If we connect two lapping timbers by nails and apply them a load which acts on nails as the shearing force, the apparent slip between two timbers is proportional to the load. But naturally there is a limit of proportion on the relation of slip and load, and if the load goes over the limit, the slip becomes gradually remarkable.
By our experimental investigation, we found that the relation of slip and load has a proportional limit, when the maximum bearing pressure about nail-holes attaines the proportional limit of bearing of timbers. Then we may propose a principle of design of connection by nails as following procedure.
At first we must obtain the proportional limit of bearing of the timbers by the material test, then we assume most suitable safety-factor and decide an allowable bearing pressure; - this safety-factor may be nearlly equal to the unit and be more or less than the unit.
Secondly, making the maximum bearing pressure equals to the allowable bearing pressure, we can calculate, the safe loads for nails; - wher the maximum bearing pressure is connected with the safe loads by a theory of elasticity.
