What is Structural Integrity?

Structural integrity is an engineering field that plays a fundamental part of ensuring that structures are fit to do what they are designed (fit for purpose) under normal operational conditions, and are safe when conditions exceed the original design intent. This includes supporting its own weight. Its aim is to prevent deformation, breaking and catastrophic failure of a structure due to load, allowing the structure to perform its duty reliably (being whole and undivided) throughout its predicted lifetime.

Integrity is not just a case of good design; it needs to be maintained for the life of a structure. This requires inspection and maintenance at periodic intervals. Engineers ensure structures are safe, reliable and perform their designed function throughout their lifetime.

What are the Causes of Structural Failure?

Structural failure can occur from a range of different sources. The type of failure is often associated with the industry, environment and application of the structure. The primary reasons for failure are as follows:

• Weak structures. The structure is not strong enough to withstand the load to which it is subject. This is usually due to inappropriate geometric design or material choice
• Structural deterioration. The structure deteriorates due to corrosion, fatigue, wear, rot or creep. Fatigue failures often begin when cracks form at regions of high stress. These cracks grow when subject to cyclic loading, resulting in sudden failure. This is usually due to inappropriate geometric design, material choice or maintenance
• Manufacturing errors. This includes using the wrong materials or not following manufacturing procedures or standards. It can also result from poor workmanship or components being out of tolerance, etc
• Defective material. The materials don’t conform to standards, resulting in a lower load bearing capacity than designed.
• Improper environmental considerations. Engineers may neglect mitigating features for certain environmental conditions, such as natural disasters
• Improper operational conditions. The structure is not used for its intended purpose

At What Temperature Does Steel Lose Structural Integrity?

Structural steels are used in most large construction projects, such as buildings and bridges, in the form of girders etc. The performance of the steel is vital to maintain the required integrity. High temperatures are known to weaken steel, which begins to soften at around 425°C and loses about half of its strength at 650°C. At these temperatures, the steel will begin to buckle and twist if subject to high loads, which will impede structural integrity.

Consequently, engineers must take into account the environmental temperature range that a structure will be subject to over its life span.

How to Calculate the Integrity of Structures

Engineers combine an array of considerations into the design process, such as materials performance, stress analysis and fracture mechanics.

Once built, a construction will need inspection and maintenance to maintain its integrity. To do this, an engineer might:

• Carry out inspections to identify damage. This might involve the use of non-destructive testing (NDT)
• Check that a structure has been built according to the appropriate designs, procedures and standards
• Check that a structure is being used appropriately for the environment designed for
• Recommend and design modifications to address areas of concern

Source: TWI