Low Permeability of Concrete for Bridge Deck Overlay, MLR-89-1, 1993

The penetration of chloride ions from deicing salts into the portland cement concrete of bridge decks can cause corrosion and serious damage to the reinforcing steel. Concrete properties which prevent chloride penetration into the bridge deck and provide a good structural and economic wearing surface are desirable. A variety of mix designs have been tried in the past in search of improved performance and lower costs for bridge deck overlay concrete. A group of mixes with various designs have been tested in this project and results are being compared to determine which concrete mix appears to be the most cost effective and resistant to chloride penetration for bridge deck overlay use.

Design of Piles for Integral Abutment Bridges, HR-252, 1984

More and more, integral abutment bridges are being used in place of the more traditional bridge designs with expansion releases. In this study, states which use integral abutment bridges were surveyed to determine their current practice in the design of these structures. To study piles in integral abutment bridges, a finite element program for the soil-pile system was developed (1) with materially and geometrically nonlinear, two and three dimensional beam elements and (2) with a nonlinear, Winkler soil model with vertical, horizontal, and pile tip springs. The model was verified by comparison to several analytical and experimental examples. A simplified design model for analyzing piles in integral abutment bridges is also presented. This model grew from previous analytical models and observations of pile behavior. The design model correctly describes the essential behavioral characteristics of the pile and conservatively predicts the vertical load-carrying capacity. Analytical examples are presented to illustrate the effects of lateral displacements on the ultimate load capacity of a pile. These examples include friction and end-bearing piles; steel, concrete, and timber piles; and bending about the weak, strong, and 45° axes for H piles. The effects of cyclic loading are shown for skewed and nonskewed bridges. The results show that the capacity of friction piles is not significantly affected by lateral displacements, but the capacity of end-bearing piles is reduced. Further results show that the longitudinal expansion of the bridge can introduce a vertical preload on the pile.

Steel Diaphragms in Prestressed Concrete Girder Bridges, September 2004

Over the years, bridge engineers have been concerned about the response of prestressed concrete (PC) girder bridges that had been hit by over-height vehicles or vehicle loads. When a bridge is struck by an over-height vehicle or vehicle load, usually the outside and in some instances one of the interior girders are damaged in a bridge. The effect of intermediate diaphragms in providing damage protection to the PC girders of a bridge is not clearly defined. This analytical study focused on the role of intermediate diaphragms in reducing the occurrence of damage in the girders of a PC-girder bridge that has been struck by an over-height vehicle or vehicle load. The study also investigated whether a steel, intermediate diaphragm would essentially provide the same degree of impact protection for PC girders as that provided by a reinforced-concrete diaphragm. This investigation includes the following: a literature search and a survey questionnaire to determine the state-of-the-art in the use and design of intermediate diaphragms in PC-girder bridges. Comparisons were made between the strain and displacement results that were experimentally measured for a large-scale, laboratory, model bridge during previously documented work and those results that were obtained from analyses of the finite-element models that were developed during this research for that bridge. These comparisons were conducted to calibrate the finite element models used in the analyses for this research on intermediate diaphragms. Finite-element models were developed for non-skewed and skewed PC-girder bridges. Each model was analyzed with either a reinforced concrete or two types of steel, intermediate diaphragms that were located at mid-span of an interior span for a PC-girder bridge. The bridge models were analyzed for lateral-impact loads that were applied to the bottom flange of the exterior girders at the diaphragms location and away from the diaphragms location. A comparison was conducted between the strains and displacements induced in the girders for each intermediate-diaphragm type. These results showed that intermediate diaphragms have an effect in reducing impact damage to the PC girders. When the lateral impact-load was applied at the diaphragm location, the reinforced-concrete diaphragms provided more protection for the girders than that provided by the two types of steel diaphragms. The three types of diaphragms provided essentially the same degree of protection to the impacted, PC girder when the lateral-impact load was applied away from the diaphragm location.

Feasibility Study of Strengthening Existing Single Span Steel Beam Concrete Deck Bridges, June 1961

Iowa has the same problem that confronts most states in the United States: many bridges constructed more than 20 years ago either have deteriorated to the point that they are inadequate for original design loads or have been rendered inadequate by changes in design/maintenance standards or design loads. Inadequate bridges require either strengthening or posting for reduced loads. A sizeable number of single span, composite concrete deck - steel I beam bridges in Iowa currently cannot be rated to carry today's design loads. Various methods for strengthening the unsafe bridges have been proposed and some methods have been tried. No method appears to be as economical and promising as strengthening by post-tensioning of the steel beams. At the time this research study was begun, the feasibility of posttensioning existing composite bridges was unknown. As one would expect, the design of a bridge-strengthening scheme utilizing post-tensioning is quite complex. The design involves composite construction stressed in an abnormal manner (possible tension in the deck slab), consideration of different sizes of exterior and interior beams, cover-plated beams already designed for maximum moment at midspan and at plate cut-off points, complex live load distribution, and distribution of post-tensioningforces and moments among the bridge beams. Although information is available on many of these topics, there is miminal information on several of them and no information available on the total design problem. This study, therefore, is an effort to gather some of the missing information, primarily through testing a half-size bridge model and thus determining the feasibility of strengthening composite bridges by post-tensioning. Based on the results of this study, the authors anticipate that a second phase of the study will be undertaken and directed toward strengthening of one or more prototype bridges in Iowa.

Bonding Agents for Portland Cement Concrete and Mortar, August 1983

Structural repairs of bridges piers and abutments require patching concrete or mortar be placed at various thickness. Whether concrete or mortar is use depends upon the depth of the patch to be made. In some instances, the use of a liquid bonding agent has been specified in the mixes as well as in a grout scrubbed onto the surface to be patched prior to the mix placement. Most of the bonding agents presently approved by the Iowa D.O.T. are polyvinyl acetate (PVA) or some type of latex. In a general discussion with a consultant about various types of bridge repair materials and processes, the subject of bonding agents was discussed at some length. It was the opinion of the consultant that the usage of polyvinyl acetates should be discontinued because of possible deterioration of this material with time. Some of these materials apparently re-emulsify in a high - moisture environment causing serious patch deterioration. As a result of this information, a study was initiated to determine the durability of these materials.

Strengthening of an Existing Continuous-Span, Steel-Beam, Concrete-Deck Bridge by Post-Tensioning, HR-308, 1990

The need to upgrade a large number of understrength and obsolete bridges in the U.S. has been well documented in the literature. Through several Iowa DOT projects, the concept of strengthening simple-span bridges by post-tensioning has been developed. The purpose of the project described in this report was to investigate the use of post-tensioning for strengthening continuous composite bridges. In a previous, successfully completed investigation, the feasibility of strengthening continuous, composite bridges by post-tensioning was demonstrated on a laboratory 1/3-scale-model bridge (3 spans: 41 ft 11 in. x 8 ft 8 in.). This project can thus be considered the implementation phase. The bridge selected for strengthening was in Pocahontas County near Fonda, Iowa, on County Road N28. With finite element analysis, a post-tensioning system was developed that required post-tensioning of the positive moment regions of both the interior and exterior beams. During the summer of 1988, the strengthening system was installed along with instrumentation to determine the bridge's response and behavior. Before and after post-tensioning, the bridge was subjected to truck loading (1 or 2 trucks at various predetermined critical locations) to determine the effectiveness of the strengthening system. The bridge, with the strengthening system in place, was inspected approximately every three months to determine any changes in its appearance or behavior. In 1989, approximately one year after the initial strengthening, the bridge was retested to identify any changes in its behavior. Post-tensioning forces were removed to reveal any losses over the one-year period. Post-tensioning was reapplied to the bridge, and the bridge was tested using the same loading program used in 1988. Except for at a few locations, stresses were reduced in the bridge the desired amount. At a few locations flexural stresses in the steel beams are still above 18 ksi, the allowable inventory stress for A7 steel. Although maximum stresses are above the inventory stress by about 2 ksi, they are about 5 ksi below the allowable operating stress; therefore, the bridge no longer needs to be load-posted.

Strengthening of Existing Single Span Steel Beam and Concrete Deck Bridges, HR-238, Part 1, 1983

The Phase I research, Iowa Department of Transportation (IDOT) Project HR-214, "Feasibility Study of Strengthening Existing Single Span Steel Beam Concrete Deck Bridges," verified that post-tensioning can be used to provide strengthening of the composite bridges under investigation. Phase II research, reported here, involved the strengthening of two full-scale prototype bridges - one a prototype of the model bridge tested during Phase I and the other larger and skewed. In addition to the field work, Phase II also involved a considerable amount of laboratory work. A literature search revealed that only minimal data existed on the angle-plus-bar shear connectors. Thus, several specimens utilizing angle-plus-bar, as well as channels, studs and high strength bolts as shear connectors were fabricated and tested. To obtain additional shear connector information, the bridge model of Phase I was sawed into four composite concrete slab and steel beam specimens. Two of the resulting specimens were tested with the original shear connection, while the other two specimens had additional shear connectors added before testing. Although orthotropic plate theory was shown in Phase I to predict vertical load distribution in bridge decks and to predict approximate distribution of post-tensioning for right-angle bridges, it was questioned whether the theory could also be used on skewed bridges. Thus, a small plexiglas model was constructed and used in vertical load distribution tests and post-tensioning force distribution tests for verification of the theory. Conclusions of this research are as follows: (1) The capacity of existing shear connectors must be checked as part of a bridge strengthening program. Determination of the concrete deck strength in advance of bridge strengthening is also recommended. (2) The ultimate capacity of angle-plus-bar shear connectors can be computed on the basis of a modified AASHTO channel connector formula and an angle-to-beam weld capacity check. (3) Existing shear connector capacity can be augmented by means of double-nut high strength bolt connectors. (4) Post-tensioning did not significantly affect truck load distribution for right angle or skewed bridges. (5) Approximate post-tensioning and truck load distribution for actual bridges can be predicted by orthotropic plate theory for vertical load; however, the agreement between actual distribution and theoretical distribution is not as close as that measured for the laboratory model in Phase I. (6) The right angle bridge exhibited considerable end restraint at what would be assumed to be simple support. The construction details at bridge abutments seem to be the reason for the restraint. (7) The skewed bridge exhibited more end restraint than the right angle bridge. Both skew effects and construction details at the abutments accounted for the restraint. (8) End restraint in the right angle and skewed bridges reduced tension strains in the steel bridge beams due to truck loading, but also reduced the compression strains caused by post-tensioning.

Strengthening of Existing Single Span Steel Beam and Concrete Deck Bridges, HR-238, Part II, 1985

The unifying objective of Phases I and II of this study was to determine the feasibility of the post-tensioning strengthening method and to implement the technique on two composite bridges in Iowa. Following completion of these two phases, Phase III was undertaken and is documented in this report. The basic objectives of Phase III were further monitoring bridge behavior (both during and after post-tensioning) and developing a practical design methodology for designing the strengthening system under investigation. Specific objectives were: to develop strain and force transducers to facilitate the collection of field data; to investigate further the existence and effects of the end restraint on the post-tensioning process; to determine the amount of post-tensioning force loss that occurred during the time between the initial testing and the retesting of the existing bridges; to determine the significance of any temporary temperature-induced post-tensioning force change; and to develop a simplified design methodology that would incorporate various variables such as span length, angle-of-skew, beam spacing, and concrete strength. Experimental field results obtained during Phases II and III were compared to the theoretical results and to each other. Conclusions from this research are as follows: (1) Strengthening single-span composite bridges by post-tensioning is a viable, economical strengthening technique. (2) Behavior of both bridges was similar to the behavior observed from the bridges during field tests conducted under Phase II. (3) The strain transducers were very accurate at measuring mid-span strain. (4) The force transducers gave excellent results under laboratory conditions, but were found to be less effective when used in actual bridge tests. (5) Loss of post-tensioning force due to temperature effects in any particular steel beam post-tensioning tendon system were found to be small. (6) Loss of post-tensioning force over a two-year period was minimal. (7) Significant end restraint was measured in both bridges, caused primarily by reinforcing steel being continuous from the deck into the abutments. This end restraint reduced the effectiveness of the post-tensioning but also reduced midspan strains due to truck loadings. (8) The SAP IV finite element model is capable of accurately modeling the behavior of a post-tensioned bridge, if guardrails and end restraints are included in the model. (9) Post-tensioning distribution should be separated into distributions for the axial force and moment components of an eccentric post-tensioning force. (10) Skews of 45 deg or less have a minor influence on post-tensioning distribution. (11) For typical Iowa three-beam and four-beam composite bridges, simple regression-derived formulas for force and moment fractions can be used to estimate post-tensioning distribution at midspan. At other locations, a simple linear interpolation gives approximately correct results. (12) A simple analytical model can accurately estimate the flexural strength of an isolated post-tensioned composite beam.

Strengthening of an Existing Continuous-Span, Steel-Stringer, Concrete-Deck Bridge, HR-333, 1993

The need to upgrade understrength bridges in the United States has been well documented in the literature. The concept of strengthening steel stringer bridges in Iowa has been developed through several Iowa DOT projects. The objective of the project described in this report was to investigate the use of one such strengthening system on a three-span continuous steel stringer bridge in the field. In addition, a design methodology was developed to assist bridge engineers with designing a strengthening system to obtain the desired stress reductions. The bridge selected for strengthening was in Cerro Gordo County near Mason City, Iowa on County Road B65. The strengthening system was designed to remove overstresses that occurred when the bridge was subjected to Iowa legal loads. A two part strengthening system was used: post-tensioning the positive moment regions of all the stringers and superimposed trusses in the negative moment regions of the two exterior stringers at the two piers. The strengthening system was installed in the summers of 1992 and 1993. In the summer of 1993, the bridge was load tested before and after the strengthening system was activated. The load test results indicate that the strengthening system was effective in reducing the overstress in both the negative and positive regions of the stringers. The design methodology that was developed includes a procedure for determining the magnitude of post-tensioning and truss forces required to strengthen a given bridge. This method utilizes moment and force fractions to determine the distribution of strengthening axial forces and moments throughout the bridge. Finite element analysis and experimental results were used in the formulation and calibration of the methodology. A spreadsheet was developed to facilitate the calculation of these required strengthening forces.

Detection of Steel Corrosion in Bridge Decks and Reinforced Concrete Pavement, HR-156, 1977

The Iowa Department of Transportation initiated this research to evaluate the reliability, benefit and application of the corrosion detection device. Through field testing prior to repair projects and inspection at the time of repair, the device was shown to be reliable. With the reliability established, twelve additional devices were purchased so that this evaluation procedure could be used routinely on all repair projects. The corrosion detection device was established as a means for determining concrete removal for repair. Removal of the concrete down to the top reinforcing steel is required for all areas exhibiting electrical potentials greater than 0.45 Volt. It was determined that the corrosion detection device was not applicable to membrane testing. The corrosion detection device has been used to evaluate corrosion of reinforcing steel in continuously reinforced concrete pavement.

Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials, Construction Report, HR-1069, 1998

The function of dowel bars is the transfer of a load across the transverse joint from one pavement slab to the adjoining slab. In the past, these transfer mechanisms have been made of steel. However, pavement damage such as loss of bonding, deterioration, hollowing, cracking and spalling start to occur when the dowels begin to corrode. A significant amount of research has been done to evaluate alternative types of materials for use in the reinforcement of concrete pavements. Initial findings have indicated that stainless steel and fiber composite materials possess properties, such as flexural strength and corrosion resistance, that are equivalent to the Department of Transportation specifications for standard steel, 1 1/2 inch diameter dowel bars. Several factors affect the load transfer of dowels; these include diameter, alignment, grouting, bonding, spacing, corrosion resistance, joint spacing, slab thickness and dowel embedment length. This research is directed at the analysis of load transfer based on material type and dowel spacing. Specifically, this research is directed at analyzing the load transfer characteristics of: (a) 8-inch verses 12-inch spacing, and (b) alternative dowel material compared to epoxy coated steel dowels, will also be analyzed. This report documents the installation of the test sections, placed in 1997. Dowel material type and location are identified. Construction observations and limitations with each dowel material are shown.

Ultra-Thin Portland Cement Concrete Overlay Extended Evaluation, January 2005

In this day of the mature highway systems, a new set of problems is facing the highway engineer. The existing infrastructure has aged to or past the design life of the original pavement design. In many cases, increased commercial traffic is creating the need for additional load carrying capacity, causing state highway engineers to consider new alternatives for rehabilitation of existing surfaces. Alternative surface materials, thicknesses, and methods of installation must be identified to meet the needs of individual pavements and budgets. With overlays being one of the most frequently used rehabilitation alternatives, it is important to learn more about the limitations and potential performance of thin bonded portland cement overlays and subsequent rehabilitation. The Iowa ultra-thin project demonstrated the application of thin portland cement concrete overlays as a rehabilitation technique. It combined the variables of base preparation, overlay thickness, slab size, and fiber enhancement into a series of test sections over a 7.2-mile length. This report identifies the performance of the overlays in terms of deflection reduction, reduced cracking, and improved bonding between the portland cement concrete (PCC) and asphalt cement concrete (ACC) base layers. The original research project was designed to evaluate the variables over a 5-year period of time. A second project provided the opportunity to test overlay rehabilitation techniques and continue measurement of the original overlay performance for 5 additional years. All performance indicators identified exceptional performance over the 10-year evaluation period for each of the variable combinations considered. The report summarizes the research methods, results, and identifies future research ideas to aid the pavement overlay designer in the successful implementation of ultra-thin portland cement concrete overlays as an lternative pavement rehabilitation technique.

Evaluation of Dense Bridge Floor Concrete Using High Range Water Reducer, May 1983

The objectives of this research project are: (1) To determine the feasibility of proportioning, mixing, placing and finishing a dense portland cement concrete in a bridge floor using conventional mixing, placing and finishing equipment. (2) To determine the economics, longevity, maintenance performance and protective qualities of a dense portland cement concrete bridge floor when using a high rangewater reducing admixture. The purpose of a high range water reducing admixture is to produce a dense, high quality concrete at a low water-cement ratio witj adequate workability. A low water-cement ratio contributes greatly to increased strength. The normal 7 day strength of untreated concrete would be expected i n 3 days using a superplasticizer. A dense concrete also has the desirable properties of excellent durability and reduced permeability. It is felt that a higher quality, denser, higher strength portland cement concrete can be produced and placed, using conventional equipment, by the addition of a high range water reducing admixture. Such a dense concrete, w i t h a water/cement ratio of approximately 0.30 to 0.35, would be expected to be much less permeable and thus retard the intrusion of chloride. With care and attention given to obtaining the design cover over steel (2% inches clear), it i s hoped that protection for the design life of the structure will be obtained. Evaluation of this experimental concrete bridge floor included chloride content and delamination testing of the concrete floor five years after construction. A comparitive evaluation o f a control section o f concrete without the water reducing admixture was conducted. Other items o f comparison include workability during construction, strength, density, water-cement ratio and chloride penetration.

Design and Performance Verifcation of Ultra-High Performance Concrete Piles for Deep Foundations Final Report, November 2008

The strategic plan for bridge engineering issued by AASHTO in 2005 identified extending the service life and optimizing structural systems of bridges in the United States as two grand challenges in bridge engineering, with the objective of producing safer bridges that have a minimum service life of 75 years and reduced maintenance cost. Material deterioration was identified as one of the primary challenges to achieving the objective of extended life. In substructural applications (e.g., deep foundations), construction materials such as timber, steel, and concrete are subjected to deterioration due to environmental impacts. Using innovative and new materials for foundation applications makes the AASHTO objective of 75 years service life achievable. Ultra High Performance Concrete (UHPC) with compressive strength of 180 MPa (26,000 psi) and excellent durability has been used in superstructure applications but not in geotechnical and foundation applications. This study explores the use of precast, prestressed UHPC piles in future foundations of bridges and other structures. An H-shaped UHPC section, which is 10-in. (250-mm) deep with weight similar to that of an HP10×57 steel pile, was designed to improve constructability and reduce cost. In this project, instrumented UHPC piles were cast and laboratory and field tests were conducted. Laboratory tests were used to verify the moment-curvature response of UHPC pile section. In the field, two UHPC piles have been successfully driven in glacial till clay soil and load tested under vertical and lateral loads. This report provides a complete set of results for the field investigation conducted on UHPC H-shaped piles. Test results, durability, drivability, and other material advantages over normal concrete and steel indicate that UHPC piles are a viable alternative to achieve the goals of AASHTO strategic plan.

Investigation of Two Bridge Alternatives for Low Volume Roads, Volume 1 of 2 Concept 1: Precast Steel Beam Units, HR-382, 1997

Recent reports have indicated that 23.5% of the nation's highway bridges are structurally deficient and 17.7% are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86% of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement. In a recent investigation (HR-365 "Evaluation of Bridge Replacement Alternatives for the County Bridge System") several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69%) have the ability and are interested in utilizing their own forces to design and construct short span bridges. In reviewing the results from HR-365, the research team developed one "new" bridge replacement concept and a modification of a replacement system currently being used. Both of these bridge replacement alternatives were investigated in this study, the results of which are presented in two volumes. This volume (Volume 1) presents the results of Concept 1 - Steel Beam Precast Units. Concept 2 - Modification of the Beam-in-Slab Bridge is presented in Volume 2. Concept 1, involves the fabrication of precast units (two steel beams connected by a concrete slab) by county work forces. Deck thickness is limited so that the units can be fabricated at one site and then transported to the bridge site where they are connected and the remaining portion of the deck placed. Since Concept 1 bridge is primarily intended for use on low-volume roads, the precast units can be constructed with new or used beams. In the experimental part of the investigation, there were three types of static load tests: small scale connector tests, "handling strength" tests, and service and overload tests of a model bridge. Three finite element models for analyzing the bridge in various states of construction were also developed. Small scale connector tests were completed to determine the best method of connecting the precast double-T (PCDT) units. "Handling strength" tests on an individual PCDT unit were performed to determine the strength and behavior of the precast unit in this configuration. The majority of the testing was completed on the model bridge [L=9,750 mm (32 ft), W=6,400 mm (21 ft)] which was fabricated using the precast units developed. Some of the variables investigated in the model bridge tests were number of connectors required to connect adjacent precast units, contribution of diaphragms to load distribution, influence of position of diaphragms on bridge strength and load distribution, and effect of cast-in-place portion of deck on load distribution. In addition to the service load tests, the bridge was also subjected to overload conditions. Using the finite element models developed, one can predict the behavior and strength of bridges similar to the laboratory model as well as design them. Concept 1 has successfully passed all laboratory testing; the next step is to field test it.