Table of Contents
SAFETY CONCEPT IN STRUCTURAL STEEL DESIGN
In the members of the structure, there will be a gap between the internal load and the internal resistance. The gap can be filled in one of two ways:
a) In elastic design, the permissible stresses are reduced by a factor of safety to a value less than the material’s strength.
b) In ultimate strength design, the internal load is multiplied by a factor known as the load factor, whereas ultimate strength is calculated using yield or buckling strength.Letbe the internal load be the increase in Let is the internal strength, it is the external strength.If it is the potential under-strength,
The estimated strength should be equal to the internal load multiplied by a factor larger than one, according to this formula. This is the most comprehensive load analysis, in which the entire strength of the system is assessed and loads are enhanced by a load factor.AlsoIN STRUCTURAL STEEL DESIGN, THE SAFETY CONCEPT
The dividing factor is known as the factor of safety, and it is used in the elastic design approach.
Factor Of Safety
The factor of safety is added to the yield stress of the material in the elastic design of steel structures to obtain the working stress or permitted stress in the material.
The following factors are taken into account while determining the value of the factor of safety:
After testing a large number of specimens, the average strength of a material is established. Varying specimens of a given structural material have different strengths.The values of design loads are still unknown, however dead load values may be accurately calculated. However, because live load, impact load, wind load, snow load, and other factors are dependent on available statistics, they cannot be determined with precision. These loads’ probable values have just been determined.
The values of internal forces in various structures are determined by the analysis methods used. Different approaches have varying degrees of precision. More precise are the procedures that include comprehensive analysis.
A small value of factor of safety may be used if the structure’s analysis is done precisely.Various processes are performed on structural steel during fabrication. When a hole is punched in a structural member, the surrounding material is distorted, resulting in substantial residual stresses. Warping and buckling of elements can occur during the welding process. Welding creates a lot of residual stress. Uncertain stress is applied to structural members.
The effects of temperature changes and support settling are unknown. These effects frequently cause damage to a well-designed structure. The capability of
Load Factor (Q)
The load factor is determined by the nature of the load, the support circumstances, and the structural member’s geometrical shape. The applied load is directly proportional to the bending moment at any segment. As a result, the bending moment M is proportional to the bending moment W.
The totally plastic moment is related to the collapse load as well.clip image016If the maximum bending moment isn’t reached,if the maximum working load is equal to,where Z denotes the elastic modulus
Working stress or acceptable stress is denoted by the letter f.Again,Where= modulus of plasticity, andSteel yield stress is a term that refers to the tension that a piece of steel
Alternatively, load factor Q = S x FS is the shape factor, which is equal toas well asF is the safety factor employed in the elastic design.In general, 1.85 is used as the load factor for gravity loads.
When wind loads are taken into account, the allowed stress is increased by a factor of two.percent. For wind loads, this reduces the load factor to 1.4
It’s the ability to rebalance the load. Simple beams are predetermined. Because the fixed beam is 2 degrees uncertain, it has two redundant actions. Because an indeterminate construction can transfer the load, a fixed supported beam is preferable. When the load increases, the support becomes plastic and the beam becomes simply supported. Simply supported, on the other hand, does not go through the plastic hinge stage and instead fails immediately.
1. Site adaptations: If the structure is a building, for example, the designer must create a plan that includes appropriate arrangements for rooms, corridors, stairways, windows, elevators, emergency exits, and other features, all of which must be adapted to the site so that it is feasible, aesthetically pleasing, and cost-effective. Functional planning is the term for this.
2. Structural scheme: Functional planning determines the structural scheme. The structural design comprises the location of columns in buildings; it must be worked out in conjunction with the functional plan, and sufficient space between the finished ceiling and finished floor must be expected for column placement.
3. Structural analysis: After the loads have been defined and the design has been laid out, structural analysis must be carried out to determine the internal forces.
4. Member proportionality: Members must be proportioned with a safety factor in mind.
5. Safety factor: When developing design specifications to provide appropriate values for margins of safety, reliability, and probability of failure, the following factors must be considered.Material variability in terms of strength and other physical qualities Uncertainty about the anticipated Loads Internal forces are estimated with great precision.Corrosion could occur.The extent of the devastation and the number of people who died there significance of the operation Workmanship quality
The structural design safety can be assessed in one of two ways:Design with Allowable Stress Designing a load and resistance factor