Considering Engineering Judgment in Forensic Investigations

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As engineers advance through school and embrace their larval state as practitioners, they eventually encounter the concept of “Engineering Judgment.” For many, initial perceptions of the phrase are dubious or even dismissive, inferring shortcuts bypassing important steps. These notions usually evolve as most realize it is more than a “gut-feeling;” the foundations of technical knowledge, expertise, and professional standards can only be forged in a slow kiln of gained experience. This truth rings especially true for forensic consulting engineers whose engineering judgment takes on additional dimensions including navigating emotionally-charged situations, time-sensitive contemplations, and recent or impending catastrophes. In most cases, engineering judgment is required long before any actual analysis is undertaken.

Using an adaptation of a recent interactive NCSEA Structural Summit Presentation and national NCSEA Webinar, several real-world case studies exhibiting engineering judgment are presented herein. Before learning how the author applied judgment, the reader is invited to reflect on proposed considerations and determine what actions they would choose had they stepped into the fray, and then compare with what was actually decided. The cases are not meant to proclaim decisions as right or wrong, but rather to encourage immersion in the thought experiment process and applying one’s own engineering judgment to uniquely challenging scenarios.

Constructed in 1873, a small riverside town’s oldest brick building, and a favorite restaurant to generations of locals, became the focus of an early summer morning emergency: a dumpster fire had spread and engulfed large portions of the treasured structure. The engineer receives a call with urgency typical of a no-notice incident response, but with a new wrinkle: the building is still on fire.

Engineering consulting is often a difficult job, with difficult tasks and demands for quick decisions. This time, before even accepting the assignment, engineering judgment is required as the engineer considers how to evaluate the state of the emergency:

Interested in the uniqueness of the challenge, after some internal deliberation, the engineer chooses to visit the site immediately, consulting a senior colleague en route to discuss strategies and get another valued opinion. Upon arrival, the engineer is greeted by the local fire chief who promptly demands, “I need you to tell us to take down the building.” Moments later, distraught building owners begin pleading for the engineer to save the historic landmark (Fig.1).

Amidst a tense scenario with conflicting parties and no time to burn, the engineer considers how to characterize their own responsibility:

Since safety of the fire fighting crew was paramount, the engineer defers fire-related decisions to the fire chief, but suggests that if an inspection can be undertaken reasonably safely, it may be possible to save the remaining portions of the structure. Through continued extinguishing efforts, the flames are controlled, but the engineer struggles with how to gain reasonably safe access beyond grade level observations from afar. On a hunch (and perhaps manifesting a childhood dream) the engineer asks the chief if the high-reach aerial ladder truck currently in use by a hose-wielding firefighter can be utilized for a better view. Surprisingly, the chief agrees, and after donning the appropriate PPE, the engineer climbs to the top of the fully extended ladder.

The new perspective makes all the difference (Fig. 2). It becomes clear that while the north and west walls of the second floor are severely damaged, the east and south walls are intact, including most of the historic east facade. Equally important, the second-floor framing is largely intact but is now supporting a tremendous amount of debris.

After descending, the engineer relays thoughts to both the fire chief and the owners. Assuming the fire can be extinguished, the remaining portions of the building can be saved but in doing so there are two short-term key considerations: structural stability and public safety.

Regarding stability, since the intact second-floor framing is overloaded, the debris should be removed as quickly and delicately as possible. Further, given the compromised roof and second-floor diaphragms, the remaining partial walls require shoring from both the inside and outside.

Due to the unbraced west and south exterior walls, street and sidewalk closures are required to address public safety. But as with any scenario where the engineer recommends temporary closures, the question of extent lingers. The fire chief wants to minimize disruption to the roads and local businesses, meanwhile the engineer worries that if the unstable, two-story walls fall outward, the debris can catapult into the storefronts across the street, endangering people and property. As the engineer considers barricades, a stroke of ingenuity is offered by another engineer on site representing the town: a series of tall roll-off steel dumpsters could be ordered and lined up in the far parking lanes of the opposing streets. The two-layered steel wall will form a barrier protecting the storefronts and are cheaper and faster to mobilize than designing and constructing a traditional wall. In this case, utilizing engineering judgment meant receiving good ideas from other sources which helped wisely set appropriate, effective boundaries.

Aligning the many swift decisions and recommendations, the judgment-based plan worked. Barricades and shoring provided protection and stability, the remaining iconic facade was saved, the damaged areas rebuilt, and the community was thrilled to have its favorite haunt reopened for business.

A high school building, originally built in 1924, with at least four large additions over the decades, stands proud: a two-story fortress of brick masonry, protecting a century of history and serving as the centerpiece of a thriving urban community. One sleepy June morning, merely a week after the start of summer vacation, a maintenance team discovers a partial roof collapse, stirring the staff, administration, and the surrounding neighborhood. Soon after, the engineer is contacted and conscripted into the investigation.

Upon arrival, response activity is underway including limited shoring of one exterior wall and a tarp draped over the newly sunken roof area. Inside, initial inspection on the first floor offers only seemingly innocuous displaced ceiling tiles but prying open the door of a second-floor classroom reveals a tangled mess of collapsed open-web steel bar joists and an accumulated heap of roofing, ceiling tiles, and classroom furniture. Anecdotal input from some brazen roofers who had been walking on the debris pile informed the engineer they had heard some building groaning noises, but that the pile had only moved “a little” during their emergency tarping work (Fig. 3). Eager to investigate, but short on information and registering a likely framing overload, the engineer contemplates various notions of what areas should be accessed and how:

The engineer elects to continue investigating from stable surrounding positions but chooses not to enter on top of or beneath the collapse debris. That risk is unreasonable, despite the roofers’ assurances. After a few hours of observation and discovering original building drawings, the engineer confers with the on-site response team to discuss short-term key considerations: water management and restricting access.

While ponding water often raises concern of additional load accumulation, inspections also reveal the electrical switchgear for the entire campus is housed in a basement vault adjacent to the collapse and had reportedly filled and been pumped out once already. With redirectional tarps and basic drainage provisions already deployed, safe maintenance of the makeshift system was critical to prevent water from ponding on top of the collapse, which may exacerbate it, or from collecting in the basement which could debilitate the entire complex.

Staff curiosity dictates strict closures around the collapsed area, both inside and outside the school. Fortunately, existing fire separations and structural isolation provide an opportunity for installation of hard barriers and keyed entrances to deter and protect would-be explorers.
After the initial considerations, uneasy whispers and assumptions run rampant, with various opinions swirling about how much of the building needs to be demolished, how quickly the school can be re-opened, and how did this all happen. It takes the engineer numerous meetings with the school board to eschew others’ aggressive demolition plans and recommends to the decision-makers that the engineer be allowed to conduct a surgical disassembly of the remaining wall and debris pile.

With the help of a skilled deconstruction team, salvaged artifacts reveal the roof joist bearing seats were corroded through and the supporting masonry wall eroded. An iterative cycle of section loss and a sliding bearing loss ended in a sequence of joist failures and catastrophic collapse (Fig. 4.). Though the failure surprisingly occurred at the high side of the roof slope, brick patterns and mortar coloration suggested years of parapet infiltration and deterioration led to a prior coping and wall replacement decades ago, but hidden structural damage just below the roof was never understood, accessed, or addressed. With the cause understood and with the failure located specifically in the 1926 addition, the engineer wonders: Where else might this condition be looming? Which of the building sections need to be reviewed (Fig. 5)?

At a minimum, the engineer recommends review of the other 1926 areas, any similarly constructed conditions, and conditions of similar age. Select inspection openings expose pristine conditions at the remaining steel joists bearings while a series of thorough attic inspections reveal the 1924 and 1959 vintage building portions host a completely different, wood-framed system and confirm that they are in good condition.

To support these positive results, the school board requests the engineer present findings in a forum with administration, staff, and parents to alleviate remaining community concerns regarding the aged building. Balancing helpful intentions against liability concerns, the engineer mulls whether to present findings in a public forum.

Ultimately, the engineer presents to a standing-room-only gathering. The results are conveyed and questions answered in a largely successful forum, notwithstanding a scuffle between staff and an overeager local news reporter, and an unfounded accusation that the engineer should be imprisoned for culpability with regard to the performance of a building designed and built over 50-years before their birth.

With demolition of the unstable areas complete and plans for replacement emerging, the engineer’s focus shifts to conducting a life safety analysis and working with local fire authorities to ensure re-occupancy of the building. As August arrives the final letter and drawings are approved and school opens on time. Years later, a brand-new building segment is opened, replacing the collapsed portion with new classrooms and new interactive spaces to enrich student experiences.

After an elementary school is glanced by an EF-1 tornado, the district superintendent and a trusted construction management partner contact the engineer to request assistance.
Completed in 1997, with a 2001 southern addition, the long, sweeping crescent shaped building’s two stacked stories each feature a double-loaded central hallway serving classrooms on either side. The building framing includes sloped open-web steel joists bearing on interior and exterior concrete masonry walls with an indented mechanical equipment rampart in the middle (Fig. 6).

Upon arrival to site, the engineer assesses each room on each level for distress. At the southern end of the second floor, the engineer finds isolated concentrations of vertically displaced joists and separated/shattered bond beams and disengaged grout, including areas where chunks of concrete masonry had fallen through the ceiling (Figs. 7 and 8). Throughout the rest of the building, concrete masonry cracks are observed near the upper corners of most windows. In characterizing concerning, event-related damage the engineer considers various possibilities:

The corner cracks exhibit no evidence of recent origin, and many have dust within or paint across their gaps (Fig. 9). Accordingly, the engineer’s concerns are reduced to the more severely distressed area at the southern end of the second level. Hearing this provisional conclusion after already canceling a few days of school, a school official poses a question for the engineer’s next deliberation: How much of the school needs to be closed:

The engineer outlines two key considerations: in terms of damage, only a handful of second floor rooms require closure. However, since some instabilities remained, until joists and CMU walls are repaired, vertical shoring will be required. Analysis of the second-floor precast hollow core concrete structural system determines it cannot support shoring loads—the shoring towers will need to extend into the undamaged, first floor classrooms as well. The engineer expected shoring would be too disruptive, thus forcing the closure of six additional classrooms, rendering the school out of space and forcing temporary relocation of the entire institution. In an inspiring act of resilience, inconvenience gave way to resourcefulness, as the principal and affected teachers instead choose to decorate the shore towers and simply work around them. With this flexibility and repurposing of other spaces within the facility, classes resume the following week.

With prompt repairs the stated priority, working with the city and state authorities having jurisdiction, and coordinating with the construction manager, the engineer advises postponing a causation report and moving forward with two repair packages: one for concrete masonry repairs (short lead time, weather-sensitive) and a second phase for damaged steel bar joists (longer lead time, no weather implications). The repair team works stealthily and strategically to limit noise disruptions and successfully complete the masonry work before winter holiday break. They finish the joist repairs a few months after - under budget and ahead of schedule. Once the shoring towers are removed, the ceilings are restored, and the walls receive a fresh coat of paint, the entire school community is elated to finish school year the way they had originally intended.

Engineering judgment is not merely an antiquated euphemism. It is real, reliable, and becomes increasingly critical as situations become more complex. Though intangible and impossible to physically hold, engineering judgment must be grasped and executed by practitioners in all facets of project decisions, especially in unstable scenarios. It is the net sum of each individual’s education, expertise, and experience but regardless of how many decades of experience one has, the best way to hone engineering judgment is to confer with technical colleagues along the way. Healthy skepticism and rigorous discussion ultimately lead to better results allowing us to achieve project objectives agreeable to all parties and protect the public along the way. ■

About the Author

Ross J. Smith, PE, LEED AB BD+C, CDT, is a Principal at WJE with over 25 years’ experience in investigations of structural and architectural failures related to water infiltration, fire, wind, snow, condensation, and unique material failures. He also works in structural evaluation, repair design, construction quality control, and building enclosure commissioning (BECx). He is experienced in new building design, sustainable construction, peer reviews, and litigation assistance.