A 18-story office building is to be constructed at a site consisting of sands and silty sands to a depth of about 42 m, at which bedrock is encountered. The sands and silty sands are medium dense near the ground surface, and become progressively denser with depth. The soils have fine contents typically less than 10%. SPT N60 values in 5 borings at the site are summarized in Table

 1. The water table is at a depth of 7.5 m. The building will be a steel frame structure with insensitive finish and has a rectangular footprint, with plan view dimension of 55 m x 64 m. Columns are spaced 9 m apart in both direction. The average permanent load is 160 kPa over the entire building footprint or about 13,000 kN per column.   

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