Papers in This Issue

This October 2013 issue of the Journal features 14 technical papers and two case studies. We begin this issue with a paper entitled “Santiago Calatrava’s Alamillo Bridge and the Idea of the Structural Engineer as Artist,” by Guest et al. The structures of Santiago Calatrava are noted for their adventurous forms, and Calatrava is heralded as a hybrid architect/engineer whose works represent an integration of both disciplines. While there have been a number of publications on Calatrava's structures, nearly all have focused on their architecture or artistry without addressing how well they fulfill the requirements or represent great works of structural engineering. In this paper, the authors perform a thorough structural analysis of one of Calatrava’s most well-known bridges to determine how well it achieves the goals of structural engineering. This work provides insight into how well Calatrava’s works represent engineering as art and what we can learn from his works in the context of great works of structural art.

Four papers in this issue focus on the evaluation of bridges or their components using different approaches. In the paper entitled “Finite-Element Analysis and Load Rating of Flat Slab Concrete Bridges,” Davids et al. build on prior studies that indicate that the equivalent-strip-width method, prescribed by AASHTO and widely used for the analysis of flat-slab bridges, may be overly conservative and may lead to underprediction of bridge structural capacity. The authors present the development of finite-element (FE) analysis software designed specifically for the load rating of flat-slab bridges. The FE software formulation and convergence have been verified by comparison with predictions from commercial FE software under realistic loading scenarios. Results of live load tests of an instrumented, in-service flat-slab bridge are reported. The FE model–predicted slab moments were shown to be conservative relative to the moments inferred from the load-test data for a range of truck positions. Fourteen in-service flat-slab bridges were load rated with both FE analysis and the equivalent-strip-width method to assess the degree of conservatism inherent in the AASHTO approximate analysis. The results show an average increase in rating factor of approximately 26% when using FE analysis and that 58% of the bridges predicted to be under capacity using AASHTO approximate methods are sufficient based on FE analysis.

In the paper entitled “Laboratory Load Tests and Analysis of Bailey Bridge Segments,” King et al. present the experimental work of two full-scale Bailey bridge segment load tests. The Bailey bridge segments were tested using a 130-t universal tester. The midspan deflections of panel assemblies were observed during the loading. Axial strains of several critical members were also measured. The axial capacities of the top chord members are compared with the calculated AASHTO nominal axial compression resistances. Experimental results are also compared with elastic and inelastic analyses using unsymmetrical sections. Test results show that (1) the inelastic lateral buckling occurred in compression chord members; (2) AASHTO-LRFD Article 6.9.4 generally predicts conservative results; (3) the effect of partial fixity of connections on the response of the structural model is insignificant and may be neglected in the analysis; and (4) a two-dimensional (2D) nonlinear inelastic analysis predicts a higher load-carrying capacity because it is not able to capture the out-of-plan stability behavior. It is recommended that Bailey-type bridges may be tested in their actual loading conditions to investigate their exact behavior, and more work is needed in the area of numerical modeling to simulate nonlinear inelastic lateral torsional behavior of Bailey-type bridges. The California Department of Transportation (CALTRANS) is currently working closely with several prefabricated modular truss bridge manufacturers to develop guidelines for temporary prefabricated modular steel truss bridges. Research findings presented in this paper are beneficial to this development.

In the paper entitled “Health Assessment of a Plate Girder Railway Bridge under Increased Axle Loads,” Srinivas et al. carry out full-scale field testing and performance evaluation studies on a typical steel-plate girder railway bridge under increased axle loads. One of the primary objectives of the study has been to evaluate longitudinal forces resulting from increased axle loads of freight wagons. The bridge superstructure is extensively instrumented to measure the responses under various static and dynamic tests carried out using the test-train formation with increased axle loading. The strategies adopted for evaluating the structural response parameters are discussed. Also, dispersion of the longitudinal force from the rail to the superstructure is evaluated using an innovative fixture along with the appropriate instrumentation scheme. It is found that around 50% of the longitudinal force generated at rail level has been transferred to the bridge substructure of the instrumented span. The remaining fatigue life of the bridge has also been evaluated using different damage models and is estimated to be around 150 years using the load spectra adopted in this study. The methodologies developed and implemented for health assessment of plate-girder bridges would pave the way for undertaking timely maintenance.

In the paper entitled “Experimental Tests of Truss Bridge Gusset Plate Connections with Sway-Buckling Response,” Higgins et al. present a research program on the experimental behavior and strength of large-size bridge-type gusset plates. The research program focused on sway-buckling behavior, and test variables included plate thickness, compression diagonal flexural stiffness, initial out-of-plane imperfection, and member-load combinations. Unique to this test program has been the direct consideration of different compression diagonal out-of-plane flexural stiffnesses on plate buckling behavior and capacity. Results showed that sway-buckling behavior and ultimate capacity were affected by initial out-of-plane imperfections of the plate and the out-of-plane bending stiffness of the truss compression diagonal. Results also showed that the effective length factor $K$, a parameter used in present load-rating guides, did not accurately predict sway-buckling capacity, and the Whitmore section approach may not be the best approximation for use in plate sway-buckling behavior. A stepped column approach has been shown to illustrate and predict the plate-member stiffness interaction on buckling capacity.

Four papers in this issue focus on dynamic behavior of bridges. In the paper entitled “Fragility Analysis of Retrofitted Multicolumn Bridge Bent Subjected to Near-Fault and Far-Field Ground Motion,” Billah et al. focus on the fragility-based seismic vulnerability assessment of retrofitted multicolumn bridge bents. Fragility curves have been developed to assess the relative performance of various retrofit methods under both near-fault and far-field ground motions. The probabilistic seismic demand model (PSDM) is used in generating the fragility functions. Using nonlinear dynamic analysis, fragility curves have been developed for multicolumn bridge bents retrofitted with four different retrofit techniques, specifically carbon fiber–reinforced polymer (CFRP) jacketing, steel jacketing, concrete jacketing, and engineered cementitious composites (ECC) jacketing. Following the performance-based evaluation approach, this study aims to investigate the effectiveness of different retrofitting methods to minimize the overall seismic vulnerability of deficient bridge bents. To investigate the seismic responses of the retrofitted bridge bents, a total of 40 earthquake excitations, of which 20 are near-fault and 20 are far-field ground motions, are used to evaluate the likelihood of exceeding the seismic capacity of the retrofitted bridge bents. The use of fragility curves for retrofitted bridge bents will aid in expressing the potential impact of retrofit on bridge bent vulnerability. The results obtained from this study indicate that the bridge bents retrofitted with ECC and CFRP jackets possess less vulnerability at different damage states under both near- and far-field earthquakes.

In the paper entitled “Experimental and Numerical Studies of Nonstationary Random Vibrations for a High-Pier Bridge under Vehicular Loads,” Yin et al. investigate the nonstationary vibration of a high-pier bridge under vehicles with variable speeds. A full-scale vehicle model with 12 degrees of freedom (DOFs) has been used, whereas vehicle wheels were considered as patch contact instead of point contact with the bridge road surface. The vehicle-bridge coupling equations were established by combining the equations of motion of both the bridge and the vehicle using the displacement relationship and the interaction-force relationship at the contact patches. The midspan deflections resulting from the stationary and nonstationary inputs were compared with the measured responses under different parameters, including vehicle acceleration and vehicle deceleration. The verified results showed that the proposed method can accurately simulate the vibration of the bridge under vehicles moving with variable speeds. Using the stationary random process to model the road-surface disturbance to vehicles with variable speeds, the dynamic effects can be either underestimated or overestimated. The proposed method was then used to study the ride comfort for vehicles moving with variable speeds on high-pier bridges.

In the paper entitled “Influence of Dynamic Properties and Position of Rivulet on Rain–Wind-Induced Vibration of Stay Cables,” Chen et al. combine an experimental study and computational fluid dynamics (CFD) simulations to investigate the influence of dynamic properties and position of upper rivulet on rain-wind–induced vibration (RWIV) of stay cables. Reproduction of the RWIV of a stay cable model is first performed based on artificial rainfall wind-tunnel tests with an ultrasonic transmission thickness measurement system (UTTMS) that can obtain the characteristics of rivulets on the surface of the stay cable model. Based on the test results, CFD simulations are then employed to study the aerodynamic influence of an upper rivulet using two different CFD models: a vibrating-cable model with a moving upper rivulet and a vibrating-cable model with a fixed upper rivulet. CFD simulations suggest that the existence of the upper rivulet does not sufficiently excite RWIV. When an upper rivulet oscillates in a specific range at the same frequency as a cable, it can significantly vary the aerodynamic force acting on the cable. In such situations, aerodynamic resonant excitation will lead to the occurrence of RWIV.

In the paper entitled “Experimental and Numerical Assessment of the Three-Dimensional Modal Dynamic Response of Bridge Pile Foundations Submerged in Water,” Wei et al. present an experimental program conducted to investigate the effects of fluid-structure interaction on the modal dynamic response of three reduced-scale bridge pile foundations submerged partially or totally in water. The vibration periods of the specimens are measured for the two lateral modes and first torsional mode using ambient and forced-vibration tests. The results are presented and discussed as a function of surrounding water levels and the number and geometric patterns of the piles. Three-dimensional (3D) FE models of the tested specimens surrounded by different water levels are built, and the results are successfully validated against the experimental data obtained. The built numerical models are used to compute 3D modal hydrodynamic pressures. A systematic analysis of the period ratios and 3D hydrodynamic loads is presented to characterize the effects of pile cap, water height, and number and geometric pattern of the piles on dynamic response. The experimental and numerical results of this research allow a better understanding of the complex, dynamically induced fluid-structure interaction effects in the response of deep-water bridge pile foundations.

Three papers in this issue are related to precast members. The paper entitled “Combined Shear and Bending Behavior of Joints in Precast Concrete Segmental Beams with External Tendons,” Li et al. investigate the behavior of joints in precast concrete segmental bridges when they are subjected to combined shear and bending. Nine specimens of precast concrete segmental beams (PCSB) with external tendons were match casted and tested: six of the specimens were tested under combined shear and bending, two specimens were tested under pure bending, and one specimen was tested under direct shear. Failure processes and modes, joint resistance, and strains of stirrups and prestressing tendons were recorded in the tests. Based on the results of the experiment, the study analyzed the mechanism of combined shear and bending resistance for dry and epoxied joints when loads are located in the immediate vicinity of the joint. Additionally, simplified failure modes of dry and epoxied joints subjected to combined shear and bending were presented in this paper. On the basis of the simplified failure modes, formulas were deduced for evaluating the resistance of joints when failure occurs in joint sections with loads applied in the immediate vicinity of the joints. The formulas provided a rational prediction of the joint resistance under combined shear and bending, which, in turn, verified the rationality of the proposed failure modes.

In the paper entitled “Structural Performance of Precast/Prestressed Bridge Double-Tee Girders Made of High-Strength Concrete, Welded Wire Reinforcement, and 18-mm-Diameter Strands,” Maguire et al. present the development of high-strength precast, prestressed double-tee girders for bridge construction. These girders use high-strength concrete (103 MPa), Grade 550 welded-wire reinforcement, and 18-mm-diameter Grade 1860 prestressing strands at 51- by 51-mm spacing. The double-tee section was used to simplify girder production and erection and maximize span-to-depth ratio, which improves construction economy and speed. To evaluate the efficiency of the developed girders, two full-scale 15.24-m-long, 1.21-m-wide, and 0.5-m-deep single-tee girders were fabricated by a precast producer and tested at the University of Nebraska structural laboratory. Transfer length measurements, development length testing, flexure capacity testing, and vertical and horizontal shear testing were conducted for each specimen. Test results have shown that the proposed high-strength bridge double-tee girder can be designed using the current AASHTO-LRFD Bridge Design Specifications. Preliminary design charts for different girder sizes were presented to demonstrate the efficiency of these girders for short- and medium-span bridges.

In the paper entitled “Performance of Posttensioned Curved-Strand Connections in Transverse Joints of Precast Deck Panels,” Wells et al. investigate posttensioned, curved-strand connections for single-panel replacement in the case of precast concrete deck panels. The capacity of the proposed curved-strand connection was investigated to compare its behavior with that of other systems that are currently in use. The curved-strand connection was found to be comparable with a standard posttensioning system. The ultimate capacity of the curved-strand connection in negative bending was found to be 97% of the standard posttensioning.

The remaining two technical papers in this issue are in different areas of bridge engineering. In the paper entitled “Portable and Rapidly Deployable Bridges: Historical Perspective and Recent Technology Developments,” Russell and Thrall present a critical analysis of the history and state of the art of portable and rapidly deployable bridge technology, primarily for U.S. systems. Four types of deployable systems are presented, including (1) rapidly erectable gap-crossing bridges (e.g., Bailey bridge, medium-girder bridge), (2) vehicle-launched bridges (e.g., armored vehicle–launched bridge, dry-support bridge), (3) river-crossing solutions (e.g., M4T6, improved ribbon bridge), and (4) causeways (e.g., Navy elevated causeway system, lightweight modular causeway system). Discussion of each design emphasizes the technology itself, its application throughout history, and evolution of the forms in relation to one another. The paper concludes with a discussion of the future of these technologies. It provides the first review of portable and rapidly deployable bridge technology in civil engineering literature and is of general interest to those who would like to learn more about this technology for military and disaster-relief purposes.

In the paper entitled “Passive Force-Deflection Curves for Skewed Abutments,” Rollins and Jessee investigate the passive force-deflection relationship for skewed abutment walls subjected to thermal expansion. To determine the influence of skew angle on the development of passive force, laboratory tests were performed on a wall with skew angles of 0, 15, 30, and 45°. The wall was 1.26 m wide and 0.61 m high, and the backfill consisted of dense compacted sand. As the skew angle increased, the passive force decreased substantially, with a reduction of 50% at a skew of 30°. An adjustment factor was developed to account for the reduced capacity as a function of skew angle. The shape of the passive force-deflection curve leading to the peak force transitioned from a hyperbolic shape to a more bilinear shape as the skew angle increased. However, the horizontal displacement necessary to develop the peak passive force was still between 2 and 4% of the wall height. In all cases, the passive force decreased after the peak value, which would be expected for dense sand; however, at higher skew angles, the drop in resistance was more abrupt. The residual passive force was typically 40% lower than the peak force. For nearly all skew angles, the transverse shear resistance exceeded the applied shear force on the wall, so transverse movement was minimal. Computer models using the plane-strain friction angle were able to match the measured force for the no-skew case as well as for skewed cases when the proposed adjustment factor was used.

In the case study entitled “Creep Effects on the Reliability of a Concrete-Filled Steel Tube Arch Bridge,” Ma and Wang determine the influence of concrete creep on the serviceability reliability of concrete-filled steel-tube (CFST) arch bridges, which have found wide application in China. The structural-creep effect was analyzed by Model B3 and the age-adjusted effective modulus method. The reliability analysis was performed by Monte Carlo simulation with Latin hypercube sampling method, considering random variables involved in three aspects: creep-model uncertainty and variations of material and geometric properties. The analytical results show that the serviceability reliability of CFST arch bridges decreases as a result of creep and that creep-model uncertainty is the most important factor for the structural creep effects and serviceability reliability.

In the case study entitled “Fatigue Life of Piles in Integral-Abutment Bridges: Case Study,” Razmi et al. present guidelines that will help determine the amount of deformation in piles, evaluate the type of deformation (elastic versus plastic), and determine the fatigue life of the piles in integral abutment bridges (IABs). To illustrate the steps of the process, the case of an IAB is studied in which the length of the bridge is varied as a parameter between 122 and 549 m. The effect of bridge length on daily and seasonal strain amplitude in piles and daily and seasonal fatigue life is evaluated. Plastic deformation was observed in all bridges analyzed, indicating a possibility of low-cycle fatigue in these bridges. Palmgren-Miner is used to evaluate the combination effects of both daily and seasonal temperature cycles and the contribution of each cycle type. The results show that daily cycles are the main cause of damage and that the contribution of seasonal temperature cycles is negligible. The fatigue life was found to be about 42 years in a bridge with a length of 122 m and decreases exponentially as the length of the bridge increases to 9.5 years in a 549-m-long bridge.