why is the i-beam better than the solid rectangular beam in constructing bridges?
83815
The I-beam puts its mass where it will do the most good, at the top and bottom (assuming a vertically applied load) where the compressive and tensile stresses are greatest.
555711
The "secret" is rebar (reinforcing bars of iron).  Poured concrete is of cource fluid and would leak unless poured into water-proof forms (slabs).  The rebar becomes embedded in the concrete and gives it extra strength once the concrete is cured.  Thus the road bed is much thinner than the main supports (that hold up the weight of traffic and the entire bridge).
284837
Answering that question depends on many things:\n\n1- What material do you want to construct with (concrete, steel, timber....)\n\n2- The type of stresses acting on the member under study\n\nthese two keywords shall guide you to the design criteria, however, I can tell you a general criteria for designing anything.... you have one equation, one of its sides is the actual stress acting which can be calculated as follows\n\nstress= force / area of cross section\n\nand the other side is to be the allowable stress stated in the material's code under the corresponding case of loading (if the member is designed for moment and sheer, the flexure and the sheering allowable stresses should be taken into consideration)\n\nthe actual stress should'nt exceed the allowable but even be less that the allowable with a reasonable factor of safety.
761947
neither ..I would construct a wider bridge as I think a bigger erection would be useful in these circumstances
448243
minimal. \npower to weight ratio is significantly more important, as is wing design (the "lift" it can generate).\nplacement only concerns the weight distribution.
856591
You left out a LOT of info, like\n1) Loaded as column or beam?\n2) If beam, concentrated or distributed load?\n3) What kind of wood?\n4) Answer based on engineering equations or building code?
526830
Depends on what you are fabricating. \nAre you talking about making the material itself or fabricating structural components from stainless materials?\n\nAnd what type of material? What grade of stainless? What configuration? Angle iron or I-beam? Welded or bolted?\n\nSounds like you need to talk with an experienced estimator and/or structural engineer.
847529
One of the vibration modes in an earthquake is a horizontal or side-to-side motion.  A triangular building can be thought of as an arch.  While it is better capable of handling vertical forces (i.e., the building itself), an arch can also deal with horizontal forces.\n\nA rectangular building, however, has its weight resting on vertical pillars or walls.  These stuctures are designed to hold the weight of the building that is pressing down vertically.  They can't handle too much horizontal force else the weight of the building will come down at a angle outside the footprint of the walls.\n\nAn easy example is to take a sheet of cardboard and bend it in two.  Put the free ends on a table and push the folded side back and forth.  You should see that the side towards which you're pushing will resist the force.  Now take another sheet of cardboard and make two parallel folds in it.  As before, put the free ends down on a table.  Now push one of the top edges in the same manner.  You should be able to easily flatten the cardboard.
435357
I construct life size bridges from toothpicks which are strong enough to be used by pedestrians all over the UK.\nI've recently retired though as it takes up quite alot of my time and alot of glue.
548986
The simple answer?  For ease of calculations.  When you load a pinned truss, the only forces which will exist are along the axis of the members.  When you load a welded truss, however, there will be some forces generated by the bending of the members.  This would make the amount of additional information and calculation almost prohibitively difficult for the average person.  In most situations, the answers you need for design and analysis are close enough to the "pinned" answers, so engineers do it that way.  Does this cause some error?  Sure, but engineering is just a way to apply modeling equations to the real world, and comes with some errors anyway.  That's (one of the reasons) why they design with safety margins and factors...
987781
Not sure what you are asking exactly, but in the world of machine design, a structure is an assembly whose number of degrees of freedom is zero. More simply, one in which there is no relative motion. The most basic 'structure' is a simply supported beam. Another very obvious structure is a truss. An arch is a structure as well but it is technically a preloaded structure, i.e., is has negative 1 degree of freedom. There are many types of joints, but all can be classified on how many degrees of freedom they allow. Often call full or half joints. The six lower pairs (joints with surface contact rather than line or point contact between links) are 1) revolute joint, 2) prismatic joint, 3) Helical joint, 4) cylindrical joint, 5) spherical joint, 6) planar joint\n\nReaction is a little different. According to Newtons 3rd law, any force exerted from one body onto another is reacted by the second onto the first. In engineering, we are concerned with how and where a body reacts these forces. For instance, a simply supported beam with a large mass in the middle will react the mass equally at both ends. However, if we move the load so that it is directly above one of the supports, the other support will not contribute any reaction force to support the load.
590343
I have an idea for you. Go to the site I provided for the source. It's a truss bridge with an arch. The best of both worlds. The most important thing is the arch. That is where all of the strength comes from in a bridge. I hope that helps.
290922
I'm not sure what a microstructure is really but I know that on softer soil or ground that often a floating concrete structure design is used, beginning in the 1880s or maybe earlier.  Because the gorund is soft, instead of driving piles down to the bedrock, they covered a large area with a steel grid and filled it with concrete, this allowed them to start building skyscrapers and larger structures.  It may be a little different today, but the floating idea was that it ballanced itseld, and heavy objects, really heavy, are placed to maintain this balance so it doesn't tilt.  Sorry if you already know all of this and it is no help, I just thought it was interesting.
115208
engineered wood is stronger.
955988
Well, almost every engineered product such as cars and bridges and rockets and even iPods require drawings to show how they're going to be made.  Even for 3D objects, those drawings are still largely 2D, and 2D geometry is indispensible in the development of those 2D drawings.  This is true even for computer workstations that work with 3D representation of products, because all the cross sections are still 2D, and engineers need those cross sections to help with the analysis.
1145134
so that the signals can come in...and bounce back out....it saves energy....also...it can gather more signals than just a flat plate that will let signals just bounce off the surface\n~Brendon
789492
An engineer, would require the weight "per foot" of the beams, and the number and location of support locations under each beam.\n \nFirst is to calculate the "dead load" and "deflection" of beams.\n\nSecond, afterwards one may calculate the live load and prescribe its bearing upon beams....\n\nIt's all in the details, the details, the details...\n\nThis is the best I can do , with what information you presented...