STEEL CONSTRUCTION AND TEAM EFFORT PROMOTE AFFORDABLE DESIGN FOR NYC APARTMENT HIGH-RISEModern Steel Construction / September 2001

Neil Wexler, P.E.

Market-rate housingis driven by costs.Because of the in-come constraintsinherent in renting

apartments at market rates, construc-tion costs must be kept within accept-able limits for the project to be viable.In cities such as Manhattan wherehigh-end residential construction is thenorm, many developers are not famil-iar with the variable-cost benefits avail-able from using structural steel toconstruct residential buildings. A Man-hattan apartment building located at215 E. 23rd Street, scheduled for occu-

pancy this autumn, is testimony to thecost benefits of structural steel, as wellas its potential for creative adaptationto meet the special needs of residentialconstruction. The 22-story buildingcontains 74 apartments targeted tomarket-rate rental or slightly better.The site it occupies is 48’ wide with six-story buildings on each side. Theground floor provides commercialspace, and the basement houses me-chanical rooms, storage and otherbuilding services. The facade is re-cessed at the seventeenth floor to com-ply with zoning setback requirements.

When owner/contractor LevineBuilders, Inc. of Queens, NY, made theinitial decision to use steel framing forthe project, the first objective for theconsulting structural engineer was tomaximize the available variable-costbenefits. To make the project work, thechallenge facing the designers collec-tively was to squeeze an extra floorinto a vertical site plan constrained bythe New York City building code. Thatmeant achieving a 9’ - 2 5/8” floor-to-floor finished height for a total of 22residential floors, an especially ambi-tious undertaking for steel framing,which is commonly perceived to re-quire 12’ from floor to floor.

Structural engineer, Wexler & Asso-ciates, and project architect, ADG, Ar-chitecture and Design P.C., both basedin New York City, met that challengeby working hand-in-hand from projectinception. The shallow floor system,designed by Wexler, required an ex-traordinary degree of coordination inboth the structural and architecturallayouts.

The structural system for the build-ing consists of a conventional steelframe with metal deck and concretefloors supported on composite steelbeams. To minimize the floor sand-wich, partitions are aligned with thebeams, allowing the ceilings to bepushed to within 6” of the bottom ofthe metal deck. With little headroomavailable, fitting ductwork and cablesneeded for services required tight con-trol and close coordination with all thetrades.

Selected to provide a two-hour firerating, the floor system consists of 31/4” of lightweight concrete coveringmetal deck 3” thick. Total floor thick-ness of 61/4” is therefore comparable toconcrete flat plate construction. Thefloor system allows a maximum spanof 13’, producing room dimensions inthe acceptable range for market-rateapartments.

Raising ceilings to the top of thebeams also served to maximize archi-tectural ceiling height. Following ap-plication of sprayed fireproofing tometal decks, the ceilings were finishedwith sheet rock, and soffits were cre-

September 2001 / Modern Steel Construction

(Left) Construction is nearing completion for autumn occupancy of new market-rate apartments at 215 E. 23rd Street in New York City. (Below) Standard moment connections were used in all directions. Construction photos by Gaston Dubois & Associates, New Hyde Park, NY.

ated at the beams and girders. Steelframing afforded additional design lat-itude by virtue of its given advantagesover concrete: allowing increased roomsize by eliminating the need for thickconcrete shear walls, steel framing per-mitted increasing room size, and rela-tively fewer columns yields morecolumn-free space for greater designflexibility.

Designed entirely for function andcost, other elements of the floor struc-ture include cambered, unshored com-posite construction, which is moreefficient than shored composite beamsor bare steel. Furring fastened to themetal deck also contributes to both costand height savings in the ceiling as-sembly.

The recess at the seventeenth floorwas framed on special 14” deep steelgirders. Special seated connections forthese heavy girders were welded to thecolumns.

The lateral-load resisting systemconsists of spandrel moment frames inboth directions. Eighteen differentwind and seismic load combinationswere considered, and the structure wasdesigned to withstand the most unfa-vorable combination. To resist uplift,rock anchors were lowered below thefootings and embedded into thebedrock (Manhattan Shist) at four loca-tions. Special base plates were de-signed to connect the anchors throughthe foundation to the steel columnsabove. Safety factors of 1.5 or betterwere designed for uplift and sliding atthe building base.

Back to the future for multi-family housing

The structural design for 215 E. 23rdStreet takes full advantage of the inher-ent advantages afforded by steel con-struction. Its superior efficiencyrelative to concrete permits the use ofsmaller transfer girders and reducestotal weight, along with lateral andgravity loads, for reduced foundationrequirements. The ductility of steel isan added benefit for seismic design.And the use of prefabricated steel of-fers further opportunities for reducingcosts by increasing the pool of suppli-ers for competitive bidding.

From the 1930s through the 1950s,high-rise apartment buildings weretypically built using structural steel.Many hundreds of those buildings in

New York City are still in use today.Now, buildings such as 215 E. 23rdStreet are matching the floor-height ad-vantage that helped sustain the domi-nance of concrete construction in thedecades that followed the first steelage. As tangible proof that steel is moreversatile than ever, the designs forthose buildings are sure to change per-ceptions and open eyes to new possi-bilities for residential construction.

Neil Wexler, P.E., is President ofWexler & Associates in New York City.

STRUCTURAL ENGINEER: Wexler & Associates, New YorkCity

ARCHITECT: ADG, Architecture and Design P.C.,New York City

STEEL FABRICATOR: Namasco, Suwanee, GA (AISC member)

GENERAL CONTRACTOR: Levine Builders, Douglaston,Queens, NY

SOFTWARE: RISA 2D

RAM SBeam for designing com-posite steel members

View of metal deck and fire-protected beams prior to gypsum board installation.

Framing the beams at the partition lines allowed ceilings to be raised close to thebottom of metal decking. Fireproofed decking is now ready for sheet rock, andsoffits will be added for an aesthetic finished look.