COVER FEATURE

An Innovative Design Solution for Precast Prestressed Concrete Buildings in High Seismic Zones

Robert E. Englekirk, Ph.D, S.E. Ch ief Executive Officer Englekirk & Nakaki, Inc. (EN I) Los Angeles, California

Dr. Englekirk has been a strong advo­cate of the use of precast structural systems in seismic areas. He co­founded ENI in 1994 in response to a need within the community to develop new building systems. In 1995, he won PCI's Martin P. Korn Award for his paper " Development and Testing of a Ductile Connector for Assembling Precast Concrete Beams and Columns." This latter paper forms the theoretical basis for much of the work discussed in this current paper. In addition to his work at EN I, Dr. Englekirk also serves as an ad junct professor at the Univer­sity of Ca li forn ia at San Diego.

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The author describes the deve lopment of an imaginative new structural system for precast, prestressed concrete buildings in high seismic zones. The key element in the system is the beam-to-column connection that is comprised of high performance ductile rod connectors. Fully tested, the design concept was applied to a four­story parking structure. The design features of the building are described together with the fabrication and erection highlights of the precast components. With the success of th is new structural system, the future prospects of precast, prestressed concrete buildings in high seismic zones look particularly bright.

U ntil now, the West Coast of the United States has not been fa­vorable to the construction of

precast, prestressed concrete struc­tures. To aggravate matters, the 1994 Northridge earthquake induced build­ing officials to tighten codes of prac­tice and thereby make it even more difficult for design professionals as well as owners and developers to specify precast concrete products in their projects.

Part of the problem is that in the high seism ic zones of the United States, structural systems are governed by the Uniform Building Code (UBC). Be­cause the provisions of the UBC are very prescriptive, the detailing require-

ments for concrete systems limit the ability of an engineer to develop a pre­cast frame system that does anything other than emulate the physical layout and performance of a comparable cast­in-place structure. Frequently, cast-in­place seismic systems are used to pro­vide lateral support for precast concrete buildings , causing structural design problems as well as coordination and scheduling difficulties at the jobsite.

To alleviate this situation , the Pre­cast/Prestressed Concrete Institute (PCI) together with the National Sci­ence Foundation (NSF) have spon­sored the Precast Seismic Structural Systems (PRESSS) program. Also, the Precast/Prestressed Concrete Manu-

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Fig. 1. Wiltern Center Parking Structure, Los Angeles, California.

facturers Association of California, Inc. (PCMAC) is carrying out a vigor­ous marketing program in the area.

All these efforts, however , will come to no fruition unless individual design engineers and owners/develop­ers take it upon themselves to develop new structural solutions and then courageously implement them in real world precast, prestressed concrete structures.

This article describes how, in only 4 years, an "idea" for a new structural system was transformed into an actual building (see Fig. 1) . The objective was to create a plant cast building that could provide functional and aesthetic freedom and yet survive, virtually without damage, an earthquake of catastrophic magnitude. The design features of the building are described together with the production and erec­tion aspects of the precast concrete components. The construction sched­ule and cost of the project are ana­lyzed . Lastly, the problems encoun­tered on the job are discussed as well as how a prospective user might ef­fectively exploit the attributes of the system.

July-August 1996

SYSTEM OBJECTIVES

An idea usually evolves from con­victions. For more than 20 years the author has been convinced that the post-yield behavior of concrete frame beams could be significantly enhanced if the shear transfer mechanism and the inelastic behavior region were sepa­rated. The author has never liked to rely on welding to establish a load path and is convinced that the attainment of optimal construction speed requires the use of dry connectors. Given these be­liefs, the objectives of the system that emanated from the idea were first de­fined and then vigorously pursued by the development team.

Among the most important of these objectives were: • The system must be capable of at­

taining the levels of distortion that are likely to be experienced during an earthquake of catastrophic pro­portions.

• The system must function satisfacto­rily after a catastrophic seismic event, i.e., it must continue to serve its purpose after the earthquake.

• The assembly process must not re-

quire special knowledge or unusual quality control measures to attain behavioral objectives, i.e., the erec­tion steps must be simple.

• The precast concrete components must be easily fabricated and not re­quire a significant investment in forms, i.e., rectangular form shapes are imperative.

• The connection assembly must allow for tolerances that are ac­cepted in the construction industry.

• Design/application flexibility is es­sential, i.e., the system cannot dic­tate either function or aesthetic.

• The developed system must be eco­nomical or it will not be used. The attainment of these objectives

was only possible because many tal­ented people (see Acknowledgment) were challenged by the concept and had the courage to think with absolute freedom, proffering how best a specific objective might be attained. Without perseverance and creativity, the opti­mal attainment of one objective usu­ally compromises the attainment of other objectives. The end result was that all objectives were attained and the mission was accomplished.

45

Fig. 2. Typical structural framing floor plan.

THE CHALLENGE Shortly after the Northridge earth­

quake occurred, The Ratkovich Com­pany, a Los Angeles based developer, approached the author's firm with a request to design a parking structure.

The developer had the following requirements: • A request to build a four-story park­

ing structure servicing a market, an office building and a historical the­ater used primarily for high caliber performances.

• The parking structure was to be lo­cated in an inner city area of Los Angeles where ensuring personal safety of the structure's occupants was of paramount concern, particu­larly because the garage was to be open 24 hours per day.

• The site was at the time being used as surface parking for the office building tenants. In order to build a structure on the site, the developer had to rent parking space for the of­fice building tenants at an alternate site nearby at a cost of $1200 per

46

day. Because the garage was to be adjacent to the "art-deco" theater, the developer wanted a garage that would join and yet serve as a visual transition between the market and the theater.

• The structure would be cost effec­tive in spite of its location in Seis­mic Zone 4, the highest seismicity zone in the United States.

THE SOLUTION

In 1992, Englekirk & Nakaki, Inc. initiated development of a connector, based on a completely different con­cept than traditional emulation design. The connector assembly was produced by Dywidag Systems International (DSI). It is called a Dywidag Ductile Connector© (DDC). The DDC allows precast concrete beams to be bolted to a precast column, simplifying con­struction while at the same time im­proving seismic behavior. Like a surge protector for a computer system, this connector contains a "capacitor" that

limits the loads to the balance of the system, while maintaining its integrity through very large earthquakes.

The "capacitor" is the ductile rod. This rod is made of a very high quality steel material, with controlled post­elastic properties. The balance of the connector components are designed and manufactured using capacity de­sign procedures so that they remain elastic even as the ductile rod yields. Thus, all post-elastic behavior occurs in the rod itself, protecting the beam and column from any possible damage.

The system was tested in April 1993 at the University of California at San Diego. The DDC system sustained more than 25 cylces of large displace­ment, including story drifts of 4.5 per­cent without damage.

A major hurdle was overcome when the International Conference of Build­ing Officials (ICBO) gave formal ap­proval for the new DDC connector as­sembly to be used. This was a key victory because the new connector maximizes the inherent advantages of precast concrete. Now, there was a precast concrete frame that not only satisfies code requirements, but will perform better than competing materi­als when subject to very large seismic displacements. Given this general ap­proval, the designers proceeded to de­velop specific precast frame details.

STRUCTURAL SYSTEM A structural system must provide a

load path for both vertical and lateral loads. Functional and aesthetic free­dom increasingly demand that the lat­eral and vertical load paths be com­bined in a frame. When the lateral load path is likely to be subjected to earthquake-induced loads and defor­mations, it must also be capable of ab­sorbing earthquake-induced energy. This requisite "toughness" is referred to as ductility, or the ability to bend and yet not break.

The structure pictured in Fig. I was built at 3780 Wilshire Boulevard in Los Angeles, California. The plan di­mensions of the building are about 191 x 210ft (64 x 58 m) for a total floor area of 160,000 sq ft (14900 m2).

The lateral load path for this building is provided by eight ductile frames

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~venly distributed throughout the 40,400 sq ft (3753 m2

) floor plate. A typical structural floor plan of the

building is shown in Fig. 2. Precast, prestressed girders span 32 ft (9.76 m) and double tees span 60 ft (18.3 m).

The uniqueness of the system stems from the fact that the entire lateral load resisting system can be fabricated offsite and assembled merely by bolt­ing the beams to the columns. Accord­ingly , it is the DDC connector that creates the uniqueness , because the components were all standard precast concrete members.

The beam-to-column connector hardware is developed from a standard DDC assembly shown in Fig. 3. In this structure, two standard assemblies (see Fig. 4) were placed at each end of each frame beam and the base of each frame column. This doubling of the connector assemblies is not a system requirement, but it was cost effective despite the fact that it required the use of relatively large frame beams and columns. Note that the beam and col­umn sections were 36 x 42 in. and 36 x 36 in. (915 x 1067 mm and 915 x 915 mm), respectively.

The key item governing behavior is the button head (ductile) rods that are cast in the columns and footings (see Fig. 3), for it is these ductile rods that ensure superior earthquake performance by absorbing earth­quake-induced energy with each post-yield cycle. As shown in Fig. 3, the steel transfer block is secured to two high strength Threadbars by an­choring nuts. This subassembly is then cast into the frame beam and column base.

The precast beam and column are connected by 1112 in. (38 mm) diame­ter high strength bolts (ASTM-A490). These bolts transfer tension loads and clamp the transfer block to the heads of the ductile rods. Shear is trans­ferred by friction. Construction dead load shear transfer is activated by the pretensioning of the high strength bolts.

Subsequent shear demands are de­veloped from passively activated com­pression loads that are flexurally in­duced ; accordingly, one need not be concerned with the quality of the as­sembling process once the system is in

July-August 1996

~ COLUMN

TIE ROD

DUCTILE ROD

POCKET~--

I . ~-...

1'-3" TEMPORARY CORBEL

It 4" XS" X 1 '-2 1/2" FOR EACH 2 ------, ROD GROUP

(2)-13fa" DYWIDAG THREADBARS Wj----, HEX NUTS

1 1/ " DIA. A490 BOLTS PRtTENSIONED TO 1 48k EACH

Elevation

Plan View

I

I I I I I I I I I I I I I L ______ _

1 .3A-· DIA. DYWIDAG DUCTILE RODS

Fig. 3. Elevation and plan of a beam-to-column connection showing Dywidag Ductile Con nector.

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Fig. 4. Dywidag button head ductile rods being assembled prior to installation .

place. This is an especially important feature in earthquake prone areas be­cause intended performance is as­sured. Note that a detailed develop­ment of the load path is contained in Refs . 3 and 4.

The shear-friction transfer mecha­nism makes it possible to provide erection tolerances. Such tolerances normal to the column face are pro­vided by the oversized bolt holes in the transfer block. Longitudinal toler­ances are attained through the inclu­sion of 1 in. (25.4 mm) of shim pack placed on either the column or beam side of the transfer block.

The initial thinking of the design team envisioned the need for a remov­able erection corbel for the beam but Spancrete of California, who fabri­cated and erected the building, felt that this step was unnecessary. Spancrete, a PCI-plant certified producer mem­ber, headquartered in Irwindale, Cali­fornia, was selected for this project be­cause they have for many years been known for the high quality of their products and superior service.

FABRICATION The team approach allowed Span­

crete to begin fabrication of the pre­cast frames far ahead of the site prepa­ration work . This saved the owner significant costs because the offsite re­placement parking did not have to be provided until Turner Construction

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Fig. 5. Precast colu mn being lowered into pos ition using guide studs.

mobilized onto the site, while giving Spancrete the freedom to match cast the frames one at a time.

The column cages were tied with the ductile rods in place (see Fig. 5). The columns were poured after the ductile rods were bolted to the column form. After they had cured sufficiently to allow them to be moved , the columns were placed on a flat casting bed, with the beam forms between them. Bolts were placed, but not tight­ened, through the beam connector block and into the ductile rods within the columns. A planned field tolerance of 1h in. (13 mm) between the beam and column was accommodated in the formwork. The beam cage was set in the form, and the beam was cast. The entire process took just 4 to 5 days per three-story frame.

The UBC requires that special mo­ment-resisting concrete frames be in­spected by a special inspector (Section 1701.5, ICBO, 1994). This require­ment can be met during fabrication by specially trained quality control per­sonnel employed by the producer, re­sulting in significant savings to the owner for it eliminates the need to hire an independent inspection agency at the plant.

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Fig. 6. Column bolts being fastened manually into foundation.

ERECTION The erection process used by Span­

crete was simple . Precast seismic columns were dropped over temporary guide studs (see Fig. 5) inserted into the ductile rods that were cast in the footing . Shims were set to plumb the column at the appropriate height then the bolts were manually tightened (see Fig. 6).

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Fig. 7. Erection of parking structure showing precast frame beam being lowered into place between columns.

Once the bounding columns were in place, precast beams were lowered into position (see Fig. 7) . Two bolts were then placed at the bottom of the beam and tightened using a calibrated torque wrench (see Figs. 8, 9, and 10) once the beam was properly aligned. The applied torque need only be enough to support the weight of the frame beam.

The total erection time for each frame was between 5 to 8 hours in­cluding initial bolt torquing. Most of the time, it was accomplished in less than 6 hours.

After the frame was assembled, the erector checked the final alignment. Adjustments were not required but, had they been required , they could have been easily accomplished be­cause bolting to this point was mini­mal. With the installation and tighten­ing of the remaining bolts , the full seismic capacity of the frame was at­tained. It should be mentioned that grouting the gap between the beam and column or hardware accommodat­ing the blockout shown in Fig. 3 is not a structural requirement.

SYSTEM ECONOMY The Ratkovich Company, a creative

developer, has for years been intrigued with plant fabricated construction for residential and office building applica-

July-August 1996

tions. They also believe that the most economical structure is produced by a team that includes the contractor. This design-build approach allows for an exploitation of creative structural sys­tems that are not possible given the traditional design/bid/build format.

Accordingly, The Ratkovich Com­pany first retained the design team, which included architect Greg Petroff and Robert Englekirk Consulting Structural Engineers, Inc. Conceptual plans were developed and given to Turner Construction Company who then established a preliminary budget and schedule. Next, the design team, in conjunction with Turner Construc­tion, developed reasonable alternative structural schemes, each of which were then priced.

Spancrete of California proposed two precast schemes, each of which appeared to be less expensive than the cast-in-place alternatives. One system proposed a shear wall braced building while the other incorporated the DDC in a precast ductile frame. Conceptual estimating is difficult when an experi­ence base exists for one system but not for the other. Nevertheless, Spancrete and Turner were able to factor in all elements that would affect construc­tion costs. Unfortunately, and all too often, thi s project cost approach is abandoned in favor of preparing an es­timate from a quantity survey and his-

Fig. 8. Alignment of bolt prior to tightening process.

Fig. 9. Bolt tightening process using torque wrench .

Fig. 10. Only enough torque was applied to support weight of frame beam.

torical data. This method entirely dis­regards the economies generated by plant precasting as well as a reduction in field labor and other trade activities.

Once Spancrete was on board, an-

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Table 1. Cost model (Sched ule 1 ).

Work item Cost

Site work $230.000

Foundations 230,000

Precast concrete 1.580.000

Topping slab 460.000

Stairs/towers/ miscellaneous iron 300,000

Two glass enclosed elevators 160.000

Electrical 300.000

Plumbing 105.000

Miscellaneous 230.000

Total cost $3,595,000

Note: Each line item includes the contractor' s general

conditi ons, overhead. and profit.

other design iteration was undertaken as Spancrete's cost saving suggestions were incorporated into the design. The DDC/Spancrete proposal turned out to be the most cost effective system even including absent time considerations. Turner's estimate was confirmed dur­ing construction.

The functional constraints imposed on this parking structure by the multi ­use (market, theater and office build­ings) occupancy requirement signifi­cantly affected construction costs . Internal and external speed ramps were required to accommodate the various tenant requirements. Never­theless, the cost model of Schedule I (see Table 1) demonstrates how effec­tive the design/build process can be, especially with complex structures.

The cost per gross square foot of parking including that which is on­grade under the structure was $22.30 per sq ft. The multiple ramping pro­gram and other project specific re­quirements significantly di sto rt unit cost figures. If undistorted unit prices were applied to a more conventional parked ramp, four-level structure, the price of a provided parking space would be on the order of $5000.

Most impressive is the construction schedule. Schedule 2 (see Fig. II) de­scribes the working weeks required to complete each of the independent con­struction operations. The erection of the precast concrete system required only 16 working days.

Preconstruction activities can also be accelerated by the design/bu ild pro-

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Mobilize

Site Demo

Earthwork

Foundations

Erect Precast

Topping Slab Rough/Pour

Elevators/MEP

Site work

Finishes/Final

7Wssks

Structural System

Fig. 11. Construction schedule (Sc hedu le 2).

Fig. 12. Cast-in-place subassembly at 3.5 percent drift (Cyc le 3). Note extensive cracking.

cess because precast concrete shop drawings can be developed simultane­ously with construction documentation as can the precasting process itself.

DESIGN SIMPLICITY AN D ACCEPTANCE

Strength methods are easily applied in the design process. A single assem­bly (see Fig. 3) is capable of develop­ing a reversible tensile load (T11 ) of 282 kips (1254 kN). The distance be-

tween the force couple is adjustable and can accommodate any beam depth. The load path on either side of the DDC is designed to sustain DDC loads at an overstrength to ensure their sub-yield behavior. Earthquake defor­mations and energy absorption are thereby confined to the ductile rods shown in Fig. 3.

This scheme differs from cast-in­place ductile frame construction where these actions must occur in the beam adjacent to the face of the column.

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The DOC is superior for two reasons: First, the material from which the

rods are made is more ductile than re­inforcing bars, and second, buckling of the rods during the compressive load cycle is prevented by the confin­ing concrete in the beam-to-column joint.

The approval and acceptance pro­cess for a proposed design is facili­tated by the existence of comparative tests and a quality control program, both of which have been accepted by ICBO and the City of Los Angeles, where the building described in Fig. 1 was built. The superiority of the DDC system is best exemplified by compar­ing Figs. 12 and 13.

Fig. 12 describes the behavior of a prototypical cast-in-place ductile beam-to-column subassembly, which has been subjected to only three cy­cles of post-yield deformation at a story drift angle of 3.5 percent. The test was conducted at the National In­stitute of Standards and Technology (NIST). 1 This test is used as a baseline standard for the NSF/PCJ/PCMAC funded PRESSS research program whose goal is the development of pre­cast concrete in all areas where seis­micity is a consideration.

Compare Fig. 12 to Fig. 13, which describes the condition of two precast beams and a column connected by a DDC assembly after it has been sub­jected to 16 cycles of po.st-yield be­havior, the last three of which were at drift angles of 3.5 percent. The sub­assembly test of Fig. 13 , privately funded by the author, was performed at the University of California at San Diego (UCSD) under the supervision of Professors Priestley and Seible.<

The test specimen differs from that described in Fig. 3 only in that button head forgings replace a machined rod which was screwed into an anchoring block embedded in the column .< Fur­ther, the minor spalling of the column shell has been mitigated by increasing the size of the threaded head and the inclusion of a larger confining shim plate at the column face.

From a connector reliability per­spective, it is important to realize that the bolts in the test program were not pretensioned. The DDC connection system can survive virtually any num-

July-August 1996

Fig. 13. Crack pattern of precast concrete frame assembly at 3.5 percent drift. Very little cracking is evidenced.

ber of severe earthquakes. If required, it can even be replumbed by manipu­lating the shim packs. The ductile frame system shown in Fig. 13 is ob­viously a superior system, especially from a damageability perspective.

SUGGESTIONS TO PROSPECTIVE USERS

The DDC was developed for the high rise frame building market. Any building that can be braced by a cast­in-place concrete or steel ductile frame is a candidate. A distributed bracing program would also allow the facile inclusion of entirely precast floor sys­tems. Imagine how much time could be saved through the use of an entirely plant cast vertical and lateral load car­rying system, especially if the skin is also precast and preglazed . Accord­ingly, the horizons are unlimited and this bodes well for precast concrete in the next century.

Like every system, the DDC system requires attention to certain details. In the design process, some attention must be paid to how and when the loads are imposed on the connector both in shear and flexure . In the de­scribed building, for example, four bolts had to be pretensioned in order to deliver the shear capacity required

to support the girder and precast dou­ble tees.

Initially, only the bottom bolts were pretensioned so as not to impose flex­ural loads generated by the erection of the precast component on the upper set of ductile rods. Once the precast components were set, the upper as­sembly was tightened and the topping placed. Flexural loads imposed on the upper ductile rods by the topping and live load need not be considered in a first yield determination of seismic strength.2 ..

Frame girder-to-column connections should be square. Accordingly, frame girders should not be sloped unless tol­erances are carefully checked. Precast concrete erection crews and inspectors are not trained to install or inspect high strength bolts. Preconstruction meet­ings and dry runs will ensure a smooth first time assemblage. Care must be taken not to overtighten the bolts.

This requires that AISC Specifica­tions be followed and that the torquing wrench be calibrated. Load washers are effectively used to allow for the subsequent verification of the desired level of bolt pretensioning. The erec­tion process on the prototype went smoothly and Spancrete crews were able to assemble an entire frame usu­ally in less than 6 hours.

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Fig. 14. Fin ished parking stru cture without landscaping.

NEED FOR NEW BUILDING SYSTEMS

American businesses are continually challenged by society to produce better and yet more economical products. Bu­reaucratic controls seem to thwart rea­sonable efforts yet they will continue to be a part of the process. Fortunately, the control process is becoming more cognizant of society' s needs and their role in the satisfaction of these needs. Academia is also responding by devel­oping the tools necessary to the confir­mation of new products.

In the construction area, this is in the form of laboratories that are capable of testing full or large scale subassemblies and in the development of computers and software packages that predict or confirm the behavior of structural sys­tems. Effectively used, these tools can significantly shorten the idea-to-real-

52

ization time frame. It is, however, im­perative that the development of an idea proceed in a logical manner.

Ideas abound but do not always re­sult in real life structures. To be suc­cessful, the path to realization should start with the involvement of a com­pany that is interested in and capable of pursuing the idea. The idea devel­opment stage must carefully consider the cost effectiveness of the product, because without cost effectiveness the idea will not be realized.

Component testing and system anal­ysis must be carefully undertaken be­cause large scale testing is an ex­tremely expensive way to refine a design. Testing the system is essential but not easily done. Behavior objec­tives must be confirmed not only by the loading program but also by the appropriateness of the instrumentation and the documentation.

A protocol for the approval of a sys­tem may need to be developed, as it was in this case, to establish a pass/fail criterion. The DDC moved from an idea to a constructed reality in less than 4 years, but the process required the dedicated efforts of a company created specifically to develop sys­tems. The success of this venture can be attributed to the close collaboration between the owner/developer and the design and construction teams.

COMPLETED BUILDING The Wiltern Center Parking Struc­

ture was essentially complete at the end of May 1996. Landscaping and other fixtures are yet to be fully real­ized. However, the facility is now being fully utilized.

The developer, design team, precaster and contractor were very happy with the

PCI JOURNAL

completed structure (see Fig. 14). The finished structure satisfied the func­tional and aesthetic objectives, as well as the cost and schedule constraints.

The functional constraints imposed on this parking structure by the needs of the diverse users significantly af­fected construction cost as did the aes­thetic amenities which included two glass enclosed elevators. Of the $22.30 per sq ft required to complete the building, structural costs were a very cost effective $14.10 per sq ft. The construction schedule extended over an 18-week work period, from contractor mobilization to final com­pletion. The structural shell, including foundations, accounted for just 7 weeks of this time (see Fig. 11).

CONCLUDING REMARKS PCI and the industry have been

preparing diligently for the next cen­tury. A program supportive of this ac­tion plan is already in progress in Cali­fornia. The successful completion of the Wiltern Center Parking Structure is a major step in solidifying this ef­fort. It should be emphasized that the new precast system is not limited to parking structures but can be applied to many types of high rise buildings.

Tough, inexpensive plant cast build­ings are now a reality . Precast con­crete buildings no longer need be viewed as "houses of cards," but can be recognized as the buildings most likely to survive earthquakes of catas­trophic proportions without damage. This structural superiority is due to the fact that the DDC system is tougher than comparable cast-in-place con­crete and structural steel systems.

New construction methods and sys­tems will be developed in unprece­dented numbers as the constru~tion in­dustry addresses the needs of an ever-expanding urban population. Ac­cepted procedures for realizing ideas are now in place and this should allow

July-August 1996

JURY COMMENTS ON HARRY H. EDWARDS INDUSTRY ADVANCEMENT AWARD

The Wiltern Center Parking Structure won PCI' s Harry H. Edwards Industry Advancement Award for 1996. The following was the jury's citation:

"This all-precast, prestressed concrete parking structure, situated in a high seismic zone, demonstrates how a brilliant idea, backed by full-scale tests, became a reality. Newly developed high performance beaded duc­tile rods were used in the beam-to-column connection, giving the precast frames post-yield ductility while maintaining the integrity of the joint. The straight forward constructability and cost effectiveness of the struc­tural system speaks well for the future of precast concrete in regions of high seismicity."

our construction industry to meet the demands of the 21st Century.

ACKNOWLEDGMENT The Wiltern Center Parking Struc­

ture would not have been successfully completed without the input of numer­ous individuals. In particular, the au­thor wishes to express his appreciation to Suzanne Dow Nakaki, president of Englekirk & Nakaki, Inc., for her valuable ideas in the design and exe­cution of the project; Juergen Plaehn, former vice president of Dywidag Sys­tems International, for taking the ini­tiative in the development of the Dy­widag Ductile Connector; Nigel Priestley and Frieder Seible, profes­sors of structural engineering, Univer­sity of California at San Diego, for carrying out the full-scale test assem­bly program.

CREDITS The following companies were re­

sponsible for the design and construc­tion of the Wiltern Center Parking Structure: Owner: Wiltern Associates, Lo s Ange­

les, California Developer: The Ratkovich Company,

Los Angeles, California Architect: Greg Petroff, Los Angeles,

California

Engineer of Record: Robert Englekirk, Consulting Structural Engineers, Inc. (REI), Los Angeles, California

System Developer: Englekirk & Nakaki , A Systems Development Corporation, Inc. (ENI) , and Dy­widag Systems International (DSI)

General Contractor: Turner Construc­tion, Los Angeles, California

Precast Concrete Manufacturer: Span­crete of California, Irwindale, Cali­fornia

REFERENCES 1. Cheok, G. S., and Lew, H. S., "Perfor­

mance of 1h -Scale Model Precast Con­crete Beam-Column Connections Sub­jected to Cyclic Inelastic Loads," NIST 4433 , National Institute of Standards and Technology , Gaithersburg , MD , October 1990.

2. Paulay, T. , and Priestley, M. J. N., Seis­mic Design of Reinforced Concrete and Masonry Buildings, John Wiley & Sons, Inc., New York, NY, 1992.

3. Nakaki , S. D ., Englekirk, R. E. , and Plaehn, J. L. , "Ductile Connectors for a Precast Concrete Frame," PCI JOUR­NAL, V. 39, No. 5, September-October 1994, pp. 46-59.

4. Engleldrk, R. E., "The Development and Testing of a Ductile Connector for As­sembling Precast Concrete Beams and Columns," PCI JOURNAL, V. 40, No. 2, March-April 1995, pp. 36-51.

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