Step 2 --Calculate the shear (y''') in the four segments

Input := 

yppp1[x_] = V0/ EI - Integrate[ w1[u]/EI, {u,0,x}];
yppp2[x_] = yppp1[30] - Integrate[ w2[u]/EI, {u,30,x}];
yppp3[x_] = yppp2[60] - Integrate[ w3[u]/EI, {u,60,x}];
yppp4[x_] = yppp3[100] - Integrate[w4[u]/EI, {u,100,x}];