1,721,104 research outputs found
Seismic design of box-type unreinforced masonry buildings through direct displacement-based approach
No full textIn the last decade, displacement-based seismic design procedures have been recognised to be effective alternatives to force-based design (FBD) methods. Indeed, displacement based design (DBD) may allow the structural engineer to get more realistic predictions of local and global deformations of the structure, and hence damage, under design earthquakes. This facilitates the achievement of performance objectives and loss mitigation in the lifetime of the structure. Nonetheless, DBD needs further investigation for some structural types such as masonry buildings. In this paper, a direct displacement based design (DDBD) procedure for unreinforced masonry (URM) buildings is presented and critically compared to FBD. The procedure is proposed for box-type URM buildings with reinforced concrete slabs, bond beams and lintels above openings, which have shown acceptable seismic performance in severe earthquakes preventing out-of-plane failure modes. Seismic design of a three storey brick masonry building in a high seismicity region is discussed as a case study. The effects of ordinary and near-field design earthquakes, as well as load combinations and accidental eccentricity prescribed by current codes, were investigated. Finally, design solutions provided by FBD and DDBD were optimised and their construction costs were estimated. It was found that, particularly at small epicentral distances, neglecting the combination of horizontal seismic actions and accidental eccentricity may induce significant underestimation and an ideally more uniform distribution of strength demands on URM walls. In addition, construction costs resulting from DDBD may be significantly lower than those related to code based FBD procedures
Blast fragility and performance-based pressure-impulse diagrams of European reinforced concrete columns
No full textTerrorist attacks and accidental explosions can induce abnormal loads on building structures, producing local damage to single primary components or even progressive collapse. Few probabilistic investigations have been carried out to assess the risk of blast damage to structural components and progressive collapse. This study aims at evaluating the blast fragility of reinforced concrete columns for two classes of European residential buildings: those designed only for gravity loads according to past codes and those designed for earthquake resistance according to Eurocode 8. After uncertainty in material strengths, column dimensions, reinforcement ratios and blast capacity model was characterised, Monte Carlo simulation was performed. Blast capacity was defined through pressure impulse equations that establish a relationship between the dynamic nature of blast load and damage. The output was the derivation of blast fragility surfaces and probabilistic pressure impulse diagrams at multiple limit states which may be used for quantitative risk analysis and performance-based design/assessment
Risk-targeted safety distance of reinforced concrete buildings from natural-gas transmission pipelines
No full textNatural-gas pipeline accidents mostly result in major damage even to buildings located far away. Therefore, proper safety distances should be observed in land use planning to ensure target safety levels for both existing and new buildings.
In this paper, a quantitative risk assessment procedure is presented for the estimation of the annual probability of direct structural damage to reinforced concrete buildings associated with high-pressure natural-gas pipeline explosions. The procedure is based on Monte Carlo simulation and takes into account physical features of blast generation and propagation, as well as damage to reinforced concrete columns. The natural-gas jet release process and the flammable cloud size are estimated through SLAB one-dimensional integral model incorporating a release rate model. The explosion effects are evaluated by a Multi-Energy Method. Damage to reinforced concrete columns is predicted by means of pressure– impulse diagrams. The conditional probability of damage was estimated at multiple pressure–impulse levels, allowing blast fragility surfaces to be derived at different performance limit states. Finally, blast risk was evaluated and allowed the estimation of minimum pipeline-to-building safety distances for risk- informed urban planning. The probabilistic procedure presented herein may be used for performance- based design/assessment of buildings and to define the path of new natural-gas pipeline networks
Stochastic nonlinear finite element analysis for collapse investigation of a historic stone balcony
No full textForensic investigations based on stochastic finite element (SFE) simulations can be a rational tool to assess the structural performance of existing structures, particularly in the case of ancient constructions which are affected by high uncertainty levels. In this study, the collapse of a historic piperno stone balcony is investigated through a series of nonlinear SFE analyses. After that the geometrical model of the element was created according to on-site and laboratory surveys, an experimental programme was carried out to characterise some physical properties and the mechanical behaviour of piperno stone. The latter is a volcanic building stone that has been used for a long time in the monumental architecture of Naples and Campania region in Southern Italy, so it is currently preserved by cultural heritage offices. Experimental data were found to be in agreement with those available in the literature for similar piperno stones.
A Monte Carlo technique was used to reproduce the spatial heterogeneity of stone properties throughout the structural element, according to statistics provided by experimental tests. Nonlinear finite element analysis with displacement control was run for each random realization of material properties and assumption of boundary conditions, allowing a huge number of load–displacement capacity curves to be derived. The mean collapse load of the balcony was found to be very close to the total load expected at the moment of collapse, hence providing a proof to the forensic investigation
Flow-type landslide fragility of reinforced concrete framed buildings
No full textFlow-type landslides may be triggered by several events such as heavy rainfalls, typically producing huge losses. Landslide risk may be rationally evaluated and mitigated with probabilistic approaches. In this paper, physical vulnerability of reinforced concrete buildings to flow-type landslides is assessed. Fragility analysis was carried out by assuming flow velocity as intensity measure, several damage states, and different mechanical models for beams, columns and masonry infill walls. Uncertainties in landslide impact loading, material properties, size and reinforcement of members, and capacity models were taken into account. Both earthquake-resistant and gravity-load designed framed buildings were assessed as being representatives of two building classes. Based on Monte Carlo simulation and a specific fragility analysis methodology, a set of landslide fragility curves were derived. Analysis results show that landslide fragility significantly depends on the presence and type of infill walls, which influences both out-of-plane and in-plane failure modes of walls themselves and RC frames. In addition, the proposed landslide fragility curves demonstrate that seismic design of RC buildings also plays a key role in the mitigation of their flow-type landslide fragility
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
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