1. SACS automatically generates a PILE HEAD STIFFNESS TABLE

The pile head stiffness table automatically generated by SACS contains tables for calculating the initial stiffness in the four degrees of freedom: axial, lateral, rotational, and torsion.

PSI eliminates the requirement to reformulate the pile stiffness matrix at each iteration, which requires a higher computation time by forming a table of pile head stiffness coefficients for a range of values expected in the solution. The pile head stiffness used for any iteration is found by linearly interpolating between table coefficient values. Iterations are continued until an approximate solution (within 5 percent) is found. PSI then proceeds using a fine-tune procedure, which recalculates the individual pile stiffness for each iteration.

2. Final forces/deflections have different values ​​in the pile head and structural coordinates

Final forces/deflections results in PILE HEAD COORDINATES and STRUCTURAL COORDINATES are not simply an exchange of X, Y, Z coordinates (i.e., the Z value in PILE HEAD COORDINATES is directly assigned to X in STRUCTURAL COORDINATES), because the maximum direction of translational displacement is consistent with the +Y axis direction of PILE HEAD COORDIANTES, and the Y axis direction of each pile is likely to be different, while the structural coordinates X, Y, Z are fixed. The conversion of results between the two coordinate systems requires consideration of vector decomposition. This is explained in detail in the manual as follows:

Out-of-plane displacement results occur for the following reasons:

3. Comparison results between INTERNAL FORCES and PILE HEAD FORCES:

By comparing the INTERNAL FORCES and PILE HEAD FORCES, we can know whether the upper structure load and the reaction force of the pile are balanced (because it is considered through iterative calculation, it is judged by a certain DIFFERENCE (%))

4. PILE stress UC results:

The ‘PILE MAXIMUM UNITY CHECK SUMMARY’ reports the maximum stress UC value for each pile.

The ‘PILE GROUP SUMMARY’ reports the maximum stress UC value from the stress results of all piles for each pile unit at each depth.

 

5. SOIL MAXIMUM AXIAL CAPACITY SUMMARY RESULTS:

CAPACITY (INCL. WT): The actual axial bearing capacity of the soil minus the weight of the pile from the pile head to the bottom of the pile

SAFETY FACTOR: The CAPACITY value is divided by the maximum load value to get the safety factor

UNITY CHECK: This value does not represent the result of structural stress, but is calculated based on the safety factor of the corresponding clause of the corresponding specification.

For example, under extreme conditions of the API specification, the allowable safety factor is 1.5, so the calculation of ‘UNITY CHECK’ in the following example is: take the smaller value between the compression safety factor and the tension safety factor, which is 11.59 here, UC=1.5/11.59=0.129, and keep two decimal places 0.13.

It should be noted that in this report, the working condition that produces the maximum axial load is not necessarily the working condition for UC verification, because the safety factor under extreme conditions is 1.5, and the safety factor under operating conditions is 2.0, which results in the maximum allowable bearing capacity under extreme conditions being greater than the maximum allowable bearing capacity under operating conditions. For this reason, when checking the UC here, the axial load of the working condition that produces this UC (the working condition at the far left of each row and adjacent to the UC value) must be used as input, and the working condition corresponding to the maximum axial load cannot be directly used as the checking working condition. In short, the UC cannot be simply calculated using the safety factor in the report and the safety factor specified in the specification.

When NORSOK calibration is selected in the model file, a GAMMA factor of 1.3 will be used, and the line next to ‘S O I L M A X I M U M A X I A L C A P A C I T Y S U M M A RY’ will output ‘AXIAL PILE CAPACITIES INCLUDE AN GAMMA FACOR OF 1.30’