Blast Loading - Structural Analysis and Design - Forum - Structural Analysis and Design - Bentley Communities.pdf

3/25/2015

Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

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Blast Loading Hi.. I'm new here. I'm not so good in english. sorry if there's a mistake. I want to simulate a blast loading using staad pro. My model is a skid consist of a base structure, 4 pressure vessels, 4 pumps, and piping. The skid has a top platform or walkways to be use for maintainence. What is the steps and parameter to design the blast loading. From what i know, it can be simulate using time history definition. I've done the definition and i don't what is the next step. What need to be done at the basic load case? What is need to do at the Analysis/Print tab? Is there any parameters to be set at the Design tab?

Thanks and best regards. faiz

http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/49708

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3/25/2015

Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

muhammad faiz abdul rahman

5 Replies (Most Recent Reply) Chris Conrad Hi faiz, Welcome to BE Communities, and don't worry about the English, we all speak the common language of "engineering" here. You are correct that blast loading can be simulated in STAAD.Pro by using a time history analysis. The first step is to get the time history data to represent the blast profile. This is likely to consist of a series of time-force data pairs, and would probably come from someone who could accurately quantify the effects of the blast that the structure must be designed for. The time history definition will also include related data like the arrival time(s) and damping. The time history definition will take the form of: DEFINE TIME HISTORY TYPE 100 FORCE 0.00001 -0.000001 0.005 -650 0.01 -800 0.015 -825 0.02 -825 0.025 -800 0.03 -700 0.035 -350 0.04 -250 0.045 -500 0.05 -730 0.055 -600 0.06 -350 0.065 -280 0.07 -450 0.075 -600 0.08 -550 0.085 -440 0.09 -415 0.095 -410 0.1 -420 ARRIVAL TIME 0.0 0.1 DAMPING 0.07 The next step is to model the gravity loads on the structure using commands like SELFWEIGHT, ONEWAY LOAD, ELEMENT LOAD, etc. This will take the form of: LOAD 1 LOADTYPE None TITLE GRAVITY LOAD SELFWEIGHT Y -1 LIST 1 TO 295 ONEWAY LOAD YRANGE 13 43 ONE -0.15 GY ELEMENT LOAD 257 259 261 263 265 267 TO 270 272 274 TO 277 279 281 TO 284 286 288 290 292 http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/49708

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Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

294 295 PR -0.2

Then the dynamic load needs to be modeled. This takes the form of: LOAD 2 DYNAMIC LOAD CASE SELFWEIGHT X 1 SELFWEIGHT Y 1 SELFWEIGHT Z 1 TIME LOAD 21 25 FX 1 1 37 41 FX 1 2 In the sample block of code above, the dynamically active masses are defined by specifying their magnitudes and the directions in which they are capable of vibrating. (In this case, the only dynamically active mass is the selfweight of the model, and it is capable of vibrating in the global X, Y, and Z directions.) Next, the dynamic loading is established. In this case, the dynamic load is applied as forces defined by the first time history load type, and it is applied at nodes 21 and 25 at the first arrival time (time zero), and identical forces are applied at nodes 37 and 41 at the second arrival time (0.1 seconds after time zero).

The analysis is initiated by a PERFORM ANALYSIS command as follows: PERFORM ANALYSIS PRINT ANALYSIS RESULTS FINISH A time history analysis is a dynamic analysis that will extract the modes and frequencies of the structure. As with any dynamic analysis, we need to pay attention to the results of the Eigenvalue Extraction to ensure that Participation Factors are high enough to substantiate the analysis. The program defaults to extracting the first six modes of vibration, but if after reviewing the participation factors, it is decided that they are not high enough, we can request more modes to be extracted by using the command CUT OFF MODE SHAPE n, where n is the number of modes requested. After reviewing the results, we may also choose to extend the duration of the time history analysis beyond the end of the forcing function, to be able to observe vibrations and to be sure we have achieved maximum amplitudes. This can be done using the command CUT OFF TIME n, where n is the desired end time in seconds. http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/49708

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3/25/2015

Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

When the analysis is successful, and when participation factors are sufficiently high, and when you are convinced that you have captured the time that has the maximum effects on the structure, then you can move on to creating load combinations, issuing design parameters, design commands, etc. Hope this is helpful as a starting point. There is some good reference information in the online program documentation. We also cover some of this material in our online training entitled Dynamics and Seismic Analysis. The next one is coming up on May 5th if you're interested. The following link lists all of the currently scheduled delivery times for that course: http://lms.bentley.com/us/desktopmodules/SearchResults.aspx? catId=0&tabindex=3&tabid=16&description=CRS-STR-STAAD-Dynamics-Seismic-AnalysisCRS&count=9&cat1=2&cat2=3&cat3=4&cat4=5&cat5=6&cat6=7&cat7=8&cat8=9&cat9=213&SortI tems=Title%20DESC,StartDateNoTime%20ASC Cheers, Chris

muhammad faiz abdul rahman In reply to Chris Conrad:

Hi Chris. Thank you very much for your detail explanation. I'll check my simulation back. I've got several questions. LOAD 1 LOADTYPE None TITLE GRAVITY LOAD SELFWEIGHT Y -1 LIST 1 TO 295 ONEWAY LOAD YRANGE 13 43 ONE -0.15 GY ELEMENT LOAD http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/49708

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Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

257 259 261 263 265 267 TO 270 272 274 TO 277 279 281 TO 284 286 288 290 292 294 295 PR -0.2 Is the above block of code from ur explanation is related to blast loading or just an example for basic loading commonly use? Do i need to specify the location of the blast center point? I've proposed to my bos to send me for the course that you have show. I hope they'll approve my proposal.

Chris Conrad In reply to muhammad faiz abdul rahman:

Hi Faiz, Glad to help out. That block of code was just a sample of the gravity loading from a model. It was unrelated to blast loading. The blast load will ultimately get assigned directly to specific nodes, so the time history data needs to anticipate that and be in a form that is conducive to being assigned to individual nodes. It would be nice if we could identify an "area" on a building wall and assign the blast profile to the "area", but unfortunately, the program is not set up to receive input in that way, so we have to assign the time history loads directly to specific nodes. Hope to see you in one of the upcoming classes. Cheers, Chris

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3/25/2015

Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

static In reply to Chris Conrad:

Chris: How do you know when Participation Factors are high enough to substantiate the analysis? Would you please elaborate? Thank you very much. IV

Chris Conrad In reply to static:

IV, I can provide you with the following reference to ASCE 7-05, which actually pertains to Response Spectrum Analysis: 12.9.1 Number of Modes. "An analysis shall be conducted to determine the natural modes of vibration for the structure. The analysis shall include a sufficient number of modes to obtain a combined modal mass participation of at least 90 percent of the actual mass in each of the orthogonal horizontal directions of response considered by the model." Cheers, http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/49708

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Blast Loading ­ Structural Analysis and Design ­ Forum ­ Structural Analysis and Design ­ Bentley Communities

Chris

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