Last Updated: 2023.6

Wind

Basic Wind Speed (V): corresponds to a 3-sec gust speed at 33 ft (10 m) above the ground in Exposure Category C. Will be affected by patching for Metric vessels, the conversion from old to current will be to multiply the old value by 0.2778 and then round up to the nearest whole number. Units on form will be mph in Customary and m/s in Metric.

Wind Exposure Type: can be A, B, C or D for 1998 (A is not an option for later years).

Importance Factor (I): This is an input by the User. Its range is set to 0.77 to 1.15. If the User inputs a value outside this range it will give a popup message that informs the User they are outside the range. This value is only used in Wind calculations of 2005 and earlier.

Ground Elevation Factor (Ke): This field only affects Wind Codes ASCE 7-16 and newer. It will default and patch from older vessels to 1. Range is 0.8 to 1. Outside this range, have popup warn user of typical range.

Directionality factor (Kd): This is a User input. It will default and patch from older vessels to 1. Range is 0.8 to 1. Outside this range, have popup warn user of typical range.

Force Coefficient (Cf): This is a User input. This will default to 1.2, it will range from 0.5 to 2. Outside this range, have popup warn user of typical range. It is the force coefficient to be used in determination of wind loads for other structures.

Supported by other structure: It is new check box, defaults to false. This has an effect on what Wind calculations are performed.

Horizontal Coefficient (GCr)h: This is a new field. It is a product of external pressure coefficient and gust-factor to be used in determination of wind loads for rooftop structures.

Roof Height of Supporting Structure (h): It is the mean roof height of a building or height of other structure. It is a new field and will default to 0.

Topographic Factor (Kzt): The wind speed-up over hills, ridges, and escarpments. This ranges from 1 or greater and values entered outside this range will cause a pop up message about being outside the range.

Building Damping Coefficient: This is a field for skirt supports only.

Wind Pressure: This input is only an option for User Defined Wind. It allows the user to directly input the wind pressure. Be mindful of the units.

Allow Wind Pressure to vary at different elevations: This checkbox is only an option for User Defined Wind for skirt supported vessels. If the checkbox is checked, the user may input multiple wind pressures at different elevations in the Attachments/Loadings screen under the Wind tab.

Add. Orthog. Load Fraction: Inputting a value adds additional wind loading at 90 degrees (orthogonal) to the main load as a fraction. If you want to have 30% orthogonal load, input 0.30. For vertical vessels (skirt supported, leg supported, lug supported or support ring supported), vector calculations are then used and the resultant vector load will be determined an used in the calculations. For horizontal vessels (saddle supported), this is handled in the calculation of Qc. This value defaults to zero.

Gust Effect Factor (G): This is a User input. It will default to 0.85. Range is 0.85 and greater. Outside this range, a popup warning will appear to user of typical range.

Seismic

0.2 S Spectral Response Acceleration (Ss): mapped MCE_R, 5 percent damped, spectral response acceleration parameter at short periods.

1 s Spectral Response Acceleration (S1): mapped MCE_R, 5 percent damped, spectral response acceleration parameter at a period of 1 s.

Occupancy and Risk Category: The Use or Occupancy of Buildings and Structures designated by the specific Seismic Code.

Site Class: Based on the site soil properties. Where soil properties are not known in sufficient detail to determine the site class, Site Class D shall be used unless the authority having jurisdiction or geotechnical data determines Site Class E or F soils are present at the site.

Response Modification Factor (R): response modification coefficient as given by the specific Seismic Code.

TL: long-period transition period as defined by the Seismic Code, only affects skirt supported vessels.

Fa: short-period site coefficient (at 0.2 s-period). The greater of this value or that returned from tables in the referenced code will be used. Note that some cases for Site Class E and F do NOT have values in the codes, so it is critical that a value is input in these cases. This value is not used for ASCE 7-22 and later codes.

Fv: long-period site coefficient (at 1.0 s-period) The greater of this value or that returned from tables in the referenced code will be used. Note that some cases for Site Class E and F do NOT have values in the codes, so it is critical a value is input in these cases. This value is not used for ASCE 7-22 and later codes.

S_MS: the maximum short-period spectral response factor. This value is calculated for codes earlier than ASCE 7-22 and will not appear as an input. For ASCE 7-22 and later, this value is input by the designer.

S_M1: the maximum 1 second spectral response factor. This value is calculated for codes earlier than ASCE 7-22 and will not appear as an input. For ASCE 7-22 and later, this value is input by the designer.

Skirt is sensitive to buckling: This checkbox only applies to Skirt supports. And if checked it will adjust the C_R-I value to a greater value in some cases resulting in a higher load value.

ap: the amplification factor related to the response of a system or component as affected by the type of seismic attachment; this is only used for vessels designs as supported by another structure. This value is not used for ASCE 7-22 and later codes.

C_AR: the component resonance ductility factor; this is only used for vessel designs supported by another structure. This value is used for ASCE 7-22 and later codes.

R_mu: the structural ductility reduction factor; this is only used for vessel designs supported by another structure. This value is used for ASCE 7-22 and later codes.

Use ASCE 15.4.1 Step 2 exception: Checking this box will invoke the exception as described in ASCE and will adjust the Cs calculation and typically results in a lower load value.

z: height in structure of point of attachment of component with respect to the base, the ratio of z/h is what is used in the calculations and so specific units are not required as long as z and h are input in the same units; a z/h ratio of 1 is conservative. This is only used for vessels designs as supported by another structure.

Supported by another structure: This has an effect on what Seismic calculations are performed. When checked the vessel will use calculations treating it as a piece of equipment inside a larger structure or building instead of as a self-supporting vessel. This typically results in larger loads.

h: average roof height of structure with respect to the base, the ratio of z/h is what is used in the calculations and so specific units are not required as long as z and h are input in the same units; a z/h ratio of 1 is conservative. This is only used for vessels designs as supported by another structure.

Force Ip to 1.5: Checking this box will force set the component importance factor to 1.5. This is only used for vessels designs as supported by another structure.

Consider Vertical Seismic Effect: This option allows the user to choose whether to evaluate vertical seismic effect and defaults to checked as the building codes required the vertical effect in most scenarios. When unmarked, the Cev value is set to zero.

Min. Weight Fraction as Lateral Load: This box gives the user the capability of setting a certain percentage of the weight as the minimum lateral load used in support analysis. The input is a fraction in decimal form. This field defaults as zero.

Tv: This is a user input for the ASCE 7-16 and later code years. The default is set to 0.1 to give conservative estimations within the software. The user can input values but only the range from 0 to 2 is usable within the equations. Values outside of this range will be taken equal to the upper or lower bound.

Top Force Multiplier: This input is only an option for User Defined Seismic for skirt supported vessels . This should be entered as a decimal (e.g. 10% would be entered as 0.1). This value will be used to set a portion of the vessel horizontal seismic load at the top of the vessel (Weight * Top Force Multiplier * FPV * Ceh), the remaining horizontal seismic load will then be vertically distributed over the vessel based on the weight distribution and the k factor.

Force Distribution Factor: This input is only an option for User Defined Seismic for skirt supported vessels. It ranges from 1 to 2. The building codes determine this value based on the period of vibration of the vessel. This affects the vertical distribution of the horizontal seismic load. Higher k values push more of the load to the top of the vessel using the formula (W*H^k)/Sum(W*H^k) where W represents the weight of a segment of the vessel and H represents the elevation to the c.g. of that vessel segment.

Add. Orthog. Load Fraction: Inputting a value here will add additional seismic loading at 90 degrees (orthogonal) to the main load as a fraction. If you wish to have 30% orthogonal load, input 0.30. For vertical vessels (skirt supported, leg supported, lug supported or support ring supported), vector math will be used and the resultant vector load will be determined an used in the calculations. For horizontal vessels (saddle supported) this is handled in the calculation of Qc. This value defaults to zero.

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