96 



PRACTICAL STRUCTURAL DESIGN 



The longer support increases the bending moment and the holding 

 down strength of the fastenings must be investigated. The leg 

 is sometimes run across the top of the girder and bent down on 

 the other side and there fastened, which is sometimes good, but the 

 increase in material added to the cost of fastenings and the cost 

 of labor to drive them amounts to more than the cost of the addi- 

 tional thickness necessary to prevent straightening. A stirrup 

 strong enough to carry a load without bending is more satisfactory 

 than one confessedly weak with which fastenings must be used. 



Tops of beams and girders should not be cut to make a seat 

 for stirrups. This weakens the timber, so the under side of the 

 floor planking should be cut to make pockets for the stirrups. A 

 cheaper method is to lay a strip of wood to carry the flooring on 

 top of the beam between stirrups. When the floor is double the 

 under layer may be cut away at the stirrups, the upper layer being 

 amply strong to carry over the small hole. Fig. 62 is reproduced 

 from " Ryerson's Ready Reference." The stirrups illustrated are 

 made of wrought iron and the recommendation is made in the book 

 that the following sizes mentioned in the table should in general 

 be used for the size of joist supported, the stirrups, unless other- 

 wise specified, being furnished in. smaller than nominal size of 

 timber or joist. Wall hangers rest on plates as shown. 



TABLE OF STIRRUP SIZES AND CAPACITIES 



Another method for carrying the ends of joists on a girder when 

 head room is to be saved and the joists cannot rest on top of girders 

 is shown hi Fig. 63. This depends upon shearing resistance of 

 the spikes. First find the width of bearing required for each joist 

 by dividing the reaction by the bearing strength across the grain. 

 Use nails having a length practically three times the thickness 

 of the bearing strip as a minimum, so they will go into the girder 



