Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: loadcase Subarea: Original Author: Bentley Technical Support Group Comments, Questions, and Answers about Static Earthquake Load Case In AutoPIPE Item #1, Question: Can the seismic input be explained again in the new version of AutoPIPE V8i 09.06.xx.xx and higher? Answer : Start by selecting load> Static Earthquake. By default there is already 1 seismic load case E1, using the mouse change the Seismic Code from User to ASCE 2010, Using the mouse, select the gray box on the left hand side of E1 to highlight the entire row, and press the Modify Selected button: Fill in the fields as required, see online help for details on all fields. Press OK button to enable the application to calculate the gravity factors to be applied to the model for the active load case. Press the New button as required to add additional load cases. Note: A maximum of ten (10) earthquake load cases can be used in a model at any one time. Note: the information in AutoPIPE was gathered from the USGS earthquake hazard maps and Data website Item #2, Comment: A real world seismic response of the piping system is probably somewhere between a linear and non-linear behavior since pipes may jump off supports and friction is no longer present So running a non-linear and a linear analysis then finding the maximum loads between the 2 results may yield the most real world results. Item #3, Comment: When using "ASCE 2010" Seismic Static Load Generator, The component response factor Rp is an important factor for calculating the seismic ground acceleration. Rp = 12 is common for stress, but ASCE-2010 paragraph 13.4.1. states that for supports/structure reactions to use a value NOT higher than 6: One Recommendation is to run 2 sets of seismic cases Rp = 6.0 (Support & Anchor Reactions) Rp = 12.0 (Pipe stresses) Item #4, Comment: Depending on your type of analysis (i.e. Linear or Non-linear) there are options for load case combinations: Linear Analysis: On the Combinations dialog, select the "Combination Options" button, and place a check mark next to "Add Negative Occasional Cases", From the online help: If this option is selected, the program will generate default Non-Code combinations for negative occasional load cases in addition to the default Non-Code combinations for positive occasional load cases of seismic and wind only, i.e. GRTP1+W1, GRTP1-W1, GRTP1+E1, GRTP1-E1, etc. The default state is unchecked. This option will be disabled (grayed out) if the "Add default Non-Code combination" option is unchecked or if the static analysis = non-linear. Some behaviors: • Disabled when 'Disable Auto Non-Code Combination' checked • Always Enabled for B31.8, B31.4 Offset, B31.8 Offset, CSA Z662 Offset • KHK (Enabled only for level 2) • All other codes (Enabled when one or more load sets are linear) Non-Linear analysis For static seismic cases we recommend a minimum of 8 cases as shown here which will provide the accurate non-linear support load combinations and occasional code stresses. Define minimum of 8 static seismic cases: +/- X +/- Y (4) and +/- Z +/- Y (4) where Y = Vertical Note: You would typically use OP1 as the initial state. Seismic loads at the load case level e.g. E1, E2 etc are combined as load vectors algebraically to get a resultant loading. Horizontal X and Z seismic loads are typically not combined in the same load case. Seismic guidelines recommend analyzing two non-concurrent horizontal seismic loadings. It is common to consider separate loadings for X and Z directions in different load cases E1 and E2 both with vertical Y component. So only cases SUS +E1 to SUS +E8 need to be considered for occasional stress compliance. Item #5, Comment For most tall structures, the greater seismic accelerations occur at the top of the structure / building. We can use the AutoPIPE's Insert> Xtra Data> "Member Static Earthquake factors " or " Point Static Earthquake factors " commands to model the increased seismic accelerations upward through the building / supporting steel structure. Typically component amplification between 1 and 2.5 Item #6, Comment: What is the recommended Seismic support spacing? Answer: MSS SP-127-2001 (Bracing for piping Systems Seismic - Wind - Dynamic) recommends a lateral seismic support every 40ft and longitudinal support every 80ft. But just note this guideline tends to be conservative and over predict number and size of seismic supports. Item #7, Question: In my project, there are piping systems that must be analyzed based on code calculations (i.e. Boiler piping, etc. ) and other systems that are called BOP (Balance Of Plant) piping that is non-crucial piping that has lower specifications for analysis than other code required piping. As such the Seismic G factors are different for these different systems. So How can I apply the correct G factor in our model? Answer: Please consider using 1 of the following options: Option #1: If the piping is not connected to gether and are really disconnected systems. Recommend that they be analyzed in different models with different settings as needed. Option #2: When using Load> Static Earthquake, the "G" force is applied to the entire model. There is no way of dictating different static earthquake loads factors to specific piping segment support. Option #3: Apply the earthquake as a MSRS ananlysis. See the following file that was installed with AtuoPIPE on your computer: C:\ Bentley\ AutoPIPE V8i SELECTseries\ Documents\ AutoPIPE_MSRS_Example1.pdf This is a good tutorial on how to perform a MSRS on a piping system. You would group the supports for one type of piping system into one support group, then all the other piping system supports into another support group, and apply the different responses as needed. Item #8: Gravity + thermal + User load cases added together give incorrect results on support in AutoPIPE, why? See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU! Gravity + thermal + User load cases added together give incorrect results on support in AutoPIPE, why?
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