The design of steel structures includes the selection of cross-section type, construction method, operation and construction site. Design in steel frame buildings is very essential. Below we will learn more about the design of these structures.

In order to be able to obtain the required materials for structures, much attention must be paid to one stage of construction, which is the stage of structure analysis and design. When the building is of steel frame type, the design and analysis of steel structures becomes more important. These structures are framed and the role of the frame in them is to stabilize the entire structure and transfer dead loads, live loads, earthquake and snow loads from the structure to the foundation.

In calculating, analyzing, designing and strengthening steel structures and placing columns for these structures, the greatest attention should be paid to criteria such as the type of cross-section, the method of laying and arranging the cross-section, the support distances, the type of bracing or clamps, the type of structure strengthening system and the location of the structure.

These analyzes are usually designed using advanced software. Software like ITBS, Sep and Safe are used for this purpose. In general, the purpose of designing a structure is to specify the configuration, dimensions and specifications of its parts. In order to analyze and review, you must first know the types of steel structures.

Types of steel structures

Hot rolled frame structures: Sections made in iron smelting and manufacturing plants.

Cold-rolled frame structures or LSF: sections connected outside construction plants and with different tools; These sections are mostly used in villa buildings outside the city.

Shell structures, such as liquid or gas storage tanks, and suspended structures, which are mostly used in parametric architectural works and designs.

Different methods for analyzing and designing steel structures

Steel structures are analyzed and designed in the following three ways:

- Allowable stress design (ASD) or elasticity method
- Maximum strength or plastic design method
- Finite State Design (LSD) method

Below, we will learn about each of these methods separately.

Allowable stress design (ASD) or elastic method

The allowable stress method is one of the oldest methods of analysis and design of steel structures. In this method, the effects of possible decrease in resistance and possible increase in loads are done with the help of a factor called confidence factor and in just one step. In this method, the structural elements are designed so that the calculation stresses in them do not exceed the permissible values under the influence of the assumed operational loads. The formula of this method is as follows.

(Reliability factor > 1) / (Failure stress or yield stress) = Allowable stress

Maximum strength or plastic design method (LRFD)

In LRFD method, safety is done in two stages and load increase is considered using load coefficients and resistance reduction is considered using resistance reduction coefficients. In this method, the ultimate design resistance or ultimate bearing capacity of the member in each section must be greater than or equal to the current voltages in that section under the action of the calculated loads on the structure.

LSD limit state design method

In this method, part of the reliability factor is applied to the loads and part of the reliability factor is applied to the resistors. This means that both loads increase and resistance decreases. Design uncertainty is due to both loads and resistances; Therefore, it is better to consider both doubts and uncertainty separately.

Design and analysis of the structure according to steel specifications

Steel structures should be designed and analyzed based on steel properties such as tensile, shear, hardness, creep, displacement and fatigue. Below we mention these cases and their impact on the design and analysis of steel structures

Shear properties in the analysis and design of steel structures

The shear strength at rupture is usually determined under shear stress. This resistance should be about 0.57 times the yield stress of the steel. Shear elastic modulus expresses the ratio of shear stress to shear stress in the elastic range of structural steel. Usually, the shear elastic modulus of structural steel can be taken as 75.84 GPa or the following formula can be used to calculate the shear elastic modulus.

(G =E/2(1+μ

G: Elastic shear model of steel

E: Steel elasticity model

U: Poisson’s ratio

Difficulty in designing steel structures

Stiffness is the resistance of structural steel against inelastic deformation. The Test Standard and Definitions for Mechanical Testing of Steel Parts (A370-05) typically specifies three different test models for evaluating the hardness of steel. These tests include the Brinell test, the Rockwell test, and the portable test.

These tests are able to estimate the hardness of structural steel. Determination of steel hardness is used not only to test the uniformity of various products, but also to evaluate the tensile strength of steel.

Creep in the design of steel structures

The creep rate is determined according to the gradual change in steel stress under constant pressure. In some cases, creep is caused by constant stress or by fire. Of course, experts sometimes agree that creep can be omitted in the design and construction of frame steel structures. But regarding the effect of creep on fire, this cannot be ignored.

Analysis and design of steel structures according to the method of clamps or reinforcement

One type of analysis and design of steel structures is performed according to the bracing method. Clips or supports are very important and necessary to increase the building’s resistance to earthquakes and winds. In this case, a horizontal strengthening system must be created on the building to transfer lateral forces to the foundation and prevent horizontal displacement.

The magnitude of the horizontal forces applied due to wind depends on the following factors:

Wind speed

Aerodynamic shape of the building

Facade surface condition

Methods of hardening or hardening

The structural steel frame can be reinforced in one of the following ways:

Solid tire systems

Wind truss frame systems

Design of steel structures according to the components of the building’s internal spaces

Choosing the right system for the interior components of a building depends on various factors. The following methods are commonly used in the construction of steel beam-based roofs:

Concrete slab in situ on suitable molds

Precast concrete slab

Steel deck with in-situ concrete