🔹 Introduction
In any German-engineered hangar, rafters are one of the most critical structural elements. They form the roof framework, transferring loads from the roof covering to the vertical columns.
In simple terms:
👉 Rafters = the backbone of the roof system
🔹 What Are Rafters?
Rafters are inclined structural members that:
- Support roof loads (dead + live + environmental)
- Connect to columns or ridge beams
- Define the roof slope and geometry
They are typically made from:
- Hot-rolled steel sections (I-beams, H-beams)
- Built-up welded sections (for large spans)
🔹 Types of Rafters Used in Hangars
1. 📐 Tapered Rafters (Most Common in German Design)
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Technical Concept:
- Depth varies along the length
- Thicker near supports (high moment zones)
- Thinner at mid-span
Engineering Advantage:
- Reduces steel weight
- Matches bending moment distribution
2. 🔺 Truss Rafters
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Technical Concept:
- Made of multiple members forming triangles
- Loads converted into axial forces
Engineering Advantage:
- Ideal for spans > 60–100m
- Lightweight yet strong
3. 🌉 Straight Uniform Rafters
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Technical Concept:
- Same cross-section throughout
- Simple fabrication
Engineering Trade-off:
- Easier to build
- Less material-efficient than tapered rafters
🔹 Load Transfer Mechanism
Rafters are responsible for carrying multiple loads defined under
Eurocode EN 1991:
- Dead Load (DL): Roof sheets, insulation
- Live Load (LL): Maintenance loads
- Wind Load (WL): Uplift + lateral pressure
- Snow Load (SL): Critical in European climates
Load Flow:
Roof → Rafters → Columns → Foundation
🔹 Bending Moment Behavior
For a typical rafter:
- Maximum bending moment occurs near supports
- Minimum at mid-span (in portal frames)
That’s why German designs prefer tapered rafters.
🔹 Connection Details (Highly Critical)
🔩 Rafter-to-Column Connection
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- Moment-resisting connections
- High-strength bolts (pre-tensioned)
- Sometimes welded plates
🔗 Ridge Connection
- Connects two rafters at the top
- Must handle compression + alignment forces
🔹 Design Considerations
1. Span Length
- Short span → simple rafters
- Long span → truss or tapered rafters
2. Deflection Limits
- Excess bending causes roof sagging
- Controlled using stiffness design
3. Lateral Stability
- Rafters need:
- Purlins
- Bracing systems
to prevent buckling
4. Thermal Expansion
- Steel expands with temperature
- Expansion joints may be required
🔹 Why German Rafters Are Unique
✔ Optimized using structural analysis software
✔ Fabricated with high precision
✔ Designed per Eurocode EN 1991
✔ Minimize material while maximizing strength
🔹 Common Failures (If Poorly Designed)
- Buckling due to insufficient bracing
- Excess deflection
- Connection failure
- Wind uplift damage
🔹 Final Insight
Rafters are not just beams—they are engineered load-distribution systems that:
- Define the roof geometry
- Control structural performance
- Ensure long-term stability
In German hangars, rafters are precision-optimized components, making the structure both lightweight and extremely strong.