How to start structural design 1

[heavenly]

Hi freinds
I am new to structural design field. Now i have to design a table with square tubes ,above these tubes, plate will be siiting which carries 100Kgs load & This plate carries a tensile force of 1900N at the edge
Now my question is ,how to bring assurence of my design,like how to decide following aspects
tube height
tube cross section
Bending moment of tubes due to tensile load
material selection.., etc

Thanks in before

John

 

[DaveAtkins]

You can't design anything until you do an analysis--using statics, figure out the moment, shear, and axial force in each member. Choose members accordingly, then check deflections.

DaveAtkins

 

[Ussuri]

This is how I would go about it, although this is not exhaustive and I will have missed bits. I have never tried to write this down so it might come out as gibberish.

First step is usually to come up with the scheme outline. This is where you think about overall geometry.

Does it look right?
Is it in proportion?
Think about the actual purpose of what you are designing, will it work?
Think about the details such as connections. How will it be fabricated? Can it be done quickly and efficiently? Can it be done safely?
What about economics? Is one material cheaper than another? Is one easier to get? What will be cheapest?

Next is to think about the structural concept and load transfer.

Is it going to be stable?
Is it braced or moment resisting?
How do you want your structure to work bearing in mind you want to transfer your forces to a foundation of some description?
Do you have degrees of redundancy?
Do some initial hand calcs to get a feel for the forces expected and select initial member sizes based on this.

Step Three identify all the possible loads which may be applied to your structure. These may be from dead weight, imposed loads from plant or operational?
Are there dynamic effects from rotating machinery?
Seismic effects?
Wind loading?
Accidental loads such as impact?
Does it need fire resistance?
Does it need to be lifted?

Work out how these can be combined, will some of them act at the same time. Identify any load factors if you are doing an ultimate limit state design. At this point you can do a load rundown to assess the foundation loads for foundation design.

Once you have an outline arrangement and the loads/combinations applied to it you are in a position to begin your analysis. This is where you determine the forces (axial, moment, shear, torsion) within the members, What deflection you get, is it acceptable?

You can do you analysis by hand using standard structural approaches if it is straightforward. The more complicated it becomes it them makes sense to use an analysis package, but always backed up with spot hand calculations to verify the output from the model.

After you have completed your analysis you know the maximum forces you expect in each member. You now need to design each of your members within the structure. Basically you are checking to ensure the members you have used have sufficient strength to resist the forces applied to them without failing. You may be checking for flexural capacity (local and lateral buckling), shear capacity, torsional resistance, strut buckling, tension capacity, maximum stresses and strains, and any combinations of these.

Once you confirm the members are OK, you need to check the joints and connections. Bolted or welded.

I guess this is pretty brief and the actual design process is rarely a straight through process as you end up having to revise it when something doesn’t work but it gives you an idea.

 

[woodengineer]

I would suggest working under a P.E. for this project.

Jordan