Shear Force & Bending Moment Explained

 

Civil Engineering me Shear Force (V) aur Bending Moment (M) beam design ke sabse fundamental aur important concepts hote hain. Ye dono parameters decide karte hain ki beam safe hai ya fail ho sakti hai. 👉 Click here for the best video tips

Aaj hum ek simply supported beam with uniformly distributed load (UDL) ke example se in dono concepts ko step-by-step samjhenge.

🔹 Given Data (Problem Details)

👉 Length of Beam (L) = 6 meter

👉 Uniform Load (q) = 10 kN/m

👉 Beam dono ends par supported hai (Simply Supported Beam)

🔹 Step 1: Support Reactions Calculation

👉 Formula:

👉 RA = RB = (q × L) / 2

👉 Calculation:

👉 (10 × 6) / 2 = 30 kN

✔️ Left Support Reaction (RA) = 30 kN

✔️ Right Support Reaction (RB) = 30 kN

👉 Ye reactions beam ko balance me rakhte hain (equilibrium condition)

🔹 Step 2: Shear Force (V) Concept

👉 Shear Force wo internal force hota hai jo beam ko cut (kaatne) ki koshish karta hai

👉 Behavior samjho:

Left end par shear force +30 kN hota hai

Dheere-dheere load ki wajah se decrease hota hai

Beam ke center par 0 ho jata hai

Right end par −30 kN ho jata hai

👉 Important: ✔️ Shear Force ka diagram linear (straight line) hota hai

✔️ Isse hum SFD (Shear Force Diagram) kehte hain

🔹 Step 3: Bending Moment (M) Concept

👉 Bending Moment wo force hai jo beam ko bend (modne) karta hai

👉 Maximum bending moment center par aata hai

👉 Formula:

👉 Mmax = (q × L²) / 8

👉 Calculation:

👉 (10 × 6²) / 8 = (10 × 36) / 8 = 45 kN·m

✔️ Maximum Bending Moment = 45 kN·m (center par)

👉 Important: ✔️ Bending Moment Diagram (BMD) parabolic (curve) hota hai

🔹 Physical Understanding (Concept Clear karo)

👉 Socho beam par load laga hai:

Shear Force beam ko slide/cut karne ki koshish karta hai

Bending Moment beam ko jhukane (bend) ki koshish karta hai

👉 Isi wajah se:

Support par beam strong honi chahiye (shear ke liye)

Center par beam strong honi chahiye (bending ke liye)

🔹 Important Summary (Exam + Site dono ke liye)

👉 Supports par: ✔️ Shear Force = Maximum (±30 kN)

✔️ Bending Moment = Zero

👉 Center par: ✔️ Shear Force = Zero

✔️ Bending Moment = Maximum (45 kN·m)

🔹 Key Points (Yaad rakhne wale)

✔️ Shear Force max at supports

✔️ Bending Moment max at center

✔️ SFD → Straight line

✔️ BMD → Parabolic curve

✔️ V → Beam ko cut karta hai

✔️ M → Beam ko bend karta hai

🔹 Practical Use (Site + Design)

👉 Ye concepts use hote hain:

Beam design me

RCC structure analysis me

Load calculation me

Structural safety check me

👉 Agar SFD & BMD galat hua to: ❌ Beam crack ho sakti hai

❌ Structure unsafe ho sakta hai

📌 Conclusion

Shear Force aur Bending Moment Civil Engineering ke backbone concepts hain. Inhe samajhna bahut zaroori hai chahe aap student ho ya site engineer. Proper understanding se aap safe aur efficient design kar sakte ho.