Also please refer example 9-5 on page 505, where a method has been shown to calculate the modulus of subgrade reaction in case load displacement results are not available. Please refer page number 503, equation(s) 9-6a and 9-7.

See in there for more guidance if you have a copy. I am used to FOUNDATION DESIGN TEXT BOOK By BOWLES. This is due to having 60% to 70% more load (Of Total Load) on RAFT at the center then at the edges. Of Raft then what is the basis of using different values for Ks at the edges and the center? How will you justify different values? Not by averaging of Edge displacements and Center Displacements. If you do not have LOAD-TEST results at the Center and Edges Value Modulus Of Subgrade Reaction comes from LOAD-TEST done by Soil Consultants usually 300 ft apart. Posted: Fri 3:48 pm Post subject: Modulus Of Subgrade Reaction comes from LOAD-TEST. settlement at corners and center of the foundation and then use the fact that ks=(DeltaQ/DeltaZ) to get the modulus?ДЄlso, I think that using uniform ks value at all points is not the exact simulation of the site conditions because settlements are different at center and at ends. Through this formula we can get DeltaZ, ie. Can't the Immediate settlement relation be used to calculate the modulus of subgrade reaction at center and edges? Okay Pandya ji, I agree and endorse your valuable explanation. Why you (Structural Engineer) want do soil consultants work? Pay him some nominal fee to get these settlement values. Give your Soil Consultant estimated Foundation-Reactions ( I add 20% to these foundation reactions for safety) and ask him to give you Immediate, Long-Term and Differential settlements. GIVEN BY SOIL CONSULTANT TO ALLOWABLE SETTLEMENTS. IN A LAYRED SOIL SETTLEMENT IMEDIATE, LONG TERM AND DIFFETENTIAL COMESДЇROM SOIL COINSULTANTS NON-LINEAR ANALYSIS. THIS COMPUTER DEFLECTIONS AND SPRING FORCESДЄRE USED ONLY TO CALCULATE ACTUAL BEARING PRESSURES, SHEAR AND FLEXURE DESIGN OF CONCRETE RAFT. If you need to adjust this Ks at the edges you can modify Ks = 414.72 K/ft to any number you want.Д«) I NEVER USE MY COPUTER RAFT ANALYSIS OUT-PUT DEFLECTIONS AS SETTLEMENT CALCULATIONS. And that is a fairly acccurate representation of soil support of Raft. So Ks in computer model is aready calculatedД«ased on Tributary area. unit (Deflections in FT.) your Spring Constant under each node Let us say your soil consultant gives you K = 30 pci or Lb/inch***3. Your Plate Element model grid is 4ftX4ft in plan with 4ft thickness. Let us say you are using STADD/PRO PLATE AND SHELL ELEMENT for a 100ft.X100ftx4ft thick Raft Foundation. SINGLE SPRING CONSTANT IN STAAD/PRO OR RISA-3D PLATE ELEMENT MODEL FOR RAFT FOUNDATIONS:ДЄ)This not a problem. Posted: Fri 10:18 am Post subject: SINGLE SPRING CONSTANT IN STAAD/PRO OR RISA-3D PLATE EL. Can seniors please share their experience? Is the assignment of a unique 'ks' value justified? But, in actual scenario the settlements are larger under the center point and lesser towards the ends. Here the 'ks' is based on tributary area. Using a uniform 'ks' value under a rectangularly loaded footing will produce constant settlement at each point. Now, I have noticed that, consultants tend to use the same 'ks' value ( where ks is the modulus of subgrade reaction) under all points in combined footings or rafts. To simulate elastic foundation we use springs. We know that the base contact pressure contributes to the settlement in footings and that there is no dependence of modulus of subgrade reaction on base contact pressure.

Posted: Fri 8:27 am Post subject: Modulus of Subgrade Reaction. Use online scanners here and here to upload downloaded attachment to check for safety. Warning: Make sure you scan the downloaded attachment with updated antivirus tools before opening them.

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