Design of non-ductile steel elements on the seismic overstrength factor

[h-badawy]

Dear experts

For the seismic design category (C ,D & E ),where is the provision/section in the code (ASCE OR AISC) discuss/describe the design of non-ductile elements like connections, base connections, bracing ,…etc., on the overstrength factor.and also is there any exception we can consider to avoid this such factor in the design?

Thank you

 

[driftLimiter]

Overstrength factors are specified by ASCE 7-16 for different systems. ASCE 7 contains building level requirements for application of overstrength, and then reference documents such as ACI 318 and AISC 341 contain lateral system level requirements for application of overstrength.

There are a fairly large number of provisions requiring overstrength, some have exceptions while others do not.

You would do well to understand the AISC 341 and ASCE 7 Ch 12 requirements if undertaking a ductile steel design in SDC C or above.

 

[h-badawy]

Thank u driftlimiter
Actually i read ASCE 7- chapter12 and AISC341 as well , but i did not find any items speak clearly about the design of brittle elements such as steel connections , base connection , strut , bracing ,..etc.,.
Only section 12.10.2 and the writer speak about the collector elements in the concrete buildings .
It is not clear for concrete.

Thank you

 

[driftLimiter]

It depends heavily on the selected seismic system. For example Ordinary concentrically braced steel frames system requirements Chapter F Section 4a (1) (i) (AISC 341 V2) says: ... "The forces in braces in tension shall be assumed to be the least of the following: (b) the load effect based upon the amplified seismic load.

The 'amplified seismic load' is nothing more than Overstrength Factor times E. There are many other references therein. Sometimes the language is not consistent.

Following ASCE7 for seismic requires the use of structural systems in table 12.2-1 or alternate approved system. So there isn't general guidance about ' brittle elements'. THere is specific guidance provided for the selected structural system.