Here is an update on the status of educational activities related to the Quacking Moment.


First, a quick recap.  Several years ago, when I was teaching my concrete design class, I suddenly started speaking like Elmer Fudd.  The "cracking moment" is a value of bending moment at which a concrete beam will first start to crack.  But I pronounced it as the "Quacking Moment".  The students burst out laughing and then didn't really pay attention to the rest of the class (at least that was the excuse they offered that day). 


To help advance their education, I thought it was important for a follow up.  So I provided a valuable lesson the next day to further define the "Quacking Moment".  On a simply supported beam of length, "L", with a load of P-duck at the beam's center, the quacking moment is defined as:


M quacking = P-duck * L / 4


A free body diagram for the calculation is illustrated in the figure below.

blog post photo

Note that this is a calculation for the quacking moment without impact.  If the duck waddles or otherwise bounces up and down on the beam, an additional percentage of  the weight of P-duck should be included to account for dynamic effects.


Now for the update.  Several former students have been kind enough to share their experiences with the quacking moment.  A student that I’ll call "Norm" emailed from California to say that he was studying for the PE exam.  Unfortunately he lost valuable study minutes when his review guide mentioned the cracking moment but he remembered using different terminology.  Another student, "Julia", commented that she was attending a project design meeting at her firm where the cracking moment was discussed.  She burst out laughing, and then she had to explain to her colleagues why.  She found that it was difficult to explain. 


I hope there will be more news to share on the Quacking Moment.