Structural engineering help

In summary, the conversation discusses the deflection and maximum bending moment for a timber beam and a joist under specific conditions. The deflection of a timber beam is determined by its dimensions, load, and Young's modulus, while the maximum bending moment for a joist is calculated using its section modulus, span, and UDL. Calculating these values involves considering the end conditions and orientation of the beam or joist, and can be done using tables or calculus.
  • #1
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Will a timber beam deflect more than is safely permitted?
If a timber beam has dimensions of 225 mm by 75 mm and holds a UDL of 3.5 kN/m over a span of 4m. And If Young’s modulus for the timber is 10 kN/mm2, how much will the beam deflect?


A joist bending moment calculation?
A joist has section modulus 187.5 x 103 mm3 and the span is 3.8 m. It carries a Uniformly Distributed Load (UDL) of 1.7 kN/m.

What is the maximum bending moment for the joist
 
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  • #2
k_blow said:
Will a timber beam deflect more than is safely permitted?
A beam is not safe if its maximum stress exceeds the allowable stress for that material. The deflection is not safe only if the stresses are not safe, or if a Code requires a deflection limit (to prevent plaster cracking, for example, if it is a floor beam supporting a ceiling, or for appearance,unsightliness, etc.)
If a timber beam has dimensions of 225 mm by 75 mm and holds a UDL of 3.5 kN/m over a span of 4m. And If Young’s modulus for the timber is 10 kN/mm2, how much will the beam deflect?
Please show your attempt at a solution. What are the end conditions? Which way is the beam oriented? Beam deflections for uniform loads are given in tables, as a function of the load, span, elasticity modulus, and geometric properties of the beam; or can be calculated using calculus.


A joist bending moment calculation?
A joist has section modulus 187.5 x 103 mm3 and the span is 3.8 m. It carries a Uniformly Distributed Load (UDL) of 1.7 kN/m.

What is the maximum bending moment for the joist
Please show your work attempt, please.
 
  • #3
?

I would approach this question by first determining the maximum bending moment for the joist using the formula M = WL^2/8, where M is the maximum bending moment, W is the uniformly distributed load, and L is the span of the joist. Plugging in the given values, we get M = (1.7 kN/m)(3.8 m)^2/8 = 2.79 kNm.

Next, I would calculate the deflection of the beam using the formula δ = (5WL^4)/(384EI), where δ is the deflection, W is the uniformly distributed load, L is the span of the joist, E is the Young's modulus, and I is the moment of inertia. The moment of inertia for a rectangular beam is (bh^3)/12, where b is the width of the beam and h is the height. Plugging in the given values, we get I = (75 mm)(225 mm^3)/12 = 1.64 x 10^6 mm^4.

Substituting all values into the formula, we get δ = (5)(1.7 kN/m)(3.8 m)^4/(384)(10 kN/mm^2)(1.64 x 10^6 mm^4) = 0.012 mm.

Based on this calculation, it appears that the deflection of the beam is well within the safe limit. However, it is important to note that this is a theoretical calculation and other factors, such as the quality of the timber and any potential defects, should also be considered to ensure the beam can safely withstand the given load. It is always best to consult with a professional structural engineer for an accurate assessment and to ensure the safety and integrity of any structure.
 

What is structural engineering?

Structural engineering is a branch of engineering that deals with the design, construction, and maintenance of structures such as buildings, bridges, and other man-made structures. It involves the analysis of the forces and stresses acting on a structure and the determination of the most suitable materials and methods to ensure its stability and safety.

Why is structural engineering important?

Structural engineering is important because it ensures the safety and stability of structures. Without proper structural engineering, buildings and other structures may collapse or fail, causing harm to people and property. Structural engineering also plays a crucial role in the design and construction of sustainable and efficient structures.

What services do structural engineers provide?

Structural engineers provide a range of services, including structural design and analysis, construction supervision, project management, and structural inspection and assessment. They also collaborate with architects and other professionals to ensure that structures are designed and built according to safety and design standards.

What qualifications do structural engineers have?

Structural engineers typically have a degree in civil or structural engineering. They may also have a master's degree in structural engineering or a related field. In addition, they are required to obtain a license to practice in their respective state or country, which requires passing a rigorous exam and meeting experience and education requirements.

How can a structural engineer help with my project?

A structural engineer can help with your project by providing expertise in structural design and analysis. They can ensure that your structure is safe, stable, and meets all relevant building codes and regulations. They can also provide guidance and advice on material selection and construction methods to optimize the performance and longevity of your structure.

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