In this paper, we propose the design oriented method on the ultimate lateral shear capacity of the steel frames with concentric inverted V-shaped braces and verify its effectiveness by the test results of the half-scale steel frames, that were conducted under the U.S.-Japan Cooperative Research Program Utilizing Large-Scale Testing Facilities.

A part of this paper was submitted to ASCE Structures Congress, Sep. 15-18, 1986, at New Orleans, U.S.A.

The steel frame is modeled to be the moment-resisting frame portion consisting of beams and columns, and the brace portion with the pin-ended beam in the braced bay. The ultimate lateral shear capacity of the total frame is given by the summation of the ultimate lateral strength of the both portions. The strength of the moment-resisting frame portion is calculated by the limit analysis using the virtual work method. The strength of the brace portion is given by the summation of twice as much as the ultimate compressive strength of the brace in the post-buckling large-deflection range and the contributing strength of the braced bay beam to the lateral shear strength. The contribution of the braced bay girder is conservatively estimated by 2Mgp/h, where Mgp is the full-plastic moment of the beam and h is the story height.

This method is applied to the weak beam frame, which means that the mid-span of the braced bay beam will be pulled down and yielded by the vertical resultant force which applies to the mid-span of the beam in the braced bay caused by the braces in the post-buckling, and to the frame where the first mode of vibration will fully affect its ultimate lateral shear capacity.

The ultimate lateral shear capacity by the method was confirmed to be a good approximation on the lateral shear strength of the half-scale test frames even in the large-deflection range.