Civil Thinking

Problem Statement

Beam Subjected to Distributed Loading

A prismatic beam of span 1 m is subjected to the following loading and support conditions.

Supports:
• Support at x = 0 m
• Support at x = 1 m

Distributed Loads:
• 1 kN/m acting from x = 0 to 1 m

Required:
• Determine the support reactions
• Draw the Shear Force Diagram (SFD)
• Draw the Bending Moment Diagram (BMD)

Structural Configuration

Beam structural configuration

Free Body Diagram

Beam free body diagram

Equations of Equilibrium

Equilibrium equation M = 0 Expanded form W1·0.5 + R2y·1 = 0 Substitution 1 kN×0.5 m + 0.5 kN×1 m = 0 Solved reaction

Equilibrium equation Fy = 0 Expanded form W1 + R1y + R2y = 0 Substitution 1 kN + 0.5 kN + 0.5 kN = 0 Solved reaction

ΣFy check 1 kN + 0.5 kN + 0.5 kN = 0 = 0 ΣM check 1 kN×0.5 m + 0.5 kN×1 m = 0 = 0

Shear Force Diagram

Shear Force Diagram for Loaded Beam under Distributed Loading

Shear Force Values

Position (m)Shear (kN)Remark
00.5Start of beam
0.50Zero shear location
1-0.5End of beam
1-0.5Just before point load / reaction
10Just after point load / reaction

Bending Moment Diagram

Bending Moment Diagram for Loaded Beam under Distributed Loading

Bending Moment Values

Position (m)Moment (kN·m)Remark
00BeamStartMoment
00AtPointLoadMoment
00AtDistLoadStartMoment
0.5-0.125ZeroShearMoment
10BeamEndMoment
10AtPointLoadMoment
10AtDistLoadEndMoment

Bending Moment Checks at Key Sections

s = 0
(0.5) × 0 = 0
ΣM = 0
s = 0
(0.5) × 0 = 0
ΣM = 0
s = 0
(0.5) × 0 = 0
ΣM = 0
s = 0.5
(0.5) × 0.5 = -0.25
0.125 (UDL resultant)
ΣM = -0.125
s = 1
(0.5) × 1 = -0.5
(0.5) × 0 = 0
0.5 (UDL resultant)
ΣM = 0
s = 1
(0.5) × 1 = -0.5
(0.5) × 0 = 0
0.5 (UDL resultant)
ΣM = 0
s = 1
(0.5) × 1 = -0.5
(0.5) × 0 = 0
0.5 (UDL resultant)
ΣM = 0

Solution

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