What is the best angle for a truss bridge?


Design engineers normally try to keep it at 45° as it is the best compromise.

There are advantages in having a steeper angle for the diagonal members and also disadvantages. Greater depths with lesser number of panels and steeper angles result in lesser chord forces. But that also results in increase in the number of panels and consequently more diagonal members and and also vertical members, thus increasing amount of fabrication work.

If the depth of the truss is decided and frozen from functional or architectural or other considerations, and if you try to increase the width of the panels to reduce their numbers then the angle will be very shallow and the axial forces in the diagonal members will increase. The truss will also deflect a little more.

Deciding the optimum panel widths, the optimum truss depths and the optimum angles for the diagonals is a skilled trial and error task for the designer.

Most designers start with 45° and then fine tune it to a little more or a little less on a case to case basis.

These days, computer software has made the task of experimenting convenient and possible .

Various “what if” cases can be examined, unlike in the pre-computer era where intuition, past experience and precedents guided the designers.

Gopalkrishna Vishwanath

Original article link: https://www.quora.com/What-is-the-optimum-angle-for-a-truss-bridge#:~:text=Design%20engineers%20normally%20try%20to,result%20in%20lesser%20chord%20forces.


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