Senior housing and care facilities haveused virtually every structural system nor-mally employed in relatively simple struc-tures: wood frame, masonry bearing walland concrete plank, structural metal stud,steel, precast concrete, poured-in-placeconcrete, and so on. The selection of theappropriate system or combination of sys-tems is usually the result of an evaluationof at least 12 factors.

CONSIDERATIONSThis chapter reviews these 12 factors andhow they can lead to the choice of a sys-tem. This section is followed by a reviewof typical issues faced when using themost common structural systems.

Soil ConditionsPoor soil conditions can have a major im-pact. A site requiring expensive piles maychoose a system such as steel that haslonger spans and requires fewer footingsand supporting piles. Unstable or variablesoils, subject to differential settlement,may preclude less flexible systems, such asbearing walls. In addition, the presence ofa high water table may preclude the inclu-sion of a basement, especially for build-ings over four stories. If poor soil foundon a site dictates that it must be removedprior to construction, the inclusion of abasement may be more economical be-cause soil must be removed anyway. Somesoil types, when located in zones subjectto seismic activity, can dictate much ofthe structure. As these examples indicate,it is advisable to have some basic geotech-nical data prior to making the selection ofa structural system or the decision to in-clude a basement.

The Program and ConceptThe program of uses and whether they willbe directly above or below one anotherfrom floor to floor is also a major factor. Abuilding that contains only nursing unitsor apartments can select from the simplestsystems because the required spans areshort. Spaces such as major dining or mul-tipurpose rooms need longer spans and arelikely to be reconfigured over time, andmid- or high-rise stacking of program islikely to require more complex systems.

Applicable CodesAt least three code issues directly impactthe choice of a system: the required loadsand subsurface soil conditions, the build-ing code use group and related permittedconstruction type, and special structuralrequirements to deal with extraordinaryconditions such as a hurricane or earth-quake. In addition, the choice of floorsystems can be influenced by fire-rating

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Conditions in selection of structural systems1. Soil conditions2. The program and concept3. Applicable codes4. Potential code changes5. Flexibility6. Impact on finished-ceiling and building height7. Material delivery and construction timing8. Local construction capabilities and preferences9. Ease of construction and schedule

10. Cost of the selected system11. Cost impact on other systems12. Appearance and aesthetic potential

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requirements, the ability to run mechani-cal systems and sprinkler lines, and theassembly thickness when overall buildingheight is an issue. The typical design liveloads are 40 pounds per sq ft (psf ) forresidential units and 100 psf for com-mon spaces.

If unusually heavy loading is re-quired in some areas to account for spe-cial radiology equipment, compact files,rooftop mechanical equipment, orswimming pools located above gradewithin the building structure, the addeddead load for these items for that partof the structure can be in the range of100 psf for mechanical systems to up to300 psf for some compact file systems.If known in advance, these loads can besupported by most systems.

More prescriptive are the use groupsand construction types incorporated inmost codes. Some states define assistedliving, the housing parts of a CCRC,congregate living, and other senior livingoptions as multifamily housing. In manystates, housing can be wood-frame up tofour stories. In others, wood-frame seniorhousing is permitted but restricted toone or two stories.

In addition, a growing number ofstate and local codes mandate structuresthat can withstand extreme stresses orloads, such as those generated by hurri-canes or earthquakes. In most cases,these requirements point the design teamtoward the more complex and oftenmore costly systems, such as steel or con-crete in multistory construction.

Potential Code ChangesThe codes governing senior housing andcare facilities are all subject to change,and some of these changes can influencethe selection of a structural system. For

example, the International BuildingCode, which many states are now adopt-ing—in whole or with modifications—astheir state building codes, has the poten-tial to alter the system choice. In thiscode, assisted living facilities with morethan 16 units are defined as use group I-1, and combustible structural frames,such as wood, are permitted for struc-tures up to four stories high.

In general, there has been a trend to-ward more code restrictions on the use ofcombustible structures for frail or con-fused populations that are hard to evacu-ate. Some experts argue that the additionof sprinklers as well as smoke and fireprotection is far more important thanthe relative combustibility of the struc-ture, but this argument is not necessarilyprevailing.

In general, it is good practice to de-sign to meet any likely future code re-quirements. This avoids the need for fu-ture waivers or upgrades in other systems(such as sprinklers).

FlexibilityMost successful buildings have to ac-commodate some growth and change.Over the last 20–30 years, senior livingenvironments have had to accommo-date more change than many otherbuilding types. For example, the in-creased frailty of many occupants, thedesire for more space and privacy, andother factors have required many spon-sors to reconfigure the basic buildingblocks of their facilities: resident rooms,nursing units, or apartment units.Some structural systems, such as theuse of bearing walls between units (vs.exterior walls and one corridor wall)can be very inflexible. The altering ofconcrete planks may also be problemat-

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ic if the desire is to cut through thefloor, as structural strands generallycannot be cut. Wood-frame and largerspan structures tend to be more accom-modating of change.

Impact on Finished-Ceiling and Building HeightSome structural systems, such as two-way(flat-plate) concrete slabs or bearing wallsand concrete plank, allow the designteam to minimize floor-to-floor height.The structure is only 7–9 in. thick andcan double as the finished ceiling. Othersystems, such as trusses or structural steelbeams, are often 10–15 in. deeper, andusually need to be covered by a hungceiling that adds 14–18 in. more thanflat-plate or concrete plank floors to theoverall floor-to-floor height.

Material Delivery andConstruction TimingThe choice of a system can have a signifi-cant impact on the project schedule.Some structural materials, such as wood,concrete blocks, poured-in-place con-crete, and structural studs, are readilyavailable. Others, such as structural steel,can have long lead times. Careful plan-ning can reduce the schedule impact, butdelivery time can still influence thechoice of systems.

Local Construction IndustryPreferences and CapabilitiesVirtually all local construction marketshave preferred systems, as well as systemsthat are rarely used. For some areas, pre-stressed or post-tensioned concrete, forexample, is rarely used. Local preferencesand familiarity typically result in lowercosts.

Ease of Construction and ScheduleIn addition to local preferences, some sys-tems are selected due to their ease of con-struction (particularly wood or metal-stud framed buildings) and the construc-tion schedule, to diminish the impact ofsevere winter weather conditions. If theconstruction schedule is such that con-crete would be placed or masonry bearingwalls constructed during winter months,the steel-frame or structural-stud buildingsystem is often selected to avoid the ne-cessity of heating and protecting thestructure while concrete or mortar cures.

Cost of the Selected SystemBecause of the economics of most se-nior living projects, first cost is always amajor factor.

Cost Impact on Other SystemsWhat has been less well understood bymany owners and their design teams isthe structural system’s cost impact onother building systems. For example:

• The systems that add to floor-to-floorheight can add significantly to thecosts of interior partitions, exteriorskin, and other systems.

• When systems must be covered, atleast part of the cost of the droppedceiling and soffits should be consid-ered in the structural cost

• Some systems, such as wood rooftrusses in some states, require addi-tional sprinklers and fire protection.

• Some systems, such as bearing wallsand structural steel, can complicate(and increase the cost of ) the distrib-ution of ducts, conduits, and othersystems.

Considerations

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� Trusses at the WeinbergVillage Winter Garden areboth structurally functionaland aesthetically important.Weinberg Village,Pittsburgh, Pennsylvania.Perkins Eastman ArchitectsPC. Photograph by JimSchafer.

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Appearance and AestheticsIt is uncommon for the structure to be ex-pressed in most senior living environ-ments, but when it is, its appearance canbe important. For example, some designteams dislike the joints inherent in theplank system. Others find the runningelectrical services and sprinkler lines on theceilings created by flat plate concrete slabsto be a significant aesthetic problem, andtherefore place these utilities in walls.There are, however, some opportunities toexpose the structural system as an impor-tant part of the project’s design vocabulary.

STRUCTURAL SYSTEM TYPESBased on the factors discussed above,there are some issues that come up fre-

quently in the review of options. The fol-lowing is a brief summary of the discus-sion surrounding nine of the most com-mon structural systems.

Wood-FrameWith the exception of buildings in someurban areas, senior housing is predomi-nantly wood-frame. This system is typical-ly inexpensive, it can be implemented bya wide variety of contractors, it is fast, andit can be flexible. The span limitations canbe overcome with trusses, laminatedbeams, heavy timber, or mixing with steelor other systems in larger spaces. Themost common reason for not using woodis current or probable future code restric-tions on combustible structural systems.

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Source: Perkins Eastman Architects PC.

CHARACTERISTICS OF STRUCTURAL SYSTEMS

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Another potential disadvantage is that theflooring surface can feel bouncy underfootin high traffic areas.

Structural StudThe use of steel studs instead of wood iscommon. It often has a slightly highermaterial cost, but it is noncombustible. Itsother advantages and limitations are similarto those of wood-frame construction, yetan additional problem can occur especiallyin exterior walls. Water damage or mois-ture problems can lead to a loss of structur-al integrity, even if the steel is galvanized.

Bearing Wall and Concrete PlankA third frequently used option is a combi-nation of masonry bearing walls and pre-cast concrete plank. Again it is a simplemethod, familiar to many contractors, rel-atively low in cost, and relatively quick toimplement. The span limitations can beovercome by mixing it with other systemsfor larger spaces. The major problemswith this system are its relative lack offlexibility; performance on unstable soil;height limitations (50–70 ft in most con-struction markets); impact on the distrib-ution of mechanical, electrical, plumbing,and fire-protection systems; and the occa-sional shortages of masons and/or precastcompanies. Senior housing projects oftenhave large quantities of open dining andcommon space on ground-level floors,which become difficult to achieve withthis system. In addition, many designteams object to using the underside of theplanks as the ceiling for the space below.When this objection leads to having ahung acoustical tile or sheetrock ceiling tocover mechanical/electrical distributionsystems and the uneven joints betweenplanks, some of the cost advantages of thissystem are eroded.

Steel and Concrete PlankThe fourth option eliminates some, butnot all, of the objections to bearing walland plank. This option has minimalheight limitations (as long as the beamsare in the same plane as the walls), isquite flexible, performs adequately onunstable soil, and rarely suffers from alack of skilled manpower. On the otherhand, steel requires fire-proofing, hungceilings are almost always required, steelcan have long delivery times, and thefloor-to-floor heights are greater.

Steel and Poured-Concrete DeckThis option has somewhat the samecharacteristics as the steel and plank sys-tem, except that it is more costly and thedepth of the system is greater than thatfor steel and concrete plank, due to theinclusion of intermediate beams.

Precast ConcretePrecast concrete can be used for morethan exterior wall systems. It is also usedin some locations for the columns,beams, and bearing walls. It is also acommon structural choice for garages,site bridges, and other simple long-span,heavy-load structures. Some areas, how-ever, are not served by a nearby sophisti-cated precast company. Moreover, manysenior living facilities do not have thescale and degree of repetitiveness neces-sary for precast to be cost effective.

“Beam-and-Slab” Poured-in-PlaceConcreteConcrete is commonly used in manyparts of the country. It is a particularlycommon choice for projects that musthave a noncombustible structure or mustwithstand significant lateral loads, suchas those produced by hurricanes. It is

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also relatively easy to build in most localconstruction markets, and it can producea relatively flexible building. Poured-in-place, however, tends to be relatively ex-pensive and often has greater thicknessthan steel-and-concrete plank.

“Flat-Slab” Poured-in-PlaceConcreteA two-way, flat-slab concrete structure is a common choice for taller residentialbuildings since it minimizes floor-to-floor height, is fast to build, creates afinished ceiling with the underside ofthe slab, permits flexible column place-ment, and is relatively easy to brace orstiffen for lateral loads. This option,however, requires substantial reuse offorms (usually created by a mid- tohigh-rise program) and an experiencedstructural concrete subcontractor tomake the cost acceptable. Even whenthese conditions are met, flat-plate struc-tures are usually substantially more ex-pensive than some of the other options.

Prestressed and Post-TensionedConcreteThese two options have some of thesame advantages and disadvantages offlat-plate, but are less frequently used.The systems can be thinner than flat-plate but are also more costly. In addi-tion, there is less flexibility in cutting theconcrete in future modifications, due tothe locations of structural steel tendonsembedded in the concrete. The construc-tion industry in many parts of the coun-try does not have the experience to im-plement these systems.

As a final point, it is common to em-ploy two or more systems in a single pro-ject. In some CCRCs, for example,poured-in-place has been used for thefoundations, precast in the garages, struc-tural stud for residential wings, andstructural steel for the common areas.Overall, the selection and design of astructural system, or combination of sys-tems, is an issue with significant cost,aesthetic, and functional implications.

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