3. FOUNDATIONS 3-1. A4\'x4footing supports a column with a 6000 pound load at it

Question

3. FOUNDATIONS 3-1. A4'x4footing supports a column with a 6000 pound load at its center How much stress (pressure" in this case) will be in the soil immediately below the footing? The soil has been tested. It has been found that the soil settles two inches for every 1000 psf of stress placed on it. How much will this footing settle? 3-2. A three-story hotel is to be constructed at the edge of a lake, with part of the building extending into the lake to provide immediate access to docks, etc. The building frame will consist of six concrete columns spaced as shown below, and each column rests on a square footing, which bears onto the soil below. To keep the natural beauty of the site, the soil cannot be prepared in the usual manner. Instead, the building will have to be founded on the three soil types existing at the site. Samples of each soil type are taken from the site and tested by a geotechnical firm, which results in the stress-deflection relations shown in the graph below. These graphs show the amount of settlement in inches that each soil will undergo as load per square foot is increased. determined bearing In addition to the stress-deflection relations, the engineers capacity. It was found that all three soils have the same capacity of 2500 psf. Do the following a. Find the minimum dimensions for the square footing under each column to prevent the soil bearing capacity from being exceeded. (provide the answer in lengths: i.e. 3'x 3', not just area.) It is desirable to prevent any column from settling more than any other, otherwise, floors are no longer level and cracks form in concrete. For each column of this structure determine the minimum footing size such that this requirement is met. Note that footings also must satisfy this requirement of part a. Round all answers to nearest 6" (0.5 feet). Be careful about the direction that you round b. 25 40 40 PLAN 40 PS ST 120 PSF SECTLON A-A

Explanation / Answer

3-1

Since the load acting over the 4 ft X 4 ft is given as 6000 lbs

Assuming that the stress imposed on the soil immediatly will be transfered to the strata beneath the footing,

The pressure exerted just below the footing is equal to = 6000/(4*4) = 375 lb/sq/ft.

b) since the soil is settles by 2 inchs for every additional pressure of 1000 psf, The total settlement experienced by the footing at the pressure of 375 psf = 2*(375/1000) = 0.75 inchs = 19.05 mm

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