Interactive Roofing Timber Structure Design Simulator

Roofing Timber Structure Design Simulator

Created By: Ir. MD Nursyazwi

This simulator is based on proper engineering calculation and analysis methods for timber structure design. However, it is essential to always consult a local professional engineer for any actual construction or design project. Professional oversight ensures compliance with local building codes and a safe, reliable final product.

Instructions on How To Use

1. Select your desired design standard and truss type from the dropdown menus.
2. Input the structural parameters and applied loads in the fields below. All values should be in meters (m), kilonewtons per square meter (kN/m²), or megaPascals (MPa).
3. Click the "Calculate Design" button to run the simulation.
4. Review the generated "Data Output" and the animated "Graphical Simulation" to visualize the recommended structural members.
5. Explore the "Science Explanations" and "References" for further academic context.

Data Input

Design Standard MS 544 (Malaysia) BS 5268 (British) EN 1995 (Eurocode 5) NDS (American)

Truss Type King Post Truss Queen Post Truss Fink Truss Howe Truss Warren Truss Pratt Truss

Rafter Size

Purlin Size

Batten Size

Roof Span (m)

Rafter Spacing (m)

Purlin Spacing (m)

Batten Spacing (m)

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Dead Load (DL) in kN/m²

Live Load (LL) in kN/m²

Wind Load (WL) in kN/m²

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Allowable Bending Stress (fb) in MPa

Allowable Deflection (Delta_allow) in mm

Graphical Simulation

An animated 3D-like representation of the recommended structural members.

Data Output

Enter parameters and click 'Calculate' to see the results.

Graphs and Charts

A visual representation of the calculated load factor.

Science Explanations

The design of timber roofing structures is governed by principles of structural mechanics, adhering to established engineering standards to ensure safety and stability. The system is fundamentally composed of a hierarchy of members:

• Rafters: These are the primary inclined members supporting the roofing system, transferring loads from the purlins and roof covering down to the walls or columns. Their sizing is dependent on the roof span, which dictates the bending moment, and the rafter spacing.
• Purlins: Running perpendicular to the rafters, purlins provide a framework to support the roof covering. They are subjected to both gravity and wind loads, and their required cross-sectional properties are determined by the purlin spacing and the span between rafters.
• Battens: The smallest members, battens are laid on top of the purlins to support individual roof sheeting or tiles. Their design is a function of the batten spacing and the imposed loads from the covering material.

The simulation uses a simplified approach to determine the design load (P_d), which is a factored combination of the applied loads. The most common load combinations include:
P_d = 1.2 x Dead Load + 1.6 x Live Load or 1.2 x Dead Load + 1.6 x Wind Load
The final design load is the largest value from these combinations. This load is then used to calculate the internal forces on each member. For instance, the maximum bending moment (M) for a simply supported beam is given by:
M = (P_d x L^2) / 8
where L is the member span. The required section modulus (Z_req) is then determined by the flexural stress formula:
Z_req = M / Allowable Stress
where Allowable Stress is the allowable bending stress of the timber. The simulation selects a member with a section modulus greater than the required value.

Beyond the Basics: A Glimpse into Professional Analysis

While the formulas above provide the foundational principles, a full professional analysis involves more detailed checks to ensure safety and code compliance. Here are some of the critical factors that a structural engineer would consider:

• Bending Stress (fb) and Material Properties: The bending stress is the maximum stress a timber member can withstand before failing. It is a fundamental property of the timber grade that dictates the member's strength. The design check ensures that the applied stress does not exceed the permissible bending stress. The Material Properties also include the Modulus of Elasticity (E), which is a measure of the material's stiffness.
• Deflection (Delta_allow): This is a serviceability limit state that governs how much a structural member is allowed to bend or sag under load. While a member may be strong enough to avoid failure, excessive deflection can lead to non-structural damage (like cracks in finishes) and an uncomfortable feeling of "bounce." The simulation checks if the calculated deflection exceeds your specified allowable deflection.
• Shear Capacity: This is the ability of a member to resist forces that cause it to slide or "shear" apart along the grain. This is especially critical near supports or connection points where shear forces are highest. A timber member's shear capacity is determined by its cross-sectional area and shear strength.
• Compression Perpendicular to Grain: Timber has different strengths depending on the direction of the force relative to its grain. It is much stronger in compression parallel to the grain than perpendicular to it. This is a crucial check at bearing points and connections where a member rests on another.

References

• Malaysian Standard: MS 544
• British Standard: BS 5268
• Eurocode Standard: EN 1995 (Eurocode 5)
• American Standard: National Design Specification (NDS) for Wood Construction

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