Skip to main content \(\require{cancel}\let\vecarrow\vec
\renewcommand{\vec}{\mathbf}
\newcommand{\ihat}{\vec{i}}
\newcommand{\jhat}{\vec{j}}
\newcommand{\khat}{\vec{k}}
\DeclareMathOperator{\proj}{proj}
\newcommand{\kg}[1]{#1~\mathrm{kg} }
\newcommand{\lbm}[1]{#1~\mathrm{lbm} }
\newcommand{\slug}[1]{#1~\mathrm{slug}}
\newcommand{\m}[1]{#1~\mathrm{m}}
\newcommand{\km}[1]{#1~\mathrm{km}}
\newcommand{\cm}[1]{#1~\mathrm{cm}}
\newcommand{\mm}[1]{#1~\mathrm{mm}}
\newcommand{\ft}[1]{#1~\mathrm{ft}}
\newcommand{\inch}[1]{#1~\mathrm{in}}
\newcommand{\N}[1]{#1~\mathrm{N} }
\newcommand{\kN}[1]{#1~\mathrm{kN} }
\newcommand{\MN}[1]{#1~\mathrm{MN} }
\newcommand{\lb}[1]{#1~\mathrm{lb} }
\newcommand{\lbf}[1]{#1~\mathrm{lbf} }
\newcommand{\Nm}[1]{#1~\mathrm{N}\!\cdot\!\mathrm{m} }
\newcommand{\kNm}[1]{#1~\mathrm{kN}\!\cdot\!\mathrm{m} }
\newcommand{\ftlb}[1]{#1~\mathrm{ft}\!\cdot\!\mathrm{lb} }
\newcommand{\ftlbf}[1]{#1~\mathrm{ft}\!\cdot\!\mathrm{lbf} }
\newcommand{\inlb}[1]{#1~\mathrm{in}\!\cdot\!\mathrm{lb} }
\newcommand{\lbperft}[1]{#1~\mathrm{lb}/\mathrm{ft} }
\newcommand{\lbperin}[1]{#1~\mathrm{lb}/\mathrm{in} }
\newcommand{\Nperm}[1]{#1~\mathrm{N}/\mathrm{m} }
\newcommand{\kNperm}[1]{#1~\mathrm{kN}/\mathrm{m} }
\newcommand{\kgperkm}[1]{#1~\mathrm{kg}/\mathrm{km} }
\newcommand{\psinch}[1]{#1~\mathrm{lb}/\mathrm{in}^2 }
\newcommand{\pqinch}[1]{#1~\mathrm{lb}/\mathrm{in}^3 }
\newcommand{\psf}[1]{#1~\mathrm{lb}/\mathrm{ft}^2 }
\newcommand{\pqf}[1]{#1~\mathrm{lb}/\mathrm{ft}^3 }
\newcommand{\Nsm}[1]{#1~\mathrm{N}/\mathrm{m}^2 }
\newcommand{\kgsm}[1]{#1~\mathrm{kg}/\mathrm{m}^2 }
\newcommand{\kgqm}[1]{#1~\mathrm{kg}/\mathrm{m}^3 }
\newcommand{\Pa}[1]{#1~\mathrm{Pa} }
\newcommand{\kPa}[1]{#1~\mathrm{kPa} }
\newcommand{\aSI}[1]{#1~\mathrm{m}/\mathrm{s}^2 }
\newcommand{\aUS}[1]{#1~\mathrm{ft}/\mathrm{s}^2 }
\newcommand{\unit}[1]{#1~\mathrm{unit} }
\newcommand{\ang}[1]{#1^\circ }
\newcommand{\second}[1]{#1~\mathrm{s} }
\newcommand{\lt}{<}
\newcommand{\gt}{>}
\newcommand{\amp}{&}
\definecolor{fillinmathshade}{gray}{0.9}
\newcommand{\fillinmath}[1]{\mathchoice{\colorbox{fillinmathshade}{$\displaystyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\textstyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptstyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptscriptstyle\phantom{\,#1\,}$}}}
\)
Section 8.4 Shear and Bending Moment Diagrams
Shear and moment diagrams are graphs which plot the internal shear and bending moment against the length of the beam.
They allow us to
see the internal forces throughout the entire beam so that we can optimize the design to prevent failures and reduce the overall weight and cost of the structure. A beam is most likely to fail at points where shear and moment are greatest and these diagrams help us find these points.
The previous section presented a method to find the internal forces at a
single point, which is useful; but to find the shear and moment at
every point we need a more powerful approach. The following sections discuss three different methods to produce shear and bending moment diagrams, and concludes with a comparison of the advantages and disadvantages of each approach.
Beams can be supported in a variety of ways as shown in
Figure 8.4.1 . The common support methods are
Simply Supported Supported by a pin on one end and a roller at the other.
Cantilevered Fixed at one end, and unsupported at the other.
Overhanging One or both ends overhang the supports.
(a) Simply Supported(b) Cantilevered(c) Overhanging Figure 8.4.1. Beam SupportsWe will limit our analysis to these three support systems, and since beams primarily support vertical loads, axial forces will not be considered in this section.
