This document describes new or enhanced features of STAAD Foundation Advanced (SFA) since the CONNECT Edition V9.3 (Release 188.8.131.52).
Wind load generation for vertical vessels per PIP STC01015 2017 / ASCE 7-2010
For vertical vessels, wind load generation is now available per the April 2017 edition of the PIP STC01015 code which in turn directs the user to the Wind load generation chapters of the ASCE 7-2010 code as mentioned in section 184.108.40.206 of the PIP document.
The salient aspects of the implementation of the code are:
Step 1: Computation of the wind pressure from equation 29.3-1 of ASCE 7-10.
The equations mentioned in that section of the code, for the English unit system (foot, pound),
qz= 0.00256*Kz*Kzt*Kd*V^2 lb/ ft2
as well as the SI unit system (meter, kNs),
qz= 0.00613*Kz*Kzt*Kd*V^2 N/m2
have been implemented.
The input that the engineer needs to provide are:
V - Basic Wind Speed in mph or meter per second (Section 26.5 has guidelines for this)
Kd = wind directionality factor defined in Section 26.6 of ASCE 7-2010
Exposure category – B, C or D – as per Section 26.7.3 of ASCE 7-2010
Kz = Based on the exposure category, program selects the value of velocity pressure exposure coefficient evaluated at height “z” from the table provided in Section 29.3.1
SFA does not take the values from the table directly. Instead, it calculates Kz from the formulae provided at the bottom of Table 29.3-1. An extract from the code is shown below.
Kzt = Topographic factor defined in Section 26.8.2.
Note: If site conditions and locations of structures do not meet all the conditions specified in section 26.8.1 of the code, one is allowed to set Kzt to 1.0. Since there are no provisions in SFA to specify site conditions (ridge, escarpment or hills), a value of 1.0 is used for Kzt.
G = gust-effect factor from Section 26.9
Cf = Net force coefficient from Fig 29.4-1
Step 2: Computation of the force at various heights above the ground, and the resulting shear and moment at the top of pedestal
The force due to wind acting at various levels along the height of the pedestal and vessel is calculated using the guidelines provided in Chapter 29 of ASCE 7-2010. Specifically, equation 29.5-1 is used to determine the force at various heights “z” above the ground.
F = qz * G * Cf * Af [Af= Height segment x Width or diameter]
Table 29.3-1 on page 310 of ASCE 7-10 is used to find the exposure coefficient Kz and the height ranges for which it is applicable.
The region spanning the distance between the ground level upto the top of the vessel is divided into various height segments as explained in Table 29.3-1 and the wind force is calculated for each segment. The force is considered to act at the mid-height of the respective segments, which provides the level arm for calculating the moment at the bottom of the pedestal.
Below are the screens from the program’s user interface where the wind load data is provided.
The output produced by the program is as shown below.
Generation of Load Combinations per PIP STC01015 for Vertical Vessel foundations
For vertical vessels in the PLANT mode of SFA, load combinations can now be generated for vertical vessel foundations per the Process Industry Practices standard titled
PIP STC01015 Structural Design Criteria – April 2017 Revision
Section 4.2.1 of that standard states that load combinations need to be generated per the ASCE standard
ASCE/SEI 7-10 - Minimum Design Loads for Buildings and Other Structures
Hence, users will be able to find this code in SFA under the name
PIP STC01015-April 2017/ASCE 7-10
as shown in the next figure.
The combined set of rules of these two codes is illustrated in Tables 6 and 7 of the PIP document under section 220.127.116.11, and those are the ones implemented in SFA too.
An inspection of the load combinations listed in these tables will reveal that certain basic load data needs to be specified before the combinations can be generated, such as,
etc., as mentioned in section 4.1 of the PIP STC01015-April 2017 document. In SFA, these can be specified in the primary load cases page as shown below.
Load combinations per Table 6 are generated under the heading Service Load Combinations, and, load combinations per Table 7 are generated under the heading Ultimate Load Combinations.
Grouping of isolated footings has been re-instated
For isolated footings, older versions of SFA (the version 8 series or older) had an option called Create Group. This option was used to obtain a single footing size that can be applied to all the support nodes that are included in the current isolated footing job. In other words, all the support nodes in that job would be assigned the same footing size. However, this feature had been disabled during the past few versions of SFA for various reasons.
This has now been re-instated.
This option can be found under the Tools menu.
In order for the program to successfully determine a single size, the conditions that must be satisfied are:
To execute this operation,
Select the “Create Group” option as shown in the figure above, and, specify a job name when prompted for that.
The calculations will begin soon after that. Note that the process will involve more time than what is required for a “Set Dimension” or a “Calculate Dimension” operation.
Typically, the result of this operation would be that all the footings will receive the same size as the largest one obtained from a Calculate Dimension operation. However, if for any reason, any of the footings are found to fail with that size, the program will iterate again until a single successful size is obtained for all of them. In certain instances, a smaller plan size (than the largest size described above) too may be found to be suitable.
Note that the grouping exercise is performed only for the “dimensions” of the footing. It does not apply to the reinforcement provided within the individual footings and hence that may be different between the footings.
Calculation reports are created for each footing providing the details of the analysis and design performed, based on the final size that is assigned to them.
The summary table may be used to examine the size and reinforcement details for all the footings in a compact page.
This feature has been restored for all design codes available in the program’s General mode.
Miscellaneous enhancements and correction of defects