The origin of the steel skyscraper

Posted August 23rd 2017

Although they are undoubtedly still impressive, skyscrapers have become a common feature of modern cities that we have become accustomed to seeing on busy skylines such as New York and London. Constantly evolving, they push the limits of architectural design, with the Burj Khalifa pushing an imposing 828 metres in height. However, this is a far cry from the humble origins of the modern skyscraper which began in 1884 with a small structure of only 10 storeys in Chicago.
The Home Insurance Building of Chicago, designed by William Le Baron Jenney, was the first structure to utilize a steel skeleton on the interior to support its weight. This is one of main factors a building must have in order to be classed as a skyscraper in modern architecture so despite the relative lack of height, the Home Insurance Building is what kickstarted the evolution of skyscrapers.
Jenney was the man who came up with the idea of relying on the strength of metal to support his vision, rather than stone. At the time the building was constructed this was unheard of and the city of Chicago halted construction of the building at one point to investigate its stability, so new was the idea. Although Jenney initially thought an iron frame would be the best option, he switched this to steel half way through the project, which would go on to become an incredibly important decision.
As architects began to incorporate steel and other metals into the construction of their buildings, it became possible to start pushing the limitations of height as buildings became stronger and more stable. Although the first skyscraper may only have been 10 stories tall, todays skyscrapers are defined as having at least 40-50 floors and are usually higher than 100 metres, although many go far above this. Modern skyscrapers do not have load bearing walls as they used to, due to their height, and instead architects must consider how to counteract things like wind and seismic loads through their structure. Most modern skyscrapers use a tubular design, a concept made popular by designer Fazlur Rahman Khan in the 1960s, as this allows them greater flexibility in their design rather than having to confirm to a rectangular or box shape. There are many famous examples of both designs still in existence.

How does heating metal affect its properties?

Posted August 14th 2017

Applying heat to different metals can have a dramatic effect on them and can completely alter their structural, magnetic and electrical properties. There are several methods that can be used to change metals through heat, in order to enhance more favourable qualities, and the varying methods that are used will depend upon the metal and the desired result.

Thermal Expansion

Heating metal can increase its volume, length and surface area, as the heat displaces atoms from their usual position which alters the structure. This is known as thermal expansion and the amount of growth depends on the metal. Examples of this can be seen in everyday life when things such as pipework in bathrooms and the plumbing of houses expand and contract in hotter and cooler months. A common side effect of this is burst pipes.


Iron, cobalt and nickel are all naturally magnetic materials, or ferromagnetic materials. When heat is applied to them it can reduce their natural magnetic properties to a point so low that it is completely gone. This point, which is different for every metal, is known as the Curie temperature. For cobalt this is 1110 degrees Celsius whereas Nickel is much lower at only 330 degrees Celsius.


Some metals are able to effectively reduce, or halt, the flow of an electric current. This is known as resistance and how resistant a metal is depends on how quickly electrons are able to pass through it. When metal is heated, electrons can gather energy more quickly which allows them to move faster and thus increases the level of resistance as they are more likely to scatter and collide. Similarly, a drop in temperature can result in a drop in resistance as the electrons move more slowly.

Different heat treatments include the processes of annealing, normalising, hardening and tempering. These are used to alter the properties of various metals and gain an end result better suited to the intended use of the metal. The aim may be to strengthen, soften, increase ductility or provide uniformity to name a few.


What is galvanizing?

Posted August 5th 2017

Galvanizing, or galvanization, is the term used for the process of applying a layer of zinc to steel or iron, in order to create a protective coating. It is commonly used as a method of protecting metals from corrosion as the layer of zinc prevents the metal from oxidizing.

There are several ways in which galvanizing can protect the base metal. Firstly, it creates a protective layer which protects the base metal from corrosion by offering sealed protection from the surrounding environment. The zinc will prevent elements such as water getting through, unless it is scratched or damaged badly enough to expose the metal underneath. The outer layer of zinc usually slows the corrosion of the base metal too, preserving its longevity through ‘galvanic corrosion’.

There are several methods of galvanizing.

Hot-dip galvanizing

The method of hot-dip galvanizing involves submerging the base metal in molten zinc, to produce a thick and robust ‘outer shell’. This method is quick to perform, which makes it economically attractive, but it is not suitable for use on everything and can be inconsistent in the results it produces.


Pre-galvanizing has similarities to hot-dip galvanizing and involves cleaning sheet metal before immersing it in hot, molten zinc. Large steel coils can be quickly galvanized using this method, with more reliable and uniform results than hot-dip galvanizing. However, once the coil is cut to produce smaller pieces of metal uncoated edges are left exposed.


Electro-galvanizing utilises an electric current to deposit zinc ions on the base metal, as opposed to melting the zinc like other methods. The zinc ions are deposited on the positively charged base metal, and in a similar way to pre-galvanizing this method is popularly used on large rolls of sheet metal. This method offers a consistently uniform coating, but it is generally thinner than the results obtained using the method of hot-dip galvanizing.

Although the process of galvanizing offers a lengthy period of protection, some damage is inevitable if exposed to the elements and over the years the coating will degrade. If proper measure are taken, such as regular paint coatings and maintenance then the life of the galvanized steel can be prolonged.