Some homework help needed on beam calculations.

[bluespark1978]

Hi there all new here and looking for a bit of help please.

I have a question to work through which is as follows.

A beam of mild structual steel has a solid cross section of 100mm and is simply supported by two supports 3m apart. Calculate the dead load that can safely be supported when applied to the beam.

I have been told by my lecturer that I need to include ultimate strength in bending and in shear, the max load, max shear, selection modulus and max bending stress.

From my books I have values for the ultimate shear strength = 320N/mm^2, the fraction for dead load which is 0.25.

Any ideas on where I should start please?

Thanks.

[PinkertonD]

Your lecturer has already given you the things you need in order to solve the problem.

The idea of homework is to make you think and understand stuff in order to solve problems. If you think asking for help on the internet is considered "understanding" then this course is not going to be for you.

Where would you go if you were putting together a garden and needed specific advice on shrubs and flowers suitable for thriving in your area?

[wderrick]

Although doing the problem for you will not help you learn, I will help you with the mindset necessary to get started on it. In this problem, instead of being given the load and asked to find the stresses acting on the beam, you are told to find the load, when given your ultimate/max stresses. I would still approach this problem the exact same way except you will use a variable for the load. Start by making a free body diagram. you did not mention if it is a distributed load, or a concentrated load, but simply adjust what I say accordingly. Keep in mind that your end supports will be upward forces of exactly half of the load (variable/2). After that I would make your shear and bending moment diagrams. From that you can find your maximum (which will end up being the center and ends of the beam most likely). Then it is time to analyze the section of the beam, things like your cross sectional area, section modulus, and Moment of inertia are all shape specific equations, hopefully you have the resources to find those. finally after that it is time to look at your stress and bending equations, again, these are situation specific. The appropriate equations can either be derived or found using charts, I do not know what it is your prof will require. Once you have your stress and bending equations, go ahead and plug in your variables, including your given max stress.

If this was not enough guidance for you to solve the problem, then you need to either read your book, or go to your profs office hours for help...

beam analysis and all engineering mechanics is one of the most commonly used engineering practices out of college, I recommend you put the effort into UNDERSTANDING it. This problem is extremely elementary, it makes me wonder if you are actually learning your mechanics of materials class?

[bluespark1978]

Thanks for your replies. The course is distance learning and not very well organised, you can't just walk into the lecturers office and ask your queries and usually takes 3 to 5 weeks for a reply to any questions, so I can assure you that it is not a case of not putting the effort in to understand the work. Thank you for your comments and I will be going back to the drawing board and having another go at it.