Abstract: Over the past few years, the South Island of New Zealand has been subject to significant sequences of earthquake shaking. In particular, 2010-2011 events affected the city of Christchurch resulting in large scale demolition of buildings. Also, the recent and continuing 11/2016 events caused severe damage in the countryside, in small towns, and moderate damage further afield. This paper describes “low damage construction” methods being used in NZ, and especially in the Christchurch rebuild, to limit the possibility of building demolition in future large seismic events. The buildings used in the Christchurch rebuild are generally supported by structural steel framing. These steel buildings include BRB systems, EBF systems with replaceable active links, rocking systems, base isolation using friction pendulum systems and/or lead-rubber dissipaters, RBS beams, lead extrusion dissipaters, yielding flexural dissipaters, and friction connections. Concerns about a number of currently used systems are discussed.
Abstract: After the 2010-2011 Canterbury earthquakes, much of the Christchurch Central Business District (CBD) was demolished and a new city has emerged in its place. A series of interviews conducted with key professionals involved with the reconstruction, together with data collected from various sources has made it possible to identify some of the drivers that have influenced decisions about the selection of structural material and specific structural systems used. Here, quantitative results obtained from this study are presented, in terms of structural systems, size of building in terms of square foot, as a function of time since the earthquake. The Christchurch rebuilding experience is most significant, providing a unique insight into some of the mechanisms that can dictate structural engineering decisions during the post-earthquake reconstruction of a modern city.
Abstract: Buildings in seismic zones are required to provide proper stiffness and load-bearing capacity to resist frequent earthquakes, and possess proper ductility and energy-dissipating capacity to prevent collapse under rare earthquakes. To meet these requirements, the concept of structural energy-dissipation techniques for the bi-functions of load-bearing and energy dissipating are proposed. A number of structural metal energy-dissipation elements, such as buckling-restrained steel plate shear walls, non-buckling corrugated steel plate shear walls, two-level yielding steel coupling beams and energy-dissipative columns, have been developed. They are designed to provide stiffness/strength to guarantee the operation of buildings under frequent earthquakes, but also dissipate energy to reduce seismic effects to a considerable extent for collapse-prevention of buildings. The experimental and theoretical studies on these structural metal energy-dissipating dampers are presented. The efficiency of these structural dampers for disaster mitigation of buildings against earthquakes are also presented to provide a reference for their practical application.
Abstract: Lightweight steel constructions are one of the innovative constructional systems steadily increasing in spread due to their huge benefits in respect to more traditional constructional systems. Typical lightweight steel products, usually combined with gypsum, wood and cement based panels, can be used to build both structural and nonstructural systems. After a brief description of the most common lightweight steel constructional systems, this paper describes the state of the art by focusing the attention on their behaviour under seismic actions. In particular, the main past and ongoing research themes are briefly summarised and a critical comparison among seismic codes available in North America, Europe and Oceania is presented. Finally, an overview of studies carried out on this topic at the University of Naples Federico II is presented and latest research activities involving the seismic performance assessment of both lightweight steel structural and nonstructural architectonic systems though shake-table tests is provided.
Abstract: Buckling-restrained braces (BRBs), which were first applied in 1989 in Japan, are now widely used worldwide as ductile seismic-proof members in seismic zones, such as those in Japan, USA, Taiwan, China, Turkey, and New Zealand. Although the design procedures of BRBs and their applications are described in the design codes and recommendations of several countries, they do not necessarily cover all the required aspects. Moreover, various new types of BRBs are still under investigation by many researchers. In this paper, the early history of BRB research and development and state-of-the-art views on the items required to design BRBs for obtaining stable hysteresis are briefly overviewed. This is followed by a summary of various representative application concepts and up-to-date investigations.
Abstract: First the Canterbury earthquake series of 2010/2012 and then the Kaikoura Earthquake of 2016 have significantly impacted the building stock in central and southern New Zealand, subjecting a wide range of buildings and building components to earthquake shaking ranging from moderate to severe. The economic and social costs of these earthquakes have been severe, but the lessons learned on how buildings and building systems designed and detailed to New Zealand provisions have performed have been invaluable. We have learned more about this from these earthquakes then from the many reconnaissance trips undertaken to overseas earthquakes over the 50 years of the New Zealand Society for Earthquake Engineering. This paper focusses on the performance of steel framed buildings in two major New Zealand cities, Christchurch and Wellington, with greatest emphasis on multi-storey buildings, but also covering light steel framed housing. It addresses such issues as the magnitude and structural impact of the earthquake series, how the various systems performed against the design expectations and briefly covers some of the research underway to quantify where there were differences between the observed performance and the expected performance.
Abstract: An empirical methodology to evaluate damage by the use of two damage indicators for 2D steel/concrete composite structures is proposed. This methodology has been established with aid of the results of an extensive parametric study regarding the non-linear behaviour of 48 steel/concrete composite frames subjected to 100 far-fault records. A large number of inelastic dynamic analyses are conducted by increasing the earthquake motions to lead the frames to several levels of non-linear response. The results of the analyses show that the characteristics of the structure and the ground motions affect damage of the structures. The results are post-processed by the use of statistical methods to generate expressions, which show the effect of the abovementioned parameters and give an evaluation of the damage indicators utilised here. In particular, given the characteristics of the frames and the record, someone can compute the maximum damage found in beams and columns. Finally, one example serves to show the use of the developed formulae and demonstrates their validity.
Abstract: The paper deals with a multi-mode pushover procedure that considers higher mode effects, frequency content of response spectra as well as nonlinear interaction between modes. Pushover analyses are conducted with story-specific generalized force vectors. Each force vector is calculated through modal analysis and builds up the instantaneous distribution of forces acting on the structure when the interstory drift at each story attains its maximum value during the seismic motion. In order to improve the computational cost effectiveness, both mode truncation and limitation in the number of generalized pushovers are used by checking, however, the accuracy in the evaluation of the interstory drifts at all levels. The target interstory drift is calculated through three different modal combination procedures.
Abstract: This paper quantifies the collapse risk and earthquake-induced losses for a wide range of archetype buildings with special concentrically braced frames (SCBFs). The collapse risk and expected economic losses associated with repair, demolition and collapse are computed based on a performance-based earthquake engineering framework developed within the Pacific Earthquake Engineering Research Center. It is shown that the collapse risk of the steel SCBF archetypes may be significantly overestimated when the influence of the gravity framing system on the lateral frame strength and stiffness is ignored. It is also found that the building-specific earthquake loss assessment is significantly overestimated at low probability of occurrence seismic events (i.e., 2% probability of occurrence in 50 years) when the gravity framing system is not modeled explicitly as part of the nonlinear building model. For frequent and design-basis seismic events (i.e., 50 and 10% probability of exceedance over 50 years of building life expectancy), acceleration-sensitive nonstructural component repairs govern the building losses regardless of the employed nonlinear building model representation. For the same seismic events, steel brace flexural buckling contributes to structural repair losses.