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In order to establish the design theory for elastic flexural-torsional buckling of simply supported steel beams under combined loads, the total potential equation considering the combination of transverse loads of different types, different loading points and unequal end moments was proposed first. Then the general calculation formula for critical moment Mer and for the coefficients C'1, C'2a and C'3 were derived by employing Rayleigh-Ritz method. The relationships of C'1, C'2a and C'3 for combined load and C1, C2 and C3 for single load were established. The general calculation formula for critical loads was also derived by employing Rayleigh-Ritz method, and the correctness of the general formula was checked by numerical example. Finally, self-weight of steel beams was considered for checking its influence on the critical loads. The conclusions show that the general formula of Mer for combined load has the same form as the formula for single load. The self-weight of steel beam has a negligible effect on the values of critical loads. [ABSTRACT FROM AUTHOR]

The axial compressive static test of the strengthened steel columns were studied to investigate the influence of initial load on mechanical characteristics of steel columns after weld strengthening process. The experiment included three columns strengthened by welding under different initial loads and one steel column without strengthening for comparison. The sections of the specimens were I section and doubly symmetric. The strengthening type of steel columns were welding the steel plates symmetric at the end of two flanges to connect the steel plates and the columns and the welding is along the whole length of column. The constraint of steel column end used single hinge support to achieve the rotation around the weak axis. The strain distribution on web of steel column before and after strengthening, buckling modes, deformation caused by strengthening weld and stability bearing capacity were discussed. In addition, the test results were compared with the theoretical results calculated by codes. The test results show the strain of web is increased after steel columns is cooled and the strain-stress redistribution occurs because of welding process. The biggest preload in test is equivalent to 71.7% of the stability bearing capacity of the un-strengthened columns, and the stability bearing capacity of steel column does not decrease obviously after strengthening. The stability bearing capacity and residual deformation after strengthening are affected by initial load and initial geometric imperfection. [ABSTRACT FROM AUTHOR]

In order to facilitate the rapid construction of steel, a new type of splice joint, named preloaded moment-resistant joint, was developed for splice H-shape steel column. In this paper, reversed cyclic loading tests were conducted on three specimens, to investigate its failure mode, internal force continuity and stress distribution characteristics, as well as influencing factors of load-bearing capacity and rigidity of column. The experimental results indicate that the buckling deformation appears in the flange of the column, the high pretension exerted on high-strength bolts keeps the column sustaining larger bearing capacity. The stiffeners of the joint play an important role to support the flange, with low stress and no buckling deformation. The hysteretic curves demonstrate the small lateral sway and little energy dissipation of column. The maximum shear deformation angle of joint zone is 0.002 3 rad, ensuring the rigidity continuity and load bearing capacity of column. The results demonstrate the joint has good seismic performance. [ABSTRACT FROM AUTHOR]