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  • Chassis Breakage

    Discussion in 'Calculations' started by binulagos, Jan 31, 2013.

    1. binulagos

      binulagos Member

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      Can any one help me since iam having problems with breakage of chassis for flat body trailers.
      The beams used are H beams of 18 inches height.The max load of trailer is 40 tons.Any design will be a great help to me.The length of trailer is 12 metres
       
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    3. Lochnagar

      Lochnagar Well-Known Member

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      You are not specific about what exactly the problem is:-
      compressive flange of I beam - buckling - because it is not adequately supported transversely
      excessive loading - resulting in excessive stress at some point
      cyclic loading - resulting in fatigue cracks
       
    4. ChrisW

      ChrisW Well-Known Member

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      If you are seeing breakage rather than bending I suggest you check the design does not 1)apply a point contact load, 2) have a sudden change of stiffness anywhere, 3) have a hole pattern for bolting etc in a straight line, 4) have any welding on or near the top/bottom faces 5) any welding whatsoever on high strength or heat treated steel.
      I would expect an H section to bend rather than break so look for all these issues.
       
    5. Dan Pohly

      Dan Pohly Member

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      I agree with the replies of both Lochnagar and ChrisW - they are giving you good information. In addition, please realize that trailers are rated in several ways and you should understand exactly what the 40 ton rating refers to. Trailers can be rated by: 1) frame capacity - this is an evenly distributed load along the length of the trailer; 2) the lesser of axle, wheel and tire ratings; 3) concentrated load rating; and perhaps there are even more types of ratings. For example, your trailer may be rated for 40 tons but 20 is supposed to be over the trailer axles and 20 over the truck axles. A 40 ton concentrated load in the center of the frame, as another example, may exceed the frame distributed load rating. Please review the trailer manufacturer's documentation to see what the 40 ton rating means and then consider whether the actual loading is consistent with the rating.
       
    6. Suresh Navandar

      Suresh Navandar New Member

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      I agree with all reply, You have to be specific what is exact problem of bending or it is breakage. Also how load is distributed. In my opinion, you have to make your section with gussets & truss if you want to reduce section thickness, but it will increase in cost of production. Every thing is depends on cost VS no of production.
       
    7. binulagos

      binulagos Member

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      THANKS everybody for the valuable responses.The load carrying is cement and it is uniformly distributed.We are having problems of breakage or cracks on beams only when the load carried is cement.As i mentioned the beams used is 18 inches which is having a flange thickness of 15 mm and web thickness of 12 mm.The breakage or crack is seen near to axle area and sometime near the middle portion of the chassis.We have about 8 cross beams of same size welded across with the two main beams.
       
    8. Lochnagar

      Lochnagar Well-Known Member

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      It is a puzzling story - and without seeing some photographs of the exact detail it is hard to comment. The story that this problem is only occurring when the semi trailer is carrying cement is puzzling - however, I might suggest that there is something "different" about the route that the semi trailers are taking - when they are carrying cement - since cement is usually carried to a construction/building site - which generally tend to have very rough terrain - which could be generating loads that might not have been envisaged at the design stage - the chassis could be flexing considerably - the suspension units might be bottoming out on the rough terrain.
      The I beams should have web stiffeners at the point where the suspension units are welded on (whether they be steel springs with equalizing beams - or air suspension units). Additionally, web stiffeners are usually fitted to deal with the tension field in the web. The "weld detail" - is crucial too - for a good design too - and if the design has been poorly detailed in this respect - this will not help matters.
      In engineering - the "devil is in the detail of the design" - and without some pictures I think it will be difficult for any one of us to comment further.
       
    9. binulagos

      binulagos Member

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      Thanks Mr Lochnagar.I will soon post the pictures
       
    10. binulagos

      binulagos Member

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      Dear all,
      pl find the attached pictures......may be this can help me[​IMG][​IMG]
       
    11. binulagos

      binulagos Member

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      Dear all,
      pl find the attached pictures......may be this can help me

      IMG01726-20130204-1506_zpsd6aa245e.jpg

      IMG01724-20130204-1136_zpse28b1198.jpg
       
      Last edited by a moderator: Feb 5, 2013

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