Reliability assessment of timber connections through ultrasonic inspection of bolts.

摘要

Connections between structural members are critical elements which typically govern the performance of structural assemblies. When connections in timber structures are loaded beyond the yield point, residual ductility and energy dissipation capacity are compromised. The goal of this research is to develop an ultrasonic inspection technique to detect and quantify internal connection damage for subsequent assessment of structural reliability of bolted timber connections.; An innovative ultrasonic inspection technique is proposed for nondestructive assessment of bolted timber connections which exhibit mode III yield behavior. Permanent angular deformation in bolts caused by loading beyond the connection yield point is detected by coupling an ultrasonic probe to the head of the bolt and analyzing the time domain signal from pulse-echo inspection. Permanent angular deformation in the range {dollar}0spcirclethetasb{lcub}H{rcub}le 10spcirc{dollar} is measured ultrasonically with an accuracy of {dollar}pm{dollar}1.5{dollar}spcirc{dollar} at 95% confidence for 12.7 mm (0.5 in.) diameter bolts installed in double shear Southern Pine connections.; Detection of permanent angular deformation in bolts is an effective indicator of connection damage based on strong linear correlation with connection displacement and energy dissipation. Although the ultimate load capacity is not typically compromised by excursions beyond the yield point, reductions in residual ductility and energy dissipation capacity occur as the permanent angular bolt deformation increases in connections.; Maximum load, ductility and energy dissipation capacities for the connections in this study were modeled as random variables with lognormal distributions. A two-parameter Weibull distribution provided the best fit for connection yield load data. Structural reliability indices of {dollar}2.65lebetale 3.05{dollar} were calculated on a connection yield load basis, and {dollar}4.04lebetale 4.76{dollar} on an ultimate load basis. A new technique was proposed for determining updated structural reliability indices on the basis of residual connection ductility. The inherent uncertainty in ultrasonic pulse-echo inspection was explicitly addressed in reliability assessments. Updated reliability indices on the basis of residual connection ductility were evaluated in conjunction with load-based reliability indices to determine the need for repair of damaged timber connections.