r-, ARRY H. EDWARDS INDUSTRY ADVANCEMENT AWARDS Design-Construction Features of 1988 Winning Projects Emerald People's Utility District Headquarters Facility • Florida's Turnpike Over 1-595 and North New River Canal nnovative ideas and their implementation are two neces- sary ingredients in the continued success and longevity of any industry. As a stimulus to developing such ideas within the precast and prestressed concrete industry, in 1984 the PCI established the Industry Advancement Award. The award was renamed the Harry H. Edwards Industry Advancement Award in 1986 to honor the late Florida professional engineer who was instrumental in the formation of the Prestressed Concrete Institute and the early development of prestressed concrete in the southeast United States. Specifically, the award recognizes individuals or companies for developing fresh concepts that hold the potential to move the industry to the next generation of technology for industry materials, products, processes and applications. The judging of this program is held in conjunction with the annual PCI Design Awards Program and the announcement of the 1988 award winners was given in the September- October 1988 issue of the PCI JOURNAL. The purpose of this article is to give design-construction details, drawings and other data of the two winning projects. This information is provided to readers of the PCI JOURNAL with the hope they will further extend the concepts to other projects or develop fresh ideas of their own. PCI JOURNALJMarch-April 1989 29
Transcript
r-,
ARRY H. EDWARDSINDUSTRY
ADVANCEMENTAWARDS
Design-Construction Features of 1988 Winning Projects
Emerald People's Utility District Headquarters Facility
• Florida's Turnpike Over 1-595 and North New River Canal
nnovative ideas and their implementation are two neces-sary ingredients in the continued success and longevity of
any industry. As a stimulus to developing such ideas withinthe precast and prestressed concrete industry, in 1984 thePCI established the Industry Advancement Award. Theaward was renamed the Harry H. Edwards IndustryAdvancement Award in 1986 to honor the late Floridaprofessional engineer who was instrumental in the formation ofthe Prestressed Concrete Institute and the early development ofprestressed concrete in the southeast United States.
Specifically, the award recognizes individuals or companiesfor developing fresh concepts that hold the potential tomove the industry to the next generation of technology forindustry materials, products, processes and applications.The judging of this program is held in conjunction with theannual PCI Design Awards Program and the announcementof the 1988 award winners was given in the September-October 1988 issue of the PCI JOURNAL.
The purpose of this article is to give design-constructiondetails, drawings and other data of the two winning projects.This information is provided to readers of the PCI JOURNALwith the hope they will further extend the concepts to otherprojects or develop fresh ideas of their own.
Precast concrete beams and hollow-core floor and roof slabs were designedto act as a duct system enabling the thermally massive structural system to becooled by flushing it with outside air during the night. Under this system, heatabsorbed by the structural frame during warm days can be flushed out at nightto cool the building. On winter mornings, heat can be extracted from thestructure and used to preheat the building.
Jury Comment: "An ingenious idea for saving energy consumption throughthe use of precast concrete elements."
T his facility is the headquarters for acustomer owned electric utility serving
14,000 meters in rural Lane County, Oregon.The total area of the facility (comprising anoffice building, warehouse, and vehiclestorage/maintenance area) is 46,970 sq ft(4370 sq m) while the floor area of the officebuilding is 24,255 sq ft (2256 sq m).
in the office building, precast prestressedconcrete components were built andassembled in an innovative way that helps toreduce energy consumption by two-thirdsover conventional office building design.Custom built hollow beams are combinedwith conventional hollow-core slabs in athermally massive structure that absorbs
internal heat during the day. At night thesystem can he flushed with cool night air toprecool the building or heated air can bedrawn out to preheat the building in thewinter. Thin hollow-core slabs also allowedhigh windows for daylighting withoutincreased floor-to-floor heights.
A major goal in the design of this facilitywas to emphasize the utility's strongcommitment to energy conservation anddemonstrate new techniques in itsachievement. Two strategies, namely,Daylighting and Thermal Mass with NightVentilation, were chosen to gain dramaticenergy savings and prestressed concretecomponents were fundamental to each,
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•The first -- Daylighting -- relics on highceilings that allow tall windows to sendnatural light deep into the building. Thisreduces the need for artificial lighting and,with the loss of that heat source, cooling loadsare reduced as well. A usual, floor-to-floorheight in an office building is about 13 ft(3.96 m). With the beams placedperpendicular to the exterior walls, 8 in. (203mm) thick hollow-core slabs with a 4 in. (102mm) topping slab could be used for the deckleaving 12 ft (3.66 m) of uninterrupted heightto the ceiling.
The rule of thumb for daylighting says thatthe area of building receiving natural lightmust be within a distance of 2.5 H froth thewindow wall, Since H equals the height ofthe windows, it follows that the higher theceiling, the wider the building can be. With12 ft (3.66 m) high windows on both the northand south sides, the overall building widthcould then be 60 ft (18.3 m). Other deckstrictures would have required higher floor-to-floor heights. Hollow-core slabs allowed astandard height. In addition, its exposed,
smooth, bottom surface was perfect for theinward direction of natural light and thereflection of indirect artificial light. Onlypaint was needed.
• precast concrete components made evenmore important contributions to the secondstrategy -- Thermal Mass with NightVentilation. This approach depends on theuse of thermally massive materials exposed tothe interior of the building. Through the daythese materials slowly absorb heat frompeople and indirect lighting.
The system is then cooled on summer nightsby flushing with cool night air, thusprecooling the building and leaving it ready toabsorb new heat in tie morning. Heat storedin die thermally massive structural system canalso be drawn out of the frame and blown intothe space to preheat the building on wintermornings.
Another design rule of thumb (about allthere is to go by at this time) says that aminimum of 1 sq ft (0.093 sq in) of exposedconcrete surface per square foot of floor areais required for absorption. This was achieved
PCI JOURNAL^March-April 1989 31
TRELLIS
PRECAST DOUBLE BEAM
PRECAST HOLLOW-CORESLAB EXPOSED TO SPACEBELOW ------
CORE FLUSHINTAKE
AIR
SUSPENDED ACOUSTICBAFFLES
V VAV SUPPLYDUCT,
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CONCRETE BLOCK FIN WALLS
/CARPETED FLOOR
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/UPPER WINDOWS FOR DAYLIGHT
/-LIGHT SHELF B INDIRECT LIGHTSLOWER WINDOWS FOR VIEW
ONVENTIONAL RETURN DUCT
SCHEMATIC OF BUILDING SHOWING PRINCIPAL COMPONENTS
AIR INTO OUTSIDE END OF BEAMCAVITY FROM BUILDING SPACE
AIR OUT OF INSIDE END OF BEAMINTO CORE FLUSH RETURN DUCT
8'CMU BEARING/SHEAR WALL
TYPICAL PRECAST BEAM BEAM AT BEARING/SHEAR WALLS
DETAIL OF AIRFLOW IN BEAM /DECK ASSEMBLY
w
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by exposing all hollow-core floor and roofdecks. Concrete beams and concrete masonryunit fin walls add to that area. A diagramshowing a typical bay of the building isincluded and describes all the components ofthe system. Another drawing, showing howthe units are assembled to pass air through thebeam and hollow-core deck system, is alsoincluded.
The system takes advantage of the holes inslabs by leaving them open to the air spacescontained within the double beams describedearlier. Night ventilation is accomplished byblowing cool night air into the interior spaces,then drawing that air into openings at the endsof the beams. The air is distributed throughthe beam cavities to the holes in the hollow-core slabs where a special core flush return airsystem draws the air through the cores andout in alternate double beams into a ductsystem that either exhausts the warm air in thesummer or blows it into the building space inthe winter.
One of the more interesting facts about thisdesign is that while no precedent could befound for this method, it was all easily
Number and Description of Precast/Prestressed Concrete Components.
• Precast concrete columns14 - 16 x 16 in. (406 x 406 mm) columnscustom built to various heights for the slopingroof.Precast concrete beams
26 floor and roof beams, specially built in theform of tuning forks with two 8 x 24 in. (203x 610 mm) sides separated by an 8 in. (203mm) air space, with 20 and 30 ft (6.1 and 9.1in) simple spans. Beams are joined wherethey arc supported on concrete masonry unitbearing/shear walls at their outside ends; theopen inside ends straddle the precast columns.• Precast hollow-core floor and roof slabs75 hollow-core floor and roof slabs, 8 in_ (203mm) thick and 23 ft 4 in. (7.1 m) long leavingan 8 in. (203 mm) gap over the beam cavity ateach 24 ft (7.3 m) hay.•An additional 75 hollow-core slabs are usedconventionally around the building onstandard precast beams.
PCI JOURNAL/March-April 1989 35
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accomplished with standard precastcomponents. Of course, the beams werecustom made but with precasting that is bothsimple and economical. And it was throughthe use of conventional components andmaterials used, in many cases, in new ways orin new combinations, that made long terraeconomy possible under existing utility rateconditions.
Conventional office buildings in the PacificNorthwest can be expected to require about50,000 Rtu/sq ft/year under current energyconscious building codes. This design, whenevaluated by D.O.E., 2. C. is predicted to useless than 22,000 Btu/sq ftlyear, a savings oftwo-thirds in energy consumption -- anexcellent model to Emerald's customers andother utilities.
Implementation of ConceptThe real beauty of this concept is that
conventional and simple custom prestressedconcrete components could be assembled in anew way to help achieve dramatic energysavings without having to resort to costlyspecial fabrications. This made it possible topredict a reasonable pay back period thatmade the whole concept viable. (Increasedfirst costs were largely due to a sophisticatedcomputerized energy management controlsystem.)
As the details of the concept were worked
out, little precedent for these methods eitherin built projects or in industry promotion andguidance for designers was available.Consequently, much of the design andcomputer modeling was based onassumptions and rules of thumb. The clientwas advised that this was somewhatexperimental and that with monitoring, thearchitect-engineer might learn much thatwould help other projects in the future.
It appears that the industry could benefitfrom the promotion of thermally massiveprestressed concrete frame systems that canachieve important energy savings inbuildings. This should involve research intothe thermodynamics of the materials andcomponents. (At the beginning, for example,no information was available on how fasthollow-core slabs would give up their heat tocool air passed through their cores.)
Energy conservation will only become moresignificant as a design goal as energy ratesrise. The prestressed concrete industry shouldplay a major role in its accomplishment.
The total cost of the project (which includesthe office building, warehouse, vehiclestorage/maintenance area) was $4,061,000.The cost of the precast concrete work for theoffice building alone was $140,820.
The project was completed in February1988. During the past year the facility hasbeen operating to the total satisfaction of theowner, designers and company employees.
PCI JOURNALiMarch-April 1989 37
Florida's Turnpike Over 1-595and North New River CanalBroward County, Florida
Construction Inspector: Hunter/Reynolds, Smith & Hills Inc.,Hialeah, Florida.
Precast Prestressed Concrete Manufacturer: Capeletti Brothers, Hialeah, Florida.General Contractor: Triple R. Paving, Hialeah, Florida.Owner: Florida Department of Transportation, Tallahassee, Florida.
A special touch shoring system made it possible to span 151 ft (46 m) with anAASHTO Type V simply supported beam. With shoring at midspan, whilecasting of the deck, composite action would be ensured after concrete curingand load release. Substantial cost savings can be realized using this scheme.
Jury Comment: "A brilliant concept which can be applied advantageously toincrease prestressed concrete bridge spans."
T his project consists of twin structures,five spans each. The original design
concept centered around the use ofprestressed AASHTO Type IV girders insimple span configuration for Spans 3, 4 and5. These three spans were 99 ft (30.2 m) longwith an overall width of 70 ft 9 in. (21.6 m).Nine Type IV girders spaced at 8 ft 1 1/2 in.(2.48 m) were to support a 7 in. (178 mm)cast-in-place concrete deck. Spans 1 and 2,with span lengths of 130 and 151 ft (39.6 and46 m), respectively, were designed usingsegmental AASHTO Type V girders.
These girders were to be supported ontemporary shores and permanent piers. Theywere to be post-tensioned after casting andcuring a 7 in. (178 mm) concrete deck. Thesespans also had nine girders at 8 ft 1 1/2 in.(2.48 m) spacings. The original designdecision to use the segmental Type V girderswas due to concern over how to haul theselong girders to the site. The substructure for
the bridges consisted of reinforced concretecast-in-place piers supported on precastprestressed concrete piles.
After award of the construction contract, thestructural subcontractor decided to explorethe possibility of eliminating the post-tensioning system. Two new concepts for thesuperstructure were considered for Spans 1and 2. The first concept was constant depth,steel, welded plate girders supporting a cast-in-place concrete deck. The second conceptwas the use of full span Type V AASHTOgirders with a simple span design.
Preliminary designs were performed forboth alternate superstructures. It wasdetermined that the structural steel alternatewould have cost considerably more than theorig nal segmental design. However, use ofthe full span Type V ahcrnate indicated thatthere would be a reasonable cost savings withthe use of this system.
The first hurdle to overcome was the
38
shipping of the 151 ft (46 m) long Type Vbeams. Preliminary investigationsdetermined that the girders could be hauled tothe site through use of special haulingequipment. The next hurdle to overcome wasthe relatively long span for the Type V girder.In order to span 151 ft (46 m) with the TypeV beams, it became necessary to increase thenumber of girders from nine to twelve beamsper span with a spacing of approximately .5 ft11 in. (1.80 m). The 130 ft (39.6 m) spansrequired no additional girders.
In addition to increasing the number ofbeams in the long span, it was necessary toshore the girders during the casting of thedeck. A single temporary bent consisting ofprecast prestressed piles and a cast-in-placeconcrete cap was erected at midspan of Span2. A touch shoring system was used tosupport the girders during the casting of thedeck and was removed after the deck hadcured sufficiently. The use of the shoring
system ensures that the composite section ofbeam and deck can he used to support thedead load of the deck itself.
The prestressed concrete girder alternateproved to he the most economical alternative,although 900 linear ft (274 m) of Type Vbeam were added to the project. Overallconstruction savings through the use of thistype of system was $104,000. The use of thealternate superstructure system was madefeasible through a value engineering changeas allowed in the construction specifications.
Shoring MethodAs outlined in the project description,
shoring was used for the construction of thesecond span of the five span bridge. Use ofshoring made it possible to span 151 ft (46 m)with an AASHTO Type V beam. Althoughshoring is used often for precast, prestressedbuilding construction, it has seldom, if ever,
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been used for the construction of a full lengthsimple span bridge. Through the use of touchshoring at midspan, the negative momentgenerated at the support causes additionalcompression in the bottom of the girder andtension in the top of the girder. These stresseshelp relieve some of the final stresses whichare realized when the shore is removed. Inother words, the composite section gainedthrough the use of shoring, helps ensure thatthe deck can be used to support its own deadweight as opposed to the entire deck weightbeing supported on the girder.
The use of shoring dramatically changes thestress history in the girder. Traditionalmethods of simple span girder construction
result in the following stress history.Stresses on the noncomposite girder consist
of the prestress stresses, and stresses due tobending moments from self weight of thegirder, dead weight of the deck, and otheradditional dead loads applied to the girderprior to curing the deck. Finally, stresses dueto the bending moments from thesuperimposed dead loads such as barriers andwearing surfaces, as well as live loads arcthen borne by the composite section whichhas better section properties.
The diagram on the right gives a summaryof the typical stress calculations that need tobe carried out for a non-shored and a shoredsituation, respectively.
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SUMMARY OF STRESS CALCULATIONS
= 149.6' Wgirder T999pIF' Wdeck= 553p1^
5= 1679 0 iri3 !69C n. 5=41038 in? 5= 2n754ir13non -Comp non - comp comp comp
Use of the shoring reduces the effects of theweight of the deck on the girder. The girderis a simple span system when supporting itsown self weight. Therefore, prior to castingthe deck, stresses result only from prestressand self weight of the beam. When die deckis cast, the negative moment at the shore isopposite the stresses caused by self weight ofthe girder.
When the deck cures and the shore isremoved, the composite section of the beamand deck now support the weight of the deck.The stress level in the girder is much reducedcompared to traditional design andconstruction methods. Finally, superimposeddead loads and live loads act on the compositesection as they would have, had the structurebeen built by conventional methods.
Erection TechniqueIn order to obtain a longer span using a
simple span design for AASHTO Type V
girders, a temporary support was placed at themidspan of the Type V girders. This shorewas snugged up to the bottom of the beam sothat when the deck was cast, the load wassupported by a two-span continuous girder ofapproximately 75 ft 6 in. (23 m) spans asopposed to a single span of 151 ft (46 m).
This technique creates a negative moment atthe temporary support which placescompression in the bottom of the girder andtension in the top of the girder. Once the deckhad cured, the temporary support wasremoved. The deck formed a compositesection with the girder and was much strongerthan the noncomposite girder. The loadsresulting from the removal of the temporaryshore were resisted by a composite section,reducing the resulting stresses.
Typically, the maximum span for anAASHTO Type V girder is in the range of130 ft (39.6 m). Span 1 of this projectincorporated nine Type V girders in the crosssection to span 130 ft (39.6 m). Through the
Notes (21 MPa) prior to placing slab concrete1. Construct substructures and erect
in Span 2.
temporary supports. 5. Remove deck forms.2. Set Spans 1 and 2. Snug temporary 6. Remove temporary supports after slab has
supports to bottom of beams in Span 2. cured 14 days and reached 4000 psi (283. Form and pour intermediate and end
MPa). Supports shall be lowered
diaphragms in Spans 1 and 2. Form slab uniformly, in increments as directed by the
and place deck reinforcing steel. Engineer, to prevent excessive load4. Pour slab (except Pour 2). Check
concentrations at temporary bearing pointselevations and adjust temporary supports on individual beams.as required during placement of slab in 7. Form and pour slab (Pour 2).Span 2. Note: Intermediate diaphragm 8. Contractor may form and pour Spans 3, 4concrete in Span 2 shall reach 3000 psi
and 5 independent of Spans I and 2.
PCI JOURNAL^March-April 1989 45
use of the shoring techniques and theaddition of three girders in Span 2, a span of151 ft (46 m) was feasible.
Design ImplicationsThere arc many positive implications for
the use of shoring on bridge girders. Thepotential to achieve longer spans will resultin greater use of prestressed concrete forbridge construction. In addition, the safetyfor roadways below the structures at gradecrossings can be increased due to thepotential elimination of piers. Elimination ofthe construction cost of those piers is also abenefit. Shallower sections can be used tospan greater distances, resulting in reducedheights of fill for approach roadways atgrade crossings and interchanges.
In addition to cost savings which arerealized through the use of prestressedconcrete as opposed to steel, this type ofconstruction has proven to be less expensivethan the original post-tensioned system, eventhough additional girders were necessary.
Number and Dimensions ofPrecast Prestressed ConcreteComponents.
Size of Bridge:3- 99 ft (30.2 m) spans1-130ft(39.6m)span1 -151 ft (46.9 m) spanOverall length: 578 ft (176.2 m)
Type IV Girders
Quantity Length9 97fI03/4 in. (29.8in)18 98 ft 3 in. (29.9 ni)
Type V Girders
Quantity Length9 128 ft 9 314 in. (39.3 m)12 150ft93/4in. (46.() in)
,Wtr; Quautie, giseu .dins c arc for an,..tnl( hire uul}.
The twin structure i s identical.
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Closing CommentsThe major advantage of the new value
engineering design was die elimination of thepost-tensioning method by using a simplespan with shoring.
The originally designed system ofsegmental AASHTO Type V, longitudinallypost-tensioned, included nine girders in thecross section. Although three girders wereadded in the 151 ft span, elimination of thepost-tensioning hardware and field operationsassociated with post-tensioning resulted in anet savings in construction of about$104,000. It is believed that this erectiontechnique can be used (with sonicmodification) on other bridge projects wherelonger spans need to be attained.
Basically, use of this shoring technique forbridge construction will increase span lengthswhich can result in reduced substructure costsand/or reduced depths of structure. Precastprestressed concrete girders can be mademore competitive in longer spans.
The total cost of the bridge project is$3,252,313 with the precast prestressedportion of the work (including bothstructures) amounting to $1,456,278. As aresult, the unit cost is about $80 per sq ft.This figure includes the fabrication of theprestressed girders and piles together with theinstallation and driving of the test piles.
Structure 1 was completed in July 1988 andStructure 2 is scheduled to be finished insummer 1989.
