Maximum Load on a Lintel. 



BY K. C. ^IURPH^•. 



The following method of finding the maximum load carried by a 

 lintel, or the transverse strength of masonry, is an outgrowth of an 

 attempt to make clear to my students in masonry construction a 

 method of finding the " strain which may come upon a lintel or girder 

 used to support a brick wall ovxr an opening" given in Professor I. 

 O. Baker's Treatise on Masonry Construction. 



The masonry over the opening is assumed to act as a beam fastened 

 firmly at the ends, hence the wall must be built up slowly so as to 

 allow the mortar time to harden and attain strength enough to enable 

 the masonry to act as a beam. 



It will perhaps conduce to clearness if we assume that the wall over 

 the opening is built up of thin boards instead of courses of masonry. 

 Let, then, a long thin board be placed across an opening and fastened 

 at the ends; it will sag in the center and will need one or more sup- 

 ports to keep it in place verticall)'. If a second board be placed on 

 top of this first one and fastened firmly to it so that there is no slip- 

 ping between them, tlie stiffness of the two combined in this way will 

 be greater than the two placed side by side, or placed one on top of 

 the other without being fastened together. In consequence of this 

 added stiffness, or beam action, a less amount of the added weight will 

 be carried by the temporary supports than would be carried if there 

 were no beam action or resistance. If a third board be fastened to 

 the two preceding ones in the way indicated, the stiffness of the three 

 boards combined is greater than that of the first two combined, and 

 hence the proportion of the weight of the third board carried by the 

 temporary support is less than the proportion of the weight of the 

 second carried by three supports. After a few boards have been added 

 in this way a point is reached where the increase in stiffness is suffi- 

 cient to offset the added weight. The weight on the temporary 

 support is now a maximum. The next board added will increase the 

 stiffness so that, not only is no weight added to the temporary supports, 

 but some of the weight caused by the other boards is taken off the 

 the temporary supports. Adding a few more boards in the same way 

 we have a beam stiff enough to carry its own weight without sagging 

 or one which is self-supporting. From this we see that the weight on 



(SI) KAN. UNIV. (^UAR. VOL. II. NO. 1. .TULY, 1893. 



