Papers in This Issue

This May 2011 issue of the Journal features 17 technical papers and one discussion. The issue begins with eight papers on various types of dynamic loads. In “Seismic Behavior of Self-Centering Segmental Bridge Bents,” ElGawady and Sha’lan present the cyclic behavior of four self-centering bridge bents with different construction details, including external energy dissipaters and neoprene isolation. The columns of these bents consisted of precast posttensioned concrete-filled fiber tubes (PPT-CFFT). A fifth monolithic moment-resisting concrete bent was also tested as a reference specimen. The tests showed that PPT-CFFT bents can be used in bridge construction as a lateral load resistance system. The PPT-CFFT bents without external energy dissipaters displayed a lateral drift of approximately 9.2% without experiencing significant damage or residual displacement. The PPT-CFFT specimen with external energy dissipaters reached a drift angle of 9.2% with some damage. The reinforced-concrete specimen failed at a drift angle of approximately 6.9% with substantial damage and residual displacement. In “Bearing and Shear Failure of Pipe-Pin Hinges Subjected to Earthquakes,” Zaghi and Saiidi present an experimental and analytical study to understand the behavior of pipe-pin hinges and develop design guidelines. As part of the study, six 1:3.5-scale push-off tests were carried out to assess the bearing capacity of the concrete against the pipe. The tests showed that the bearing strength of concrete is as much as twice the concrete compressive strength attributable to the confining effect of the concrete and reinforcement. In addition, to determine the shear capacity of the concrete-filled steel pipe, six concrete-filled pipe specimens were tested in pure shear, and an empirical design equation was developed to assess their shear strength. In the analytical studies, the ABAQUS finite-element (FE) package was used to perform a series of detailed nonlinear analyses. The results showed that the FE models accurately simulated the behavior of the push-off specimens and the observed modes of failure. In “Cyclic Testing of Large-Scale Rectangular Bridge Columns under Bidirectional Earthquake Components,” Khaled et al. present the results of bidirectional cyclic testing on four half-scale reinforced-concrete rectangular bridge column specimens to examine the need to account for bidirectional seismic loading in design for earthquakes expected in the eastern and western regions of North America. The prototype structures are common two-span, skewed bridge structures designed according to the seismic provisions of Canadian Standards Association (CSA) S6-06. Two specimens were designed for Montreal, Canada (east site), using 0 and 30% combination rules, resulting in longitudinal steel ratios of 0.41 and 0.57%. Two other specimens represented the columns of bridges located in Vancouver, Canada (west site), with longitudinal steel ratios of 0.97 and 1.72% resulting from the application of 0 and 40% combination rules. For both sites, the tests showed that the combination rules used in design had no significant influence on the inelastic cyclic response of the columns. The columns designed for the Montreal site exhibited satisfactory inelastic cyclic performance even if they had a longitudinal reinforcement ratio less than the current CSA S6 limit of 0.8%. All columns were subjected to biaxial shear forces corresponding to their biaxial flexural strength envelope. For all specimens, the height of the plastic hinge region was approximately equal to the smaller column dimension, rather than the larger one, as currently specified in CSA S6. In “Wave Passage and Ground Motion Incoherency Effects on Seismic Response of an Extended Bridge,” Mwafy et al. investigate the implications of ground-motion spatial variability on the seismic response of an extended highway bridge. An existing 59-span, 2,164-m bridge with several bearing types and irregularity features is selected as a reference structure. The bridge is located in the New Madrid seismic zone and supported on thick layers of soil deposits. Site-specific bedrock input ground motions are selected on the basis of a refined probabilistic seismic hazard analysis of the bridge site. Wave passage and ground-motion incoherency effects are accounted for after propagating the bedrock records to the ground surface. The results obtained from inelastic response-history analyses confirm the significant impact of wave passage and ground-motion incoherency on the seismic behavior of the bridge. The amplification in seismic demands exceeds 150%, whereas the maximum suppression of these demands is less than 50%. The irregular and unpredictable changes in structural response attributable to asynchronous earthquake records necessitate in-depth seismic assessment of major highway bridges with advanced modeling techniques to realistically capture their complex seismic response. In “Vandal Loads and Induced Vibrations on a Footbridge,” Caetano et al. investigate intentional human dynamic loads (vandal loads) and induced effects on a footbridge. The study includes the development of a numerical model to characterize the dynamic behavior of the footbridge, which is experimentally validated and used to numerically simulate the response induced by groups of pedestrians synchronized at critical bridge frequencies. The vandal load associated with a single pedestrian is characterized and compared with literature definitions. The response is then calculated considering the measured load and compared with the measured response to the excitation induced by a single pedestrian or a group with varying dimension. In “Dynamic Stress Analysis of Long Suspension Bridges under Wind, Railway, and Highway Loadings,” Zhiwei et al. present a framework for dynamic stress analysis of long suspension bridges under wind, railway, and highway loadings. The bridge, trains, and road vehicles are respectively modeled using the finite-element method. The connections between the bridge and trains and between the bridge and road vehicles are respectively considered in terms of wheel-rail and tire-road surface contact conditions. The spatial distributions of both buffeting forces and self-excited forces over the bridge deck are considered. The Tsing Ma suspension bridge and the measurement data recorded by a wind and structural health monitoring system installed in the bridge are utilized as a case study to examine the proposed framework. The results show that running trains play a predominating role in bridge stress responses compared with running road vehicles and fluctuating wind loading. In “Nonlinear Rail-Structure Interaction Analysis of an Elevated Skewed Steel Guideway,” Okelo and Olabimtan investigate the nonlinear interaction between continuous welded rail (CWR) with direct fixation of track on a concrete deck and the elevated structure that takes place through direct-fixation rail fasteners. Factors that have significant influence on this interaction include the bearing arrangement at the substructure units, trackwork terminating on the aerial structure, type of deck construction, and type of rail fasteners. To better understand the interaction mechanism, a nonlinear three-dimensional (3D) finite-element analysis of a straight, skewed, elevated steel guideway has been carried out for temperature change, temperature change with rail breaking, and train braking load cases. The study shows that nonlinear 3D modeling can give comprehensive insight into the rail structure interaction (RSI) forces. In “Lateral Vibration of High-Pier Bridges under Moving Vehicular Loads,” Yin et al. focus on establishing a new methodology considering the bridge’s lateral vibration induced by moving vehicles. Three significant factors that affect the lateral forces, including the slip angle, camber angle, and vehicle tires moving with an “S” shape, are introduced in studying the effect of the lateral forces on the lateral vibration of bridges. The bridge-vehicle coupled equations are established by combining the equations of motion of both the bridge and vehicles using displacement and interaction force relationships at the patch contact. The accuracy and efficiency of the present method are verified by comparing the simulations with the field-test results of a typical high-pier bridge, showing that the proposed method can rationally simulate the lateral vibration of the bridge under moving vehicular loads.

The next seven papers in this issue are related to precast and prestressed concrete in bridges. The paper titled “Static and Dynamic Behavior of High- and Ultrahigh-Performance Fiber-Reinforced Concrete Precast Bridge Parapets,” by Charron et al., presents new designs of precast bridge parapets made with fiber-reinforced concrete (FRC) using nonlinear finite-element calculations exploiting specific properties of high- and ultrahigh-performance FRC. The conventional reinforcement required in the FRC precast parapets varied from 0 to 50% when compared with reference built-on-site parapets. The results of the quasi-static tests indicated that precast FRC parapets possess the required strength and have ductility comparable to reference parapets. Quasi-static tests carried out after the dynamic tests indicated that the residual strength of parapets corresponds to 75 to 100% of their original capacity. The finite-element model adopted in this research satisfactorily reproduced the strength, stiffness, and failure mode of parapets. The paper titled “Flexural Testing of Precast Bridge Deck Panel Connections,” by Porter et al., focuses on the evaluation of the service and ultimate capacities of five precast deck panel connections. Full-scale tests were developed to determine the cracking and ultimate flexural strengths of two welded connections, a conventionally posttensioned connection, and two newly proposed, posttensioned, curved bolt connections. Conventionally posttensioned specimens were shown to perform well, with the highest cracking loads and 0.42 times the theoretical capacity of a continuously reinforced concrete deck panel. Curved bolt connections proposed in this paper were shown to be a promising connection detail with approximately 0.5 times the theoretical capacity of a continuously reinforced panel. Data from the welded specimens showed that some welded connection types perform significantly better than others. The experimental results also compared closely with calculated values based on finite-element modeling, which can be used for future analytical studies. The paper “Redevelopment of Prestressing Force in Severed Prestressed Strands,” by Kasan and Harries, investigates the contribution of severed or corroded strands on the flexural capacity rating of prestressed girders. A severed or corroded strand, once it reenters sound concrete, continues to be bonded to the concrete; thus stress transfer between the concrete and strand is possible and the strand prestress force may be “redeveloped” (in the sense of “transfer length”) by bond transfer at a distance from the damage location. On the basis of an experimental study, this paper clearly shows that prestress force is redeveloped at a distance from the location at which a strand is severed. Furthermore, AASHTO and American Concrete Institute (ACI) code-prescribed transfer length calculations appear to remain valid for this redevelopment behavior. The paper “Testing Method for the Tension of Vertical Prestressing Bars in Webs of Concrete Box Girder Bridges,” by Zhong et al., presents a dynamic model for the exposed segment of a vertical prestress system to detect effective tension retained in the bar. Results of laboratory experiments show that the flexural rigidity of the exposed segment in anchorage zone increases with an increase in effective tension. Both approximate and exact solutions of the dynamic model are proposed to identify the flexural rigidity. The method can be applied to actual bridges by carrying out some field experiments to fit flexural rigidity-tension relationship curves. These curves can be utilized to identify the effective tension indirectly when inherent frequency of the exposed segment is obtained. The paper “Retrofitting Short-Span Precast Channel Beam Bridges Constructed without Shear Reinforcement,” by Heymsfield and Durham, investigates retrofitting precast, nonprestressed, channel beams (PCB) used at short-span bridges to improve beam shear strength and, consequently, beam ductility. Three retrofit approaches were investigated: applying carbon fiber reinforced polymer (CFRP) strips, applying an epoxy spray-on, and retrofitting by installing shear bars within the stems of the precast channel beam. Implanting shear bars into each precast channel beam stem was found to be the optimal retrofit on the basis of improved beam strength, installation ease, and economics. The suitability of the shear bar retrofit was further explored by implementing the shear bar retrofit at the Arkansas Bridge #02992 over the Flat Hollow Branch Creek, which is a short-span precast channel beam bridge. The paper titled “Verification of Incremental Launching Construction Safety for the Ilsun Bridge, the World’s Longest and Widest Prestressed Concrete Box Girder with Corrugated Steel Web Section,” by Jung et al., focuses on the span-to-depth ratio, buckling shear stress of the corrugated steel webs, optimization of the length of the steel launching nose, detailed construction stage analysis, and the stress level endured by the corrugated steel webs during the launching process. The span-to-depth ratio of the Ilsun Bridge was found to be well-designed, using a conservative corrugated steel web design. Further, the investigation revealed that the conventional nose-deck interaction equation was not suitable for corrugated steel web bridges. As a result, a detailed construction stage analysis and measurements of this bridge were performed to examine stress levels and ensure safety during the erection process. The results revealed essential design issues, which should be considered when designing prestressed concrete box girder bridges with corrugated steel webs and when constructing them using the incremental launching method. The paper “Improved Optimization Formulations for Launching Nose of Incrementally Launched Prestressed Concrete Bridges,” by Fontan et al., proposes an objective and rigorous formulation to optimize the launching nose of a launched bridge under real constraints that a bridge designer might encounter in practice. Comparing the results obtained by the conventional process with those obtained by optimization techniques, it can be verified that some of the assumptions considered in classical design methods of a launching nose are not based on any theoretical foundation.

The remaining two papers are in the areas of timber and posttensioned concrete bridge girders. In “Behavior of Structural Composite Lumber T-Beam Bridge Girders after Fatigue Loading,” Enam et al. present results of testing of 12 new and two old/weathered structural composite lumber (SCL) T-beam bridge girders with material and preservative variations for AASHTO-specified flexural fatigue under a stress-controlled test setup simulating 60 years of service. Transverse posttension was applied to the girders, simulating real-life situations. Results from the study indicate that the girders are capable of withstanding the repetitive loads without much physical damage. A few of the laminated veneer lumber (LVL) girders had severe delamination at the SCL-epoxy interface. The fatigued girders were loaded statically up to failure and compared with the ultimate flexural strength of fresh girders. The girders did not show any appreciable strength loss attributable to one million cycles of fatigue loading. There was no effect of SCL type and preservative treatment on fatigue strength. In “Nonlinear Finite-Element Analysis of Posttensioned Concrete Bridge Girders,” Ayoub presents the development of a new nonlinear finite-element program for the analysis of posttensioned bridge girders based on the computationally efficient mixed formulation that considers bond, friction, and anchorage loss effects. The mixed formulation is characterized by its fast convergence, usually with very few finite elements, and its robustness, even under severe loading conditions. The posttensioning operation is accurately simulated using a phased-analysis technique, in which each stage of the posttensioning operation is simulated through a complete nonlinear analysis procedure. Correlation studies of the proposed model with experimental results of posttensioned specimens are conducted. These studies confirm the accuracy and efficiency of the newly developed software program.

Finally, this issue of the Journal has a discussion by Elfgren of the previously published paper “Failure Load Test of a CFRP Strengthened Railway Bridge in Örnsköldsvik, Sweden,” by Bergström et al., September/October 2009, pages 300–308. The discusser has raised the concern that the failure mode of the strengthened bridge, as presented by the authors, may not be correct.