Journal of Bridge Engineering

Recently, it has come to light that footbridges may have problems with human induced vibrations if their lateral period of vibration is of the order of 1 s. This has been highlighted by the much-publicized case of the Millennium Footbridge in London. This paper describes a similar problem associated with the historic Cragside Bridge built circa 1875. This bridge is a wonderful historic bridge built in the grounds of Cragside Manor in Northumberland, United Kingdom by the famous Industrialist Lord Armstrong. An investigation of the bridge revealed that it suffered vibration problems resulting from insufficient lateral stiffness. When lightly loaded (approximately six people) the fundamental lateral natural frequency of vibration was 2.6 Hz. This mode was predominantly a lateral mode of vibration. A computer model of the bridge was developed and various loading scenarios were investigated. As the bridge is very lightweight, the computer model showed that the natural frequency could reduce to 1.12 Hz if the bridge was loaded to 4 kPa. Extra stiffening elements were added to the computer and, depending on the superimposed load, the frequency could be increased from 1.12 to 1.57 Hz (for a 4 kPa uniform live load) and increased to 3.67 Hz for an imposed load equivalent to approximately nine people. It is believed that this will help to remedy the problem, but further research is being conducted to reduce the problem further.

In the 17th century the town of Chioggia, located in the Italian Venetian Lagoon, was connected to the mainland by an unreinforced masonry bridge called Ponte Lungo (long bridge) composed of an elegant sequence of masonry arches. The bridge withstood the many vicissitudes that this part of Italy lived through as well as the increase in static and dynamic loads brought by the 20th century. However, excessively heavy reinforced concrete additions made in the 1950s to accommodate both motorized vehicles and pedestrians quickly deteriorated by concrete spalling and rebar corrosion because of inadequate design and the aggressive environment, and the additions could not provide for the ongoing increases in needed capacity. This paper describes the design and construction of the recent Ponte Lungo renovation, which is part of a massive safeguarding effort for the Venetian Lagoon carried out by the Italian Ministry of Infrastructure and Transport together with the Venice Water Authority via the Consorzio Venezia Nuova Concessionaire (New Venice Consortium). The recent renovation of the bridge reconciled the basic idea that the original beauty of Ponte Lungo should be given back to the town of Chioggia with the need for a modern highway with sidewalks and bike paths that make the bridge a “plaza on the water” to be enjoyed by inhabitants and tourists. Construction problems were taken into account from the very beginning of the design stage, and this resulted in a very speedy and efficient construction. Design took 10 months to complete, whereas construction took about 2 years for the 200 m long bridge. The bridge was dedicated and opened to traffic on June 2, 2004.

Three-dimensional nonlinear finite element (FE) models are developed to examine the structural behavior of the Horsetail Creek Bridge strengthened by fiber-reinforced polymers (FRPs). A sensitivity study is performed varying bridge geometry, precracking load, strength of concrete, and stiffness of the soil foundation to establish a FE model that best represents the actual bridge. Truck loadings are applied to the FE bridge model at different locations, as in an actual bridge test. Comparisons between FE model predictions and field data are made in terms of strains in the beams for various truck load locations. It is found that all the parameters examined can potentially influence the bridge response and are needed for selection of the optimal model which predicts the magnitudes and trends in the strains accurately. Then, using the optimal model, performance evaluation of the bridge based on scaled truck and mass-proportional loadings is conducted. Each loading type is gradually increased until failure occurs. Structural responses are compared for strengthened and unstrengthened bridge models to evaluate the FRP retrofit. The models predict a significant improvement in structural performance due to the FRP retrofit.

The computer program STRUTBOX is presented for the transverse analysis of strutted box girder bridges, and particularly for bridges designed and constructed using the strutted box widening method. The program allows the deck prestressing and other reinforcing to be proportioned for transverse flexure, and the web stirrups and slab reinforcing to be proportioned for longitudinal shear and torsion. The program also gives an indication as to the severity of shear lag effects. The program is based on the folded plate method and is no more difficult to use than a plane frame computer program. The paper also demonstrates how the results given by a folded plate analysis can be approximated by using some simple membrane force equations in conjunction with a plane frame analysis. What is particularly interesting is that there is danger in using a plane frame analysis alone to approximate the results of a folded plate analysis for strutted box girder bridges (as well as other box girder bridges) because there are significant differences in the axial force diagrams given by the two methods.

This paper presents a method of calculation of creep and shrinkage effects for composite beams. It is particularly applicable to Preflex and Flexstress beams, which are composed of a steel I-girder with the bottom flange encased by concrete. The concrete is prestressed by predeflection of the steel beam and the subsequent release after hardening of the concrete flange or by means of prestressing cables. The presented approach using concrete age-adjusted modular ratios allows the calculation of time-dependent stresses in the concrete flange due to creep and shrinkage, with sufficient accuracy for practical applications and without carrying out cumbersome numerical computations. The results can be extended directly to the analysis of ordinary steel–concrete composite beams. The main goal of the present paper is the calibration of the parameters which must be introduced to simplify the equations describing the system. This calibration is discussed and its sensitivity to some calculation inputs is presented. The conclusions are very encouraging and the simplified approach seems to agree very well with the results of the numerical approach.

Segmental bridges with unbonded prestressed tendons have some advantages over conventional concrete bridges, such as weather-independent construction and the corrosion protection of the prestressing tendons. This paper analyzes the behavior of a prestressed segmental bridge with unbonded tendons under combined loading of torsion, bending, and shear. According to experimental research, a modified skew bending model was developed to calculate the load-carrying capacity of segmental bridges subjected to combined bending, shear, and torsion. A finite element method (FEM) was used to investigate the deflection behavior of such a structure and to check the theoretical model. The theoretical and FEM research results compared favorably with test results. Finally, suggestions for the design and construction of segmental bridges with external prestressing were made.

A parametric study was carried out in order to understand the salient aspects affecting the distribution of compressive stresses in transversely posttensioned concrete bridge decks. Alternative finite element modeling techniques and alternative software were considered and the corresponding analytical results were compared with the experimental results from previous investigations. It was found that the distribution of compressive stresses is mainly affected by the support conditions of the girders and the axial stiffness of the diaphragms.

A new fatigue load model has been developed based on weigh-in-motion (WIM) data collected from three different sites in Indiana. The recorded truck traffic was simulated over analytical bridge models to investigate moment range responses of bridge structures under truck traffic loadings. The bridge models included simple and two equally continuous spans. Based on Miner’s hypothesis, fatigue damage accumulations were computed for details at various locations on the bridge models and compared with the damage predicted for the 240-kN (54-kip) American Association of State Highway and Transportation Officials (AASHTO) fatigue truck, a modified AASHTO fatigue truck with an equivalent effective gross weight, and other fatigue truck models. The results indicate that fatigue damage can be notably overestimated in short-span girders. Accordingly, two new fatigue trucks are developed in the present study. A new three-axle fatigue truck can be used to represent truck traffic on typical highways, while a four-axle fatigue truck can better represent truck traffic on heavy duty highways with a significant percentage of the fatigue damage dominated by eight- to 11-axle trucks.

In the case of horizontally curved steel I-girder bridges, girder and cross-frame members are frequently detailed for erection in the no-load condition as a matter of convention. As a result, it is imperative that the erection sequence used to construct such bridges be comprehensively studied to ensure that the no-load condition can be achieved in the field and that significant superstructure component fit-up problems do not occur. The current research investigates the erection of a recently constructed horizontally curved steel I-girder bridge, in which significant difficulties were encountered during erection. The bridge erection is recreated through an analytical simulation using a detailed nonlinear finite element model. The analytical results demonstrate that a condition that closely resembles the no-load condition can be achieved in the field during construction with the proper implementation of temporary support structures; and that the difficulties encountered during the erection of the subject bridge superstructure could not be attributed to the erection scheme followed.

The erection of horizontally curved steel I-girder bridges tends to be more complex than the erection of straight steel I-girder bridges. The erection of a curved steel I-girder bridge can be further complicated when the cross-frame members and girders are detailed inconsistently in an effort to force bridge components into some desirable geometric condition. Inconsistent detailing involves the intentional specification of cross-frame members that are either too long or too short to align with girder connector plates properly so as to force the girders into a given position, resulting in connection misalignments that must be resolved by applying external forces to the bridge components. The current research investigates the erection of a recently constructed horizontally curved steel I-girder bridge and highlights the fact that practice of inconsistent detailing can lead to very formidable and costly fit-up problems in the field; especially when girder sizes are large.

There are currently two methods of production for A 709 Grade HPS-485W (70 W)—quenching and tempering (Q&T) and thermomechanical controlled processing (TMCP). The TMCP enables plates to be rolled in longer lengths than is possible with Q&T; however, because of its recent introduction and a lack of material testing, relatively little is known concerning the effect of this new production method upon the intraplate variability of both tensile strength and toughness. Data from 96 tensile tests show that yield and ultimate strengths of HPS-485W (70 W) TMCP may be dependent upon plate thickness and orientation. The average yield strength was found to be lower than the 485 MPa (70 ksi) limit, while the average ultimate strength was within acceptable limits. Seventy-five Charpy V-Notch (CVN) specimens were tested, and all met the 48 J at $-$ 23°C (35 ft-lb at $-$ 10°F) AASHTO Zone III requirement for minimum toughness. Overall it was seen that HPS 485W (70 W) TMCP shows promise for bridge girder applications, but thicker plates do not currently meet all the ASTM A 709 standards, and should be reevaluated before being used in bridge construction on a large scale.

The seismic response of bridges isolated by elastomeric bearings and the sliding system is investigated under two horizontal components of real earthquake ground motions. The selected bridges consist of multispan continuous deck supported on the piers and abutments. Three different mathematical models of the isolated bridge are considered for the analytical seismic response by considering and ignoring the flexibility of the deck and piers. The mathematical formulation for seismic response analysis of various mathematical models of the bridges isolated by different isolation systems is presented. The accuracy and computational efficiency of various mathematical models of isolated bridges is investigated by comparing their responses under different system parameters and earthquake ground motions. The important parameters selected are the flexibility of deck, piers, and isolation systems. There was significant difference in the computational time required for different models, but it was observed that the seismic response of the bridges obtained from different equivalent mathematical models is quite comparable even for an unsymmetrical bridge. Thus, the earthquake response of a seismically isolated bridge can be effectively obtained by modeling it as a single-degree-of-freedom system (i.e., considering the piers and deck as rigid) supported on an isolation system in two horizontal directions.

In seismic analysis of bridges, the designer chooses the direction of the applied earthquake forces arbitrarily. This paper investigates the effects of seismic force direction on the responses of slab-girder skewed bridges in response spectrum and time history linear dynamic analyses. The combination rules for orthogonal earthquake effects, such as the $100∕30$ , $100∕40$  percentage rules and the SRSS method are also examined. It is concluded that either the SRSS or the $100∕40$  percentage rule in the skew direction should be used in the response spectrum analysis of skewed bridges. For time history analysis none of the combination rules provide conservative results. In this case, the application of paired acceleration time histories in several angular directions is recommended.

Two slab-on-girder bridge superstructures are analyzed using grillage models. Different live load placement configurations are investigated to determine the sensitivity of live load shear and moment to vehicle spacing. Results from both bridges show that the distribution factors are relatively insensitive to vehicle spacing. Therefore significant computational speedups are available when applying vehicle loads on an influence surface with a fixed spacing.