Littérature scientifique sur le sujet « Dissipation, Seismic Renovation »

In seismic European countries most of the residential building stock is highly energy-intensive and earthquake-prone because it was built before the enforcement of the most recent energy and seismic codes. Furthermore, this stock often shows a low architectural quality due to poor maintenance and/or construction and design deficiencies: for all these reasons, it needs deep renovation, but the use of common energy and seismic upgrading techniques is often unsustainable in terms of costs, work duration, and occupants’ disturbance. Therefore, new integrated, affordable, fast, and low-disruptive renovation actions are strongly needed. This study proposes an innovative energy, seismic, and architectural renovation solution for reinforced concrete (RC) framed buildings, based on the addition of cross-laminated timber (CLT) panels to the outer walls, in combination with wooden-framed panels. The two panels integrate insulation and cladding materials in order to improve the energy performance and the architectural image of the renovated building. Moreover, the CLT panels are connected to the existing RC frame through innovative seismic energy dissipation devices. In case of an earthquake, these devices in combination with the CLT panels reduce the drift demand of the building, preventing or reducing structural damages and consequent repair costs. In particular, this paper investigates the technical feasibility, the energy efficiency, and the architectural enhancement of the proposed retrofitting system. To this purpose, dynamic thermal simulations were conducted on a typical multi-story residential building from the 1960s, located in Catania, Italy. The results indicated that this retrofitting technique considerably improved the energy performance of the selected building, with a reduction of the global energy demand up to nearly 60%. The presented study is part of a larger research project aimed at also investigating, in a further stage, the seismic performance achievable by the above-mentioned renovation solution.

Focusing on the green renovation project of Shendu Building in Shanghai, China, an evaluation system is developed for the comparison of a variety of seismic control schemes for seismic retrofit of the building. A three-dimensional evaluation model is developed in MATLAB to represent the dynamic features of the structural system of the building, and nine key evaluation indices are defined for the evaluation purpose from a global view of both control efficiency and costs. The complete procedure of designing control schemes based on the retrofitted benchmark structure is presented, which may be helpful for researchers and engineers in easily testing various control schemes by using this evaluation system.

Most of the building stock in European seismic countries is highly energy-intensive and earthquake-prone since it was built before the enforcement of effective energy and seismic codes. Renovation actions that synergically integrate both energy-efficient and anti-seismic interventions are strongly needed in these countries. However, the implementation of such interventions is currently limited by barriers that are mostly related to the high cost and invasiveness of traditional seismic retrofit techniques. A new holistic design approach to the building renovation is required to overcome these barriers. This should result in innovative and integrated retrofit interventions able to specifically meet the needs of cost-effectiveness, quick installation, reduced users’ disruption, and low environmental impact. In this framework, the use of cross-laminated timber (CLT) has been recently investigated for retrofit purposes in light of its good mechanical and physical performance. In this research context, this paper illustrates a novel timber-based retrofit technology for RC framed buildings developed within the e-SAFE H2020 project. This technology consists of cladding the external building envelope with a new prefabricated timber-based shell that acts as seismic-resistant and energy-efficient skin, also contributing to renovating the architectural image of the building. The new skin combines structural CLT-based panels – equipped with novel devices for seismic energy dissipation – with non-structural wooden-framed panels. Specifically, this paper presents a construction analysis of the proposed retrofit technology, investigating its technical feasibility, versatility, and potentialities, as well as possible application limits.

Abstract The Z Machine at Sandia National Laboratories is a pulsed power facility for high-energy density physics experiments that can shock materials to extreme temperatures and pressures through a focused energy release of up to ∼25 MJ in <100 nanoseconds. It has been in operation for more than two decades and conducts up to ∼100 experiments, or “shots,” per year. Based on a set of 74 known shot times from 2018, we determined that Z Machine shots produce detectable ∼3–17 Hz ground motion 12 km away at the Albuquerque Seismological Laboratory, New Mexico (ANMO), borehole seismograph, with peak signal at ∼7 Hz. The known shot waveforms were used to create a three-component template, leading to the detection of 2339 Z Machine shots since 1998 through single-station cross-correlation. Local seismic magnitude estimates range from local magnitude (ML) −2 to −1.3 and indicate that only a small fraction of the shot energy is transmitted by seismic phases observable at 12 km distance. The most recent major facility renovation, which was intended to decrease mechanical dissipation, is associated with an abrupt decrease in observed seismic amplitudes at ANMO despite stable maximum shot energy. The highly repetitive impulsive sources are well suited to coda-wave interferometry to investigate time-dependent velocity structures. Relative velocity variations (dv/v) show an annual cycle with amplitude of ∼0.2%. Local minima are observed in the late spring, and dv/v increases through the summer monsoon rainfall, possibly reflecting patchy saturation as rainfall infiltrates near the eastern edge of the Albuquerque basin. The cumulative results demonstrate that forensic seismology can provide insight into long-term operation of facilities such as pulsed-power laboratories, and that their recurring signals may be valuable for studies of time-dependent structure.

This research is inserted in the topic of timber buildings. Many construction systems are available for building using timber, with the two main systems in residential ambit being Cross Laminated Timber and Light Timber Frame. Both systems reckon on the presence of shear walls to bear the effects of horizontal loads like seismic events or wind. This thesis deals with timber shear walls, and is divided into two parts: the first part is related to the ultimate and serviceability limit states rules to be included in upcoming versions of the building codes, while the second part presents a novel use of CLT walls as seismic renovation for existing buildings, as part of a European project. The first part of the thesis, which is presented in three papers, is closely related to the process of producing new building codes, and aims at an easier integration between research and codification. The initial focus is the behaviour of Cross Laminated Timber subjected to in-plane loading. Eurocode 5 currently lacks a part concerning this product and the discussion is still ongoing regarding the methods for stresses evaluation and on the strength values to adopt for safety verifications. The first paper tackles this problem by analysing different calculation methods currently available for the evaluation of the in-plane shear stresses, a common notation is introduced in order to have a meaningful comparison between methods proposed by different authors. All methods are then applied to a real case of existing experimental data regarding a four point bending test of CLT beams. Stiffness and strength of CLT are essential parameters for the definition of models to be adopted in codes regarding timber buildings, in particular for the calculation of shear walls. Another very common timber construction system is called Light Timber Frame: an assembly comprising a timber frame and an external sheathing layer mechanically joined to the frame. Consequently LTF walls are considered, the study is directed towards shear wall models for the evaluation of deformations. The second paper focuses on the evaluation of the displacement at the top of LTF walls subjected to horizontal loads. This is a key aspect for designers, since the limitation of deformations ensures that the building retains a satisfactory performance at serviceability limit states. The displacement is due to many different contributions, with the sheathing-to-framing deformation being one of the major ones. The paper presents a comparison between two of the proposed methods to calculate the sheathing-to-framing deformation of LTF shear walls. The influence of the nail slip contribution on the overall displacement of the top of the wall is studied also with parametric analyses, by varying both mechanical properties and geometrical dimensions. Comparison with existing experimental data is also provided. The study on shear walls regards also their lateral capacity, as well as the comparison between LTF and CLT walls of equal aspect ratio and similar restraining. In the third paper, existing cyclic test data on LTF and CLT walls were used to study the different displacement contributions and estimate the influence of the hold-down on the lateral response of the walls. A simplified capacity model is proposed for the walls, based solely on the hold-down forces. The second part of the thesis deals with the use of CLT shear walls as a mean for the retrofit of existing buildings. The need for sustainable renovation solutions and improvement of the performance of existing buildings is at the base of the European project e-Safe. The project presents a multidisciplinary approach on building renovation, from mechanical, energetic, technological and architectural point of view. In this thesis the focus is on the seismic retrofit system called e-CLT: a CLT panel is attached to the outside of existing buildings with a novel connector that acts as a friction dissipation device, thus offering additional energy dissipation in case of strong earthquakes. The fourth paper presents the first experimental campaign on this novel friction connector. Different geometries for the connector are studied and optimised, before being tested under cyclic protocol. The connector is tested on a steel setup, in order to isolate the friction behaviour and study the stability of the hysteresis loops. The results permitted to acquire new information useful for further developments on the system. The fifth paper presents a subsequent experimental campaign on the friction connector. The shape is changed and improved in light of the previous results. The setup is improved and includes also a screw connection between friction connector and CLT panel. The goal is to study the influence of the timber connection on the friction dissipative performance. An analytical model is proposed, fitted on the experimental data.

<p>This paper introduces a new idea in the reconstruction and continuation projects. By arranging damping devices, the additional damping of the structure is increased, thereby reducing the dynamic response of the structure under the new seismic precautionary criterion. This paper focuses on the study of viscous dampers which one of the damping device, introduces the energy dissipation principle of viscous dampers, and combines a two-story plane frame case to analyze and compare the dynamic response between non-damping structure and damping structure. The location and quantity of the arrangement were compared with multiple models. Through analysis, it can be seen that by equipping with viscous dampers, seismic energy can be effectively dissipated, thereby reducing the workload of structural reinforcement and having less impact on the original structure. Finally, two commonly analysis methods in damping structures are studied, direct integration method and fast nonlinear analysis (FNA), the main differences between the two analysis methods are introduced, and the calculation results of the two methods are compared and analyzed.</p>

<p>This paper introduces a new idea in the reconstruction and continuation projects. By arranging damping devices, the additional damping of the structure is increased, thereby reducing the dynamic response of the structure under the new seismic precautionary criterion. This paper focuses on the study of viscous dampers which one of the damping device, introduces the energy dissipation principle of viscous dampers, and combines a two-story plane frame case to analyze and compare the dynamic response between non-damping structure and damping structure. The location and quantity of the arrangement were compared with multiple models. Through analysis, it can be seen that by equipping with viscous dampers, seismic energy can be effectively dissipated, thereby reducing the workload of structural reinforcement and having less impact on the original structure. Finally, two commonly analysis methods in damping structures are studied, direct integration method and fast nonlinear analysis (FNA), the main differences between the two analysis methods are introduced, and the calculation results of the two methods are compared and analyzed.</p>