Merkezi çaprazlı ve moment aktaran çerçeveli karma sistemlerde %25 kuralının incelenmesi

Lateral forces induced by either earthquake or wind mostly play primary role in design of a multi-storey building. To carry the earthquake force, so many seismic force resisting systems have been developed recently. One of the most effective systems to resist the lateral earthquake forces is the dual systems that include moment frames and shear walls or braced frames together. According to ASCE 7-05, for dual systems the moment frames should resist at least 25 percent of the seismic design force. This rule is defined as 25 percent rule. In this paper the correlation between the height (the number of the stories) of the buildings and 25 percent requirement is investigated. The moment frames in dual systems considered have been designed for 15, 25 and 40 percent of seismic demand for different buildings: 12-storey, 16-storey and 20-storey. Using SAP 2000 software, linear static and push-over analysis are performed. The braced frames of the dual systems are designed with concentric braces. During linear static analysis procedure, three different models having different story numbers are modelled and each of them are separated into three. Actually, nine models are available. By extracting the moment frame from the whole model, they are designed according to 15, 25 and 40 percent of the lateral load which they are expected to resist. After finishing planar system analysis they are adapted into model again and checked in the whole system whether they are over-stressed or not. After satisfying all conditions their base force proportion to sum of base reaction is determined. In this way, all the profiles and brace dimensions are determined. To get better results the structures are analyzed in three dimension however, the 25 percent rule is checked only in the x direction. In the y-direction only braced frames resist earthquake, in the x-direction dual system (both moment frames and braced frames) resist earthquake force. In the frames which braces are already exist, columns that are not part of braced frames are leaning columns whose connections to beams and to base are pinned. In the axis having moment frames, all beam-to-column connections are rigid. They are designed intentionally in this way to understand the events after yielding of the braces. By push-over analysis, the expected behaviour of the structures is tried to be found out. Then the systems have been examined with non-linear static analysis using SAP 2000 software. While applying non-linear analysis on the structures an approximate method is used. The structures are pushed in x directions about 3 percent of their height rather than the target displacement demands determined by a method. After obtaining the pushover curves, the target displacements are calculated and the performance point is determined. All the checks especially base shear distribution are done with respect to this point. During analysis procedure, the secant stiffness is used for hinge unloading method instead of unload entire structure option due to convergence problem. The FEMA hinge properties are assigned to frames. They are checked by hand calculation whether they meet the requirements of ASCE 41-06 or not. For this reason a cantilever column and a moment frame are analyzed. When compared to results, an agreement is observed. The axial hinge is assigned to in the middle of the braces. The P-M3 hinge is assigned to columns bottom and top parts. Delibrately, the P-M2-M3 hinge are not used, because M2 moment values are negligible. However, when they are used, convergence problem in SAP 2000 is encountered during analysis. Moment (M3) hinge assigned to beams, but no hinge is assigned to the beams which they are released in both ends. The anticipated behaviour of the structures can be defined as: First, braces yield under tensile forces and buckle due to compressive forces in a ductile manner, then, the moment frames start to resist the forces dominantly.At this time, the need of additional strength achieved by ensuring that the moment frames are capable of providing at least 25% required lateral strength is investigated Also the relation between the story number and this rule is examined. During Time-History Analysis procedure, three different earthquake ground motions to represent the design based earthquake are taken from PEER. In addition, the systems are checked for Maximum Considered Earthquake. All the earthquake data satisfies the ASCE7-05 conditions. They are chosen according to the seismic zone criteria. In the models, initially the ramp functions are defined. Then earthquakes are defined. All the earthqukes are scaled. For a better scientific approach, the verification with another software is obligation. For that reason, OpenSEES is used to verify the results. The half of the building is modeled in this software. This model is developed in such a way to represent the whole structure. Only x-direction elements are added to the models. The beams and braces in transverse direction are not included in the models. However, their loads and self-weights are added to system joints as point loads. In order to prove that the models in OpenSEES represent the real models, gravity and eigen model analysis are conducted. In the gravity analysis, the column axial forces are checked. In the eigen modal analysis, the first mode direction and the natural vibration periods of the structures are compared. According to comparison of the periods, the OpenSEES models are more rigid. Their natural vibration periods are lower than SAP 2000 models. However the values are found to be comparable. In addition to this, the push-over analysis is carried out to compare the nonlinear behaviour of the models each other . Then, non-linear dynamic analyses are done and their results are evaluated after completions of analyses. For the assessment of seismic performance of each building, story drifts, displacements and base shear distribution are evaluated. In the SAP 2000 models, the stages of plastic hinges and their distribution are also checked. The results are found as expected. Plastic hinges occur in the brace members under axial compressive force. Plastic hinges can also be observed in the moment resisting frames. Compared to brace hinges, their stages are more closer to IO, LS. Consequently, all systems are performed well and there is no clear evidence to show that one model is exhibiting better performance than the other.