>> most of the unbalanced force is vertical
The hor. and ver. max amplitude of unbalanced force shall be the same because
Fv= me*omega^2*sin(omega*t)
Fh= me*omega^2*cos(omega*t)
For your case it's probably the unbalanced force is high above mounting skid so the overturn moment causes the big tensile load in anchor bolts, but anyway, here is some of the guidelines and references for you
PIP STE05121-2006 Anchor Bolt Design Guide
The advantages of pretensioning are as follows:
a. Can prevent stress reversals on anchors susceptible to fatigue weakening
b. May increase dampening for pulsating or vibrating equipment
c. Will decrease, to some extent, the drift for process towers under wind or
seismic load
d. Will increase the frictional shear resistance for process towers and other
equipment
ACI 351.3R-04 Foundations for Dynamic Equipment
From section 4.4.1.1 on page 45
4.4.1.1 Fatigue issues—For many dynamic equipment foundations, the cyclic stresses are small, and engineers choose to not perform any specific fatigue stress calculations. Other equipment can require more significant consideration of cyclic stresses. In such cases, ACI 215 provides guidance, particularly where the flexural characteristics of the founda- tion are most important.
Some of the methods used by firms to implicitly or explicitly address fatigue include:
• Proportioning sections to resist all conventional loads plus three times the dynamic load;
• Designing such that concrete modulus of rupture is not exceeded while including the inertial loads from the concrete motion. In certain cases, the computed modulus of rupture is reduced by 50% to approximate permissible stresses reduced for fatigue;
• Reducing by as much as 80% the strength reduction factors specified by ACI 318; and
• Recognizing that cracking is less likely in structures built with clean, straight lines and not having re-entrant corners and notches.
For anchor bolt design as per ACI 318-08, please check
From section 4.4.2.1 on page 46
4.4.2.1 Performance criteria/anchor bolts —The structural performance criteria for anchor bolts holding dynamic machinery require that sufficient clamping force be available to maintain the critical alignment of the machine. [red]The clamping force should allow smooth transmission of unbalanced machine forces into the foundation so that the machine and foundation can act as an integrated structure. Generally, higher clamping forces are preferred because high clamping forces result in less vibration being reflected back into the machine.[/red] In the presence of unbalanced forces, a machine that has a low clamping force (400 psi [2.8 MPa]) at the machine support points can vibrate more than the same machine with high clamping forces (1000 psi [7 MPa]). Precision machines in the machine tool industry sometimes have clamping forces as high as 2000 psi (14 MPa) to minimize “tool chatter.” [red]Instead of more refined data, designing for a clamping force that is 150% of the anticipated normal operating bolt force is good practice. A minimum anchor bolt clamping force of 15% of the bolt material yield strength is often used if specific values are not provided by the equipment manufacturer. Higher values are appropriate for more aggressive machines. Clamping force, also known as preload, is developed by pretensioning the anchor bolt.[/red]
4.4.2.2 Capacity—[red]The capacity of each anchor bolt should be greater than design loads to provide adequate reserve capacity.[/red] Conditions can change over time due to machine wear or changes in operating conditions. Properties as given in the cited ASTM standard specifications of the steels commonly used for anchor bolts are listed in Table 4.3 and 4.4. Because the number and diameter of anchor bolts are determined by the machine manufacturer, the engineer can maximize capacity by specifying the higher-strength steels. The practi- cable capacity of an anchor bolt is typically 80% of the yield strength, not the full tensile strength.
4.4.2.3 Anchor bolt preload—To avoid slippage under dynamic loads at any interface between the frame and chock and soleplate, or chock and foundation top surface, the normal force at the interface multiplied by the effective coefficient of friction must exceed the maximum horizontal dynamic force applied by the frame at the location of the tie-down.
