Jane Embury looks at wind loading and glazing systems.
We’ve recently seen the chaos that bad weather can bring. Storm Christoph was just the latest named storm to hit the UK.
It caused flooding around a factory producing a crucial Covid-19 vaccine in north Wales.
It also led to some 2,000 properties in the north of England and north Wales being evacuated.
But while our weather can be atrocious, it pales into insignificance with what can happen in other parts of the world.
In the Pacific, the responsibility for naming tropical storms is coordinated through the World Meteorology Organization (WMO).
Fourteen regional governments submit 10 names each, and the WMO Regional Specialized Meteorological Center (RSMC) in Tokyo is then responsible for naming each storm.
Katrina
It’s a little different in the Atlantic. Tropical storms that reach a wind speed of 39mph are given a name while, if it reaches 74mph, it is redefined as a hurricane – while keeping its original name.
Normally, names can be reused after six years – except when reuse of a particular name would be considered insensitive. Katrina, for example, has been deleted from reuse.
That 2005 hurricane brought massive destruction to Louisiana, Mississippi and Alabama. It also killed nearly 2,000 people and caused more than $100 billion in damage.
Katrina is therefore the bad sheep whose name has been officially deleted. But it was a different member of the hurricane family that was of greater significance for the glass industry.
Andrew, in 1992, was the second costliest hurricane in US history, after Katrina. Dozens were killed and, and, at the time, it was the costliest ever natural disaster for insured losses.
National and regional governments and the insurance industry stepped in to drastically improve building codes. One important addition to the code was a requirement for missile-impact resisting glass.
Andrew
Many of the technological advances made to glass and its framing systems stem from Hurricane Andrew. In countries or regions at risk from tropical storms, advanced glazing systems are now a requirement of building regulations.
One primary advance has been in understanding wind loading. In other words, the amount of wind that architectural glass is able to withstand. That, of course, depends on a number of variables such as the building’s height and the size of the glass spans.
Simplistically, in high winds, the exposed side of the glass is subjected to compressive stresses. The opposing side is subjected to tensile stresses. Glass has a high resistance to the former, and a lower resistance to the latter. Its breaking point depends on how it reacts to each stress.
In the UK, BS 6399 and BS 6262 apply, with further guidance supplied by the Centre for Window and Cladding Technology (CWCT). Elsewhere, other standards apply.
These standards allow for a calculation of the uniform load resistance that a glazing system is able to sustain without breaking. They take into consideration, among other things, glass dimensions and its type and thickness.
Typhoon
These are standards that we use when advising customers, here in the UK and internationally. For example, we have supplied roof glazing to a major banking group in Hong Kong, for a corporate-critical project of immense importance.
The glass and framing systems had to provide fire resistance and bomb resistance. Crucially, in a typhoon zone, also to have high wind load characteristics.
Nearer to home, we also supplied to Ocean Terminal in Edinburgh. While Scotland is not in a tropical storm zone, the glass spans used in the retail and leisure complex were particularly large.
The spans were therefore so heavy that wind loading became a significant factor and why our systems were chosen. We were able to combine wind loading with other critical safety factors in a non-intrusive steel frame.
A current debate is how climate change is likely to impact on the strength and frequency of tropical storms. It’s agreed that we’re now in a climate emergency.
Wind is caused by the movement of air masses. The main influence on wind movement is temperature difference between the earth’s equator and poles. It’s generally agreed that global warming is making things worse.
Dynamics
The glass and glazing industry has invested significantly to understand the dynamics of high wind loading and blast pressures. That research has led to glass and framing systems to keep the glazed element intact and in its frame.
Understanding those dynamics has pushed the boundaries of what is now possible with glass. For example, we successfully tested one of our advanced systems against the blast from a lorry bomb.
Of course, bomb blast and wind load cannot be equated. The former is an explosive dynamic shock, while the latter is a static load.
But it demonstrates how glass, an intrinsically fragile material, can be made immensely strong. We do therefore now have glazing systems that are resistant to blast or wind pressures.
Those tropical storms put Christoph into perspective, despite all the disruption to peoples’ lives and loss of property.
We simply hope that, globally, better weather prevails.
Photo by Anandu Vinod on Unsplash
