50-Year-Old Prestressed Segmental Concrete Bridges

The first prestressed segmental concrete bridge in the United States opened to traffic was a small bridge in Madison County, Tennessee. The bridge was constructed using prestressed concrete segments and was opened to traffic in October 1950. Prestressed concrete beams were placed side by side to form the superstructure of the bridge. The construction of this bridge and several other similar prestressed concrete bridges are described herein. The existing condition of eleven prestressed concrete bridges remaining in Tennessee is given. Only minor spalling, leaching, and horizontal cracking are present in the superstructure after fifty years of service. Many of the design features introduced in this design can be found in today’s modern precast segmental concrete bridges.     

Compound Shear-Flexural Capacity of Reinforced Concrete–Topped Precast Prestressed Bridge Decks

Modern concrete bridge decks commonly consist of stay-in-place (SIP) precast panels seated on precast concrete beams and topped with cast-in-place (CIP) reinforced concrete. Such composite bridge decks have been experimentally tested by various researchers to assess structural performance. However, a failure theory that describes the failure mechanism and accurately predicts the corresponding load has not been previously derived. When monotonically increasing patch loads are applied, delamination occurs between the CIP concrete and SIP panels, with a compound shear-flexure mechanism resulting. An additive model of flexural yield line failure in the lower SIP precast prestressed panels and punching shear in the upper CIP-reinforced concrete portion of the deck system is derived. Analyses are compared to full-scale experimental results of a tandem wheel load straddling adjacent SIP panels and a trailing wheel load on a single panel. Alone, both yield line and punching-shear theories gave poor predictions of the observed failure load; however, the proposed compound shear-flexure failure mechanism load capacities are within 2% accuracy of the experimentally observed loads. Better estimation using the proposed theory of composite SIP-CIP deck system capacities will aid in improving the design efficiency of these systems.     

Design and Construction of a Bridge in Very High Performance Fiber-Reinforced Concrete

The design, technology, and construction of a small road bridge made of very high performance fiber-reinforced concrete is described in this paper. The bridge consists of precast prestressed concrete beams with a cast-in-place ordinary concrete deck. A preliminary experimental investigation was conducted to define the mix design, to establish the properties of the material and its durability, and to study the flexural behavior of the prestressed concrete beams with and without the concrete deck. The effect of steel fibers at the structural level, where there is an influence of constitutive behavior and size effects, was analyzed by testing a prestressed beam using very high performance fiber-reinforced concrete without fibers. The establishment of the structural properties of the material then allowed the design of the final section of the bridge beams and the definition of a model to justify the design rules adopted. This project represents an attempt to demonstrate the industrial feasibility of very high performance concrete structural elements manufactured with conventional raw materials and usual production techniques and to evaluate the production technology when utilizing steel fibers.     

Evaluation of Economic Impact of Three-Dimensional Modeling in Precast Concrete Engineering

Sophisticated three-dimensional parametric modeling software for design and detailing of precast/prestressed concrete construction is currently under development. The technology holds the potential to reduce costs, shorten lead times, and avoid errors in production and erection. To date, however, no rational assessment has been made of the costs and benefits of adoption. No standard methodology exists for the assessment of the benefits of information technology in the construction industry. This paper establishes a qualitative checklist of the expected costs and benefits for precast construction, proposes hypotheses for estimating them, and presents data to support initial assessment of the magnitude of the short-term factors. It also establishes a bench mark of engineering costs for North American precast companies. The bench mark is intended for ongoing assessment of the planned integration of the technology in the member companies of the North American Precast Concrete Software Consortium.     

Structural Behavior of Short Span Precast Channel Beam Bridges without Shear Reinforcement

This paper presents findings of a research study conducted by the writers for the Arkansas State Highway and Transportation Department. The study investigated precast nonprestressed concrete channel beam sections cast without shear reinforcement used in short, multispan bridges. The original objective of the study was to establish a correlation for inspection purposes between the beam’s visual deteriorated state and its corresponding approximate structural capacity. However, during four-point load testing of 33 beams, it was found that beam strength was more a function of a beam’s concrete compression strength rather than deterioration state. A national survey of state transportation departments within the contiguous states was conducted by the authors and found that 13 states currently use precast channel beam bridges. The particular section considered in this paper is a 5.79?m (19?ft) precast channel beam section used to cross small streams and depressions; however constructed without shear reinforcing steel. Bridges using these sections were constructed in the 1950s through to the early 1970s and were designed for H15 loading. Thirty-three formally in-service beams, in various states of deterioration, were load tested. The writers found that the majority of the beams exhibited load capacity greater than the initially required H15 design strength. Second, member strength was a function of concrete compressive strength. Of the 33 beams load tested, 28 beams showed ductile behavior; conversely, the other five beams failed without exhibiting a yield plateau.     

Unique Requirements of Building Information Modeling for Cast-in-Place Reinforced Concrete

The building information modeling (BIM) tools that have matured for structural steel and precast concrete construction are not suitable for production modeling of cast-in-place (CIP) reinforced concrete structures. The main reason is that CIP structures are monolithic in nature, as opposed to the discrete objects that are typical of steel and precast. A consortium of 12 major contractors and design firms collaborated over a one-year period to formulate the functional requirements for development of a BIM tool for cast-in-place reinforced concrete. The functional requirements were derived from a process model used to scope and understand the processes surrounding reinforced concrete design and production. The functional requirements were finally expressed as a set of object schemas, defining relations, methods, and attributes needed. These are essential for software companies to incorporate in their BIM tools to provide for the unique needs of modeling CIP structures.     

超大跨度预应力混凝土梁施工技术

文章以赤峰国际会展中心工程为背景,深入探讨本工程超大跨度预应力混凝土梁施工的关键技术,详细介绍了施工过程中的材料准备、混凝土梁模板及支撑体系的设计、预应力钢筋安装、混凝土浇筑及养护、孔道灌浆等主要环节,对大跨预应力混凝土梁的施工具有较高的参考价值。     

Flexural Behavior of an Ultrahigh-Performance Concrete I-Girder

The flexural behavior of an ultrahigh-performance concrete (UHPC) was investigated through the testing and related analysis of a full-scale prestressed I-girder. A 28?ksi (193?MPa) compressive strength steel fiber reinforced concrete was used to fabricate an 80?ft (24.4?m) long AASHTO Type II girder containing 26 prestressing strands and no mild steel reinforcement. Intermediate and final behaviors, including cracking, flexural stiffness, and moment capacity, were investigated. Test results are compared to predictions based on standard analytical procedures. A relationship between tensile strain and crack spacing is developed. The uniaxial stress-strain response of UHPC when subjected to flexural stresses in an I-girder is determined and is verified to be representative of both the stress and flexural stiffness behaviors of the girder. A flexural design philosophy for this type of girder is proposed.     

Utilization of Precast Concrete Elements in Building

Precast concrete components can be used in building construction within a comprehensive “closed” system, or as separate elements in conjunction with any building method. The feasibility of this second possibility was examined within the framework of a conventional building system and the following alternatives of elements utilization: prestressed modular floor slabs, exterior walls, and a combination of slabs and exterior walls. Each of these alternatives was compared to the conventional system without precast elements. The following criteria were used as a basis for the comparison: the labor requirement, the direct building cost (labor and materials), the construction time, and other considerations of more subjective nature. The findings of the study indicated that the utilization of precast elements might considerably reduce the labor requirement on site, and the project construction time. The direct building costs were almost unaffected by the alternative solutions.     

Long-Term Behavior of Continuous Precast Concrete Girder Bridge Model

Continuous concrete box girder bridges composed of precast reinforced and prestressed concrete beams with a U cross section and a cast-in-place top slab are frequently used for medium spans due to their competitiveness. The service behavior of such bridges is very much influenced by their segmental construction, due to time-dependent materials behavior that makes it difficult to accurately predict the stresses, strains, and deflections at long term. A 1:2 scale model of a two-span continuous bridge was tested in order to study its behavior during the construction process and under permanent loads. Time-dependent concrete properties, as well as support reactions, deflections, and strains in concrete and steel, were measured for 500 days. Important time-dependent redistributions of stresses and internal forces throughout the bridge were also measured. The test results were compared with analytical predictions obtained by means of a numerical model developed for the nonlinear and time-dependent analysis of segmentally erected, reinforced and prestressed concrete structures. Generally good agreement was obtained, showing the adequacy of the model to reproduce the structural effects of complex interactive time-dependent phenomena.     

Development of Flexural Strength Rating Procedures for Adjacent Prestressed Concrete Box Girder Bridges

An investigation was conducted on noncomposite prestressed precast concrete adjacent-box-beam bridges that suffered catastrophic failures resulting from the corrosion of the prestressing steel. These failures highlight the need to improve the methods used to detect corrosion damage and, subsequently, to load rate the damaged members. Currently, the inspection of concrete box girder sections relies on visual methods that correlate longitudinal and transverse cracking, spalling, and exposed strands with the rated level of performance of the member. To improve the current inspection techniques, visual assessment methods were examined through the destructive evaluation and material characterization of seven box-beam segments. The research results indicate that the fabrication techniques used for box-beam construction in the 1950–1960 time period allowed for large variations in construction tolerance. Half-cell methods were shown not to provide an accurate or reliable method of identifying the corrosion of prestressing strands. Longitudinal cracking was shown to be an accurate and reliable indicator of the underlying corrosion of prestressing strands. The probability of corrosion on strands adjacent to longitudinal cracks was determined and quantified. On the basis of the results, a new recommendation for determining the residual flexural strength of corroded prestressed beams is provided.     

Transverse Posttensioning Design of Adjacent Precast Solid Multibeam Bridges

Adjacent precast, prestressed multibeam bridges have often been used for medium- and short-span bridges. However, there have been longitudinal cracking problems in shear keys and overlays commonly seen on some adjacent precast multibeam bridges during their service years. The fundamental reason for the problem is the poor transverse connection. Transverse posttensioning is important to the transverse connection design, although the posttensioning varies largely from state to state. Especially for adjacent precast solid multibeam bridges without diaphragms, there are no theoretical justifications for designing the transverse posttensioning. In this study, an approach based on the concept of shear friction, which is used for designing the transverse posttensioning in adjacent precast solid multibeam bridges, is presented. Furthermore, a newly rehabilitated bridge was load tested with the primary purpose of evaluating the effect of transverse posttensioning under truck load. Also, the calibration of a numerical model was conducted. At last, suggestions about design and construction of shear keys, with reference to the experience in other states, are presented for the practice in the state of Maryland.     

Experimental Performance of Full-Depth Precast, Prestressed Concrete Overhang, Bridge Deck Panels

The performance of a new full-depth precast overhang panel system for concrete bridge decks is investigated experimentally. In contrast to conventional cast-in-place deck overhangs, the proposed full-depth precast overhang system has the potential to speed up construction, reduce costs, and improve safety. Load-deformation behavior up to factored design load limits is first investigated. The panel is then loaded near its edge to examine the collapse capacity and the associated failure modes—particularly the influence of panel-to-panel connections that exist, transverse to the bridge deck axis. Comparative tests are also conducted with a conventional cast-in-place overhang system. When compared to the conventional cast-in-place overhang behavior, the experimental results show that the precast full-depth overhang introduces different behavior modes, largely due to the influence of the partial depth panel-to-panel connection, which reduces the capacity by some 13%.     

Inspecting the Lightweight Precast Concrete Panels in the Woodrow Wilson Bridge Deck of 1982

This paper presents the results of a detailed inspection of the deck panels of the Woodrow Wilson Bridge installed in 1982. The original cast-in-place concrete deck, constructed in 1962, was replaced with full-depth lightweight precast concrete deck panels that enabled rapid construction with minimal traffic disruption. The inspection of the Woodrow Wilson deck provides valuable information about the performance of the precast concrete panels, joints, and connections after 20 years of very harsh traffic loads and environmental stressors. The deck panels performed well overall, with the only serious problems at expansion and contraction joints. All of these joints exhibited cracking and rusting. The most prevalent type of cracking appeared to be due to restrained shrinkage between the new polymer concrete, the older precast panels, and the rigid steel joints. This location is more vulnerable to cracking and leaking because there is no prestress across the joint. The multilayered corrosion protection methods used for the transverse and longitudinal post-tensioning tendons were very successful.     

Effects of Temperature Variations on Precast, Prestressed Concrete Bridge Girders

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.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Concept Development

This paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck that is cast and prestressed with the girder provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is a perceived problem with durability of longitudinal joints used to connect adjacent girders. This paper presents the results of a study to assess potential alternate joint details based on constructability, followed by testing of selected details. Seven reinforced concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement were tested along with a specimen reinforced by continuous bars for comparison. Test results were evaluated based on flexural capacity, curvature at failure, cracking, deflection, and steel strain. Based on the survey and the experimental program, a headed bar detail with a 152 mm (6 in.) lap length was recommended for replacing the current welded steel connector detail.     

预应力混凝土用钢棒的研究现状

预应力混凝土用钢棒由于其特点明显,在中国建筑、水利行业得到了广泛的应用。从原料使用、冶炼工艺、轧制工艺方面介绍了国内外预应力混凝土用钢棒的现状,并进行了分析对比;介绍了连铸-连轧以及深加工中的新技术;分析了中国目前预应力混凝土用钢棒发展存在的问题和所遇到的瓶颈。针对中国预应力混凝土用钢棒的未来发展做了相关分析。     

Experimental Investigation of Shear Capacity of Precast Reinforced Concrete Box Culverts

This study presents an experimental program to investigate the shear capacity of precast reinforced concrete box culverts. Each culvert was subjected to monotonically increasing load through a 254?mm×508?mm (10?in.×20?in.) load plate in order to simulate the HS20 truckload per AASHTO 2005. Instrumentation included strain gauges, high-resolution laser deflection sensor, and automated data acquisition. Four tests were conducted on 1.22?m×1.22?m×1.22?m (4?ft×4?ft×4?ft) box culverts. The location of the load plate was varied to identify the position, which introduces the maximum shear stresses. Laser sensor data and dial gauge readings were recorded to measure the deflection profile of the box culvert. Strain gauges were placed on the steel reinforcement to measure axial strain at locations of maximum positive and negative bending moments. The test results include reporting the loads at which each crack initiated and propagated. The displacement profile of the top slab from the laser instrumentation output along with the load versus maximum deflection for each culvert is also reported.     

Construction of Pressurized, Self‐Supporting Membrane Structure on Moon

This paper draws attention to the importance of readiness time (i.e., the time it takes to develop the necessary supporting infrastructure on the Moon for the structure to be ready for use) of a lunar structure. It illustrates a rational process of determining readiness time using for an example the pressurized self‐supporting membrane structure (PSSMS), a concept proposed in 1989. To assess manpower requirement for construction, it is necessary to assess the productivity of a construction crew on the Moon, taking into consideration the hazardous conditions they confront, and the encumbrances due to the use of space suits and other protective systems. These handicaps can be compensated to some extent by making maximum use of mechanical and automatic equipment. The procedure adopted here is to determine the manpower requirement for a similar construction on Earth, then adjust it to the conditions on the Moon. Once the productivity factor relative to Earth is determined, the manpower requirement for lunar construction can be assessed.     

Behavior of Prestressed Concrete Strengthened with Various CFRP Systems Subjected to Fatigue Loading

Many prestressed concrete bridges are in need of upgrades to increase their posted capacities. The use of carbon fiber-reinforced polymer (CFRP) materials is gaining credibility as a strengthening option for reinforced concrete, yet few studies have been undertaken to determine their effectiveness for strengthening prestressed concrete. The effect of the CFRP strengthening on the induced fatigue stress ratio in the prestressing strand during service loading conditions is not well defined. This paper explores the fatigue behavior of prestressed concrete bridge girders strengthened with CFRP through examining the behavior of seven decommissioned 9.14?m (30?ft) girders strengthened with various CFRP systems including near-surface-mounted bars and strips, and externally bonded strips and sheets. Various levels of strengthening, prestressing configurations, and fatigue loading range are examined. The experimental results are used to provide recommendations on the effectiveness of each strengthening configuration. Test results show that CFRP strengthening can reduce crack widths, crack spacing, and the induced stress ratio in the prestressing strands under service loading conditions. It is recommended to keep the prestressing strand stress ratio under the increased service loading below the value of 5% for straight prestressing strands, and 3% for harped prestressing strands. A design example is presented to illustrate the proposed design guidelines in determining the level of CFRP strengthening. The design considers the behavior of the strengthened girder at various service and ultimate limit states.