Many project managers require scanning for concrete coring services. The reason may be due to a repair procedure or re-stressing due to out-of-range elongation readings. Because of the offset stresses, post-tensioned slabs are self-supporting at lower concrete strengths, and are generally ready for forms to be stripped and reshores to be installed within 24-72 hours of concrete placement. Advanced Post-Tension is a premier provider of material, equipment, and expertise across the continental United States. This is very important in building complex structures like bridges because it involves demanding geometry requirements like variable super elevation, grade changes, and complex curves. A post-tensioned concrete slab on grade will typically be 8 inches thick and use 3000 psi concrete. Infraspect, Clearwater Florida has developed and patented the first post-tension tendon scanner and inspection service aptly named TendonScan. . It also provides protection against damage by mechanical handling and serves as a barrier that prevents moisture and chemicals from reaching the strand. As soon as the concrete has gained strength the cables are pulled tight to develop tension, and anchored against the outer ends of the concrete before the loads are applied. Coring occurs when sections of concrete are removed. Potable, lightweight, wireless, and accurate. Post-tensioned anchorage components for bonded and unbounded tendons. According toFHWA, the MFL (Magnetic Flux Leakage) methods can be used to detect the location and extent of corrosion in post-tensioned and precast prestressed strands in concrete girders, and breakage of wires and strands in post-tensioning tendons and pre-stressing strands. FREDERICK 8119 Indian Peaks Ave. Coring is completed to analyze the strength of existing concrete. Controlled de-tensioning by means of clamps. Technical . At Tendon Systems LLC, we strive to provide high quality engineering services. Let's take a look at basically what a tendon is and why it is important. There are two main types of posttensioning: unbonded and bonded (grouted). Post-tensioned slabs allow for long spans with fewer supports or thinner spans for a given distance. Post-tensioning helps engineers offset the weaknesses of concrete in two ways. This is, of course, over and above the potential hazards associated with suddenly releasing the energy in a post-tension tendon. Infraspects TendonScan will locate the loss of metallic area inside an external post-tension tendon. In this system, tendons which may be located inside the concrete are tensioned after the concrete has hardened. Bonded systems are more commonly used in bridges, both in the superstructure (the roadway) and in cable-stayed bridges, the cable-stays. TendonScan is a non-destructive post tendon inspection service that can be accomplished with relative ease. Even so, most companies only offer scanning services and not additional concrete services such as coring and restoration. Post-Tensioning Repair Products. The magnetic field will spread out when it comes across the small air gap that is created by the crack because the air which cannot support as much magnetic field per the unit volume as the magnet can. https://www.concretenetwork.com/post-tension/. Jacking stress is 80% of the tendon's ultimate strength (F pu) = 216 ksi. For residential construction, tendons at 48 inches on center are common. Some additional benefits of building with post-tensioning are: As we all know, concrete is the basic material used in construction for its compressive strength. The Tendon Systems blog is a resource for industry news and analysis, gear care, maintenance and safety best practices. Email: info@advancedposttension.com This corrosion occurs due to improper grouting procedures and the accumulation of bleed water. The sub-figures on the left (b, d, and f) represent the load-balancing method applied to a segment of the member.The prestressing tendon is removed and is replaced by the forces that it exerted when in place . In that year, a tradition began that we have successfully continued on a global scale until today. To overcome this problem, a steel reinforcement bar or rebar is used to limit the cracks by embedding them in the concrete structure. Infraspect is a complex bridge inspection, non-destructive testing (NDT), and robotic engineering company. Advanced Robotic Bridge Inspections provide more quantitative data to better budget for maintenance and repairs. , Two critical pieces of a post-tension tendon are the high-strength steel cable that makes up. Steel strands are placed in a duct, placed in the forms or outside the forms, and tensioned prior to loads being placed. Afterward, once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or tensioned, and anchored against the outer edges of the concrete." Tendons may be located either within the concrete volume (internal prestressing) or wholly outside of it (external prestressing). Overall, completing a site survey through scanning keeps buildings, and people, safe. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); We offer the most advanced nondestructive testing methods to assess the integrity of your assets worldwide. Post-tensioning of elevated slabs is a construction process that requires experience, coordination, knowledge, and preparation. Anchorages are another critical element. Thus, it is felt that meaningful conclusions and recommendations can be drawn from the study executed herein. BUSINESS HOURS Monday - Friday: 6:00AM To 5:00PM. Continue reading for more information on locating tendons in post-tensioned concrete. The Benefits Of Magnetic Flux Leakage for bridge inspections and international bridge inspections. Post-tensioning allows construction to be conducted in less time and at a lower price. Current manual inspection procedures would not detect this type of corrosion until it is too late. Internal structures and makeup of the tendons are revealed. Figure 3 highlights the features of the rigorous method and its comparison with the load-balancing method. This approach is often used in precast concrete structures such as parking garages, office buildings and others. When post tensioning concrete, the pre-stressing assembly is tensioned after the concrete has attained a specified strength. Profiling. . For more than 30 years, Tendon Systems has been an industry-leading provider of post-tensioning, barrier cable, and restoration services throughout the country. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. An October 2016 report by the FDOT stated Recent corrosion failures of post-tensioned (PT) tendons in the Ringling Causeway Bridge. A post-tensioning tendon is made up of one or more pieces of prestressing steel, coated with a protective coating, and housed inside of a duct or sheathing. In unbonded construction, the plastic sheathing acts as a bond breaker between the concrete and the prestressing strands. To promote the use of post-tensioning in buildings, bridges, silos and tanks, ground floor slabs and other structural types throughout the UK construction industry. The tendons, like rubber bands, want to return to their original length but are prevented from doing so by the anchorages. With todays post-tensioning techniques and materials, amazing structures are appearing worldwide. This compensates for the tensile stress that the concrete may undergo as a result of external loads and reduces or eliminates deformation and cracking. The tendons are replaced by their uplift effect (balanced load) on the member. In bonded systems, two or more strands are inserted into a metal or plastic duct that is embedded in the concrete. All Rights Reserved. The strand coating material reduces friction between the strand and the sheathing and provides additional corrosion protection. This means that it can bear its own weight. Sometimes, when it all goes sideways, the person running the saw (or drill, or nailgun) realizes that something has gone wrong before the tendon is completely severed. Post-tensioning Pretensioning Post-Tensioning Steel tendons are stressed after the concrete has been placed and gained sufficient strength at the construction Bonded PT Unbonded PT site NPCA 1 fThe Precast Show 2014 Pre-Tensioning: Pre-Tensioning: Precast elements are transported to the site. System can be demounted and substituted through the presence of an inner steel The unit also transmits data wirelessly to the human inspector in a wheeled cart above. Restoring concrete may include the addition of fiber reinforced polymers (FRP) or epoxy injections for cracks. The products comprise a complete range of post-tensioning components including. The unit is automated and powered by a battery. TendonScan for the first time gives the bridge or asset owner the information they need to properly allocate their assets to make repairs in a timely manner. In buildings, they are typically only used in heavily loaded beams such as transfer girders and landscaped plaza decks where the large number of strands required makes them more economical. We offer the most advanced nondestructive testing methods to assess the integrity of your assets worldwide. Post-tensioning tendons are made up of more than one group of prestressing steel. Why werent current inspection practices sufficient enough to find issues before corrosion became so severe? Post-tensioning is a technique that strengthens concrete systems. Post-tensioning is applied with the help of a post-tensioned tendon which is an assembly of high-strength prestressing steel bar or strand, sheath, or protective duct often made up of plastic, grout, or corrosion preventing coating and anchorage. The anchorage consists of an iron casting and a conical, two-piece wedge which grips the strand. Which has a protective coating for high strength. Post-tensioned tendons are used in bridge construction, building construction, box girder roadways, tennis courts, dams, and other large concrete structures. Commercial foundations will have much more steel. Contents 1 Pre-tensioned concrete 2 Post-tensioned concrete Infraspect is a complex bridge inspection, non-destructive testing (NDT), and robotic engineering company. WHY YOUR POST TENSION TENDONS NEED TO BE PROPERLY STRESSED. Recommendations: During the detensioning process, the post-tensioning tendon will have to be "over-stressed A post-tensioning tendon is made up of one or more pieces of prestressing steel, coated with a protective coating, and housed inside of a duct or sheathing. Because they are stressed, even a small amount of damage can significantly affect the stability of the cable. Three questions on tendon stressing are often raised among post-tensioning crews. In most post-tensioned residential buildings, there is a fair amount of coordination between the post-tensioning (PT) contractor and MEP trades. 1) Profiling : Read the drawings and identify the type of tendons, layout, locations, number of strands per tendon, the sequence of laying, number of tendons per pour, etc. strand. Which is placed inside a tube or casing in a concrete slab. Perfectly tuned to external post-tension tendons, the software shows the location and percentage of loss of metallic area. The stressing operation is monitored to ensure that tendons receive their design-intended force. This corrosion can allow for air, water, and other environmental contaminants to enter the steel and weaken the overall structure. Take a look at some of what GPR can detect: GPR is an excellent concrete scanning method because it locates tendons deep in the concrete. The banded tendons are in the column strips and there are no tendons in the parallel middle strips. This sagging and deflection is caused due to the daily use of the concrete structure and can result in cracks that can weaken the structure. Evolved from a . Post-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast. This allows for reduced quantities of reinforcing steel and thinner slabs for a given span. Post-Tensioning Tendon A post-tensioning \"tendon\" is defined as a complete assembly consisting of the anchorages, the prestressing strand or bar, the sheathing or duct and any grout or corrosion-inhibiting coating (grease) surrounding the prestressing steel. In contrast, when there is damage, due to broken wire or wear. Construction Companies in Thanjavur, Tamil Nadu, Civil Engineering WhatsApp Group Link Join Now, Types of Concrete Admixtures in Construction Works, Quality Control Engineer Role And Responsibilities. The design and calculation of all the components were performed according to the new European code ETAG-013, which verification is an . Post-tensioning allows for engineers to design with an, Live Ends, Dead Ends, and Intermediates Anchoring Post-Tension Tendons. Forces in Post-Tensioned Tendons. Before casting, corrugated ducts are often installed into the concrete along the centroidal axis. An operative hit by the debris sustained relatively minor injuries, however the consequences could have been much worse. The flux leaks out of the metal near the defect. This data may also inform the plans of the project. Tendons when they are placed are sometimes not grouted properly and sometimes due to age or environmental issues the grout may crack. Post-Tension Tendon inspection service for bridge inspections helps keep our bridges and box girder roadways safe. Tendons shorter than 15 ft in length are rarely used; designers are encouraged to use non-prestressed reinforcement . Post-tensioning is used in all large concrete structures. The robot then runs along the tendon using its sensors to locate faults, openings, and corrosions. Based on the percentage and amount of loss, the asset owner can determine where further actions need to be taken. First, precompression allows the engineer to use the compressive strength of concrete to offset the natural stresses that build up in a concrete slab. Suncoast Post-Tension The orange plastic sheathing of the post-tensioning tendons is clearly visible on the top slab of this Galveston, Texas, project, which employed a flat-plate framing configuration. It also ensures the safety of the structure and of the public. The strands are anchored into the cast-iron anchor head using the standard wedges. 2) Stop Cutting! ***Notice that the 0.5 and 0.6 have the same Avg. We supply single strand, unbonded post-tension tendons, stressing equipment, and installation drawings. We have substantial experience in the selection and installation of all strengthening techniques. 1. Where most MFL units cannot provide proper data for post-tension tendons. Our material is assembled in the United States, and we can source domestic raw materials on demand. If you take a magnet that is cracked, but not broken completely in two, form a north pole and a south pole at each edge of the crack, as shown in the Figure below. The case is from a project of 13 floors with the post-tension slab. For example, using a 100-foot tendon (L = 100 x 12 inches) with Modulus of Elasticity of 28,500 ksi. The post-tensioning tendons (Pre-stressing steel cables) are kept inside plastic ducts or sleeves which are placed in the position before pouring concrete. Elongation*** _____ Post-Tensioning Institute recommends an allowable elongation range of plus/minus 7% of the Average Tendon Elongation for unbonded post-tensioning tendons. What causes post-tensioned tendon failure? Asset owners need better information in order to make more intelligent budgetary decisions.. Infraspect specially configured software can provide results long before a tendon needs to be repaired or replaced. Wireless, Portable, and Accurate. Tendon Systems designs and builds large-scale post-tensioning systems. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Post-tensioned slabs are thinner and less heavily reinforced than conventional slabs. Required fields are marked *. AURORA HEADQUARTERS 14800 E. Moncrieff Place Aurora, CO 80011 303-576-2200 Sales@Barton-Supply.Com. These processes assure the durability of the PT tendons but if these processes are done improperly then it can compromise the durability of the tendons causing tendon failure. Since post-tensioned concrete is cast in place at the job site, there is almost no limit to the shapes that can be formed. New grout material has been formulated especially for post-tensioning to minimize bleed water formation but the occurrence of corrosion also happened with the use of new grouts. This protects the tendons from corrosion and damage. This method also provides better reinforcement and increases the integrity of structures. In the US bridges are inspected every two years and bridges with any deficiencies are typically inspected every year. The unit is attached to the post-tension tendon and the post-tension tendon inspection can, Robots Meet Bridge, Road Inspection Ex-NHDOT Chiefs Company Paves the Way With New Tech. If the tendons are corrupted, then the concrete slabs overhead can collapse as well. A post-tensioning tendon is made up of one or more pieces of prestressing steel, coated with a protective coating, and housed inside a duct or sheathing. The spacer frames serve as templates for . Post-tensioned structures that have been compromised by corrosion, tendon failure, structural modifications or change of use may benefit from the installation of supplemental strengthening. Post-tension anchors distribute the force from the tendon into the concrete around the tendon ends. |, Protect tendons from damage and corrosion. The tendon cables are tensioned after the concrete is cast. https://onlinepubs.trb.org/Onlinepubs/trr/1989/1211/1211-005.pdf. We use Free Form Reinforcement with adjusted Bar Diameter and Bending Radius parameters to represent tendons (ducts) and Rebar Couplers for anchorage systems. The second unit locates section loss and corrosion. This shows the human inspectors exactly where they need to repair or replace the tendons. The post-tensioning technique involves installing and tensioning tendons in a concrete element, thereby applying compressive stress to the material. Without post-tension tendons, large slabs of concrete would crack and collapse under load. To promote best practice in the design, procurement and execution of post-tensioned structures. Post-tensioning is a method of reinforcing concrete with high strength steel tendons in relatively inexpensive concrete to produce efficient, lighter weight designs compared to traditionally reinforced structures. Post-tensioning applications include high rising buildings, office and apartment buildings, parking, structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and . For bonded systems, the prestressing steel is encased in a corrugated metal or plastic duct. Horizontal applications (such as beams, slabs, bridges, and foundations) typically employ strands. All Rights Reserved. For example, although a restoration may be planned, the details of the project may not be set in stone until after the GPR scan is complete. This means each floor contains less material, the building is shorter and lighter, and each floor has more headroom. Prestressed metal is manufactured according to the necessities of ASTM A-416 and the everyday strands are 0.50 and 0.60 inches in diameter. Concrete core drills are highly precise machines that require knowledgeable operators. Tendon damage, especially when caused by construction methods, is money down the drain. The unit is a 16lb battery-powered robot, that crawls along the tendon. A research article written by Seunghee Park and Changgill Lee offers the Principals of Magnetic Flux Leakage to help explain. This method is using a clamp around the tendon that picks up the force of the. In post-tension reinforced slab on grade foundation the concrete of the foundation is reinforced to prevent cracking and hold the concrete together when it bends by the installation of tendons that compress the concrete. In building and slab-on-ground construction, unbonded tendons are typically prefabricated at a plant and delivered to the construction site, ready to install. GET A QUOTE. The entire process is accomplished with non-destructive testing methods to ensure the best possible results. REQUEST A BID . Weak concrete may need to be reinforced or even demolished in some cases. These are: Scanning is the first step to any kind of post-tensioned concrete maintenance, demolition or repair. While it is an integral part of all post-tensioning operations, its results can . Tendons The basic element used in post-tensioning systems is called tendons. When the jack releases the strand, the strand retracts slightly and pulls the wedges into the anchor. The data collected from these sensors can be collected for real-time assessment and also stored for later comparison that can show progression in deterioration. Typically when it is too late and the tendon needs immediate attention. To achieve unbonded prestressing it is possible simply to use a flexible, corrosionresistant protective product instead of the cement grout, normally grease or wax . Ground Penetrating Radar uses radar pulses to survey a sub-surface. The cells or cavity containing the tendons . Basically, Revit model lines represent the projection of the tendon geometry in the plan view. Fig 3: Steel tendons used in Post Tensioning of Slab. Deterioration progression over time on additional inspections can help asset managers better budget for maintenance and repairs. 3. Once the geometry of the bridge falsework has been obtained, prefabricated spacer frames are set into place. Stressing. Cracking in post tensioned slabs prior to tensioning the strands/tendons is very common and this situation has a specific name called "Restrained to Shortening" or RTS cracks. 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