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Hi all! Can you please help me to understand the behavior of gravity columns in seismic event? After reading section 18.14 of ACI, I understood that it is okay for gravity columns to go to yielding under seismic event. If the demands on gravity columns exceeds the capacity during seismic event...

We donot design the gravity columns for the forces induced by lateral seismic load, correct? But we have to ensure we provide the detailing as per section 18.14 of ACI so that columns maintain its integrity during seismic event.

Yes, columns are not the part of lateral load resisting system. So do you mean only the vertical component of seismic component should be considered for the design?

Hi all! Do we design the gravity columns using the load combinations that have seismic component in it? Aren't the gravity columns are designed to resist gravity loads only? Can you please make the concept clear for me? I saw following load combinations being taken for the design of gravity...

It is defined as shown below. Area load is applied to the slab under SDL load case.

Hi all! I am running into an error message while performing modal analysis using ritz vector. Please see attached image. My model works fine if I switch to eigen vector. Can you please help me understand what is the error here and how can we debug?

Thank you all for useful information. I haven't understood the behavior of gravity columns during seismic event. What kind of gravity column behavior we expect during seismic event? Of course they won't be designed for high forces that will be induced during the seismic event. Gravity columns...

Hi all! Can you please help me understand the section 18.14 of ACI (Members not designated as part of the seismic-force-resisting system)? Section 18.14.2.1 tells you to apply gravity load and design displacement. For the gravity columns, in computer model we will have pinned at the ends. This...

Hi! I am applying a response spectrum along x direction (RSX). The diaphragm should have the chords shown by black arrow but if I checked the sign of resultant forces both are positive. If I was applying ELF it matches the sign convention. I am not understanding why is this happening for the...

Thanks all! @Athalus-> I heard this for the first time. If force is transferred for joist to deck does the deck has enough shear capacity in the direction perpendicular to the ribs to withstand the diaphragm shear generated? Can you please provide reference to this concept if you know any?

Hi all! I am trying to understand the diaphragm behavior for bare steel deck supported by joist (let's say at 6 ft o.c) on perpendicular direction. I think when structure is laterally loaded, deck should be provided with sufficient shear strength to resist the shear stress generated on diaphragm...

Hi all! My structure has precast sandwich wall (insulation in between two concrete walls) for lateral force resisting. How do you guys model this wall appropriately in ETABS? Any suggestions will be greatly appreciated?

Thanks! I was looking at second edition.

I don't think there is an example for STMF in AISC seismic manual. I can find for other systems but not for STMF.

Hi all! Lets say I have a beam element (assume similar to reduced beam section) which will be under compression so it has to meet table D1.1 for high ductile member. I am thinking since whole member will be in compression I need to satisfy this requirement at both section cut A and B (see fig)...

Why most of the T-section does not satisfy the width-to-thickness requirement of high ductile members (Table D1.1 of seismic provision)? I am trying to use T-section for the top and bottom chords of special steel truss moment frame and looks like most of the section does not satisfy. What type...

Hi! I am modeling a structure in ETABS. I tried two different model. One with rigid diaphragm and another with semi rigid diaphragm. Floor for my structure is modeled as a bare steel deck. For the case with rigid diaphragm my moment frames are not taking any forces. Can you please help me...

This was really helpful. I appreciate.

Why is the type of diaphragm influencing the time period of the structure? Time period of structure is related to the mass and stiffness of the lateral force resisting system. Where does the diaphragm action coming into play? I considered two different models: one with rigid diaphragm and...