WROUGHT IRON AND STEEL BEAMS. 180 



of the subject is that of a steel rolled joist, 6 in. by 6 in. 

 by \ in. The span upon which this beam is tested is 5 ft.; 

 that is to say, there are 5 clear feet between the points of 

 the V supports, if such are used, or 5 ft. between the 

 centres ol the rotating supports, if these are employed. 

 Frequently it is found that the specimen is slightly twisted 

 or distorted, and when this is found to be so, it is necessary 

 to place some thin packing between the beam and its 

 supports, in the centre of its width, in order that the 

 reactions of the supports may come directly in the centre 

 of the beam, and not, as is sometimes the case, upon one 

 or other of the flanges. In cases where the section is not 

 symmetrical about a vertical centre line, any extra packing 

 that is required must be placed directly beneath the web. 



The load is usually applied at a point exactly midway 

 between the two outer supports, and the point of applica- 

 tion of this load is most frequently in the form of a V. 

 This V should have its edge dull or rounded, as it will be 



FIG. 91. Buckton's Presser Foot for Cross Bending Tests. 

 Effective Span = L - x. 



found that a sharp edge penetrates the metal and damages 

 the flanges of the specimen. To obviate this, unless the 

 V is made dull, a flat strip of steel about 1| in. wide 

 may be inserted between the V and the specimen. An 

 ingenious way of overcoming this difficulty has been 

 devised by Messrs. Buckton and applied to the machine used 

 by Mr. Charnock at the Bradford Technical School. The 

 principle of this is shown on Fig. 91. Here, instead of 

 the load being applied at one point, a pair of rotating 

 plates are employed similar to those used in some cases for 

 the end supports. By this means the load is more evenly 

 distributed, and the plates yield by rotation as the beam 



