Beam Diagrams
1. **Problem Statement:**
We have a simply supported beam of length 10 m with two downward forces: a 10 kN force at 3 m from the left support acting at an angle downward-left, and an 8 kN vertical downward force at 7 m from the left support (3 m from the right support). We need to find the shear force diagram, axial (normal) force diagram, and bending moment diagram.
2. **Calculate support reactions:**
Let the left support reaction be $R_A$ (vertical) and the right support reaction be $R_B$ (vertical). Since the beam is simply supported, horizontal reactions are zero (no horizontal loads given).
Sum of vertical forces:
$$R_A + R_B = 10 + 8 = 18 \text{ kN}$$
Taking moments about left support (point A):
$$\sum M_A = 0 = -10 \times 3 - 8 \times 7 + R_B \times 10$$
$$-30 - 56 + 10 R_B = 0$$
$$10 R_B = 86$$
$$R_B = 8.6 \text{ kN}$$
Then,
$$R_A = 18 - 8.6 = 9.4 \text{ kN}$$
3. **Shear force diagram (V):**
- Start at $x=0$, $V=R_A=9.4$ kN upward.
- At $x=3$ m, apply 10 kN downward force (component vertical assumed full 10 kN for shear since no horizontal shear given), shear drops:
$$V = 9.4 - 10 = -0.6 \text{ kN}$$
- At $x=7$ m, apply 8 kN downward force, shear drops:
$$V = -0.6 - 8 = -8.6 \text{ kN}$$
- At $x=10$ m, reaction $R_B=8.6$ kN upward, shear returns to zero.
4. **Axial force diagram:**
No horizontal forces or axial loads given, so axial force is zero along the beam.
5. **Bending moment diagram (M):**
- Moment at left support $M_0=0$.
- Between 0 and 3 m:
$$M(x) = R_A \times x = 9.4 x$$
- At $x=3$ m:
$$M(3) = 9.4 \times 3 = 28.2 \text{ kN}\cdot\text{m}$$
- Between 3 and 7 m:
$$M(x) = R_A x - 10 (x - 3) = 9.4 x - 10 (x - 3) = 9.4 x - 10 x + 30 = -0.6 x + 30$$
- At $x=7$ m:
$$M(7) = -0.6 \times 7 + 30 = -4.2 + 30 = 25.8 \text{ kN}\cdot\text{m}$$
- Between 7 and 10 m:
$$M(x) = R_A x - 10 (x - 3) - 8 (x - 7) = 9.4 x - 10 (x - 3) - 8 (x - 7)$$
$$= 9.4 x - 10 x + 30 - 8 x + 56 = (9.4 - 10 - 8) x + 86 = -8.6 x + 86$$
- At $x=10$ m:
$$M(10) = -8.6 \times 10 + 86 = -86 + 86 = 0$$
**Final answers:**
- Support reactions: $R_A=9.4$ kN, $R_B=8.6$ kN
- Shear force diagram: starts at 9.4 kN, drops to -0.6 kN at 3 m, -8.6 kN at 7 m, returns to 0 at 10 m
- Axial force diagram: zero everywhere
- Bending moment diagram: linear segments with values $M(0)=0$, $M(3)=28.2$, $M(7)=25.8$, $M(10)=0$