I have analyzed trusses for class work, but never in professional practice. In homework I am given the geometry and the applied loads, and asked to find the loads or stresses in members, not too difficult. But coming from a blank paper where do you start to design a truss or bridge, with so many types to pick from? For a simple beam I know what to do. For a complex truss, vs suspension bridge how is this decided before all the detail analysis starts? In the attached photo the bridge over the RR tracks (right side) is a truss. Over the road way a different type. I assume the RR  needs more clearance and puttinging the "depth of the beam" above the road way, provides the clearance. But why not a truss across the entire span, or the other type raised higher and extended. I assume there must be a significant cost difference but I have no practical experience to support this. Also I have seen bridges with a truss as show then other with the truss under the road bed or tracks for RR bridge. What drives the design?

Well, I got one good comment from JAG. I presume that means that he and I are the only folks left who don't know everything. I suppose that stands to reason; we are both old men! I had no idea the rest of you were so brilliant and over-informed!

To answer JAG's question, "What drives the design?" let me respond by saying "many factors." We might consider --

* cost and availability of materials (steel, concrete, stone, etc);

* cost and availability of a work force familiar with construction in various materials;

* cost and availability of machines to fabricate and erect the various bridge types;

* local and national laws and ordinances regarding height of structures, visibility blockage ("must not interfere with airport approach," "don't block the view of the mountain or the lake");

* past experience of each designer/erector (some have never worked in steel but have lots of experience in concrete and vice versa);

* opinions on aesthetics of various bridge types (suspension bridges look graceful, etc),

There are probably some more factors, but this is a start.

DrD

Hi, at first I’m so excited with your post, I actually found it by total chance.I’m new to this place, I just logged in yesterday and I’ve been noticing your comments on lots of topics and really wanted to ask you just about everything ...

I‘m from Egypt and I’m in my third year, unfortunately subjects in my college are not really taught very well; for most of the courses I get out knowing almost nothing, there might be a course or two that I manage to save my self in by learning the whole material from a lecture series on YouTube and reading textbooks, attending course at college keeps me on track really just to not dive in too much details. but it’s just hard for me to do the same in each subject, so I plan to continue studying other courses in summer on my own. 
So I wish you could help me find video course or any material really that I can follow to study...

I’m correctly studying heat transfer|| then I’ll  revisit heat transfer| since there wasn’t much time last semester to really grasp all topics but that would be after I finish studying combustion all from NPTEL course series and I should study after that hydraulic systems but I’m really really struggling with the material thought by my instructor and couldn’t find a replacement yet...
and For this summer I’ll follow Fluid mechanics and Thermodynamics NPTEL series

Welding, Fluid dynamics in,Theory of machines, Casting, Applied Thermodynamics, and Numerical Are subjects that I don’t have any clue about and I Don’t know where to start.

I have a lot of questions that I’ll write later and I really hope you’d bare with my rusty language...

Dear Fatima,

The only places where I am likely to be able to help you are Theory of Machines, Vibrations, Dynamics, Machine Design, and Numerical Methods. As a start, I suggest you download a copy of my textbook, Mechanics of Machines, Ver. 2.1, available here at the ME Forum (I'm not sure where they have put it now) or at Academia.edu or at Mekanizmalar.com. I think you may find a lot of interesting material in there. Also, write to me as you have here with other questions.

DrD

Hi DrD, I really loved the your textbook, I’m extremely excited to learn from it, at my institute they always suggest us old textbooks which is quite daunting to follow, thank you 🙏   

My next question is that I’ll move to my final year and I don’t feel like I have a clear idea of what a mechanical engineer job will look like, is that a big problem or normal?

If it is a problem how can I fix it?

What did you most enjoy studying? Did you get a buzz our of thermo and heat transfer? Are you excited by machinery? What do you think you'd like to work on in the future?

Your career is what YOU make of it. It can be this, or it can be that, or perhaps it can be the other. YOU have to choose which direction you want to go, and then make the necessary inquiries as to how to get there. Talk to the faculty, talk to any company representatives that come to campus to interview graduates, talk to everyone you can. I have no idea what the opportunities are in your location, but there are folks who do know. Ask them.

DrD

I was born in Saudi Arabia and I’ve been in Egypt for 4 years & I always looked for someone to ask him these kind of questions and really cares about answering them and not just give me a yes or no answer or suggestions based on focusing my interest on best salary or most requested areas of mechanical engineering  ...😭

 It’s an obstacle that I always find when I talk to the faculty and I don’t know how to get around it ! I just stopped asking them ... what do you think?

As for company representatives, we don’t have such people that come over at where I study but I think I can ask people that might know where I can reach those, but do I should start searching now ? Or maybe in summer? Or after graduation? Or should I even fill up my “CV” (although I don’t know with what) before I start asking and searching?

P.S. I loved studying about engineering materials  & production technology the most and I find fluid mechanics & heat transfer interesting subjects that I can’t get board of. No mach right?

Please, take your time answering & commenting ..., I think it’s a lot in one note.

You need to ask around to upper classmen, librarians, lab assistants, in addition to the faculty, and the main question is, "How do graduates of this school find jobs? Where do they make the necessary employer contacts?"\I

I'd really be surprised if no industry recruiters come to your campus. Most schools encourage this as a way to help their graduates find work.

Also, does your school offer a cooperative education (Co-Op) experience? If so, take it. If you don't know, ask in the Dean's Office. My school had one, and I wish I had done it. I had never heard of such a thing, and it was only after I was long gone that I learned that it had existed.

Ultimately, you have to find your own way. You know that many have done so before you and others are doing it right now. You cannot afford to be shy; you must put yourself out there, even if you find it difficult.

DrD