Post tensioned concrete bridge deck cracking

So this viaduct is constituted by multiple bridge span. Lots of cracks in new post tension slab inspectionnews. Shows operations involved in posttensioning of bridge deck. The concrete stress behavior and cause of cracking at the anchorage zones of top and bottom slabs of a post tensioned prestressed concrete box beam were studied. Reinforcement helps extend the life of concrete, overcoming cracking that is inherent in the material and preventing its failure. In two connections post tensioned with an initial compressive stress of 340 psi, the. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. Any post tension slab inspectors out there i am building a new home in longview, texas, and they poured our post tension slab 7 days ago. Cracks, cracks, cracks what is a reasonable level of cracking. The alternative to pretensioning is post tensioning. The reinforced connections and two post tensioned connections with 167 psi initial stress experienced cracking and leaked water by the end of the cyclic loading regime. Cracking is therefore eliminated under working load and all of the concrete may be assumed effective in carrying load.

Effective inspection and monitoring of posttensioned structures. Neglecting to design general anchorage zones or delegating this responsibility. Relationships of material propertiesproportions and concrete deck cracking concrete deck materialmixture factors effects on concrete deck cracking. We recommend using pt for temperature and shrinkage reinforcement. Longitudinal anticracking analysis for posttensioned voided.

The most common structures in hong kong are multispan concrete viaducts more than 30% of these structures are posttensioned most of the large span landmark concrete structures are posttensioned. Gustave magnel, a belgian engineer, and charles zollman, magnels student, designed the bridge. Cip, posttensioned bridges were the least likely to have transverse deck cracking because the girders and the deck shrink together and posttensioning intro duces compressive stresses in the deck. Types and causes of concrete cracking in bridges 3. Top 10 biggest mistakes made in posttensioned concrete.

The superstructure of the viaduct is supported by ten piers. An experimental investigation was conducted to examine cracking of post tensioned bridge deck anchorage zones with closely spaced anchors. Very good video showing step by step post tension slab. Laminar spalling in deck minor laminar spalling was visually noticed in the underside of the top flange deck slab during and after post tensioning of the negative moment tendons. Unlike simplespan, simplesupported, post tensioned girders that can be structurally analyzed using exact methods that are not very time consuming, the secondary moments due to prestressing in continuousspan, post tensioned. This means the foundation is reinforced by cables laid in a grid arrangement and tensioned after the concrete cures sufficiently with the intent to create. Further, structures constructed using posttensioning also benefit from the methods ability to limit cracking, reduced structural depth, ease of accommodating curved roadway alignment and low maintenance costs. A total of four posttensioned girders were salvaged from both the northbound and southbound bridge. The alternative to pretensioning is posttensioning. Scholer research engineers, joint highway research project introduction the problem of concrete bridge deck deterioration on many of our newer as well as older bridges is severe, somewhat perplexing as to cause, and difficult to solve. For this purpose, fullscale boxgirder members were made and tested.

The connections were designed for a deck replacement. Ence717 bridge engineering concrete bridges reinforced. Test cores and hammer testing indicated full homogeneity of the restored section. Precast, pretensioned, posttensioned concrete for bridge decks. Investigation of bridge deck cracking in various bridge. Developers, architects, engineers, contractors, educators and. Cip, post tensioned bridges were the least likely to have transverse deck cracking because the girders and the deck shrink together and post tensioning intro duces compressive stresses in the deck. Ence717 bridge engineering concrete bridges reinforced and. Many bridges in the state of indiana have been identified to have cracking in the concrete deck. Philadelphias walnut lane bridge, completed in late 1950, is considered the first major prestressedconcrete bridge in the u. Prestressed concrete is a form of concrete used in construction. The individual units may be either precast or cast in situ, and they are stressed together in such a way that the whole section remains in compression under both dead and live loading. One of the suspected reasons for mcreased transverse cracking observed in bridge decks used in the state ofmininesota wiis a changn.

The schematization of the typical deck span is represented in fig. Anchorage zone cracking of posttensioned bridge decks with. May 01, 2018 so this viaduct is constituted by multiple bridge span. Bridge designers have used pt both for castinplace concrete and for precast segmental construction. A posttensioned system will move 20% to 30% more than conventionally reinforced concrete. Forensic testing of post tensioned concrete girders. Vsl systems have a wellearned reputation for their quality, reliability, and durability and have been used throughout the world since 1956 to build, repair, and strengthen buildings, tanks, transportation and special structures.

Understanding the causes of some of these problems should help contractors build better post tensioned structures. Investigation of paneltopanel connections and blockouts. There are two types of deck using prestressed concrete. Segmental posttensioned concrete bridges are made of a number of units stressed together. Decorative posttensioned concrete since pt is simply reinforcement, there really arent any specific decorative applications related to post tensioning. Pdf transverse posttensioning design and detailing of. Precast, pretensioned, posttensioned concrete for bridge decks m. Posttensioning in buildings is not limited to floor slabs. Erection of fulldepth, fullwidth, precast concrete panels entran plc and aspire magazine. These blocks were strung onto prestressing cables, joints of the net section were mortared, harped tendons were post tensioned, and tendons were grouted. There are several construction issues with posttensioned concrete that are found consistently among engineers and contractors. For this reason it needs help in resisting tensile stresses caused by bending forces from applied loads which can result in cracking and ultimately failure.

Longitudinal anticracking analysis for posttensioned. The following design method can be used for normal weight concrete with specified compressive strengths up to 15. The advantages of pt as noted in the opening page are the lack of cracking or at least very narrow cracks and the ability to span farther. Each of the posttensioned concrete beams was cast at. This method of reinforcing concrete enables a designer to take advantage of the considerable benefits provided by prestressed concrete while retaining the flexibility afforded by the castinplace method of building concrete structures. Collapse of a segmental posttensioned concrete bridge r. Pretensioning and posttensioning in prestressed concrete.

Principle and modeling of concrete beamslab bridges linear elastic modeling production purposes it can be simplified as a beam or a grid the equivalent stiffness can be calculated from equation 2. Other design fac tors that moderately contributed to early cracking were. The shrinkage study was conducted on two minnesota departinenil of transportation mddot concrete bridge deck mix designs. The foundation in question was a posttension cable reinforced foundation as opposed to a foundation which is reinforced with steel rebar see the typical photograph in this article. Anchorage zone cracking of posttensioned bridge decks. Crack width evaluation in posttensioned prestressed. Posttension basics how posttensioned slabs are built the. Since pt is simply reinforcement, there really arent any specific decorative applications related to post tensioning.

Concrete water tanks are often posttensioned to reduce crack width and leakage. The cause of cracking in posttensioned concrete box girder. Post tensioned concrete construction is a little different than standard reinforced concrete construction. The test program included fullscale tests of bridge deck anchorage zones with single and closely spaced anchorages. Concrete, although strong in compression, is weak in tension. The crack width, strains and deflections of deck slabs were measured automatically according to the in. The structure consisted of precast units stressed together both lon gitudinally and transversely. Cracking has been identified in the negative and positive moment regions of bridges on both the top and bottom surfaces and can appear before or shortly after the opening of the structure to live loads. Also, because aci 302 says a reasonable level of cracking is from 0% to 3%, it implies that no cracking, 0%, is a possible, reasonable level. A broad crack may also form at a plane of bars parallel to a concrete surface, resulting in delamination, a wellknown problem in bridge decks. Bridge structures constructed using posttensioning have high intrinsic durability and are able to be built quickly with minimal impact on the human and natural environment.

Post tensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast 25 the tendons are not placed in direct contact with the concrete, but are encapsulated within a protective sleeve or duct which is either cast into the concrete structure or placed adjacent to it. Bridge design prestressed concrete bridge beam design. Precast, prestressed concrete adjacent box girders are widely used in short and mediumspan bridges. Woodward this paper describes an investigation into the collapse of a. Nov 25, 2008 post tensioned concrete is a term heard more and more in the construction industry today. The most common types of finite element used are flat shell elements a beamandslab or cellular bridge deck may require a. Significant crack widths and various degrees of cracking exist in different bridge systems. In a posttensioned beam, the tendons are stressed and each end is anchored to the concrete section after the concrete has been cast and has attained sufficient strength to. The foundation in question was a post tension cable reinforced foundation as opposed to a foundation which is reinforced with steel rebar see the typical photograph in this article. Compressive stresses are introduced in prestressed concrete either by pretensioning or posttensioning the steel reinforcement. A good rule of thumb is that a posttensioned system will move about 1 inch for every 100 feet of slab that is not restrained by a lateral system. The cause of cracking in posttensioned concrete box. Presoaked wet burlap and soaker hoses are applied to deck surface when deck has taken initial set. General principales local zone design general zone design.

Posttensioning of foundations, transfer beams and plates, posttensioned masonry and the combination of precast elements with castinplace concrete by means of posttensioning offer other interesting opportunities. Compressive stresses are introduced in prestressed concrete either by pretensioning or post tensioning the steel reinforcement. Crack width evaluation in posttensioned prestressed concrete. Structural technologies is the exclusive manufacturer of vsl posttensioning products and construction systems in the united states. This means the foundation is reinforced by cables laid in a grid arrangement and tensioned after the concrete cures sufficiently with the intent to create compression in the foundation concrete to resist cracking. Posttensioned box girder bridge an analysis approach. The term pretensioning is used to describe a method of prestressing in which the tendons are tensioned before the concrete is placed, and the prestress. Bridge 3034a traditional 7span prestressedposttensioned girders 45% 85% 75% 100%. Investigation of paneltopanel connections and blockouts for fulldepth precast concrete bridge decks 5.

The author discusses the problem of the demolition of posttensioned concrete, using as an example the demolition of nine prestressed concrete beams and the repair of others during the construction of bridges on the m3 motorway. Understanding the causes of some of these problems should help contractors build better posttensioned structures. Posttensioned box girder bridge an analysis approach using. An experimental investigation was conducted to examine cracking of posttensioned bridge deck anchorage zones with closely spaced anchors.

Cracks provide easy access for oxygen, moisture, and chlorides, and thus, minor splitting cracks can create a condition in which corrosion and cracking are accelerated. These problems are not limited to those of prestressed box girder bridges, but may occur in other types of structures with similar conditions and details. The condition of cracks in non post tensioned bridge decks worsen over the service life of the structure, with possibility of cracks extending through the deck thickness, causing corrosion in bottom layer reinforcement due to chloride penetration. Types of cracks in fresh and hardened concrete causes and.

Bridge deck cracking evaluation of performance based concrete for bridge decks. Design step 4 design of deck prestressed concrete bridge design example task order dtfh6102t63032 45 future wearing surface. The design of fulldepth precast concrete fdpc deck panels involves the design of several different components. The use of posttensioned reinforcement to construct floor slabs can result in thinner concrete sections andor longer spans between supports. Precast, pretensioned, posttensioned concrete for bridge. Unlike simplespan, simplesupported, posttensioned girders that can be structurally analyzed using exact methods that are not very time consuming, the secondary moments due to prestressing in continuousspan, posttensioned. The bridge was closely examined in 1981 when it was required to carry 50tonne concrete beams, but nothing untoward was. Thus, during the active development of prestressed concrete in the 1940s and 1950s the emphasis was on elastic methods of analysis and design. In a post tensioned beam, the tendons are stressed and each end is anchored to the concrete section after the concrete has been cast and has attained sufficient strength to safely withstand the prestressing force as shown in fig. Damage and collapse mode of existing post tensioned precast.

As a building material, concrete is strong in compression, but weak in tension. Ciria report c660 earlyage thermal crack control in concrete. Bridge division office of engineering federal highway administration washington, d. Typical maximum dimensions of fdpc deck panels there are two typical panel configurations that are primarily based on the width of the bridge.

Nchrp synthesis project 500 control of concrete cracking in bridges chapters. Woodward this paper describes an investigation into the collapse of a singlespan, segmental posttensioned concrete bridge. Effective inspection and monitoring of posttensioned. Some key variables include the size of concrete placements, continuity of multispan decks, concrete curing procedures, posttensioning strain differentials, restraint between decks and other bridge elements, and deck placement sequencing.

Refer to section 9, deck and deck systems, of this bdm for information about acceptable deck reinforcement sizes and spacing. Issues in posttensioned construction concrete construction. By the third day, i noticed a crack in the back patio, and by the fourth, there were sprawling cracks throughout the entire foundation. Half of the test specimens contained additional spiral anchorage zone reinforcement. There are several construction issues with post tensioned concrete that are found consistently among engineers and contractors. Apr 08, 2014 shows operations involved in post tensioning of bridge deck.

Each of the posttensioned concrete beams was cast at the bridge site in a single piece. The concrete stress behavior and cause of cracking at the anchorage zones of top and bottom slabs of a posttensioned prestressed concrete box beam were studied. Major test variables include the amount of prestressing and prestressing steel ratios. Document the difference in cracking between bridge.

Several sources of cracking for concrete bridge deck overlays have been identified 2, 3, 7. Recommended practice for precast posttensioned segmental. Concrete water tanks are often post tensioned to reduce crack width and leakage. These blocks were strung onto prestressing cables, joints of the net section were mortared, harped tendons were posttensioned, and tendons were grouted. Some of the cracks are more than 30 feet long, and i can feel a slight difference in the rise on each side you can even. Concrete bridge decks and deck overlays may develop cracks whenever the tensile stresses induced by either internal or external sources exceed the tensile strength of the concrete. Posttension basics how posttensioned slabs are built.

Rebar reinforcement in this case is technically allowed by code but in our experience, a properly designed post tensioned concrete slab will minimize cracking due to shrinkage. Therefore lighter sections may be used to carry a given bending moment, and prestressed concrete may be used over much longer spans than reinforced concrete. The companies that make prestressed concrete tanks are crom, dyk, natgun, and preload. The cause of cracking in post tensioned concrete box girder bridges and retrofit procedures walter podolny, jr. Jim rogers bending and flexing creates high tensile forces that can cause the concrete floor slab to crack.

Damage and collapse mode of existing post tensioned. The factors are summarized in tables 1 through 3 with brief descriptions as to how they can positively or negatively affect the degree of deck cracking. The condition of cracks in nonposttensioned bridge decks worsen over the service life of the structure, with possibility of cracks extending through the deck thickness, causing corrosion in bottom layer reinforcement due to chloride penetration. The cause of cracking in posttensioned concrete box girder bridges and retrofit procedures walter podolny, jr. Cracking in concrete bridge decks the national academies press.