Wednesday, July 18, 2007

RE: Maximum Moments in Beams



I suggest you get a copy of AISC Design Guide 15 - Rehabilitation and Retrofit Guide.  It has good information on older beams.  Your beam is a 12B16.5.  It is not a W12x16.  You can not directly use the tables from AISC 13th edition.  It is based on ASTM A992 steel.  Your beam is probably ASTM A7 or A36.  This will change the allowable shear and bending stresses.







From: Mauricio Castro []
Sent: Tuesday, July 17, 2007 9:27 AM
Subject: Maximum Moments in Beams


I am currently revising the structure of the floor of a building to make sure that the old beams will manage to carry an increase in dead load of about 7/5 of the current load. I calculated the new maximum moments and compared them to the maximum moments allowed by the beam (Using my 13th edition AISC steel construction manual).

I am getting maximum moments of about 8 kip-ft and according to the manual these beams (12 B 16.5 which are supposed to be W12x16) should resist moments up to 75.4 kip-ft. This is a noticeable difference which makes me thing that either the beam highly safe or the calculations wrong. I haven't considered safety factors yet, but even then, the safety factor would be too high. The floor is the top floor and practically only carries the weight of a reactor (around 13kips) and unfortunately the only plans are the layouts of the beams.


Does this difference in maximum moments sound right?


Mauricio Castro

Civil Engineering Student


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