IBC/UBC seismic warning

"**WARNING: IF THIS UBC/IBC ANALYSIS HAS TENSION/COMPRESSION OR REPEAT LOAD OR RE-ANALYSIS OR SELECT OPTIMIZE, THEN EACH UBC/IBC CASE SHOULD BE FOLLOWED BY PERFORM ANALYSIS & CHANGE."

 I did not understand anything from that warning but it contd to analize the structure. I wanna ask you that is my seismic analysis correct?

P.s: I entered 0.8s period values on purpose. And i know my modal analysis is wrong.

Parents
  • hI !    I have some few questions here:

    1. I would like to know if STAAD is considering rigidity of the structure due to slab when inputting slab coordinates like y range 3 3.... and so on and so forth. What i meant was by inputting y range for floor loads, is the rigidity of the slab already been considered.

    2. In connection to question one, how can I make a hole in the slab ?   I've placed y range for floor loads and it does assume the whole floor rigid-slab ?   How about the stairwell, atrium or simply floor openings?

Reply
  • hI !    I have some few questions here:

    1. I would like to know if STAAD is considering rigidity of the structure due to slab when inputting slab coordinates like y range 3 3.... and so on and so forth. What i meant was by inputting y range for floor loads, is the rigidity of the slab already been considered.

    2. In connection to question one, how can I make a hole in the slab ?   I've placed y range for floor loads and it does assume the whole floor rigid-slab ?   How about the stairwell, atrium or simply floor openings?

Children
  • Answer to question 1 :

    YRANGE or XRANGE or ZRANGE is merely a way by which one tells the program the portion of the structure where the FLOOR LOAD is being applied. A structure can have many floors, and on each floor, there can be loads of various intensities on different parts of the floor. So, if the program is to be told which region a specific load intensity is to be applied, there has to be a way by which to identify that location. XRANGE, YRANGE and ZRANGE is one of the means to identify that region. Another method is the FLOOR GROUP.

    If a slab is present on a region, and if the slab is modeled using plate elements, you can apply the load using ELEMENT LOAD instead of FLOOR LOAD. The stiffness of the slab is accounted for through the stiffness of the elements which gets calculated during the assembly of the stiffness matrix.

     

    Answer to question 2 :

    If the slab is modeled using plate elements, an opening in the slab can be modeled by ensuring that there are no elements in the region of the opening. In other words, a hole is nothing but an absence of elements on the region defined by the opening.

    If the slab is not included in the model (and thus there are no elements to model the slab), and you want to exclude the region of the opening while applying the floor load, use the appropriate values for XRANGE and ZRANGE. YRANGE is usually for identifying the elevation of the floor.