Steel is one of the popular construction materials next to concrete in the construction industry. The high strength and ductility are the primary properties of steel that make its place in almost all the famous skyscrapers around the world.
Steel structures are developed by individual steel members, welded or bolted together to get a final unit. The slender members and joints are the critical points on a steel structure that must be designed for critical stresses with utmost care. Any variation or mistake can result in structural failures of the steel structure, which varies with the type of load acting and the type of structure.
The article explains the critical failure modes of steel structures.
Types of Failures in Steel Structures
The major types of failures observed in a steel structure are:
- Compression Failure
- Tension Failure
- Flexure Failure
- Shear Failure
1. Compression Failure in Steel Structures
When considering a steel structure, the members that are subjected to compression are columns and braces. When the compression load acting on the axis of the member is high (higher than the load for which it was designed), it results in compression failure or buckling of the member.
The design of the column structure involves the determination of a parameter called the slenderness ratio. The slenderness ratio is defined as the ratio of the cross-sectional area of the structural element to the length of the member. This parameter influences buckling in structures—higher the slenderness ratio of the given member more the chance to buckle.
2. Tension Failure in Steel Structures
The tensile stress failure is observed in a member under tension load. Brace members or hangers of the steel structure are subjected to tension failure. The tensile load acting on the member pulls the member beyond its material strength, which results in the tensile failure of the member.Â
Tension failure in steel structural elements occurs in different stages. The phenomenon starts with the necking of the material cross-section and, finally, material failure. Necking is the reduction of cross-sectional area under tensile load. The failure occurs when the material section reaches the least cross-section.
3. Flexural Failure in Steel Structures
Flexural failures occur in flexural members like beams and girders. The flexural members, when subjected to a high level of flexural loadings, bend, or causes buckling. Due to the high strength of steel, they are designed to be slim and efficient. This can result in buckling or bending of the member. Heavy and thick flexural members are less susceptible to flexural failure.Â
Flexural members are subjected to flexural loads that create compression and tension forces in the member. It is not always possible to expect the loading action in the center of the flexural member. So, an eccentricity in loading is likely that would fail the compression flange of the steel beam. The eccentricity would create a twisting moment to the beam flange, and the beam starts to move laterally. This is called lateral-torsional buckling.
Lateral restraints are provided to prevent buckling in steel structures due to flexural loadings. The flexural strength is very much dependent on the material strength. The member undergoes failure if the flexural loading is greater than the material strength.
Column is a compression member that undergoes similar failure when it is subjected to bending stresses.
4. Shear Failure of Steel Structures
Steel structure is a combination of connections, i.e., member to column connection, member to girder connection, etc. Shear failure prominently occurs in these connection areas. Each connection in a steel structure has its shear stress value. If the value is not considered correctly during the design of connection, failure occurs. Steel structures are made either by bolted connection or welded connection or a combination of both.
Frequently Asked Questions
The major types of failures observed in the steel structure are:
1. Compression Failure
2. Tension Failure
3. Flexure Failure
4. Shear Failure
When the compression load acting on the axis of the member is high (Higher than what the member was designed for), it results in compression failure or buckling of the member. The design of the column structure involves the determination of a parameter called the slenderness ratio. The slenderness ratio is defined as the ratio of the cross-sectional area of the structural element to the length of the member. This parameter influences buckling in structures. Higher is the slenderness ratio of the given member more the chance to buckle.
Steel structure is a combination of connections, i.e., member to column connection, member to girder connection, etc. Shear failure prominently occurs in these connection areas. Each connection in a steel structure has its own shear stress value. If the value is not taken correctly during the design of connection, failure occurs. Steel structures are made either by bolted connection or welded connection or a combination of both.
Flexural members are subjected to flexural loadings that create compression and tension forces in the member. It is not always possible to expect the loading action in the center of the flexural member. So, an eccentricity in loading is likely that would fail the compression flange of the steel beam. The eccentricity would create a twisting moment to the beam flange, and the beam starts to move laterally. This is called lateral-torsional buckling.
Lateral restraints are provided to prevent buckling in steel structures due to flexural loadings. The flexural strength is very much dependent on the material strength. The member undergoes failure if the flexural loading is greater than the material strength.
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