Foundations overturning moment

Type of Foundation Overturning moment (lateral) Torsional moment (torsional)... 

Foundations must be designed to take the weight loads and overturning moments without transmitting vibration to other equipment and buildings. 

Figure 11-1 shows a cylindrical tower on which the wind pressure, P, tends to rotate the tower and its foundation around point A. This produces an overturning moment that is calculated as follows ... 

It was shown by equation (11-1) that the total soil loading, to be considered in the design of tower foundations, is the sum of Si, the dead load, and S2, the load caused by the overturning or wind moment. There is no overturning moment on guyed towers however, the wind pressure does have an important effect on the foundation, as the soil is required to resist the vertical component of the pull on the guy wires. 

End bearing vertical compressive resistance at the base of a foundation, distributed end bearing pressures can provide resistance to overturning moments Base shear horizontal resistance of friction and cohesion at the base of a foundation Side resistance shear resistance from friction and cohesion along side of a foundation Earth pressure mainly horizontal resistance from lateral earth pressures perpendicular to side of the foundation... 

Type of Foundation Vertical Compressive Load (Axial) Vertical Uplift Load (Axial) Horizontal Load (Lateral) Overturning Moment (Lateral) Torsional Moment (Torsional)... 

Lateral capacity of a foundation is the capacity to resist lateral deflection caused by horizontal forces and overturning moments acted on top of the foundation. For an individual foundation, lateral resistance comes from three sources lateral earth pressures, base shear, and nonuniformly distributed end bearing pressures. Lateral earth pressure is the primary lateral resistance for long piles. Base shear and distributed end bearing pressures are discussed in Chapter 8. 

Ringwall and Slab Overturning Moment/Heights The ringwall moment, M, is the overturning moment that acts immediately above the bottom plate of the tank. It includes mily the contribution of pressure on the wall and should be used for the calculation of stresses and stress resultants in the tank wall and at its connection to the base, for tank structural verification. On the other hand, the slab moment, M, is the overturning moment that acts immediately below the bottom plate of the tank. It includes the contribution of pressure on the wall together with the pressure on the tank bottom and should be used for the verification of its support structure, base anchors, or foundation. 

The most critical area of the tower design is the tower-to-foundation connection. Both shear forces and moments are at a maximum at this point. Anchor bolts are generally used at the base of steel towers. Such bolts must be proportioned to transfer overturning loads from the tower to the bolts. The bolts must be deeply embedded in the concrete footing block in order to transfer their loads to the footing reinforcement. 

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