Papers in This Issue

This February 2014 issue of the Journal features 12 technical papers, one forum paper, and one book review. Three technical papers are related to the dynamical behavior of bridges. In the paper “Time-Progressive Dynamic Assessment of Abrupt Cable-Breakage Events on Cable-Stayed Bridges,” authors Zhou and Chen propose a time-progressive nonlinear dynamic analysis approach to investigate an abrupt cable breakage event of a cable-stayed bridge. Differing from existing studies, this methodology focuses on the simulation of cable loss scenarios in a more realistic manner by incorporating stochastic moving traffic loads, dynamic bridge–vehicle interactions, and associated dynamic initial states of the abrupt cable breakage event. Several important issues associated with the proposed simulation methodology, such as the finite-element (FE) modeling option of cable breakage, different initial states of cable breakage, nonlinearity, and traffic loads, are investigated through a prototype bridge example. Finally, response envelopes in terms of moments and stresses along the whole bridge are obtained and compared by means of the proposed nonlinear dynamic simulation approach, the static approach, and the pseudodynamic approach with a dynamic amplification factor of 2.0 as recommended by the Post-Tensioning Institute (PTI) guidelines. In the paper “Cable Anchorage System Modeling Methods for Self-Anchored Suspension Bridges with Steel Box Girders,” Nie et al. investigate the multiscale modeling method for a cable anchorage system in self-anchored suspension bridges with steel box girders to improve the reliability of the conventional modeling methods. Two kinds of boundary conditions, hard and flexible, are defined and illustrated. The strategy modeling the cable anchorage system using the multiscale approach is then introduced. Based on the proposed strategy, a multiscale model of the cable anchorage system is developed for the Taohuayu Bridge, which is the largest self-anchored suspension bridge in the world. For comparison, a scale model test is carried out, and two elaborate FE models, including a traditional scale model and a full-scale model, are established according to the traditional scale modeling and full-scale modeling methods. For further validation, a full-scale whole-bridge elaborate FE model is established, called the full-scale G model. Intensive comparative study of various models demonstrates that a fuzzy region exists in the test model, scale model, and full-scale model because of the assumptions of hard boundary conditions and Saint-Venant’s principle. The fuzzy region cannot be quantitatively determined, leading to unreliable analysis results and enormous trial and error efforts. In the multiscale model, the complex boundary conditions of the cable anchorage system are accurately simulated by the flexible boundary conditions, and the influence of the fuzzy region is eliminated. The results of the multiscale model match well with the full-scale G model. It is concluded that the multiscale modeling method is the most suitable modeling method to simulate the mechanical behaviors of the cable anchorage system of self-anchored bridges with steel box girders. In the paper “Shake Table Studies of Energy-Dissipating Segmental Bridge Columns,” Motaref et al. test five one-third scale segmental bridge columns with plastic hinges incorporating different advanced materials on one of the shake tables at the University of Nevada, Reno. The columns are subjected to the Sylmar earthquake record with increasing amplitude until failure. All the models were cantilever with longitudinal steel dowels connecting the base segment to the footing. Unbonded posttensioning was used to connect the segments and to minimize the residual displacements. Energy dissipation took place mostly through the yielding of the longitudinal bars in the base segment. Conventional RC was used in the plastic hinge of a reference column. In one of the models, a built in elastomeric pad integrated with the footing and a concrete segment constituted the plastic hinge. The other two columns incorporated engineered cementitious composite (ECC) and unidirectional carbon fiber–reinforced polymer (CFRP) fabrics at the lower two segments. The effectiveness of repair with CFRP wraps was also studied by repairing and retesting the reference column. The test results showed that the proposed models with advanced materials are suitable for accelerated bridge construction in high seismic zones because of their fast construction, high energy dissipation, minimal damage in the plastic hinge zone, and minimal residual displacement.

Nine technical papers in this issue cover diverse areas of bridge engineering. In the paper “Repair of Prestressed-Concrete Girders Combining Internal Strand Splicing and Externally Bonded CFRP Techniques,” Kasan et al. present the practical case of augmenting an internal strand splice repair with externally bonded CFRP materials for the repair of collision-damaged prestressed girders, thereby overcoming the limitations of each method. They present design considerations for strand splice and externally bonded carbon fiber–reinforced polymer repair techniques both individually and in combination. A prototype example is presented. The hybrid repair approach is shown to maximize the degree of damage that may be repaired. In the paper “Prestress Loss of a New Vertical Prestressing Anchorage System on Concrete Box-Girder Webs,” Shao et al. describe a new, double-tensioned prestressing steel strands anchorage system (DTPSSAS), characterized by low prestress loss caused by prestressing tendon retraction. When it is used for short prestressing tendons in concrete box-girder webs, this anchorage system significantly reduces prestress loss. To investigate its efficiency in reducing the prestress loss, a rectangular thin plate employing the DTPSSAS is fabricated and tested. The results demonstrate that the average rate of instantaneous prestress loss decreases from 32.35% after the first tension to 2.68% after the second tension. Further, long-term observations of prestress loss with the DTPSSAS are conducted in the laboratory and in a field test. Based on the field test of a continuous concrete box-girder bridge, the average rate of instantaneous prestress loss to the control tensile stress of two strands in the web is 7.61%, and the average rate of prestress loss at 150 days is 10.53%. Concurrently, the time-dependent prestress loss is calculated with models GL2000 and CEB-FIP90 for different concrete shrinkage and creep prediction by the step-by-step calculation method. In comparison with the laboratory test results, the calculated results with the two models are greater than the test values. In addition, the effect of stress redistribution caused by the constraint of reinforcing bars to concrete shrinkage and creep is evaluated. The results reveal that the stress redistribution effect increases the vertical compressive prestress loss of concrete, indicating that the time-dependent compressive prestress loss rate of concrete is greater than the tensile prestress loss rate of prestressed tendons. In this regard, bridge engineers may need to pay attention to the stress redistribution phenomenon in vertical prestressing design. In the paper “Nonlinear Behavior and Simulation of Concrete Columns Reinforced by Steel-FRP Composite Bars,” authors Sun et al. propose steel-fiber-reinforced polymer (FRP) composite bars (SFCBs) as a new form of reinforcement for concrete structural elements, such as bridge columns. SFCBs have high initial elastic stiffness provided by the inner steel bars before yielding, positive postyield stiffness due to outer FRP after the inner steel bars yield, and superior anticorrosion performance. Furthermore, the postyield stiffness of SFCBs can be fully tailored by changing the steel-to-FRP ratio. Consequently, concrete columns reinforced by SFCBs exhibit good initial stiffness and stable postyield stiffness experimentally. One potential benefit of the stable and designable postyield stiffness exhibited by SFCB-reinforced columns is to reduce the residual displacement, which is a vital index for evaluating the postearthquake recoverability of bridges. In this paper, the mechanical properties of SFCBs and pushover behavior of concrete columns reinforced by SFCBs are first simulated numerically in OpenSees and validated with the experimental results. The influence of FRP types is further evaluated in terms of column deformation capacity. Concrete columns reinforced by steel-basalt FRP composite bars (SBFCBs) demonstrate a better performance-to-cost ratio than that of steel-carbon FRP composite bars (SCFCBs). The nonlinear dynamic analyses of SFCB columns are subsequently conducted under a suite of near-fault ground motions with noticeable acceleration and velocity pulses. The numerical results show that the residual displacement is closely correlated with the peak ground velocity (PGV) and it decreases with the increase of the postyield stiffness ratio, while the peak drift of the column stays almost the same. Finally, a design equation for residual displacement is updated with drift-dependent displacement coefficient. In the paper “Development of an Experimentally Validated Analytical Model for Modular Bridge Expansion Joint Behavior,” McCarthy et al. present the development of an analytical model representative of a common modular bridge expansion joint including its critical components, such as friction elements, equidistant devices, support bars, and center beams. The model is then validated through full-scale experimental testing of the joint. The results of this study offer a predictive model for the longitudinal motion of bridge joints excited through anticipated service or extreme events, which can be used to help determine local and global failure within the joint and make inferences as to how a bridge system could be affected. Such models provide a key step toward aiding design efforts, enabling more accurate specification of modular bridge expansion joints, and supporting functionality-based risk assessment for bridges. In the paper “Strength and Ductility of Shear Studs under Tensile Loading” Sutton et al. investigate the connection of shear studs to girders of a fracture critical bridge. Bottom flanges of a twin steel box-girder bridge are considered to be fracture-critical members in the positive bending moment region. In the event of a fracture propagating through the entire depth of a box girder, the shear studs connecting the fractured girder to the bridge deck play a crucial role in the performance of the bridge. To characterize the response of these connections, a series of laboratory tests is performed to determine the capacity and behavior associated with different stud layouts. Based on the test results, the authors propose modifications to the current American Concrete Institute equations to predict the tensile strength of shear stud connections. In the paper “Identifying Magnitudes and Locations of Loads on Slender Beams with Welded and Bolted Joints Using Strain Gauge–Based Force Transducers with Application to a Portable Army Bridge,” Bednarz and Zhu present the development of a strain gauge–based force transducer to identify magnitudes and locations of loads on noncontinuous, nonhomogeneous, slender beams with welded and bolted joints. The slopes of the bending moment curves on the two sides of a load are calculated from measured strains on a beam. Four uniaxial strain gauges are mounted to the bottom surface of the beam, with two strain gauges on each side of the load, to form a force transducer. A calibration method developed earlier can be used to account for the discrepancies between the theoretical and actual scaling factors. Four or more force transducers are needed for calibration in this work. The force transducer methodology is experimentally validated on a continuously tapered aluminum beam with a series of welded joints, a half aluminum and half steel beam with two different cross sections and a bolted joint, and a full-scale portable army bridge at the U.S. Army Aberdeen Test Center. In the paper “Capacity Assessment of V-Shaped RC Bridge Bents,” Lomiento et al. present a validation of the assessment of the flexural and shear capacity of two V-shaped RC bridge bents against experimental results from tests on one-third scale specimens. A numerical procedure based on iterative analyses taking into account the variation of vertical loads in the bent’s columns provides a satisfactory prediction of the bent’s overall performance. Based on its general agreement with the experimental data, the numerical model is also used to investigate the uneven distribution of axial load and shear force between the two columns of each bent. Three models are compared for the assessment of the shear capacity of the specimens. All the models identify the compression column as the most critical in terms of shear capacity, as confirmed by the experimental results. The University of California at San Diego model, which introduces an additional contribution due to the compression strut along the column length, appears to be less sensitive to axial load variations and to provide a reliable assessment of the shear capacity of the bents. In the paper “Live Load Distribution Factors in Two-Girder Bridge Systems Using Precast Trapezoidal U-Girders,” Mensah and Durham investigate the lever rule method to determine live load distribution factors (LDFs) in two-girder bridge systems. This method is typically more conservative than the simplified equations, which take into account key parameters such as beam spacing, span length, longitudinal beam stiffness, and slab thickness. The lever rule method for yielding LDFs does not take into account these key parameters and only considers a simple span distribution, therefore a certain degree of conservatism is implied. This study demonstrates that the lever rule method in determining LDFs in two-girder bridge systems using precast trapezoidal U-girders is not overly conservative as comparisons between live load distribution factors from finite-element analysis and the lever rule method of the AASHTO LRFD show that the lever rule method produces values for LDFs that are closely reflective of the actual response for shear and to a lesser degree for flexure. The effects of live load on parameters that include flexural response, slenderness, and span length are also considered. In the paper “Contribution of Vertical Skin Friction to the Lateral Resistance of Large-Diameter Shafts,” Ashour and Helal present a model that calculates the vertical skin friction induced by the vertical displacement component of the shaft deflection and section rotation via the utilization of a $t\text{-}z$ relationship. The model determines the shaft deflection resisting moment caused by the axial skin friction on the passive side of the drilled shaft. Up to a 40% increase in the shaft-head lateral stiffness ($K_d$; i.e., stiffer foundations) could develop as a result of the consideration of the vertical side shear resistance. The superstructure lateral response would be influenced by the variation of $K_d$. The study also shows the degrading effect of the vertical side shear on the shaft lateral stiffness with the increase of the shaft deflection. A number of full-scale drilled shaft load tests are used in comparison with the results obtained from the presented model to highlight the contribution of the vertical skin friction caused by shaft deflection/rotation to the lateral resistance of large diameter shafts.

This issue of the Journal includes the forum “Empirical Design Rules for Effective Utilization of Orthotropic Decks,” by Wolchuk. Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the Journal. This issue of the Journal also has a review of the book The Roebling Legacy, by Clifford W. Zink. The Brooklyn Bridge is the most famous bridge in America and the crowning achievement of the Roeblings. The book chronicles the story of the Roeblings and their remarkable engineering legacy over two centuries.