CAUSE AND EFFECT INVESTIGATIONS: FAÇADE DAMAGE CAUSED BY RUST JACKING

CAUSE AND EFFECT INVESTIGATIONS:  FAÇADE DAMAGE CAUSED BY RUST JACKING

Based on our inspections of facades and building envelopes in New York City, Philadelphia, Trenton, Princeton and many other cities, one very common phenomenon of façade damage is the so called “rust jacking” or “oxide jacking” or “rust burst” caused by corrosion of the steel (structural steel or otherwise).  In fact corrosion of structural steel is the single largest cause of the need for masonry repairs.  It is a phenomenon that can cause damage to structures made of stone, masonry, concrete or ceramics, and reinforced with metal components.  A definition of rust jacking is the displacement (lateral or vertical, hence the term “jacking”) of building elements due to the differential expansion of iron and steel products as the metal rusts, becomes iron oxide and increase in volume.

 

Steel jamb corrosion in a façade window

 

Since the 1850’s, to protect against spread of fire, building regulations in New York City have required the use of masonry as a building separation material.  As a result brick and stone have become the basic building materials used in New York City facades.  They have remained the most common materials used in facades, despite the evolution of façade systems from bearing masonry to infill masonry and to Cavity wall as well as curtain wall systems.  The big problem is, however, that brick and masonry facades are not waterproof and they in fact allow copious amounts of water to enter the building.  The big point we want to make is that MASONRY IS POROUS, plain and simple.  The early builders were relying on building multi-wythe masonry walls for thermal and moisture protection;  when only one wythe wall is used, then the embedded steel will be in some real trouble.

 

 

Corroded steel lintel

 

Metals can be found in buildings as basic components of the structure or used as the structural frame of the structure.  They are also found in devices and systems used to support and/or anchor façade elements.  As the exterior brick or stone or CMU wall is not waterproof, water will enter the building and corrode the steel.  Corrosion is the most common form of deterioration of metals in buildings.  It is an electrochemical oxidation process that results in the deterioration (separation and loss of mass) of the metal.

 

 

Corrosion resulting from contact of two dissimilar metals. (e.g. aluminum post and steel reinforcing).  Dissimilar metals should be isolated from each other.

 

Most commonly corrosion (rust) occurs on steel that is exposed to air and humidity and of course to water.  Other forms of corrosion are galvanic corrosion and pitting of metals.  As steel is rarely present at the very surface of a façade, only in some cases can visual inspections directly determine presence of corrosion.  However even when rust is not readily visible, its symptoms or the damage resulting from “rust jacking“, cracks or movement of façade materials, can be easily observed.  Corrosion of metals in buildings may affect not only the performance of the envelope but also the reliability of the structural frame.

 

Corrosion occurring due to stagnant chloride solution in holes. Can affect aluminum and stainless steel as well.

 

 Façade defects, such as cracks caused by deferential movement, serve to further exacerbate the issue as they allow another path for moisture to enter the wall assembly.  See examples of façade damage below.

 
 

Probable Causes/Deficiencies: Overstress due to movement/load transfer from above or behind.  Corrosion of concealed anchor.

 

 

Probable Causes/Deficiencies: Rust jacking at embedded end of lintel.

 

Case Study:  Cause of Collapse of Terracotta Facade

In one of our inspections we determined that the cause of the façade collapse was the corrosion of structural steel.  Reviews of the façade indicated that long term water infiltration through the terracotta and brick led to long term corrosion of the structural steel frame located between 4” to 8” behind the face of the building (see Photo below).

 

 

Photo above shows the close relationship between structural steel and ornamental façade.  Note the corroded steel column to the left and the corroded steel spandrel beam near the top.  The terracotta façade is laid over the steel frame. 

 

As steel becomes in contact or is saturated with rain water, it rusts.  As it rusts, the steel increases in volume.  This increase in volume could be as much as ten times the original; steel volume with concurrent loss in structural strength.  This increase in volume occurs in a confined space.  It therefore creates pressure against the brickwork or cement or stone or terracotta fixed to the steel.  Over a period of years, this increased pressure or “jacking” action on the adjoining material eventually can snap the exterior brickwork or terracotta or stone work and the brick/stone/terracotta falls off the building to the grade below.  These materials (i.e., the concrete, brick, terracotta, and stone) were not designed to withstand the jacking forces of the rusted steel (i.e., the horizontal forces) and that is they break off.

 

 

Photo above shows failed brick on façade.

 

This exterior wall deterioration is frequently encountered (and repaired) with similarly constructed steel framed buildings in New York City and all other cities.  Parapets and cornices are especially susceptible to failure due to the fact that they are exposed to weather on both interior and exterior faces.  Also, cornices project from the building face, creating an overturning effect on the parapet if not securely tied to the roof and floor structure.


Facade Repair



 Severe corrosion is commonly referred to as “steel growth” which causes “rust jacking,” or the shifting and displacement of masonry units.  When steel corrodes, the steel begins to peel, forming layers that can grow to a thickness of up to 10 times the original volume.  The added pressure from this expansion can shift, lift, or “jack” the above masonry vertically, ultimately causing cracking, shifting, lateral movement, and severe structural damage.  This extreme movement has the potential to cause catastrophic failure of the wall tie system especially if the ties consist of a brick header course.


Corrosion of structural steel is the single largest cause of the need for masonry repairs.  Depending on the severity of the corrosion, the steel may need to be replaced. We can replace steel by shoring the surrounding masonry prior to masonry removal.  This allows us to remove and replace the steel with little hassle, leaving the surrounding area unharmed.  In older buildings, flashings should also be installed, not only to direct water that enters the veneer back to the exterior, but also to protect the steel and slow the rate of corrosion.  We can help you catch steel growth at an early stage in order to perform preventative maintenance, which often prevents the need for extensive and costly structural repairs in the future.

 

Metropolitan Engineering, Consulting & Forensics (MECF)


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