Structural Progressive Collapse

Structural progressive collapse occurs due to the failure of primary structural elements that result in the failure of the adjacent structural elements. The structural failure can result in the collapse of the whole structure or a large part of it. The progressive structural collapse can due to factors such as design errors, inferior materials, or as a result of natural factors such as earthquakes and Tsunamis(Craven, 2018). A building can also experience progressive structural collapse due to deliberate acts such as terrorism, war, or demolition.

Although no building is risk-free from progressive structural collapse, engineers need to perform informed risk assessment to reduce the chances of collapse. Engineers should consider methods of improving structural integrity and robustness to cater to local failures. To prevent progressive structural collapse, engineers need to incorporate the following measures: one, structural redundancy where redundant load paths are incorporated in a vertical load-carrying system. Redundancy ensures there are alternate load paths when local failure of primary structural elements occurs. Second, engineers need to use ties when constructing structures. The failure of significant structural elements leads to load redistribution as well as the deflection of members(Starossek, 2018). The process requires load transfer to the entire structure through load paths. Tying enhances a building structure to transfer loads to the adjacent members through the load paths..

Third, engineers should employ ductility when designing steel structures. For steel structures, ductility is attained through the use of high toughness steel metals that can maintain overall and local structural stability. This is achieved by establishing connections between structural elements that surpass the toughness and strength of the material at the base. In the event of a disaster, ductility ensures links of members have the strength to navigate huge deformations caused by loss of vital structural elements(Starossek, 2018). Finally, progressive structural collapse is prevented by ensuring the structure has adequate shear strength. This is achieved by designing vulnerable locations such as slabs and perimeter beams to hold out excess shear loads that can cause bending due to the loss of an element. Engineers should ensure the shear capacity surpasses flexural capacity to guarantee a ductile response.

Three glazing system countermeasures 

The three glazing system countermeasures include blast-resistant glazing in blast enhanced frames, secondary windows, and blast-resistant fixed point glazing. Blast resistant glazing in blast reinforced frames is aimed at eliminating the risk of flying glass shards. It uses toughened glass that can resist blast pressure without damage as long as it is fitted in a rigid and robust frame(Center for Protection of National Infrastructure, 2014). The system used toughened or laminated glass and enhanced time blast frame to resist pressure from a blast. The secondary glazing is employed in situations where it is not possible to replace windows with blast-resistant glazing in blast enhanced frames. It is designed to inhibit external glazing from penetrating the building during an explosion. They are either fixed within the window reveal or where the thickness of the wall is reduced to the inner face. The final gazing system countermeasure is blast resistant fixed glazing system is used mainly in commercial buildings to reduce the visual impact of support systems (Center for Protection of National Infrastructure, 2014). This system can resist pressure from a blast since it is fixed with blast-resistant glass.

References

Center for Protection of National Infrastructure. (2014). Guidance Note: Measures to Improve the Blast Resistance of Glazing. CPNI.

Craven, V. D. (2018). How to Avoid Progressive Collapse in Your Building. Retrieved from Buildings.com: https://www.buildings.com/news/industry-news/articleid/3614/title/nist-provides-construction-strategies-to-avoid-progressive-collapse

Starossek, U. (2018). Progressive Collapse of Structures. London: I C E-Publishing.