Bridge Structures

Failure analyses of cracked splice plates made from ASTM A514 quenched and tempered steel revealed that the steel was inadequately tempered, resulting in an excessively hardened, brittle defective steel. Consequently, this steel was also susceptible to stress corrosion cracking/hydrogen stress cracking (SCC/HSC). The I-275 twin bridges contained large quantities of A514 steel that needed testing to identify any remaining defective steel. A test plan was developed that incorporated hardness testing to discriminate between acceptable and the defective A514 steels. The plan incorporated the use of the ultrasonic contact impedance and impact hardness test methods. Field hardness testing was conducted over a 10-week period beginning in October 2008. During the testing, two additional cracked splice plates were discovered that contained defective A514 steel. The hardness test methods were successfully used to identify 14 defective A514 steel plates on the two bridges.

The structural response of a steel orthotropic bridge deck is characterised by the complex interaction between its components. In the case of ribs passing continuously through cutouts in the floor beam web, the floor beam exhibits a Vierendeel type truss behaviour. The paper presents the results of a parametric study for 10 trapezoidal rib geometries in conjunction with eight types of floor beam cutouts to determine shape factors. Five rib depths of 200, 250, 300, 350 and 400 mm in conjunction with three angles of inclination 10/3, 20/9 and √3 (corresponding to h/h’ values of 10/10.44, 10/10.97 and 10/11.55 as defined by AASHTO LFRD Code) are studied. Shape factors were determined as a design aid to engineers. In addition, the results are compared to measured values derived from a full-scale orthotropic plated test specimen, especially intended for this purpose. The comparison results validate the calculation model.

Cable-stayed bridges with straight and curved deck geometry are studied for their free vibration response. A study on cable-stayed bridges with a single pylon with equal side spans is presented in this paper. Three-dimensional geometries of cable-stayed bridges with spans 120–240 m, A-shaped and H-shaped pylon are numerically investigated using FEM software ANSYS. Further response of straight bridges under El Centro earthquake loading is presented using dynamic time history analysis and the results are studied for different geometries. The effect of induced curvature in decks introduces coupling of different modes even at their initial phases whereas the modes are quite distinct in straight bridges. Under El Centro load time history bending stress, shear stress distribution in decks is studied for different geometries of straight bridges which gives the typical behaviour pattern of load sharing among the components of the cable-stayed bridge.

The construction of a new 2.4 km long bridge, crossing the sea strait between the Croatian mainland and the Pelješac Peninsula to provide the fixed road link between the whole of Croatia, has just begun. The bridge location is in a highly seismic zone with the design ground acceleration of 0.41g and on extremely bad soil. The four-lane road bridge consists of two approach bridges and the main cable-stayed bridge with continuous steel trapezoidal box superstructure. Nonlinear modal time history analysis, based on superposition of Ritz vectors, but with coupled modal equations, was utilized for seismic design. Real earthquake accelerograms for earthquakes in the vicinity (Bar, Ulcinj, Ston) and also El Centro earthquake, as well as 72 artificial accelerograms, determined by seismic study for the specific bridge location, were analysed. The analysis was carried out taking into account the proposed construction sequence.

Presented in this paper is the original seismic design and the seismic performance retrofit study against large-scale earthquakes of the Akashi Kaikyo Bridge. The Akashi Kaikyo Bridge is the world’s longest suspension bridge and was completed in 1998. In the original seismic design, an inland near-field earthquake with large magnitude was not considered for the seismic design force. Although the bridge encountered the Hyogo-ken Nanbu Earthquake in 1995, it was not seriously damaged since the earthquake occurred during its construction. Therefore, a seismic performance retrofit study against large-scale earthquakes has been started. In the seismic performance retrofit study, site-specific large-scale earthquakes including inland near-field earthquakes were defined based on the latest seismological information. As a result, it was found that target seismic performance was ensured by taking some minor countermeasures.

Forth Road Bridge is a long-span suspension bridge with a main span of 1006 m and side spans of some 408 m. Approach viaducts to the north and south bring the total length of the structure to just under 2500 m. The bridge was opened in 1964 and is used by over 24 million vehicles each year. All of the maintenance work on the bridge that requires lane or carriageway closures is carried out overnight or during limited weekend carriageway or lane closures to minimise delays to users on this important strategic and commuter route. During the first internal inspection of the main cables carried out in 2004 (40 years after opening) significant corrosion was found, leading to the retrofitting of acoustic monitoring and a system of dehumidification on the main cables. In addition, a second internal inspection was carried out in 2008 to try to establish the rate of corrosion found in the cables. The inspections and retrofitting works are described elsewhere. This paper deals with a feasibility study to determine if the main cables on Forth Road Bridge could be either replaced or augmented in the event that corrosion continued following the retrofitting of the dehumidification system. Another key area that was examined as part of the study but does not form part of this paper was the long term structural integrity of the cable anchorages.

Two techniques to upgrade the ductility and the shear capacity of reinforced concrete beams of existing highway bridge bents were examined. An experimental programme that consisted of three scaled models was conducted. The specimens were tested using statically reversed cyclic loading. The first specimen was a control specimen. The beams of the other two specimens were upgraded. External steel plates were bonded to the beam in the first upgrading technique and external steel rods were employed in the second upgrading technique. The characteristic behaviour of each specimen was experimentally clarified in terms of hysteretic behaviour, displacement response ratio, maximum displacement, damage propagation, energy dissipation, equivalent damping factor, and final failure mode. The study revealed that the two upgrading techniques could result in enhancement of the overall behaviour of the bridge bents. Upgrading the beams utilising external steel rods, however, was shown to be more effective in resisting future earthquakes. Analytical modelling of the highway frames utilising FEM was performed. The numerical simulation resulted in a satisfactory accuracy of the predicted behaviour. A calibrated baseline FE model was derived and could be employed to quantitatively identify the strengthening effect on resulting behaviour of the bridge bents. The study provides an addition to the experimental data for ductility and shear capacity enhancement of bridge bents, and may assist selecting the most appropriate upgrading technique.