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In this paper, various moment-resisting steel frames (MRSFs) are subjected to 30 narrow-band motions scaled at different ground motion intensity levels in terms of spectral acceleration at first mode of vibration  in order to perform incremental dynamic analysis for peak and residual interstory drift demands. The results are used to compute the structural reliability of the steel frames by means of hazard curves for peak and residual drifts. It is observed that the structures exceed the threshold residual drift of 0.5%, which is perceptible to human occupants, and it could lead to human discomfort according to recent investigations. For this reason, posttensioned connections (PTCs) are incorporated into the steel frames in order to improve the structural reliability. The results suggest that the annual rate of exceedance of peak and residual interstory drift demands are reduced with the use of PTC. Thus, the structural reliability of the steel frames with PTC is superior to that of the MRSFs. In particular, the residual drift demands tend to be smaller when PTCs are incorporated in the [url=http://www.xtnsteelstructures.com/steel-structure/high-rise-steel-structure/]high-rise steel structure[/url].
Currently, most of the seismic design regulations recommend the use of maximum interstory drift as the main engineering demand parameter. Nevertheless, earthquake field reconnaissance has evidenced that residual drift demands after an earthquake play an important role in the seismic performance of a structure. For example, several dozen damaged reinforced concrete structures in Mexico City had to be demolished after the 1985 Michoacan earthquake because of the technical difficulties to straighten and to repair buildings with large permanent drifts [1]. Okada et al. [2] reported that several low-rise RC buildings suffered light structural damage but experienced relatively large residual deformations as a consequence of the 1995 Hyogo-Ken Nambu earthquake even though they had sufficient deformation capacity. After examining 12 low-to-mid-rise steel office buildings (particularly 10 with structural system based on steel moment-resisting frames) structurally damaged and leaned after the same earthquake, Iwata et al. [3] highlighted that the cost of repair of leaned steel buildings linearly increased as the maximum and roof residual drift increased. Based on their study, the authors suggested that steel buildings should be limited to maximum and roof residual drift about 1.4% and 0.9%, respectively, to satisfy a repairability limit state that meets both technical and economical constraints. More recently, a field investigation in Japan indicated that a residual interstory drift of about 0.5% is perceptible for building occupants [4]. Bojórquez and Ruiz-García [5] by comparing peak and residual drift demand hazard curves have observed that if steel frames exhibit peak drift demands about 3%, they could experience residual drifts larger than 0.5%, which is the threshold residual drift that could be tolerable to human occupants, and it could lead to human discomfort [4] when subjected to narrow-band earthquake ground motions of high intensity. Therefore, several researchers have demonstrated that the estimation of residual drift demands should also play an important role during the design of new buildings [6–8] and the evaluation of the seismic structural performance of existing buildings [9–13].
In the present study, motivated by the need to reduce peak and residual interstory drift demands, PTCs are incorporated into various MRSFs. Posttensioned steel moment-resisting frames are structural systems proposed in recent years as an appropriate alternative to welded connections of moment-resisting frames in seismic zones [14–27]. They are designed to prevent brittle fractures in the area of the nodes of steel frames, which can cause severe reduction in their ductility capacity, as occurred in many cases during the 1994 Northridge and the 1995 Kobe earthquakes. The philosophy of structures with PTC is that under an intense earthquake motion, beams and columns remain essentially elastic concentrating the damage on the energy dissipating elements, which can be easily replaced at low cost. Moreover, they provide capacity of energy dissipation and self-centering which can significantly reduce the residual demands. The structural performance of the selected MRSFs is compared with the structures with PTC through incremental dynamic analysis and the estimation of the structural reliability of the frames in terms of peak and residual interstory drift demands. With this aim, four MRSFs and the same structures with PTC (here named FPTC frames with posttensioned connections) are subjected to 30 long-duration ground motions recorded at the lake zone of Mexico City where most of the damages were found in buildings as a consequence of the 1985 Michoacan earthquake. In general, it is observed that the structural reliability of the steel frames with PTC is superior to that of the MRSFs. In particular, the residual drift demands tend to be smaller than 0.5% (which is perceptible for building occupants) when PTCs are incorporated into the [url=http://www.xtnsteelstructures.com/steel-structure/steel-structure-buildings/]steel structure buildings[/url].