Abstract

This study fulfilled steady-state tensile tests and transient-state tests to investigate the mechanical properties of butt weldments,composed of Q345B base metal and E5015 electrodes,subjected to elevated temperatures.The results include the elastic modulus,yield,and ultimate strength of the butt weldments at temperatures from 20℃to 800℃.Comparison of the results shows that the welding heat affected zone(HAZ)is vulnerable to fracture when subjected to reheating above 500℃.It's more reasonable to use the results from the transient-state tests to deduce the reduction factors of elastic modulus of weldments subjected to 200℃or higher.When heating over 400℃,these reduction factors are basically in line with those of the proposal of Eurocode 3- 1 2__[1]and AISC:2005[2].The reduction factors of yield strengths of weldments,from 100～300℃and 600～800℃,should be considered the effects of welding and use the results in transient-state tests.When the temperature was between 300～600℃,the reduction factors could apply the proposal of ASCE[3].The order of heating and loading influences the material mechanical properties subjected to high temperature.In other words,the couple of physical stress fields and thermal induced stress fields is affected not only by the quantity of superposition,but also by the time series.

Based on the stress-strain curves,this paper,additionally provided the logical reduction factors of these design parameters.Furthermore,these parameters were compared with the recommendation in the current design standards,such as BS5950[4],Eurocode 3-1-2[1],AISC:2005[2],ASCE[3],AS 4100[5],and CECS 200:2006[6].The following conclusions could be drawn.

(1)It's more reasonable to use the results from the transient-state tests to deduce the reduction factors of elastic modulus of weldments subjected to 200℃or higher.At 100℃,the reduction factors,when strains exceeded 0.2%,should be obtained from the steady-state results.When heating over 400℃,these reduction factors are basically in line with those of the proposal of Eurocode 3-1-2 and AISC:2005.

(2)The effects of initial stresses are more important on the fire resistance of metal.The order of heating and loading influences the material mechanical properties subjected to high temperature.

(3)The reduction factors of yield strengths of weldments,from 100～300℃and 600～800℃,should be considered the effects of welding and use the results in transient-state tests.When temperature between 300～600℃,the reduction factors could apply the proposal of ASCE.And more,the current design standards are not applied to predict the reduction factors of ultimate strengths of weldments that influenced by the HAZ.