Hello, I'm Dan Eckenrode, the Executive Director of PCI Gulf South. I will be your moderator for today's webinar titled, Precast Pre-Stressed Concrete Piles. The aim of today's presentation is to give a general overview of what pre-stressed concrete is, review specific structural design considerations for pre-stressed concrete piles, including pile types, production methods, pile handling, and installation. The presentation will then summarize the advantages and benefits of using pre-stressed concrete piles in projects, and feature a few case studies where pre-stressed concrete piles have been successfully incorporated. Resources will be provided at the end of the presentation for further exploration of pre-stressed piles. This webinar is registered for one hour of continuing education credit, and you will earn one professional development hour or one HSW learning units with AIA. To receive credit, you must attend the full webinar and provide complete registration information. If an AIA number was provided at the time of registration, your attendance will be reported to AIA. Within one week of completion of this presentation, you will receive an email from RCEP to download your certificate. If there are any groups in attendance, we do have a group attendance form you can download in the handout section. That attendance form can be emailed to marketing at PCI.org, the same address you see on this slide. Also in the handout section, you will find regions map and a PDF of today's presentation. During the presentation, you may ask questions through the question function on your screen. We will have a question and answer session at the end of the presentation, and we'll try to get to as many of your questions as we can. You can also submit your question to the email provided, and one of the presenters will answer them. Let's begin with a brief background of PCI, which was legally chartered as a Precast Pre-Stressed Concrete Institute on June 18, 1954 in Tampa, Florida. PCI is looked at as the authority for Precast Pre-Stressed Concrete products, so much so that 45 state DOTs recognize PCI certification. PCI is made up of committees and councils which direct PCI's activities and continually add to what we call the body of knowledge. Many things were learned in the early years of the industry. Of particular importance was the development of long-line casting beds, which made Precast an affordable product because of repetitive manufacturing. Various advances in admixtures were also made, which allowed the producer to turn their beds even quicker. Accelerated and controlled curing systems ensured the concrete achieved the strength specified in the time designed for. In 1959, PCI moved its headquarters from Florida to Chicago, where it is based today. As a result of early innovations and the growing interest in Pre-Stressed products, PCI developed a certification program revolving around standard quality control procedures. The industry recognized the need for quality above all else. It is this quality system that provides assurance to owners, contractors, and specifiers that a manufacturing plan has been audited for its ability to produce quality products consistently. PCI certification requires, among other things, that the facility is audited every once every six months and has a two-day inspection of the facility. These audits are unannounced and performed by a third-party inspection agency. A typical audit will review a plant's records of design and production, as well as materials that were used in the product. PCI has also instituted a certified director's program, which ensures the precast Pre-Stressed products that are made by a certified plant are installed as designed and within PCI tolerances. PCI certification is the industry's most comprehensive certification program for both a plant and personnel. PCI is also IAS accredited. This is a map of affiliate chapters and partners at PCI. Each area of the country has an executive director who can assist with additional information relative to their region. Please contact them with further questions. At this time, I would like to introduce today's presenters. Jim Parkins is vice president and director of marketing for Concrete Technology Corporation in Tacoma, Washington. He has been involved in piling applications for 18 years, developing, estimating, and contracting for their use in marine structures and building foundations. Roy Erickson is president of Erickson Technologies Incorporated, a full-service structural engineering firm specializing in precast Pre-Stressed concrete design. He has been responsible for the structural analysis, design, and detailing of many products that incorporate precast Pre-Stressed concrete piles. At this time, I would like to pass the presentation over to Roy. Thanks, Dan. Some of the objectives we would like to cover today will be to review the definitions of unreinforced versus reinforced versus Pre-Stressed concrete elements and what Pre-Stressing is, as well as review more specific structural design considerations for Pre-Stressed piles, including pile types, production methods, pile handling and transportation, and pile installation. We will summarize the advantages and benefits of using Pre-Stressed piles in projects and provide a brief look at some of the structural design considerations for those projects. We will highlight a case study where Pre-Stressed concrete piles have been successfully incorporated. We will conclude with a review of additional resources from PCI and where to acquire that information. Before we get too much further along, let's take a moment to define what Pre-Stressed concrete is. Later in this presentation, we'll go into some detail on the engineering aspects of Pre-Stressed concrete piles, but for right now, let's just try to get a basic understanding about Pre-Stressed concrete. Concrete can be classified as either non-structural concrete or structural concrete, which is the focus of our discussion here. Structural concrete is concrete that is capable of carrying or transferring significant structural loads. For purposes of discussion, we can organize structural concrete into three basic types, unreinforced concrete, reinforced concrete, and Pre-Stressed concrete. Now, what do we mean by each of these? Unreinforced concrete is simply concrete without any reinforcement in it. While it behaves well in compression, it behaves very poorly in tension. Very low levels of tension lead to cracks, resulting in a member with no load carrying capacity at all. It also lacks ductility, so there is no early warning prior to failure. Similar to a piece of chalk breaking in two, unreinforced concrete is not typically used for structural members. Reinforced concrete contains reinforcing bars, which greatly improve its structural performance. Ordinary rebar, typically with a yield strength of 60 KSI, improve the performance of reinforced concrete members. As members are loaded, tensile stresses develop, which cause the concrete to crack. When the first crack occurs, the rebar is mobilized, and the rebar then carries the tensile force in the member. A benefit of reinforced concrete is that the reinforcement can be designed to take a significant amount of tension from the applied load, substantially increasing member capacity. The cracks can be kept small and well distributed along the member with proper detailing. The downside of reinforced concrete is that, while it can carry heavy loads, the member still cracks. Concrete cracking can cause a significant reduction in member stiffness, which leads to serviceability concerns, including diminished aesthetics, increased deflections, and exposure of the reinforcement to corrosion. To reduce or eliminate cracking and maintain member stiffness, which is important under sustained loading, members can be pre-stressed with pre-stressing strand. To maintain member stiffness, particularly during sustained loading, members can be pre-stressed with high-strength pre-stressing strands. In the case of a simple beam with transverse loading, as shown above, tension will develop in the bottom portion of the beam under load. This tension in the concrete can be offset with pre-compression in the concrete such that the net result is low or no tension in the concrete. Pre-tensioned concrete elements can be designed to limit or prevent cracking under service loads. This photo shows an ordinary rebar and a 7-wire, high-strength pre-stressing strand. Both types of reinforcement are made of steel and both are about the same stiffness. However, rebar, also known as mild steel, yields at a stress of about 60 KSI, while pre-stressing steel has an ultimate strength of about 270 KSI. Per unit area, pre-stressing steel can carry several times the force of rebar. Note in the graph above that while rebar has more strain capacity than strand, strain is typically not a governing factor in pre-stress design. And pre-stressing steel has other important properties too as compared to rebar, which will be discussed later in the presentation. There are two ways pre-stressing force can be applied to concrete members, either before the concrete is cast and hardened, also known as pre-tensioning, or after the concrete has set and hardened, also known as post-tensioning. The left photo shows a permanent pre-tensioning operation. Strands are pre-tensioned to approximately 75% of their ultimate strength and then anchored at the ends of a casting bed. Mild reinforcement is tied in place, side forms are placed along the length of the bed, and concrete is placed and cured. Once the concrete reaches its transfer strength, the pre-stressing force is transferred to the concrete by releasing the strands. Contrast this with post-tensioning where the force is applied after the concrete is cured. The photo on the right shows the longitudinal reinforcement in a bridge girder that contains both pre-tensioning strands in the lower and upper portions of the beam in four post-tensioning ducts. Similar to the beam at the left, the pre-tensioning strands will be stressed before the concrete is placed and cured and then released. After that, strands will be threaded into each duct, stressed using a hydraulic jack, and anchored at each end of the beam. Each duct is then filled with cementitious grout or a flexible filler. Once the grout is set, the strands will be trimmed off and protective caps will be applied to the anchorages. With respect to PCI products, most concrete elements are pre-tensioned alone. However, as shown above, pre-tensioning can be combined with post-tensioning to optimize a design. Let's summarize the differences between pre-tensioned concrete and post-tensioned concrete. With pre-tensioned concrete, strands are stressed before the concrete is placed. Once the concrete cures to the required strength, the pre-stressing force is transferred to the concrete. Pre-tensioned concrete elements are fabricated to high-quality standards under factory-controlled conditions. With post-tensioned concrete, tendons are stressed after the concrete has been placed and cured. Once the concrete has been cured to the required strength, the pre-stressing force is applied. Thank you, Roy. Now let's discuss where concrete piles are used, specifically in deep foundation applications. Deep foundations are required where shallow soils are inadequate for bearing capacity or there might be property line issues. Loads are transferred from or at above grade down to the soil layer that's capable of resisting the required loads. This can be accomplished by axial bearing, pile side friction, or a combination of both. Piles are commonly used to support pier or wharf structures built over the water. Piles are designed to resist both gravity and lateral loads. Here are some examples of common deep foundation types. Drilled shafts, which are sometimes known as caissons or drilled piers. They are cast in place concrete formed by pre-drilling a hole and may or may not have a steel casing. They're typically used in larger diameter applications. Another form of cast in place concrete pile is auger cast, used in smaller pile sizes. Reinforcement is typically only used in the top portion of the pile. Both of these CIP methods require the extraction and disposal of soil. Stone columns are columns of crushed stone that are used to improve the soil resistance of the site and enable heavier loads to be transferred deeper into the soil. Driven piles can be wood, steel, or concrete. They are driven with an impact or vibration hammer and densify the surrounding soils by displacement. Now we're going to focus our discussion on pre-stressed concrete piles, which are available in several shapes and sizes and are widely available nationally. A common pile is the square shape as seen on the left. Octagonal piles, as seen on the right, are used on the West Coast. Cylindrical hollow piles are used in marine applications or bridges. Typically strand patterns are symmetrical about the major axis, but asymmetric patterns are possible if needed in an application. Any shape is achievable with flexibility that concrete casting offers. It is recommended to consult your local producer for available pile types and options, as well as for costs for custom applications. We will now walk through the life cycle of a pile, from fabrication to handling to installation. Pre-stressed concrete piles are fabricated in dedicated permanent plants. Common attributes of a certified manufacturing plant include anchored bulkheads and casting beds built to resist millions of pounds of pretensioning force, long line casting beds for producing multiple products in one bed, purpose built yard with handling equipment and load out cranes, self contained operations with minimal outsourcing, which is really critical for daily production, ample space for operations and product storage, train certified personnel, and proximity to multimodal transport to deliver the products by road, train, water, etc. Precast plants provide quality control during the manufacturing process. Owners or contractors typically provide quality assurance. Plants should be PCI certified. The PCI certification program is a rigorous process for both the plant and personnel. Plants provide verification that they follow a robust quality system covering all aspects of manufacturing. This information is contained in the plant's quality systems manual, and that they employ a staff of PCI and ACI certified inspectors and technicians whose tasks include pre-pour inspections, intention verification, fresh concrete testing, hardened concrete testing, and as-cast inspection. The plant quality system ensures the concrete mixing, pre-placement inspections, stressing verification equipment are all per specification. Now we're going to focus on the materials. For the past 60 years, millions of pre-stressed piling have been installed with well-documented longevity in the harshest exposure conditions. The fundamentals of long service life are utilization of high strength, high performance concrete with low water binder ratio, inadequate cover over reinforcing. Long service life has been demonstrated over the course of time with these standard concrete materials, uncoated reinforcement, and sufficient cover. For extreme service life, there are concrete and reinforcement options available. Typical pre-cast concrete piles use high performance concrete mixes resulting in strengths of 6 to 10 KSI. These mixes have high total cementitious content, low water cement ratio, and high range water reducing admixtures to enhance workability in mixes with low water content. They use type 3 cement known as high early. It's recommended in pre-cast applications. This cement helps to obtain the high overnight strength required to transfer the pre-stressing force overnight. Type 3 is critical to maintain production efficiency and minimize costs. Pozzolans such as fly ash and slag are often used in addition to standard cement. These cementitious materials improve workability and durability. Silica fume is occasionally specified for enhanced service life. However, this significantly increases cost and may compromise workability and finishes. Occasionally, corrosion inhibiting admixtures are also requested to enhance service life. Regarding reinforcement, the implementation of pre-stressing strand was a game changer for reinforced concrete design. Early types of reinforcement could not be pre-stressed. These materials resulted in a loss of pre-stressing force as the reinforcement would relax over time. Advancements in material science led to the development of 270 KSI strand about 30 years ago. Strand sizes range in nominal diameters from 3 8ths to 0.7 inches with a common size of 1 1⁄2 inch in piles. 1 1⁄2 inch strand is pre-tensioned to 31 kips. Confinement reinforcement is used throughout the length of piles. Uncoated smooth or deformed wire per ASTM A1064 is typically used in lieu of conventional rebar. This material has a yield strength exceeding 70 KSI. The spiral diameter and tie spacing are a function of in-service design. Most piles utilize uncoated reinforcement. There are premium reinforcement options for extreme service life, which can be 2 to 10 times higher than the cost of uncoated materials. Pre-cast concrete piles are cast with multiple pieces on a long casting bed, which greatly increases efficiency and lowers product costs. Typically pile sizes are standardized and steel forms are used to ensure the cross-section dimensions are precise. Utilizing the available steel form sections of your local producer is recommended, since the standard forming cost is amortized over numerous projects. However, for large projects, consult your producer as the purchase price of a new form may make sense if it optimizes the design of a large quantity of piles. Strand pre-tensioning techniques vary by plant and or product. The primary method is to pre-tension strands against permanent embedded bulkheads in the casting bed. The pile form sits on the bed and is independent of the strands. Self-stressing forms are sometimes used. In this system, the pre-tension force is resisted using the pile formed cross-section. Pre-tension is applied either one strand at a time, or in a more complex system, multiple strands at a time. Proper pre-stress force in the strand is verified by measuring the theoretical strand elongation to actual elongation, as well as correlating the gauge pressure of the hydraulic stressing ram to the total force in the strands. After strand tensioning is complete, spiral reinforcement and other embeds are placed around the strand and secured into the form. Positional tolerances are checked. Embeds are secured with tie wire and other means to ensure they do not displace under the concrete fluid pressure during pouring. After embeds are in place, concrete mixes are placed with overhead buckets or specialized delivery vehicles like the one shown above. Conventional mixes require internal and or external vibration for consolidation. Many plants are using self-consolidating concrete, known as SCC. SCC flows under its own weight, eliminating the need for vibration and provides better finishes. The net result is a reduction in labor, both for placement as well as the sacking of piles after carrying. SCC can be attained with minor variations to conventional mix designs. Piles are generally cured by applying external heat, known as accelerated curing. Since cement hydration is an exothermic reaction, this accelerates strength gain. Methods include steam, electric, or radiant heat. Accelerated cure eliminates additional curing once the product is removed from the form because hydration is complete. Accelerated cure also is critical to attain release strength needed to detention the strand. Once the concrete has been placed, cured, and reaches the required release strength, the strands are detentioned. Pre-stress transfer methods can include detentioning multiple strands at one time with an engineered release system, or cutting individual strands in a sequential pattern to ensure equal incorporation of pre-stress force into the pile. The minimum release strength is typically 3.5 KSI to 4 KSI. It is critical to note that release strength is a calculated value, not an arbitrary value, such as a percentage of the 28-day strength. Unnecessarily high release strengths can significantly increase costs by disrupting the daily production cycle. Before leaving the materials section, I want to share an interesting material gaining traction called UHPC, ultra-high performance concrete. PCI has several initiatives researching the different sizes and shapes of UHPC piles. The difference is typical concrete mixes are composed of cement, fine, and coarse aggregate like we demonstrated above. A UHPC mix incorporates cement, pozzolan, and fine aggregates only, as well as steel fibers to resist tension. The result is a denser, less permeable mix achieving strengths of 18-24 KSI. Another benefit of this material is a reduction in conventional reinforcing, as well as lighter cross sections. The UHPC H-pile section shown below more closely converges to that of a steel H-pile with similar weight and stiffness. Consult with your local producer about the availability of UHPC. We're now going to discuss pile handling and transportation. Piles are not only designed for the final service loads, but they're checked for stresses in these conditions as well. Concrete piles need to be designed for plant handling, transportation, lifting, and rotation at the site. If the plant, either an overhead crane as shown on the right, or a travel lift as shown on the left, straddles a casting bed to remove the piles from the casting bed. Piles are typically handled in the yard by specialized straddle cranes such as a MIJAC or travel lift. It's common to use between two to four pick points based on the structural properties of the pile, as well as the length. Piling is typically stored in a stacked condition to save space, is limited by overhead crane height. Drainage supports are placed at multiple locations along the pile length so creep deformation does not occur. Drainage is analyzed to verify it can support multiple piles and to ensure it does not settle into the supporting surface. Just-in-time delivery is preferred so yard space consumption is not excessive. Transportation is a coordinated effort based on the capabilities of a pile producer and the equipment available in the region. Transportation by truck is possible for piles up to 200 feet in length with proper equipment as long as the configuration does not overstress the pile. The example in the lower right utilizes rocker bunks to evenly support the pile at four locations. Arch transportation is also common on marine projects and can provide significant savings versus truck transport. At all of these stages, long cylinder piles are subjected to highly localized stresses during the various stages of handling and transport. Movement of a pile results in highly dynamic loads so impact factors must be considered. Stresses must be checked against allowable limits in the code. These limits are set to prevent cracking during handling and transportation of the pile. Designers may need to add additional support points or lifting points as circumstance require. Resources for calculating the correct handling procedures will be discussed by Roy at the end of this presentation. This next section will discuss some of the basics of pile installation. The installation of pre-stressed concrete piles requires a specialty operator who's experienced in selecting the pile hammer and the crane size to match site logistics. There are a lot of factors involved, such as pile size, type, and length that require driving capacity of the pile, whether they're vertical or battered, and the type of substrate. The number of piles and layout of the group is also a major consideration. Site limitations must also be considered, including the impact on existing structures and noise and vibration impacts to both human and animal populations. A more in-depth review of pile installation can be found in PCI Manual 133. Occasionally, a pile may need to be longer than what can be transported or handled by the driving rig. There are several options for splicing these kinds of piles. The examples in this slide include mechanical splices or epoxy dowel connections. Splicing designs can be axial loads only or for axial and full-moment capacity. The most common method of installing pre-stressed concrete piles is by driving with an impact hammer. Commonly used hammer types are air powered, diesel powered, and hydraulic powered. The hammer selection is driven by pile type and site conditions. Consumable wood cushions are also used. Cushion selection is key in preventing damage to the pile during driving. Experienced geotechnical engineers may complete wave analysis to determine the hammer selection, predict the installed pile capacity, as well as the driving resistance and driving stresses. Sometimes pile test programs are used, which are required to verify design and installation. Occasionally, processes such as jetting, pre-drilling, sputting, or excavating are used to assist with installation of the pile in hard driving conditions. Pile driving, whether for wood, steel, or precast concrete piles, creates noise and vibrations that can affect the local population and wildlife during construction. Project-specific pile driving vibration monitoring may be required for impacts to existing structures. Some projects also include windows for installation, dictated by wildlife migration patterns. Designers should factor procurement into these project windows. The industry has deployed many techniques over the years to reduce these effects. Consult with your local producer and pile installation contractor for potential options. Now, this next slide is a video of a diesel impact hammer on a concrete pile. This concludes my portion of the presentation. I'll now hand it back to Roy to discuss the attributes and structural design of concrete piles. Thanks, Jim. With more than seven decades of successful implementation across the country, there are many advantages to using precast pre-stressed concrete piles. Advantages of pre-stressed concrete piles include standardized sections, minimal concrete waste, and high-performance materials, which result in high structural efficiency and lower initial cost. No periodic coating or maintenance required, which means lower life cycle cost. Pictured at the right is the lone surviving beachfront structure on Mexico Beach, Florida, after Hurricane Michael. The house was built with a combination of cast-in-place concrete, insulated concrete forms, and precast elements, including precast piles. It was designed for 250-mile-per-hour winds and was elevated to withstand what could be a devastating storm surge that may accompany a hurricane. From small-diameter pin piles on land to 200-foot-long single-piece marine piles in saltwater, PCPs are highly adaptable to project requirements. PCPs support a high level of sustainability by featuring local materials and labor, long service life, reusable formwork, and reduction in concrete and material waste. PCPs are manufactured under very high-quality control using nationally recognized QA-QC procedures. Finished piles are visible prior to installation. PCPs exhibit high structural efficiency. High-strength concrete and prestress allow for smaller cross-sections. Greater capacity means fewer piles with smaller footprints. Confinement reinforcement runs the full length of the pile rather than just in the upper portion. High lateral stiffness is inherent in the product. PCPs have a long design life. High-performance concrete means low permeability. Permanent axial compressive stress provides excellent crack control. This combination results in resistance to moisture intrusion and corrosion. There's accelerated construction with precast concrete elements. While the site is being prepared, the pieces are manufactured, inspected, and staged for delivery. When the products are delivered to the job site, the time required is less and the construction schedule is accelerated. There are other benefits too. Workers are exposed to fewer unsafe conditions at a plant than on a job site. Also, the process at a plant is greener through the use of local materials, local labor, and less waste. The accelerated construction benefits provided by PCPs include prefabricated elements, parallel construction activities, minimal job site time and equipment, increased onsite installation rate, and handling and installing precast piles is easier than coordinating concrete truck logistics and traffic. And displacement installation eliminates the need to dispose of spoils. An important attribute of driven piles is that every driven pile is essentially a tested pile. Most of the time, the worst loading is during driving, at least with regard to tensile stresses. If the pile makes it through installation, you've essentially proofed that pile. The photo on the right shows an impact hammer driving a rectangular pile. With each strike of the hammer, the pile develops skin friction and a resistance to the applied loading. Once the pile reaches the required loading or resistance to the applied force, the driving process stops. Each pile has therefore been tested to verify that the specified load has been attained. A successful driving process also proves that there were no hidden obstructions or that the pile had broken during installation. There are several disadvantages associated with using other pile types on your projects. These photos are examples of poor consolidation of concrete or grout mixes during installation of cast-in-place or auger cast piles. Inherent to any cast-in-place pile or drilled shaft is the possibility that when complete, the pile or shaft is not cylindrical and has flaws. Visual inspection of the pile in place is not always possible. With auger cast or drilled shafts, the contractor runs the risk of the piles experiencing necking, cracks, breaks, or bulging during installation. Poor installation methods may lead to honeycombing and exposed reinforcement. None of these happen with prestressed concrete piles. Construction for these types of piles also requires a lot more on-site construction congestion with the addition of constant concrete haul trucks and soil removal equipment. The on-site construction schedule also tends to be longer for other pile types as cast-in-place concrete and grout materials must cure before casings or other formwork can be removed or before adjacent piles can be installed. For these other pile types, there is no pre-compression, so they have much lower tensile capacity than prestressed piles. The higher strength mixes associated with precast prestressed piles also results in higher shear capacity than these other piles. Drilled-in installation also requires removal of soil, which is problematic and is extremely expensive as the soil is contaminated. Drilled-in installation is not advisable if groundwater is present at the site. With steel piles, extended service life requires expensive supplemental coating. The installed price is higher, excessive noise is caused for marine life during installation, and costs and availability are highly unpredictable. With timber piles, extended service life requires undesirable coatings to prevent organism degradation, and they have limited capacity with respect to other types. This presentation is not meant as a deep delve into the structural design requirements of prestressed concrete piles, but as an overview of important considerations in the design process. Modern prestressed concrete has been available for over 70 years. It solves most of the problems of unreinforced and mildly reinforced concrete that we discussed earlier. The application of prestress creates permanent compression in a concrete member before it is installed, which helps resolve tension issues. When we load a beam uniformly, as shown in the top figure, tension occurs at the bottom face of the beam, while compression occurs at the top face. When a member is prestressed, as shown in the middle figure, an eccentric axial force is applied to the beam, resulting in a permanently applied compressive axial force, and a moment applied in the opposite direction as that of the applied load. The summation of the stress due to the prestress and the stress due to the design loads, as shown in the bottom figure, results in significant decrease in permanent stresses in the concrete member. In the case of a concentrically applied prestress force, as shown above, a permanently applied compressive axial force is applied, but with no accompanying moment. Prestressed concrete piles are an example of a concentrically prestressed member. The characteristics and differences between rebar and prestressing strand were introduced earlier. To elaborate further on that, prestressing steel is a very high performance material. Its special metallurgical properties permit it to be stressed to a high level and then retain most of that stress over time. However, if ordinary rebar were stressed, a large portion of the prestress would dissipate due to the phenomenon of relaxation. A prestressed concrete pile goes through several stages during production. Pile design must consider each of them and not simply the final in-service condition. Each stage subjects the pile to a unique set of loads. For instance, during manufacturing, piles are cast horizontally, strands are cut, and the pile is moved to a temporary storage area when the concrete is at its lowest strength. During the handling and storage stage, the pile is stored in a horizontal position and subjected to bending moments caused by self-weight. During transportation, the pile is subjected to impact or dynamic effects. When the pile arrives at the job site, it is rotated vertically and driven. This is typically when the pile is subjected to the highest tensile stresses of its life due to axial forces down the length of the pile caused by the driving hammer. Once the piles are installed, they begin to carry their in-service axial loads as well as lateral design loads that may be quite high, especially in high seismicity regions. The strength and durability of the concrete mix is paramount when designing piles. Engineers are encouraged to contact local producers early in the process to get concrete mix information as local material supplies are regionally distinct. Minimum concrete release strength should be 3,500 psi overnight before the prestress strands are cut and the piles are stripped from the forms. Release strength is a calculated value and may need to be higher depending on stresses during handling. Typical 28-day strengths range from about 6 to 10 psi and are highly dependent on the quality of regional materials. Special consideration should be given to using appropriate materials that ensure satisfactory short and long-term performance of the piles. Transverse reinforcement typically consists of spiral reinforcement to provide confinement for axial loads and to provide ductility for lateral loading. It is also required along the length of the pile to control longitudinal cracks, which may form during driving, handling, or under design load conditions. As a side note, UHPC piles may not require transverse reinforcement in areas of low to moderate seismicity. The size and pitch of spiral reinforcement may vary along the length of the pile. For exceptionally long piles, continuous spirals may need to be spliced together to keep the confinement continuous down the entire length. Adequate concrete cover is critical for durability, but consider that increasing cover reduces moment capacity by narrowing the strand pattern. Prestressing strand patterns are generally concentric for most piling applications, with the exception of fender or guide piles, which may have horizontal loads only and act more like a beam than a column. Piles are generally stripped from their casting forms using embedded lifting eyes consisting of unstressed 7-wire strands bent to shape in the plant. Mild reinforcement is seldom used within the length of the pile other than at connections such as the head of the pile or at a splice. There are numerous ways to connect the pile to the pile cap, depending on the demand and fixity requirements. Examples include a fully embedded pile head, exposing pile reinforcement for pourback in the cap, and reinforcement bars grouted into ducts in the pile after driving. Standardized details for piling were first published in the 1960s by members of the bridge community. Many of these details are still in use today. Many of these details are still in use today in areas of low to moderate seismicity. The first PCI recommended practice was published in 1977. PCI is publishing updated design recommendations that are no longer specific to any code or pile use. These new standards are applicable to bridge, building, and marine applications. These documents provide current, state-of-the-art confinement and spiral details for pile designers. Other organizations, including ASCE, AASHTO, and ACI continue to publish more specific pile-related design specifications and codes. On any project, consider local or state specifications governing the use and availability of certain products or materials used to construct prestressed concrete piles. The pile engineer must review several pile capacities during the design process. Pile axial loads, both tension and compression, flexural or bending moments from lateral loads as well as eccentric axial loads, and various combinations of axial and bending moments, the pile engineer must design for factor demands as well as unfactored surfaceability requirements. While the axial compression capacity of a concrete pile is reduced by the effect of prestressing, the flexural resistance of a pile at both the service and strength limit states is significantly improved by prestressing and deflections of the structural system are reduced. The location of maximum moment in a pile is dependent on several factors, including the properties of the supporting soil, the properties of the pile, and the degree of fixity between the pile head and the cap or footing. The graphics shown are representative of how a geotechnical engineer may present a pile's axial and bending moment requirements. Soil layer parameters play an important role in these calculations and therefore an important part in the size, reinforcement, and tip elevation of the pile. The pile engineer performs several calculations in concert with the geotechnical engineer to complete the final design of the piles. Three major components of pile design include surface stresses, ultimate strength, and serviceability limitations. This slide depicts the stress-strain distribution across a square prestressed concrete pile subjected to a moment at the top of the pile. The pile engineer verifies that the pile capacity exceeds the pile demands and that the pile supported structure does not see excessive deformations or visible cracking. The design of precast concrete piles or any pile relies heavily on the information provided by the geotechnical professional. Design for pile-soil interaction is dependent on many variables, including soil properties as determined by a site, subsoil investigation, and or laboratory tests, installation methods, and the pile arrangement. It is important that the geotechnical professional and structural engineer work together in conjunction with the local precaster, owner, and contractor to consider options and economics. Look at it as a partnership to determine the best solutions. The geotechnical engineer should be familiar with the geology of the region and the project requirements. Piles are not just designed to meet nominal load carrying requirements, but must also meet serviceability requirements for bearing, foundation settlement, and lateral displacements. The ability of a single precast concrete pile or group of piles to resist lateral loads in their bending moments is well understood in the engineering community. In addition, the structural design must consider the environmental conditions to ensure the mix and materials meet durability and service life requirements. Pure flexural demand in piles is rare. It can occur in fender piles subject to berthing and mooring loads. More commonly, axial and flexural loads occur simultaneously. With combined axial load and flexural loads, the engineer will develop ultimate strength interaction diagrams as shown above. This provides a range of pile capacities with axial and moment combined. The effect of slenderness, which may amplify the applied moments, may also be significant. PCI has developed a very useful and powerful spreadsheet tool for the design of piles. Interaction diagrams can be developed for both unique pile sizes and shapes, as well as varying pre-stress strand patterns. The program also computes safe lifting points and dunnage points for lifting and handling. This is available online at PCI's bookstore. Let's review a project that has successfully used pre-stressed concrete piles. Capano Bay Bridge is located in Aransas County, Texas, which is approximately 45 miles north of Corpus Christi. The aim of this project was to upgrade an existing two-mile bridge over Capano Bay from a two-lane roadway to a four-lane highway. The existing bridge was 40 years old and was a little over 9,200 foot long with 229 spans and an average span length of 40 feet. As part of ongoing structural maintenance, an emergency structural repair was completed on the bridge in October of 2009. The contractor on the project was William Brothers, with Valley Pre-Stressed Products out of Eagle Lake, Texas, being the precast supplier. The bridge replacement project included using a record-breaking 179 foot, six-inch cylindrical precast pre-stressed concrete pile. Additionally, these 54-inch cylindrical concrete piles were the longest pre-stressed member to be plant manufactured, then shipped to a job site in the state of Texas. The distance traveled from the precast plant to the job site was 147 miles. The total cost of the project was slightly over $98 million. Included in this cost was shipping of high-performance concrete piles, the hammer used to drive the piles, rails, abutments, bent caps, tie beams, columns, and epoxy-coated reinforcing steel, which was used in the deck. The centerline of the new bridge is 40 feet east of the existing two-lane structure. The project, just over two miles of bridge, took four years to complete. The maximum vertical clearance of 75 feet, which was used for hurricane evacuations, and two miles of bridge consisted of 93 spans of 100 and 150 feet, respectively. The Copata Bay Bridge construction phasing and timeline of four years was broken up into three phases. Demolition, which lasted three months, phase one, which began in August of 2011, was completed within three years, and phase two, which was completed in just one year. Along with the record-breaking 480, 54-inch, 179-foot-long cylindrical piles, the project also included 330 24-inch square pre-stressed concrete piles with an average length of 84 feet, 1,120 Texas 54 and Texas 70-inch girders, and over 1 million square feet of deck panels. To conclude today's presentation, we want to ensure everyone knows where to find the various resources available to provide guidance for the design, detailing, and specifications of precast concrete piles. PCI provides a variety of resources to support the pre-stressed, precast concrete industry. Visit our website at www.pci.org for a full list of publications. Registered PCI members receive full access to online resources and discounts on the purchase of design handbooks and manuals, as well as subscriptions to various PCI periodicals and journals. PCI publishes several resources that are specific to pre-stressed pile design and installation. PCI recently published the second edition, 2019, of Recommended Practice for Design, Manufacture, and Installation of Pre-stressed Concrete Piling. Chapter 20 of the PCI Bridge Design Manual also contains a wealth of information along with AASHTO references. There are also pile design, fabrication, and installation-related articles that have appeared in various PCI journals and Aspire magazine publications, all of which are available on the PCI website for registered members. Lastly, our regional producers can provide valuable feedback on design, fee estimates, and proposals. As previously discussed, here is the Pre-stressed Concrete Piling Design Spreadsheet and User Manual. It's a very straightforward design tool with user-friendly input features, as well as informative output figures and graphs. If you follow the link at the bottom of the slide, it will take you to PCI's website and the bookstore when you can get the free copy. As mentioned at the beginning of the presentation, PCI is made up of committees and councils. Most, if not all, of the great content and technical aspects of piles are developed within this committee structure. PCI has two committees that are devoted just to piles, and these committees are responsible for the research and specifications at the Institute. External resources such as the Pile Driving Contractors Association is another great avenue of information. PCI is always focused on the future. We are currently tracking several ongoing efforts at upcoming publication. The PCI subcommittee on UHPC is reviewing requirements for design, construction of precast H-piles made with UHPC. The new PCI Pile Standard 142-21 will be published in late 2021. This standard incorporates updated requirements for the seismic ductility of piles in areas of moderate to high seismic activity. PCI and Pile Committee members are continuing to review applications of new materials in the market, including the implementation of stainless steel and carbon fiber strands. Pre-stressed concrete piles have been used for nearly 60 years and have performed consistently well. Piles perform very well on all types of sites, including extreme exposure conditions such as saltwater and marine environments, with workability mixes with low permeability and high durability. High-performance concrete has been in service for many years and is performing extremely well. With the addition of UHPC to the industry, precast pre-stressed concrete piles are becoming even more marketable in the mainstream. Guidelines and code requirements are well understood by engineers, producers, and contractors. The added benefit of strict quality control inherently built into precast plants leads to durable, dependable, standardized products. On behalf of Roy, Jim, and myself, we would like to thank you for your attendance at this webinar and hope you have learned about the important aspects of precast pre-stressed concrete piles. At this time, we would welcome any questions. Thank you.

webinar

Precast Pre-Stressed Concrete Piles

overview

structural design considerations

pile types

production methods

handling

installation

advantages