Steel Contraction Essay

1676 words - 7 pages

Construction of steel bridges in the 19th - 20th century mostly depended on the use of rivets for connection. Bridges got built at a much greater rate than any other steel or iron construction using rivets. Riveting was a better-proven and understood method of construction. They made a very strong connection when applied but were very prone to corrosion through rusting. Existing historic steel bridges are aging and experiencing increased levels of deterioration due to increased demand in vehicle weight and traffic volume. These bridges are increasing becoming weaker as the rivets used in their contact wear out leading to instability and unreliable due to the poor construction. Assessment ...view middle of the document...

Most of the inspections are routine visual inspections for determining a bridge’s functional and physical requirements. During this inspection, inspectors use tools for cleaning, sanding, probing, measuring and recording all the notable conditions. The inspectors use ladders and power lifts to access the bridges and other small hand tools such as flashlights, magnifying glasses and measuring tools.
When a crack gets observed during the initial inspection in a steel member, it needs to be identified and characterized. Inspectors usually use magnetic particle testing or dye penetrant testing. While using the magnetic particle testing, an external magnetic field, or an electric current, magnetic iron oxide particles get applied over the magnetized specimen. They then use ultra-violet light to detect the particles. When the particles are magnetic field in passed it attracts the magnetic particle, and they hold on to the edges of the affected are revealing the defect and its location. In the dye penetration type, the inspector applies a high-visual-contrast dye that penetrates to the affected surfaces revealing the defects and the locations.
The other inspections are in-depth, special and damage inspections. The in-depth inspection involves a hand-on, close-up inspection of the members below or above the water levels to note and identify vulnerabilities that do not show using the normal routine procedure. This process may also be used during the inspection of fracture-critical members.
A known deficiency gets monitored through the special inspection process. For example, it gets implemented in monitoring steel members with an identified fatigue crack up to the time that the crack can be repaired. Damage inspections get defined as unscheduled inspections used to determine the structural damage that results from extra loads or natural calamities such as earthquakes and hurricanes off from human actions such as car collisions. Unscheduled inspections mostly require the application of more advanced methods such as NDE testing.
Steel Bridges NDE Tests
Bridges made up of steel superstructures such as girder contact members or steel girders, are vulnerable to cracking which is caused by flaws in high-stress locations, weld zones, and other components prone to fatigue such as rivets. There are two common NDE technologies available for identifying, locating and assessing the cracks.
Ultrasonic testing. This uses ultrasonic waves (sound energy emitted in high-frequency) to assess the cracks. Ultrasonic testing can be used to identify and size internal cracks and surface cracks. Inspectors use ultrasonic testing on steel components’ surfaces after cleaning the surface of all corrosion and old paint. The waves travel through the steel at speeds varied by the steel’s properties until a crack (discontinuity) gets detected and reflects the signal through the, material to the receiver. The inspector then calculates the distance to the crack after the he has...

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