Bending strength of threaded connections for micropiles

The bending strength of pin-box threaded connections for mortar-filled steel tubes used as micropiles is investigated in this paper. An experimental campaign has been carried out, including forty tests subjected to four-point bending until failure. The specimens consisted of mortar-filled steel tubes with a connection at the midsection. The results indicate that the failure mode of pin-box threaded joints is brittle and originates at the root of the last engaged thread of the pin end. Moreover, the bending strength of the connection is significantly smaller than the strength of jointless tubes. The analysis of the results suggests a considerable influence of the size effect, with the bending strength decreasing as the outer diameter of the tube increases. In addition, it is shown that, within the dimensions tested, the bending strength does not increase when the relative threaded length is increased.

► We have studied the bending strength of pin-box threaded connections for micropiles. ► We carried out bending tests to failure on mortar-filled tubes with a connection. ► Threaded connections had brittle failure, with smaller strength than jointless tubes. ► Influence of joint dimensions and size effect on the bending strength is analyzed.