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p.iintiiiK rclnforring stcfl which will iinl suridusly reduce the bond may be developed; 

 but with present experience galvanizing is recommended. The protective concrete 

 coating for painted structural steel and timber should be reinforced against impacts, 

 with a gahanized wire mesh. 



Reinforced structures having a "harbor" exposure begin to show crack> m the 

 more vulnerable locations in from h\e to leu years. Many have been in service ni 

 San Francisco Hay for from 10 to 15 years without serious failure resulting from the 

 cracking. Fainting the exposed surfaces with asphalt, as specified, and maintaining 

 the coating when it deteriorates will prolong the life of these structures so markedly 

 as to make them comparable to high class structural steel construction which is 

 maintained in a similar way by inspection and painting. Various modifications of 

 asphalt are being tried by harbor engineers and may result in increased efficiency. 

 Intelligent design can also prolong the life of such structures, by sulistituting 

 slabs, arches and smooth surfaces for articulated rectangular members and tee beam 

 construction, which is characterized by high concentrations of steel m webs and 

 rectangles. Adequate bracing to prevent intensive strains on rectangular frames and 

 connections under the impact of vessels will increase durability by reducing the forma- 

 tion of tension cracks. 



Encased structural steel construction painted with red lead and graphite on the 

 steel and with asphalt on the surface of the concrete should be more durable than 

 reinforcing steel construction. In San Francisco Bay much of the concrete encased 

 steel construction now showing cracks was installed when the concrete itself was 

 considered a complete protection and the steel was consequently not painted. The 

 paint coats mentioned have been specified because they are standard products which 

 have proved satisfactory on San Francisco Harbor structures. It is possible that 

 other equally satisfactory coatings may be substituted. For the asphalt coating, it is 

 suggested that suitable coatings of coal gas tar or water gas tar may prove effective 

 in excluding air and moisture. Prepared hydrocarbon paints have not proved effective 

 for this purpose, probably because they contain excessive quantities of volatiles, 

 which leave the coating porous on evaporation. Coatings applied to embedded steel 

 should also serve to inhibit corrosion in case the concrete absorbs sea water salts. 

 Of medium-priced pigments which are inhibitors, red lead has proved satisfactory 

 for structural steel in sea water exposure. Because it reduces the bond, red lead is 

 not satisfactory for painting reinforcing steel. The question of a satisfactory coating 

 for this purpose is still in the e.xperimental stage and merits the attention and study 

 of engineers. 



Concrete encased wooden piles when properly constructed have proved a 

 satisfactory type in "harbor" exposed structures. However, methods of concreting 

 the piles in place in the water ha\'e not given as satisfactory results on San Francisco 

 Bay as have those using pre-cast concrete casings, chiefly because of the difficulty of 

 placing and tamping the concrete and of preventing contact with the sea water. 

 In piles of this type the steel reinforcement is reduced to mesh or small bars so that 

 disintegration of concrete from rusting is minimized. I'nder conditions requiring 

 excessiveh- long piles, with consequent great weight and heav\- reinforcement, the 

 jacketed pile presents advantages not only in durability but also in reducing dead 

 loads and in decreasing cost of construction. 



"Composite" structures having an "ocean" exposure deteriorate rapidly above 

 the tide line, even when constructed of high grade concrete. This is probably due to 

 the heavy impacts of waves, which open cracks to the steel, combined with con- 

 centration of sea salts from repeated drenchings with sea spray. 



