In performance based design, the hazard levels and relevant acceptable damages are clearly specified. Structural and non-structural performances are controlled by limiting stiffness, strength and members ductility characteristics. Using DISPLACEMENT AMPLIFICATION FACTORs (Cd) and force reduction FACTORs (R) related to hazard levels, this paper present a method for determination of the stiffness and strength demands needed for BFs (Braced Frames) design. It means that two force reduction FACTORs and two DISPLACEMENT AMPLIFICATION FACTORs are introduced for moderate and major earthquake levels (Immediate Occupancy and Life Safety performances) for determination of stiffness and strength demands. These FACTORs depend on ductility FACTOR, force reduction FACTOR due to ductility and overstrength FACTOR. The procedure for determination of R and Cd FACTORs and value of these FACTORs for Io and LS performance level will be presented in this paper. The results indicate that force reduction FACTORs and DISPLACEMENT AMPLIFICATION FACTORs may be easily used in performance based design methodology.

In recent decades several destructive earthquakes result in extensive structural and non-structural damage in structures that was produced by lateral DISPLACEMENTs. So, it reveals the necessity of accurate estimation of lateral DISPLACEMENT of the structures in design procedure. According to the present seismic design provisions, DISPLACEMENT AMPLIFICATION FACTOR, (Cd), is applied to acquire elastic lateral DISPLACEMENTs in order to assess inelastic DISPLACEMENTs, due to the ground motions. Besides, in many codes, these FACTORs are empirical in nature and is based on structural performance, which has been observed in the past earthquakes,On the other hand, the effect of height and number of stories is neglected. In this paper, the effect of Cd on seismic performance of steel special moment frames is evaluated. Six types of buildings are designed with different values of Cd (i. e., 4, 5, 5. 5, 6, 7, and 8). For each type of building, 5 heights (i. e., 5-, 10-, 15-, 20-and 25-stories) are considered. The finite element models are developed in Opensees. Incremental dynamic and nonlinear static analyses are performed to quantify structures’,seismic performance utilizing fragility curves and FEMA P695 methodology. The results indicate that the values of Cd provided in the codes for steel special moment frames are not completely effective on seismic performance, especially in short-rise buildings. Also, the probability of collapse of high-rise buildings is less likely with respect to the medium-rise buildings,Therefore, in high-rise buildings, increasing the amount of Cd is not necessarily recommended, because it increases the cross sections of the frame members and makes the design uneconomical.

In recent decades, several destructive earthquakes resulted in extensive structural and non-structural damage in structures, which was produced by lateral DISPLACEMENTs. Therefore, it reveals the necessity for the accurate estimation of the lateral DISPLACEMENT of structures in the design procedure.Present seismic codes using structural overstrength and the ability of energy dissipation capacity of the structures allow a structure to be designed for reduced seismic design forces with force reduction FACTOR. As a result of this, the response of the structure lies beyond the elastic region in the event of strong ground motions; thus, simple linear analyses procedures fail to predict the structure deformations accurately. On the other hand, due to complexity and time consuming nonlinear dynamic analysis, this type of analysis has not been acknowledged as an applicable method for structural engineers. Efforts in the direction of finding a procedure to estimate the maximum lateral inelastic DISPLACEMENT began years ago.According to present seismic design provisions, DISPLACEMENT AMPLIFICATION FACTOR (Cd) is being applied to elastic lateral DISPLACEMENTs in order to assess inelastic DISPLACEMENTs due to ground motions. Although, the FACTOR of Cd in the codes are not in accordance with the actual behavior of the structure, the empirical does, based on the structural performance observed in the past earthquakes and should be corrected according to the effect of height and number of stories. In this paper, the effect of Cd on seismic performance of steel special moment frames is evaluated. In this regard, six types of buildings are designed with different values of Cd (i.e., 4, 5, 5.5, 6, 7, and 8); and, in order to investigate low to high-rise buildings, 5 heights (i.e., 5-, 10-, 15-, 20- and 25-stories) are considered in two regular and irregular states. Irregularity is considered to be a mass irregularity in the first floor, so that the mass of the first floor is 50% higher than the mass of the adjacent floor. The numerical finite element models are developed in OpenSEES software. Incremental dynamic analysis (IDA) and nonlinear static analysis are performed to quantify structures’ seismic performance; Nonlinear static analyzes are performed to determine overstrength and ductility FACTORs of buildings. Also, the effect of earthquakes on buildings is investigated using incremental dynamic analysis that is accomplished with 22 far-field earthquake record pairs proposed in FEMA P695. Eventually, the effect of different values of Cd on seismic performance of the buildings are quantified and investigated using FEMA P695 methodology and fragility curves in terms of the adjusted collapse margin ratio (CMR) and the probability of collapse (Pf).The results demonstrate that the probability of collapse (Pf) of short and medium-rise buildings with Cd equal to 5.5 is higher than 10%, which is the targeted value of Pf according to design codes; therefore, considering Cd equal to 5.5 in the design of these buildings does not provide real DISPLACEMENT and leads to underestimated design of buildings. In irregular buildings, although the Pf values increased compared to regular buildings, a similar trend was observed in general. In short, the amount of Cd that leads to an acceptable performance of collapse in the structures is equal to 8, 8, 7, 6 and 5.5 in regular 5, 10, 15, 20 and 25 story buildings, respectively; moreover, similarly in 5, 10, 15, 20 and 25 story buildings with mass irregularity are equal to 7, 7, 6, 5.5 and 5.5, respectively. Based on these values, relations are proposed to correct the DISPLACEMENT AMPLIFICATION FACTOR in regular and mass irregular steel special moment frames.Also, comparison of Pf and weight of structures designed with ASCE 7-10 and ASCE 7-16 regulations revealed that design of structures according to ASCE 7-10 criteria with modified values of Cd that is presented in this paper will be economical in addition to achieve the intended collapse performance.

According to seismic design codes, nonlinear performance of structures is considered during strong earthquakes.Seismic design provisions estimate the maximum roof and story drifts occurring during major earthquakes by amplifying the drifts computed from elastic analysis at the prescribed seismic force level with a DISPLACEMENT AMPLIFICATION FACTOR. The present study tries to evaluate the DISPLACEMENT AMPLIFICATION FACTORs of conventional concentric braced frames (CBFs) and buckling restrained braced frames (BRBFs). As such, static nonlinear (pushover) analysis and nonlinear dynamic time history analysis have been performed on the model buildings with single and double bracing bays, and different stories and brace configurations (chevron V, invert V, and X bracing). It is observed that the DISPLACEMENT AMPLIFICATION FACTORs for BRBFs are higher than that of CBFs. Also, the number of bracing bays and height of buildings have a profound effect on the DISPLACEMENT AMPLIFICATION FACTORs. The evaluated ratios between DISPLACEMENT AMPLIFICATION FACTORs and response modification FACTORs are from 1 to 1.12 for CBFs and from 1 to 1.4 for BRBFs.

It is well known that during strong ground motions most of structural damages and collapses are due to excessive DISPLACEMENT of stories, and other structural and non-structural elements. Therefore one of the most important objectives in seismic design procedure is estimating the maximum inelastic (actual) DISPLACEMENT and drift of structures occurring in severe ground motions. Seismic design provisions estimate the maximum inelastic story drifts and DISPLACEMENTs occurring in major earthquakes by amplifying the drifts and DISPLACEMENTs computed from elastic analysis at the prescribed design seismic force level using a deflection AMPLIFICATION FACTOR. This parameter is useful for estimating minimum allowable space between two adjacent buildings, controlling story drift limitations and so on. In this research, the deflection AMPLIFICATION FACTOR for both DISPLACEMENT and drift of four steel concentrically braced frames (CBF) and also four steel ordinary moment resisting frames (OMRF) are studied and evaluated. For each system, 2, 4, 6, and 8-story steel building are considered. These frames are subjected to 7 selected records of ground motions having different characteristic such as frequency content, peak ground acceleration (PGA), and so on. It is concluded that the deflection AMPLIFICATION FACTOR for the systems under consideration is considerably higher than that recommended by Standard No.2800 Iran code. From the results of this research, a FACTOR for both deflection and DISPLACEMENT AMPLIFICATION FACTOR of each system under consideration is separately suggested.

Response modification and deflection AMPLIFICATION FACTORs are used in the current seismic design codes to account for the inelastic behaviour of structural systems without the need for complicated nonlinear analyses. A deflection AMPLIFICATION FACTOR, cd, is used to compute the expected maximum inelastic DISPLACEMENT from the elastic DISPLACEMENT induced by the design seismic forces. The response modification FACTOR, R, expressed as either a force reduction FACTOR or a behavior FACTOR, is used to reduce the linear elastic design response spectra. It is generally expressed as the product of three FACTORs: overstrength FACTOR, ductility FACTOR, and redundancy FACTOR. This paper tries to evaluate these FACTORs for steel intermediate moment-resisting frames. For this purpose, two dimensional steel building models with different number of stories have been designed and analyzed. After obtaining pushover curves of the models, two different approaches have been adopted to calculate the effective parameters of the response modification and deflection AMPLIFICATION FACTORs from pushover curves; the first approach that is suggested by seismic code provisions, like ATC-19, FEMA-356 and Iranian Standard No. 2800, uses the idealized pushover curve to specify the effective parameters, and the other approach that is recommended by FEMA-P695 gets the parameters directly from pushover curves. The obtained results from these two approaches for the above-mentioned FACTORs have then been compared with each other and with the recommended values of these FACTORs in the Iranian Standard No. 2800. In this evaluation, ductility FACTOR of the response modification FACTOR has been calculated based on the relations proposed by Newmark and Hall, Lai and Biggs, and Nassar and Krawinkler. According to the obtained numerical results, the average response modification FACTOR resulted from the FEMAP695 approach is 5.26, while this FACTOR was obtained 3.98 based on the Iranian Standard No. 2800 approach. Considering the recommended R FACTOR of the Iranian Standard No. 2800 for the ultimate limit state design of steel intermediate moment-resisting systems equaling 5, it is obvious that the results from the FEMA-P695 approach are more compatible with the code recommendation. In addition, the average over strength FACTORs, according to the FEMA-P695 and Iranian Standard No. 2800 approaches, are 2.37 and 1.80, respectively, when the recommended value of this FACTOR in the Iranian Standard No. 2800 is 3. The average deflection AMPLIFICATION FACTOR obtained from both approaches is 3.67 that is slightly less than the recommended value of 4 for this FACTOR in the Iranian Standard No. 2800.

Currently, the framed-tube and outrigger-braced systems are known as two conventional load bearing systems in tall buildings. These structural systems can be used in tall buildings with high efficiency to provide the necessary lateral stiffness and strength against lateral forces due to earthquakes or strong storms. On the other hand, increasing the stiffness of these structures augments the relative importance of flexibility of the underlying soil and the resulting added DISPLACEMENTs. This paper aims to study the seismic behavior of framed-tube and outrigger-braced tall buildings on flexible soil in comparison to a rigid base. For this purpose, a range of 10 to 50-storey steel buildings with both structural systems on flexible and rigid bases are analyzed dynamically and the maximum base shear and lateral roof DISPLACEMENT are calculated. Also for comparing the benefit of each system, the total weight of steel used per system in each case is calculated. Results indicated that the design spectrum of Standard 2800 overestimates the response of the studied systems. Overall, the tubular system more economically provides the necessary stiffness and strength of the building system.