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For the lateral loading analysis, each connection is modelled either as fixed or pinned; The structure should be modelled as detailed on the drawing and to be constructed on site. I would not exclude anything.... each member stiffness and joint rotation input has to be right. A frame should be modelled as it is.

Design: You assume "pinned" for analysis. Detailing & Construction: You still detail the column for reinforcement to anchor fully into the base....with compression anchorage provision of rebar into base....hence partial fixity is always there.

A good question. No base is fully pinned or fully fixed! 1. Engineering judgements are needed for base fixity, and experienced engineer use this judgement to analyse, design AND detail the column/base connection. 2. Fixed based require large footings - uneconomical in most instances; also, very difficult to get full fixity with a pad bases once the base rotates under moment. Only piled foundations with thick pile caps may offer anything close to full fixity! 3. Sometimes (not common) column flexural stiffness (EI/L, 4EI/L, 3EI/L etc) is used to derive "partial fixity" for analysis purposes. Majority of column/base connections are inherently partially fixed - but in analysis this is ignored. 4. I have analysed buildings with pinned bases, and then re-analysed the same frame for serviceability wind deflection assuming 10-20% fixity! All an engineering judgement call. 5. Pinned bases are used as a matter of course for most designs of concrete frames. There are exceptions to this rule: (a) for portal frame type crane buildings require fixed bases to limit lateral sway of frame (H/400), and make sure crane does not come off the crane rails; (b) Multi storey steel frames often use ‘fixed bases’ to limit frame sway at bottom, and design foundations accordingly. 6. In Pakistan I would always assume pinned bases for analysis purposes (although 10-20% fixity will always be inherent e connection of column/base, which helps but should not be assumed in analysis). Although this leads to higher moment on columns between first and second floors, and hence lower column needs to be sized the same as column above. 7. With a ‘fixed base’ frame the lowest column will attract greater damage to lowest column/beams during an earthquake. seismic regions. With ‘pinned base’ less damage to the column would occur and more to the beam ...beams are easier to strengthen later then columns! 8. My Conclusion: Use pinned bases in rc frame upto say 5-6 storey high for analysis purposes. Note design is half the story, make sure you sketch the critical reinforcement connection details for the steel detailer & fixer too. Hope this helps?

1. A beam is fixed, where no rotation of beam column joint occurs, or pinned, where the beam is free to rotate. 2. In most RC detailing the top bar runs through the column, for robustness, so you always get some fixity. 3. Get a detailing manual (ACI detailing manual maybe) and see how a "true pin" can be detailed with rebar/reinforcement. .... a sort of intersection of the 'X' pin-points the "pin" location, putting it simply.

1. The geotechnical engineer - the soil specialist - should provide you the modulus of subgrade / elastic spring stiffness in his SI Report. Get in contact with him - this is the best and safest option. He is best placed to offer advice. 2. I have found that the geotechnical engineers often provide subgrade modulus to structural engineers by undertaking a CBR test, and then correlate the subgrade modulus to CBR value. They use a (0.6m x 0.6m, or) 1m x 1m plate for the test. The reason they don't do it that they would need to bring in heavy weights to do the test, hence they don't bother! I am sceptical of the CBR test as it only gives the strength of the soil in the near surface - In my view it does not give much of an information at depth. 3. In the absence of any information consult Bowles book on Foundation Analysis and Design I know has a table - which gives the different ranges of subgrade modulus based on various soil types. I don't have the book handy but recall it from distant past. If someone has the Bowles book handy, then they can help.