Steel structure solution

With its advantages of light weight, high strength, short construction cycle and excellent recyclability, steel structures have been increasingly widely used in modern construction and engineering fields.However, in the actual design, manufacturing, transportation, installation and maintenance process, steel structure components and their connection nodes may encounter various problems, these problems are directly related to the safety, applicability and durability of the structure.In order to effectively prevent and solve these problems, it is essential to have an in-depth understanding of the basic concepts, material properties, structural behavior and related norms and standards of steel structures.The purpose of this part is to sort out the basic knowledge in the field of steel structure and lay the foundation for subsequent discussion of solutions to specific problems.

(1) Overview of steel structure system

The composition of steel structures usually includes steel plates, steel strips, shaped steels (such as H-shaped steels, I-beams, channel steels, angle steels, etc.), steel pipes and other components, which are welded, bolted or riveted to form a skeleton system that bears and transmits loads.According to the structure form and force characteristics, common steel structure systems can be divided into the following categories：

(2) Material properties and performance requirements

Steel is the main material of steel structure, and its performance directly affects the overall behavior and reliability of the structure.The structural steels commonly used in engineering are mainly carbon structural steels (such as Q235, Q345) and low-alloy high-strength structural steels (such as Q345, Q460).Key material performance indicators include：

Yield strength: The stress when the material begins to undergo plastic deformation, which is the main basis for structural design.
Tensile Strength: The maximum stress that the material can achieve before breaking.
Elongation: The ratio of the total elongation of the material to the length of the original standard distance when it is pulled off, reflecting the plastic deformation capacity of the material.
Modulus of Elasticity: The ratio of stress to strain in the elastic deformation stage of a material determines the stiffness of the structure.
Impact Toughness: The ability of a material to absorb energy and resist fracture under impact loads is particularly important for structures in low-temperature environments.
Fatigue Strength: The ability of a material to resist fatigue damage under cyclic load.
Weldability: Whether the material is easy to form through the welding process and has the characteristics of good joint quality.
Corrosion resistance: The ability of a material to resist erosion by environmental media.

Choosing the right steel grade and ensuring its quality are essential to ensure the safety and economy of the structure.At the same time, the geometric dimensional accuracy and surface quality of steel will also affect the stability (such as local stability) and connection performance of components.

(3) Main failure modes and risks

Steel structures may face a variety of potential risks and problems during their design and service life, and their failure modes can be mainly summarized into the following categories：

Overall Instability (Overall Instability):
Component instability: Such as the instability of the bending of the axis-pressed member, the instability of the bending and torsion of the bending member, and the loss of local stability of the plate under the action of shear stress or bending stress.
Overall instability: such as the instability of the rotation of the connecting nodes of the frame beams and columns, the instability of the bending in or out of the plane of the frame as a whole, and the overall instability of the bending member.
Fatigue Failure: Under the action of cyclic loads (such as mechanical vibration, dynamic load, temperature difference stress), the structure or component cracks and gradually expands and eventually breaks when the stress is much lower than the tensile strength of the material.
Material Deterioration (Material Deterioration):
Environmental factors: such as corrosion, deterioration of steel performance caused by chloride ion erosion, and damage to fire resistance.
Accidental events: such as local or overall damage caused by fire, explosion, impact, etc.
Connection Failure: The welded joint or bolted connection fails under the action of load, such as weld fracture, bolt shear, and enlarged punching of the connecting plate.
Manufacturing and installation defects: Dimensional deviations that do not meet the design requirements, poor welding quality, installation is not vertical or the connection is not dense, etc., may cause stress concentration or reduce the carrying capacity.

A full understanding of these basic knowledge will help to analyze specific problems in a more targeted manner in subsequent chapters and propose effective solutions to ensure the safe and reliable operation of steel structures.

1.1 Overview of steel structure system

Steel structure, as an extremely widely used structural form in modern civil engineering, its core advantage lies in giving full play to the excellent mechanical properties of steel, such as high strength, light weight, good plasticity, corrosion resistance (protected by coating or coating), fast construction speed, and flexible modeling design.These characteristics make steel structures perform well in a variety of engineering scenarios, covering a wide range of fields such as bridges, high-rise buildings, industrial plants, long-span venues, nuclear power plants and even marine platforms.

The overall construction of steel structures usually depends on a series of well-designed components, including beams, columns, supports, secondary beams, platform plates, etc.These components are reliably connected by welding or bolts, etc., to jointly withstand and transmit external forces (such as gravity loads, wind loads, snow loads, seismic effects, etc.) to ensure the safety and stability of the structure.In the design and construction of modern steel structures, the use of high-strength steel is becoming more and more common, which further improves the safety reserve of the structure, reduces the amount of steel used, and optimizes economic performance.

In order to facilitate the understanding of the characteristics and application scenarios of different steel structure systems, the following lists several main types of steel structure systems and their basic conditions：

Overview of the main steel structure system

Understanding these basic systems will help to discuss the common problems that may be encountered in steel structure design and their solutions in the future.Different systems have their own focus on material selection, connection methods, node design, wind resistance, seismic resistance, etc., and need to be reasonably selected and designed according to specific engineering needs.