Cantilevers in many modern buildings exceed historical precedents and proportions. These cantilevers can be unenclosed balconies and enclosed occupiable rectangular volumes of buildings. Enclosed portions of buildings are found in New York City buildings in which the Owners have purchased air rights over adjacent properties or within property lines and above such ground features as driveways. The cantilevers are typically steel-framed for air rights buildings and integrated with diagonals or Vierendeel trusses that extend into the overall building framing. For enclosed occupiable cantilevered stories constructed within property lines, the protruding structural framing is typically steel and attached to the building framing with beam-to-column connections. The last type of framing is of particular interest. The design of long cantilevers, cantilevered enclosed occupiable stories, and atypical back-span conditions require consideration and caution on the part of the designer. Engineers should carefully review layouts, bracing, stiffness, deflection compatibility, detailing, and vibration that can affect more than one cantilevered floor to avoid problems during construction and the long-term performance of cantilevered structures.
…
Author Archives : Julie Mark Cohen, Ph.D., P.E., SECB
Julie Mark Cohen is a Consulting Structural and Forensic Engineer and an Historian of Engineering Design. Her research is entitled “Cognitive Errors in Recurring Failures of Engineered Artifacts.” Her eventual book is entitled Unintentional Engineering Failures by Design. (jmcohen@jmcohenpe.com)
On April 29, 2021, I attended a virtual meeting of SEAoNY’s President’s Breakfast Roundtable: Engineering Post-Pandemic. In my assigned break-out room, I listened to the attendees talk about the push for “sustainability” and, to achieve this goal, “optimization” of structural framing. This article discusses the evolution of engineering over the past decades and notes the consequences of misunderstanding “optimization.” It reiterates my observation that a lack of 3-D structural framing systems resulted in damage to many structures during the 1994 Northridge earthquake. These structures were pulled apart in the same manner as they were designed – that is, as a collection of two-dimensional vertical and horizontal planes of framing.
…
Recurring Structural Failures
Forensic practice in structural engineering typically entails seeking technical causes of failures. Occasionally, discussions of technical causes are disseminated through publications or conference presentations. However, the underlying or root causes of failures are seldom disseminated, because they are rarely sought. …
“Put away your swords. They will get rusty in the dew.”
– Othello, Act 1, Scene 2, by William Shakespeare, circa 1603
Corrosion has been a problem since the beginning of the Iron Age, circa 1200 BC. Before the Industrial Revolution, corrosion was recognized and respected in hand-produced objects, such as weapons. After the advent of machinery that was used to fabricate metal alloys for structural framing members and components exposed to the elements, corrosion found new targets. The metal alloys include but are not limited to wrought iron, cast iron, hot-rolled steel, and stainless steel. …