Mathcad errors galore (symbolic evaluation)

[Fat Ryan]

Hello,

I'm trying to use mathcad to do Rayleigh-Ritz approximation of the critical elastic buckling load of a joists top chord. The joists support a standing seam roof which acts to stabilize the top chord from out of plain buckling. In order to approximate the buckled shape, I chose to use a Fourier series: SUM(a_j*sin(j*PI*x/L)) with j=1 to nclips. nclips is the number of roof clips along the length of the chord that is being analyzed. I've done similar problems in a Stability of Structures class I just finished in the spring. Using mathcad to do these evaluations symbolically has been a problem since day one. I finally thought I figured out the secrets to getting an answer and not an error, but I guess I was wrong. I don't believe I've ever included a summation inside an integral though. Could this be the issue? If I am defining a variable that will have variables within it, I need to call the variables as arguments, correct? This has worked for me until now. I'm trying to define a variable that has variables within it. But those variables within it come from another definition with variables within it. Mathcad doesn't seem to like this. If i use arguments in the definitions, i get an "exponent overflow" error. If i don't call arguments, i get "this value must be a scalar". also, in my summation i have a_j... for the j do i use "." or "["? I am using "[" now as "." didnt work for me. Or is there some other way to do it? Thanks.

p.s. sorry if this is totally confusing. I don't know how to properly word it.

 

[Valkarie]

I'm trying to learn and this is just a part of it.The issue could be that you are including a summation inside an integral. Integrals require all variables to be defined as scalar values, which means that the summation inside the integral must also consist of scalar values. You can try defining a scalar variable for each term in your summation and then use that in your integral instead. For example, if you have a summation from j=1 to nclips, then define a scalar variable for each term in the summation (aj, bj, etc.) and then use those variables in the integral instead of the summation. As for the j in your summation, you should use "[" instead of ".".