1,721,251 research outputs found
Probabilistic assessment of in-plane lateral strength of masonry walls with external composite strengthening systems
No full textRecent post-earthquake reconnaissance missions have shown a high degree of damage to unreinforced masonry (URM) structures. Externally bonded systems based on fibre-reinforced polymers (FRPs) and fabric-reinforced cementitious matrices (FRCMs) may be used to increase lateral capacity of existing URM walls.
In this paper, the in-plane lateral strength of tuff stone masonry walls in both as-built and strengthened conditions is investigated. Diagonal FRP strips and FRCM composite are considered as strengthening systems. Based on capacity models as well as statistics and probability distributions for material properties, geometry and models, a probabilistic analysis was carried out through Monte Carlo simulation. Shear force versus axial force strength domains corresponding to several percentile levels were derived. Simplified dimensionless equations were finally obtained via robust regression analysis as a practice-oriented tool for both design and assessment of externally-strengthened masonry walls
Probabilistic strength domains of masonry walls reinforced with externally bonded composites
No full textUnreinforced masonry (URM) has been used to build up a large number of structures and infrastructures since ancient times, and is still employed in modern construction. In recent earthquakes, URM buildings have sustained a high degree of damage due to in-plane loading, demonstrating a pressing need for retrofitting. In the last years, externally bonded fibre-reinforced polymers (FRPs) and fabric-reinforced cementitious matrices (FRCMs) have been proposed as effective solutions for seismic retrofit of URM walls and their use is rapidly increasing worldwide.
In this paper, the in-plane lateral strength of tuff stone masonry walls in both as-built and strengthened conditions is investigated. Diagonal FRP strips and FRCM composite, applied on both sides of walls and through single plies, are considered as strengthening systems. Based on capacity models as well as statistics and probability distributions for material properties, geometry and models, a probabilistic analysis was carried out by using plain Monte Carlo simulation. The output of that analysis consists of shear force versus axial force strength domains corresponding to the 16th, 50th and 84th percentile levels. Simplified equations, in a dimensionless format, are finally provided by using robust regression. Such an output represents a practice-oriented tool for both design and assessment of externally-strengthened masonry walls
Comparative assessment of load-resistance factor design for FRP-reinforced cross sections
No full textIn the last decades, codes have implemented the load-resistance factor design (LRFD) approach to achieve a certain safety level in structural sections. Recently, the same philosophy established in the case of steel bars was adapted for reinforcement by innovative materials such as fiber-reinforced polymers (FRPs). LRFD is claimed to be a semi-probabilistic approach, although the implied safety is not intelligible by practitioners, being hidden into the so-called safety factors (SFs) prescribed by codes, which should account for load- and strength-affecting heterogeneities. Often, especially in the case of FRP reinforcement, the SFs differ from one code to another because of the format of the design equations. The objective of the simple study presented in the paper is to compare the safety levels, expressed in terms of conventional probability of failure, for different codes at the state-of-the art with respect to the design of FRP-reinforced concrete worldwide. The purpose is to investigate how the different equation formats, design values of material properties, and partial safety factors, affect the implicit design safety and whether it is similar among international guidelines. The study considers design of cross sections in bending at the ultimate limit state according to: ACI 440.1R-06 (US guidelines), CAN/CSA-S806-02 (Canadian guidelines), and CNR-DT 203/2006 (Italian guidelines, for which sensitivity of design to SFs is also investigated). For comparison purposes, design of steel-reinforced sections is considered according to the recent Italian regulations. Results indicate that reliability indices achieved with design procedures are generally comparable among the considered codes, and larger than that referring to steel reinforcement
Uncertainty in early warning predictions of engineering ground motion parameters: what really matters?
No full textFrom the engineering perspective, the effectiveness of earthquake early warning systems (EEWS) depends only on the possibility of immediately detecting the earthquake and estimating the expected loss at a location of interest, in order to undertake actions to manage/mitigate the risk before the strike. The simplest proxy for the earthquake's destructive potential is the peak ground acceleration (PGA), which is predicted through probabilistic seismic hazard analysis in the framework of EEW. In this paper, the effects of different sources of uncertainty on the prediction of PGA are assessed with reference to the ISNet (Irpinia Seismic Network) EEWS. First the analyses show how the uncertainty of the ground motion prediction equation (GMPE) dominates those of magnitude and distance, almost independently of the information available for the event. Secondly, based on these findings, information-dependent lead-time maps are provided for the Campania (southern Italy) region. Finally, different real-time magnitude estimators are compared in terms of errors in the prediction of PGA, as a more efficient estimator may give additional lead-time for risk reduction
REXEL: computer aided record selection for code-based seismic structural analysis
No full textIn code-based seismic design and assessment it is often allowed the use of real records as an input for nonlinear dynamic analysis. On the other hand, international seismic guidelines, concerning this issue, have been found hardly applicable by practitioners. This is related to both the difficulty in rationally relating the ground motions to the hazard at the site and the required selection criteria, which do not favor the use of real records, but rather various types of spectrum matching signals. To overcome some of these obstacles a software tool for code-based real records selection was developed. REXEL, freely available at the website of the Italian network of earthquake engineering university labs (http://www.reluis.it/index_eng.html), allows to search for suites of waveforms, currently from the European Strong-motion Database, compatible to reference spectra being either user-defined or automatically generated according to Eurocode 8 and the recently released new Italian seismic code. The selection reflects the provisions of the considered codes and others found to be important by recent research on the topic. In the paper, record selection criteria are briefly reviewed first, and then the algorithms implemented in the software are discussed. Finally, via some examples, it is shown how REXEL can effectively be a contribution to code-based real records selection for seismic structural analysis
Statistical analysis of reinforcing steel properties for seismic design of RC structures
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Computer aided seismic input selection forthe new Italian seismic code
No full textThe recently released Italian seismic code avails of the work of the Istituto Nazionale di Geofisica e Vulcanologia concerning the seismic hazard analysis of the Italian territory. This is reflected in the definition of seismic action on structures based on site-dependent elastic acceleration spectra closely approximating the uniform hazard spectra for each site, making the Italian seismic code one of the most advanced with respect to this issue, at least in Europe. This also affects the seismic input selection for non-linear structural analysis if appropriate tools are available to practitioners. The definition of the design spectra and the selection of ground motion suites according to the code are first reviewed here. Subsequently, a discusson how a specific software developed by the authors, REXEL, may help in finding record sets compatible with design spectra, is presented. Some illustrative examples are used factually to show how the new code and REXEL easily permit a rational record selection applied to earthquake engineering
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