Composite Sections
Mechanics of Materials · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- The bending stresses in a beam composed of dissimilar materials (Material 1 and Material 2) where E1 > E2 are:
- The composite section is transformed into a section composed of a single material. The centroid and then the moment of inertia
- are found on the transformed section for use in the bending stress equations.
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
A steel-reinforced timber beam is analyzed as one of the composite sections using a transformed area. Given modulus of material 2 (E_2) = 13,700 ksi; modulus of material 1 (base) (E_1) = 26,800 ksi, determine the modular ratio (n).
Given
Find
modular ratio (n)
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except n is given, so isolate n symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 1 — schematic for Transformed area (composite sections) — solve for modular ratio — Composite Sections
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for n:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning n = 0.5112 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1.0224 — kept a factor of two that cancels in the correct rearrangement.
- 0.2556 — dropped that same factor in the other direction.
- 0.5623 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A flitch beam with steel plates bolted to wood is treated as composite sections. Given modulus of material 1 (base) (E_1) = 5,100 ksi; modular ratio (n) = 14.4500, determine the modulus of material 2 (E_2) in ksi.
Given
Find
modulus of material 2 (E_2), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_2 is given, so isolate E_2 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 2 — schematic for Transformed area (composite sections) — solve for modulus of material 2 — Composite Sections (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_2:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_2 = 73,695 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 147,390 — kept a factor of two that cancels in the correct rearrangement.
- 36,848 — dropped that same factor in the other direction.
- 81,065 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A composite steel-concrete deck is transformed into composite sections for stress analysis. Given modulus of material 2 (E_2) = 5,000 ksi; modular ratio (n) = 4.6500, determine the modulus of material 1 (base) (E_1) in ksi.
Given
Find
modulus of material 1 (base) (E_1), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_1 is given, so isolate E_1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 3 — schematic for Transformed area (composite sections) — solve for modulus of material 1 (base) — Composite Sections (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_1:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_1 = 1,075 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2,151 — kept a factor of two that cancels in the correct rearrangement.
- 537.6 — dropped that same factor in the other direction.
- 1,183 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A steel-reinforced timber beam is analyzed as one of the composite sections using a transformed area. Given modulus of material 2 (E_2) = 16,100 ksi; modulus of material 1 (base) (E_1) = 13,700 ksi, determine the modular ratio (n).
Given
Find
modular ratio (n)
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except n is given, so isolate n symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 4 — schematic for Transformed area (composite sections) — solve for modular ratio (case 2) — Composite Sections (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for n:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning n = 1.1752 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2.3504 — kept a factor of two that cancels in the correct rearrangement.
- 0.5876 — dropped that same factor in the other direction.
- 1.2927 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A flitch beam with steel plates bolted to wood is treated as composite sections. Given modulus of material 1 (base) (E_1) = 14,100 ksi; modular ratio (n) = 4.6000, determine the modulus of material 2 (E_2) in ksi.
Given
Find
modulus of material 2 (E_2), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_2 is given, so isolate E_2 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 5 — schematic for Transformed area (composite sections) — solve for modulus of material 2 (case 2) — Composite Sections (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_2:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_2 = 64,860 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 129,720 — kept a factor of two that cancels in the correct rearrangement.
- 32,430 — dropped that same factor in the other direction.
- 71,346 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A composite steel-concrete deck is transformed into composite sections for stress analysis. Given modulus of material 2 (E_2) = 13,700 ksi; modular ratio (n) = 1.8500, determine the modulus of material 1 (base) (E_1) in ksi.
Given
Find
modulus of material 1 (base) (E_1), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_1 is given, so isolate E_1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 6 — schematic for Transformed area (composite sections) — solve for modulus of material 1 (base) (case 2) — Composite Sections (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_1:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_1 = 7,405 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 14,811 — kept a factor of two that cancels in the correct rearrangement.
- 3,703 — dropped that same factor in the other direction.
- 8,146 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A steel-reinforced timber beam is analyzed as one of the composite sections using a transformed area. Given modulus of material 2 (E_2) = 25,800 ksi; modulus of material 1 (base) (E_1) = 11,100 ksi, determine the modular ratio (n).
Given
Find
modular ratio (n)
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except n is given, so isolate n symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 7 — schematic for Transformed area (composite sections) — solve for modular ratio (case 3) — Composite Sections (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for n:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning n = 2.3243 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.6486 — kept a factor of two that cancels in the correct rearrangement.
- 1.1622 — dropped that same factor in the other direction.
- 2.5568 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A flitch beam with steel plates bolted to wood is treated as composite sections. Given modulus of material 1 (base) (E_1) = 7,900 ksi; modular ratio (n) = 3.3500, determine the modulus of material 2 (E_2) in ksi.
Given
Find
modulus of material 2 (E_2), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_2 is given, so isolate E_2 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 8 — schematic for Transformed area (composite sections) — solve for modulus of material 2 (case 3) — Composite Sections (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_2:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_2 = 26,465 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 52,930 — kept a factor of two that cancels in the correct rearrangement.
- 13,233 — dropped that same factor in the other direction.
- 29,112 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A composite steel-concrete deck is transformed into composite sections for stress analysis. Given modulus of material 2 (E_2) = 14,500 ksi; modular ratio (n) = 7.3000, determine the modulus of material 1 (base) (E_1) in ksi.
Given
Find
modulus of material 1 (base) (E_1), in ksi
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except E_1 is given, so isolate E_1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 9 — schematic for Transformed area (composite sections) — solve for modulus of material 1 (base) (case 3) — Composite Sections (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for E_1:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning E_1 = 1,986 ksi to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 3,973 — kept a factor of two that cancels in the correct rearrangement.
- 993.2 — dropped that same factor in the other direction.
- 2,185 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections
A steel-reinforced timber beam is analyzed as one of the composite sections using a transformed area. Given modulus of material 2 (E_2) = 8,900 ksi; modulus of material 1 (base) (E_1) = 5,400 ksi, determine the modular ratio (n).
Given
Find
modular ratio (n)
Start with the thinking
- The governing relation printed in this handbook section is Transformed area (composite sections).
- Everything except n is given, so isolate n symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Composite sections made of two materials are analyzed using the modular ratio to transform one material into an equivalent area of the other.
Figure 10 — schematic for Transformed area (composite sections) — solve for modular ratio (case 4) — Composite Sections (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for n:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning n = 1.6481 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 3.2963 — kept a factor of two that cancels in the correct rearrangement.
- 0.8241 — dropped that same factor in the other direction.
- 1.8130 — rounded an intermediate value before the final step.
Reference: FE Handbook — Mechanics of Materials: Composite Sections