The ratio of the load causing collapse to the working load is called ______.
load factor
The question asks about the specific ratio that relates the load a structure can withstand before collapsing to the load it is designed to handle under normal working conditions. This ratio is a crucial concept in structural engineering, particularly in limit state design or plastic design, as it provides a measure of safety margin.
Load Factor Definition
The ratio of the load causing collapse to the working load is specifically known as the load factor. It represents the multiplier by which the working load must be increased to reach the collapse load of the structure.
Mathematically, the load factor is defined as:
Load Factor = $\frac{\text{Collapse Load}}{\text{Working Load}}$
Where:
- Collapse Load is the maximum load the structure can support before it fails or collapses. This is often determined through plastic analysis in structural design.
- Working Load (or service load) is the load that the structure is expected to carry during its normal operation. This is the load based on everyday use and environmental conditions (like wind, snow, etc.).
A higher load factor indicates a larger margin of safety between the expected working loads and the load that would cause failure.
Analyzing the Options
Let's look at the provided options:
| Option | Term | Explanation |
|---|---|---|
| 1 | collapsing factor | This term is not standard terminology used in structural engineering for this specific ratio. The correct term is "load factor". |
| 2 | shape factor | Shape factor is a property of a cross-section, defined as the ratio of the plastic section modulus to the elastic section modulus. It relates to the geometry of the cross-section and its plastic moment capacity, not directly the ratio of collapse load to working load for the entire structure. |
| 3 | moment factor | Moment factor often refers to coefficients used in structural analysis (like in design codes) to modify moments for factors like buckling or second-order effects. It is not the ratio of collapse load to working load. |
| 4 | load factor | As defined above, the load factor is precisely the ratio of the load causing collapse (ultimate load) to the working load (service load). This aligns with the definition given in the question. |
Significance of Load Factor
The concept of the load factor is central to structural design methodologies, especially in limit state design. Designers determine the expected working loads and then apply appropriate load factors to calculate the design loads. These design loads are compared against the ultimate strength or capacity of the structural members to ensure a sufficient safety margin against collapse.
Ensuring an adequate load factor is critical for the safety and reliability of buildings, bridges, and other structures.
Based on the definitions and comparison with standard structural engineering terms, the ratio of the load causing collapse to the working load is called the load factor.
Important Questions from Plastic Analysis
A triangular beam section having base width ‘b’ and height ‘d’ the section modulus for beam strength is
The shape factor for a solid circular section of diameter D is equal to:
In a steel beam, when the width to thickness ratio of the compression flange is sufficiently large, local buckling of compression flange may occur even before extreme fibre yields. Such sections are generally known as
If the shape factor of a section is 1.5 and the factor of safety to be adopted in 2, then the load factor will be
The plastic theory is generally used for
