The existing Forth Road Bridge spans the Firth of Forth in Scotland. The main suspension bridge, with central span of 1006 m, has two multi-span approach viaducts leading up to the main crossing. The deck of the approach viaducts comprises a pair of longitudinal steel box girders supporting a series of transversely spanning steel girders, both acting compositely with a reinforced concrete deck. The steel girders of the approach viaducts are supported on steel roller and rocker bearings on concrete portal piers which vary in height between 11 m and 40 m. An initial study of the bearings identified that the rollers had locked up due to corrosion and distortion, and the concrete beneath the bearings and elsewhere on the pier tops had deteriorated due to chloride contamination. Assessment showed that structural deficiencies in the pier were exacerbated by both the concrete deterioration and change in articulation.These factors led to the decision to replace all the bearings on the viaducts. This paper outlines the design of the strengthening and modifications to the bridge to facilitate bearing replacement, together with a detailed description of the design of the temporary works needed to maintain the bridge's articulation during jacking. IntroductionThe Forth Road Bridge (Figure 1) spans the Firth of Forth and was completed in 1964. The main structure is a three-span suspension bridge. At each end of the bridge, there are two multispan approach viaducts comprising a pair of longitudinal steel box girders with cross-girders supporting a concrete deck slab as shown in Figure 2. The approach viaducts carry two carriageways, each with two lanes, and extend from the abutments to the side towers, which are shared with the main suspension bridge. The total width of the structure is 36 m.The box girders rest on steel roller and rocker bearings on reinforced concrete portal piers, varying between 11 m and 40 m high, founded on rock. The articulation of the two viaducts is shown in Figure 3 During inspections and displacement monitoring, the existing roller bearings were found to exhibit little or no movement and varying amounts of corrosion. At the north side tower, the only roller bearing on the north viaduct, the roller was found to be nearing the limit of its movement range. Figure 4(a) shows a typical roller bearing, and Figure 4(b) shows the roller at the north side tower. Structural assessment of the rollers bearings to BS 5400-9-1:1983 (BSI, 1983) and BS EN 1337-4 (BSI, 2004a showed that the original bearings did not meet modern geometrical limits and were significantly overstressed to the codes.The rocker bearings were generally found to be in a better condition than the rollers, although some corrosion was present. A typical rocker bearing is seen in Figure 5. A structural assessment was also performed on the rocker bearings, which generally found that the bearings complied with the requirements set out in BS EN 1337 -6:2004 (BSI, 2004b).An inspection of the pier tops showed concrete delamination occurring at ma...

The Dubai Metro light-rail scheme is a flagship project in the United Arab Emirates and the longest fully automated rail system in the world. The first line of the rail system was opened in September 2009 with a second line due for completion in 2010. These first two lines include 35 elevated stations along their combined 76 km length. This paper describes the design and construction of the steel truss footbridges developed as part of the station context planning work for all of the elevated stations. The footbridges are all fully enclosed, air-conditioned corridors with the widths of many dictated by the provision of automated walkways. A key aspect to the footbridge design concept was to develop a modular system that could be rapidly designed for scores of differing span arrangements to be suitable for each unique location. Several of the footbridge truss elements comprised structural hollow sections, and the new rules in Eurocode 3 were adopted to design many of the connections between such members. With simply supported spans up to 45 m long and external cladding creating irregular shaped cross-sections, wind tunnel testing was required to demonstrate aerodynamic stability of the footbridges. Several erection methods were also considered to minimise the installation time of completed footbridge spans over the major Dubai highways, and the pre-camber and deflection analysis associated with the methods adopted for lifting were also important aspects considered in the design. Other critical design issues resolved included the design of fillet-welded connections in place of full-strength full-penetration butt welds and the design of several special spans for connecting into non-standard stations and entrance structures. Bridge Engineering Volume 164 Issue BE1 Dubai Metro footbridge design Smith, Smith, Chiarello and Ho

Walton Bridge comprises a steel thrust arch with pad foundations supporting a steel–concrete composite ladder deck. The arch ribs have parabolic profile and varying hexagonal cross-section, tapering from springing points to crown, and span 96·1 m. The total rise of the arch is 14·77 m with a span to rise ratio of 6·5. The bridge deck is suspended from the arch by bar-type hangers. Continuous end spans carry the bridge deck between the arch and end abutments, which are full-height reinforced concrete. This paper discusses the method of design employed, including the impact of construction methodology and environmental constraints, together with analysis of aerodynamic effects. It focuses on a number of innovations that were introduced and challenges that were resolved. Two key issues had to be addressed. First, the arch design utilising plastic section properties with reductions to account for the continuously curved steel plating making up the arch ribs. This required local non-linear analysis to demonstrate that the curved arch plating had similar, but slightly reduced, strength and ductility to an equivalent flat plate with the same width and thickness. Hand calculation methods were developed from the results of the analysis. Second, the design and specification of bar-type arch hangers for brittle fracture and fatigue, with insufficient industry guidance on either subject: there is little codified guidance on toughness requirements for bars or on fatigue testing taking angular tolerances at end connections into account, arising both from initial setting-out tolerances and displacements in service from variable actions including temperature effects.

<p>Walton Bridge comprises a steel thrust arch with pad foundations supporting a steel-concrete composite ladder deck. The arch ribs have parabolic profile and varying hexagonal cross-section, tapering from springing points to crown, and span 96.1 m. The total rise of the arch is 14.77 m with a span to rise ratio of 6.5. The bridge deck is suspended from the arch by bar-type hangers. Continuous end spans carry the bridge deck between the arch and end abutments, which are full height reinforced concrete. This paper discusses the method of design employed, including the impact of construction methodology and environmental constraints, together with analysis of aerodynamic effects. It focuses on a number of innovations that were introduced and challenges that were resolved. Two key issues were:</p><ul><li> <p>Arch design utilising plastic section properties with reductions to account for the continuously curved steel plating making up the arch ribs;</p></li><li> <p>Design and specification of bar-type arch hangers for brittle fracture and fatigue, noting that there was insufficient industry guidance on either subject.</p></li></ul>