Repairs to Steel Framed Transition Building
By Stephen McDermott
Steel framed and masonry transition buildings were constructed between 1890 and 1950. They are called transition buildings due to the introduction of steel columns and beams into mass masonry construction that was popular prior to this period.
The introduction of steel columns, steel floor and roof beams as the main structural components of a building became simpler to design and erect a structure. Once steel was introduced as the material for the main frame of the building, construction of such buildings became unlimited as to the heights that could be achieved, as well as the speed in which they could be built. The construction of the main steel frame is similar to modern steel construction, although the assembly of the parts varies from built-up steel section versus monolithic steel sections.
During this time period the interaction of the steel frame and masonry construction and the impact on long-term performance of the exterior facing steel frame and masonry cladding was poorly understood.
Prior to steel frame construction, masonry structures were designed and built with a simple method: the taller the structure, the larger the masonry supports needed to be. Steel frame transition buildings posed an unknown long-term effect with respect to the masonry. The mason viewed the steel frame as an element which could be encased fully within the masonry wall construction. The long-term effect of encasing the steel in masonry results in the trapping of moisture within the masonry and creating oxidation of the steel frame. Masonry alone will transmit moisture causing the encased steel to corrode and expand. As steel expands it grows in volume and two things occur: lateral and vertical displacement of the exterior masonry and loss of steel strength. This develops over decades.
Repairs to transition buildings take many forms from coating the exterior walls to reduce water infiltration to exposing the steel frame to augment the steel due to section loss and installing a waterproofing onto the steel frame to control future corrosion.
Every transition building performs differently depending on the actual construction of the masonry and steel interface and the overall water tightness of the masonry façade. In order to identify the extent of corrosion of the steel frame a destructive review program should be performed to provide an assessment of the extent of active corrosion, determine the impact of the corrosion on the structure, and remediation or repairs.
Buildings are usually designed for a particular life span which varies with respect to the construction materials and details of the material. It is not uncommon for a transition structure with an intended design life span of 80 years to be extended for an additional 50 years or more with the proper maintenance. Periodic review of transition buildings and façade repairs to control water infiltration are necessary to achieve a longer building life.