Bridges substructures

Marti, T., Rbsselet, S. J., Titani, K., and Walsh, K., Identification of disulfide-bridged substructures within human von Willebrand factor. Biochemistry, 26, 8099-8109, 1987. 

Two more complex examples of this reaction type are used in work on the total synthesis of quinocar-cin and gelsemine. A vinyl sulfide is employed as nucleophile in an Af-acyliminium cyclization to produce the bridged substructure of quinocarcin (equation 96).A genuine equivalent of the Mannich reaction is put to practice in a synthetic approach to gelsemine (equation 97). The iminium intermediate, simply generated by protonation of the enecarbamate, apparently reacts only with the enol shown in (128). 

Galvanized-steel rebars can be used as a preventative measure to control corrosion in reinforced concrete structures exposed to carbonation or mild contamination with chlorides, such as chimneys, bridge substructures, tunnels and coastal buildings. 

In the 1980s, anodes based on titanium meshes activated with special oxides (especially ruthenium and iridium) or conductive paints were developed. The technique, by now utihsed beyond North America, is applied not only to bridge decks, but also to bridge substructures (girders, cross beams, piers), and marine structures, parking garages, industrial, office and residential buildings, etc. 

Schell HC, Manning DG. Evaluating the performanee of cathodie proteetion systems on reinforced concrete bridge substructures. Materials Performance, July 1985. 

Figure 7.5 Thermal sprayed zinc being applied to a bridge substructure in the Florida Keys. Courtesy Florida DOT.

This has recently been developed further into a small yogurt pot sized anode with a single connecting wire that can be inserted into core holes in the concrete and wired together to produce a galvanic discrete anode system (Figure 7.8). They have been used predominantly on multi-storey car parks and on bridge substructures. 

Has performed well in bridge substructures and steel framed masonry and brick clad buildings and monuments. 

Figure 7.14 Conductive mortar anode applied to a marine bridge substructure.

Inevitably an inhomogeneous material like concrete will show variation in the chloride content nnless very large samples are taken due to the variation in the ratio of paste to aggregate. There will also be some variation due to the local ability of the matrix to resist chlorides. Further, in many atmospherically exposed structures there will be very large differences in chloride content due to the differences in exposure. For instance, on a bridge substructure there will be areas of water rundown that are exposed to very high levels of chlorides while adjacent areas are comparatively unaffected. Chloride laden water may pond at some sites (e.g. on the top of beams, especially if they are horizontal). At the bottom of the beam the water may evaporate leaving the chloride behind. 

Charleson, A.W.(1970) The Dynamic Behavior of Bridge Substructures. University of Contebury, Christchurch, New Zealand. 

Properties of a Bridge Substructure. Bulletin of the Seismological Society of America, Vol.61, No.6. 

The concrete strength grade of main girder is C50, and its elastic modulus is 3.45 x 10" MPa. The concrete strength grade of bridge substructure is C30, and its elastic modulus is 3.00 X 10 MPa. Posson s ration of concrete is 0.2. Mander model (Zhang 2003) is used to define the constitutive model of pier concrete, which is the constitutive model of confined concrete. 

Intermediate piers of road bridges with beam, slab, box and mixed decks consist of solid or void columns with or without caps and bearings located between the superstructure and its piers that transfer action effects from decks to bridge substructures. 

Figure 3.2 Chloride profiles of marines bridge substructure (Yaquina Bay bridge soffit)...

Encasement on substructure columns is less routine than overlay application on decks. The concrete is broken out w here it is damaged and an oversized shutter is applied. Concrete is then pumped or placed into the shutter enlarging either the whole column or the damaged section. This technique is extensively applied on structures such as vharves and bridge substructure.s in marine environments. 

The ability of nitrites to stop corrosion when added to concrete has been known for many years and a proprietary calcium nitrite additive has been used in a number of structures including bridges and car parks, Florida DOT is carrying out trials of the use of calcium nitrite in their bridge substructures to prevent marine corrosion in the bridges on the Florida coast. 

There are several hundred bridge substructures protected with coating anodes in the UK and Europe, and dozens of buildings. There are also hundreds of parking structures in the USA and Canada with conductive paint coating anodes applied to them,... 

Figure 6.14 (a) Thffrmal sprayed zinc anode being applied using an electric arc. (bj The bridge substructure can be fully enclosed to avoid environmental contamination. 

One of the earliest experiments with a clamp on anode system was on Oregon Inlet bridge in North Carolina, This system consisted of plastic strips ivith a conducting gel on the in.side that were fixed vith plastic screws on to the bridge substructure. The problem was the even flo v of current as there were too few anodes, too widely spaced apart (Figure 6,16). This system was not pursued and the bridge was destroyed in a gale around 1990. 

Severe corrosion of reinforced concrete bridge substructures in the splash zone in Florida coastal condition. has led to work on systems for use in those conditions only by Florida DoT. Several clamp on systems have been on trial including conductive rubber mats with zinc metal and wood or recycled plastic clamps with zinc or titanium mesh. The sea vater ensures a good electrical (ionic) connection to the concrete. The systems work from low tide level, or below, up to the top of the splash zone. Some have been in operation for several years. A system using tape and plates to secure the titanium mesh anode has also been experimented with in Australia, along with a scre v on plate (Figure 6.17). 

Figure 6.1-6 The experimental clamp t>n anode system t>n a bridge substructure.

The two zinc systems described above, the thermal spray and the clamp on system, have also been tested as SACP for bridge substructures in marine conditions. 

Sacrificial anodes can be used in continuously w etted environments. These systems are not yet fully understood but they seem to be. successful as arc sprayed zinc on marine bridge substructures. They need less maintenance than the impressed current systems. One problem with the zinc system is the environmental impact during. praying. If enclo.>iure is required during spraying, the costs can be very... 

Field tests in the Florida Keys showed that the anodes retained physical integrity for at least 4.5 years. Laboratory test indicated that concrete resistivity does not represent a main limiting factor in performance of such anodes and that periodic water contact (as encountered in the splash/evaporation zone of marine bridge substructures) is actually necessary for long-term anode performance. This low-cost method is a competitive alternative to impressed current cathodic protection systems and a significant improvement over gunite repairs. SHRP-S-405, 10... 

Collision forces on bridge substructures are commonly applied as follows ... 

Hoit, M., McVay, M., and Hays, C. 1996. Florida Pier Computer Program for Bridge Substructure Analysis Models and Methods , Conference Proceedings, Design of Bridges for Extreme Events, FHWA, Washington, D.C. 

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