11.21. The pin-jointed structure shown in Fig. P11.21 is constructed of two 0.025- m-diameter tubes having the following properties: A = 5.4 × 105 m², I 3.91 x 10 m, E 210 GPa. The stress-strain curve for the tube 2.5m B 6.3 kPa T4.2 kPa FIGURE P11.21. material can be accurately approximated by three straight lines as shown. If the load P is increased until the structure fails, which tube fails first? Describe the nature of the failure and determine the critical load. 11 22 Time 0.075 0.075 dwith the logo 0.025