timber-nailing anchorage for flooring to the top of asteel girder.Timber decking consists of two layers of 3-inchplanks. The lower layer, called the flooring, is laid atright angles to the stringers and nailed with two 60dspikes to each stringer crossing. The upper layer, calledthe tread (fig. 10-7), is laid securely and nailed at a 90°angle to the flooring.Most of the flooring planks and all of the treadplanks are cut to lengths that will bring the ends of theplanks flush with the outer faces of the outside stringers.However, at 5-foot intervals along the superstructure, aflooring plank is left long enough to extend 2 feet 8inches beyond the outer faces of the outside stringers,The extension serves as support for the curb risers, thecurb, and the handrail posts, as shown in figure 10-7.The curb risers consist of 3-foot lengths of 6 by 6timbers, one of which is set in front of each handrailpost as shown. A continuous 2 by 6 handrail is nailedto 4 by 4 handrail posts. Each handrail post is supportedby a 2 by 4 knee brace, as shown.An end dam, such as that shown in figure 10-8, isset at each end of the superstructure. This prevents theapproach of the road to the trestle from washing outor eroding between the abutment and the girders.PILE DRIVING TERMINOLOGY ANDTECHNIQUESLEARNING OBJECTIVE: Upon completingthis section, you should be able to identify thetypes of piles used in heavy construction andstate the procedures for constructing a timberpier.The principal structural members in manywaterfront structures are piles. There are differenttypes of and uses for piles. The common terms usedwith piles and pile driving are explained below.Figure 10-7.-Details of superstructure of a timber trestle.Figure 10-8.-End dam.TYPES OF PILESA pile is a load-bearing member made of timber,steel, concrete, or a combination of these materials. Itis usually forced into the ground to transfer the loadto underlying soil or rock layers when the surface soilsat a proposed site are too weak or compressible toprovide enough support.Timber BearingTimber bearing piles are usually straight treetrunks cut off above ground swell with the branchesclosely trimmed and the bark removed. Occasionally,sawed timbers may be used as bearing piles.CHARACTERISTICS.— A good timber pile hasthe following characteristics:It is free of sharp bends, large or loose knots,shakes, splits, and decay.It is uniformly tapered from butt to tip.The centers of the butt and tip are end points ofa straight line that lies within the body of thepile.Cross-section dimensions for timber piles shouldbe as follows:Piles shorter than 40 feet, tip diameters between8 and 11 inches, and butt diameters between 12and 18 inches.Piles longer than 40 feet, tip diameters between6 and 8 inches, and butt diameters between 13and 20 inches. The butt diameter must not begreater than the distance between the pile leads.PREPARATION FOR DRIVING.— Timberpiles can be damaged while being driven, particularlyunder hard-driving conditions. To protect a pile againstdamage, cut the butt of the pile squarely (so the pilehammer will strike it evenly) and chamfer it. When a10-4
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