Seismic Analysis

I am analysing a platform attched to the vessel. I applied UBC load in the seismic definition. While running the program, i am getting an error as"    **ERROR- STRUCTURE HAS NO WEIGHT ABOVE THE BASE FOR UBC ANALYSIS". can anyone clarify this.

Anonymous
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  • (Someone has replied this way)

    Although the error message has been reported in the context of analysis per UBC 1997, it is a generic message that pertains to all codes that are based on the ELFP method. 

    In those codes, we will find equations that describe how the shear at the base of the structure has to be distributed among the various levels of the structure. Those equations contain the term h, which is the height of any given level above the base.

    This implies that the ELFP is to be applied only on those structures whose geometry consists of various levels and floors. The supports of the structure must all be at the lowest level; h for any level would then be measured above the supports.

    Your model has only one level which is just the foundation level alone. So, all the entities—beams and nodes—are at just a single elevation; 'H' is hence zero, and the lateral forces cannot be computed. Unless you include the columns and beams of at least one or more floors and make the model resemble a frame having distinct Y coordinates, seismic analysis cannot be performed. 

    There is extensive coverage of seismic analysis in the book written by Kris Sathia. You can find the details at

    https://store.bentley.com/en/products/books/WAD00908A10001--Principles-of-Structural-Analysis

    This topic is discussed in section 2.4.16 on page 224 of that book.

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  • (Someone has replied this way)

    Although the error message has been reported in the context of analysis per UBC 1997, it is a generic message that pertains to all codes that are based on the ELFP method. 

    In those codes, we will find equations that describe how the shear at the base of the structure has to be distributed among the various levels of the structure. Those equations contain the term h, which is the height of any given level above the base.

    This implies that the ELFP is to be applied only on those structures whose geometry consists of various levels and floors. The supports of the structure must all be at the lowest level; h for any level would then be measured above the supports.

    Your model has only one level which is just the foundation level alone. So, all the entities—beams and nodes—are at just a single elevation; 'H' is hence zero, and the lateral forces cannot be computed. Unless you include the columns and beams of at least one or more floors and make the model resemble a frame having distinct Y coordinates, seismic analysis cannot be performed. 

    There is extensive coverage of seismic analysis in the book written by Kris Sathia. You can find the details at

    https://store.bentley.com/en/products/books/WAD00908A10001--Principles-of-Structural-Analysis

    This topic is discussed in section 2.4.16 on page 224 of that book.

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