The Research On Holding Ability Of Self Tapping Screws In Decking Application

In recent years,the construction quantity of decking road are larger and popular.It is valuable of practice and theory to study the connecting abilities of self-tapping screws in decking road.Decking road is made up of wooden tread,support skeleton and self-tapping screws.Duo to good mechanical capacity in harden and anti-torsion,the self-tapping screws have a good ability against the broken in decking road works.The screw holding force is a key factor in the connection performance of self-tapping screws.It is composed of friction and squeezable force imposed on screw’s body inside the wood.The parameters affecting the holding force of self-tapping screws are mainly focused on:screws material,thread form and screw surface coating.Screw material and surface coating have little effect on holding force.However the screw thread form,including screw diameter,bottom diameter,pitch,lead,thread length,thread angle,screw tip angle are key parameters affecting the holding force.The result shows that the long pitch(2.5mm)have better holding force than short pitch(1.6mm),some increase 10%;the thread lead has a little influence on the holding force;Once the length of thread reaches a certain value(8d),the excessive part has little effect on the holding force.The angle of thread will affect the holding force theoretically,but the test results show it is not obvious,partly in reason of small gap to test.The angle of screw tip affects the splitting resistance of the wood,which may cause to reduces the squeezed strength inside wood.There is no wood split in the test,so the effect of screw angle is not obvious.The experimental datum are overall to be referred for the future dynamic research of screw holding force.