Bridges prestressed concrete

The most widely used anodic inhibitors are calcium and sodium nitrite, sodium benzoate and sodium chromate. With the exception of calcium nitrite, no other chemical is available in North America as a proprietary product. Nitrites have been used in the USA for more than 14 years and for nearly 40 years in Europe. Calcium nitrite is marketed as a non-chloride accelerator, as well as a corrosion inhibitor. For 25-30% solids in solution, dosage rates range from 2 to 4% by weight of cement depending on the application [50]. Calcium nitrite has been used in bridges, parking and roof decks, marine and other prestressed concrete structures that are exposed to chloride attack. 

Demolition of prestressed concrete bridge beams with expls 3 D62... 

Demolition of Prestressed Concrete Bridge Beams with Explosives is discussed by J.A. Dennis in Engineer Research and Development Labs Rept 1830, Fort Belvoir, Va (Sept 1965)... 

The volume includes 37 papers. Discussions cover the verification of flat plate analyses by model studies long-term behavior of small composite prestressed concrete bridge beams studies of a prestressed concrete girder with web openings the structural behavior of a hyperbolic cooling tower under static loadings models of shear wall structures ... 

In the present discussion, reinforced concrete and prestressed concrete corrosion control methods are combined. Although prestressed concrete bridges have special concerns such as anchorage in both posttensioned and pretensioned structures and ducts for post-tensioned structures, the general corrosion control methods are applicable to both prestressed and conventional reinforced bridges. 

Conventional reinforced concrete bridges refer to those with superstructures made of reinforced concrete. In general, prestressed concrete and steel bridges will have... 

Multiple Protection Systems Corrosion inhibitors are used in multiple corrosion protection systems in conjunction with epoxy-coated rebars and low-permeability concrete, in particular, for marine applications. Epoxy-coated seven-wire strands are not commonly used for prestressed concrete bridge members. Corrosion inhibitors are used in place of coated seven-wire strands in the prestressed highway construction industry. 

Even at densities of the order of 5 Amp/m the possible hydrogen-induced cracking does not favor electrochemical method of chloride removal from prestressed concrete structures. Pilot scale treatments showed it to be feasible and simple to treat full-sized reinforced-concrete bridge members, although difficult to conduct the treatment on concrete piers. One of the main difficulties is to predict the duration of treatment to reach the chloride levels to acceptable levels where corrosion is under control. Preliminary studies suggested a total charge of 600-1,500 A-h/m with a total treatment time of 10-50 days. 

Structural collapses of reinforced concrete structures due to corrosion are rare. The author knows of two multi-storey parking structures in North America which have collapsed due to deicing salt induced corrosion (Simon, 2004). A prestressed concrete bridge collapsed in Wales dne to deicing salt attack on the strands hidden from investigation (Woodward and Williams, 1988), and another one in Enrope. Usually concrete damage would have to be well advanced before a strncture is at risk. 

Galvanic cathodic protection systems have been used extensively since the early 1990s in Florida on prestressed concrete bridge support piles in the sea. One of the reasons the galvanic system is used there is because concrete resistivity is low due to the marine exposure conditions. The Florida systems frequently incorporate a distributed anode of zinc fixed on the atmospherically exposed concrete and bulk zinc anodes in the water which pass current through the low resistance sea water to protect the submerged area as shown in Figure 7.4. 

The Limon River Bridge, constructed of 95% prefabricated and prestressed concrete elements. 

Maracaibo Lake Bridge is 9 km long, situated in the southern part of Maracaibo city and spans Maracaibo Lake at one of its narrowest parts. The maximum height of the bridge table is 50 m above lake level. The bridge is a prestressed concrete structure the beams of 46.6-m length were prefabricated on shore and later incorporated in the construction process. A total of 544 beams were constructed. For the foundations prestressed cylinder piles were sunk to a maximum depth of 60 m. The bridge has 137 piers with spans of 235, 85, 46.6, and 36.6 m. 

Lee J.H., Kalkan L. Analysis of Thermal Environmental Effects on Precast, Prestressed Concrete Bridge Girders Temperature Differentials and Thermal Deformations [J]. Advances in Structural Engineering, 2012,15(3) 447 60. 

Chen, YY. et al. 2008. Design of Shenzhen Nanshan prestressed concrete continuous girder bridge with corrugated steel webs. The proceedings of 2008 national bridge academic conference 160-165. 

Wang, S. et al. 2009. Application of prestressed concrete composite box-girder structure with corrugated steel webs in bridge engineering in China. Journal of Architecture and Civil Engineering 26(2) 15-20. 

Zhu Hanhua, Chen Mengchong and Yuan Yingjie. Cracks Analyses and Control of Prestressed Concrete Continuous Box-girder Bridge. Beijing the Chinese people s traffic press 2006. p37-84. 

Nowak, A. S. Park, C. Casas, J. R. 2001. Reliability analysis of prestressed concrete bridge girders comparison of eurocode, Spanish Norma lAP and AASHTO LRFD. Structural Safety 23 331-344. 

Fig. 16.2. Recorded signals from a prestressed concrete bridge dne to different canses, from Fricker and Vogel [2006]. a) wire break, b) drilling c) chipping...

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