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FOUNDATION FOOTING. Foundation. The foundation system of building, its substructure, is a critical link in transmission of building loads to the ground. Foundation is a structure built to transfer the dead loads and live loads or weight of building to the material below . .
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Foundation • The foundation system of building, its substructure, is a critical link in transmission of building loads to the ground. Foundation is a structure built to transfer the dead loads and live loads or weight of building to the material below.
CLASSIFICATION • Foundation are generally classified as either deep or shallow. The depth bearing area of shallow foundation generally is no deeper than about the width of the bearing surface. Deep foundation provide support for a structure by transferring the loads to competent soil and rock at stone depth below the structure.
Shallow Spread Combine Strip Deep Basement Caissons Piles Foundation
Shallow foundation • Shallow foundation can be either footing or pad. They consist reinforced concrete slabs formed directly on a prepared soil base. Footing may be spread, combined, or continuous. Terzaghi and peck define that shallow foundation as the footing width equal to or greater than its depth.
Spread footing • Spread footing They typically 0.9 to 2.4 to 3m square. Their bearing surface is typically less than 2.5 times their width (<2.5B).
Combine footing • Combine footing are similar to spread footing but support two or more columns
Continuous or Strip • Continuous or Strip footing is an elongated shallow foundation that typically support as single row of column or a wall or other type of strip loading.
D B Shallow Footings By definition D/B < 4
Very Large Concentrated Weight Large Distributed Weight Low Weight Strong Rock Applications Weak Soil Weak Rock or distributed over competent Soil
Load limitations Shallow foundations can cope with compression and inclined loads Shallow foundations are limited in tension capacity by the footing weight D C
Limit States Serviceability Ultimate
Deep Foundation • It is opposite to shallow foundation. It has been developed to increase bearing capacity/stability and reduce settlement by build them deeper than shallow one due to building going larger and heavier.It can be divided into 3 types as details later on.
Very Large Concentrated Weight Large Distributed Weight Low Weight Strong Rock Basement Basement Weak Soil Weak Rock or distributed over competent Soil
Caissons Open CaissonsPneumatic Caissons Box Caisson (floating)
Methods • Pile driving formulae • Static load test • Dynamic or Statnamic load test • Static formulae
F s tc D Pile driving formulae • e.g. Hiley formula Ru = e.W.h . (set + tc / 2) • Newton’s law - two rigid bodies • Efficiency? • Static resistance only • Correlate • MORE details later
Qs Pu Axial Capacity W Pu = Qb + Qs - W Qb
Pshaft Axial Capacity Fu Fu + W = Pbase + Pshaft W Shear failure at pile shaft Pbase Bearing failure at the pile base
Pshaft,t Tension Capacity Tu - W = Pshaft,t < Pshaft,c Shear failure at pile shaft
Very Large Concentrated Weight Large Distributed Weight Low Weight Applications Soft to Firm Clay Dense Sand Strong Rock
Pug Group Capacity Pile Cap • Overlapping stress fields • Progressive densification • Progressive loosening • Case-by-case basis Pug¹n.Pup Pug = e.n.Pup
