AbstractThe paper presents the experimental and numerical study of a mild steel replaceable dissipation device. The dissipater is made of a milled-down mild steel bar that is confined by a steel tube ...filled with either grout or epoxy. The use of a reduced area concentrates yielding and plastic straining over a defined length while the tube prevents buckling. The device has been widely adopted in posttensioned rocking systems, and extensive experimental research was carried out on wall and beam-column subassemblies using this external dissipater. As part of those experimental programs, some component testing was carried out; nevertheless, a more comprehensive study was necessary to cover a wider range of geometric and mechanical parameters. The main objective of this research was to calibrate and suggest design parameters to support the design of the dissipation device. The paper shows a comprehensive experimental program under quasi-static cyclic loading carried out with varying geometrical parameters. This work forms the basis for the development of more refined analytical and numerical models to simulate the behavior of the device. In particular, the onset of the dissipater interaction with the confining tube and its buckling mechanism were targeted. Further numerical simulations made use of a fiber element–based model that was capable of capturing the full range of deformation mechanisms highlighted in the experimental program. Using this model, an extensive parametric analysis was carried out to determine significant design parameters, such as the maximum force in the dissipater and the buckling onset strain. Analytical models were also presented to predict the monotonic behavior of the dissipater and provide calibration of the hysteretic force-displacement rule proposed in the final part of the paper.
During an earthquake, the detachment and local interaction between infill wall panels and surrounding frame can occur, potentially leading to significant local damage to both structural and ...non-structural elements, if not global collapse. Yet, a procedure to assess the relative deformation mechanism in terms of detachment shape and values, rather than, and in addition to, the diagonal compression strut mechanism and associated internal panel strain and stress path, is still missing in the literature. Therefore, in this paper the concept of shape functions is proposed and adopted to assess the seismic displacement incompatibility between infill walls and the surrounding frame structure. A parametric study on different typologies of infilled frames is developed to investigate the key parameters affecting the infill-frame detachment. The proposed concept of shape functions can support the design/retrofit of improved construction details, such as shear keys and/or steel dowels, in view of either decoupling or strengthening retrofit/repair strategies. Moreover, as infill-frame detachment can lead to damage to energy enhancement rehabilitation solutions, such as external thermal insulation systems, which are becoming more common nowadays in view of the international target towards a significant reduction of energy consumption and CO
2
emission, it is suggested to implement the proposed displacement-compatible design check to assess and detail for adequate displacement capacity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Major advances have been observed in the last decade in seismic engineering with further refinements of performance-based seismic design philosophies and definition of corresponding compliance ...criteria. Following the worldwide recognized expectation and ideal aim to provide a modern society with high seismic performance structures, able to sustain a design level earthquake with limited or negligible damage, emerging solutions have been developed for high-performance, still cost-effective, seismic resisting systems, based on adequate combination of traditional materials and available technology. In this paper, an overview of recent developments and on-going research on precast concrete buildings with jointed ductile connections, relying on the use of unbonded post-tensioned tendons with self-centering capabilities, is given. A critical discussion on the conceptual behavior, design criteria and modeling aspects is carried out along with an update on current trends in major international seismic code provisions to incorporate these emerging systems. Examples of existing on site applications based on a recently developed cable-stayed and suspended solution for frame systems are provided as further confirmation of the easy constructability and speed of erection of the overall system.
AbstractThe unbonded posttensioned rocking and dissipative technology was first developed as the main outcome of the PREcast seismic structural systems (PRESSS) Program in the United States. After ...the first developments and significant refinement, the technology was extended to steel and, more recently, timber structures. The timber version, referred to as prestressed laminated (Pres-Lam) system can be either implemented for timber walls (single or coupled) or frames or a combination of the above, with unbonded posttensioning and supplemental dissipation devices. In unbonded posttensioned dissipative wall systems a combination of recentering capacity and energy dissipation leads to a controlled rocking mechanism, which develops a gap opening at the wall base. This generates an uplift displacement that is transferred to the floor diaphragm. This vertical displacement incompatibility can represent a potential issue if the connection detailing between floor and lateral resisting system is not designed properly. The same issue can be mitigated by adopting an alternative configuration of the rocking/dissipative wall system, based on the use of a column–wall–column posttensioned connection. This concept, originally proposed for precast concrete walls and referred to as prestressed wall with end column (PreWEC), has been extended and adapted to posttensioned timber structures and validated through experimental testing. The paper presents the design, detailing, and experimental testing of a two-thirds scale wall specimen of this alternative configuration. Different wall configurations are considered in terms of posttensioning initial force as well as dissipation devices layout. The experimental results confirm the excellent seismic performance of the system with the possibility to adopt multiple alternative configurations.
Economic earthquake losses can be mitigated through either building retrofit strategies and/or, to some extent, risk‐transfer to the (re)insurance market. This paper proposes a computational ...framework to select the optimal combination of seismic retrofit and insurance policy parameters for buildings. First, a designer selects a suitable retrofit strategy. This is implemented incrementally to define interventions with increasing retrofit performance levels. The cost of each intervention is calculated, along with the cost of property rental while the retrofit is implemented. Alternative insurance options are considered. For each retrofit‐insurance combination, the insured and uninsured economic losses within a given time horizon are estimated. The optimal retrofit and insurance combination minimizes the tail value at risk of the life cycle cost. The selected confidence level for this metric depends on the homeowner's risk aversion. The proposed framework is illustrated for a case‐study archetype Italian reinforced concrete frame building retrofitted with concrete jacketing, also considering the Italian retrofit tax incentives/rebates called “Sismabonus.”
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
AbstractIn this study, an analytical procedure for the evaluation of the expected performance of existing reinforced concrete (RC) beam-column joints before and after being retrofitted using ...fiber-reinforced polymer (FRP) composite materials is presented. Focus is given on the evaluation of the shear-strength versus deformation properties of the panel zone region either in the as-built or FRP-retrofitted configuration. Based on experimental and numerical evidence as well as on physical models representing the mechanics of the joint region, principal tensile stresses versus joint shear deformation relationships are adopted and preferred to more traditional nominal shear-strength rules, to evaluate, within a step-by-step iterative procedure, the combination of the joint shear contribution provided by the FRP composite material and that provided by the concrete core alone. The use of principal stresses allows one to directly account for the effects of variation of axial load, typically neglected in the assessment and retrofit of beam-column joints. The hierarchy of strength and sequence of events (damage mechanisms) expected within a beam-column subsystem are visualized via M-N interaction performance domains, used as a basis for a performance-based retrofit philosophy. Specific limit states or design objectives are targeted, with attention given to both strength and deformation limits. The proposed analytical procedure is validated on the results of a set of experimental tests available in the literature. With the intention to provide a simple design tool that can be easily implemented by practicing engineers, a worked example for the evaluation of the expected performance of an FRP retrofitted beam-column joint is provided and used as a basis for a parametric study to illustrate the effects of different strengthening schemes on the behavior of strengthened exterior joint panels under various axial load levels.
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FGGLJ, IZUM, KILJ, NUK, PILJ, SAZU, UL, UM, UPUK
AbstractThis paper investigates the relative effect of material properties and structural details in the joint panels on the seismic fragility of existing reinforced concrete (RC) frames. Five ...building classes with different structural details (particularly in the joint panels) and material characteristics are defined according to different past design codes, for a three-story and a six-story archetype geometry. Based on nonlinear static or nonlinear dynamic analysis procedures, results from the study show that the effect of structural details on seismic fragility of the considered structures is negligible for damage states involving an essentially elastic behavior. Conversely, it is much higher for life-safety and near-collapse damage states, and it is considerably higher than the effect due to materials. Therefore, in the diagnosis phase, higher emphasis should be given to on-site investigations of actual reinforcement content/layout rather than to invasive material testing. The uncertainty related to the structural details described here is practically related to exterior, rather than interior, joint panels. Cover removal for one of those joints may potentially eliminate this specific uncertainty. As a practical action, in situ testing of RC frames should involve the cover removal of at least one exterior joint panel regardless of the required target “level of knowledge” of the existing structure.
In this article, the development of a new low damage clay brick infill wall system has been reported. The solution enables an engineer to control the drift level after which the infill wall damage ...can be allowed. This is achieved by utilizing a system of individual rocking clay brick infill panels rather than a single squat infill wall, which minimizes the interaction between the infill wall and the structural system until a selected design drift level. The solution is a workaround for the controversial aspects of clay brick infill walls, which are brittleness, or lack of deformability/ductility and unreliable strength. The seismic performances of an as-built unreinforced clay brick infill wall and the developed low damage clay brick infill wall system were evaluated by 2D quasi static tests. The results were calibrated and used for the analysis of a typical New Zealand building model in order to observe the effects of the as-built and the low damage infill wall systems on the maximum inter-story drift profiles of the structure.
Past design codes consider infill walls within frame buildings as non-structural elements; thus, these walls have been typically neglected in the analysis of a building. The observations made after major earthquakes in recent years have repeatedly shown that infill walls interact with the structural system during seismic actions and modify the behavior of the structure. More recent code design provisions recognize the complexity of such interactions and require either (a) consider these effects of frame-infill interaction during the design and modeling phase or (b) assure no or low-interaction of the two systems with proper detailing and arrangements in the construction phase. To consider the interaction in the design stage can be impractical and in most cases does not solve the actual problem related to their brittle behavior. On the other hand, considering the low interaction, not much technical information/design guide is available to the engineers, which is the problem tackled in this article.
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