Modified Yield Line Theory for Full-Depth Precast Concrete Bridge Deck Overhang Panels

Full-depth precast deck slab cantilevers also referred to as full-depth precast concrete bridge deck overhang panels are becoming increasingly popular in concrete bridge deck construction. To date, no simple theory is able to estimate the overhang capacity of full-depth concrete bridge deck slabs accurately. Observations suggest that interaction between flexure and shear is likely to occur as neither alone provides an accurate estimate of the load-carrying capacity. Therefore, modified yield line theory is presented in this paper, which accounts for the development length of the mild steel reinforcing to reach yield strength. Failure of the full-depth panels is influenced by the presence of the partial-depth transverse panel-to-panel seam. When applying a load on the edge of the seam, the loaded panel fails under flexure while the seam fails in shear. Through the use of the modified yield line theory coupled with a panel-to-panel shear interaction, analytical predictions are accurate within 1–6% of experimental results for critical cases.     

Influence of Reinforcement on the Behavior of Concrete Bridge Deck Slabs Reinforced with FRP Bars

This paper presents the results of an experimental study to investigate the role of each layer of reinforcement on the behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars. Four full-scale concrete deck slabs of 3,000?mm length by 2,500?mm width and 200?mm depth were constructed and tested in the laboratory. One deck slab was reinforced with top and bottom mats of glass FRP bars. Two deck slabs had only a bottom reinforcement mat with different reinforcement ratios in the longitudinal direction, while the remaining deck slab was constructed with plain concrete without any reinforcement. The deck slabs were supported on two steel girders spaced at 2,000?mm center to center and were tested to failure under a central concentrated load. The three reinforced concrete slabs had very similar behavior and failed in punching shear mode at relatively high load levels, whereas the unreinforced slab behaved differently and failed at a very low load level. The experimental punching capacities of the reinforced slabs were compared to the theoretical predictions provided by ACI 318-05, ACI 440.1R-06, and a model proposed by the writers. The tests on the four deck slabs showed that the bottom transverse reinforcement layer has the major influence on the behavior and capacity of the tested slabs. In addition, the ACI 318-05 design method slightly overestimated the punching shear strength of the tested slabs. The ACI 440.1R-06 design method yielded very conservative predictions whereas the proposed method provided reasonable yet conservative predictions.     

Application of Suspension Bridges Stiffened by Prestressed Concrete Slabs in China

Four suspension bridges stiffened by prestressed concrete slabs were designed and constructed on highways in southwestern mountainous areas of China. These bridges are the first applications of its kind in China. This paper discusses the site condition, adaptability, and design and construction features of these bridges. These bridges have single suspension spans between 278 and 388?m and deck width between 14.4 and 15.0?m. The longitudinal distance between hangers is only 5?m, which is relatively small for this bridge type, and there are only two lanes. The dual direction prestressed concrete slabs are 0.6?m deep, and its wind blocking area is relatively small. Dynamic analysis and wind tunnel tests verify that the wind resistance requirements are easily satisfied.     

Longitudinal Cracking Distress on Continuously Reinforced Concrete Pavements in Illinois

The Illinois Department of Transportation (IDOT) initiated a failure investigation to determine the distress mechanisms causing premature longitudinal cracking on continuously reinforced concrete pavements (CRCP) on several Illinois interstates. The longitudinal cracking approximately followed the embedded reinforcement steel and occurred in both the driving and passing lanes. In this paper, the results from field visual surveys, coring, and petrographic analyses are reported along with a review of archival construction and material records of the distressed CRCP sections. A laboratory forensic study was also performed on several field extracted slabs. The results of the field and laboratory investigation show the cracking was not initiated by steel corrosion, deleterious reactions in the concrete materials, or an inadequate structural design. Rather, the cracking is related to settlement of the steel bars in the concrete. Settlement cracking is conventionally thought to occur only in concrete slabs and decks with plastic (high slump) concrete and small values of bar cover depth, while the studied CRCP sections have large values of cover depth and were cast with stiff (low slump) concrete. The settlement was likely caused by the relative settlement of heavy steel bars (22?mm diameter) within the lower density concrete during the original CRCP construction. The technique of placing the steel bars in the fresh concrete (called tube-feeding) further contributed to the development of this distress, and this practice is no longer employed by IDOT.     

Mechanically Fastened FRP-Strengthened Two-Way Concrete Slabs with and without Cutouts

The feasibility of strengthening concrete slabs in flexure, with and without cutouts, using the mechanically fastened (MF) FRP technique is investigated. Two series of large-scale reinforced concrete slabs are tested. The first series is comprised of five slabs without a cutout, and measuring 2,600×2,600×120?mm; the second series consists of four slabs of the same dimensions with a central cutout measuring 800×800?mm. The mechanically fastened system is found to be a valid alternative to the externally bonded system resulting in a rapid, economic, and effective strengthening technique for two-way concrete slabs. The increases in ultimate capacities of the MF FRP-strengthened slabs range between 30 and 70% over those of the unstrengthened specimens. In addition, finite-element modeling of MF FRP-strengthened slabs is introduced in this study. The interfacial behavior between the MF FRPs and the concrete substrate is accounted for by using appropriate interfacial models. Very good agreement is obtained between the test results and the numerical predictions.     

Constructing a Complex Precast Tilt-Up-Panel Structure Utilizing an Optimization Model, 3D CAD, and Animation

This paper presents the concept used to construct a complex residential tilt-up-panel structure utilizing three-dimensional (3D) modeling and animations. The residence comprises of 108 precast concrete panels of varying rectangular shapes with “dog legs” and window and door “cutouts” that look like an assembled jigsaw puzzle. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often in 90° joints between panels. 3D animations were used to experiment with the construction process on the computer screen prior to construction in order to avoid potential costly on-site errors. In addition, the 3D animations were also used as a training tool for the contractors. This paper focuses on describing the methodology used to integrate a crane selection algorithm and optimization model with 3D modeling and animation for the selection, utilization, and location of cranes on construction sites. Analytical optimization processes were used to decrease the traveling time and distance of the selected crane, to improve the crane lifting sequence and to minimize the use of panel casting slabs.     

Multilevel Formwork Load Distribution with Posttensioned Slabs

Formwork and the associated shoring represent a significant proportion of the costs associated with the construction of multilevel concrete structures. To minimize these costs, a limited number of formwork and shoring sets are recycled up the structure as construction progresses, eliminating the need for a new set of formwork and shoring with each new slab. When a slab is posttensioned using draped tendons, slab lift occurs as a portion of the slab self-weight is balanced. The formwork and shores supporting that slab are unloaded by an amount equivalent to the load balanced by the posttensioning. This produces a load distribution through the structure that is inherently different from that of a conventionally reinforced slab. This paper presents two design methods suitable for modeling the multilevel formwork process for posttensioned slabs: A modification to the simplified analysis method and a finite element model—both techniques will be of immediate use by industry practitioners and of interest to researchers examining the load distribution phenomenon. The paper also summarizes the findings of one of only a few research projects in which actual shore loads were monitored during the construction of a multilevel posttensioned building, which is used to validate the proposed design models.     

Simulation of Concrete Paving Operations on Interstate-74

The objective of this paper was to study and optimize the concrete paving operations taking place in the reconstruction project of Interstate-74 using computer simulation. To achieve this objective, field data were collected during construction, and were then used to determine adequate probabilistic density functions for the activities’ duration and to test a developed simulation model. Upon testing, the developed model was used to study the impacts of resources on the flow of operations and on the cost effectiveness of the construction process. In general, application of simulation methods to concrete paving operations was successful and its accuracy was acceptable as compared to field measurements. Based on the results of a sensitivity analysis of the critical resources, multiple factors were considered in the decision-making process to ensure that all aspects of the operation are evaluated. This includes total operation time, productivity, costs of the operation, average truck delay, and idle times for the paver and the spreader. For the conditions pertinent to this construction site, ten trucks, one paver and one spreader, and three finishing and plastic-covering crews are recommended. Using this set of resources would result in a prompt and effective execution of the operation. Practical implementation and limitations of the developed model in similar construction operations is discussed.     

Case Study of Urban Concrete Pavement Reconstruction on Interstate 10

Many urban concrete pavements in California need to be reconstructed, as they have exceeded their design lives and require frequent maintenance and repair. Information is needed to determine which methodologies for pavement design, materials selection, traffic management, and reconstruction strategies are most suitable to achieve the objectives of California Department of Transportation’s (Caltrans) long-life pavement rehabilitation strategies (LLPRS) program. To develop construction productivity information for several construction windows, a case study was performed on a Caltrans concrete rehabilitation demonstration project near Los Angeles on Interstate-10, where 20 lane-km was successfully rebuilt using fast setting hydraulic cement concrete (FSHCC) with one weekend closure for 2.8 lane-km and repeated 7- and 10-h nighttime closures for the remaining distance. The concrete delivery and discharge controlled the overall progress. In terms of the number of slabs replaced per hour, the 55-h weekend closure was 54% faster than the average nighttime closure. An excellent traffic management strategy helped to reduce the volume of traffic during the weekend closure and minimize the traffic delay through the construction zone.     

In-Situ Evaluation of Two Concrete Slab Systems. I: Load Determination and Loading Procedure

The primary objective of in-situ load testing is to assess the safety and serviceability of an existing structural system with respect to a particular load effect. At this time, the most appropriate loading level and procedure, as well as the associated evaluation criteria are being reconsidered in light of technological advances in construction methods, analytical tools, and monitoring instrumentation. The in-situ load test method for reinforced concrete systems described in the ACI Building Code Requirements for Structural Concrete, namely the 24–h load test method and its evaluation criteria, has been in use for several decades, but may no longer serve the needs of contemporary construction and engineering practices. As a result, other load test methodologies and associated evaluation criteria are under development. This paper and a companion paper describe the rationale and application of an alternative approach to the determination of load level, loading procedure, instrumentation requirements, evaluation criteria and outcomes for two field projects. The first case study is relative to a posttensioned concrete slab where many areas were characterized by tendon and reinforcement misplacement, resulting in inadequate flexural strength and inadequate shear/flexure transfer at column/slab intersections. The second case study is the structural evaluation of a typical floor bay of a two-way reinforced concrete slab system, presenting distributed cracking at the positive and negative moment regions. Finite-element-method models were created for both structures to aid the load test design. The numerical models validated the field observations.     

Flexure of Two-Way Slabs Strengthened with Prestressed or Nonprestressed CFRP Sheets

This paper presents a study on the flexural behavior of two-way reinforced concrete slabs externally strengthened with prestressed or nonprestressed carbon fiber-reinforced polymer (CFRP) sheets. Four large-scale flat plate slabs (3,000?mm×3,000?mm×90?mm) are tested and a nonlinear three-dimensional finite-element analysis is conducted to predict the flexural behaviors of the tested slabs, including the load-deflection response, strain distribution, crack propagation, and crack mouth opening displacement. An increase in the load-carrying capacity of 25 and 72% is achieved for the slabs strengthened with nonprestressed and prestressed CFRP sheets, respectively, in comparison to the unstrengthened slab. A reduction of the deflections up to 32% in service is noted for the strengthened slabs. The unstrengthened slab shows very ductile behavior, whereas, progressive failure is observed for the strengthened slabs, exhibiting pseudoductility in postpeak behavior. Stress redistribution between the internal and external reinforcement is significant in the slab strengthened with prestressed CFRP sheets.     

Structural Evaluation of Cement Concrete Roads in Mumbai City

Plain jointed concrete pavements laid in Mumbai City (India) during the early 1990s were structurally evaluated using a falling weight deflectometer (FWD) and testing of concrete cores extracted from the pavement slabs. The ultrasonic pulse velocity (UPV) of the concrete in the cores was determined first and then the cores were crushed under compression. The pavement deflections were found to be within the limits as suggested in the Indian codes and the international literature. The joint conditions were also found to be satisfactory. The design strength of the concrete was back-calculated from the compressive strength of the cores and was found to conform to the design specifications. However, the construction quality was found wanting as the thickness of pavement slabs at a few locations was lower than that specified and it has resulted in cracking of the slabs. The dynamic modulus of elasticity of concrete as determined by the FWD was found to correspond well with that computed from the UPV of cores and from the compressive strength of concrete. A method is suggested to estimate the structural parameters of uncracked pavement slabs from the dynamic modulus of elasticity obtained through the indirect method of UPV testing which is less expensive compared to evaluation by the FWD.     

Shear Strength of One-Way Concrete Slabs Reinforced with Fiber-Reinforced Polymer Composite Bars

This paper evaluates the shear strength of one-way concrete slabs reinforced with different types of fiber-reinforced polymer (FRP) bars. A total of eight full-size slabs were constructed and tested. The slabs were 3,100?mm?long×?1,000?mm?wide×200?mm?deep. The test parameters were the type and size of FRP reinforcing bars and the reinforcement ratio. Five slabs were reinforced with glass FRP and three were reinforced with carbon FRP bars. The slabs were tested under four-point bending over a simply supported clear span of 2,500 mm and a shear span of 1,000 mm. All the test slabs failed in shear before reaching the design flexural capacity. The experimental shear strengths were compared with some theoretical predictions, including the JSCE recommendations, the CAN/CSA-S806-02 code, and the ACI 440.1R-03 design guidelines. The results indicated that the ACI 440.1R-03 design method for predicting the concrete shear strength of FRP slabs is very conservative. Better predictions were obtained by both the CAN/CSA-S806-02 code and the JSCE design recommendations.     

Slip-Form Application to Concrete Structures

Because of superior speed and productivity, slip forms were extensively utilized as a potential formwork candidate in constructing concrete structures for the past few decades. Typical projects that employ this formwork technique are: Core of high-rise buildings, silos, telecommunication towers, cooling towers, heavy concrete offshore platforms, etc. The research presented in this paper aims at studying slip-form application to cores and silos, assessing its productivity, and determining its appropriate speed as well as auxiliary resource combinations. Simulation models are developed in which the potential control units in a slip-form system are described for cores and silos. Data are collected from several case study projects. A set of charts has been developed to predict productivity considering different stoppages, core cross section area, slipping (jacking) rate, and concrete placing methods. These charts play an essential role in managing slip-form application to cores and silos. Results show that the developed simulation models predict the productivity of case study projects with 99.70 and 99.30% accuracy for cores and silos, respectively. The presented research is relevant to both researchers and practitioners. It provides practitioners with charts that assist in scheduling and managing the required resources for slip-form application. In addition, it provides researchers with simulation models and framework for implementing slip forms to core and silo construction.     

Dynamic Behavior of Deck Slabs of Concrete Road Bridges

This paper treats the dynamic effect of traffic actions on the deck slabs of concrete road bridges using the finite-element method. All the important parameters that influence bridge-vehicle interaction are studied with a systematic approach. An advanced numerical model is described and the results of a parametric study are presented. The results suggest that vehicle speed is less important than vehicle mass and that road roughness is the most important parameter affecting the dynamic behavior of deck slabs. The type of bridge cross section was not found to have a significant influence on deck slab behavior. The dynamic amplification factor varied between 1.0 and 1.55 for the bridges and vehicles studied. These results should be validated by further work.     

Structural Performance of Hybrid GFRP/Steel Concrete Sandwich Panels

Precast/prestressed concrete sandwich panels consist of two concrete wythes separated by a rigid insulation foam layer and are generally used as walls or slabs in thermal insulation applications. Commonly used connectors between the two wythes, such as steel trusses or concrete stems, penetrate the insulation layer causing a thermal bridge effect, which reduces thermal efficiency. Glass fiber-reinforced polymer (GFRP) composite shell connectors between the two concrete wythes are used in this research as horizontal shear transfer reinforcement. The design criterion is to establish composite action, in which both wythes resist flexural loads as one unit, while maintaining insulation across the two concrete wythes of the panel. The experiments carried out in this research show that hybrid GFRP/steel reinforced sandwich panels can withstand out-of-plane loads while providing resistance to horizontal shear between the two concrete wythes. An analytical method is developed for modeling the horizontal shear transfer enhancement using a shear flow approach. In addition, a truss model is built, which predicts the panel deflections observed in the experiments with reasonable accuracy.     

Numerical Investigation of Fiber Reinforced Polymers Poststrengthened Concrete Slabs

The present work deals with the numerical simulation of fiber reinforced polymers (FRP) poststrengthened scaled concrete slabs in order to predict their load carrying behavior. The used strengthening materials are FRPs which are of increasing interest in civil engineering applications such as textile reinforced concrete tubes, cables of cable-stayed bridges, or even entire bridges. The numerical results are compared with experiments which were conducted at the Univ. of California, San Diego, and are described in detail by H?rmann in 1997; H?rmann et al. in 1998; and later by Seim et al. in 2001. The slabs are modeled for the numerical simulation first in a two-dimensional design space, assuming a plane stress condition for the concrete and the fiber reinforced polymer, and second in a three-dimensional design space with multilayered shell elements in order to include the varying response across the depth of the slabs. The used material model for reinforced concrete was developed by Menrath et al. in 1998 and has been enhanced for multilayered shell elements by Haufe et al. in 1999. It is based on multisurface plasticity, consisting of two Drucker–Prager yield surfaces and a spherical cap, and exhibits fracture energy based evolution laws for the softening regime. The reinforcement is taken into account as additional stress contribution in a smeared manner using a one-dimensional constitutive law based on an elastoplastic isotropic hardening model.     

Economic Evaluation of Reinforced Concrete Structures with Columns Reinforced with Prefabricated Cage System

A new reinforcement system termed the prefabricated cage system (PCS) that can be used as an alternative to the rebar reinforcement cage is economically evaluated. PCS is a prefabricated reinforcement that enables easier, faster, and more reliable construction. Use of PCS shortens the construction schedule time and lowers total construction cost. This is important to both owners and construction contractors. The engineering economics methods presented in this paper would also be of interest to researchers. Reinforced concrete structures with PCS reinforced columns have been considered in this research, as it is one of the major applications of PCS. Various parameters affecting the economics of PCS are reviewed and a case study structure is analyzed comparing the costs of the structure with rebar reinforced columns to costs of the structure with PCS reinforced columns. The investigation shows that using PCS results in a 33.3% time savings and a 7.1% cost savings over rebar for each column. This results in an average of 3.6% savings on total project cost; an average of 22.2% savings on total column costs; 20.4% savings on total project time period, and 33.3% savings on columns construction time period. The cost savings are estimated based on production of small quantities of PCS reinforcement. Mass production of PCS reinforcement would result in even higher cost savings.     

Performance of Dowel Bar Retrofit Projects in Texas

In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required 50–75?mm thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade support. This is significant in that there are no effective and practical methods to improve subbase conditions in existing concrete pavement, whereas DBR can restore pavement conditions at a reasonable cost. However, not all DBR projects were successful. In one DBR project, faulting in the range of 6.4–9.5?mm occurred after less than 2 years of treatment. Forensic investigation revealed voids under the dowel bars, which indicates poor consolidation of the grout material. Efforts are currently underway in TxDOT to improve specifications for grout materials and DBR construction.     

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.