,. 3. For each sol-strctre nteracton pont, generate a sol pressre load, p, sng p = A p = 0 otherwse > p where A s the nteracton area assocated wth the nteracton node. 4. Rn Pdsp analyss to get sol dsplacement, sol. 5. Check the dsplacement resdal and, converged, save the reslts and stop the analyss. 6. Adjst the nodal stness or apply nodal dsplacements. I and rat > sol sol < 0 then the sol has moved above rat, so nstead o adjstng the sprng spport stness a nodal dsplacement s mposed, eqal to the sol dsplacement, sol, to ensre that the rat s ltedp by the sol. Otherwse a new sprng stness s calclated rom k = GSA Tranng Notes Rat and Pled-rat Analyss 3 o 6 sol mn A

4 Note that or advanced sers there s a dampng parameter, d, that adjsts the stness pdate. Ths can have a vale between 0 and 1, wth the dealt beng 0. In ths case the new stness s: k = d k + 1 prev ( d ) sol 3.2 Iteraton scheme or ple nteracton nodes The program terates throgh the ollowng steps ntl convergence s reached: 1. For each nteracton node, generate sprng spports n all three drectons based on the ntal stness o Ple Sol Interacton Coecent (PSIC) crve and the sol stness at the nteracton pont, the spport stness s calclated rom k = k s k c Where K s s the sol stness n the relevant drecton and K c s the ntal stness o PSIC crve. 2. Rn GSS lnear statc analyss to get nodal dsplacements ple and sprng-spport orces,. 3. For each ple nteracton pont, calclate the pressre load, p, on sol sng the relatve dsplacement between ple and sol, sol maxmm stress and PSIC crve 4. Rn Pdsp analyss to get sol dsplacement, sol. 5. Check the compatblty o sol dsplacement, ple dsplacement, ple sol nteracton pressre and ple eqlbrm, satsed, save the reslts and stop the analyss. 6. Calclate compensaton orce com to ple nteracton node to be sed n next GSS analyss snce the spport sprng stness on ple nteracton nodes are kept constant drng ths teraton analyss, so the real reacton rom the sol to the ple wll be the orces n the sprng mns the compensaton orce, Where: com compensaton orce to ple nteracton node spport sprng orce o ple nteracton node com = c c correct sol reacton orce to ple nteracton node whch s eqal to the sol pressre load, p calclated on step 3 tmes the contact area o ple nteracton node. 7. Add the compensaton orce com to ple nteracton node as nodal load and go to step 2. 4 Analyss A rat or pled-rat analyss s set p sng the Analyss Wzard rom the `Analyss New Analyss Task men command. Select Rat analyss on the rst page o the wzard, on the second page o the wzard, the sol analyss method (Mndln or Bossnesq) as well as acceptable resdals can be dened or the analyss. I t s a pled-rat analyss, Mndln analyss shold be selected, otherwse the analyss wll not rn. The dampng rato and dealt ntal spport stness can also be dened on ths page by clckng btton Dampng and Stness, bt normally they do not need to be changed and the dealt vales are approprate. At the start o the analyss the dealt ntal spport stness s assgned to all rat nteracton nodes GSA Tranng Notes Rat and Pled-rat Analyss 4 o 6

5 and constant spport stness or ple nteracton nodes wll be calclated as explaned above, then the teraton wll start. As the analyss s an teratve process, a progress dalog box s pop p drng the analyss and the resdals and dampng rato can also be adjsted drng the analyss. 5 Reslts The reslts o a rat or pled-rat analyss are presented n the same way as the reslts rom other lnear statc analyss. Analyss reslts o sol (dsplacements or stresses) wll also be presented n the same way as the reslts n Pdsp program, bt they can be vewed drectly wthn GSA. In GSA the nteracton orces between the rat and the sol are reported as sol nodal reslts, whch may be vewed on Otpt Vews or on Graphc Vews as dagrams or contors. The Total Loads & Reactons otpt that GSA oers as a Global Reslt n Otpt Vews reports the total reacton at sol spports. The dsplacements o the rat and ple nteracton nodes can be vewed as Nodal Dsplacements n GSA. The eqvalent sol stness at each o the nteracton nodes s eqal to the sol spport orce dvded by the dsplacement at the node n the relevant drecton. See also `Create New Rat Model tool below. Pdsp reslts can be vewed by selectng the `Data Rat Pdsp Data Reslts men command. 6 Notes On Rat and Pled-rat Analyss 6.1 Mltple GsRat analyses More than one rat analyss can be rn on a sngle GSA model and mltple sets o GSA reslts can be stored. However only one set o Pdsp reslts are held, relatng to the last case analysed. 6.2 Export and mport o Pdsp data Pdsp data les (*.pdd) can be mported nto GSA sng the `Fle Import Pdsp men command. The analyss reslts n Pdsp data wll be gnored n the mport snce they are meanngless when mported nto GSA. The Pdsp data generated n GSA can also be exported nto Pdsp ormat sng the `Fle Export Pdsp men command. I GsRat reslts exst when exportng Pdsp data the eqvalent sol loads wll be calclated and they wll be exported along wth the other Pdsp data. 6.3 The `Create New Rat Model tool Ater the completon o a converged rat analyss t s possble to generate a new rat model n whch spport stnesses eqvalent to the sol acton are added to the crrent rat model. Ths s done sng the `Tools Rat Analyss Create New rat Model men command. Creatng a new model n ths way wll mody the crrent model so t s recommended that the crrent model be saved beore gvng ths command. The spport stnesses are derved rom the sol reacton orces and the nodal dsplacements. I rat analyss reslts exst or several analyss cases then an analyss case mst be selected or the calclaton. 6.4 Contnaton rns The Create New Rat Model tool can be sed to restart a rat analyss, e.g. ater dong a rat analyss and then rn ths tool command, a new model wll be created wth eqvalent spport stness to the sol beneath, then rther rat analyss can bb rn more qckly. In ths way the preserved spport stnesses rom rnnng ths tool command wll be sed as the ntal stnesses o the rat nteracton node n the new rat analyss and ths wll speed p the new rat analyss snce the ntal spport stness may be more close to the actal sol stness. It s sometmes sel to do an ntal analyss wth coarse convergence crtera to examne the potental or convergence. The rat analyss can then be contned by sng the Create New Rat GSA Tranng Notes Rat and Pled-rat Analyss 5 o 6

6 Model tool to generate a new model wth revsed ntal spport stnesses and then analysng wth more demandng convergence crtera. 6.5 Vew analyss progress on Graphc vew All Graphc vews are pdated ater each teraton drng a rat analyss, ths means that the progress o the analyss can be observed on graphc vew drng the analyss, e.g. the dsplacements, bendng moment and contact pressre etc can be vewed drng the analyss or each o the teratons. GSA Tranng Notes Rat and Pled-rat Analyss 6 o 6