CONSTRUCTION OF EPURIES OF BENDING MOMENTS

Lecture

Consider an example of constructing plots of transverse forces Q and bending moments M x

1. We depict the design scheme (Fig. 5.2, a).

CONSTRUCTION OF EPURIES OF BENDING MOMENTS

Fig. 5.2 (a, b)

2. Determine the reaction supports. Initially, we choose an arbitrary reaction direction (Fig. 5.2a).

Since the reaction of R B with a minus, we change the chosen direction to the opposite (Fig. 5 2,6).

Check:

The values of the reactions found are shown in Fig. 5.2 b.

3. The design scheme has three power sections.

4. 1 section About 1 , About 2 :

The origin of coordinates is chosen at the leftmost point O 1 . Consider the equilibrium of the cut-off part of the beam (Fig. 5.3).

Fig. 5.3

Internal forces arise in the section:

Section II O 2 B;

The origin of the coordinates is transferred to the beginning of the O 2 segment (Fig. 5.4).

Fig. 5.4

On the 2nd segment in the moment equation, the arguments (Z 2 ) have the 2nd degree, which means that the plot will be crooked of the second order, i.e. parabola.

In the second section, the transverse force changes sign (the beginning of the section + ga, and at the end -ga), then on the plot M x there will be an extremum at the point where Q = 0. Determine the coordinate of the section in which the value M x is extreme, equating the expression of transverse force on this site is zero.