downstream of Hoover Dam, this struc-ture is eloquently anchored into the sheer rock faces of the historic Black Canyon. The main segment of the bridge, which is a twin-rib concrete arch and steel compos-ite structure, spans approximately 1,060 ft from wall to wall. Over the course of two weeks in the middle of January 2013, three professional engineers and three engineers in training—all professional rope access technicians—from Stantec rappelled, climbed, ascended, traversed, and crawled over, under, inside, and around every inch of this structure to thoroughly document the bridge’s structural condition.

The National Bridge Inspection Stan-dards were established in 1968 by Con-gress following the tragic collapse on De-cember 15, 1967, of the Silver Bridge, which connected Point Pleasant, West Virginia, with Gallipolis, Ohio. Since then every bridge structure, whether of the size of the Golden Gate Bridge or as small as a 20 ft clear span culvert in a rural locale, must be inspected at intervals not to exceed 24 months unless the Federal Highway Administration rules otherwise. The Hoover Dam Bypass is considered one of the newest national monuments (al-

though it has not officially been designat-ed as such), and this 1,905 ft long struc-ture is being inspected at intervals of two years or less by NDOT-approved inspec-tors. The personnel and engineering teams who inspect and evaluate our nation’s in-frastructure are very specialized civil and structural engineers and technicians who sometimes receive little recognition for the important tasks they perform. Their basic training and certification are mandated by law through the Code of Federal Regulations (title 23, part 650) and are overseen by the Federal Highway Administration, but not all bridge inspectors are “created equal.” In the early 1980s only a handful of en-gineers would have had the audacity to tell a client that they were going to utilize ropes and harnesses to perform an “inspec-tion” and believe the client would actually hire them. Just 30 years later this practice has taken firm hold in the United States and is achieving wider acceptance and

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Rising 880 ft above the Colorado River, the majestic Hoover Dam Bypass poses formidable challenges to bridge inspectors. And that is why the rope access technicians who performed a thorough inspection of the bridge in January are invaluable.

By Ryan Nataluk, P.E.

he Mike O’Callaghan–Pat tillMan Memorial Bridge, often referred to as the Hoover Dam Bypass,

is a very large, complex, and strategically important struc-ture that carries U.S. Route 93 between Nevada and Ari-zona over the Colorado River. (See “Engineering’s Newest Marvel,” by Dave Zanetell, P.E., M.ASCE, David Goodyear, P.E., S.E., P.Eng., M.ASCE, Jeff St. John, P.E., M.ASCE, Bri-an Lomax, and Danny Sullivan, Civil Engineering, October 2011, pages 56–65, 86–87.) I can vividly remember the awe and inspiration I felt the first time I viewed this struc-ture. I was at the Hoover Dam observation area, and it was

shortly after Stantec had been selected by the Nevada Department of Transportation (NDOT) to perform statewide inspections that would include this marvel. While looking at the bridge with a dropped jaw that day, I thought about my bridge inspection career and realized that this is why we specialize in condition assessments and rope access. In less than four months from that date, my team and I were rappelling down to the arch for the first time to begin our inspection using industrial rope access methods.

Rising 880 ft above the water surface of the Colorado Riv-er approximately 30 mi southeast of Las Vegas and 1,500 ft

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T

F i r s t P e r s o n

High Over

Hoover Dam

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As Nicholas Cioffredi, P.E., a senior bridge inspection engineer

for Stantec, notes, “You’re so focused on the task at hand,

inspecting this engineering marvel, doing your job, and making sure that you’re safe that it can take a while to stop long enough to

absorb the exposure of it all. It’s not often you get to hang devoid of contact with any structure while

looking down on the Hoover Dam.”

As Nicholas Cioffredi, P.E., a senior bridge inspection engineer

for Stantec, notes, “You’re so focused on the task at hand,

inspecting this engineering marvel, doing your job, and making sure that you’re safe that it can take a while to stop long enough to

absorb the exposure of it all. It’s not often you get to hang devoid of contact with any structure while

looking down on the Hoover Dam.”

To view a video of the project, visit our digital edition at www.asce.org/cemagazine,

or view the app at www.asce.org/ceapp.V

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practice each year. At this time it is estimated that approxi-mately 100 professional engineers—and probably twice that number of inspection technicians—utilize rope access to perform bridge inspections in accordance with the National Bridge Inspection Standards. This pool of specialized profes-sionals provides hands-on inspection of the most difficult-to-reach locations on any bridge to better provide owners with a clear, comprehensive evaluation of the structure.

Within the state of Nevada, the NDOT is responsible for managing the inspection of 1,972 public bridges owned by state and local agencies. Of that total, 1,116 are owned sole-ly by the state, and the NDOT is responsible for maintaining them. State-owned (“on-system”) structures are typically lo-cated on the national highway system or are on state or interstate travel routes, whereas locally owned (“off-system”) structures typically car-ry locally owned city and county roadways. In comparison with other states and the District of Columbia, Nevada is routinely ranked as hav-ing one of the best inventories in America. In

order to maintain a statewide inventory of this stature, inspec-tions must be thorough, must be on time, must meet Feder-al Highway Administration metrics, and must provide the vital information—including essential maintenance recom-mendations—required to prolong service life. The NDOT’s exceptional attention to public safety complements in an im-portant way the safety-driven nature of the work executed by teams like ours.

In June 2012 we were selected to assist the NDOT struc-tures staff with the inventory, inspection, and load rating of Nevada’s bridges. The selection process followed the NDOT’s standard request for proposals process and featured competi-tive submissions by many nationally recognized engineer-

ing firms. During the selection process, the NDOT was specifically interested in the quali-fications of the inspection team, the current and past inspection projects performed by that team, and the team’s overall rope access inspec-tion capabilities. These considerations were important to the NDOT during the selection

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Steve Stanley, a bridge and construction inspector for Stantec, was a member of the core Stantec team, all of whom are professional rope access technicians.

Ryan nataluk’s account:

ThrOughOut my adult life I have taken great pleasure in adventur-ing on some of North America’s

largest mountains, dropping into some of the deepest caves, and scal-ing a handful of the tallest and most technical rock walls around. I certain-ly don’t consider myself to be specifi-cally gifted at any of these activities, but these goal-oriented, adrenaline-pumping excursions are generally how I have enjoyed my spare time over the years. When I first discov-ered, in 1998, that I could utilize my engineering training in conjunction with my mountaineering, caving, and rock-climbing skills, I could hardly be-lieve it. I must have said a thousand times or more since then, “You mean I get to rappel, ascend, and climb this (bridge, building, tower—whatever) and you’re actually going to pay me for what I find and document?” I can truly say that I love my job....most of the time. I say “most of the time” so as not to give an unreason-able expectation to any engineer interest-ed in bridge inspection. It has its glorious days, and it has its not-so-glorious days. Inspecting the Hoover Dam Bypass on rope is a privilege, and I feel honored to have done so.

The professional work that my team and I performed for the Nevada Depart-ment of Transportation (NDOT) this past January holds many similarities to my interests outside of work: extensive training, detailed planning, mitigating dangers, taking small things seriously, teamwork, and thinking safety! I am a registered professional engineer in sever-al states, including Nevada and Arizona, and serve as the project manager and lead bridge inspector for this statewide in-spection project for the NDOT. With re-spect to any project, I feel a responsibility to fully ensure the team’s well-being and overall project success for the team and the client. First and foremost is the safe-ty of my team members. For this work, I fully knew that my team was ready and had all of the professional inspec-tion experience and rope skills necessary to complete this work to the NDOT’s

complete satisfaction. I also knew that the physical environment in southern Nevada can be extremely harsh to even the most honed human body. Temper-atures in the summer can rise to 120ºF and be so dry that the wind will suck every drop of moisture from your skin and lungs. Fortunately, the inspection this year took place in January, and con-ditions were more favorable than in, say, July, but many dangers still existed. The two things that worried me the most were dehydration and fatigue deriving from long, physically demanding days in high temperatures and hot, strong wind. Lucky for us, Mother Nature was fairly temperate during our visit, and the team was able to complete the objectives like the pros they are.

When conducting work outside of the office within Stantec, our mandatory practice is to have on-site daily preinspec-tion meetings to discuss the day’s work, review safety protocols, review the inspec-tion plan, and gauge the team’s physical and mental state. We want to discuss and review everything that could potentially take place and ensure each team member knows his role and responsibilities.

I have climbed hundreds of bridges and structures in my career, but it would be a lie to suggest that I did not have some apprehension the first time I rappelled off this bridge. I must have checked my an-chors, harness, and gear at least 10 times before leaving the bucket of the NDOT’s underbridge inspection unit to embark on the 750 ft rebelay 880 ft off the sur-

face of the Colorado River. This tech-nique is very handy to utilize in the inspection of truss bridges, arches, and other structures that require both vertical and horizontal move-ment to complete the job.

One full rebelay between span-drel columns took upward of four hours. Therefore, once an inspec-tor left the deck of the bridge, he was going to be “on rope” for quite a while. A lot can happen in four hours, and this was my greatest con-cern for the team. The temperature can rise, the wind can pick up, a thunderstorm can roll through, or a person can overexert himself. Each team member had to be prepared for just about anything, including carrying all of the water and food

required. Escape and rescue plans need-ed to be ready for execution at any mo-ment. I am glad to report that there was not one single incident on this project, and the team performed flawlessly over the two-week inspection.

No project can proceed and end smoothly without the teamwork and cooperation of all members and stake-holders. Each project requires the col-laborative, dedicated effort of several agencies and teams. This project ben-efited from exceptional commitment from the NDOT divisions dealing with structures, underbridge inspection ve-hicles, and traffic control; the Hoover Dam Police Department; and the Ne-vada Highway Patrol. Our team also benefited from the advanced rescue training and on-site support provided by Gemini Rope Access Solutions. All of these partners and their roles are criti-cal to project success, and they work in conjunction with our core Stantec team: Nick Cioffredi, Frank Block, Tom Ritz, Matt Bialowas, and Steve Stanley. What I’ve come to appreciate in working with these gentlemen is the trust and con-nection we share as climbing partners. They are sincere friends and dedicated members of the same inspection team and are uniquely qualified to perform this specialized work for agencies like the NDOT throughout the nation.

Ryan Nataluk, P.E., is a senior structural engineer and the bridge inspection program manager for Stantec Consulting in Denver.

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The personnel and engineering teams who inspect and evaluate our nation’s infrastructure

are very specialized civil and structural engineers and technicians who sometimes receive little

recognition for the important tasks they perform.

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process because of its need to maintain public safety and preserve Nevada’s sta-tus of having one of the best-ranked in-ventories in the country. Additionally, the NDOT must inspect and maintain not only such “typical” bridge and cul-vert structures as concrete and steel overpasses, underpasses, box culverts, and pipes but also such structures in its inventory as the Hoover Dam By-pass and the Galena Creek Bridge,which require more ad-vanced engineering and access techniques to facilitate in-depth evaluations.

We were fortunate to have inspected and evaluated some of the largest and most iconic bridges in America. Our team, composed of professional en-gineers and engineers in train-ing, has evaluated structures ranging from New York City’s George Washington, Queens-boro, and Brooklyn bridges to small timber bridges in rural lo-cales. The team selected to in-spect the Mike O’Callaghan–Pat Tillman Memorial Bridge is the same team that inspect-ed the structure that replaced the Silver Bridge. Our collec-tive experience gives us insight into several key areas of bridge inspection, including perspec-tive on the nation’s structural history and future through our detailed involvement in design, fatigue, retrofits, and failures. This, combined with our expe-rience in evaluation, access plan-ning, and assessment of material defects and properties, qualified our team for this momentous in-spection. Just as important, all members of our team of engi-neers and technicians hold cer-tifications in specialized access and inspection methods ranging from rope access to underwater diving to nondestructive testing.

WOrking at extreMe heights may appear to most to be an exercise in

lunacy, but in actuality it is safer than crossing a busy street in a major U.S. city. Utilizing rope access techniques to perform work on the nation’s highway

infrastructure is a much safer practice than placing an engineer, a technician, or a worker, along with mechanical equipment, in a traditional work zone. Our clients also find that it’s more cost effective. According to recent data com-piled by the Federal Highway Adminis-tration’s Work Zone Mobility and Safety Program, “There were 87,606 crashes in work zones in 2010. This is 1.6 percent

of the total number of roadway crashes (5,419,345) in 2010. Most crashes in work zones do not lead to fatalities. In 2010 work zone crashes, 0.6 percent were fatal crashes, 30 percent

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“I have climbed hundreds of bridg-es and structures in my career, but it

would be a lie to suggest that I did not have some apprehension the first time I rappelled off this bridge. I must have

checked my anchors, harness, and gear at least 10 times before leaving the buck-

et,” says Ryan Nataluk, P.E., Stantec’s bridge inspection program manager.

FRank Block’s account:

The OPPOrtunity to inspect the Mike O’Callaghan–Pat Tillman Me-morial Bridge was a once-in-a-life-

time experience (although I’m hopeful for a return trip in 2015). I can remember first hearing that we were awarded the contract for statewide bridge inspections. I was very interested in travelling around a state in which I had spent little time. I then came to realize the scope of the project and that our in-spections would include the re-cently completed Hoover Dam Bypass structure. My interest quickly turned into a mild ob-session. I began to pore over In-ternet photographs and articles on the bridge while thoroughly conveying my interest in this in-spection to the decision makers assembling the inspection team. It is only the most iconic and nationally recognized structure since the Golden Gate!

The weeks leading up to the inspection were filled with plan-ning the inspection sequence, rounding up ropes, organizing equipment, and coordinating with the Nevada Department of Transportation (NDOT) and police staff while completing work on other inspection proj-ects. Add in a few last-minute time constraints to the daily schedule, the possibility of high winds, and the overwhelming obliga-tion to provide our best, and you might be able to grasp the anxiety as the first day of inspection neared. But the long hours and apprehension were more than justified the first time the underbridge inspection vehicle (UBIV) bucket low-ered from beneath my feet and left me suspended 880 ft above the canyon floor.

The inspection itself unfolded al-most flawlessly. After meeting and de-veloping a level of understanding with the NDOT traffic control staff, the UBIV operators, and the Hoover Dam Po-lice Department, our job as inspectors turned into directing the resources of these teams in an efficient manner in order to set up anchors and get as many

inspectors as possible “on rope” evalu-ating the structure. Our experience en-abled us to create a detailed outline of which ropes would be needed to access each column and arch segment, and our estimates of the time that would be re-quired to complete each inspection en-abled the team to share equipment and put as many as five inspectors on rope simultaneously. As the team member in charge of planning the rope allocations and inspection sequencing, this was my primary concern. I was also a little

concerned about how my body would physically hold up for two weeks dur-ing which I would regularly be making rope ascents of nearly 300 ft. I believe I ascended approximately 1,150 ft of ver-tical rope during the inspection, nearly the length of four football fields!

Of course, there will always be a few barriers to climb over with inspec-tions like this (pun intended). During the fourth day of the inspection, wind speeds in the canyon gusted in ex-cess of 25 mph, essentially grounding the UBIVs, our primary means of ac-cess to the superstructure. Fortunate-ly, the southeast corner of the bridge is shielded by a large rock outcropping that reduced the wind to an acceptable

15 mph. This enabled three inspectors to access the pier columns, abutment, and superstructure at the east end. The second team of three inspectors, how-ever, was left without means of UBIV retrieval from the arch interiors. In or-der to regain terra firma, a rebelay sys-tem was devised and anchored over the bridge railing and down to the top of the south arch rib below. The team had gained access inside the hollow arch ribs earlier in the morning, set anchors and ropes, and descended through the inte-

riors of both ribs for the purpose of performing a complete inte-rior inspection meeting all con-fined-space entry requirements.

The work was labor inten-sive, but the work setting was incredibly rewarding. Each time I stepped into the UBIV bucket and rode out over the bridge rail of this iconic struc-ture, I couldn’t help but be overcome by a state of pure wonderment at the beauty and grandeur of the Black Canyon and the Hoover Dam spread out before me. This, coupled with the adrenaline from the incredible height at which I was suspended and with the unsettling, somewhat fitful motions of the hydraulic plat-form, made for a nervously eu-phoric experience. The best by far was each time the UBIV platform pulled away and left me hanging on my rope, away from the roar of the diesel en-

gines and traffic of the bridge deck and alone with my spandrel column and the incredible view around it. I’ve nev-er been so careful to check my rigging and safety backup as I was each time I inched gingerly toward the bottom edge of the arch and then below into the sea of air extending 880 ft to the river below. There’s something instinc-tive that tells you, “You shouldn’t be here—get back on solid ground.” But at the same time, the rush is too good to pass up. Of course, these sensations are placed quickly in check with the re-minder that “I have a job to do.”

Frank Block, P.E., A.M.ASCE, is a project engineer for Stantec Consulting in Denver.

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were injury crashes, and 69 percent were property damage-only crashes.” If you compare these statistics with the 0.0 percent of fatalities connected and associated with the use of technical rope access work, you can clearly deduce that rope access work is very safe. That safety is also enjoyed by the traveling public. Not only is our work keeping the struc-tures safe for travel, but rope access also enables us to work unnoticed. More often than not, motorists do not see us and therefore are not distracted by us.

In addition to safety, rope access provides an economical way for owners to evaluate such assets as bridges, buildings, dams, tanks, and towers. In most situations there is no need

for the costly endeavor of shutting down traffic lanes for a full-blown traffic control setup. Additionally, there is little need for expensive mechanical equipment and specialized staff to lift or suspend the engineers or workers. A growing propor-tion of the rope access technicians in the United States and Canada—whether they perform inspections, maintenance, window washing, or other vertical work—are members of and certified by the Society of Professional Rope Access Tech-nicians. The organization’s mission, according to its web-site, is to “advance the safe use of rope access through educa-tion, developing standards, and administering certifications.” Stantec has nearly 20 professional engineers and engineers in

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nicholas cioFFRedi’s account:

The anChOrs were set. we tugged and pulled our anchor slings every which way from the

safety of the underbridge inspection ve-hicle bucket and then checked to make sure there was no chance of movement. There wasn’t. Still, I’d be lying if I said there wasn’t a moment of relief that first time the bucket dropped out from underneath me and I was floating, the Colorado River 880 ft below.

The first time I was “on rope” on this structure I was out for four hours. And

once you’re on rope, you’re on rope. Nobody’s going to come get you. No-body’s going to come and hang out.

On Hoover, we were actually on four ropes most of the time. You have to have ropes attached to both ends of the span so you can maneuver along the bridge length. You pull on one and re-lease the other so you can position your-self where you want. It takes a little bit of acrobatics, I guess.

It might have been the morning of the third day on rope before I stopped and turned around to face the chasm below and realized where I was. Ev-erything was very slow and surreal for a moment. I couldn’t help thinking, “What an amazing privilege!” That’s

when I realized that our job has its perks.

You’re so focused on the task at hand, inspecting this engineering mar-vel, doing your job, and making sure that you’re safe that it can take a while to stop long enough to absorb the ex-posure of it all. It’s not often you get to hang devoid of contact with any struc-ture while looking down on the Hoover Dam.

We always say, “There’s no glory in bridge inspection,” but Hoover was a glory job.

Nicholas Cioffredi, P.E., is a structural en-gineer and senior inspector for Stantec Con-sulting in Denver.

Tom A. Ritz, P.E., a senior structural engineer for Stantec, is “on rope”

during the inspection of the Hoover Dam Bypass.

Tom A. Ritz, P.E., a senior structural engineer for Stantec, is “on rope”

during the inspection of the Hoover Dam Bypass.

Stantec’s extensive rope access inspection experience with various bridge types and access difficulties guided our study of the bridge plans. In combination with insight provided by the NDOT staff, this experience revealed the most viable rope anchor locations, which in this case were primarily at the connections between the steel tub girders and the pier caps. At these locations, ropes could be anchored at the corners of each pier such that an inspector would have a line of sight across two faces of the pier column from one rope setup. This plan would allow inspectors to observe 100 percent of the column surface from just two rope setups at opposing cor-ners. The plan would also pro-vide access to the foundations and portions of the arch ribs at the base of the columns.

In order for an inspector to safely move longitudinal-ly across each spandrel bay via rope, the system must utilize dual sets of two ropes and an-chors located at opposite ends approximately 110 ft apart. In this configuration, the inspec-tors can ascend and descend both sets of ropes congruently in order to position themselves at any point between. This method is referred to as rebelay if it involves one looped system of two ropes and as rope-to-rope transfer if it relies on two separate dual-rope systems.

The arch ribs of the bridge are hollow and had to be in-spected from the interior for indications of internal defects. Once inside, inspectors re-quired a set of 700 ft long ropes to descend and ascend the steep interiors of the arches. Confined-space rope access requires an-other level of safety and training. The stagnant air inside the arch ribs requires continuous mon-itoring via four-gas air monitors. Each inspector is equipped with a monitor, and the readings are radioed to the access supervisor at prescribed intervals.

When using rope access, one of the most important as-pects of the plan is to know how much rope will be needed. You need the requisite length of rope below you as you de-scend through the inspection; otherwise, it would be like driving across Death Valley on a quarter of a tank of fuel. You simply won’t make the full journey. There aren’t going to be any rope stations along the way. Again, careful study of the bridge plans was necessary to complete the detailed approach. The rope length necessary to descend the spandrel and pier columns is equal to the vertical height of the pier and foundation plus an additional 10 to 15 ft for anchors and maneuverability. Inspection of the spandrel columns

and arch rib sections called for more careful calculation. The ropes would have to reach diagonally between spandrel col-umns across the bay, as well as below the arch rib and ev-erywhere between. Needless to say, these inspection routes called for some very long lengths of rope. We deployed up to 1,500 ft of rope for a single rebelay on the outer spandrel bays. Considering that we routinely had three climbers on rope at once, we needed more than 5,500 ft of rope on-site, not including rescue rigs.

Now that a detailed plan was in place to access and in-spect the structure, rigging the ropes and anchors was all that remained. In order to ob-tain the necessary access to the superstructure and the top of our rope systems, mechani-cal equipment would have to be used.

UBIV equipment can be very efficient when access-ing the superstructure of such multispan structures as the Mike O’Callaghan–Pat Till-man Memorial Bridge, of-ten requiring just a single deployment of the UBIV plat-form. Utilizing the UBIV ca-pabilities, inspectors can ac-cess the superstructure to set up the rope system and an-chors as planned while evalu-ating the interior and exterior of each girder. Once the rope systems are in place, inspec-tors can then deploy from the UBIV platforms. Imagine, at one moment you are in a se-cure bucket only to have it drop out from beneath you,

leaving you dangling free almost 1,000 ft off the ground—and with no parachute!

The inspection went as planned, aside from a single high-wind day that led to downtime for the required mechanical equipment. The in-

spection was completed ahead of schedule halfway through the seventh day. The structure’s impeccable condition was indicative of the care taken during design and construction and made for a relatively effortless inspection, especially in view of the bridge’s size and complexity. At the time of the inspection the bridge had been open to traffic for less than 27 months. As for the crossing’s future, it seems certain it will stand proudly in the Black Canyon for decades, if not centu-ries, to come—an infinity compared with the brief time that will elapse before its concrete facades are graced by the ropes and prying eyes of the next inspection, in 2015. cE

Ryan Nataluk, P.E., is a senior structural engineer and the bridge inspection program manager for Stantec Consulting in Denver.

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training who have been trained and certified by this group. What type of engineer chooses this line of work? Con-

sider the composition of our team: all of our rope access per-sonnel are full-time bridge engineers. We have assembled a team of engineers who have parlayed professional and recre-ational passions into a profound resource for public safety. When accessing remote, hard-to-reach locations, we are able to assess the significance of defects while “on rope.” That’s why our team is composed exclusively of bridge engineers with extensive inspection, design, and analysis experience. We need to know what we are evaluating. And we like being able to see details and defects up close. Most engineers never have that opportunity. Travel is an inherent part of inspec-tion, and finding senior engineers who are passionate enough about bridges, preserving public safety, and assisting agen-cies to leave home for days on end isn’t always easy. We train extensively with our gear and participate in rescue scenarios so that it all becomes second nature to us. We like the long, hard days on rope when on the job. Not all members of our rope access team were ini-tially climbers, but all have a love of adven-ture, the outdoors, and bridge engineering. Climbing isn’t always clean and fun either; in fact, more often than not, we encounter debris, bird waste, and cockroaches.

Planning an inspection of a structure on the scale of the Mike O’Callaghan–Pat Till-man Memorial Bridge begins with a solid understanding of the structure’s design: what to look for, where to look for it, and which access to use. The Hoover Dam By-pass is constructed primarily of reinforced, cast-in-place, and precast concrete elements with the addition of steel tub gird-ers that support the deck across its 16 spans. Each of these materials, as well as the manner in which they are assembled, is susceptible to deterioration, which may lead to weaken-ing and therefore to maintenance work. It is important to understand these potential deficiencies when planning and performing an inspection. At the 880 ft level, for example, what are the deficiencies that we might encounter?

Typical visual defects of reinforced concrete include crack-ing, delamination, and spalling in the concrete, coupled with potential corrosion of exposed reinforcing. Cracking in con-crete can be an indication of shrinkage of the concrete sur-face during curing, of corroding internal reinforcing that is expanding, or of overload causing flexural or shear stresses in the concrete element. These deficiencies can be detrimental to the structure on which they are observed. Consider that even a small crack can allow moisture and chlorides to pen-etrate through the concrete surface and begin to corrode the underlying reinforcing. Areas of particular concern occur at portions of the structure at which high shear and moment loads or zones of high compressive stresses exist.

Steel elements provide their own set of typical visual defects, for example, paint loss, corrosion, distortion, and cracking. The loss of paint and corrosion typically correlate. Even minor defects in the paint system may allow corro-sion of the underlying steel, undermining the paint system

around it and exacerbating failure. Corrosion is a concern as it leads to section loss of the affected steel, resulting in loss of load capacity.

Distortion can be indicative of stresses beyond the elas-tic limit state, resulting in permanent out-of-plane bending, twisting, or elongation of an element. These conditions must be evaluated carefully to interpret indications of stress rever-sal possibly caused by the likes of high transverse wind load-ing, seismic events, or immobility of the structure.

Fatigue cracking is a science unto itself and in general terms results from repeated loading over a high number of cycles. Certain design and construction details can increase the fatigue susceptibility or intensify the loading cycles ac-celerating localized fatigue. These details are classified as fa-tigue-prone details and are typically associated with welded connections in tensile regions of an element. Welds add a significant level of additional constraint or localized tension to the steel, reducing available yielding capacity. Category

D and higher details are of specific concern, as are design and construction decisions that place two or more welds in close proximity.

Cuts in steel members also can be problematic, especial-ly when encompassing abrupt changes in cut or direction through the material—for example, 90-degree cut copes. These details are often performed in the field and are well un-derstood by modern designers and builders alike. Smooth, rounded details transfer stress uniformly, allowing for less concentration of stress.

Discovering potential material defects of a structure and determining the locations at which they are most likely to occur are essential when planning access for a “hands-on” inspection.

Access to these areas on the Mike O’Callaghan–Pat Till-man Memorial Bridge, given its size and location between the steep walls of the Black Canyon, is more difficult than on other structures. An underbridge inspection vehicle (UBIV) typically can be used to access the undersides of the deck, girders, abutments, and top portions of the piers but is not able to reach much beyond 40 ft vertically from the bridge deck. This limitation leaves a large portion of the structure inaccessible through traditional inspection access methods. This is where we apply the ascending, descending, and tra-versing mobility of rope access. Rope access is one of the only suitable methods for inspecting the substructure of the Mike O’Callaghan–Pat Tillman Memorial Bridge.

[56] C i v i l E n g i n e e r i n g o C T o b E r 2 0 1 3

Frank Block, P.E., A.M.ASCE, left, and Tom A. Ritz, P.E., rappel down to an arch of the Hoover Dam Bypass.

We like the long, hard days on rope when on the job. Not all

members of our rope access team were initially climbers, but all have a love of adventure, the

outdoors, and bridge engineering.