A three$-$point bend beam shown in Figure $1$ was tested to measure the value of GF$.$ Thebeam was loaded downward as shown in the figure. The dimensions of the beam are S $=800$ mm$,$ b $=100$ mm$,$ and t $=100$ mm$.$ The initial notch length a$0$ was equal to $50$ mm$.$The values of W$0=620$ N$.$mm and S$0=1\mathrm{.}6$ mm were measured. The density of concreteis $2400$ kg$/$m$3.$ Calculate the value of GF $.$Figure $1.$ Three$-$point bend beam