Impact Load

An impact load is a dynamic load applied suddenly — a vehicle striking a guardrail, a dropped weight hitting a floor, a falling object striking a beam — and the effect of an impact load is greater than the effect of the same weight applied gradually, because the sudden application produces a dynamic amplification, a magnification of the force that can be twice or three times the static equivalent, and the structural engineer must account for this by applying an impact factor, a multiplier that increases the design load to reflect the reality that the world does not always deliver its weight gently.

The Tribune article appeared on a Wednesday in mid-May.

It was not on page three of the Metro section, where the original collapse story had run. It was on the front page, above the fold, with a photograph of the debris field and a headline that Ada read standing in the lobby of her building, where the doorman left the delivered newspapers on a table beside the mailboxes, and the headline said:

PARKING GARAGE COLLAPSE TRACED TO DESIGN ERROR PROMINENT ENGINEER'S CALCULATIONS FAULTED IN CITY REPORT

Ada picked up the paper. She read the article in the elevator, the car ascending through the building, carrying her and the newspaper and the weight of the words through the shaft of the structure she lived in, and the article was written by a reporter named Kevin Dao who had obtained a copy of the preliminary report — public record, once filed with the building department — and who had done what reporters do, which is to translate the technical into the narrative, the engineering into the human, the structural failure into a story about people.

The article named Hardin. It named his professorship at IIT. It named his textbook. It quoted a former colleague calling Hardin "a pillar of the Chicago structural engineering community," and the word "pillar" was either a coincidence or a reporter's instinct for structural metaphor, and either way it landed, because a pillar that fails is a pillar that was carrying something it could not carry, and the article was saying that Hardin was this, a pillar that had failed.

The article named Ada. "Dr. Ada Nowak, a senior forensic engineer at Alford & Associates and a former student of Prof. Hardin's, authored the report that identified the design deficiency." The sentence contained the fact of their relationship, the student-teacher connection, and the sentence was constructed to let the reader understand the weight of that connection without stating it explicitly, the way a well-detailed structural drawing conveys the forces without writing them on every member.

The article quoted the families' attorneys. It quoted the building department. It quoted a structural engineering professor at Northwestern who said the preliminary findings "appear to identify a significant design oversight" and who noted that the misclassification of a bearing wall was "a fundamental error that should have been caught during the review process."

Should have been caught. Should have been caught during the review process.

Ada read this sentence and thought about Keane saying Martin reviewed the interesting parts and she thought about how the review process is a load path in itself, the load of verification travelling from the calculations through the reviewer to the stamp, and if the review is cursory or selective or distracted, the load of verification does not arrive at the stamp, and the stamp is applied without the load it is supposed to carry, and the stamp is then a hollow thing, a seal without substance, a bearing wall that bears nothing.

She arrived at the office. The office was different today. The receptionist looked at her with a particular alertness, the awareness that Ada was now a person who had been in the newspaper, and the awareness created a field around her, a perimeter of attention that she could feel the way you feel a change in air pressure, not with any specific sense but with a general awareness that something in the environment has shifted.

Alford was waiting in his office.

"You've seen it," he said.

"I've seen it."

"The phone has been ringing since six a.m. The Tribune wants a comment. Channel 7 wants an interview. The Sun-Times wants a comment. Three law firms want copies of the full report. The ASCE Illinois Section wants to know if we'll present the findings at their June meeting."

"No interviews. No comments beyond the report. The report speaks for itself."

"That's what I've been telling them. But Ada — this is going to get louder. The families are going to file suit. Hardin's insurer is going to file a response. There will be depositions. You will be deposed. You will be qualified as an expert witness. You will sit in a room and a lawyer will ask you to explain, in language a jury can understand, why three people died in a parking garage."

"I know."

"Are you ready for that?"

Ada considered the question. Ready was not a structural term — you could not calculate readiness, could not model it, could not assign it a factor — but readiness was a real condition, a state of preparedness that was either sufficient or insufficient, and Ada assessed her own readiness the way she assessed a structure: by examining the elements, checking the connections, tracing the load paths.

The elements: her knowledge of the failure, which was thorough. Her documentation, which was complete. Her analysis, which was verified. Her conclusions, which were supported by the evidence.

The connections: her relationship with Alford, which was strong. Her collaboration with Brin, which was functioning. Her communication with the building department, which was professional.

The load path: from the evidence through the analysis through the report through the testimony through the jury through the verdict, each step a transfer point, each transfer requiring clarity and precision and the kind of calm that engineers maintain in the field when the building is cracked and the dust is settling and the answer to the question is it safe to go in depends on the accuracy of their assessment.

"I'm ready," she said.

"Good. Because Hardin has retained Schiff & Brennan."

Ada knew the name. Schiff & Brennan was a litigation firm that specialized in defending engineers and architects in professional liability cases, and they were good, they were very good, and their strategy in every case was the same — attack the investigator's methodology, attack the investigator's conclusions, attack the investigator's credibility, distribute the blame as widely as possible so that no single defendant bears the full weight, and in a case like this the distribution was easy because there were so many defendants: Hardin for the design, Keane for the calculations, the architect for directing the wall, the contractor for building it, the inspector for accepting it, the assessment firm for not investigating the cracks, the owner for not performing the monitoring.

"They'll try to spread the load," Ada said.

"They will. And they'll try to discredit you by using your relationship with Hardin. They'll say you were biased — either biased against him because of some personal grudge, or biased in his favor and therefore any finding adverse to him must be reluctant and therefore more damning. They'll find a way to use the relationship regardless of its nature."

"The relationship was professional. He was my teacher. I was his student. I haven't spoken to him in fifteen years prior to this investigation."

"They won't care about the characterization. They'll care about the perception. A former student investigating her former mentor — the narrative writes itself."

Ada looked out Alford's window, at the South Branch of the Chicago River below, brown and slow and carrying its own load of sediment and sewage and rainfall and the accumulated runoff of the city's impervious surfaces, and the river was a load path, the hydrological equivalent of a structural system, every drop of rain that fell on the city's roofs and streets and parking lots eventually finding its way to the river, the river carrying it to the lake, the lake carrying it into the vastness of the water, and the system worked as long as the capacity of the channels was adequate, and when the capacity was exceeded — in a storm, in a flood — the system failed and the water went where it was not supposed to go, and this was the same principle, always the same principle.

"Rich, the report is technically sound. The analysis is correct. The evidence is documented. I am confident in the findings and I will defend them in any forum. The relationship with Hardin is a fact, not a bias. If anything, the relationship makes the findings more painful, not less rigorous."

"I know. I'm not questioning the work. I'm preparing you for the fight."

The fight came faster than she expected.

On Thursday, the day after the Tribune article, Hardin's attorneys filed a response with the building department challenging the preliminary report's findings. The response was forty-three pages of technical rebuttal, prepared by a forensic engineering firm retained by Schiff & Brennan, and the rebuttal argued three things:

First, that the collapse was caused primarily by the corrosion of the connections, not by the design deficiency, and that the corrosion was the result of inadequate maintenance by the building owner, specifically the failure to maintain the waterproofing membrane and the failure to perform the recommended monitoring.

Second, that the demand-to-capacity ratio calculated by Ada was overstated because it used Exposure Category C for wind loads rather than Exposure B as specified in the original design, and that using the correct exposure category reduced the ratio from 1.47 to 1.12, which was still overstressed but by a smaller margin, and the smaller margin was within the range that the material reserves could accommodate, and therefore the design deficiency alone was not sufficient to cause the collapse.

Third, that the review process at Hardin & Keane was consistent with the standard of care for structural engineering firms of that size and that time, and that the principal's review was appropriately focused on the non-routine aspects of the design, and that the gravity loads at the east wall were a routine condition that would not ordinarily be singled out for detailed review.

Ada read the rebuttal in her office with the door closed. She read it carefully, the way she read everything, checking each argument against the evidence, testing each claim against her analysis, and she found the arguments to be what she expected — partially valid, partially misleading, constructed to create reasonable doubt rather than to establish truth.

The first argument — corrosion as the primary cause — was partially valid. The corrosion had contributed to the collapse. But the corrosion would not have caused the collapse if the connections had been adequately designed, because adequate connections with corrosion still retain a factor of safety, and the factor of safety absorbs the reduction in capacity from corrosion, and the connections at Lake-Wabash had no factor of safety to begin with, so the corrosion consumed capacity that did not exist, and this was the rebuttal to the rebuttal, and Ada wrote it in her notes.

The second argument — the wind exposure — was a legitimate technical disagreement. Ada had used Exposure C. The original design used Exposure B. The code allowed either, depending on the engineer's judgment about the site conditions, and reasonable engineers could disagree. But the disagreement did not change the fundamental finding, because even at Exposure B the ratio was 1.12, which was still overstressed, still above 1.0, still a condition where the demand exceeded the capacity, and the margin between 1.12 and 1.0 was twelve percent, and twelve percent was not enough to explain twenty years of satisfactory performance followed by sudden failure, and the corrosion was the additional factor that pushed the 1.12 past the point of no return.

The third argument — standard of care — was the one that would be fought in court. The standard of care is the legal standard against which a professional's conduct is measured, and the question is not whether the professional was perfect but whether the professional did what a reasonably competent professional would do in the same circumstances, and this question is answered by expert witnesses who testify about what they would have done, and the testimony is subjective, and the subjectivity is where the lawyers find their space.

Ada set down the rebuttal. She looked at the wall of her office. She thought about the three arguments and the three names and the three points on her timeline where the trajectory could have changed — the design phase, the construction phase, the assessment phase — and she thought about how the rebuttal was doing exactly what Alford had predicted, distributing the load, spreading the blame, reducing the force on any single defendant by sharing it among many.

And the distribution was not entirely wrong. The blame did distribute. Keane had made the error. Hardin had missed it. Voss had questioned it and been overruled. Roth had seen the consequences and deferred. The owner had ignored the recommendation. Each person in the chain bore a portion of the responsibility, and the portions could be debated and the proportions could be argued, and this was what the court would do, this was the function of the litigation, to determine the distribution, to assign the percentages, to convert the chain of failures into a schedule of liability.

But the origin was the origin. The zero on page 87. The beam that became a wall without the analysis being updated. The classification that was wrong. And the stamp that made it official.

Ada picked up the phone and called Brin.

"I need you to run the analysis at Exposure B. I want our own numbers for the 1.12 ratio. I want to show that even at their preferred exposure category, the connections were overstressed. And I want to run a time-dependent analysis — creep, corrosion, fatigue — to show the progression from 1.12 on day one to failure at year twenty. I want to close the gap between their argument and ours."

"How detailed?"

"Detailed enough that a jury can follow it. Simple enough that a lawyer can't confuse it."

"That's a narrow window."

"It's the only window we have."

She worked through the evening. She worked through the next day. She worked through the weekend, skipping the Sunday visit to Evanston, the second Sunday she had missed, and the guilt was the impact load — sudden, amplified, greater than the static equivalent, the dynamic force of a daughter who was not where she was supposed to be hitting the structure of the daughter who was where she needed to be, and the two structures were the same structure, and the impact was internal.

She called the nursing home on Sunday afternoon. She spoke to the nurse on duty, who said Zofia had had a quiet day, had eaten lunch, had sat in the recliner by the window, had not asked for Ada.

Had not asked for Ada.

The datum was ambiguous. It could mean that Zofia was content, that the Sunday passed without the expectation of a visit, that the routine had not yet been established firmly enough to be missed. Or it could mean that Zofia had not remembered that Ada came on Sundays, that the connection between Sunday and daughter had been lost, that another room had fallen and the falling was silent because Zofia had not noticed the room was gone.

Ada set the phone down. She looked at the analysis on her screen — the time-dependent model, the creep curve, the corrosion profile, the degradation of capacity from day one to year twenty — and the curve was a slope, a gradual descent from the initial condition to the failure condition, and the curve looked like the thing it described, a line going down, capacity diminishing, reserve shrinking, the distance between standing and falling narrowing year by year until the distance was zero and the line crossed the threshold and the structure was no longer a structure but a debris field.

The curve for the parking structure.

The curve for her mother.

The same shape. The same slope. The same threshold.

Ada closed the laptop. She sat in the silence of her apartment on a Sunday evening in May and she listened to the building hold her and she thought about impact loads and how the code provides a factor for them — an impact factor that increases the design load to account for the dynamic amplification — and she thought about whether there was an impact factor for guilt, for the sudden arrival of the knowledge that you have chosen work over the person who gave you the work, who gave you the precision and the honesty and the bearing walls, and the impact factor would be large, would be two or three times the static equivalent, and the capacity of the daughter would need to be checked against the amplified load, and Ada checked it, sitting in the dark, and the result was marginal, the capacity barely exceeding the demand, the factor of safety approaching one.

She went to bed.

On Monday she brought the time-dependent analysis to Alford.

"The curve closes," she said. "Starting from a demand-to-capacity ratio of 1.12 at Exposure B on day one, the corrosion reduces the capacity by approximately one percent per year, and the creep increases the demand by approximately half a percent per year, and the combined effect is a convergence — the capacity curve going down and the demand curve going up — and the curves cross at approximately year eighteen, and the collapse occurred in year twenty, and the two-year gap is accounted for by the uncertainty in the corrosion rate and the variability in the actual loading."

"This is good work."

"This is the answer to their rebuttal. They say the corrosion caused the collapse. We say the corrosion finished what the design started. The design put the building on the wrong side of the threshold. The corrosion pushed it over."

"The design loaded the gun. The corrosion pulled the trigger."

Ada looked at him. The metaphor was not structural. The metaphor was violent, was human, and it was accurate, and she hated it.

"Yes," she said. "That's what happened."

She went back to her office. She added the time-dependent analysis to the report. She revised the conclusions. She checked the numbers. She ran the analysis one more time, the final time, and the curve closed, and the numbers were the numbers, and the report was nearly done.

The impact of the public attention continued through the week. Two more articles. A television segment. An editorial in the Sun-Times about the adequacy of the building department's inspection process. A letter to the editor from a structural engineer defending Hardin. A letter to the editor from a resident of the building next to the parking structure, who described the night of the collapse — the sound, the dust, the running — and Ada read this letter and thought about 0.8 seconds and the three names and the weight.

The impact factor amplified everything. The attention amplified the significance of the findings. The significance amplified the pressure on Ada. The pressure amplified the guilt about the missed Sundays. The guilt amplified the fear about her mother's decline. The fear amplified the doubt about her own capacity. And the doubt amplified the silence in her apartment on the seventh floor, where Ada sat in the evenings and carried the live load of a life that was changing faster than she could calculate.

She would not miss another Sunday.

She would bring pierogi. She would sit in the visitor's chair. She would hold her mother's hand. She would say the things that needed to be said and hear the things that needed to be heard and the visit would be the relief, the periodic reduction in stress that allows the material to stabilize, the removal of the live load so the dead load can be carried alone, the rest that the dough needs, that the material needs, that Ada needed.

She would not miss another Sunday.

The building held. The night passed. The live load shifted. The impact was absorbed.

The structure stood.