Level Of Seismic Protection Research Articles

Seismic Retrofitting of Historic Masonry Structures with the Use of Base Isolation—Modeling and Analysis Aspects

ABSTRACTThe seismic retrofitting measures which are appropriate for buildings belonging to the architectural heritage are limited, since the extent to which such buildings are allowed to be altered is severely limited. In the paper the possibilities which exist for the implementation of base isolation in the case of the seismic upgrade of unreinforced masonry (URM) structures belonging to the valuable architectural heritage have been investigated. A new methodology for the modeling of URM buildings, based on an equivalent frame model with plastic hinges, was used for this purpose. A case study involving a typical neo‐renaissance masonry building is presented, in which base isolation is implemented, and a comparison is made with the response of the building in its original state. A refined approach for the selection of proper isolation devices is proposed which is based on the nonlinear static (pushover) analysis of such buildings and on the desired level of seismic protection, with reference to the code-based damage limit states. Additionally, the incremental nonlinear dynamic analyses were also applied in order to estimate what increases in seismic safety could be achieved if the employed base isolation system was used in the case of different seismic intensities.

Roof Isolation with Tuned Mass-based Systems and Application to a Prefabricated Building

The earthquake-resistant design of prefabricated buildings is currently the focus of attention, especially for industrial buildings that require a high level of seismic protection. The standard design approach, based on ductility requirements, may succeed in preventing building collapse during a severe earthquake, but at the expense of accepting a high damage level at the column bases. To improve the seismic performance of such buildings, different innovative techniques have been proposed. However, these have not been widely implemented in engineering practice due, among others, to the lack of simple conceptual design methodologies. To achieve this goal, a methodology for the design of a roof isolation system is presented, where the roof isolation serves as non-conventional tuned mass damper (TMD), giving a significantly reduced response in terms of displacements and forces. To that effect, design expressions for the TMD period and damping, depending on the building and soil characteristics, are proposed: The expressions have been calibrated based on numerical parametric time history analyses considering Eurocode 8 spectrum—compatible accelerograms. The application of the proposed methodology is demonstrated for a two-story prefabricated building.

Seismic design and performance evaluation of steel-frame buildings designed using the 2005 National building code of Canada

The seismic design provisions in the current edition of the National building code of Canada significantly differ from those in the earlier version of the code . Although the code has moved from the earlier prescriptive provisions towards a more performance-based design, such design principles have not yet been fully implemented. In the present work, four ductile steel moment-resisting frame buildings with heights of 5, 10, 15, and 20 storeys, were designed for Vancouver using the newer code, and their performances were studied to determine the level of seismic protection implied in the code. Synthesized and scaled real ground motion records were used to evaluate the nonlinear dynamic response of these structures. Although the buildings achieved the collapse prevention performance objective of the code, variations in evaluated performance parameters for the different buildings were observed. Also, building performance was found to be affected by the presence of infill walls, as well as by the nature of selected ground motion records and the methods used to scale them to Vancouver uniform hazard spectra.

Seismic design implications of revisions to the National Building Code of Canada

This paper begins with a brief introduction to Canadian seismicity and the history of seismic code development in Canada; a summary of major changes planned for the 2005 edition of the National Building Code of Canada follows. Areas of major change include seismic hazard, site effects, irregularities, force reduction factors and methods of analysis (dynamic analysis now being preferred). The implications of the proposed changes are presented in terms of impact on seismic design force for several structural systems located in regions of high, moderate and low seismicity; implications for seismic level of protection and the seismic design process are also discussed. The paper concludes with a discussion of ongoing seismic code development issues.

Overview of seismic provisions of the proposed 2005 edition of the National Building Code of Canada

The proposed 2005 edition of the National Building Code of Canada (NBCC) will contain very significant changes in the provisions for seismic loading and design. A brief history of the NBCC seismic provisions is presented followed by a discussion of the reasons for introducing such major changes in the next edition of the code. The major changes to the seismic provisions are summarized; this includes updated hazard in spectral format, change in return period (probability of exceedance), period-dependent site factors, delineation of effects of overstrength and ductility, modified period calculation formulae, explicit recognition of higher mode effects, rational treatment of irregularities, triggers for special provisions incorporated directly in classification of structural systems, and placing dynamic analysis as the normal "default" method of analysis for use in seismic design. The impact of these changes on the seismic level of protection is considered by comparing the 2005 NBCC and 1995 NBCC base shear coefficients for a selection of common structural systems located on a range of site conditions in three urban areas having low to high levels of seismic hazard, i.e., Toronto, Montréal, and Vancouver.Key words: seismic, design, loading, code, hazard, buildings, structures, foundations, period, analysis.

Evaluation of the level of seismic protection afforded to reinforced concrete shear wall systems

This paper presents the results of an investigation into the seismic level of protection afforded to reinforced concrete shear wall systems. The vulnerability and damage potential of a 30-storey building consisting of a coupled shear wall as well as noncoupled shear walls as lateral force resisting systems is evaluated. The structure, which is similar to an existing building designed and constructed in Vancouver, is designed in accordance with the 1995 National Building Code of Canada and detailed using the provisions of CAN3-A23.3-M94 (1994). Elastic analysis is performed using both two-dimensional and three-dimensional shell element models for lateral loading with and without the effects of torsion. Element design specifications are used to create moment curvature envelopes to describe the members (beam and wall) deformation characteristics. These characteristics are incorporated into the nonlinear pushover analysis and dynamic inelastic time history analysis. The level of protection investigation illustrates that the coupled and noncoupled shear wall systems exhibit excellent performance following excitations of two and three times the design level earthquake. Maximum interstorey drift and element damage levels are within the acceptable limits for life-safe performance.Key words: seismic, reinforced concrete, shear walls, coupling beams, performance, inelastic, dynamic, design.

Evaluation of the seismic level of protection afforded to steel moment resisting frame structures designed for different design philosophies

Evaluation of the seismic level of protection afforded to steel moment resisting frame structures designed for different design philosophies

Evaluation of the level of seismic protection afforded to reinforced concrete shear wall systems

Evaluation of the level of seismic protection afforded to reinforced concrete shear wall systems

Vasco da Gama Bridge, Portugal

The new Tagus River crossing in Portugal is 17,300 m long, including three interchanges, a 5-km-long section on land and a continuous 12,300-m-long bridge. Since the project is of great importance, a very high level of seismic protection was specified, far higher than usual for ordinary structures. Thus seismic considerations significantly influenced the design of the crossing, especially of the cable-stayed Main Bridge with a 420-m-long span across the main navigation channel.

Seismic level of protection for building structures

The seismic level of protection of building structures is concerned with the performance of the structures during strong seismic shaking. Performance expectations, for both functionality and life-safety objectives, are related to structural response parameters such as deflection, interstorey drift, and damage. This article describes a research framework for the evaluation of the level of protection and its potential application to the evaluation of the level of protection provided by the seismic provisions of the National Building Code of Canada (NBCC). This framework is described in terms of four distinct facets or dimensions, namely seismic hazard, seismic design, response and damage, and vulnerability. The evaluation of the NBCC level of protection for a variety of building types is discussed, including a detailed description of a pilot project on a six-storey reinforced concrete office frame structure. A brief description is given of other potential applications of the framework, including rehabilitation strategies for existing buildings, repair and replacement costs, and seismic design for low to moderate seismic hazard regions.

Seismic level of protection for building structures

Seismic level of protection for building structures