Second Order Effects of Gravity under Horizontal Earthquake Load and Preventive Measures

Building only with shallow foundation may overturns under earthquake load. This paper intends to investigate the building overturn principle and adopt fundamental measures to prevent such dangers. After consider the building self-weight P-Δ effect(Second order effect) and take the building as research object, one can find that if we increase building foundation width and decrease building height, resistant moment M_R can be larger than overturn moment M_o at the rotating beginning. And the building is safe. Another way to increase the building overall stability is to use raft pile groups which are common method to prevent the overturn of building. There are two possible combined stress groups on the surface between piles top surface and building foundation bottom surface. One is compressive stress and shear stress when the earthquake acceleration is not too large. The other is tensile and shear stress when the earthquake acceleration is extremely large. To ensure the safety of the building, professional engineers can design the pile-raft connections stress not to exceed the allowable combined stress.