Journal of Bridge Engineering

The use of curved composite bridges in interchanges of modern highway systems has become increasingly popular for economic and aesthetic considerations. Bridges with a concrete deck composite with a steel multicell section can adequately resist torsional and warping effects induced by high curvature. Although current design practices in North America recommend few analytical methods for the design of curved multicell box girder bridges, economical requirements in the design process point to a need for a simplified design method. This paper summarizes the results from an extensive parametric study, using the finite-element method, in which simply supported curved composite multicell bridge prototypes are analyzed to evaluate the moment and deflection distributions between girders, as well as the axial forces expected in the bracing system, due to truck loading as well as dead load. Results from tests on four, 1/12 linear-scale, simply supported curved composite concrete deck-steel multicell bridge models are used to substantiate and verify the analytical modeling. The parameters considered in the study are cross-bracing system, aspect ratio, number of lanes, number of cells, and degree of curvature. Based on the data generated from the parametric study, expressions for moment and deflection distribution factors are deduced. Expressions for the maximum axial force in bracing members are also derived. An illustrative design example is presented.

When estimating the stability of a long-span bridge under wind, the basic study is most often made by considering the wind as it approaches the bridge at right angles to its long axis. However, maximum wind at a given site seldom approaches exactly normal to this axis, but will generally be skew instead. A common assumption is that a given skew wind velocity will be critical for flutter if its cosine component normal to the bridge deck equals the critical bridge normal-wind velocity. Although this does not provide a completely inaccurate estimate, the latter can be sharpened somewhat by considering an available physical approximation to the aeroelastic wind-structure interaction under the skew wind. This approximation is derivable from the experimental analysis of the wind-normal flutter condition and its associated key flutter derivatives, particularly the one linked to deck torsional instability.

This paper presents the results of a parametric study that investigated the effect of multilanes and continuity on wheel load distribution in steel girder bridges. Typical one- and two-span, two-, three-, and four-lane, straight, composite steel girder bridges were selected for this study. The major bridge parameters chosen for this study were the span length, girder spacing, one- versus two-spans, and the number of lanes. These parameters were varied within practical ranges to study their influence on the wheel load distribution factors. A total of 144 bridges were analyzed using the finite-element method. The computer program, SAP90, was used to model the concrete slab as quadrilateral shell elements and the steel girders as space frame members. Simple supports were used to model the boundary conditions. AASHTO HS20 design trucks were positioned in all lanes of the one- and two-span bridges to produce the maximum bending moments. The calculated finite-element wheel load distribution factors were compared with the AASHTO and the National Cooperative Highway Research Program (NCHRP) 12-26 formulas. The results of this parametric study agree with the newly developed NCHRP 12-26 formula and both were, in general, less than the empirical AASHTO formula (S/5.5) for longer span lengths [>15.25 m (50 ft)] and girder spacing >1.8 m (6 ft). This paper demonstrates that the multiple lane reduction factors are built into the newly developed distribution factors for steel girder bridges that were presented in the NCHRP 12-26 final report. It should be noted that AASHTO LRFD contains a similar expression that results in a value that is 50% of the value in the equations developed as a part of NCHRP 12-26. This is due to the fact that AASHTO LRFD consider the entire design truck instead of half-truck (wheel loads) as the case in the NCHRP 12-26 report and the AASHTO Standard Specifications for Highway Bridges. Therefore, this paper supports the use of the new distribution factors for steel girder bridges developed as a part of NCHRP 12-26 and consequently the distribution factors presented in the AASHTO LRFD Bridge Design Specifications.

Incremental launching is a competitive construction method for medium-span prestressed concrete bridges. Compared with other techniques for in situ casting, in short bridges it is an alternative to the use of falseworks and reduces the cost of labor with the same investment. In longer bridges it is an alternative to movable shuttering systems and reduces both investment and labor cost. Compared with segmental precasting, it may reduce both investment and the cost of prestressing, which may be partial instead of total, with the same advantages in terms of industrial production. Due to its competitiveness and overall quality, this construction method is widely used in Europe. During launch, the superstructure is moved over fixed bearings. The superstructure dead load produces temporary flexural and shear stresses within the cross section that are quite different from those produced by the service loads and, consequently, require special prestressing schemes, thoroughly illustrated in this paper.

The loads, construction procedures, and material behavior influence the performance of the bridge deck as well as its structural integrity. This paper includes a thorough investigation to identify the probable causes of cracking in reinforced concrete bridge decks, particularly at early ages. The objectives of the study were addressed through a literature review process and a comprehensive nationwide survey. Experiments were performed to establish the magnitude of the modulus of elasticity of concrete at early ages as well as the curvature it can withstand without cracking. A computer program was developed to take into account the loads due to sequence of pours. A compendium was developed to categorize the various causes of cracking to identify appropriate procedures that may control this cracking. The parameters considered in the investigation were age of concrete, stage and sequence of pours, curing procedures, heat of hydration, strength gain, thermal changes, and construction type. Results of the literature review and survey indicated that in most cases, cracking of concrete may be attributed to the high evaporation rate and high magnitude of shrinkage. Other factors include the use of high slump concrete, excessive water in the concrete, insufficient top reinforcement cover, insufficient vibration of the concrete, inadequate reinforcing details of the joint between the new and old deck, sequence of pour, and weight and deflection of the forms. The calculated curvatures for the selected bridges were smaller than the curvatures needed to crack dynamically loaded fresh concrete in a laboratory environment.

This study deals with the stress distribution in concrete deck slabs on composite steel beams used with integral abutment bridges. The applied loading is composed of one or more side-by-side HS20-44 trucks. The finite-element method is used to analyze two bridge structures with different numbers of beams, beam spacings, and supporting piles. The transverse and longitudinal slab stresses in the deck slab are investigated in the positive and negative bending regions near and away from the integral abutment. The slab stresses in the integral abutment bridges are compared with the corresponding stresses induced in the slab of equivalent jointed bridges. The results indicate that integral abutment bridges distribute the loads in the deck slab more uniformly than their jointed counterparts. The maximum stresses in the transverse direction of the slab can be 25–50% lower in the integral bridges than in their corresponding simply supported ones.

This paper deals with the behavior of reinforced concrete, partially prestressed concrete, and prestressed concrete beams, subjected to cyclic loading and then strengthened by means of external prestressing. The comparison between the experimental tests and the numerical analyses shows that the load-carrying capacity of the rehabilitated structure is greater than that of the old one plus the increase needed to cancel the bending moment decrease due to the external tendons. The prestressed concrete beam tested shows that stresses in the concrete exceed the stability limit, whereas the reinforcement does not yield. In spite of the considerable increase of its load-carrying capacity under monotonic loading, the efficiency of this beam, if subjected to a load history similar to that prior to strengthening, is doubtful.

During the last three decades, cable-stayed bridges have proven to be first-class structures providing vital transport links. Together with the construction process, erection procedure, and site conditions, the choice of material for the deck is a principal factor in the overall cost of construction. The effects of variable long-span bridge loads on the design of steel, composite, and concrete decks are investigated. Recent American and British long-span bridge loads have been used that are based on direct observations of modern traffic conditions. The three-dimensional finite-element models prepared for the study are based on the geometric and material properties of the Quincy Bayview cable-stayed bridge. Many cable arrangements are considered for the studied concrete, composite, and steel decks. A nonlinear analysis of the cable-stayed bridge models is carried out. The results of the different deck materials are compared. It is shown that the choice of material for the deck can be greatly affected by the distribution of stays and by the intensity of the live load adopted.

The objective of the work of this paper was to investigate analytically the feasibility and advantages of applying various combinations of steel jacket retrofit measures developed for single-column bent bridges to multicolumn bent bridges. To achieve the objective, an existing nonlinear dynamic bridge analysis program with elastic–perfectly plastic column behavior and a conventional hysteresis model was modified in order to include softening behavior from column damage and a more realistic hysteresis rule for cyclic loading. A 2D structural model of an actual bridge was used to evaluate column retrofitting measures by applying a typical seismic record. Both partial and full column retrofit strategies were shown to result in decreased maximum earthquake response and decreased plastic deformation of columns for the bridge bent compared to the case without retrofitting, but to varying degrees. However, for some partial retrofit strategies, the plastic hinge rotation at the unretrofitted columns was deemed to be unacceptable. Therefore, it was concluded that partial column retrofit strategies are viable only if combined with an evaluation of the ductility capacity of the bridge.