existing buildings the new italian provisions for probabilistic seismic assessment

In Europe, the reference document for the seismic assessment of buildings is the Eurocode 8-Part3, whose first draft goes back to 1996 and, for what concerns its safety format, has strong similarities with FEMA 276. Extended use of this document, especially in Italy after the 2009 L'Aquila earthquake has shown its inadequacy to provide consistent and univocal results. This situation has motivated the National Research Council of Italy to produce a document of a level higher than the one in force, characterized by a fully probabilistic structure allowing to account for all types of uncertainties and providing measures of performance in terms of mean rates of exceedance for a selected number of Limit States (LS). The document, which covers both reinforced concrete and masonry buildings, offers three alternative approaches to risk assessment, all of them belonging to the present consolidated state of knowledge in the area. These approaches include, in decreasing order of accuracy: (a) Incremental dynamic analysis on the complete structural model, (b) Incremental dynamic analysis on equivalent SDOF oscillator(s), (c) Non-linear static analysis. In all three approaches relevant uncertainties are distinguished in two classes: those amenable of description as continuous random variables and those requiring the set-up of different structural models. The first ones are taken into account by sampling a number of realizations from their respective distributions and by associating each realization with one of the records used for evaluating the structural response, the latter by having recourse to a logic tree. Exceedance of each of the three considered Limit States: Light or Severe damage and Collapse, is signaled by a scalar indicator Y, expressing the global state of the structure as a function of that of its members, taking a value of one when the Limit State is reached. For the first two LS's, which relate to functionality and to economic considerations, the formulation of Y is such as to leave to the owner the choice of the acceptable level of damage, while for the Collapse LS the formulation is obviously unique. An application to a real school building completes the paper

Pushover Analysis for Plan Irregular Building Structures

Nonlinear static procedures (NSPs), also known as "pushover methods", represent the most used tool in the professional practice for assessment of seismic performance of building structures. Most of the methods subscribed by major seismic codes for seismic analysis of new or existing buildings have been originally defined for simple regular structures

Seismic risk assessment of liquid overtopping in a steel storage tank equipped with a single deck floating roof

Major earthquakes have demonstrated that Natech events can be triggered by liquid overtopping in liquid storage tanks equipped with floating roofs. Thus, research on the dynamic behaviour of steel storage tanks with floating roofs is still required. In this paper, the seismic risk against liquid overtopping in a real steel storage tank with a floating roof was analysed using a simplified model that was validated by a refined finite element model based on the arbitrary Lagrangian-Eulerian approach. The simplified model utilizes the Lagrangian of a floating roof-fluid system and is capable of providing a response history of the floating roof. It was demonstrated that it could predict the maximum vertical displacement very accurately, while some differences were observed in the response history of vertical displacement. The computational time for a single response history analysis based on the simplified model amounted to a few minutes, which is significantly less demanding compared to hours required for response history analysis in the case of the refined FE model. The simplified model is thus appropriate for the seismic fragility analysis considering the overtopping limit state. It is shown that the fragility curves are significantly affected by the liquid filling level. The risk for liquid overtopping is quite high in the case of a full tank. However, by considering the variation of filling level during the year, the overtopping risk was observed reduced by approximately 30%. Alternatively, the approximate fragility analysis for the liquid overtopping can be performed by utilizing the Eurocode formula for the vertical displacement of liquid. This approach is straightforward, but the formula does not account for the higher mode effects, which may result in overestimated seismic intensity causing overtopping, as discussed in the paper

New methods for assessment and design of structures in seismic zones: present state and research needs

Significant advances have been accomplished in the last decade in the seismic protection of structures, based on the introduction and refinement of innovative conceptual approaches. The main drawbacks and inconsistencies related to traditional force-based design approach have been recognized as well as the critical role of displacement or deformation demand in characterizing the structural damage and thus the performance of the system when subjected to different level of ground motion intensity. A common generalized trend of developing and adopting displacementldeformation- based approaches within a performance-based design philosophy has resulted. In this contribution, a state-of-the-art critical review of the current research developments in seismic design and assessment methods based on performance based philosophy, either purely or partially relying on displacement-based or deformation-controlled approaches, will be provided. The influences on recent major code revisions and modifications, as well as on preliminary design guidelines, will be discussed, while reviewing the conceptual fundaments of the different approaches and underlining main sources of uncertainties and possible future developments

Seismic performance of a floating roof in an unanchored broad storage tank: Experimental tests and numerical simulations

Liquid steel storage tanks equipped with floating roofs are critical components of industrial facilities because they often store hazardous material. Major earthquakes have caused large vertical displacements of floating roofs. Consequently, roof failure and/or content loss has occurred, which has seriously endangered the surrounding environment and community. Therefore, research interest in this topic remains high, giving rise to experimental campaigns and investigatory studies concerning design and assessment approaches. The present paper aims to validate a simplified model (SM) using both a refined finite element (FE) model and experimental data. This model could later be used in the vulnerability and risk assessment framework based on numerous seismic analyses. The first part of the paper briefly introduces a shaking table test performed on a scaled steel storage tank equipped with a floating roof. This test provided useful experimental data about the vertical displacement histories of floating roofs subject to seismic loading. Subsequently, both a SM and a refined FE model aimed at simulating the shaking table test are introduced and described. Relevant experimental and numerical outcomes are then presented and discussed. Finally, in order to highlight the most relevant parameters involved, we performed a parametric study related to the SM. It is shown that both the refined FE model and the SM were capable of simulating the roof vertical displacement histories observed in the shaking table test. The former model has higher fidelity but appears to be excessively time-consuming, whilst the latter is more suitable for risk assessment purposes

Influence of infilled masonry wall on vibration properties and dynamic responses of building structures to earthquake ground excitations

In analysis and design of structures to earthquake ground excitations, often only mass of the infilled masonrywalls are considered.Their stiffness and strength are neglected or only approximately considered by using equivalent brace elements. A number of empirical relations proposed by different researchers are available in the literature to derive the equivalent brace elements of infilled masonry walls. These empirical relations differ from each other. In this study, both experimental tests and numerical simulations are carried out to investigate the influence of infilled masonry wall on vibration properties and dynamic response and damage of RC frame structures to earthquake ground motions. The experimental test results will be used to calibrate the numerical models of RC frames with or without masonry infill. The calibrated numerical models are then used to perform a series of simulations of RC frames without or with masonry infill. The results are compared with those derived using equivalent brace members. The empirical formula of defining the equivalent brace members that leads to the best predictions of RC frame structures with masonry infill to earthquake ground excitations is identified

Structural Behavior Analysis and Optimization, Integrating MATLAB with Autodesk Robot

The concepts of structural behavior analysis and optimization have started to be combined in the latest decades with an increasing trend also due to the need of often meeting performance targets, high structural complexity and costs. Nonetheless, existing approaches tackled this issue mainly in the domain of static calculations or referring to a specific type of optimization (e.g., size, topology or geometry). A new methodology is proposed to systematically perform different types of analysis (e.g., linear and nonlinear), by exploiting the Autodesk Robot Structural Analysis API through MATLAB. This approach involves the adoption of ActiveX technologies for the manipulation of COM (Component Object Model) objects in the MATLAB environment. A real-world example of linear dynamic modal analysis is also presented and a synthetic diagnostic of the structure is conducted based on the displacements resulting from the calculation

Potential Use of Locked Brick Infill Walls to Decrease Soft-Story Formation in Frame Buildings

The objective of this study is to investigate the effects of a new type of infillcalled locked brick infill adopting horizontal sliding jointsin reducing the soft-story formation in reinforced concrete (RC) frames with code-conforming seismic detailing. Nonlinear static time-history analyses were performed on multistory planar frames with only the upper stories infilled in order to force the soft-story irregularity. The parameters of frame and infill elements that were used in numerical simulations were obtained from half-scale RC infilled frame tests that had been performed by the author covering single story-single bay frames infilled with standard and locked bricks. The numerical simulations showed that the use of locked bricks to form infill walls has the potential to decrease the soft-story/weak-story formation in comparison to standard bricks due to its shear sliding mechanism and decreased upper-story/first-story stiffness, even in buildings that have noninfilled first stories. (C) 2014 American Society of Civil Engineers

Dynamic response of existing steel frames with masonry infills under multiple earthquakes

Existing steel moment-resisting frames in several seismic regions worldwide are often characterised by high vulnerability to earthquakes due to insufficient local and/or global ductility. Therefore, it is of paramount importance to assess their response under strong motions and provide cost-effective retrofitting remedies. However, the current code-based assessment framework utilized in Europe for assessing existing structures is inadequate and requires improvement, especially to account for the contribution of masonry infills as they significantly influence the seismic response of steel buildings. To this end, the H2020-INFRAIA-SERA project HITFRAMES (i.e., Hybrid Testing of an Existing Steel Frame with Infills under Multiple Earthquakes) aims at experimental evaluation of a case study building representative of non-seismically designed European steel frames. This paper presents the dynamic response analyses of the case study building and serves as a theoretical prediction of the experimental results for HTTFRAMES. The case study building is analysed as a bare, an infilled and a retrofitted frame with buckling restrained braces (BRBs), respectively. It is subjected to the natural seismic sequence recorded during the 2016-2017 Central Italy earthquakes. The modal properties of the case study building are determined first, followed by the investigation of its non-linear dynamic response. The dynamic tests are performed with the earthquake records scaled to different intensity levels to simulate the structural performance under different limit states according to Eurocode 8-Part 3. The impact of masonry infills and BRB-retrofit is also investigated by comparing the response of models with different configurations. It can be concluded that appropriately-designed BRBs are effective in protecting steel frames from experiencing critical damage during earthquakes and reducing significantly the transient and residual drift

Life-cycle cost analysis of design practices for RC framed structures

The objective of this study is to perform life-cycle cost analysis on three design practices namely weak ground storey, short and floating columns and their combinations. Life-cycle cost analysis is recognized as the only suitable tool for assessing the structural performance when the structure is expected to be functional for a long period of time. Lifecycle cost analysis is considered in this study assessing the behaviour of the three design practices against earthquake hazard. Although, a number of checks are performed in order to reduce the influence of these design practices on the seismic behaviour of reinforced concrete (RC) framed structures, it was found that the total life-cycle cost of partially infilled RC designs is significantly increased compared to that of the fully infilled one. Through the test example examined in the framework of this study general conclusions are obtained regarding the behaviour of the three design practices