Journal of Bridge Engineering

A new concrete bridge deck cast onto glass fiber–reinforced polymer (GFRP) stay-in-place (SIP) structural forms is studied. The forms, which replace the bottom layer of conventional rebar, are essentially flat plates with T-up ribs. They span between support girders spaced at 1,772 mm and are lap-spliced using adhesive and mechanical fasteners. Special attention was given to the detailing of monolithic connections between the deck and girders to simulate continuity. The flange of the supporting concrete girders had a rough surface finish and protruded steel stirrups and mimicked AASHTO Type III girders. Five full-scale decks were tested to (1) compare the novel system with a conventional RC deck, (2) examine the effect of eliminating a top layer of orthogonal GFRP rebar, (3) assess a practice commonly used in bridge deck tests of using simple spans resting on neoprene pads, neglecting connection to girders, and (4) examine a commercially available all-GFRP deck, using the same GFRP panels but with a top GFRP plate fastened to the T-up ribs. Four auxiliary flexural specimens were tested to examine the lap-splice. The concrete deck with GFRP SIP form showed 33% higher strength than the conventional RC deck. It also achieved a peak load 7.8 times higher than the service load plus impact. Deflection under the service load was less than span/1,600. Remarkable deformability and pseudoductility was achieved at ultimate load, beyond punching shear, because of the progressive failure of the lap-splice. The simply supported deck failed at a slightly lower strength than the monolithically cast one but had a much lower stiffness.

The main objective of this study was to develop a rapid and effective repair method using carbon fiber–reinforced polymer (CFRP) fabrics for earthquake-damaged circular RC bridge columns based on apparent damage states. A computational method was developed to estimate the shear resisted by concrete, spirals, and CFRP jacket and the confinement pressure provided by spirals and the CFRP jacket using measured strains at different damage states. It was concluded that even yielded spirals partially contribute to shear strength in damaged columns; however, their contribution to confinement is negligible. Based on this finding, repair design guidelines for standard columns were developed to aid bridge engineers in quickly determining the number of CFRP layers needed based on the apparent damage, column aspect ratio, diameter, and longitudinal steel ratio. In addition, a simple softened steel material modeling method was developed for use in pushover analysis of repaired columns, and good agreement was observed in terms of stiffness, dissipated energy, and strength between the measured and calculated responses.

Efforts to prevent the debonding failure mode of externally bonded fiber-reinforced polymer (FRP) strengthening systems have led to the investigation of many different kinds of anchorage systems. An effective anchorage system allows externally bonded FRP reinforcements to continue carrying load, even after debonding occurs. In this study, an experimental program was performed on six full-scale RC T-beams strengthened in shear using externally bonded carbon FRP sheets with three different anchorage systems, the so-called (1) discontinuous mechanical anchorage (DMA) system, (2) sandwich discontinuous mechanical anchorage (SDMA) system, and (3) additional horizontal strips (HS) system. The experimental results showed that the SDMA system performed best, followed by the DMA and HS systems. The RC T-beams strengthened with the SDMA system showed a 59–91% increase in shear strength, altering the failure mode from FRP debonding to FRP rupture. In addition, the shear contribution of internal transverse steel reinforcement (stirrups) changes, depending on the types of anchorage system.

This paper presents the behavior of a new composite deck system for twin-girder bridges subjected to moving-wheel fatigue load. The one-half scale system consists of a RC slab with transverse rib stiffeners welded to steel deck plates, which can eliminate the need for posttensioning frequently required for twin-girder bridges. A carbon-fiber-blended cementitious adhesive is used to improve the bond between the concrete slab and the steel deck. The response of the deck system shows a rapid increase in deflection within early fatigue cycles, followed by gradual development when the cycle and loads increase. Energy dissipation of the slab and the level of elastic recovery are discussed. A damage index based on the two-term Weibull function is employed to quantify the degree of fatigue damage. The Weibull damage model reasonably agrees with the simple Palmgren-Miner rule from a practical point of view and supports the adequacy of the proposed system in fatigue configurations. A postfatigue test is conducted to examine the residual capacity of the deck system with emphasis on bond performance of the cementitious adhesive. Bond failure between the concrete and steel deck is not observed, thereby corroborating the effectiveness of such an adhesive on improving the composite behavior of the system.

To study extremely low-cycle fatigue performance of steel bridge structures, a total of nine steel bridge piers with unstiffened thick-walled box sections were tested in this study. The effects of various parameters, including cross-sectional shape (with or without an extension part), loading pattern, and width-thickness and slenderness ratios were investigated. Experimental results demonstrate that ductile cracks occurred at the column base in all specimens regardless of cyclic-loading histories and that ductile crack initiation life is sensitive to loading pattern, cross-sectional shape, and the width-thickness ratio. In all tests, the ductile crack began in the pier-to-base weld, and subsequent cyclic loads resulted in the ductile cracks growing at the weld toes along web and flange directions and then propagating into the base metal, which triggered an obvious decrease in strength capacity. A significant delay was observed between ductile crack initiation and maximum strength capacity. Moreover, ductile crack initiation and propagation may be accompanied by local buckling.

Two precast prestressed high-strength concrete and high-strength self-consolidating concrete pedestrian bridges were designed and erected in Rolla, Missouri, for an in situ investigative study to monitor time-dependent losses. Using the temperature and strain data monitored by the vibrating wire strain gauges within the beam cross sections, time-dependent losses were determined and compared between the bridges and various empirical expressions presented by AASHTO and the Precast/Prestresed Concrete Institute.

Multiattribute utility functions are widely used for multiobjective optimization of project selection problems in network-level bridge management, based on their capability of incorporating multiple performance measures and decision-makers’ preferences. However, the existing way of using them needs to be improved. First, the addition of individual projects’ utility values to obtain a total utility score for a candidate project portfolio may lead to biased solutions because such additivity property is not always valid. In addition, there is an increasing need to express the network-level performance of bridges in terms of raw performance measures, which are most meaningful to decision makers, to reflect the impacts of systemwide investment. To address these issues, the paper presents a method that first evaluates the network performance of each candidate project portfolio using network-level performance measures prior to employing a multiattribute utility function and then identifies the optimal portfolio with the best network performance. This method effectively incorporates decision-makers’ preferences into decision making, avoids possible bias from nonassumption of additivity, and interprets investment performance directly in terms of raw performance measures.

Thermal gradients were measured through the section of the I-35W St. Anthony Falls Bridge, a posttensioned concrete box girder bridge in Minneapolis, Minnesota, over the course of 3 years. The magnitudes and shapes of the measured thermal gradients were compared with various design gradients, and a fifth-order curve was found to best approximate the shape of the gradients. The responses of the structure to the largest measured thermal gradients were compared with stresses and deformations predicted by finite-element modeling given applied design gradients. The measured structural response was found to be best predicted when the finite-element model of the bridge was subjected to a fifth-order design thermal gradient scaled to match maximum top surface temperature values proposed by AASHTO LRFD Bridge Design Specifications for the region. Stresses and deformations predicted by finite-element modeling using the AASHTO LRFD bilinear design gradients were found to be considerably lower than those derived from measured results. Recommendations for design thermal gradients are proposed.

Recent research has shown that the dynamic amplification factor (DAF) to be applied to free-flowing traffic-induced load effect may not be as high as previously thought. Therefore, congested traffic states may govern extreme load effect at lower bridge lengths than currently assumed. Thus, there is a need for a methodology that incorporates both free-flowing and congested traffic states in the calculation of lifetime load effect. It should allow for the relative frequency of occurrence of the different forms of traffic and any form of DAF function that may arise. This paper presents such an approach and also presents a general probabilistic DAF formulation for inclusion. Using measured traffic, the approach is applied to a range of bridge lengths and load effects employing a variety of DAF approaches from the literature, in addition to the new DAF formulation. Using a critical traffic index, it is shown that the governing form of traffic is very sensitive to the dynamic amplification model used. Further, depending on this model, congested traffic can govern short spans, and for other spans, a combination of free- and congested-flow traffic states must be considered.

A new concept has been developed for connecting spread footings and precast columns in bridges. The socket connection is constructed by precasting the column, erecting it, and casting the reinforced concrete footing around it. This system saves construction time on site because, in little more than the time needed to construct the footing, both the column and footing can be constructed. Site erection is facilitated by the fact that the field tolerances are essentially unlimited. The longitudinal column bars are straight and are terminated with mechanical anchors. This arrangement improves constructability, because no bars cross the interface between the column and footing, and it provides better transfer of forces in the connection region than is possible with conventional bent-out longitudinal bars. The surface of the column is roughened to improve adhesion to the surrounding cast-in-place concrete. Axial-load tests demonstrated that the connection can resist column axial loads far above those expected in practice. Cyclic, lateral-load tests demonstrated that the seismic performance of the connection is at least as good as, if not better than, that of a comparable cast-in-place system. The recent deployment of the new system in a highway overpass provided both field experience and initial estimates of the potential time savings.

Conventional design and evaluation procedures usually classify steel through-truss bridges as single-load-path structures; however, their historic performance has demonstrated considerable structural resiliency. This paper presents a study of the Grand River Bridge, a Pratt through-truss bridge in Cayuga, Ontario, Canada, that systematically investigates the load paths not conventionally assumed in design and evaluation. The bridge with individual truss members removed was analyzed using nonlinear finite-element analyses to investigate the alternative load paths and associated critical members and responses. A system reliability analysis was conducted to evaluate the failure probabilities of the bridge accounting for the member resistance uncertainties. The bridge was found to be sufficient to carry its nominal dead load, even for the worst case of removal of an end post. The end bottom chord and hanger vertical were found to be the critical tension chord and web member, respectively. If multiple alternative load paths exist, the variability of the system collapse load is much less than that of the critical member resistance.