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Floor diaphragms play several roles in the seismic response of dual systems: support vertically spanning components, transfer lateral forces to walls and frames, provide restraint to columns and walls, tie the structure together, and enable redundant load paths for lateral forces. In many buildings after events as recent as the 2010-2011 Christchurch earthquakes, floor diaphragms were unable to perform one or more of these functions, leading to extensive damage and collapse. Research consistently highlights three underlying causes: a failure to ensure the integrity of the load path, underestimation of in-plane forces, and poorly understood interactions with walls, supporting beams and RC moment frames. Most recent and ongoing research has focused on modifying the prescriptive code provisions, and indeed many codes–but not all- have been consequently updated. Such prescriptive rules, however, are not helpful for assessing existing buildings, comparing alternate means and methods, or in displacement-based design (DBD) for which a performance-based design (PBD) framework is necessary. This paper proposes a new performance-based framework for the seismic design of reinforced-concrete (RC) floor diaphragms with or without precast elements. The floor diaphragm performance limit states (LS) are re-defined in terms of the observed failure modes (FM). Results from prior research on these failure modes are used to select damage measures (DM, e.g. ‘crack width’) for pairs of FM and LS. Expressions for DMs in terms of engineering demand parameters (EDP, e.g. , ‘strain’) are derived from experimental results or from first principles. EDPs are the basic output from numerical analysis in PBD; this paper comments on the suitability of different analytical approaches. [ABSTRACT FROM AUTHOR]

• Validation of a finite element, for moment-axial-shear interaction of RC frames is presented. • Nonlinear force-based finite element formulation is used. • The Disturbed Stress Field Model is used as the constitutive relationship. • Load-deformation responses and failure modes of RC elements are accurately predicted. This paper focuses on a novel finite element formulation which can predict the bending moment-shear force-axial force interaction of reinforced concrete frames and walls, and validate it against 170 experiments available in literature. This distributed plasticity element is established on force-based finite element method, where the relationship between element nodal forces and section forces are exactly known. Hence, element discretization is nonessential when modelling frames using this formulation, reducing the number of degrees of freedom in the numerical model compared to displacement-based formulations. The computations are carried out at four hierarchical levels, namely structure, element, section and fibre. There are two nested iterative procedures at the structure level and the section level. In the existing formulation, these iterative procedures are computationally demanding due to use of initial stiffness matrices. Furthermore, it uses Modified Compression Field Theory at the fibre level, which has inherent drawbacks compared to its more evolved version, the Disturbed stress Field Model. The current study refines the iterative procedures at structure and section levels to fully operate with tangent stiffness matrices to improve the speed of convergence. In addition, the Modified Compression Field Theory is replaced with the Disturbed stress Field Model at the fibre level to compute fibre resisting force for a given fibre deformation, accounting for both averaged behaviour and local crack slip. The novel element is validated by comparing the predicted results with experimental results of 170 tests found in the literature. It is shown that the novel element predicts the load carrying capacity well with an average experimental-to-predicted load carrying capacity ratio of 0.99 and a coefficient of variation of 12.8%. Furthermore, the element can be used to discuss the different failure mechanisms of reinforced concrete frame elements. [ABSTRACT FROM AUTHOR]

Liquid storage tanks are widely used in the industry and can contain not only harmless substances but also various ones that can be explosive and toxic or pollutant, thus implying that both the structure and the content must remain safe and operational under different types of loading. The same applies to any tank-connected plant system/item. Yet, past earthquakes repeatedly demonstrated that even if structural damage is prevented in the shell, severe occurrences may still be observed due to sloshing phenomena, which drive the tank-fluid system response with high impacts in case of accidental release of chemicals. Therefore, this paper studies an energy dissipation system consisting of floating roof and external dampers that are utilized to control liquid vibration by augmenting the level of damping. In order to evaluate its effectiveness at the design-level earthquakes, a series of explicit nonlinear dynamic analyses have been performed, and comparisons are provided between floating roofed steel cylindrical tanks equipped with supplemental devices and counterparts without them. Changes in seismic performance because of geometrical variations in the tank (i.e. aspect ratio) and seismic input (i.e. far and near field earthquakes) have been quantified by means of experimentally validated numerical models that account for material and geometrical nonlinearities, as well as for fluid-structure interaction in an explicit manner. Shake-table tests available in the literature have been simulated, and the proposed modelling criteria show a good fit with experimental data on two tank specimens. Analysis data sets involving three tank geometries reveal that even if the dissipation system targets mainly large-capacity tanks, it can be effectively used to enhance the performance of any system, reducing the sloshing wave height which can be excessive especially when the tank is subjected to severe near field ground motions. • Dynamic response of liquid storage tanks with floating roof is examined numerically. • Tanks with floating roof are analysed with and without dampers used to control liquid vibration. • Experimentally validated numerical models are developed to simulate different tank geometries. • Nonlinear sloshing of the fluid is reproduced by the Arbitrary Lagrangian-Eulerian formulation. • Sloshing wave height peaks can be effectively reduced, thus mitigating damage and related issues. [ABSTRACT FROM AUTHOR]

Seismic performance-based design approach is currently implemented in modern building codes. Design requirements and provisions ensure an adequate structural performance under different intensity levels of seismic action. However, the probability of attainment of a performance level is implicitly considered in the code design approach (provisions and requirements); for instance, the minimum requirements in concrete structures cannot be simply correlated to the probability of collapse of the building as well as to its overall structural response. The aim of this work is to assess the vulnerability with respect to the collapse limit state of industrial single-story RC precast buildings designed according to the current Italian seismic code. The comparison between the Italian code and the Eurocodes is provided throughout the paper. A parametric study is performed by investigating the safety against the collapse of 40 RC single-story precast structures. Multi-stripe analyses are performed by non-linear dynamic analyses at 10 intensity levels. The fragility of the structures is defined by means of the incremental N2 method, which has been demonstrated to be a suitable method for evaluating the collapse capacity of single-story precast buildings. The results demonstrate that the buildings are safe against the collapse mainly because of the structural overstrength with respect to seismic actions. The modelling assumptions are also validated in order to demonstrate the negligible influence of the cracking on the collapse as well as the importance of the geometrical nonlinearities for precast buildings. [ABSTRACT FROM AUTHOR]

The seismic response of buildings not specifically designed to resist earthquake actions can be generally improved by allowing the structure to dissipate an appropriate amount of energy. The use of passive devices for improving the seismic performance of precast concrete structures is investigated herein. In industrial and commercial precast concrete buildings, these devices can be successfully applied at the beam-to-column connections of hinged portal-frames, in order to increase the connection degree of fixity and the dissipated energy during a seismic event. The specific aspects and efficiency of passive dissipation devices based on rotational friction with and without the addition of a re-centring device is analyzed herein. Such devices may be applied both to existing and new buildings; indeed, they are able to mitigate the inter-storey drift demand, to limit the damage at the column base and to reduce residual drifts. A design procedure is developed in the paper for portal-frames implementing the investigated devices. A case study representing a single-storey precast concrete portal-frame is selected. The design procedure is applied to the case study, considering various devices configurations. The structural performance is assessed by means of non-linear time history analyses. [ABSTRACT FROM AUTHOR]

• Parametric design for rocking walls with mild steel dissipaters. • Energy dissipation and post-tensioning design equations in hybrid walls. • Displacement based design for hybrid walls. In recent years, important benefits for the seismic design of precast reinforced concrete wall structures have been obtained from the use of jointed wall-to-foundation connections, where gap openings are permitted, thus resulting in a rocking motion. The lumped rotation at the wall base protects the panels from damage, while gravity loads and unbounded post-tensioned (PT) tendons, designed to remain elastic, re-center the structure after an earthquake, thus solving the problem of residual displacements. External dissipaters, herein partially unbounded mild steel bars, limit the amplitude of lateral displacements providing the required dissipating capacity. The resulting response is characterized by flag-shaped hysteretic loops. The paper investigates the parameters that may influence the design of rocking walls with supplemental energy dissipation devices in the form of mild reinforcing steel and aims to develop a parametric approach for the design of such systems. In this research, an analytical system of non-dimensional equations is developed for the design of PT tendons and dissipaters: location, area and prestressing force of the former, and location, area and unbounded length of the latter. A parametric approach suitable for the design practice is developed. This allows obtaining a simplified, quick, and accurate approach for the selection of PT tendons and energy dissipaters following a performance-based design approach. The procedure has been applied to a selected case study and validated by means of non-linear time history analyses. [ABSTRACT FROM AUTHOR]

The seismic performance of non-structural elements is now recognized to be a key issue in the seismic assessment and earthquake related loss estimation of buildings, both at the individual and regional scale. The evaluation of the seismic demand on non-structural elements in many modern building codes is often based on inaccurate distributions of floor accelerations. For this reason, some design oriented simplified methodologies have been developed recently to predict floor response spectra in reinforced concrete buildings. Although the influence of masonry infills on the seismic performance of reinforced concrete buildings has been widely demonstrated, infills are generally neglected both in the design and in the evaluation of floor response spectra, which could lead to un-conservative design of non-structural elements. In this paper, the effect of masonry infills on absolute acceleration and relative displacement floor response spectra for reinforced concrete buildings subjected to frequent (serviceability level) earthquakes is investigated through a probabilistic framework. A database of one hundred masonry infilled reinforced concrete frames, representative of the European context, was generated and each building analyzed through nonlinear time history analyses. From the results of these analyses, the acceleration and displacement response spectra at different floor levels of both bare and infilled frame archetypes were then computed. The effectiveness of the most common assumptions made in regional risk models to estimate the non-structural losses is investigated and a first attempt at a more refined approach taking into account the effect of masonry infills is proposed. [ABSTRACT FROM AUTHOR]