Editor’s Note

This July 2011 issue of the Journal features seven technical papers and one discussion in diverse areas of bridge engineering. In “Fatigue Evaluation of Rib-to-Deck Welded Joints of Orthotropic Steel Bridge Deck,” authors Ya et al. present fatigue test results of the 300-mm-wide specimens with three details, 80% partial joint penetration (80%PJP), weld melt-through (WMT), and both combined. The specimens were cut out from the full-scale orthotropic deck specimens of 16-mm-thick deck plate. In the fatigue test, the deck plate was subjected to cyclic bending loading and the rib free from loading. The fatigue fracture surfaces show that the presence of WMT might affect the initiation of fatigue cracks. The propensity to the root cracking rather than the toe cracking has been observed. Results show that test results satisfy S-N curves in JSSC-E (80 MPa at $2\times 106$ cycles) or AASHTO-C (89 MPa at $2\times 106$ cycles).

In “Shear Lag Analysis in Prestressed Concrete Box Girders,” author Zhou presents analysis of shear lag effect in box girders by considering the effects of prestressing on shear lag in box girders. Analysis results show that the shear lag effect in box girders under prestressing is more apparent than that under uniformly distributed or vertical concentrated loads. The values and distributions of shear lag coefficients relate to the anchorage locations of prestressing and the distributions of internal forces along the girder under combined uniformly distributed load and prestressing. The negative shear lag under the uniformly distributed load and prestressing may occur both at the midspan of a simply supported box girder and at the fixed end of a cantilever box girder.

In “Comparison of Ambient Vibration Response of the Runyang Suspension Bridge under Skew Winds with Time-Domain Numerical Predictions,” authors Wang et al. present a modified version of the mean wind decomposition method that directly uses wind monitoring data from structural-health monitoring systems (SHMS). A method for the time-domain buffeting analysis is presented and is implemented in ANSYS, where self-excited forces are modeled as elemental aeroelastic stiffness and damping matrices. This entire numerical procedure, implemented in MATLAB and ANSYS, is applied to buffeting analysis of the Runyang Suspension Bridge during Typhoon Matsa. Results show reasonably good agreement between analysis and measurement data. The paper also discusses characteristics and mechanism of buffeting responses of long-span bridges for further studies.

In “Extrapolation for Future Maximum Load Statistics,” Fu et al. discuss using short-term load data to extrapolate or project to remote future maximum load, as practiced in structural design code development and/or calibration. However, this approach has not been adequately evaluated or validated because of the lack of long-term data. The authors address this issue by proposing a new extrapolation method based on the understanding of the importance of the load probability distribution’s high tail. This approach significantly reduces the mathematical length of extrapolation/projection and thus increases its reliability. The authors also evaluate the extrapolation process by using quantitative indexes.

In “Experimental Behavior of Bridge Beams Retrofitted with Postinstalled Shear Connectors,” authors Kwon et al. present experimental investigation of an approach of strengthening floor systems consisting of a noncomposite concrete slab over steel girders by connecting existing concrete slab and steel girders by postinstalled shear connectors to permit the development of composite action. Five large-scale noncomposite beams were constructed, and four of these were retrofitted with postinstalled shear connectors and tested under static load. The retrofitted composite beams were designed as partially composite with a 30% shear connection ratio. A noncomposite beam was also tested as a baseline specimen. Test results show that the strength and stiffness of existing noncomposite bridge girders can be increased significantly. Strengthened partially composite girders demonstrated an excellent ductility when postinstalled shear connectors were placed near the zero-moment regions to reduce slip demand on the connectors. The test results also show that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders strengthened using postinstalled shear connectors.

In “Indicial Functions for Bridge Aeroelastic Forces and Time-Domain Flutter Analysis,” authors Zhang et al. present a detailed numerical algorithm for time-domain flutter analysis of elongated bridges, with a particular emphasis on some problematic issues with regard to the application of the indicial functions. Theoretical description and numerical results indicate that aeroelastic forces expressed by indicial functions are equivalent to those with flutter derivatives, if the model parameters are well identified. However, this is merely an equivalence of frequency spectrum, and the transient characteristics of the indicial functions so identified may therefore be not physically true. This may result in excessively distorted aeroelastic forces and extraordinary time-consuming attenuation of the incorrect transient responses. To avoid such problems, a methodology of linear searching of the indicial function parameters in predefined ranges is developed, based on which the influence of some important factors, such as the time step size and numerical ranges of model parameters, are investigated. Numerical results show that a large time step size may induce noticeable additional phase differences between simulated aeroelastic forces and structural motions, thus affecting the total work accumulation and the flutter threshold.

In “Simplified Lateral Analysis of Deep Foundation Supported Bridge Bents: Driven Pile Case Studies,” authors Robinson et al. investigate a simplified approach for modeling soil- and foundation-system-supported bridge bents by applying it to three bridges that represent three pile types and three superstructures. This point-of-fixity approach is applied by modeling the bridge bent substructure as an elastic frame. Models of these bridges are compared through more refined analyses in FB-MultiPier, with SAP as an independent verification tool, by using pile sections with nonlinear soil, pile, and pile cap material properties. The results for simple pile bents show that an equivalent frame model provides similar moment, shear, and displacement values to those obtained from both the SAP and MultiPier nonlinear analyses. Analysis results also indicate that the equivalent frame model parameters are particularly sensitive to the comparable selection of both axial and lateral loads.

This issue includes a discussion of a technical note, “Discussion of ‘I-35W Bridge Collapse’ by S. Hao,” from the September/October 2010 issue of Journal of Bridge Engineering. In light of the collapse of the I-35 bridge, the discusser presents interesting and useful insights on important issues, such as (1) factors reducing strength and durability of steel bridge members, (2) inspectors’ qualifications to identify dangerous conditions, and (3) mandatory independent reviews of major bridge projects.