Displacement-based seismic retrofit design for non-ductile RC frame structures using local retrofit interventions at beam-column joints

Paper 192In the past design codes, infill panels/walls within frame buildings have been considered as non-structural elements and thus have been typically neglected in the design process. However, the observations made after major earthquakes even in recent times (e.g. Duzce 1999, L’Aquila 2009, Darfield 2010) have shown that although infill walls are considered as non-structural elements, they can interact with the structural system during seismic actions and modify the behaviour of the structure significantly. More recent code design provisions (i.e.,NZS4230, Eurocode 8, Fema 273) do now recognize the complexity of such interactions and require either a) consider these effects of frame-infill interaction during the design and modelling phase or b) assure no or low interaction of the two systems with proper detailing and arrangements in the construction phase. However, considering the interaction in the design stage may not be a practical approach due to the complexity itself and in most cases does not solve the actual problem of brittle behaviour and thus damage to the infills. Therefore, the purpose of this particular research is to develop technological solutions and design guidelines for the control or prevention of damage to infill walls for either newly designed or existing buildings. For that purpose, an extensive experimental and numerical research programme has been planned. The concept, background on infill practice in New Zealand and the research programme will be briefly described in this paper

New Zealand contributions to the global earthquake model’s earthquake consequences database (GEMECD)

The Global Earthquake Model’s (GEM) Earthquake Consequences Database (GEMECD) aims to develop, for the first time, a standardised framework for collecting and collating geocoded consequence data induced by primary and secondary seismic hazards to different types of buildings, critical facilities, infrastructure and population, and relate this data to estimated ground motion intensity via the USGS ShakeMap Atlas. New Zealand is a partner of the GEMECD consortium and to-date has contributed with 7 events to the database, of which 4 are localised in the South Pacific area (Newcastle 1989; Luzon 1990; South of Java 2006 and Samoa Islands 2009) and 3 are NZ-specific events (Edgecumbe 1987; Darfield 2010 and Christchurch 2011). This contribution to GEMECD represented a unique opportunity for collating, comparing and reviewing existing damage datasets and harmonising them into a common, openly accessible and standardised database, from where the seismic performance of New Zealand buildings can be comparatively assessed. This paper firstly provides an overview of the GEMECD database structure, including taxonomies and guidelines to collect and report on earthquake-induced consequence data. Secondly, the paper presents a summary of the studies implemented for the 7 events, with particular focus on the Darfield (2010) and Christchurch (2011) earthquakes. Finally, examples of specific outcomes and potentials for NZ from using and processing GEMECD are presented, including: 1) the rationale for adopting the GEM taxonomy in NZ and any need for introducing NZ-specific attributes; 2) a complete overview of the building typological distribution in the Christchurch CBD prior to the Canterbury earthquakes and 3) some initial correlations between the level and extent of earthquake-induced physical damage to buildings, building safety/accessibility issues and the induced human casualtie

Damage Mitigation Strategies of ‘Non-Structural’ Infill Walls: Concept and Numerical-Experimental Validation Program

In the past design codes, infill panels/walls within frame buildings have been considered as non-structural elements and thus have been typically neglected in the design process. However, the observations made after major earthquakes even in recent times (e.g. Duzce 1999, L’Aquila 2009, Darfield 2010) have shown that although infill walls are considered as non-structural elements, they can interact with the structural system during seismic actions and modify the behaviour of the structure significantly. More recent code design provisions (i.e.,NZS4230, Eurocode 8, Fema 273) do now recognize the complexity of such interactions and require either a) consider these effects of frame-infill interaction during the design and modelling phase or b) assure no or lowinteraction of the two systems with proper detailing and arrangements in the construction phase. However, considering the interaction in the design stage may not be a practical approach due to the complexity itself and in most cases does not solve the actual problem of brittle behaviour and thus damage to the infills. Therefore, the purpose of this particular research is to develop technological solutions and design guidelines for the control or prevention of damage to infill walls for either newly designed or existing buildings. For that purpose, an extensive experimental and numerical research programme has been planned. The concept, background on infill practice in New Zealand and the research programme will be briefly described in this paper

Material Property Uncertainties versus Joint Structural Detailing: Relative Effect on the Seismic Fragility of Reinforced Concrete Frames

This 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

A computational framework for selecting the optimal combination of seismic retrofit and insurance coverage

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.

Parametric Investigation of Seismic Interaction Between Precast Concrete Cladding Systems and Moment Resisting Frames

This paper presents the results of a preliminary numerical investigation into the interaction between precast concrete cladding systems and moment resisting frames. Macro-scale models of cladding systems are implemented in existing lumped plasticity models for moment resisting frames. Different failure mechanisms and various configurations are considered in order to show the effect of the entire cladding system upon a structure’s seismic behavior. Several parameters are varied in order to establish their associated influence on the overall structural response. Results show that it is clearly more advantageous to have a failure mechanism governed by the connection than one governed by either the panel or the frame. An experimental program is now underway building on what has been learnt from the parametric investigation. The authors intend to continue the research to successively develop improved or innovative low-damage cladding-moment resisting frame systems. They also aim to produce simple design tools that provide easy inclusion of the seismic effects of cladding-frame interaction

Non-linear analysis of RC masonry-infilled frames using the SLaMA method: part 1—mechanical interpretation of the infill/frame interaction and formulation of the procedure

The simple lateral mechanism analysis (SLaMA) is an analytical method to assess the force–displacement capacity curve of Reinforced Concrete (RC) structures composed of frames, cantilever walls or dual wall/frame systems. The current version of the method was proposed in the 2017 New Zealand guidelines for the seismic assessment (NZSEE in New Zealand Society for Earthquake Engineering, the seismic assessment of existing buildings—technical guidelines for engineering assessments, Wellington, 2017). Regarding frame structures, the possible influence of infill walls is currently considered locally with checks on the RC members. However, it is universally known that infills have a major effect on the global capacity curve of the frame. In this paper, a comprehensive SLaMA method for infilled frames is proposed, which allows considering the influence of the infills on the global force–displacement curve without any numerical algorithm. The extended SLaMA method is herein formalised and it is validated in a companion paper (part 2) through an extensive parametric analysis. The extended SLaMA is based on the possibility to separately calculate the base shear contributions of the frame and the infills, in turn based on global equilibrium considerations. Such considerations also allow defining a novel procedure to post-process the results of pushover or time-history analyses where infills are modelled as diagonal struts, or to interpret experimental tests. This allows, within a single numerical analysis, to decouple the frame and infills contributions to the base-shear capacity. The decoupling procedure is herein demonstrated for an ideal two-storey, one-bay masonry-infilled frame with different infills configurations

NMIT Arts & Media Building - Damage Mitigation Using Post-tensioned Timber Walls

Paper 090The NMIT Arts & Media Building is the first in a new generation of multistorey timber structures. It employs an advanced damage avoidance earthquake design that is a world first for a timber building. Aurecon structural engineers are the first to use this revolutionary Pres-Lam technology developed at the University of Canterbury. This technology marks a fundamental change in design philosophy. Conventional seismic design of multi-storey structures typically depends on member ductility and the acceptance of a certain amount of damage to beams, columns and walls. The NMIT seismic system relies on pairs of coupled LVL shear walls that incorporate high strength steel tendons post-tensioned through a central duct. The walls are centrally fixed allowing them to rock during a seismic event. A series of U-shaped steel plates placed between the walls form a coupling mechanism, and act as dissipators to absorb seismic energy. The design allows the primary structure to remain essentially undamaged while readily replaceable connections act as plastic fuses. In this era where sustainability is becoming a key focus, the extensive use of timber and engineered-wood products such as LVL make use of a natural resource all grown and manufactured within a 100km radius of Nelson. This project demonstrates that there are now cost effective, sustainable and innovative solutions for multi-story timber buildings with potential applications for building owners in seismic areas around the world

Feasibility and Detailing of Post-tensioned Timber Buildings for Seismic Areas

Paper 53This paper describes the structural design and selection of construction detailing for low-rise multi-storey timber buildings using a new and exciting structural timber system. This system, originally developed for use with pre-cast concrete, combines the use of un-bonded post-tensioning techniques and additional sources of energy dissipation. This system eliminates residual displacement, while greatly reducing the damage to structural members during a significant seismic event. The paper shows how this new structural system can be used with large size structural timber members manufactured from laminated veneer lumber (LVL) or glulam timber, for use in multistorey buildings, with lateral load resistance provided by post-tensioned structural timber frames or walls, separately or in combination. An extensive on-going research program at the University of Canterbury, New Zealand has tested a wide range of beam-to-column, wall-to-foundation and column-to-foundation connections under simulated seismic loading, all giving excellent results. As part of this contribution, a case study of the design methods, construction options, cost and feasibility of a six storey timber office building in a moderate seismic area is carried out. The structural design of this building allowed investigation of different methods of structural analysis, and the development of many construction and connection details offering feasibility of rapid construction. Total building cost was evaluated and compared to equivalent steel and reinforced concrete options

Energy refurbishment planning of Italian school buildings using data-driven predictive models

In the current practice, the design of energy refurbishment interventions for existing buildings is typically addressed by performing time-consuming software-based numerical simulations. However, this approach may be not suitable for preliminary assessment studies, especially when large building portfolios are involved. Therefore, this research work aims at developing simplified data-driven predictive models to estimate the energy consumption of existing school buildings in Italy and support the decision-making process in energy refurbishment intervention planning at a large scale. To accomplish this, an extensive database is assembled through comprehensive on-site surveys of school buildings in Southern Italy. For each school, a Building Information Modelling (BIM) model is developed and validated considering real energy consumption data. These BIM models serve in the design of suitable energy refurbishment interventions. Moreover, a comprehensive parametric investigation based on refined energy analyses is carried out to significantly improve and integrate the dataset. To derive the predictive models, firstly the most relevant parameters for energy consumption are identified by performing sensitivity analyses. Based on these findings, predictive models are generated through a multiple linear regression method. The suggested models provide an estimation of the energy consumption of the “as-built” configuration, as well as the costs and benefits of alternative energy refurbishment scenarios. The reliability of the proposed simplified relationships is substantiated through a statistical analysis of the main error indices. Results highlight that the building's shape factor (i.e., the ratio between the building's envelope area and its volume) and the area-weighted average of the thermal properties of the building envelope significantly affect both the energy consumption of school buildings and the achievable savings through retrofitting interventions. Finally, a framework for the preliminary design of energy refurbishment of buildings, based on the implementation of the herein developed predictive model, is proposed and illustrated through a worked example application. Worth noting that, while the proposed approach is currently limited to school buildings, the methodology can conceptually be extended to any building typology, provided that suitable data on energy consumption are available