Showing different floor of load bearing walls d

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Unformatted text preview: ls, d Loading conditions preferably shown on a schematic plan indicating design combination of loads transmitted to the foundation. 4 Environmental Factors - Information relating to geologic history of the area, seismicity of the region, hydrological information indicating ground water conditions and its seasonal variations, climatic factors like vulnerability of the site to sudden flooding by surface run-off, erosion, etc. e) Geotechnical Information - Giving subsurface profile with stratification details ( see IS : 1892-1979t ), engineering properties of the founding strata, namely, index properties, effective shear parameters determined under appropriate drainage conditions, compressibility characteristics, swelling properties, results of field tests like static and dynamic penetration tests, pressure meter tests, etc. f) Modulus of Elasticity and Modulus of Subgrade Reaction - Appendix A enumerates the methods of determination of modulus of elasticity ( E, ) and Poisson’s ratio ( k ). The modulus of subgrade reaction ( k ) may be determined in accordance with Appendix B. g) Limiting values of the angular distortion and differential settlement, the superstructure h) can withstand ( see IS : 1904-1978$ ). A review of the performance locality. of a similar structure, if any, in the *Glossary of tempt and symbols relating to soil engineering(first revision ). tCode of practice for subsurfaceinvestigationsfor foundations (first revision ). ICode of practice for structural safety of buildings : Shallowfoundations ( second revision ). 4 IS : 2950 ( Part I ) - 1981 3 Information necessary to assess the possible effects of the new structure on the existing structures in the neighbourhood. k) Proximity of mines or major storage reservoirs to the site. 3.2 Parameters for the Analysis - These are obtained by averaging parameters ( see 3.1 ) which can be determined only for relatively number of points of the foundation soil. The accuracy with which average values represent the actual conditions is of decisive importance the final results. 4. DESIGN the less the for CONSIDERATIONS 4.1 Choice of Raft Type 4.1.1 For fairly small and uniform column spacing and when the supporting soil is not too compressible, a flat concrete slab having uniform thickness throughout ( a true mat ) is most suitable ( see Fig. 1A ). 4.1.2 The slab may be thickened under heavily loaded columns to provide adequate strength for shear and negative moment. Pedestals may also be provided in such cases ( see Fig. 1B ). 4.1.3 A slab and beam type of raft is likely to be more economical for large column spacing and unequal column loads, particularly when the supporting soil is very compressible ( see Fig. 1C ). 4.1.4 For very heavy structures, provision of cellular raft or rigid frames consisting of slabs and basement walls may be considered. 4.2 Allowable Bearing Pressure - The allowable bearing pressure shall be determined in accordance with IS : 6403-1981*. 4.2.1 In granular soils, the ultimate bearing capacity of rafts...
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