Improving the Seismic Performance of Steel Frames under Mainshock–Aftershock Using Post-Tensioned Connections (original) (raw)
Related papers
2020
The current state of practice for seismic design of typical buildings consider only a single design level event. The recent 2010-2011 Christchurch earthquake sequences have shown the devastating effects of sequential strong ground motion events for building structures that have not been repaired post-mainshock (MS). These events highlight the need for building structures that can be rapidly repaired while also showing the critical need to consider the seismic response of these structures for cascading large seismic events, when post-MS repairs have not occurred prior to a large aftershock(s) (AS). In recent years there has been a high interest in the development of alternative seismically resilient seismic-force resisting systems (SFRSs) that offer self-centering and rapid reparability characteristics. However, compared to conventional SFRSs, these alternative SFRSs are potentially more vulnerable to large MS-AS sequences as the energy dissipation of the replaceable structural fuses are typically substantially less than those used in conventional SFRSs. Although seismically resilient SFRSs have shown to provide excellent performance under a single design level MS, their seismic performance under cascading large earthquake sequences is not well understood. This paper presents nonlinear response history analyses results of the seismic performance of two distinctly different seismically resilient SFRSs that are expected to provide frame recentering and concentrate inelastic damage to only the replaceable structural fuses. Specifically, one frame system is detailed with post-tensioned beam-to-column joints that rock about the top flanges only with a steel plate infill web plate structural fuses. The second system is detailed with post-tensioned beam-to-column joints that rock about the top and bottom flanges with tension-compression steel structural fuses. The results presented provides some insight on the system performance and seismic resiliency of these alternative SFRSs under large MS-AS sequences.
Numerical analysis of steel moment resisting frames under mainshock-aftershock seismic sequences
The purpose of the visit was the development of models to accurately assess the behavior of steel structures subjected to seismic cascading events on performance levels close to collapse, and, simultaneously, propose a framework for quantifying the structural robustness considering the occurrence of a major earthquake (mainshock) and subsequent aftershock events. This report is focused on the second topic.
Seismic performance of dual-steel moment resisting frames
Journal of Constructional Steel Research, 2014
Traditionally, lateral stiffness and strength of the gravity frames in steel buildings are neglected in structural analysis. During the past earthquakes, such as Northridge, USA, 1994 and Kobe, Japan, 1995, unexpected failures were detected at beam-tocolumn connections of steel moment resisting frames (MRFs). In the aftermath of these earthquakes, extensive research has been carried out to reveal the causes of these failures. Based on the detailed observations, it is likely that the reserve capacity provided by the gravity frames prevented the highly damaged steel buildings from collapsing, since majority of the momentresisting connections failed prematurely during the Northridge earthquake (1994). Even though the influence of gravity frames (GFs) on structural behavior can be substantial, little attention is paid to evaluate its impact on structural response. With this paper, the contribution of interior GFs in seismic performance of special moment resisting steel frames (SMRFs) is evaluated. For this purpose, 4-and 9-story SMRFs were designed in accordance with the requirements of Draft Turkish Seismic Code (2016). The frames are, then, subjected to incremental dynamic analysis. To evaluate the contribution of the interior GFs on the overall seismic performance of structural system, inelastic behavior of shear tab (simple) connections at beam-to-gravityonly columns were idealized as semi-rigid joints. A general purpose structural analysis software, ETABS, is utilized for the analyses. The results of the study are presented in terms of story drifts, base shear vs. roof displacement.
Seismic Response and Design of Post-Tensioned Steel Moment Resisting Frames with Friction Components
2002
A post-tensioned friction damped connection (PFDC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The connection includes friction components on the beam flanges with post-tensioned (PT) high strength strands running parallel to the beam. The connection minimizes inelastic deformation to the connection components and requires no field welding. Nonlinear analyses were performed on a 6-story, 4-bay steel MRF with PFDCs to study its response to strong ground shaking. A performance based design approach was developed to design the PFDC-MRF. The results demonstrate that the seismic performance of a PFDC-MRF is satisfactory in terms of strength, energy dissipation, deformation, and self-centering capability. The analysis indicate that the seismic performance of a PFDC frame can exceed that of a frame with conventional moment resisting connections.
Moment resisting steel frames under repeated earthquakes
In this study, a systematic investigation is carried out on the seismic behaviour of plane moment resisting steel frames (MRF) to repeated strong ground motions. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised due to lack of time. In this work, thirtysix MRF which have been designed for seismic and vertical loads according to European codes are first subjected to five real seismic sequences which are recorded at the same station, in the same direction and in a short period of time, up to three days. Furthermore, the examined frames are also subjected to sixty artificial seismic sequences. This investigation shows that the sequences of ground motions have a significant effect on the response and, hence, on the design of MRF. Additionally, it is concluded that ductility demands, behaviour factor and seismic damage of the repeated ground motions can be satisfactorily estimated using appropriate combinations of the corresponding demands of single ground motions.
Location of Semi-Rigid Connection Effect On The Seismic Performance of Steel Frame Structures
2021
In design steel frames, combining semi-rigid and rigid connections can result in better structural performance, particularly in seismic locations. In this study, the effects of semi-rigid beam-to-column connections located on the seismic performance of steel frame structures are investigated. The analysis uses six and twelve-story moment resisting steel frames (MRSF) with rigid, semi-rigid, and dual beam-column connections. These frames are designed according to the Egyptian design codes. Drain-2Dx computer program and seven earthquake ground motions are used in the non-linear dynamic analysis. The rotational stiffness of beam-to-column connections is indicated through the end fixity factors with a value equal to 0.6. The performances of these frames are evaluated through the roof drift ratio (RDR), the maximum story drift ratios (SDR), and the maximum column axial compression force (MACF). The results indicated that the quantities of fundamental periods, roof drift ratio, the story...
2013
A new self-centering steel post-tensioned connection using web hourglass shape steel pins (WHPs) has been recently developed and experimentally validated. The connection isolates inelastic deformations in WHPs and avoids damage in other connection parts, like beams and columns. WHPs do not interfere with the composite slab and can be very easily replaced without bolting or welding, and so, the connection enables rapid return to building occupancy in the aftermath of a strong earthquake. This paper presents a simplified nonlinear model for the connection that consists of nonlinear beam-column elements, and hysteretic and contact spring elements appropriately placed in the beam-column interface. The model was calibrated against experimental results and found to accurately simulate the connection behaviour. A prototype building was selected and designed both as a conventional steel moment-resisting frame (MRF) and as a self-centering steel MRF (SC-MRF) using the proposed connection. Seismic analyses show that both MRF and the SC-MRF have comparable storey drifts, and highlight the ability of the SC-MRF to eliminate damage in beams and residual drifts. The paper also shows that damage repair for the MRF will be costly and disruptive after the design basis earthquake, and, not financially viable after the maximum considered earthquake.
Experimental studies on full-scale post-tensioned seismic-resistant steel moment connections
Six full-scale interior connection subassemblies of post-tensioned wide flange beam-to-column moment connections were tested. Each was subjected to inelastic cyclic loading up to 4% story drift to simulate earthquake loading effects. Bolted top and seat angles are used in the connection, along with posttensioned high strength strands that run parallel to the beam. These strands compress the beam flanges against the column flange to develop the resisting moment to service loading and to provide a restoring force that returns the structure to its pre-earthquake position. The parameters studied in these experiments were the initial post-tensioning force, the number of post-tensioning strands, and the length of the reinforcing plates. The experimental results demonstrate that the post-tensioned connection possesses good energy dissipation and ductility. Under drift levels of 4%, the beams and columns remain elastic, while only the top and seat angles are damaged and dissipate energy. The lack of damage to the beams, columns, and the post-tensioning enable the system to return to its plumb position (i.e., it self centers). Closed-form expressions are presented to predict the connection response and the results from these expressions compare well with the experimental results.