This paper reports results of tests of four model bridge piers. The principle objectives of this ... more This paper reports results of tests of four model bridge piers. The principle objectives of this experimental program were to verify the axial load-moment curvature P-M-phi relationship for hollow columns and to examine the validity of the plane-section assumption for hollow-pier sections. This was necessary to validate completely the computer analysis programs for the design of slender, nonprismatic, and hollow concrete bridge piers. It is concluded that the plane-section assumption is valid for rectangular solid and cellular cross sections if the unsupported wall length to thickness ratio does not exceed six.
The principal objective of the study was to examine the concept of improving bridge deck design b... more The principal objective of the study was to examine the concept of improving bridge deck design by the application of transverse prestressing and to specifically examine the improvement of durability due to protection from chloride-induced corrosion. The secondary objective was to provide structural design related recommendations for proper use of modern prestressing systems to ensure effective distribution of transverse prestress throughout deck slabs. To fulfill these objectives, the research was divided into three areas. The first area was the durability phase, in which the primary emphasis was the experimental investigation of prestressed concrete specimens exposed to an aggressive chloride environment. The second area was the structural phase in which both experimental and analytical studies were conducted to investigate the structural aspects of transverse prestressing. The final phase was the formulation of design recommendations for transverse prestressing which incorporated the findings from the structural and durability studies. The results from the durability study indicate that current specifications for the design of reinforced concrete decks which implicitly permit crack widths under service loads of 0.011 in. are inadequate for protection of steel reinforcement from chloride-induced corrosion. Transverse prestressing is effective in reducing corrosion because it permits a "crack-free" slab under service loads. However, to reduce the risk of corrosion from long-time exposure to an aggressive chloride-containing environment, a minimum concrete cover of about 2.5 in. over steel reinforcement and a maximum water-cement ratio of 0.45 in the concrete is needed. In addition, special attention must be given to the prestressing system to ensure full encapsulation and thus prevent penetration of aggressive corrosion-producing substances. The results from the structural study indicate that diaphragms have a significant effect on the distribution of stress in transversely prestressed bridge decks. To overcome [...]
Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology re... more Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology responsible for corrosion, deterioration and failure. The problem of repair cracking has become widespread not only with respect to severe environments which are intensifying restrained volume change stresses but also with respect to repairs in relatively benign environments. Cracking accelerates the penetration of aggressive substances into the concrete and repair material from the exterior environment which in turn aggravates any one or a number of various mechanisms of deterioration. Moisture transport mechanism in the repaired structures is a tool for transferring an outer standard environment into an inner environment, and from one inner environment (existing substrate) into another (repair material). The crack resistance of concrete repair is bearing on three equally important "elephants": (1) design details and specifications; (2) repair materials; (3) in-situ workmanship and quality control. This study demonstrates that the properties of cementitious repair materials have to be engineered for dimensional compatibility with existing concrete to improve their resistance to cracking. How good should the cementitious composite material used for repair of existing concrete structures be? How good is good enough. The paper summarized the factors involved and approaches taken when selecting cementitious repair materials. Performance criteria are presented for the selection of dimensionally compatible repair materials and standard material data sheet protocols. The recommended approach can enable material quality improvement, more accurate service life prediction, and satisfactory performance of repaired concrete structures during their intended service life.
Wind- and rain-induced vibrations of cables on cable-stayed bridges are a relatively new phenomen... more Wind- and rain-induced vibrations of cables on cable-stayed bridges are a relatively new phenomenon. While some observers report hearing about such vibrations ten or 12 years ago, typically in Japan and Europe, it is only in the past few years that research has begun here in the United States. A study coordinated by the Texas Dept. of Transportation centers on vibrations at the Fred Hartman bridge, Baytown, Tex., which was opened in 1995, and the Veterans Memorial bridge in Port Arthur, Tex., which opened in 1991. The University of Texas, Austin, Texas Technological University, the University of Kentucky and Johns Hopkins University are contributing to the study and the Virginia firm of Whitlock, Dalrymple Poston & Assoc., working with these institutions. This article explores the possible reasons for the vibrations, as well as proposed remedial systems. Among them are restraining systems, dampers and strakers. The vibrations cause mororists concern, and can cause metal fatigue and other problems. Remediation can be costly. Design procedures are also suggested. A sidebar discusses the interim remediation work at the Fred Hartman bridge, and offers comments from engineers who have designed many cable-stayed bridges.
It is likely that poor construction practice, not a lack of quality of the materials, is to blame... more It is likely that poor construction practice, not a lack of quality of the materials, is to blame when this shotcrete has manifested signs of deterioration. Investigation of the conditions of over 100 prestressed concrete tanks, many of which were built over 30 years ago, proved that dry-mix shotcrete is a very durable material. This article discussed case histories concerning the overall long-term performance of shotcrete used in the construction of prestressed concrete tanks built more than 30 years ago.
A brief history of post-tensioned concrete construction in North America is provided. Case studie... more A brief history of post-tensioned concrete construction in North America is provided. Case studies of an internal tendon bridge constructed 30 years previously and an externally post-tensioned precast segmental bridge are provided. Research on the durability of grouted post-tensioned concrete structures in the USA is reviewed. Strategies for improving the durability of post-tensioned structures include improved grouting materials, physical property testing prior to construction, use of pre-packaged grouts if appropriate, planning and documenting grouting procedures, inspection after grouting, and training and certification. For the covering abstract see ITRD E114200.
A field investigation was conducted to assess the structural and durability implications of bridg... more A field investigation was conducted to assess the structural and durability implications of bridges constructed in chromite ore processing residue (COPR) fill. The findings are based on visual inspection and various testing of 31 bridges, located in known chromium and nonchromium sites in and around Hudson County, New Jersey. Various types of observed deterioration of the concrete bridge substructures are documented for each of the study bridges. Of the 31 bridges, approximately half (15) of the bridges underwent more extensive nondestructive testing, including determination of chloride ion content and pH, determination of the presence of alkali-silica reactivity, impact-echo for assessment of integrity, and measurement of half-cell corrosion potentials where exposed reinforcement was available to document the causes of observed deterioration. On the basis of the study results, it is concluded that observed deterioration of the bridges is a result of classical causes, such as chlori...
Diagnosing flaws without destroying the structure is the first step to cost-effective repairs. Im... more Diagnosing flaws without destroying the structure is the first step to cost-effective repairs. Impact-echo is one of the more successful nondestructive evaluation (NDE) methods that have been developed recently to probe the internal condition to structural concrete. In the impact-echo technique, a transient stress pulse is introduced into the test object by mechanical impact on the surface and monitored by a displacement transducer placed close to the point of impact. Speed of the wave measurement is a function of concrete density, aggregate type, moisture content and other factors, and is established in an area of known sound concrete before testing is done on unknown areas. In concrete plates such as slabs, the impact-echo response reflects the plate bottom or any internal cracks or flaws. Examples are given of tests done on a concrete slab, bridge, building balcony and other structures. A sidebar discusses tests being done with mobile equipment on concrete pipe.
It is estimated that $500 million dollars is spent annually for repair of bridge decks which suff... more It is estimated that $500 million dollars is spent annually for repair of bridge decks which suffer from deterioration. The major cause of bridge deck deterioration is corrosion of reinforcing steel induced by exposure to chlorides from deicers and salt water spray. Dissolved salts seep into bridge decks primarily at crack locations and cause steel corrosion which sets up a splitting force because of the volumetric expansion and eventually breaks the concrete. This report briefly presents background information on the mechanism of corrosion of steel reinforcement in concrete, and summarizes the observations and findings from an experimental corrosion study. A simple test specimen was developed to simulate the behavior of a transversely prestressed bridge deck subjected to an aggressive deicing salt exposure. The experimental program investigated the primary variables affecting corrosion of steel in prestressed concrete: concrete cover, crack width, protective coatings for steel reinforcement, type of prestressing protective system, concrete quality, and level of prestressing. Behavioral trends are presented as determined from half cell potential measurement of the nonprestressed reinforcement, chloride analysis of the concrete, and visual observation from a post mortem autopsy of the specimens.
Transverse prestressing is an attractive concept with substantial benefits in both economy and im... more Transverse prestressing is an attractive concept with substantial benefits in both economy and improved durability. This report summarizes a series of interrelated physical tests and computer analyses which were conducted to provide necessary information for development of design criteria for transverse prestressing of bridge decks. It addresses such important design areas as the effective distribution of edge prestressing force across a bridge slab as affected by both diaphragm and girder restraints, realistic friction losses in transverse prestressing systems, and the behavior of transversely prestressed decks under typical wheel loadings. The principal attention is focused on slab and girder bridges, but analytical results are extended to box girder bridges. Experimental verification of the analysis programs allowed substantial parameter studies to be carried out with reasonable confidence. The results of the major experimental and analytical studies are summarized in this report.
The objective of this study is to investigate the use of deck prestressing as a method of improvi... more The objective of this study is to investigate the use of deck prestressing as a method of improving durability of bridge decks with the aim of developing suggested AASHTO Specification design requirements to facilitate its use. The results from an experimental test series of prestressed concrete specimens subjected to an aggressive deicing salt exposure and from an experimental and analytical investigation of the structural behavior of a fully composite slab-girder bridge model indicated that deck prestressing is a viable corrosion-protection design alternative. It has already been used in numerous box girder bridges to improve structural efficiency. Specific recommendations for improving durability of bridge decks by deck prestressing and for proper design of deck prestressing are included in this report. These recommendations are presented in a form suitable for inclusion in the AASHTO Bridge Specifications. Several design examples are included to illustrate the design recommendations and to compare costs to those of current bridge deck designs using conventional reinforced concrete.
This paper reports results of tests of four model bridge piers. The principle objectives of this ... more This paper reports results of tests of four model bridge piers. The principle objectives of this experimental program were to verify the axial load-moment curvature P-M-phi relationship for hollow columns and to examine the validity of the plane-section assumption for hollow-pier sections. This was necessary to validate completely the computer analysis programs for the design of slender, nonprismatic, and hollow concrete bridge piers. It is concluded that the plane-section assumption is valid for rectangular solid and cellular cross sections if the unsupported wall length to thickness ratio does not exceed six.
The principal objective of the study was to examine the concept of improving bridge deck design b... more The principal objective of the study was to examine the concept of improving bridge deck design by the application of transverse prestressing and to specifically examine the improvement of durability due to protection from chloride-induced corrosion. The secondary objective was to provide structural design related recommendations for proper use of modern prestressing systems to ensure effective distribution of transverse prestress throughout deck slabs. To fulfill these objectives, the research was divided into three areas. The first area was the durability phase, in which the primary emphasis was the experimental investigation of prestressed concrete specimens exposed to an aggressive chloride environment. The second area was the structural phase in which both experimental and analytical studies were conducted to investigate the structural aspects of transverse prestressing. The final phase was the formulation of design recommendations for transverse prestressing which incorporated the findings from the structural and durability studies. The results from the durability study indicate that current specifications for the design of reinforced concrete decks which implicitly permit crack widths under service loads of 0.011 in. are inadequate for protection of steel reinforcement from chloride-induced corrosion. Transverse prestressing is effective in reducing corrosion because it permits a "crack-free" slab under service loads. However, to reduce the risk of corrosion from long-time exposure to an aggressive chloride-containing environment, a minimum concrete cover of about 2.5 in. over steel reinforcement and a maximum water-cement ratio of 0.45 in the concrete is needed. In addition, special attention must be given to the prestressing system to ensure full encapsulation and thus prevent penetration of aggressive corrosion-producing substances. The results from the structural study indicate that diaphragms have a significant effect on the distribution of stress in transversely prestressed bridge decks. To overcome [...]
Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology re... more Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology responsible for corrosion, deterioration and failure. The problem of repair cracking has become widespread not only with respect to severe environments which are intensifying restrained volume change stresses but also with respect to repairs in relatively benign environments. Cracking accelerates the penetration of aggressive substances into the concrete and repair material from the exterior environment which in turn aggravates any one or a number of various mechanisms of deterioration. Moisture transport mechanism in the repaired structures is a tool for transferring an outer standard environment into an inner environment, and from one inner environment (existing substrate) into another (repair material). The crack resistance of concrete repair is bearing on three equally important "elephants": (1) design details and specifications; (2) repair materials; (3) in-situ workmanship and quality control. This study demonstrates that the properties of cementitious repair materials have to be engineered for dimensional compatibility with existing concrete to improve their resistance to cracking. How good should the cementitious composite material used for repair of existing concrete structures be? How good is good enough. The paper summarized the factors involved and approaches taken when selecting cementitious repair materials. Performance criteria are presented for the selection of dimensionally compatible repair materials and standard material data sheet protocols. The recommended approach can enable material quality improvement, more accurate service life prediction, and satisfactory performance of repaired concrete structures during their intended service life.
Wind- and rain-induced vibrations of cables on cable-stayed bridges are a relatively new phenomen... more Wind- and rain-induced vibrations of cables on cable-stayed bridges are a relatively new phenomenon. While some observers report hearing about such vibrations ten or 12 years ago, typically in Japan and Europe, it is only in the past few years that research has begun here in the United States. A study coordinated by the Texas Dept. of Transportation centers on vibrations at the Fred Hartman bridge, Baytown, Tex., which was opened in 1995, and the Veterans Memorial bridge in Port Arthur, Tex., which opened in 1991. The University of Texas, Austin, Texas Technological University, the University of Kentucky and Johns Hopkins University are contributing to the study and the Virginia firm of Whitlock, Dalrymple Poston & Assoc., working with these institutions. This article explores the possible reasons for the vibrations, as well as proposed remedial systems. Among them are restraining systems, dampers and strakers. The vibrations cause mororists concern, and can cause metal fatigue and other problems. Remediation can be costly. Design procedures are also suggested. A sidebar discusses the interim remediation work at the Fred Hartman bridge, and offers comments from engineers who have designed many cable-stayed bridges.
It is likely that poor construction practice, not a lack of quality of the materials, is to blame... more It is likely that poor construction practice, not a lack of quality of the materials, is to blame when this shotcrete has manifested signs of deterioration. Investigation of the conditions of over 100 prestressed concrete tanks, many of which were built over 30 years ago, proved that dry-mix shotcrete is a very durable material. This article discussed case histories concerning the overall long-term performance of shotcrete used in the construction of prestressed concrete tanks built more than 30 years ago.
A brief history of post-tensioned concrete construction in North America is provided. Case studie... more A brief history of post-tensioned concrete construction in North America is provided. Case studies of an internal tendon bridge constructed 30 years previously and an externally post-tensioned precast segmental bridge are provided. Research on the durability of grouted post-tensioned concrete structures in the USA is reviewed. Strategies for improving the durability of post-tensioned structures include improved grouting materials, physical property testing prior to construction, use of pre-packaged grouts if appropriate, planning and documenting grouting procedures, inspection after grouting, and training and certification. For the covering abstract see ITRD E114200.
A field investigation was conducted to assess the structural and durability implications of bridg... more A field investigation was conducted to assess the structural and durability implications of bridges constructed in chromite ore processing residue (COPR) fill. The findings are based on visual inspection and various testing of 31 bridges, located in known chromium and nonchromium sites in and around Hudson County, New Jersey. Various types of observed deterioration of the concrete bridge substructures are documented for each of the study bridges. Of the 31 bridges, approximately half (15) of the bridges underwent more extensive nondestructive testing, including determination of chloride ion content and pH, determination of the presence of alkali-silica reactivity, impact-echo for assessment of integrity, and measurement of half-cell corrosion potentials where exposed reinforcement was available to document the causes of observed deterioration. On the basis of the study results, it is concluded that observed deterioration of the bridges is a result of classical causes, such as chlori...
Diagnosing flaws without destroying the structure is the first step to cost-effective repairs. Im... more Diagnosing flaws without destroying the structure is the first step to cost-effective repairs. Impact-echo is one of the more successful nondestructive evaluation (NDE) methods that have been developed recently to probe the internal condition to structural concrete. In the impact-echo technique, a transient stress pulse is introduced into the test object by mechanical impact on the surface and monitored by a displacement transducer placed close to the point of impact. Speed of the wave measurement is a function of concrete density, aggregate type, moisture content and other factors, and is established in an area of known sound concrete before testing is done on unknown areas. In concrete plates such as slabs, the impact-echo response reflects the plate bottom or any internal cracks or flaws. Examples are given of tests done on a concrete slab, bridge, building balcony and other structures. A sidebar discusses tests being done with mobile equipment on concrete pipe.
It is estimated that $500 million dollars is spent annually for repair of bridge decks which suff... more It is estimated that $500 million dollars is spent annually for repair of bridge decks which suffer from deterioration. The major cause of bridge deck deterioration is corrosion of reinforcing steel induced by exposure to chlorides from deicers and salt water spray. Dissolved salts seep into bridge decks primarily at crack locations and cause steel corrosion which sets up a splitting force because of the volumetric expansion and eventually breaks the concrete. This report briefly presents background information on the mechanism of corrosion of steel reinforcement in concrete, and summarizes the observations and findings from an experimental corrosion study. A simple test specimen was developed to simulate the behavior of a transversely prestressed bridge deck subjected to an aggressive deicing salt exposure. The experimental program investigated the primary variables affecting corrosion of steel in prestressed concrete: concrete cover, crack width, protective coatings for steel reinforcement, type of prestressing protective system, concrete quality, and level of prestressing. Behavioral trends are presented as determined from half cell potential measurement of the nonprestressed reinforcement, chloride analysis of the concrete, and visual observation from a post mortem autopsy of the specimens.
Transverse prestressing is an attractive concept with substantial benefits in both economy and im... more Transverse prestressing is an attractive concept with substantial benefits in both economy and improved durability. This report summarizes a series of interrelated physical tests and computer analyses which were conducted to provide necessary information for development of design criteria for transverse prestressing of bridge decks. It addresses such important design areas as the effective distribution of edge prestressing force across a bridge slab as affected by both diaphragm and girder restraints, realistic friction losses in transverse prestressing systems, and the behavior of transversely prestressed decks under typical wheel loadings. The principal attention is focused on slab and girder bridges, but analytical results are extended to box girder bridges. Experimental verification of the analysis programs allowed substantial parameter studies to be carried out with reasonable confidence. The results of the major experimental and analytical studies are summarized in this report.
The objective of this study is to investigate the use of deck prestressing as a method of improvi... more The objective of this study is to investigate the use of deck prestressing as a method of improving durability of bridge decks with the aim of developing suggested AASHTO Specification design requirements to facilitate its use. The results from an experimental test series of prestressed concrete specimens subjected to an aggressive deicing salt exposure and from an experimental and analytical investigation of the structural behavior of a fully composite slab-girder bridge model indicated that deck prestressing is a viable corrosion-protection design alternative. It has already been used in numerous box girder bridges to improve structural efficiency. Specific recommendations for improving durability of bridge decks by deck prestressing and for proper design of deck prestressing are included in this report. These recommendations are presented in a form suitable for inclusion in the AASHTO Bridge Specifications. Several design examples are included to illustrate the design recommendations and to compare costs to those of current bridge deck designs using conventional reinforced concrete.
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