Support Reactions of a Trapezoidal Slab with Three Points of Support

$W_1 = 3600 \left[ \frac{1}{2}(2.20)(5.40) \right] = 21,384 ~ \text{N}$

$W_2 = 3600 \left[ \frac{1}{2}(1.60)(5.40) \right] = 15,552 ~ \text{N}$

$W = W_1 + W_2 = 36,936 ~ \text{N}$
 

$\Sigma M_{R1} = 0$

$3.6R_C = (5.4 - 1.8 - 1.2)W_1 + (1.8 - 1.2)W_2$

$3.6R_C = 2.4(21,384) + 0.6(15,552)$

$R_C = 16,848 ~ \text{N}$
 

 

$\Sigma M_C = 0$

$3.6R_1 = (1.8 - 0.6)W_1 + (5.4 - 1.8 - 0.6)W_2$

$3.6R_1 = 1.2(21,384) + 3(15,552)$

$R_1 = 20,088 ~ \text{N}$

$R_A + R_B = 20,088 ~ \text{N}$   ←   Equation (1)
 

$\Sigma M_{R2} = 0$

$1.1R_A = 0.2(36,936)$

$R_A = 6,715.64 ~ \text{N}$
 

 

From Equation (1)
$6,715.64 + R_B = 20,088$

$R_B = 13,372.36 ~ \text{N}$
 

Summary:
R_A = 6,715.64 N       Answer: [ B ]
R_B = 13,372.36 N       Answer: [ C ]
R_C = 16,848 N       Answer: [ A ]