Learning Objectives. A Brief History

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1 Slide 1 Precast Structures and Frames Miles L. Blackman, P.E. Slide 2 Learning Objectives Discuss precast concrete characteristics, advantages and benefits, typical construction methods and construction applications. Understand precast applications and uses. Review typical precast building components. Learn about the manufacturing processes that give precast concrete its consistent high quality. Gain insight on technical considerations including connections, construction and erection. Understand the precasters role in assisting the design team with its goals. Access industry resources available to designers of precast structures. Slide 3 A Brief History The single most important event that led to the launch of the prestressed concrete industry in North America was the construction of the technically innovative, Walnut Lane Memorial Bridge in Fairmont Park in Philadelphia, Pennsylvania in

2 Slide 4 Prof. Gustav Mangel, University of Ghent, Belgium A Brief History This prestressed concrete bridge became a reality because of the vision, persistence and courage of a few extraordinary individuals. Prof. Mangel described the concept of pre-compressed concrete to his students using his well-known illustration of a stack of books Slide 5 A Brief History The books on the bottom are like precompressed concrete: using a compressive force, they support their own weight plus significant superimposed loads, represented by the books on top. Slide 6 7-Wire High Strength Strand Long-Line Casting Beds Permanent Steel Forms Admixtures High Early-Strength Concrete Accelerated Curing A Brief History Early innovations included 7-wire strand, long-line casting beds; highquality, permanent steel forms; specialized chemical admixtures; high early-strength concrete; accelerated curing with heat; and more

3 Slide 7 What is Precast/Prestressed Concrete? The combination of high strength steel to resist tensile stress and concrete to provide compressive strength and durability make this composite material adaptable to many applications. Slide 8 PRESTRESS FORCE What is Precast/Prestressed Concrete? CAMBER Upward Deflection Created by Prestressed Strand is Camber PRESTRESS FORCE Once the concrete is cured, the strand force is released from the abutments. This causes the steel strands, which are under high tension, to try to return to their original length. A compression force is created in the bottom of the component, and camber. Slide 9 PRESTRESS FORCE What is Precast/Prestressed Concrete? LOADING UPWARD FORCE EFFECT DUE TO PRESTRESSING The Effect of Camber Resists Downward Deflection When Loads Are Applied PRESTRESS FORCE The compressive force and upward force on the concrete from the strands helps offset applied loads. The combination of durable concrete and highstrength steel results in a lasting strength that ensures retention of the component s durability throughout its lifetime.

4 Slide 10 PCI s Dictionary of Terms. Total Precast... Substantial core and shell of the structure are comprised of precast components. Many types of commercial applications. Allow for tailored design as necessary. Architectural choices are limitless. Slide 11 Applications Parking Structures Residential Offices Manufacturing Institutional Others Slide 12 Applications Parking Structures Residential Offices Manufacturing Institutional

5 Slide 13 Applications Parking Structures Residential Offices Manufacturing Institutional Slide 14 Applications Parking Structures Residential Offices Manufacturing Institutional Slide 15 Applications Parking Structures Residential Offices Manufacturing Institutional

6 Slide 16 A C B F E Double-tee System C Typical Precast Building Components D G A C Hollowcore Plank System B E F A. Load-bearing architectural spandrel B. Exterior column C. Double-tee or Hollowcore plank D. Interior column E. Inverted tee beam or composite beam F. Shear wall G. Stairs C D Slide 17 Spandrel Slide 18 Interior Columns

7 Slide 19 Exterior Columns Slide 20 Double Tees Double Tees derive their name from their shape. The vertical elements are called stems and the horizontal deck element is called the flange. Economical spans start at approximately 50 ft. and can exceed 100 ft. Double tees are used for floors, roofs, bridge members AND wall panels. Pre-topped tees are used in parking structures with a thickened flange and no field-poured topping. Slide 21 Hollow-core slabs can simultaneously provide a floor surface and a ceiling surface which require very little finish work. There are a variety of manufacturers with thicknesses ranging from 6 inches to 16 inches Maximum spans are about 60 ft. for typical residential loading. Fire ratings up to 4 hours. Hollow-Core Planks

8 Slide 22 Inverted tee beam Slide 23 Shear Walls Slide 24 Precast stairs, stairwells and landings are erected with the balance of the structure, allowing workers easy access to all working levels. Stairs and Landings

9 Slide 25 Load-bearing walls become perimeter structural-gravity support for floors and roof Eliminates need for perimeter structural framing Wall Panels Slide 26 Precast/Prestressed Structural Systems A Complete Structural System Using precast concrete components together as a complete structural system creates a design in which the whole is greater than the sum of the parts. For example, combining precast/prestressed hollowcore plank or double tees with precast beams and columns creates a durable, fire-resistant structure that is quick to erect and cost efficient due to the compressed construction schedule. Slide 27 Precast/Prestressed Structural Systems Rigid Frame System All lateral loads are transferred to a momentresisting frame that ties beams and columns together with rigid connections. The need for shear walls is eliminated.

10 Slide 28 Precast/Prestressed Structural Systems Exterior Shear Wall System In general, an exterior shear wall system permits greater design flexibility because it eliminates the need for a structural core. By combining gravity load bearing function with lateral load resistance, the exterior shear wall system is also, in general, more economical. Slide 29 Precast/Prestressed Structural Systems Interior Shear Wall System Lateral loads are transmitted by floor diaphragms to a structural core of precast shear walls. The shear wall can be tied together vertically and at corners to form a structural tube that cantilevers from the foundation. Slide 30 Connections: Transfer Load Restrain Movement Provide Stability Design Must Include: Adequate strength Ductility Proper detailing Account for tolerances Responsibility: Typically provided by the precast fabricator based on loads or forces provided by the EOR. The Connections

11 Slide 31 Manufacturing Process PCI-Certification Insist on it! Ensures that plant has developed and documented an in-depth, in-house quality system based on time-tested, national industry standards. Understanding the manufacturing process will help you see how quality control and efficiency are achieved. Slide 32 Precast structural elements are generally prestressed. Manufacturing Process Long Line Forms Slide 33 Architectural precast can be conventionally reinforced or prestressed. Manufacturing Process Panels are Set

12 Slide 34 Manufacturing Process Place Concrete Slide 35 After the concrete has cured, products are removed from the forms and moved to the storage yard. This is where postpour measuring, cleaning, cutting, special finishing, etc. will take place. Manufacturing Process Cure, then Strip Forms Slide 36 Architectural Precast Wall Panels Form-Liner Finish Glaxo, Research Triangle Park, NC Casting with a form liner can create unique textural effects. Form-liner designs can be selected from a broad range of inexpensive stock liners, or a custom style can be created from existing materials or a specific design.

13 Slide 37 Architectural Precast Wall Panels Special Finishes ACID ETCHED RIBBED FORM LINER SAND BLAST EXPOSED AGGREGATE Improvements in the fabrication process have created more refined finishes. These range from delicate finishes achieved by surface acid etching or light abrasive blasting to bold textures and patterns, created by using form liners. Rich, colorful textures also can be produced by chemically exposing colorful coarse aggregates. Slide 38 Acid Etch Architectural Precast Wall Panels Sandblast Exposed Aggregate A designer can achieve strikingly different colors and textures from a single precast mix simply by varying the finish treatment. The single mix shown here has three different finishes. This multiple-finish technique offers an economical yet effective way to heighten aesthetic interest. Slide 39 Architectural Precast Wall Panels Replicating Flame-Finished Granite The Hearst Tower, Charlotte, NC To create a flame-finished granite appearance in architectural precast, an appropriately colored precast-mix design needs only to be sandblasted. In this comparison, the sandblasted precast in the foreground closely matches the actual flame-finished granite in the background.

14 Slide 40 Architectural Precast Wall Panels Chemical Retarders Chemical surface retarders effectively highlight the full color and natural beauty of the precast coarse aggregate. Here, the chemical retarder is being removed with plain water immediately after casting. Slide 41 Architectural Precast Wall Panels Brick Faced Precast These brick-faced precast units can be erected quickly as one large panel, at any time of the year. This application has become more popular across the country due to escalating costs for field labor and the scarcity of skilled masons. Slide 42 Architectural Precast Wall Panels Encapsulated Rigid Insulation Frequently, architects encapsulate rigid insulation within architectural precast panels to generate higher energy efficiency and achieve additional advantages. These panels consist of a layer of precast that is poured into the form, after which the insulation is placed and another layer of concrete is added.

15 Slide 43 Construction and Erection Considerations By considering construction and erection as the job is designed, cost and schedule can be positively impacted. Slide 44 Construction and Erection Considerations DO s and DON Ts Some keys to economy Fabrication Delivery Installation Slide 45 Repetition is key to economy Fabrication

16 Slide 46 Keys to Fabrication Economy Fabrication Many forms are made of wood and can be expensive. Minimize number of molds and maximize the number of castings from each mold. Slide 47 Must be able to deliver and handle on-site Maximum Panel Dimensions (Varies) 12 Tall x 40 Long Preferred 14 Maximum Width 50 maximum length Maximum Panel Weight Common Payload of 40,000 lbs Affected by Local Conditions Limited by Regulatory Agencies Permits and Escorts Delivery Slide 48 The site must be properly prepared by the Contractor to allow truck and crane access around the site. Access roads? Staging areas? Crane pads? Delivery Properly Prepare Site

17 Slide 49 Installation Must have close access for ease of erection Avoid Circumstances Requiring Double Handling. Slide 50 Plan for crane position in the design stage (Tower). Installation Slide 51 Anticipate crane size, reach and erection sequence to minimize crane moves and setups. Installation Sequence

18 Slide 52 Get a Precaster involved as early as possible to: Provide design & engineering support. Provide value engineering & cost support. Assist in material selection & aesthetic considerations Generally, expedite the project and save you money. Design Considerations Early Design Involvement Slide 53 Engineer of Record (EOR) Define system concepts Define codes & design criteria Lateral stability analysis May be assigned to precaster Topping/Diaphragm Design Precast Engineer Individual Component designs Connection designs Responsibilities Slide 54 Specifications Clearly specify the code and code edition for the project. Specify the loads and fire ratings required Specify connection forces where they cannot be determined by the precaster. Clearly specify connection finishes required. Specify PCI certification. Specify the proper Quality Control. Structural elements with Arch finishes may fall under MNL 116 rather than MNL 117.

19 Slide 55 Serviceability Total Precast Structures are not as heavy as perceived, perhaps less than 20% additional weight over composite steel. Higher floor dead load can improve vibration performance over steel framed floors. Total Precast Structures feature built-in fire resistance Slide 56 Green Design Re-usable Forms Typically steel forms that are used over and over. Recycled Materials Fly ash, Steel, Recycled aggregate Local & Renewable Materials 85% of precast concrete is made up of naturally occurring and local materials (sand and stone). Compared to other materials extraction requires low amounts of energy and they go directly into the finished product Transported and erected within 200 miles of plant. Thermal mass influences: Heat absorption and loss Thermal lag Energy consumption Slide 57 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits

20 Slide 58 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits Slide 59 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits Slide 60 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits

21 Slide 61 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits Slide 62 Long clear spans High load capacity Fire resistance Durability Acoustical performance Thermal mass Benefits Slide 63 Single source Speed of construction All weather construction Design flexibility Benefits

22 Slide 64 Single source Speed of construction All weather construction Design flexibility Benefits Slide 65 Single source Speed of construction All weather construction Design flexibility Benefits Slide 66 Single source Speed of construction All weather construction Design flexibility Benefits

23 Slide 67 PCI - Ongoing industry support Publications PCI Design handbooks (6 th ) Technical literature Guide Specifications PCI JOURNAL ASCENT Website Resources Slide 68 Resources Slide 69 Questions? This concludes the Presentation on Total Precast Structures and Frames. Thank you for your time! PCMATexas.org PCI.org