土木工程建筑外文文献及翻译 第4页
4. Loading history
Specimens were tested by applying cycles of alternated load with tip displacement increments of _y as shown in Table 4. The tip displacement of the beam was imposed by servo-controlled actuators 3 and 4. When the axial force was to be applied, actuators 1 and 2 were activated such that its force simulates the shear force in the link to be transferred to the beam. The variable axial force was increased up to 2800 kN (630 kip) at 0.5_y. After that, this lo- ad was maintained constant through the maximum lateral displacement.
maximum lateral displacement. As the specimen was pushed back the axial force remained constant until 0.5 y and then started to decrease to zero as the specimen passed through the neutral position [4]. According to the upper bound for beam axial force as discussed in Section 2 of this paper, it was concluded that P =2800 kN (630 kip) is appropriate to investigate this case in RBS loading. The tests were continued until failure of the specimen, or until limitations of the test set-up were reached.
5. Test results
The hysteretic response of each specimen is shown in Fig. 13 and Fig. 16. These plots show beam moment versus plastic rotation. The beam moment is measured at the middle of the RBS, and was computed by taking an equiva- lent beam-tip force multiplied by the distance between the centerline of the lateral actuator to the middle of the RBS (1792 mm for specimens 1 and 2, 3972 mm for specimens 3 and 4). The equivalent lateral force accounts for the additional moment due to P– △ effect. The rotation angle was defined as the lateral displacement of the actuator divided by the length between the centerline of the lateral actuator to the mid length of the RBS. The plastic rotation was computed as follows [4]:
where V is the shear force, Ke is the ratio of V/q in the elastic range. Measurements and observations made during the tests indicated that all of the plastic rotation in specimen 1 to specimen 4 was developed within the beam. The connection panel zone and the column remained elastic as intended by design.
5.1. Specimens 1 and 2
The responses of specimens 1 and 2 are shown in Fig. 13. Initial yielding occurred during cycles 7 and 8 at 1_y with yielding observed in the bottom flange. For all test specimens, initial yielding was observed at this location and attributed to the moment at the base of the specimen [4]. Progressing through the loading history, yielding started to propagate along the RBS bottom flange. During cycle 3.5_y 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 5_y with the increased axial compression load to 3115 KN (700 kips) a severe web buckle developed along with flange local buckling. The flange and the web local buckling became more pronounced with each successive loading cycle. It should be noted here that the bottom flange and web local buckling was not accompanied 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 5.75_y. 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 completely fractured, the web began to fracture. This fracture appeared to initiate at the end of the RBS，then propagated through the web net section of the shear tab, through the middle stiffener and the through the web net section on the other side of the stiffener. The maximum bending moment achieved on specimen 1 during the
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