The fourth question
Let AC midpoint be e and CD midpoint be f.
First, calculate the bearing reaction. Only bearing A bears horizontal reaction, and FA level = 10kN(←).
With the bending moment at point A being zero, Ma = 0 and FB vertical =45kN(↑), the vertical reaction force of bearing B is obtained.
According to the overall stress balance, FA vertical =35kN(↑).
Dismantle the lower part after obtaining the reaction force of the bearing, and only keep the calculation of the upper structure (only keep the stress and dismantle the bearing).
The analysis shows that the graph only needs to calculate each node and ef; The force acting on the BD section is very simple, so we start with BD to calculate:
According to the local stress balance, the BD section has only axial force and no shear moment, so the BD section is 0.
Then calculate the AC part. According to the component balance, there is horizontal force in AC section and shear force in AE section. AE segment Fs= 10kN(-) and CE segment Fs=0. It is known that the shear strives for bending moment, MA=0, ME =-20kN·m, MC=0, and the connection is sufficient.
Finally, calculate the CD segment. Knowing that MC=MD=0, it is easy to get that MCD is a parabola. According to the formula 1/8qL? get
MF = = 40kN·m, even a parabola, the shear diagram obtained according to the bending moment diagram is an oblique straight line, the shear force at point F is 0, the shear force at point C is 40kN, and the shear force at point D is -40kN, even.
The fifth question
Let three concentrated loads be F 1, F2 and F3 from left to right.
First, find the influence diagram of the bending moment at point C. According to the formula MC=ab/L, it is easy to get MC =-15/8m =-1.875m..
The stress is not evenly distributed, so the maximum area is not needed. Just put three concentrated loads at point C for calculation.
F 1 at point c, MC =-52.5kn m.
F2 is placed at point C, and MC =-77.5kn m..
F3 is placed at point C, and MC =-68.75kn m..
Mcmax =-77.5 kn·m was obtained.
The sixth question is extremely simple. Once a quantity is introduced into the formula, the result will come out. If you really don't understand, I'll show you after dinner this afternoon.