Should a Building Blow Down During Construction?

After an unseasonably warm day, a cold front passed through the New York City metropolitan area on the evening of Monday, 06 December 2021. Along with much colder temperatures, the cold front brought high wind gusts. In Jersey City, New Jersey gusts approaching 60 miles per hour were reported.  Around 8:45 pm, the Jersey City Fire Department received a call for a building collapse with possibly trapped occupants. A four-story building under construction had partially collapsed, displacing five to ten feet off of its foundations, striking an adjacent two-story dwelling and damaging a school. At least 10 residents of adjacent buildings were displaced, some likely permanently because the damaged adjacent dwelling will reportedly be demolished. City officials believe that elements of the partially-constructed building were collapsed by high wind.

It is early in the investigation, of course, and as I have said before, it is not useful to attempt to draw conclusions immediately after a failure. Publicly available information is likely incomplete, may include imprecise or inaccurate information (there are slight discrepancies as to the time of the incident and early reporting identified the building as being three stories) and important details can get lost in the reporting process. More will be learned as the destroyed building is disassembled and removed. More yet will be learned in the course of the litigation that will inevitably follow. I do not have any answers, but I have a lot of questions.

Society, the engineering and architecture professions, and the construction industry generally no longer tolerate “act of God” failures except in extreme circumstances. Despite some contractors having insisted to me that “we don’t get hurricanes here” high winds can happen anywhere during any season and building codes account for that. For a site in Jersey City without exacerbating topographic effects, the design wind speed is about 115 miles per hour (mph). That value represents a three-second gust at a height of 10 meters with an average return period of 700 years. For winds below this threshold, failures of elements and connections should be unlikely, and therefore the collapse risk due to wind effects is very low. In the past, wind design was based on a 50-year return wind speed, which would be about 100 mph. Below that wind level, the risk of wind damage should be low. The wind speeds in the building code do not exactly correspond to the wind gust speeds reported by meteorologists. But it is fairly evident that 40 mph to 60 mph wind gusts should not have damaged the building had it been complete at the time.

The building was not complete at the time. Generally, it is the construction contractor’s responsibility to ensure the stability of work in progress. While December is sort of between the end of hurricane season and the beginning of nor’easter season in the northeast, some high winds are to be expected during the course of a project. There are non-mandatory standards to help evaluate loads on partially complete structures and their stability, but they are not widely used. The use of such a standard would call for bracing incomplete walls for a wind speed of 75 mph to 80 mph, still less than what was recorded. Platform framing techniques appeared to be used to construct the building. The walls for a given story usually need to be braced until the floor platform above is in place and the walls are sheathed. Photographs and video from local news outlets show the building essentially enclosed except for the front wall. The front was framed but had large openings and no sheathing. Why? Keeping one end of the structure open can in effect pressurize the sheathing, adding to the suction applied to certain surfaces as the wind passes over or around the structure. That could create unexpectedly high loads, but would it more likely move the building or tear apart the walls and floors? There seems to be more of the former than the latter.

Leaving the front wall unsheathed would ordinarily prevent the structure from having adequate lateral load resistance against wind on the sides of the building. Under significant wind pressure, the building would twist. The unsheathed side would rack, causing the perpendicular (side) walls to be out of plumb. The available news photos appear to indicate some of these sorts of displacements. It looks like the first floor collapsed entirely, leaving a debris pile in front of the building. But the framing does not appear to leave a lot of space for sheathing between windows. To allow that – and still have a lateral force-resiting system – rigid frames must be placed at each level. Creating rigid frames with wood is difficult and usually involves layering wide pieces of manufactured lumber and metal straps to create rigid square corners. Steel frames are common too. Neither types of construction are apparent in photographs. What was the intended lateral force-resisting system? Was there one?

Also, how does a new, partially constructed building fall off its foundation due to wind? Modern codes require sill plates for wood structures to be bolted to the foundation at regular intervals. The floor should be fastened to the plates and the walls fastened to the floor, providing a continuous load path from the roof to the foundation to resist all anticipated gravity and lateral loads. Sometimes the type of wall construction for the basement or crawlspace changes at the ground surface. That can result in a vulnerability where the different materials join. But in new construction, building codes require continuity of load path regardless of material changes. The answer to this question could reveal a lot about the cause of failure.

At least today, this collapse leaves more questions than answers. Most structural failures occur during construction. They are rarely the result of a single cause. Usually, some combination of design problems, inappropriate construction methods, poor quality work and inadequate oversight combine to cause a serious failure. Organizational failures within the project itself or project stakeholder organization often represent major contributing factors. Sometimes a handful of small, pedestrian, honest mistakes by competent people will coincide to produce a costly and possibly dangerous failure. That could be the case here. On the other hand, a lot is known about common causes of structural failures and some of the underlying conditions have been present for months now. An overheated construction market brings inexperienced players and even some grifters into the market. Good firms overwork staff and under-resourced projects. Delays beget delays and work is rushed in futile attempts to catch up. Corners are cut and less work is thoroughly reviewed by more experienced personnel. Such an environment sets the stage for failures, especially on smaller, routine projects that receive less attention from design professionals, constructors and regulators. Structural failures have consequences. The failure in Jersey City did not result in serious injury or death, but people are homeless in one of the highest-cost rental markets in the country. It is imperative that project stakeholders be vigilant for signs of a project going bad. They rarely correct on their own.

The information and statements in this document are for information purposes only and do not comprise the professional advice of the author or create a professional relationship between reader and author.