Novel adaptive hysteretic damper for enhanced seismic protection of braced buildings
Introduction
Among antiseismic hardwares, traditional Bilinear Hysteretic Dampers (BHDs) were introduced in the ‘70s of the last century as a viable and effective solution to mitigate the effects of strong earthquakes on braced frames [1,2]. Indeed, BHDs are usually inserted along buildings diagonal braces in order to dissipate the seismic energy through the plastic deformation of sacrificial mild steel components. This ensure a stable force-displacement (F-d) response that is not, or only marginally, affected by velocity and is conventionally described by means of an elasto-plastic model with post-yielding hardening.
Over the last thirty years, several BHDs were developed and introduced in the market. BHDs plastically deformed under axial loads [3], shear loads [4], bending [5,6], and torsion [7] have been proposed and implemented worldwide for the seismic retrofit of schools [[8], [9], [10]] and for the protection of hospitals [11] profiting of their lower cost in comparison to other technologies (e.g. fluid viscous dampers).
Among BHDs, the Shear Hysteretic Panels (SHPs) consist of a steel plate with equally spaced openings delimiting a number of dissipative laminae. The relative motion between the bottom and the upper edge of the SHP induces the shear deformation of the laminae, first in the elastic and then in the plastic regime, resulting in the typical bilinear F-d behaviour. Despite since the early ‘90 the response of honeycomb [12], rectangular [13], and hourglass [14] shear hysteretic laminae have been investigated, a widespread diffusion of SHPs among popular anti-seismic technologies has been so far constrained by the unsatisfactory strength against out of plane buckling problems.
Performance Based Design (PBD) procedures were firstly formulated by Priestely in the early 80's [15] and have been nowadays endorsed in the most advanced design codes and guidelines like the ASCE 7–16 [16] and the Eurocode 8 [17]. In particular the latter establishes two different seismic scenarios and the relevant performance requirements for the design of new structures as well as for the retrofitting of existing ones:
- 1)
under the severe “Ultimate Limit State” (ULS) scenario, featuring 10% probability of exceedance over the reference period , the structures shall be capable to withstand the dynamic seismic loads without any global or local collapse preserving as well a residual lateral strength after the quake. This requirement is usually referred as “structural safety requirement” or “no-collapse requirement”;
- 2)
the “Serviceability Limit State” (SLS) scenario provides less intense but more frequent earthquakes characterized by 10% probability of exceedance over the lower reference period . In the aftermath of the SLS seismic scenario, the structures are demanded to remain fully-operational (“damage limitation requirement”).
In order to attain the “Damage limitation requirement” target, besides the absence of structural damages, both “acceleration-sensitive”, and “drift-sensitive” non-structural components (NSCs) should be protected against detrimental high peak floor accelerations (PFAs) and interstorey-drifts since their integrity is crucial in high-technological buildings (e.g. hospitals, and emergency centers) [18]. Due to the huge number of NSCs and the wide variety of possible installation layouts, an exhaustive definition of relevant failure thresholds is still not available. However, a simple approach to the scope is the HAZUS method [[19], [20], [21]] that is based on the definition fragility curves. These functions provide the statistical distribution of the probability that the seismic demand exceeds the capacity (strength) of the NSC. Given the intensity of the seismic event, and assuming the log-normal distribution for the random variable , the probability of failure is:being the median value of the capacity (), the standard deviation, and the standard normal cumulative distribution function. The HAZUS method establishes four damage levels: (1) slight damage; (2) moderate damage; (3) extensive damage; and (4) complete damage. A list of moderate-extensive capacity limits for NSCs most common in high-technological buildings is reported in Table 1 and is based on a wide literature survey [18] that has been recently enlarged in Ref. [22]. With respect to the original list, some “displacement-sensitive” components are here also added. Indeed, it is well known that components such as storage racks, which are often tall, and heavily loaded, parapets, and chimneys could suffer extensive failure when experiencing large displacements [[23], [24], [25]]. However, due to the lack of dedicated statistical investigations, the “on-site expert judgment” is the approach suggested here for the definition of the median capacity of these components.
Although approaches more refined than the HAZUS have been recently proposed, their application is not always practical since requiring the knowledge of the natural frequency of each NSC to account for its dynamic interaction with the supporting structure by means of “floor response spectrum” analyses [23,26]. Despite the increasing number of shake table tests conducted in the last years on single NSCs [[27], [28], [29]], as well as on small or full scale structures with integrated plants and architectural elements [[30], [31], [32], [33]], this information is often missing.
The seismic response of several different layouts of frames braced through hysteretic dampers has been recently investigated through shaking table tests carried out at the University of Basilicata, Italy [41]. Maximum interstorey drifts and peak floor accelerations have been compared to those recorded for the bare frame. On one hand, the introduction of the hysteretic braces allowed a significant reduction of the frame lateral deformations while, on the other hand, caused a huge increase (up to 300%) of PFAs. Similar outcomes are also described in Ref. [42] where high PFAs, induced by the introduction of hysteretic braces for seismic-retrofit purpose, were proven to be detrimental for “acceleration-sensitive” NSCs. Enhancements in traditional seismic design methods and new approaches based on low damage methodologies and cost-efficient technologies are hence needed [43,44]. Nevertheless, in common design practice antiseismic devices are designed accounting for the “structural safety requirement” at the ULS only [[45], [46], [47], [48], [49], [50]]. In order to improve this unacceptable situation, the novel Adaptive Hysteretic Damper (AHD), capable to modulate its effective damping and stiffness based on the intensity level of the ongoing earthquake, is presented in this paper. The analytical model ruling the two-stage hysteretic behavior of the AHD is illustrated and its accuracy, as well as and the reliability of the device under multiple seismic-excitations, is assessed through displacement-controlled experimental tests carried out on a 2.4 MN prototype. Eventually a simple linear equivalent design method (based on iterative response spectrum analyses) for braced frames implementing AHDs is developed and applied for the seismic-retrofit of a real case-study building. The advantages warranted by the new proposed technology are argued and compared to the performances offered by more conventional BHDs.
Section snippets
Novel adaptive hysteretic damper (AHD)
Like in conventional SHPs, the dissipative core of the novel AHDs provides a number of shear hysteretic laminae featured by an optimized hourglass shape. In addition, in order to increase its strength against lateral buckling, the laminae does not lie on a single plane but are arranged to form a squared hollow section (Fig. 1-a). Tension and compression loads are clockwise alternatively transmitted to the corners of the pipe section inducing the shear deformation of the laminae (Fig. 1-b).
Experimental tests
The hysteretic response of the AHD, with a particular focus on its robustness under repeated cyclic motions, was investigated through displacement-controlled tests carried out at the Eucentre Lab. (Pavia, Italy) [51]. A full-scale prototype of AHD prototype, made of common structural steel S355, was manufactured by Maurer SE [52] according to the following design parameters: (1) minor hysteretic core featuring , , (2) width of the hole in the
Design procedure for buildings braced through AHDs
A design procedure dedicated to braced frames implementing the novel AHDs is proposed in Section 4.1 assuming, as starting condition, the a-priori knowledge of the structural properties of the bare frame. This circumstance is always representative of retrofitting projects while, in case of new buildings, could be attained through a preliminary design of the bare frame taking into account, for instance, the gravitational loads only. The final layout, including the dissipative braces with the
A case-study
In this Section, the proposed design procedure is applied to a real case-study building and the beneficial effects offered by the AHD, compared to traditional bilinear hysteretic dampers (BHDs), are quantified. The “Piastra building” of the hospital of Lamezia Terme, a small city located in a high seismic area in southern Italy, is selected as case-study. Despite the whole structure is composed of three independent frames interspersed by seismic joints, for sake of simplicity, only block C has
Conclusions
The Adaptive Hysteretic Damper (AHD), a novel anti-seismic device that is capable to modulate its effective stiffness and damping depending on the intensity (e.g. PGA) of the occurring earthquake, has been presented in this paper. The AHD comprises a minor and a major hysteretic cores that are arranged in series and are mutually linked through a “gap-connector”. Compared to conventional bilinear hysteric dampers (BHDs), the AHD offers: (i) not impaired structural safety under severe ULS events;
Credit author statement
E.G: Investigation; Methodology; Writing – review & editing. IS.C: Investigation; Methodology. J.D: Investigation; Methodology. P.D: Supervision. F.W: Supervision; Investigation. A.T: Supervision; Writing – review & editing
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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2023, Thin-Walled StructuresCitation Excerpt :To mitigate the seismic damage to the structural and nonstructural components, the equipment of passive dampers was proved to be an effective and economical method and extensively utilized in constructional practices [3]. Multiple passive dampers absorbing seismic energy through different mechanisms have been developed, including the friction dampers [4,5], metallic dampers [6–10] and viscous dampers [11,12]. Among the passive dampers, the friction dampers had stable hysteretic performance and prominent energy dissipation capacity which promoted their widespread application [13].
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2022, Engineering StructuresCitation Excerpt :Considering the drawbacks of the single form of dampers above, attempts are made to form a high-performance damper meeting the substantive structural demand for the continuous energy dissipation and reliable lateral stiffness against seismic actions. Gandelli et al. [31] brilliantly proposed a novel adaptive hysteretic damper (AHD) and demonstrated that the adaptive multi-stage force–displacement behavior could ensure the safety of the main structure under a severe earthquake and mitigate the peak floor acceleration under a minor earthquake. Therefore, both the structure and acceleration-sensitive non-structural components could be well protected.
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2022, Engineering StructuresCitation Excerpt :In an effort to develop a bracing system with gradually increasing post elastic hardening, Palermo et al. [18] have tried deformed braces by introducing initial out-of-straightness in order to utilize displacement-dependent geometric hardening created due to the special shape of the brace. A novel damping system for braced frames with displacement-dependent hardening has also been developed and tested by Gandelli et al [19]. Energy dissipaters of this system are ADAS-shaped elements integrated into the bracing element, while the displacement-dependent hardening feature of the system is obtained by a proper arrangement of energy dissipaters with different capacities.
Combination of different types of damped braces for two-level seismic control of rc framed buildings
2021, Journal of Building EngineeringCitation Excerpt :Specifically, in-parallel combinations of the same (e.g. HDBs) and different (e.g. HDBs and VDBs) typologies of damped braces have been proposed in the literature [25–27], where small HDBs and VDBs, working as fuses, are inserted as sacrificial elements providing damping for SDE, while large HDBs are placed to attain significant energy dissipation for BDE and MCE. Alternatively, the damping and stiffness properties of HDBs arranging in-series minor and major cores can be modulated to different seismic intensity levels [28]. Finally, hybrid hysteretic-hysteretic and hysteretic-viscous dampers with a gap-hook mechanism have improved structural performance in both near- and far-fault earthquakes [29–31].