Showing papers in "Pci Journal in 1999"

Preliminary results and conclusions from the PRESSS five-story precast concrete test Building

Abstract: A large-scale five-story precast concrete building constructed to 60 percent scale was tested under simulated seismic loading as the culmination of the 10-year PRESSS (Precast Seismic Structural Systems) research program. The building comprised four different ductile structural frame systems in one direction of response and a jointed structural wall system in the orthogonal direction. The test structure was subjected to seismic input levels equivalent to at least 50 percent higher than those required for UBC (Uniform Building Code) Seismic Zone 4. The behavior of the structure was extremely satisfactory, with only minimal damage in the shear wall direction, and no significant strength loss in the frame direction, despite being taken to drift levels up to 4.5 percent, more than 100 percent higher than the design drift level. The test validated the Displacement-Based Design (DBD) approach used to determine the required strength and confirmed the low damage and low residual drift expected of the building.

Seismic behavior and design of unbonded post-tensioned precast concrete frames

Abstract: Unbonded post-tensioned precast concrete walls are constructed by post-tensioning precast wall panels across horizontal joints using post-tensioning steel which is not bonded to the concrete. This paper describes an analytical investigation of the seismic behavior and design of these walls. Unbonded post-tensioned precast walls with strength and initial stiffness similar to monolithic cast-in-place concrete walls can be designed to soften and undergo large nonlinear lateral drift with little damage. The nonlinear behavior is primarily due to the opening of gaps along the horizontal joints. A performance-based seismic design approach is proposed in which the walls are required to resist design level ground motions with little damage and severe survival level ground motions with damage but without failure. Shear slip along the horizontal joints is prevented by design. Nonlinear dynamic analyses show that, compared to cast-in-place walls, unbonded post-tensioned precast walls undergo larger drift, but accumulate significantly smaller residual drift during an earthquake.

An Overview of the PRESSS Five-Story Precast Test Building

Abstract: At the culmination of the PRESSS (Precast Seismic Structural Systems) research program, a 60 percent scale five-story precast/prestressed concrete building will be tested under simulated seismic loading. This paper describes the prototype buildings used for design and the structural features of the test building. The buildings were designed using the direct displacement based approach, which is able to take advantage of the unique properties of precast/prestressed concrete using dry jointed construction. The test building incorporates four different seismic frame systems in one direction, and a jointed shear wall system in the orthogonal direction. Pretopped double tees are used on three floors, while the other two floors are constructed using topped hollow-core slabs. A major objective of the test program is to develop design guidelines for precast/prestressed concrete seismic systems that are appropriate for use in various seismic zones. These design guidelines can then be incorporated into the appropriate building codes.

Precast, prestressed pedestrian bridge : World's first Reactive Powder Concrete structure

Abstract: Spanning 197 ft (60 m), this precast, prestressed pedestrian/bikeway bridge in Sherbrooke, Quebec, is a post-tensioned open-web space truss containing no conventional steel reinforcement. Made up of six prefabricated match-cast segments, it was manufactured using Reactive Powder Concrete (RPC), a cement based material proportioned with sand, cement, and powders of silica fume (microsilica), and quartz, with fine steel fibers added to enhance ductility. In the top and bottom chord member, the RPC has a compressive strength of 29,000 psi (200 MPa). For the web member diagonals, RPC was confined in stainless steel tubes, attaining improved ductility and a compressive strength of 50,000 psi (350 MPa). An extensive program monitoring bridge deflections and forces in the prestressing tendons has been implemented to provide information on long-term performance of RPC.

A precast segmental substructure system for standard bridges

Abstract: A precast segmented substructure system for standardization is presented. This system is intended to support precast concrete girder superstructures in non-seismic regions and provides an alternative to current cast in place systems, particularly for areas where reduced construction time is desired. The substructure system is made up of predominantly precast elements. Four different column sizes with one basic cap shape are proposed to be assembled as single column, straddle and frame bents for varying heights and widths of standard bridges. Precasting allows for increased use of high performance concrete in the substructures, thus improving durability. In addition, the greater compressive strength of the high performance concrete is utilized to reduce the handling weight and dead load of the substructure units, facilitating construction. The construction method proposed will significantly shorten on site construction time. Shortened construction time, in turn, leads to important safety and economic advantages when traffic disruption or rerouting is necessary.

Full-scale testing of shear keys for adjacent box girder bridges

Abstract: Adjacent precast, prestressed box girder bridges are widely used in the United States, but the shear keys between the girders tend to crack and leak. Three different shear key configurations were studied, i.e., a current detail where the shear key is approximately 10 in. (250 mm) from the top of the girder and grouted with non-shrink grout, this same detail grouted with epoxy rather than non-shrink grout, and a proposed mid-depth keyway grouted with non-shrink grout. The tests were conducted on a full scale, four-beam assembly which represented part of the bridge. The results showed that the currently used shear key detail cracks due to thermal stresses generated as the beams deflect upward and downward due to daily heating and cooling. The mid-depth shear key is less susceptible to these stresses and was found to be more resistant to cracking. Loading did not appear to cause new cracking, but rather seemed to propagate existing thermal cracks.

Design of prestressed flexural sections by the unified design approach

Abstract: The Unified Design Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members was incorporated as Appendix B of ACl 318-95. The provisions are intended to unify the strength design of reinforced and prestressed concrete sections based on their ultimate behavior limit states. The new provisions affect the maximum reinforcement limits for flexural members, strength reduction factor O and moment redistribution. This paper presents a procedure for the design of prestressed flexural sections by the Unified Design Approach. Design examples are given to illustrate the design procedure. The new procedure defines a transition behavior region in which the strength reduction factor O, to be used for strength computation, varies linearly with the strain in the extreme tension steel. The design of sections falling in this behavior region involves an iterative procedure. Some design aids are given to facilitate design in this transition region.

Tendon stress in continuous unbonded prestressed concrete members - part 2: parametric study

Abstract: This paper describes a nonlinear numerical model capable of predicting the response up to failure of unbonded, partially prestressed, continuous, concrete beams, and presents a comparison of results from the model against test data. Loading pattern, type of loading and degree of concrete confinement are shown by means of a parametric study to have a significant effect on the tendon stress at ultimate. Finally, modifications are suggested to the current A23.3-94 Canadian Code equation for predicting the tendon stress at ultimate in concrete members prestressed with unbonded tendons, in order to consider the contribution from all plastic hinges likely to develop under a particular patten of loading. Predictions from the modified equation are shown to be in good agreement with available test data.

Shear behavior of concrete beams prestressed with FRP tendons

Abstract: FRP reinforcements have excellent properties for use in concrete structures including high corrosion resistance and high tensile strength. However they have some technical drawbacks, particularly their lack of ductility and low transverse strength. This study deals with an experimental investigation of the shear behavior of concrete beams prestressed with CFRP tendons. In the experimental program, the shear-tendon rupture failure mode was investigated in detail and experimentally confirmed. Shear tests showed that premature failure due to shear-tendon rupture is likely to occur in concrete beams prestressed with FRP tendons, resulting in reduced load carrying capacity. The premature failure is due to tendon rupture by dowel shear at the shear-cracking plane and is attributed to the brittle behavior and low transverse resistance of FRP tendons.

Loadbearing Architectural Precast Concrete Wall Panels

Abstract: Architectural precast concrete wall panels that act as loadbearing elements in a building are both a structurally efficient and economical means of transferring floor and roof loads through the structure and into the foundation. In many cases, this integration can also simplify construction and reduce costs. This article presents the many benefits that can be derived from using loadbearing architectural precast concrete walls in buildings. Discussed herein are the various shapes and sizes of wall panels, major design considerations, and when loadbearing or shear wall units should be the first design choice. The role of connections, shear walls, and the use of precast concrete as forms for cast-in-place concrete is explained. In general, the design methods and techniques presented in this article apply to buildings in both seismic and non-seismic areas. The latter part of this article shows how these design principles can be applied in practice in a variety of buildings. These examples illustrate the use of window wall panels, spandrels, and solid or sandwich wall panels as the loadbearing wall members. When all the advantages of using architectural precast concrete as loadbearing walls are added up, it makes good sense to use this structural form in building applications.

Enhancing seismic performance of bridge cap beam-to-column joints using prestressing

Abstract: Conventional seismic design of bridge cap beam to column joints adapted from building design methods based directly on maximum shear forces can result in non-constructable reinforcement details. In an effort to establish an alternative design procedure, three bridge tee joint systems with circular columns were designed and tested under simulated seismic loading. The design of the tee joints was based on a rational approach treating joint shear as a component of the complete joint force transfer mechanism. This enabled the amount of reinforcement to be minimized within each test joint. The feasibility of precast fabrication of concrete bridge joint system consisting of fully prestressed cap beams was also demonstrated in one of the tests.

A new approach to shear design of prestressed concrete members

Abstract: A tied-arch model is developed for the shear design of prestressed concrete members. The failure angle of the arch is calculated using conditions of equilibrium, and the angle of diagonal cracking failure is predicted in terms of shear and longitudinal reinforcement. Comparison with published test results indicate that the proposed tied arch theory provides a more accurate prediction of shear strength when compared to the LRFD or AASHTO Specification. The proposed model is useful in studying the interaction among the forces in the tie, shear reinforcement, and concrete strut of a member. While the tied arch model can be used in both design and capacity rating of regular members, it is strongly recommended in the design and capacity rating of deep beams, and beam ends to include the contribution of shear reinforcement that is usually ignored in a typical strut-and-tie analysis. Examples are provided for determining member capacity rating and shear design.

Ten years of segmental achievements and projections for the next century

Abstract: The last 10 years have seen a dramatic growth on the construction of segmental concrete bridges in North America, which is estimated to have an annual construction volume exceeding one billion dollars. The bridges have been built using both precast and cast-in-place concrete segments. This article presents summaries of the major structural features of some of the most outstanding segmental bridges constructed in North America in the last 10 years. Details concerning the design and method of construction of each project are discussed. Additionally, the future prospects and potential for segmental bridge construction in the next century are discussed.

Optimized post-tensioning anchorage in prestressed concrete i-beams

Abstract: Anchorage zones in prestressed concrete I-beams are designed to accommodate anchorage hardware and to provide adequate space for the reinforcement needed to distribute the highly concentrated post-tensioning force. Based on analytical and full-scale experimental studies, optimized anchorage zone details have been developed. The proposed standardized anchorage zone is suitable for use with a post-tensioning tendon size up to 1-0.6 in. (15 mm) diameter strands. It has a width of 28.5 in. (725 mm), which tapers for a distance of 39.4 in. (1000 mm) to the standard I-beam web width. Standard welded wire reinforcement is proposed for post-tensioning of up to three 15-0.6 in. diameter standard tendons. The use of reduced block size can result in a weight reduction of as much as 80% compared to the commonly used anchorage block. A detailed example is included to demonstrate application of the strut and tie model to the design of the anchorage zone.

Design of prestressed girder bridges using high performance concrete - an optimization approach

Abstract: The objective of this paper is to assess the potential economic benefits from the use of high performance concrete (HPC) for continuous precast, prestressed I-girder highway bridges. Unlike the traditional approach of trial and error, this approach uses mathematical optimization techniques to provide systematical procedures for obtaining optimal designs. The analytical results illustrate the cost effectiveness of HPC for bridge girders. Several practical advantages come from the use of HPC. Among the benefits is that because of increased girder capacity, the increased cost of HPC is fully offset by the reduced number of girders.

Precast pretensioned trapezoidal box beam for short span bridges

Abstract: This paper describes a new trapezoidal precast, pretensioned beam that can span up to 100 ft (30.5 m). The beam has a maximum weight of 55 tons (50 t). The new beam is presented in two different shapes: a closed, totally precast concrete shape and an open-top shape requiring a cast-in-place composite topping. To maintain continuity between adjacent beams and to eliminate the potential of reflective cracks, both shapes have shear keys and continuity reinforcement in the traverse direction. The new beam has a high span-to-depth ratio, ranging between 30 and 40, in comparison to an I-beam system, which makes it suitable for low clearance sites. It can cover a large surface area with fewer beams than the adjacent AASHTO box beams, reducing erection time and cost. The new beam also produces an aesthetically pleasing closed superstructure soffit.

Standardized design of double tees with large web openings

Abstract: This paper is the second of two papers dealing with research conducted at the University of Nebraska on the design of double tees with large web openings. The earlier paper dealt with experimental and theoretical studies as well as initial design recommendations. This phase of the project aims to further maximize and standardize opening sizes and locations. It also aims to simplify the additional design steps required to account for the presence of web openings. The results of the study show that a significant number of large openings can be incorporated into the webs of double tees without reducing the structural capacity of the member if two main conditions are met: (1) No openings are placed within a distance equal to the strand development length from the member end, and (2) additional vertical stirrups, as detailed in this paper, are provided at the edges of the openings.

Tennessee State Route 50 Bridge Over Happy Hollow Creek

Abstract: T he Harry H. Edwards Industry Advancement Award is presented each year to honor precast/prestressed concrete projects that show superior creativity and innovation, thereby advancing the technological expertise of the industry and providing new ideas with great potential for additional applications. Four projects were selected this year as worthy of special recognition for their innovation and ground-breaking technology. Brief summaries of the four projects are given below:

Comparison of shear wall deformations and forces using two approaches

Abstract: Shear walls have been used successfully in low and mid-rise precast concrete buildings for more than 35 years to provide the lateral resistance against wind and seismic forces. This study compares the lateral deformations and section forces of cantilevered shear walls in four building layouts by two different procedures. Walls that are 7 to 30 ft (2.13 to 9.14 m) long are considered with two to six stories in height. The comparison shows that the simpler beam model (with shear deformations) yields displacement and force results that are very close to the more complex finite element approach with a fine mesh. It is concluded that the beam model is an appropriate and accurate alternative to the more refined finite element method.

Loadbearing Architectural Precast Panels Provide Solution for Performing Arts Center Theater Expansion

Abstract: A $32 million renovation and expansion of the Times-Union Performing Arts Center in Jacksonville, Florida, was made possible by using loadbearing architectural precast concrete panels for the interior walls of the new theater addition. The massive panels were cast with flat exterior sides and curving, smooth interior faces to act as the acoustical walls for the theater. Erecting the huge panels required a two-stage lift involving two cranes positioned inside the theater. Another key aspect of the project came in adding two post-tensioned concrete balconies. The solid slabs were cantilevered over the ground-floor seating and supported from the precast concrete rear wall of the theater. The use of precast components saved time and labor costs and helped keep the fast-track project on schedule.

Precast soundwall panels make ideal housing components

Abstract: Existing precast concrete soundwall forms were used to produce wall panels to construct the facades for single- and multi-family residences in Chicago, Illinois. The precast concrete panels produced a fire rating that allowed designers to maximize the widths of the homes, creating more options for interior layouts. The panels also provide a quickly finished exterior frame, with the precast concrete erection finished in one day. Their texture and design emulates brick, with limestone-like accents added to provide dimensionality and to hide joints. Special care was taken in fabricating the forms to ensure mortar lines remained straight and matched at returns and joints. Using the panels also eliminated the need for foundation walls, as the panels could be placed directly on the footings of the basement. Several homes already have been built, with more in the planning stage. Ideally, the designers hope to create a modular kit approach in which components can be stored and used as needed to build various sizes of residences quickly and cost-effectively.

Precast segmental seismic retrofit for the San Mateo : Hayward bridge

Abstract: The retrofit of the San Mateo-Hayward Bay Bridge is part of the California Department of Transportation (Caltrans) effort to retrofit the toll bridges in the state of California. As part of this program, the use of precast segmental construction techniques in the San Mateo-Hayward Bay Bridge retrofit resulted in a constructable and durable retrofit for the rectangular foundations. The $102 million construction package included the seismic retrofit of 20 of these rectangular piers. This article provides an overview of the project design and construction phases. Precasting of the frames was performed on barges that were towed to the site and the frames were assembled and placed around the footings. Arms on the frames reached out to 8-12 ft (2.4-3.6 m) diameter piles driven through the bay mud to firmer soils so the system limited the excessive transverse deflections that would occur in a severe earthquake.

Architectural precast concrete beautifies Shriners Hospital for Children in Sacramento

Abstract: The new multi-million dollar Shriners Hospital for Children at the University of California-Davis in Sacramento, California, serves as the gateway to a multi-functional redeveloping medical center. Situated in an old neighborhood replete with brick residences, the nine-story hospital and its adjacent three-level above grade and three-level below grade parking structure had to reflect the existing heritage while also projecting a contemporary image. To achieve this goal, the designers created a facade using architectural precast concrete featuring spandrel panels with two sandblast finishes incorporating a variety of reveals, a band of red granite and green terra cotta medallions that protrude attractively from the wall. The adjoining parking structure also is clad with architectural precast panels that reflect the style of the hospital facade. This was all accomplished while satisfying fire safety regulations and Seismic Zone 3 code requirements. This article presents the conceptual design, architectural features of the precast facade, and seismic considerations together with the production and erection highlights of the precast components.

Design-construction of umbrella-shaped precast folded plate roofs for pavilions

Abstract: Based on a system developed in China, this article describes an umbrella-shaped precast, prestressed folded plate roof for pavilion buildings, which have been built successfully in San Pedro Sula, Honduras. The method relies on precast, prestressed flat plates and V-sections. These panels are assembled into an umbrella shape with joints formed and cast-in-place to fully integrate the structure. The author presents the design concept, structural design considerations, connections issues, panel production and erection, and joint closure. This folded plate roofing system can be used in other building applications.

Precast superstructure gives Princeton University stadium distinctive flair

Abstract: Princeton University's new multi-million dollar stadium, seating about 28,000 spectators, replaces the original structure built in 1914. Designers faced a series of challenges, including a desire to create a distinctive look and a facility to be used year-round. The stadium was conceived as a design based on performance specifications on a fast-track schedule. The structure consists of a horseshoe-shaped building surrounding lower bowl-style seating and three upper trapezoidal-shaped sections. The upper seating consists of precast concrete triple risers with built-in slots that allow daylight through to brighten the concourse underneath. Precast concrete is also used for columns, floors, stairs, shear walls, and other parts of the stadium. This article presents the conceptual design and design features of the structure, and shows how precast concrete provided the aesthetics, structural support, and facilitated erection of the stadium.

Uniquely Curved Precast Concrete Panels Define New Center of Science & Industry (COSI)

Abstract: The new $125 million Center of Science & Industry (COSI) in Columbus, Ohio, combines a new building featuring an innovatively curved precast concrete exterior and flooring system with an existing high school to create a learning center housed in an exhibit of its own. The facility's facade consists of a clothoid curve shape with precast concrete panels shaped similar to the sections of a tangerine, curving both side-to-side and bottom-to-top. Because of the intricate shapes and the need for a smooth exterior face, innovative casting, hoisting and alignment equipment and procedures had to be devised. Double tees supporting the second floor also produced challenges, with most incorporating cantilevers, some as long as 19 ft (5.79 m). The museum, which opens in November 1999, will highlight its unique precast construction techniques with cutaways in the walls to show the wall panel backs and by leaving the double tees exposed over the first level.

Case studies in structural repair of pretensioned concrete products

Abstract: Case studies show various types of repairs that are sometimes necessary to rectify precast, prestressed concrete products. The cases show types of damage that can be caused by overloading, underdesign, quality control errors, accidents, and unanticipated events. The types of repair methods discussed are epoxying cracks, applying patches, enlarging the member with steel, and adding supplementary structural members. A precast member that is only slightly damaged can simply be patched or epoxied once the source of damage is removed. One case is found to be not repairable and the member is recast due to the severity of the defect and the time and cost involved in repairing it. It is found that damage may be limited by meticulous production and quality control, good communication with erectors, and careful detailing and testing of new design concepts.

Successful testing of PRESSS five-story precast building leads to innovative seismic solutions

Abstract: Preliminary test results indicate that the PRESSS (Precast Seismic Structural Systems) five-story precast, prestressed concrete building has performed very well as predicted.