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Using solver to solve a real problem

I have just started using Mathcad, and i think it is a fantastic resource. I am trying to determine the moment capacity of a reinforced concrete beam. I have a number of equations that all depend on one another and need to solve for one of the variables. I have done this in excel using the goal seek function but i would prefer to use mathcad as it presents the results much better. I have tried to use a solve block with out any luck.

the basic theory is that some of the beam is in compression and the rest is in tension, I need to move the deviding line (the neutral axis) up or down until the forces balance, ie the sum of forces (compression and tension) are equal to zero.

I have attached the worksheet, if anyone can help i would realy appreciate it. I have highlighted the equations in yellow, they are at the bottom of the sheet.

Joe

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1 ACCEPTED SOLUTION

Accepted Solutions

Re: Using solver to solve a real problem

Have a look at the attached. I have combined some of the formulas for simplicity.

I have also removed the minus sign from the lower limit of the Integral.

Mike

17 REPLIES 17

Re: Using solver to solve a real problem

So you want to find the value of d.n, which make the resultant forces equal.

Mike

Re: Using solver to solve a real problem

Thanks for answering, yes that is exactly what I want.

Re: Using solver to solve a real problem

Have a look at the attached. I have combined some of the formulas for simplicity.

I have also removed the minus sign from the lower limit of the Integral.

Mike

Re: Using solver to solve a real problem

Thanks for helping. I realy appreciate it. If you are ever in Adelaide, I will buy you a beer.

Joe.

Re: Using solver to solve a real problem

 Thanks for helping. I realy appreciate it. If you are ever in Adelaide, I will buy you a beer.Joe.

Cheers, I'll hold you to that Mike

Re: Using solver to solve a real problem

Mike,

I have tried to apply your solution to a slightly diferent problem but i got an error

It says that "this variable is undefined" but I have defined it above, to you know what I am doing wrong? Re: Using solver to solve a real problem

Not from the image. Can you post the worksheet?

Mike

Re: Using solver to solve a real problem

Have a look at the attached.

If you change the guess value of d.n to 60, Mathcad throws an error. Always try changing the guess value when this happens.

Another trick which I find helpful is to use the Minerr function instead of find. Minerr - Returns the values of var1, var2... that satisfy the equations and inequalities in a Solve Block. Minerr differs from Find or Minimize in that, if the chosen algorithm fails to converge, whatever answer found on the last allowable iteration is returned, even if it doesn't meet the convergence criteria.

Mike

Message was edited by: Mike Armstrong - I forgot to mention - put the guess value of d.n to 50 and it works 🙂

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Re: Using solver to solve a real problem

Mike,

Here is the worksheet with the error, I have highlighted the section that I am interested in in yellow again. thanks again for your time!

Joe