Showing papers on "Prestressed concrete published in 2005"

Designers Guide to EN 1992-1-1 and EN 1992-1-2 Eurocode 2: Design of Concrete Structures. General rules and rules for buildings and structural fire design

Abstract: Basis of design Analysis Materials and design data Design of sections for bending and axial force Shear, punching shear and torsion Slender columns and beams Serviceability limit states Durability Detailing Prestressed concrete Structural fire design Compliance with the Code will satisfy the requirements of the Construction Products Directive in respect of mechanical resistance.

Damage Identification Using Modal Data: Experiences on a Prestressed Concrete Bridge

Abstract: Large scale tests with progressive damage on a prestressed concrete highway bridge have been performed to investigate the sensitivity of several damage detection, localization, and quantification methods based on modal parameters. To investigate the quality of modal parameters, the data set of one damage step was analyzed by several output-only identification techniques. Although the bridge was severely cracked, natural frequencies as well as mode shapes display only minor changes. However, the relative changes of mode shapes are larger than those observed for natural frequencies. A novel damage indicator, called mode shape area index, based on changes of mode shapes, has been developed and found as the most sensitive damage detection approach. Damage detection or localization via changes of the flexibility matrix performed better than natural frequencies or mode shapes alone. The application of the direct stiffness calculation and a sensitivity-based model update technique showed results having a high level of ambiguity about the location and quantification of damage also at the highest damage level. Evaluating the information collected in this study the test results indicate that an early stage damage identification in prestressed concrete bridges is hardly possible because of the nearly complete recovery of stiffness after closing of cracks in prestressed concrete and the effect of environmental parameters on modal data.

Effects of Temperature Variations on Precast, Prestressed Concrete Bridge Girders

Abstract: The monitoring of a precast, prestressed girder bridge during fabrication and service provided the opportunity to observe temperature variations and to evaluate the accuracy of calculated strains and cambers The use of high curing temperatures during fabrication affects the level of prestress because the strand length is fixed during the heating, the coefficients of thermal expansion of steel and concrete differ, and the concrete temperature distribution may not be uniform For the girders discussed here, these effects combined to reduce the calculated prestressing stress from the original design values at release by 3 to 7%, to reduce the initial camber by 26 to 40%, and to increase the bottom tension stress in service by 12 to 27% The main effect of applying the standard service temperature profiles to the bridge was to increase the bottom stress by 60% of the allowable tension stress These effects can be compensated for by increasing the amount of prestressing steel, but in highly stressed girders, such an increase leads to increased prestress losses ~requiring yet more strands! and higher concrete strength requirements at release

Explaining the Riddle of Tension Stiffening Models for Shear Panel Experiments

Abstract: Analyses of reinforced and prestressed concrete structures based on a smeared crack approach generally include a tension stiffening relationship to estimate the average concrete tensile stress after cracking. Many such equations have been developed over the years and show significant differences between them. In this study, three of these equations are compared and it is shown that the variation between the equations can be explained by the different bond conditions of the specimens tested to calibrate the equations. An expression is proposed to quantify this effect and sample results are shown. Use of this relationship should allow more realistic estimates of crack width and stiffness at service loads to be obtained.

Seismic Performance of Pile-Wharf Connections

Abstract: Imports and exports are essential to our economy, but the wharf structures that accommodate this activity are susceptible to earthquake damage Wharves are pile supported structures, and the pile-wharf connection is an essential element of their seismic performance Either precast prestressed concrete piles with moment-resisting connections or steel batter piles are used to provide lateral resistance, but precast concrete piles are more common Little research has been performed on the seismic performance of these precast concrete pile-wharf connections Eight experiments evaluating the seismic performance of moment-resisting precast concrete pile-wharf connections are described The test specimens simulate the wide range of practice presently noted in wharf design These connections tolerate large cyclic inelastic deformations, but they also show significant deterioration in resistance and stiffness Extended pile connections are used when the pile is driven below deck level Precast concrete pile connections are stronger than extended pile sections, but they degrade more quickly Axial load on the pile also increases connection moment capacity but results in greater deterioration in resistance Analysis shows that this degradation in resistance significantly reduces the inelastic pushover resistance and increases the inelastic dynamic response demands of the system

Prestressing Concrete Structures with FRP Tendons (ACI 440.4R-04)

Abstract: Fiber-reinforced polymers (FRP) have been proposed for use instead of steel prestressing tendons in concrete structures The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties This paper provides an overview of the ACI 4404R-04 document on “Prestressing Concrete with FRP Tendons” reported by ACI Committee 440 on “Fiber-Reinforced Polymer Reinforcements” The document is one of the Emerging Technology Series published by the American Concrete Institute The paper outlines the content of the document and the philosophy of applying FRP technology as opposed to conventional steel for prestressing The document offers general information on the history and use of FRP for prestressing applications, and a description of the unique material properties of FRP It also focuses on the current state of design, development, and research needed to characterize and ensure the performance of FRP as prestressing reinforcement in concrete structures The proposed guidelines are based on knowledge gained from worldwide experimental research, analytical work, and field applications of FRPs used as prestressed reinforcement The current development includes a basic understanding of flexure and axial prestressed members, FRP shear reinforcement, bond of FRP tendons, and unbonded or external FRP tendons for prestressing applications The document concludes with a list of research needs

Cost Optimization of Prestressed Concrete Bridges

Abstract: According to the Federal Highway Administration, almost one-quarter of the more than one-half-million U.S. bridges make use of prestressed concrete beams in their designs. In this paper, a method is presented for the total cost optimization of precast, prestressed concrete I-beam bridge systems, by taking into account the costs of the prestressed concrete, deck concrete, prestressed I-beam steel, deck reinforcing steel, and formwork. The problem is formulated as a mixed integer-discrete nonlinear programming problem and solved using the robust neural dynamics model of Adeli and Park. An example is presented to demonstrate the practical application of the methodology. Typical network convergence curves using three different network starting points demonstrate the excellent convergence and the robustness of the optimization model presented in this paper.

Ultra High Performance Concrete Highway Bridge

Abstract: Wapello County and the Iowa Department of Transportation were granted funding through the TEA-21 Innovative Bridge Construction Program to demonstrate the use of ultra high performance concrete (UHPC) in a bridge replacement project. The UHPC in the prestressed concrete beams is expected to achieve a 28-day compressive strength of up to 30,000 psi. The use of this innovative product in a threebeam cross section is intended to take advantage of the superior strength and to optimize design. The beams will be pretensioned using 0.6-inch diameter strands and without mild reinforcing steel, except to provide composite action with the cast-in-place deck. In Phase I of the multi-phase project, a 71-foot-long test beam will be tested to verify shear and flexural capacities, along with shear testing of smaller beams. If testing efforts are successful, Phase II will include the casting of 111-foot-long beams, followed by the construction of the single span bridge in the spring/summer of 2005. After construction, a monitoring program will be implemented to document the performance of this innovative product. A discussion of the design efforts and the current progress of this research project is the focus of this paper.

Stresses in External Tendons at Ultimate

Abstract: Post-tensioned segmental concrete bridges are often used for long, multispan viaducts or medium-span valley and river crossings. This article presents the research that led to the development of the equation for predicting stresses in unbonded tendons at ultimate; this equation is currently used in the AASHTO LRFD Specifications and AASHTO Guide Specifications for the Design and Construction of Segmental Concrete Bridges. The research, performed by the late Robert J. G. MacGregor, involved the construction and testing of a 1/4 scale model of a three-span, continuous, precast segmental-concrete box girder bridge, erected using span-by-span techniques and post-tensioned with external tendons. The authors discuss the results of the tests to ultimate that were dominated by flexural behavior. Predicted tendon stress increases are then compared to a large data base from other tests of beams and slabs with unbonded tendons. The authors conclude that the equation proposed by MacGregor predicts the tendon stress increases in unbonded tendons conservatively and relatively well, compared to expressions that ignore tendon length.

Strength-Fatigue Behavior of Fiber Reinforced Polymer Strengthened Prestressed Concrete T-Beams

Abstract: Strengthening concrete girders with fiber-reinforced polymers (FRP) is becoming an increasingly common practice as more research investigations are favorably qualifying the technique. However, important behavioral aspects, such as fatigue in prestressed concrete beams, are yet to be adequately evaluated. An experimental program was conducted to test five pretensioned, prestressed concrete T beams designed for specific prestressing strand stress ranges under live-load conditions. The experimental testing consisted of precracking the beams, strengthening them with carbon FRP, and mechanically loading them to study the effect of increasing the live load on strand fatigue. The beams were either loaded monotonically to ultimate capacity or cyclically fatigued and then loaded monotonically to failure. All the beams were monotonically loaded past their cracking moment at midspan prior to strengthening, to simulate girders in the field. Beam 1 was tested as a control specimen under static loading up to failure. Beams 2 and 3 were strengthened with carbon FRP to have a design stress range of 124 MPa (18 ksi) under service load condition. Beams 4 and 5 were strengthened to have a higher stress range of 248 MPa (36 ksi). For all the strengthened beams, the failure mode observed was FRP rupture. The results favorably qualify the application of FRP strengthening to increase the live load of concrete beams prestressed with straight strands.

Factors affecting the external prestressing stress in externally strengthened prestressed concrete beams

Abstract: The wide use of external prestressing system to strengthen reinforced and prestressed concrete members requires the full understanding of the behaviour of the strengthened members. At ultimate the stress in the external prestressing tendons need to be known in order to calculate the ultimate strength of the strengthened member. Several factors that can influence the increase in the ultimate stress in steel external prestressing tendons have been studied and well understood while the effect of these factors on tendons made from fibre reinforced plastics needs more research. This research was carried out to study the effect of several factors on the increase in the ultimate stress in external Parafil ropes as well as external steel tendons. These factors were related to the external prestressing system, internal prestressed and ordinary bonded steel, beam geometry and material properties. Also, the accuracy of equations proposed by the Eurocode (EC2), ACI318 and BS8110 to calculate the ultimate stress in external steel and FRP prestressing tendons was examined. The experimental and the analytical results showed that the studied factors have the same effect on both steel (up to yield) and Parafil ropes though this effect is greater in case of steel tendons. Also, factors such as tendon profile (straight or deviated), high strength of the concrete, effective tendon depth, number of deviators should be taken into consideration when calculating the ultimate stress in the external tendons.

Simplified Shear Design of Structural Concrete Members

Abstract: This report contains the findings of research performed to develop practical equations for design of shear reinforcement in reinforced and prestressed concrete bridge girders Recommended specifications, commentary, and examples illustrating application of the specifications were also developed The material in this report will be of immediate interest to bridge designers The objective of this research was to supplement the Load and Resistance Factor Design (LRFD) methods for shear design with procedures providing a direct solution for transverse and longitudinal reinforcement of concrete structures of common proportions This work focused on development of resistance equations that yield unique solutions with defined limits of applicability The recommended equations are similar in format and application to the resistance equations currently found in the AASHTO Standard Specifications The equations apply to conventional structure types such as reinforced concrete T-beams, prestressed concrete I girders continuous for live load, prestressed concrete box beams, cast-in-place post-tensioned box girders, hammerhead piers and footings, and multi-post reinforced concrete bents and footings The recommendations for additions to the LRFD specifications apply to precast concrete strengths up to 18 ksi and cast-in-place concrete strengths up to 10 ksi

State-of-the-Art Report on Precast Concrete Systems for Rapid Construction of Bridges

Abstract: More extensive use of precast concrete components, which are fabricated off-site and then connected on-site, could allow bridges to be constructed more rapidly The increased use of precast components in bridges also promises to increase work-zone safety and reduce environmental impacts for bridges that span waterways This report discusses precast concrete systems that have been used for rapid bridge construction outside of Washington State and evaluates whether they are suitable for use within Western Washington The report also identifies key features that are important for successful precast concrete system applications Information on previously used systems was gathered through an extensive review of published literature Washington State Department of Transportation design and construction engineers, precast concrete producers, and bridge contractors were also consulted to obtain their input on the positive and negative aspects of applied systems Most applications have been used in areas of low seismic potential By contrast, Western Washington is subject to strong earthquakes Because precast systems contain connections, and connections are typically vulnerable to seismic loading, a qualitative evaluation of the expected seismic performance of each system was deemed necessary The researchers identified four types of precast concrete superstructure systems: full-depth precast concrete panels, partial-depth precast concrete panels, prestressed concrete multibeam superstructures, and preconstructed composite units The four systems appear to have acceptable seismic behavior, but there are concerns associated with constructability and durability Precast concrete substructure systems have received much less attention than have superstructure systems The use of precast substructure components can provide significant time savings by eliminating the time needed to erect formwork, tie steel, and cure concrete in the substructure The success of the system depends strongly on the connections, which must have good seismic resistance, have tolerances that allow easy assembly, and be suitable for rapid construction

Implementation of Self-Consolidating Concrete for Prestressed Concrete Girders

Abstract: This report documents the first experience of using self-consolidating concrete for pretressed concrete bridge girders in North Carolina. Under construction in eastern North Carolina was a multi-span bridge which used one hundred thirty AASHTO Type III girders, each 54.8 ft (16.7 m) long. To demonstrate the full-scale field production of self-consolidating concrete, and for comparative purposes, three girders from one production line of five girders were selected for the experimentation. Two of the girders were cast with self-consolidating concrete and one with normal concrete as control. The plastic and hardened properties of both the self-consolidating concrete and the normal concrete were monitored and measured. The plastic properties of self-consolidating concrete included unit weight, air content, slump flow, visual stability index (VSI), and passing ability measured by J-ring and L-box. Hardened properties of the two concretes included temperature development during curing, compressive strength, elastic modulus, and flexural tensile strength, creep and shrinkage. The prestressing force was monitored by load cells . The transfer lengths of prestressing strands were determined by embedded strain gauges , and from the measured strand end-slips. Finally, the three girders were tested in flexure up to the design service load to determine and compare their load-deformation characteristics. Based on the satisfactory results of this study, the two prestressed SCC girders were installed in the bridge for service as other normal concrete girders.

Demonstration of Use of High-Performance Lightweight Concrete in Bridge Superstructure in Virginia

Abstract: The general objective of this research was the construction and evaluation of a bridge using high-performance lightweight concrete (HPLWC). The resulting bridge over the Chickahominy River near Richmond, Va., consists of 15 prestressed American Association of State Highway and Transportation Officials (AASHTO) Type IV girders made of HPLWC with a density of 1,920 kg∕ m3 and a minimum required 28-day compressive strength of 55 MPa . The bridge also has a lightweight concrete (LWC) deck with a density of 1,850 kg∕ m3 and a minimum required 28-day compressive strength of 30 MPa . This research study is chiefly concerned with investigating the effects of using lightweight concrete in prestressed girders on transfer length, development length, flexural strength, girder live-load distribution factor, and dynamic load allowance. Transfer length was determined to be 432 mm , or 33 db , for several girders at the time of prestress transfer. The development length was determined to be between 1,830 and 2,440 mm , w...

Performance of Double-T Prestressed Concrete Beams Strengthened with Steel Reinforcement Polymer

Abstract: In the fall of 2002, a two-storey parking garage in Bloomington, Indiana, built with precast prestrestressed concrete (PC) double-T beams, was decommissioned due to a need for increased parking-space. This led to the opportunity of investigating the flexural performance of the PC double-T beams, upgraded in the positive moment region with steel reinforced polymer (SRP) composite materials, representing the first case study where this material has been applied in the field. SRP makes use of high-strength steel cords embedded in an epoxy resin. This paper reports on the test results to failure of three beams: a control specimen, a beam strengthened with one ply of SRP and a third beam strengthened with two plies of SRP anchored at both ends with SRP U-wraps. Results showed that SRP can significantly improve both flexural capacity and enhance pseudo-ductility. Preliminary analytical work shows that the same approach used for externally bonded fiber reinforced polymer (FRP) can be satisfactorly used for SRP.

Prestress Losses in High Performance Lightweight Concrete Pretensioned Bridge Girders

Abstract: This research investigated prestress losses, creep and shrinkage of pretensioned girders made with expanded slate high performance lightweight concrete. The purpose of the investigation was to determine how long term behavior affects the prestress losses in high strength precast, prestressed concrete bridge girders. The two high performance lightweight concretes (HPLC) developed for this study had strengths of 8000 and 10,000 psi, and air dry unit weights of 116 and 118 lb/ft. Prestress losses were estimated using the American Association of State Highway and Transportation Officials (AASHTO) refined, AASHTO lump sum, Precast/Prestressed Concrete Institute (PCI), and American Concrete Institute (ACI) 209 methods. All these methods overestimated the time dependent losses. This result means that these methods are conservative for estimating time dependent losses of expanded slate HPLC girders.

Principles of structural design

Abstract: STEEL STRUCTURES Eric M. Lui Materials Design Philosophy and Design Formats Tension Members Compression Members Flexural Members Combined Flexure and Axial Force Biaxial Bending Combined Bending, Torsion, and Axial Force Frames Plate Girders Connections Column Base Plates and Beam Bearing Plates (LRFD Approach) Composite Members (LRFD Approach) Plastic Design Reduced Beam Section Seismic Design Glossary References Further Reading Relevant Websites STEEL FRAME DESIGN USING ADVANCED ANALYSIS S.E. Kim and Wai-Fah Chen Introduction Practical Advanced Analysis Verifications Analysis and Design Principles Computer Program Design Examples Glossary References COLD-FORMED STEEL STRUCTURES Wei-Wen Yu Introduction Design Standards Design Bases Materials and Mechanical Properties Element Strength Member Design Connections and Joints Structural Systems and Assemblies Computer-Aided Design and Direct Strength Method Glossary References Further Reading REINFORCED CONCRETE STRUCTURES Austin Pan Introduction Design Codes Material Properties Design Objectives Design Criteria Design Process Modeling of Reinforced Concrete for Structural Analysis Approximate Analysis of Continuous Beams and One-Way Slabs Moment Redistribution Second-Order Analysis Guidelines Moment-Curvature Relationship of Reinforced Concrete Members Member Design for Strength Two-Way Floor Systems Columns Walls Torsion Design Reinforcement Development Lengths, Hooks, and Splices Deflections Drawings, Specifications, and Construction Notation Useful Web Sites PRESTRESSED CONCRETE Edward G. Nawy Introduction Concrete for Prestressed Elements Steel Reinforcement Properties Maximum Permissible Stresses Partial Loss of Prestress Flexural Design of Prestressed Concrete Elements Shear and Torsional Strength Design Camber, Deflection, and Crack Control Acknowledgments Glossary References MASONRY STRUCTURES Richard E. Klingner Introduction Masonry in the United States Fundamental Basis for Design of Masonry in the United States Masonry Design Codes Used in the United States Seismic Retrofitting of Historical Masonry in the United States Future Challenges References TIMBER STRUCTURES J. Daniel Dolan Introduction Wood as a Material Seismic Performance of Wood Buildings Design Considerations Resistance Determination Diaphragms Shear Walls Connections Glossary References Further Reading ALUMINUM STRUCTURES Maurice L. Sharp Introduction Structural Behavior Design Economics of Design Glossary References Further Reading RELIABILITY-BASED STRUCTURAL DESIGN Achintya Haldar Introduction Available Structural Design Concepts Introduction of the Reliability-Based Structural Design Concept Fundamental Concept of Reliability-Based Structural Design Reliability-Based Structural Design Using FORM Reliability Evaluation with Nonnormal Correlated Random Variables Reliability Evaluation Using Simulation Future Directions in Reliability-Based Structural Design Concluding Remarks References STRUCTURE CONFIGURATION BASED ON WIND ENGINEERING Yoshinobu Kubo Introduction Effects of Wind Load Control of Aeroelastic Responses Wind Design Data Examples of Real Bridges Summary References Further Reading INDEX

Bending Moment–Shear Force Interaction Domains for Prestressed Concrete Beams

Abstract: The performance of a prestressed concrete beam, subjected to bending moment M together with shear force V, has been the object of many studies and is an important aspect to take into account in the design. Some models, proposed by researchers and international codes, evaluate the shear strength of prestressed beams by modifying the truss model by Morsch, so as to account for the different slope of stress fields in the web due to the prestressing action. More recent approaches add a strut-and-tie model to the traditional truss model. This paper generalizes a model that was previously proposed for box and I-shaped reinforced concrete cross sections of structural elements. The model, that now includes the effect of prestressing tendons, considers variable-depth stress fields applied to the cross section, subdivided into layers, and allows evaluation of normalized m-v design domains depending both on the web and flange reinforcement and on the slope of the prestressing steel tendons. The reliability of the method has been validated by comparing its numerical results to the strength provided by tests on reinforced concrete beams and on thin-webbed prestressed concrete beams, referred to in the literature. Finally, it has been used in the design of a pretensioned bridge beam to evaluate the additional reinforcement necessary in the flanges, as a function of the reinforcement provided to the web.

Seismic Design Methodology for Precast Concrete Diaphragms. Part 1: Design Framework

Abstract: The Precast/Prestressed Concrete Institute is conducting an "area of emphasis: research project on precast concrete diaphragms. The project has been called Diaphragm Seismic Design Methodology (DSDM). The purpose of this paper is to outline the foundation for the research by presenting the underlying design philosophy and resulting design framework that will serve as the basis for the technical papers to follow and the eventual design methodology at the projected conclusion. The objective of the DSDM project is to develop an industry endorsed design methodology for precast/prestressed concrete diaphragms including: the forces, displacements, and deformations for which the diaphragm should be designed; the diaphragm reinforcing details that can provide this performance; and the required stiffness of the diaphragm relative to the primary lateral force resisting system elements.

Characterization of the Punching Shear Capacity of Thin Ultra-High Performance Concrete Slabs

Abstract: Ultra-high performance concrete (UHPC) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel The main characteristics that distinguish UHPC from conventional reinforced concrete are its very high compressive strength (20 to 33 ksi), and the addition of steel fibers which enables tension to be carried across open cracks without conventional reinforcing steel, and a very high resistance to corrosion and degradation The mechanical properties of UHPC allow for smaller, thinner sections as compared to conventional reinforced concrete sections However, as it is a new material, the use of UHPC has been limited to a few structural applications due primarily to the high cost of the material and the lack of established design guidelines In previous research, a material model based on physical tests was used in conjunction with finite element models to develop an optimized cross-section for a prestressed UHPC girder for bridge applications The cross-section is a double-tee with bulbs at the bottoms of the webs to accommodate the prestressing strands As it is envisioned in bridge applications, the double-tees will be placed directly adjacent to one another, and the top flange will act as the riding surface after a thin asphalt overlay is placed Based on the longitudinal compressive stresses, the top flange of the girder can be quite thin However, there exists the possibility that a punching shear failure could occur from the application of a point load such as a wheel patch load if the flange is made too thin The research reported herein was initiated to characterize the punching shear capacity of thin UHPC plates and to develop recommendations on the minimum top flange thickness for the optimized double-tee Twelve small slabs (45 in x 45 in) were tested to failure to characterize the punching shear strength of UHPC The variables considered were the slab thickness (2, 25, and 3 in) and loading plate dimensions (from 1 in x 1 in to 3 in x 3 in) The results of the testing were compared to several existing models for punching shear The two equations that predicted strengths most reliably were the current ACI punching shear equation and a modified bolt pull-out equation After evaluation of the test results, the minimum slab thickness required to prevent a punching shear failure in the top flange due to an 8 in x 20 in wheel patch was determined to be 1 in Three larger slabs were also tested These slabs had the same clear span length as the top flange of the optimized double-tee and were loaded with a wheel patch load The slabs were all approximately 3 in thick and all failed in flexure rather than punching shear It was concluded that the casting method has a strong influence on the orientation of the steel fibers, which in turn influences the flexural strength in orthogonal directions in the slab The top flange thickness will be governed by transverse bending rather than punching shear, and the 3 in slabs were not able to support the full wheel load plus impact and load factor The results of this research help in the continued optimization of a UHPC shape for use in highway bridges If material use in the girder is minimized, UHPC bridges can become economically competitive with HPC bridges, but offer the benefits of more rapid construction and better durability

Repair of bridge girders with composites: Experimental and analytical validation

Abstract: This article reports on a laboratory study undertaken to investigate the flexural behavior of full-scale, damaged prestressed concrete (PC) bridge girders upgraded with externally bonded carbon fiber-reinforced polymer (CFRP) laminates. The study include test on three beams: one was used as the control beam and the other two, damaged by removing the concrete cover and by cutting two and four strands, respectively, were repaired with CFRP laminates. The authors conclude that the upgrade technique used is structurally efficient in providing the damaged beams with stiffness and strength very close to that of the original undamaged beam. They discuss analytical predictions compared to the test results in terms of flexural capacity, deflections, strains, and failure modes. The authors reiterate that the use of CFRP laminates can allow damaged PC girders to recover their original flexural capacity and stiffness.

Investigation of vibration characteristics of prestressed concrete sleepers in free-free and in-situ conditions

Abstract: The results of an experimental modal analysis of prestressed concrete sleepers in free-free and In-situ conditions are discussed. The in-situ boundary condition had a remarkable influence on the natural frequency, modal damping, and vibration mode shape of prestressed concrete sleepers, especially in the low frequency range.

Behavior of horizontal shear connections for full-depth precast concrete Bridge decks on prestressed I-girders

Abstract: This article reports on a study of the horizontal shear resistance of the connection between full-depth precast concrete bridge deck panels and prestressed concrete girders. This connection consists of isolated shear connectors extending from the precast I-girder into a block-out pocket in the precast deck panel. The blockouts and the haunch between the panel and the beam are grouted. In the study, 36 push-off tests were performed to investigate the strength and behavior of the connections. The factors investigated included type of grout, haunch height, and area of reinforcing steel crossing the interface. In addition, several alternate shear connector details were tested. Results showed that there was no significant difference in peak shear stress between specimens with 1, 2, and 3 in. haunch heights. The extended stirrups must be detailed to have a minimum of 5 in. embedment into the deck panel. The alternate shear connectors in this study are viable for use with the precast panel system. Proper embedment and spacing of connectors will ensure yielding of the steel and ductile behavior of the interface. The authors conclude that, of currently known horizontal shear resistance equations, the one presented in the AASHTO LRFD Bridge Design Specifications is the best predictor of the strength of the specimens.