Thrust blocks

The next type of joint is weld overlays, which are often utilized to eliminate the need for costly thrust blocks [Fig. 4-2(p)]. In designing the pipe an analysis was made to ensure that it possessed sufficient longitudinal strength. It makes sense, then, to make the weld joints be at least as strong as the longitudinal strength of the pipe rather than just as an internal pressure-seal pipe. 

Thrust blocks or other approved methods or devices for anchoring mains and components should be provided where needed to prevent movement of underground lines and should not interfere with drainage for hydrants. Refer to NFPA 24 for additional guidance. 

The thrust of a rocket motor is measured statically by using load cells where axial thrust is generally measured. A rocket motor is mounted on a trolley placed on rails and the load cell fixed at the head end of the rocket is butted against the thrust block to measure the axial thrust. 

A thrust block may be defined, for our purpose, as a ceramic anchor, set in the substrate to prevent the movement of a brick facing placed over it. It is used to direct the expansion of a brick lining (or surfacing) in one direction only, rather than in both. On a floor, this may be used to prevent damage to the capping and brick lining of a trench or pit when it is undesirable to place an expansion joint adjacent to it. 

Thrust blocks are also necessary when two intercepts enter a trench close together, or at opposite sides of the trench a few feet apart. Standard design calls for an expansion joint in the brickwork not closer than 2 ft. or further... 

Fig. 1.29 A cross section of a megabar pressure cell (1) cylinder and diamond anvils (cf. Fig. 26, left), (2) piston, (3) thrust block, (4) fulcrum, (5) lever arms, (6) body of the lever assembly, (7) torque nut, (8) Belleville springs, (9) spring holder. The ratio B/A results in a 5 1 force multiplication on the piston . (Reprinted with permission from Rev. Sci. Instr., 50, 1002, (1979).)...

Up to 1914, the use of tilting pad bearings for the thrust blocks of ships had barely commenced although It was this application which was eventually going to lead to the real boom in interest In Mr. Michell s bearings. 

Wallsend test work the first pivoted pad main thrust blocks were commissioned. These were for the first all-geared destroyers, H.M.S. Leonidas and Lucifer, built by Messrs. Palmer of Jarrow and engined by the Parsons Marine Co., and the thrust blocks for the channel steamer Paris, built by Messrs. Denny of Dumbarton. Of these vessels the Paris was first on trial in June and July 1913 (8) with twin thrust blocks taking 239 kN (54,000 Ibf) each at about 300 revolutions per minute, (9). 

The largest thrust blocks made during this period were for Che battlecruiser H.M.S. Hood, launched on 22 August 1918 (16). Hood was a four screw ship with 36,000 horse power transmitted per shaft and a maximum load of 1,000 kN (224,000 Ibf) applied to each thrust bearing. Figure 6 shows models of the Mlchell single collar thrust block as installed and the multicollar version originally proposed. 

GIBSON, J.H. The Mlchell thrust block, Trans. Institution of Naval Architects, Vol 61, 1919, 248 - 259. 

SCALE MODELS OF THE MICHELL THRUST BLOCK INSTALLED ON H.M.S. HOOD AND THE PLAIN MULTICOLLAR VERSION ORIGINALLY PROPOSED. 

ONE OF THE THRUST BLOCKS FOR H.M.S. HOOD WITH THE TOP COVER REMOVED. 

Exhibit 13-44 shows one way to bun a hot line underground. The line should be backfilled with a mixture that is equal parts sand and vermiculite, allowing for a thickness of at least 4 in (100 mm) around the entire line. The line is anchored as required by the stress engineer, through the use of concrete thrust blocks. This Insulating mixture of sand and vermicu-lite allows the line to expand as necessary. 

Several equations can be used to calculate the result of Poisson s effect on the pipe in the longitudinal direction in terms of stress or strain. Equation provides a solution for a straight run of pipe in terms of strain. However, where there is a change in direction by pipe bends and thrust blocks are eliminated through the use of harness-welded joints, a... 

---