32 



Regarding the details of construction, it is quite proper to call atten- 

 tion to the stupid disproportion in strength of the columns, cups, and 

 sills, and particularly to the inadequate bearing areas of stringers 

 upon caps and of columns against caps and sills. 



The use of mortises for joining the columns to the caps and sills, how- 

 ever, should be discouraged. It reduces the bearing areas, increases 

 the amount of work in the fitting, provides places in the lumber for 

 the accumulation of moisture, and is in every respect an unsuitable 

 construction, borrowed from ancient roof building, where it may do 

 less harm, being all the time under cover and absolutely dry. 



1 inclose a sketch, showing a much cheaper and better construction 

 (tig. 6). In place of two vertical and two slanting legs, use four ver- 

 tical legs. It is obvious that the tit of the outside slanting legs requires 

 accurate work, consequently takes more time and money, whereas the 

 four vertical legs being of the same length, require no special fitting. 



4Strs.Lon6LeafPini 

 ^JCaps.White Oak 



'Posts 



Sills. 



Sc*L£g Inch =1 Foot 

 Fii,. 6.— Showing construction with lour vertical legs. 



Next, use three-quarter-inch iron dowel pins to connect columns to 

 caps and sills, and further use diagonal braces bolted through with 

 three-quarter-inch bolts and large 2-inch washers, so that the trestle 

 bent will be a compact, rigid structure which, if necessary, can be 

 lifted with a hoist and set up in place. 



I inclose another sketch, showing two vertical legs and two slanting, 

 outside legs, using dowel pins, wooden splice pieces, and bolts for con- 

 necting the whole in the one rigid frame (fig. 7). 



By using dowel pins the bearing of post on caps and sills is not 

 impaired. The posts can be proportioned without making additions 

 for mortises. The work of fitting is very much reduced. The larger 

 amount of ironwork in the form of bolts and washers is not a disad- 

 vantage, since these can be used again in the renewal of the structure. 



The detail of corbel bearings, as provided in Mr. Johnson's design, is 

 to be commended; but I would not commend using short stringers the 

 length of only one panel. The stringers should always be the length 



