The strong ones emerge in the last few days fears for the stability of the 432 Park Avenue skyscraper in Manhattan (New York). The building, a streamlined one reinforced concrete tower of 425 m and 102 floors mainly used to house luxury apartments, appears to suffer from unusual structural issues – cracking phenomenon and presence of widespread cracks – raising doubts among residents and professionals. What is the nature of these problems from a technical point of view? And how much do you really need to worry about?
How the 432 Park Ave skyscraper in Manhattan is made
With a height of approximately 425 m and 102 floors, 432 Park Avenue is one of the tallest residential skyscrapers in the world and is among the most impressive in the United States. Although it once held the record as the tallest residential building in the Western Hemisphere, that record is now held by Central Park Tower. The load-bearing structure is made of high-strength reinforced concrete, with framed systems and a central stiffening core that guarantees global stability and the right resistance against horizontal forces (such as actions produced by the wind).
To counteract the strong oscillations induced by the wind and limit daily annoyances to residents – typical for such slender buildings – a damping system of the TMD (Tuned Mass Dampera technology similar in all respects to that used in the famous Taipei 101).
The distinctive architectural element is the facade: a grid in white concrete obtained through a special mixture that appears to be at the center of the current disputes regarding the damage observed. However, there is still no clear technical evidence of this.
The skyscraper problems that have alarmed New York
The skyscraper is affected by a widespread cracking phenomenon, present and evolving for some time and in several points of the structure. However, official documents are missing, technical assessments that allow the severity of the damage and its location to be precisely assessed. From the material circulating on the net, we observe a distribution of cracks on different levels, but it is not clear whether these involve primary structural elements or secondary parts, such as infills or cladding. It is therefore possible that some of the most obvious cracks – those that at first glance appear most dangerous – perhaps concern components of the building organism without a structural role. In X’s post below you can see the cracks and structural problems.
In any case, regardless of the position and type of damage, it is clear that the building – considered as a whole, not only in the structural part but also in the building components secondary – manifests a condition of stress anomalous, which represents the beginning of a problem to be addressed. While concrete cracking is a known phenomenon and generally tolerated within certain limits in structural calculation, the presence of extended cases in ordinary conditions is not acceptable and should be contained already in the design phase: in essence therefore, there are some problems!
Is the 432 Park super skyscraper in danger of collapsing?
A crack pattern that does not show worsening over time could have a limited impact on the load-bearing capacity of the structure. In engineering terms, this type of damage corresponds to exceeding one serviceability limit state (acronym SLE), and not one ultimate limit state (acronym as SLU), which represents a much more severe static condition, which needs to be carefully safeguarded. Violation of an SLE compromises the functionality of the work, its appearance and durability over timebut does not imply an immediate risk of collapse.
However, if neglected, the problem can accelerate the degradation phenomena typical of reinforced concrete: the cracks favor the entry of atmospheric agents, exposing the reinforcements to corrosion. Over time, steel bars can lose strength (as they corrode), and this can continue until structural safety is compromised, leading the structure to breach an Ultimate Limit State.
Furthermore, extensive cracking increases the risk of concrete fragments detaching from the facadeswith potential dangers for pedestrians in the surrounding areas. In fact, episodes of this type seem to have already occurred recently.
