The real and virtual systems are shown in Fig. 7.18(b) and (c), respectively. The x coordinates used for determining the bending moment equations for the three members of the frame, A B, B C, and C D, are also shown in the figures. The equations for M and M_{v} obtained for the three members are tabulated in Table 7.11 along with the axial forces F and F_{v} of the members. The horizontal deflection at joint C of the frame can be determined by applying the virtual work expression given by Eq. (7.35):

\begin{aligned} 1\left(\Delta\right)=& \sum F_{v}\left(\frac{F L}{A E}\right)+\sum \int \frac{M_{v} M}{E I} d x \end{aligned}      (7.35)

\begin{aligned} 1\left(\Delta_{C}\right)=& \sum F_{v}\left(\frac{F L}{A E}\right)+\sum \int \frac{M_{v} M}{E I} d x \\ 1\left(\Delta_{C}\right)=& \frac{1}{A E}\left[\frac{3}{4}(-12.5)(15)+\frac{1}{2}(-11.67)(20)-\frac{3}{4}(-27.5)(15)\right] \\ &+\frac{1}{E I}\left[\int_{0}^{15} \frac{x}{2}(-1.67 x) d x\right.\\ &\left.+\int_{0}^{20}\left(7.5-\frac{3}{4} x\right)\left(-25+12.5 x-x^{2}\right) d x+\int_{0}^{15} \frac{x}{2}(11.67 x) d x\right] \\ (1  \mathrm{k}) \Delta_{C}=& \frac{52.08  \mathrm{k}^{2}-\mathrm{ft}}{A E}+\frac{9,375  \mathrm{k}^{2}-\mathrm{ft}^{3}}{E I} \end{aligned}

Therefore,

\begin{aligned} \Delta_{C} &=\frac{52.08  \mathrm{k}-\mathrm{ft}}{A E}+\frac{9,375  \mathrm{k}-\mathrm{ft}^{3}}{E I} \\ &=\frac{52.08}{(35)(29,000)}+\frac{9,375(12)^{2}}{(29,000)(1,000)} \\ &=0.00005+0.04655 \\ &=0.0466  \mathrm{ft}=0.559  \mathrm{in} \\ \Delta_{C} &=0.559  \mathrm{in} . \rightarrow \end{aligned}

Note that the magnitude of the axial deformation term is negligibly small as compared to that of the bending deformation term.