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Experimental seismic response of a resilient 3-storey post-tensioned timber framed building with dissipative braces
No full textWith the increased number of multi-storey buildings in seismic areas, research efforts have been focused on developing earthquake resilient systems, such as low-damage techniques based on the combination of post-tensioning and dissipating devices. This paper describes the experimental study performed on a 3-storey post-tensioned timber framed (Pres-Lam) building equipped with energy dissipating systems. The testing project consisted of three phases adopting different configurations of the experimental model: (1) post-tensioning to beam-column joints only, (2) post-tensioning and dissipative rocking mechanisms and (3) post-tensioning and dissipative braces. The main objective of this paper is to experimentally investigate on the seismic response of a large-scale specimen with dissipative braces located in high seismic area, considering construction details similar to those adopted in practical applications. During the experimental campaign, the test frame was subjected to more than one hundred ground motions considering a set of seven spectra-compatible earthquakes at increasing intensity levels. The dissipating bracing system with external replaceable hysteretic dampers improves the seismic resilience of multi-storey Pres-Lam buildings, showing inter-storey drift comparable to those with rocking walls, with full recentring capability and without structural damages or post-tensioning losses through seismic tests
Modeling of post-tensioned timber framed buildings with hysteretic bracing system: preliminary analysis.
No full textThe increasing demand for multi-storey timber framed buildings in seismic areas has led to the developing of damage limiting systems. The self-centering rocking mechanisms combined with dissipative systems, such as dissipative bracing is a high-performance system that can prevent major structural damage and minimize residual drifts during strong earthquakes. This paper shows the modelling of a three-dimensional, three-storey, two-third scaled, post-tensioned timber framed model equipped dissipative bracing systems and compares the numerical simulations with the experimental results obtained at the structural laboratory of the University of Basilicata. The hysteretic bracing system is composed by V-inverted timber brace in series with U-shaped flexural steel plates. During preliminary shaking table tests, the specimen was subjected to two earthquake inputs at different intensity levels. The braced model was developed using an appropriate combination of elastic elements with lumped rotational and linear springs, by means of two different software OpenSees and SAP2000. Both numerical outcomes of nonlinear dynamic analysis are in good agreement with the global and local seismic experimental response of the braced model and of the hysteretic dampers. Based on the validation of the numerical models further studies of optimization of design methods and a complete probabilistic characterization of Pres-Lam building performances will be develope
Testing requirements of hysteretic energy dissipating devices according to Italian seismic code
No full textAnti-seismic displacement dependent devices are used to improve the dynamic characteristics of the structural system of buildings and bridges. Performance and functional requirements of energy dissipating devices are specified in most new seismic design codes. In this paper nonlinear dissipative capacity of hysteretic dampers is evaluated by specific experimental tests and compared with the Italian code testing requirements. Quasi-static and dynamic experimental testing have been performed on U-shaped flexural steel plates (UFPs) devices. Controlled-displacement tests considering a specific loading protocol have been performed to define the cyclic behavior of UFPs. Shaking table testing considering a random sequence of seismic inputs have been carried out on a 3D, 2:3 scaled, three-storey post-tensioned timber framed building with dissipative bracing systems based on UFPs. The reliability of the testing procedures required by codes for prototype and production control tests is discussed in terms of number of cycles and of cycles to failure
RETROFITTING OF R.C. FRAME BUILDINGS WITH DOUBLE CONCAVE CURVED SURFACE ISOLATOR SLIDERS CHARACTERIZED BY OVER-STROKE DISPLACEMENT CAPACITY
No full textBase isolation system is one of the most widespread passive control system techniques currently used for seismic protection of buildings and bridges. At the ultimate limit state, isolating devices are designed to attain the design displacement at the Maximum Credible
Earthquake (MCE), while the superstructure remains in the elastic range for earthquake intensity corresponding to the Design Basis Earthquake (DBE). Among various isolation devices the friction pendulum sliders and elastomeric bearings are the most economical and
practical system. Acceptable probabilities of collapse for seismically isolated frame structures could be achieved by a suitable isolator displacement capacity.
This study considers the effects of restraining rings and of the over-stroke displacement capacity of double concave curved surface slider (DCCSS) isolators on the structural seismic
response. The seismic behaviour of base isolated six-storey reinforced concrete frame building case study retrofitted for seismic site of L’Aquila has been evaluated considering earthquake intensity levels at Collapse Limit State. Different configurations of the base isolation
system, with end-stops placed at maximum isolator displacement capacity or with extra-stroke
displacement capacity, have been investigated. In this paper, the results of non-linear static
and dynamic analyses at the MCE are compared
Dynamic Seismic Response of Nonlinear Displacement Dependent Devices versus Testing Required by Codes: Experimental Case Studies
No full textPassive energy dissipation systems are one of the most resilient solutions to mitigate the seismic risk of structures. In case of strong motions, they can confine the eventual damages into easily replaceable anti-seismic devices. The performance characteristics of nonlinear displacement dependent devices (NLD) shall be defined by the force-displacement cyclic behavior, as well as the expected number of cycles related to both the duration of the earthquake and to the fundamental frequency of the structural systems. The aims of this paper are the comparison between the dynamic results of two different experimental campaigns performed on NLDs included in dissipative bracing systems and the assessment of the reliability of quasi-static testing procedures proposed by current seismic codes for type tests and factory production control tests. The number of cycles under the design earthquake of hysteretic dampers were experimentally evaluated through shaking table testing. Two experimental case studies of a two-story steel frame and of a three-story post-tensioned timber frame both with bracing systems including flexural steel dampers, hysteretic dampers (HDs), and U-shaped flexural plates (UFPs) respectively, were analyzed. Controlled-displacement tests of NLDs were performed considering quasi-static loading procedures specified by codes. Shaking table tests were carried out considering almost the same seismic sequence composed by a set of seven natural earthquakes at increasing peak ground acceleration (PGA) levels. More than one hundred inelastic cycles were experimentally recorded from dynamic tests before the failure of devices in both cases. In line with American standards testing requirements, the number of cycles at the design PGA level, estimated from shaking table tests and from non-linear dynamic analyses, shows a decreasing trend with the increase of ductility demand
Dissipative bracing system for post-tensioned timber framed buildings: Experimental testing of U-shape hysteretic dampers
No full textThis paper describes the experimental quasi-static tests performed at the structural laboratory of the University of Basilicata on hysteretic dissipative dampers consisting of Ushaped steel plates (U-shaped Flexural Plate) to be used for dissipative bracing systems. The cyclic tests, are preparatory for shaking table testing of a 3D, 2/3rd scaled, three-storey post-tensioned timber framed building equipped with dissipative bracing systems composed by V-inverted timber rods and two UFPs in series, designed for each storey to yield in a controlled manner. In order to optimize the design procedure of the UFP dampers, the analytical models available in the literature for the definition of the elastic stiffness and yield force of the devices are compared with the results of quasi-static experimental tests. Furthermore, in order to verify the robustness of the seismic protection technique, a parametric analysis is carried out considering non-linear numerical models, varying the characteristics of the dissipative bracing design parameters. Finally, the preliminary results of the shaking table tests on the braced structure are compared with those of the bare structure in order to validate the effectiveness of the dampers in the control of the seismic response
Displacement based design of post-tensioned timber framed buildings with dissipative rocking mechanism. Soil Dynamics and Earthquake Engineering
No full textThis paper presents a seismic displacement-based design method for post-tensioned timber (Pres-Lam) framed buildings equipped with passive energy dissipation systems. In displacement-based design a target drift is specified, then the corresponding design forces are determined in order to size the post-tensioning and dissipative devices. The design procedure has been applied to a 2/3 scaled, 3-dimensional, 3-storey post-tensioned timber framed building. Yielding steel angles were used to create a dissipative rocking mechanism at the beam-column and column-foundation connections. The specimen was constructed and dynamically tested at the structural laboratory of the University of Basilicata, as part of a collaborative campaign with the University of Canterbury. Shaking table tests were performed considering different specimen configurations, without (free rocking) and with (dissipative rocking) the addition of dissipative steel angles. Seismic testing confirmed the effectiveness of hysteretic energy dissipation systems on the reduction of the maximum inter-storey drift. Experimental results are compared with non-linear dynamic analysis in order to verify the reliability of the design procedure
Modelling of post-tensioned timber-framed buildings with seismic rocking mechanism at the column-foundation connections
Get PDFThe need to mitigate damage of buildings even after strong earthquakes has led to the development of high-performance seismic resisting systems. Extensive studies have been made in the last decade on the development and use of jointed ductile connections and on the effects of rocking vibration systems in reducing seismic damage of buildings. A recently developed technology for construction of multi-storey timber buildings called Pres-Lam system uses long lengths of prefabricated laminated timber and binds them together using pre-stressing steel tendons. When appropriately combining unbounded post-tensioned tendons, or rocking columns with additional sources of energy dissipation devices, a hybrid system is obtained, with self-centering and dissipative properties, leading to a characteristic flag-shape hysteresis behaviour. A three-dimensional, three-storey, two-third scaled, post-tensioned timber frame model was tested at the structural laboratory of the University of Basilicata. During shaking table tests, two different configurations of the test model have been studied considering column-table connections with and without the activation of dissipative steel angles. This paper focuses on different numerical modelling of the rocking mechanisms at the column-foundation connections. Two different modelling have been considered for two different test configurations by means of a pinned base or an appropriate combination of nonlinear rotational springs, for free rocking and a suitable combination of gap elements and linear springs or rotational springs, for dissipative rocking. The numerical outcomes of nonlinear dynamic analysis are compared with experimental test results providing an adequate representation of the seismic response
RINTC-E project: The seismic risk of existing Italian RC buildings retrofitted with seismic isolation
No full textThis paper reports on the results of an ongoing Research Project, funded by the Italian Civil Protection Department, aimed at the evaluation of the risk of collapse and usability-preventing performance levels for existing buildings. This paper, in particular, describes the results of nonlinear time-history analyses (NTHA) carried out on two different RC buildings retrofitted with isolation systems. The two buildings are located in two different sites, Naples and L’Aquila characterized by medium and high seismicity for Italy, and are designed for gravity loads only and according to outdated seismic codes respectively. The buildings have been retrofitted using three different isolation systems: (i) high damping rubber bearings; (ii) rubber bearings and flat sliding bearings; (iii) curved surface sliders. The results point out that all isolation systems work effectively in limiting the onset of damage of non-structural members for seismic intensities much higher than the action required by the current design code. On the other hand, they show a little margin towards collapse, beyond the design intensity level. In particular, the collapse of the superstructure turns out to be the dominant collapse mode, especially for the building designed for gravity loads only
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