Over-strength Coefficient of Concrete and Steel Structure

[CloudSan1]

I have a building system with a concrete column and a steel angle truss as shown in the attached photos. Both the concrete columns and the truss are part of the earthquake resisting system.

Where does this belong in the Structural System Classification? What is the over-strength coefficient?

I initially assumed that this is a Special Composite Steel and Concrete Moment Frame with R=8.0 (under Steel Moment-Resisting Frame System) but a friend of mine suggested that this belongs to the Cantilevered Column Building System with R=2.2.

Any idea what is the correct classification of this structural system?

Does anyone have guides or reference which describes the different types of structural systems in detail since UBC97 only describes some of the system and not in detail.

Thanks.


Pictures:

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https://res.cloudinary.com/engineering-com/image/upload/v1633060922/tips/Truss_full_model_z6iioa.jpg

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https://res.cloudinary.com/engineer...60925/tips/TRUSS_ENGTIPS-Model_001_gqpnfb.jpg

]

 

[HTURKAK]

Your friend is right .. If ASCE 7 is applicable, the subject system is defined at Table 12.2-1 Design Coefficients and Factors for Seismic Force-Resisting Systems with G. CANTILEVERED COLUMN SYSTEMS G 1,G 2, G 3 ( with R values 2.5,1.5 and 1.0 and Overstrength Factor, Ω0 values with 1.25 )

I would like to remind also the use of overstrength fsctor;


12.2.5.2 Cantilever Column Systems. ....Foundation and other elements used to provide overturning
resistance at the base of cantilever column elements shall be designed to resist the seismic load effects, including overstrength of Section 12.4.3.

 

[CloudSan1]

Thanks for the comment Hturkak.

If this is a cantilevered column, does it mean that warehouses with similar figure can also be considered a cantilevered column system? Say for example if the columns and rafters are all W-Flange steel or a concrete column and a W-Flange rafter.

 

[HTURKAK]

If the columns and roof beam(s) have rigid connection, in this case the system will be Moment-resisting frame system , say IMF , R will be R = 4.5.

( i.e. Gable frames , portal frames with rigid connections..)

 

[CloudSan1]

I see now. But is there a way to make the structure that I posted an IMF or SMF with R = 4.5 or higher, or maybe a Special Truss Moment Frame with R=6.5? Say for example making the truss-column connection rigid by welding the truss plate to the column main bars (not sure about this method) so it will have a moment connection.

 

[HTURKAK]

May be better if you post a sketch... I do not see or say IMO , it is not reasonable to provide moment connection with steel roof truss to PC concrete column..
But this is my opinion and remember; this is World Wild Web..

Suggest you consult with an experienced eng and improve your knowledge for seismic behavior of structures..

Good Luck..

 

[JLNJ]

A Special Moment Frame has many, many, many requirements with which you need to comply. You can’t assume it’s an SMF just because it’s a moment frame.

If you are in a high seismic area you will need some help from an experienced engineer. One who knows the difference between fixed and pinned bases.