【正文】 e that the bottom flange and web local buckling was not acpanied by a significant deterioration in the hysteresis loops. A crack developed in specimen 1 bottom flange at the end of the RBS where it meets the side plate during the cycle . Upon progressing through the loading history, 7_y, the crack spread rapidly across the entire width of the bottom flange. Once the bottom flange was pletely fractured, the web began to fracture. This fracture appeared to initiate at the end of the RBS，then propagated through the web section of the shear tab, through the middle stiffener and the through the web section on the other side of the stiffener. The maximum bending moment achieved on specimen 1 during theDuring the cycle y, specimen 2 also showed a crack in the bottom flange at the end of the RBS where it meets the wing plate. Upon progressing thou gh the loading history, 15 y, the crack spread slowly across the bottom flan ge. Specimen 2 test was stopped at this point because the limitation of the test setup was reached. The maximum force applied to specimens 1 and 2 was 890 kN (200 kip). The kink that is seen in the positive quadrant is due to the application of the varying axial tension force. The loadcarrying capacity in this zone did not deteriorate as evidenced with the positive slope of the force–displacement curve. However, the loadcarrying capacity deteriorated slightly in the neg ative zone due to the web and the flange local buckling. Photographs of specimen 1 during the test are shown in Figs. 14 and 15. Severe local buckling occurred in the bottom flange and portion of the web next to the bottom flange as shown in Fig. 14. The length of this buckle extended over the entire length of the RBS. Plastic hinges developed in the RBS with extensive yielding occurring in the beam flanges as well as the web. Fig. 15 shows the crack that initiated along the transition of the RBS to the side wing plate. Ultimate fracture of specimen 1 was caused by a fracture in the bottom flange. This fracture resulted in almost total loss of the beam carrying capacity. Specimen 1 developed rad of plastic rotation and showed no sign of distress at the face of the column as shown in Fig. 15. . Specimens 3 and 4 The response of specimens 3 and 4 is shown in Fig. 16. Initial yielding occured during cycles 7 and 8 at 1_y with significant yielding observed in the bottom flange. Progressing through the loading history, yielding started to propagate along the bottom flange on the RBS. During cycle initiation of web buckling was noted adjacent to the yielded bottom flange. Yielding started to propagate along the top flange of the RBS and some minor yielding along the middle stiffener. During the cycle of a severe web buckle developed along with flange local buckling. The flange and the web local buckling bec ame more pronounced with each successive loading cycle. During the cycle y, the axial load was increased to 3115 KN (700 kips) causing yielding to propagate to middle transverse stiffener. Progressing through the loading history, the flange and the web local buckling became more severe. For both specimens, testing was stopped at this point due to limitations in the test setup. No failures occurred in specimens 3 and 4. However, upon removing specimen 3 to outside the laboratory a hairline crack was observed at the CJP weld of the bottom flange to the column. The maximum forces applied to specimens 3 and 4 were 890 kN (200 kip) and 912 kN (205 kip). The loadcarrying capacity deteriorated by 20% at the end of the tests for negative cycles due to the web and the flange local buckling. This gradual reduction started after about to rad of plastic rotation. The loadcarrying capacity during positive cycles (axial tension applied in the girder) did not deteriorate as evidenced with the slope of the force–displacement envelope for specimen 3 shown in Fig. 17. A photograph of specimen 3 before testing is shown in Fig. 18. Fig. 19 is a Fig. 16. Hysteretic behavior of specimens 3 and 4 in terms of moment at middle RBS versus beam plastic rotation. photograph of specimen 4 taken after the application of rad displacem ent cycles, showing yielding and local buckling at the hinge region. The beam web yielded over its full depth. The most intense yielding was observed in the web bottom portion, between the bottom flange and the middle stiffener. The web top portion also showed yielding, although less severe than within the bottom portion. Yielding was observed in the longitudinal stiffener. No yiel ding was observed in the web of the column in the joint panel zone. The un reduced portion of the beam flanges near the face of the column did not show yielding either. The maximum displacement applied was 174 mm, and the maximum moment at the middle of the RBS was times the plastic mom ent capacity of the beam. The plastic hinge rotation reached was about rad (the hinge is located at a distance from the column surface,where d is the depth of the beam). . Strain distribution around connection The strain distribution across the flanges–outer surface of specimen 3 is shown in Figs. 20 and 21. The readings and the distributions of the strains in specimens 1, 2 and 4 (not presented) showed a similar trend. Also the seque nce of yielding in these specimens is similar to specimen 3. The strain at 51 mm from the column in the top flange–outer surface remained below % during negative cycles. The top flange, at the same location, yielded in pression only. The longitudinal strains along the centerline of the bottom–flange outer face are shown in Figs. 22 and 23 for positive and negative cycles, respectively. From , it is found that the strain on the RBS bees several times larg er than that near the column after cycles at –