Assign_5_2011_solution - University of California, Davis...

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1 University of California, Davis Department of Civil and Environmental Engineering ECI-173 Foundation Design MEMORANDUM TO: ECI-173 Students Date: February 22, 2011 FR: Jason DeJong SUBJECT: Assignment No. 5 (Due Tuesday March 1 @ 5 pm) NOTE: Office hours next week Monday 12:30 – 3:00 instead of this Thursday 10-12. Question 1: A 2-story reinforced concrete frame structure is to be supported on square spread footings. Column spacing ranges from 6 to 9 m. The vertical loads (dead plus live) for the columns range from 600 t0 1,600 kN. The site is roughly flat with little surface vegetation or organic soil. A footing embedment of 1.0 m is considered reasonable for this site. Subsurface conditions consist of a 40-m deep alluvial deposit of sands (USCS classifications were SP, SW, and SP-SM) overlying competent bedrock. The sand layer is known to be dense to very dense below depths of about 20 m. The groundwater is at approximately 9 m depth. Three borings with Standard Penetration Tests were performed within the building footprint (fewer borings than would be required, but this keeps the problem simpler). The energy ratio for the SPT tests was 75%. The measured N values (or blow counts) are summarized below and included in an Excel spreadsheet posted on the class web site for your convenience. A unit weight of 19 kN/m3 is reasonable to assume. (a) Recommend a maximum tolerable settlement for this structure based on the guidelines by Skempton and MacDonald (1956). (b) Determine the minimum allowable footing width and corresponding allowable net bearing pressures for column loads of 600, 1100, and 1600 kN. Your design must satisfy both bearing capacity with a factor of safety of 3.0 and tolerable settlement requirements. Use a spreadsheet to perform your calculations. Clearly indicate your assumptions and the basis for any estimated soil properties. To do this you will need to: Consider the N value profiles over an appropriate depth of influence (from bottom of footing to the depth of influence) after correcting for energy. Select an appropriate representative N value over the depth of influence. Estimate an appropriate friction angle based using Salgado’s method based on SPT values, etc. (as exemplified in class). You will want to select a representative friction angle over the depth of influence of the footing. Perform calculations for settlement using Burland and Burbidge SPT method (modify spreadsheet from previous homework) and for capacity (again by modifying spreadsheet from previous homework). You can assume a settlement time of 30 yrs.
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This note was uploaded on 03/24/2011 for the course ECI 173 taught by Professor Dejong during the Spring '11 term at UC Davis.

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Assign_5_2011_solution - University of California, Davis...

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