Quadruple riveted butt│ ¾ │ 1 │ 7.13 │ 84 │ ¾ │ ⅞ │ 1 │ 6.51 │ 83 │ 11/16 │ 1 │ 1 │ 5.84 │ 81 │ ⅝ ──────────────────────┴─────────┴────────┴────────┴──────────┴───────── Pipes used as compression members of a bridge are stiffened by riveting standard rolled steel sections longitudinally on the pipe. [Illustration: FIG. 78.—Lock Bar Pipe. ] Lock Bar Pipe is a steel pipe with a special form of joint made by the East Jersey Pipe Corporation. It is arranged as shown in Fig. 78 and has the advantage of developing the full strength of the plate. It is equivalent to a joint with 100 per cent efficiency, which permits the use of thinner plates. =101. Design of Wood Stave Pipe.=—In the design of wood stave pipe[66] the entire bursting pressure is taken up by steel bands wrapped around the outside of wood staves which make up the shell of the pipe. The pipe is not designed to resist external loads except those which may be overcome by the internal pressure in the pipe. The thickness of the staves is fixed by experience. The sizes of staves and bands recommended by J. F. Partridge[67] are given in Table 40. The size of the steel bands can be determined from the expression; _S_ = _Cr_(_R_ + _t_) in which _S_ = the total stress in the band; _R_ = the radius of the inside of the pipe; _t_ = the thickness of the stave; _r_ = the area of bearing per unit length of the band on the wood. For circular bands it is assumed as the radius of the band; _C_ = the crushing strength of wood, usually taken at 650 pounds per sq. in. The preceding expression can be derived easily by the application of the laws of mechanics, and from it the expression for the distance between bands follows logically. It is, _p_ = _S_⁄(_PR_ + _kt_) in which _S_ = the strength of the band; _p_ = the distance between bands; _P_ = the intensity of bursting pressure in the pipe; _R_ = the radius of the inside of the pipe; _t_ = the thickness of the staves; _k_ = the swelling strength of wood, usually taken at 100 pounds per sq. in. [Illustration: FIG. 79.—Shoe for Wood Stave Pipe. ] Transverse joints between staves are closed by inserting metal strips between them, or by shaping the edges irregularly so that they fit closely together with an irregular joint. Transverse joints between all staves at any one point are avoided by splitting the joints between staves. Longitudinal joints between staves are usually made smooth and are closed by steel bands which are drawn tight about the pipe by inserting the ends in coupling shoes as shown in Fig. 79. [Illustration: FIG. 80.—_B_ in Formula _W_ = _CwB_^2 ]