Suspension 150 m: four moving loads, BM at 40 m

Assumption. The two girders share the load equally, so each girder/cable carries half of every wheel load. No dead load is given, so only the moving train is considered.

Part 1: Maximum BM at 40 m from the left support

For a three-hinged stiffening girder (span $L$ = 150 m, dip $d$ = 20 m) a unit load at distance $a$ gives

$$H = \frac{M_{0C}}{d},\qquad M_x = M_{0x} - H\,y_x,\qquad y_x = \frac{4d\,x(L-x)}{L^2}$$

At $x$ = 40 m: $y_x = \dfrac{4(20)(40)(110)}{150^2} = 15.644$ m, so $y_x/d = 0.7822$. The influence-line ordinate for $M$ at 40 m is

$$\eta(a) = M_{0x}(a) - \frac{y_x}{d}\,M_{0C}(a),\quad M_{0x} = \begin{cases} a(L-x)/L & a \le x \\ x(L-a)/L & a > x \end{cases},\quad M_{0C} = \frac{a}{2}\ (a \le 75)$$

The ILD peaks at the section ($\eta$ = 13.69 m at $a$ = 40 m), is positive up to $a$ = 60.8 m and negative beyond, so the loads must be bunched near the section. Trying the train (200 kN leading, to the right) and moving it in small steps, the maximum occurs with the 150 kN load at the section (40 m): loads are at 44, 40, 36 and 32 m.

Sum for the whole train = 9056.0 kN m. Each girder takes half:

$$M_{max,40} = \frac{9056.0}{2} = 4528.0\ \text{kN m}$$

Neighbouring positions give less (for example, with the 200 kN load at 40 m the sum is 8829.3 kN m, and with the 300 kN load at 40 m it is 8682.7 kN m), confirming the maximum.

Part 2: Maximum tension in the cable

$H$ is greatest when the mid-span moment $M_{0C}$ of the simple beam is greatest. Scanning the train gives the maximum when the 300 kN load is at mid-span (loads at 83, 79, 75, 71 m):

$$M_{0C} = 26825\ \text{kN m (whole train)},\qquad \text{per girder } 13412.5\ \text{kN m}$$ $$H_{max} = \frac{13412.5}{20} = 670.62\ \text{kN}$$

The tension is greatest at the supports, where the slope is $\tan\theta = 4d/L = 0.5333$:

$$T_{max} = H\sqrt{1+\tan^2\theta} = 670.62\times 1.1333 = 760.04\ \text{kN}$$

Answer: Maximum BM at 40 m = 4528.0 kN m per girder (with 150 kN load at the section); maximum cable tension = 760.04 kN in each cable (at the supports).