JUNE 12, 2017 m enr.comJUNE 12, 2017 m enr.com

ICONIC EYRIE

UPGRADE THE EMPIRE STATE BUILDING’S STEEL BROADCASTING TOWER?

WEAVE A SKYSCRAPING, HURRICANE-DEFYING

WORKERS’ NEST FIRST (P. 26)

INSIDE: THE

TOP 100

PROJECT

DELIVERY

FIRMS

open-air observatory at the 86th floor and premium viewing spaces at the 102nd and 103rd levels. Annually, these

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SPINNING ACHRYSALIS

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W hen engineers made plans to

reinforce and up-grade the carrying capacity of the Em-pire State Building’s mast and tower by adding 39 tons of steel, they had to find a way to protect pedestrians from fall-ing rivets, tools and materials. Roofing the observatory and building bridges over the sidewalks 1,250 ft below were lousy options. The top of the iconic New York City building has an

Workers weave a cocoon of steel, aluminum and cloth to create a safe work space far above the streets of Manhattan By Tom Sawyer

spaces host about 4.3 million visitors and generate about $85 million in revenue. Soaring above the busy streets, a 200-ft-tall steel broadcast tower bristles with antennas that generate about $20 million more. Together, the

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SEPTEMBER DAWN

By the light of blue LEDs illuminating the top of the Empire State Building, Local 40 ironworker Ruben Villagran nears the end of another shift at 6:10 a.m. He is working on one of the aluminum truss towers of the Haki Trak system, whose vertical rails capture and support the ballistic-fabric walls of a workspace cocoon.

BROADCAST HUB

The mast of the Empire State Building is topped by a premium, glazed observation space at the 102nd floor and an open-air VIP parapet at the

103rd. A temporary, hard-sided workspace and support for the “cocoon” brace back to the

conical ice shield above the VIP parapet; the cocoon floor is at the top of the steel panels. Fabric panels rise about 25 ft to a solid roof. The cocoon surrounds the lower part of the

broadcast tower, which has just been reinforced to carry backup antennas for a similar

array (here, seen above the worker on the cocoon roof). To improve future configuration flexibility, the strengthening goes well beyond

immediate requirements.

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observatory, mast and tower are the

crowning jewel of the 86-year-old

icon, which is owned by the Empire

State Realty Trust Inc.

The search for an alternative to

scaffolding dates to February 2014,

when the ESRT’s building engineer, engineer-of-

record Thornton Tomasetti, site safety engineer Plan

B Engineering and contractor Skanska USA Building

Inc. began to consult with New York City Dept. of

Buildings officials to devise a plan that would not only

protect the public and workers but also allow for the

strengthening of the mast and tower without having

to resort to sidewalk bridges.

They came up with a design for a sheltering

“cocoon,” which sits on a 560-sq-ft aluminum ele-

vated work platform, or “dance floor.” The platform

is braced from below by steel brackets through the

conical ice shield, which is there to shatter ice falling

from the tower.

Further, the outer edges of the dance floor are

guyed by cables leading up to the roof of the cocoon

and the tower above. Encircling the exposed base of

the tower just above the ESB’s roof, the floor is

enclosed by walls created by aluminum truss towers

arranged in an octagon and bridged by panels of

ballistic cloth, which slide in edge tracks from bottom

to top. To reduce exposure to dangerous winds, the

panels can be drawn down in a few minutes by rollers.

“The planning of the project took two years, in-

cluding six months to design the cocoon and [perform

the wind] testing in Florida,” says Tom Durels, ESRT’s

executive vice president and director of leasing and

operations. “That gives an idea of the amount of

thought and engineering that went into it.”

The assembly is designed to meet city codes for a

300-psf live load and a three-second wind gust of 98

mph. “It was wind-tunnel-tested to failure at 140 miles

per hour, and it was the test-sample support structure

that failed. It wasn’t the envelope,” says Peter Sjolund,

the ESRT’s senior vice president of construction. “You

are on the top of the Empire State Building, the most

famous office building in the world. You don’t want to

be on ‘film at 11.’ ”

Stealthy Work

Scott Seydor was project manager for the cocoon con-

struction. An architect, he joined Skanska USA in 2011

as a design manager for mission-critical, design-build

data-center work, which brought him to the attention

of Skanska executives looking for someone with a

strong design background to manage mission-critical

work in the Empire State Building, he says. One one

such project, Seydor managed the replacement of the

Art Deco mast’s 480 pieces of glass between the 90th

floor and 101st floor.

When he heard of the mast-strengthening project,

Seydor says he jumped at the chance to manage it, too.

“I said, ‘We can do it right. We can do it safe. Let me

do it. The project needs to be done.’ ” He adds, “I live

in Philly. I get up at 3:30 in the morning because I get

to do this. … I am an architect, and this is the most

iconic building in the world.”

Few New Yorkers—not to mention the hundreds

of thousands of annual visitors who meander around

the observation decks—are aware of the work being

performed above them by a small Skanska USA crew

and the handful of steelworkers from Skanska Civil

NE, a sister business unit. “It’s such a small space,

there’s only so many guys you can throw at it,”

Seydor observes.

Because the materials-handling path makes use of

the passenger elevators and public observation areas,

crews had to construct and, starting this week, will

COVER STORY

PROJECT DELIVERY

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Handrail

Cocoon roof

Cocoon tower

Fabric panel

Handrail

Light-gaugesteel siding

Iceshield

“Dance floor” support

Existing tower withnew steel panels

TOPPER The temporary cocoon structure encloses the base of the broadcast tower as it emerges from the truncated cone at the building’s roof.

LOGISTICAL CONSTRAINTS

Ultimately, all materials are delivered by brute force up a series of ladders and out through a submarine hatch in the ice shield. The fi rst workspace was created on a temporary extension of the skirt around the ice shield, which was given steel-sided walls to protect the workers as they next assembled the aluminum platform and fabric cocoon above.

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have to deconstruct the cocoon between the hours of

2 a.m. and 7 a.m., when the public spaces are closed.

From the loading dock, materials are navigated

through security scanners, down to a lower concourse

and up a service elevator to the 79th floor, where they

are carted to a passenger-elevator bank for a lift to the

85th floor and then transferred to a manually operated

1930s “mast elevator” for a ride to the 102nd floor.

After that, materials are hoisted up ladders and through

hatches by hand and with chain falls out through a

single “submarine hatch” in the flat-topped conical

roof that crowns the building.

Due to handling constraints, including the size of

the legacy elevator in the mast, the largest piece taken

up was a 6-ft, 4-in.-long W12 steel beam, says ESRT’s

Sjolund. A support for the platform framing, it weighs

2,833 lb.

To maneuver beams out of the submarine hatch and

into place, the assembly sequence first required the

installation of chain hoists on lifting booms projecting

from the tower. The steel beams were placed first,

building up the ice-shield roof just beyond the perim-

eter of the planned dance floor. Then, crews erected a

hard-sided wall around the first work area to prepare

for assembly of the dance floor, just above.

Creating a Safe Space

While there is only a few feet between the cone and

the hard side, the clearance creates a small storage area

and just enough of a safe space to bolt and splice the

hundreds of pieces of aluminum beams, floor plates

and vertical truss sections required to create the alu-

minum floor, towers and roof of the cocoon, which

begins just overhead.

The purpose of the work is to increase the steel tow-

er’s carrying capacity by beefing up the lower section of

tower above the roof, as well as by reinforcing its ties

into the structure. The ironworkers accomplished the

work with hundreds of pieces of steel plate and bar of

various thicknesses, with the majority of it 1 1/4-in.

plate, stitch-welded and bolted to the existing steel. The

maximum dimensions and weight of the components

are strictly constrained by the tortured logistics required

to get them there and the frequent need to fit them

between and around the structural features of the exist-

ing tower. “If we could have brought up 25-foot-long

pieces, we would have loved it,” says Sjolund.

The strengthening work included several phases,

the first of which started in fall 2015 and involved

strengthening the tower legs as they enter the build-

ing’s roof and carry loads down to the 101st level.

Crews added bars and plate to the existing steel by

replacing rivets with longer torsion-control bolts or

fitting plate between existing members and introducing

new braces, gussets and diagonals.

On the 101st to 103rd levels, the interior work re-

quired opening ceilings, walls and floors in public

spaces and was conducted during an around-the-clock,

three-week push during February and March 2016. It

was the only part of the work that interrupted visitor

access to the observatory spaces, and the interruption

affected only the smaller, premium spaces on the 102nd

and 103rd levels.

Work inside the completed cocoon enabled the

next phase of the tower strengthening. “The cocoon

allowed us to work uninterrupted through inclement

weather and 24/7, without disruption to our broad-

casters,” Sjolund says.

COVER STORY

PROJECT DELIVERY

SAFETY, SAFETY, SAFETY Wearing climbing helmets and fall protection, a crew of about a dozen Local 40 ironworkers as-sembled the 22-ton cocoon, beginning in late May 2016. The first steps were in the open air, but by the time the cocoon was finished and the workspace en-closed, “you could have been working in your basement,” says Scott Seydor, Skanska’s project manager through the assembly phase. The sound of the faraway city streets are lost when the wind rises and the cocoon’s fabric sides start rustling like luffing sails.

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TOWER SET

A triangular “Tomcat Truss”

tower segment is set in place (above)

as the cocoon frame takes form. All

assembly work atop the building had to

be accomplished between 2 a.m.

and 7 a.m., during the hours when the public observation areas below were

closed. Now that the tower

strengthening has been accomplished, cocoon disassembly

soon will begin.

PHOTOS COURTESY OF SKANSKA USA AND ESRT

HANDCRAFTED Worker (center) positions a Hugen portable drill to make a hole for a torsion-control bolt to fasten steel plates to the existing tower structure. Once positioned, a switch activates the drill’s electromagnetic base to hold it in place. Ironworkers (above) adjust a template to mark locations for new holes.

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To strengthen the tower, crews

welded and bolted on additional steel.

Further, crews enclosed the lower

part of the tower in new steel plate.

When workers need to de-energize

and service the existing upper

antenna array, the new, lower backup antenna array will

be used to continue broadcasting and its steel-plate

backing will protect the workers from radio-frequency

radiation as they climb up.

Antenna Upgrade

The mast’s antennas are licensed to third-party televi-

sion and radio broadcasters and data communications

providers. Further, space in the building’s upper floors

is leased to house transmission equipment and related

facilities, including “multichannel combiners” that send broadcasts of multiple

frequencies through common antenna arrays.

Nineteen FM radio and about a dozen television channels currently broadcast

from the tower. The FM stations use either a primary array about 100 ft above

the building’s roof or, lower down, the 50-year-old Alford Antennas backup

array, to which signals can be diverted when changes or repairs are needed on

the primary array.

Signals are conducted from the channel combiners on a lower floor via 31/8-

in.- or 61/8-in.-dia copper-clad coaxial cables in nitrogen-filled jackets. “We call it

plumbing—think … of 6-inch-diameter copper pipe,” says Ed Driscoll, the

ESRT’s manager of broadcasting. The big copper lines rise through the upper

floors and travel up the tower to the antenna. Having run additional lines for the

new backup array, the antenna installers will soon start to hang the 4.5-ton backup

array on the now-strengthened tower. Work will begin after the cocoon comes

down in mid-June.

A 2014 reconfiguration plan mapped out an upgrade to the tower’s antenna-

carrying capacity. The addition is driven by market forces, according to the ESRT’s

most recent quarterly SEC filing.

“The business of broadcasting TV and radio signals over the air is in flux,

due to deteriorating industry fundamentals and the ongoing Federal Commu-

nications Commission spectrum auction, and there is competition from other

broadcasting operations,” the statement acknowledges. New generations of

broadcasting equipment are expected to begin populating the tower in the

months and years to come.

Moving On

“One of the things about working on the Empire State Building, the world’s most

famous building, is we are constantly innovating and have the benefit of working

with the world’s leading experts,” says ESRT’s Durels. “Building this protective

cocoon is an example of that,” he notes, adding that the project “may lead others

to see what can be done on towers worldwide when it comes to this type of work.”

Seydor will not be around for the cocoon demolition. After years of getting up

at 3:30 a.m. and commuting 240 miles a day to lead what he calls a project of a

lifetime, the project manager has moved on to work closer to home at Genesis

Engineers, Plymouth Meeting, Pa. “It was … an incredible project. They knew

it wasn’t just a job to me—it was a passion,” he says. “This is the Empire State

Building: Things are different here.”

COVER STORY

PROJECT DELIVERY

TEMPORARY WORKS Part of the temporary works installed to facilitate cocoon construction, outriggers and chain hoists jut from the tower above the cocoon’s hard roof. The cocoon roof and deck were engineered for 300-psf dynamic loading and impacts from falling objects, as per code. The new screen antenna array will be installed in the space where the cocoon is now; the new array will look like the existing array (at left, between the X-shaped “turnstile” antennas). The turnstile antennas are scheduled for removal. The tall white column is a digital television antenna installed for CBS in 1999.