تأثیر طول ناحیه ویژه و نحوه تقویت آن بر عملکرد لرزه‌ای سیستم خرپای متناوب

The staggered-truss system has been proposed as a lateral load resisting system in the structural steel framing for high-rise buildings, which was developed in Massachusetts Institute of Technology in 1960s. The system consists of a series of storey-high trusses spanning the total width between two rows of exterior columns and arranged in a staggered pattern on adjacent column lines. the system has the columns only on the exterior walls of the building, the usual interior columns are omitted. Thus, the staggered-truss system can provide a full width of column-free area. In the system, the role of energy absorption and endurance of inelastic deformations is responsible for the special segment of truss, so that the ductility of structure is provided by the development of plastic hinges in this region. Although, in the special segment of truss an opening near the center of span must be provided to permit a width and height of sufficient proportions which is used as a corridor. Hence, the effects of this opening must be investigated in the performance of this system. In this study, the effects of the special segment length and its strengthening pattern on the seismic performance of staggered-truss system are investigated. In order to achieve this purpose, an 8-storey steel staggered-truss system with a 1/8-scaled studied in work of Zhou et al. [14] is selected and considered subjected to the low cyclic loading. First, the finite element (FE) model of this structure, in which both the material and geometric nonlinearity, is provided in ABAQUS software, and the validation of the model is controlled by experimental and numerical study and of Zhou et al. [14]. The results of modeling this structure show that the FE model of this structure has appropriately accuracy. Then, the seismic performance of the system is evaluated by considering the various lengths of the special segment and the proposed strengthening patterns in the special segment. The results of the evaluation show that the use of special segments with great length make the entire structural capacity is not fully utilized. Hence, when the large opening is required the regions must be properly strengthened. In this study, different patterns of the special segment, including strengthening of chords, strengthening of vertical members of the special segment and the strengthening pattern proposed by the Manual Number 14 of AISC code are investigated. Since the plastic hinges are usually formed at the chords of the truss, the strengthening of chords has the greatest effect on increasing the initial stiffness and strength of structure. Instead of the strengthening of the total length of the chord, a part of both ends of the special segment is also strengthened, so that its performance is as same as that of the strengthening of the total chord. It is noted that the strengthening of the special segment is one of the ways to increase the initial stiffness and resistance structure, but this strengthening must not omit the performance of the fuse in the truss system, and the conditions of strong beam and weak column are provided. Based on the FE analytical results, the suggestions of this study can be considered for the design of staggered-truss system.