Research On Steel Beam-columns Strengthened By Welding While Under Load

Considering that in China the demands for reinforcement of steel structures have intensively appeared in industrial constructions, and that the potential demands in public and civil buildings can be expected, it possess great application value to revise technical codes for strengthening steel structures. As the most traditional and important method of strengthening steel structures, the technology of strengthening by welding under load has now not only been widely used in various structural reinforcement engineerings, but also been granted high expectations for its ease of operation and durability and reliability of effect. Being placed under load is the existing state of steel structures. Thus it takes profound knowledge of performance features during and after welding strengthening, as to complete welding operation and achieve goal of reinforcement in this normal state of loading. However, foreign researches lack specific or practical provisions although start early. While the existing domestic code has been left in disrepair for years, which quantitively refers to Soviet Union’s experiences, lacks scientific basis and accordingly no more suits for current needs.This paper proceeds from overall grasp of related researches, engineering applications and technical code status of structure strengthened by welding under load at home and abroad. The welding heat effect problem of welding strengthening under load is specifically compared and analyzed, and the provisions framework of domestic code and specification to solve the problem of strengthening by welding under load is thoroughly combed. Then experimental and numerical study of beam-column strengthened by welding under load is carried out, which fills in the blanks of domestic and foreign researches. The welding heat problem is studied and discussed significantly, and by combining testing results with finite element influence factor analysis a new method of solving the basic problems of strengthening by welding under load is proposed within present design provisions framework. The new method would strengthen the systemicness and scientificalness of domestic standard. The main research contents of this paper are as follows:(1)Static test of steel beam-columns strengthened by welding under different initial loads is carried out, with strengthening scheme selected by symmetrically welding steel plates to outside surface of flanges. The displacement changes of specimen and welding stress and strain distribution of web are discussed during welding strengthening while under load, as well as the buckling mode and stability bearing capacity after strengthening.(2)Non-linear finite element analyses(FEA) neglecting and considering welding heat effect are applied in turn to simulate 4 specimens respectively, while the analyses also consider body-shell element coupling, contact and friction. Then by comparison with testing results the FEA are verified reliable. And further the plastic penetration, welding temperature field, strain-stress redistribution between flange and strengthening plate and flange margin yield capacity are acquired, which can not easily be measured by test.(3)Taking different factors like initial loads, eccentricities, slender ratios and classes of welding heat input into account meanwhile expanding the parameters, FEA considering welding heat effect are applied to simulate 72 steel beam-columns. The to-be strengthened and strengthened steel beam-columns are all included in the whole-process analyses of loading and the effect of these various factors are acquired.(4)By comparison of influence factor analysis results, domestic and foreign test results and codes calculatiton results, a new suggested coefficient and formula for calculating welding residual deformation of steel members strengthened by welding under load are proposed. Simultaneously, constructive suggestions for out-plane stability capacity of steel beam-columns are put forward. These will provide reference and basis for the revision of Chinese national standard “Design code for strengthening steel structure”.