Limit State Design of Shallow Footings as Per Eurocode 7 and Its Comparison with is Code WSM

Abstract

Structural Design Practice has transformed from conventional Working Stress Method to Limit State Method—Load and Resistance Factor Design (ACI) or Partial Safety Factor approach (IS Code). Geotechnical Design Philosophy is in the transformation stage to implement Load and Resistance Factor Design (LRFD). Eurocode-7 accommodates three design approaches (DAs) that allow partial factors to be introduced at the beginning of the calculations (strength partial factors) or at the end of the calculations (resistance partial factors), or some intermediate combinations thereof. IS 6403 provides guideline to calculate ultimate bearing capacity for shallow foundations. It gives bearing capacity factors and other factors, viz., inclination factors, depth factors, shape factors, etc., and accounts for the effect of water table. To calculate allowable bearing pressure a Factor of Safety 2.50 is recommended separately by IS 1080. Eurocode 7 provides guideline for proportioning shallow foundations using partial safety factors for Action, Material Parameters, and Resistance. The Action includes Dead Loads as well as Imposed Loads. Material Parameters includes shear parameters “c” and “φ” in drained and/or undrained state. The Resistance Factors are assigned based on the design methods used. For shallow foundations three design approaches are considered for which partial safety factors are given. Parametric study is carried out to compare the ratio of capacity obtained from IS Code WSM and EC7 LSM for different soil type (c-soil, phi—soil, and c-phi soil) keeping other parameters constant.