Bridge members

E.R. Evitt, Catalytica Associates, Inc In their work with amide-linked cofacial porphyrins, Collman and Anson have only observed 100% four-electron O2 reduction in the four-atom-bridged member of the series. Your comments implied four-electron O2 reduction is observed with the five and eight as well as four-atom bridged methylene-linked cofacial porphyrins you have prepared. Is such activity observed for the compounds with longer linkages ... 

Investigations on the electron spin resonance of the radical anions 29 31> of [2.2]-and higher [n.n]paracyclophanes have shown that delocalization of the unpaired electrons over both aromatic nuclei is scarcely possible until the number of bridge members n >3 31>. In open-chain compounds of the type Ar-[CH2] -Ar the corresponding condition is n> 1. This would suggest that the mechanism responsible for the transfer of elec-... 

The term restricted is employed here to distinguish this system from annulated, de-hydro, and bridged members of the family. 

Reliable nondestructive methods for providing assurance to the owners that the built structures have met constmction specifications are not available. The main concern is whether the ducts in the posttensioned bridge members have been completely filled with the grouts and whether there is uniform coverage over the prestressing steel. 

An FHWA study by Thompson and Lankard (19, 20) reviewed the effect on the corrosion of steel in the concrete of several variables, including cement type, mineral admixtures, water-to-cement ratio, and aggregate type. This study showed silica fume to be the most effective mineral admixture in the mitigation of corrosion of steel rebar. It also suggested that careful selection of the concrete mix components could extend the life of a concrete bridge member. It is estimated that use of a silica fume admixture provides an increase of expected life of 10 years beyond that provided by black steel rebar in conventional concrete. 

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. 

YP Virmani, Corrosion Inhibitors for Bridge Members , FHWA Technical Note on Corrosion Protection Systems, Structures Division, Office of Engineering Research and Development, Dec. 1997. 

Virmani, Y.P. (1997). Corrosion Protection Systems for Construction and Rehabilitation of Salt-contaminated Reinforced Concrete Bridge Members. Proceedings of the International Conference on Repair of Concrete Structures - From Theory to Practice in a Marine Environment, Svolvaer, Norway, pp 107-122. 

In addition to the rehabilitation techniques produced in Step 9 for the fatigue-life extension of critical bridge members and their connections, a set of alternative rehabilitation scheme will be produced which can be used efficiently and economically to improve overall static and dynamic service-load capacity of each characteristic group of the railroad bridge structural systems. For this purpose various repairing and strengthening schemes will be analysed from the engineering point of view. 

The holding plate 70, as best shown in Fig. 15, is provided with two types of spaced perforations 72 and 73, the former constituting circular boles and the latter being in the form of spaced, substantially semi-circular openings separated by an intermediate bridging member 74 integral with the plate 70. 

The generalized reliability index as a standard reUa-bility measure of bridge members may be defined as ... 

Metallophosphorus compounds may be divided into two broad classes (1) those which contain phosphorus (P) and metal atoms (M) only (2) those which contain phosphorus, metal and at least one other kind of atom E, where E is most commonly C, bnt can also be B, N, O, S or almost any other non-metal (p-block) atom. Most compounds in this latter class contain at least one E-P-M bridge. Members of class (1) (Sections 8.1 through 8.7) are usually known as metal phosphides, and most of those belonging to class (2) (Sections 8.8 through 8.20) as metallophosphorus complexes. 

FIGURE 1.3.1 The underside of a steel bridge member exhibiting significant corrosion. Courtesy of the Texas Department of Transportation, 2007. All rights reserved. 

National Cooperative Highway Research Program (NCHRP) (1985a), Report 226, Damage Evaluation and Repair Methods for Prestressed Concrete Bridge Members . 

Shanafelt, G. O. and Horn, W. B. (1980), Damage evaluation and repair methods for prestressed concrete bridge members . National Cooperative Highway Research Program (NCHRP) Report 226, Project No. 12-21, Transportation Research Board,... 

Bassetti, A., Nussbaumer, A. and Hirt, A. (2000a), Fatigue life extension of riveted bridge members using pre-stress carbon fibre composites , in Steel Structures of the 2000s, ECCS, Istanbul, pp. 375-380. 

Liu, X., Silva, R R. and Nanni, A. (2001), Rehabilitation of steel bridge members with FRP composite materials . Proceedings of CCC 2001, Composites in Construction, Porto, Portugal, October 2001, eds J. Figueiras, L. Juvandes and R Furia, pp. 613-617. 

Bassetti, A., Nussbaumer, A., Colombi, P., 2000b. Repair of riveted bridge members damaged by fatigue using CFRP materials. In Advanced FRP Materials for Civil Stmctures, Bologna, Italy, 19th October 2000, pp. 33—42. 

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