Question

Which of the following is true in a fixed beam having concentrated load at one-third point?

(a) first hinge is formed at centre of beam

(b) after first hinge, moment at that point increases

(c) after first hinge, moment at that point decreases

(d) after first  hinge, moment at that hinge remains constant

I got this question by my school principal while I was bunking the class.

The query is from Plastic-Collapse Load topic in chapter Plastic and Local Buckling Behaviour of Steel of Design of Steel Structures

Answer 1

Correct answer is (d) after first  hinge, moment at that hinge remains constant

For explanation I would say: In a fixed beam having concentrated load at one-third point, first hinge forms at one of the end supports. As load is increased further, moment at this hinge remains constant at Mp, while the moments at the other support and load point increase until second hinge is formed. When load is further increased, the moment at these two hinges remain constant at Mp, until third and final hinge is formed to make the beam a mechanism. The final ultimate load will be 33% higher than first hinge load.