154 research outputs found
Collapse of corrugated metal culvert in Northern Sardinia: analysis and numerical simulations
No full textThe paper illustrates the possible causes of collapse of a Corrugated Metal Culvert (CMC), occurred in Northern Sardinia after an extreme rainfall event in 2013. The possible causes of collapse are related to the conditions before and during the rainfall. Erosion and corrosion phenomena, which caused material decay and an improper water flow, have been discussed. Numerical analyses were performed to identify buckling multipliers with a finite element model simulating the effect of combined erosion and corrosion. The analysis showed a greater sensitivity in terms of buckling resistance when the soil erosion is concentrated in the lower portion of the culvert rather than in the lateral one
Experimental pull-out tests and design indications for strength anchors installed in masonry walls
No full textThis study deals with the identification of the mechanical behavior of chemical anchors embedded in masonry walls. 108 pull-out tests are carried out in five types of masonry walls built with clay brick or vertically perforated units with cement mortar. Different parameters are taken into account: embedment depths, masonry type, anchor position (injection either in brick units or in mortar joints). The axial load capacity and the failure mode are observed for each test. The results are examined by means of elastic and plastic models assessing the efficiency of anchors installed in headers, stretchers or mortar joints. The anchors injected in mortar joints are shown to have much greater pull-out capacity than that found for anchors in bricks. Passing from 90 to 160 mm of embedment depth, a minimum increase by 40% of pull-out strength is observed. The most common failure modes are the sliding failure, which occurs for short anchors or weak masonry, and mixed sliding/cone failure, for long anchors or strong masonry. An analytical model is proposed to design anchors in order to avoid or at least to limit brittle masonry failures and to identify the field of application of uniform stress models
Analysis of seismic risk on existing dams. Part I: an example of masonry structure
No full textThe paper deals with the analysis of a gravity masonry dam in Italy. Its mechanical properties are defined by means of experimental tests on the dam and the bedrock. A 3D finite element model was implemented in Abaqus and the analysis suggested by the Italian code for dams was performed. Verifications in terms of stresses, in non-linear range assuming a concrete damaged plasticity model for masonry, were made, showing their compatibility with both tensile and compressive strengths
Analysis of seismic risk on existing dams. Part II: an example of concrete structure
No full textThe paper deals with the analysis of a light-weight gravity concrete dam in Italy. Its mechanical properties are defined by means of experimental tests on the dam and the bedrock. A 3D finite element model was implemented in Strand 7 r.3.4 and the procedure described by the Italian code for dams was performed. Verification in terms of stresses, in non-linear range were made, to assess the structural safety and vulnerability to piping effects
Failure evidences of reduced span bridges in case of extreme rainfalls the case of Livorno
No full textThe heavy rainfalls occurring in Italy in the last few years focused the attention on the vulnerability of the land and the related infrastructures. Critical situations involving losses of human life and deterioration or failure of relevant structures are frequent. These events were due to: (1) improper land-use; (2) aging of infrastructures, (3) insufficient maintenance and protection; (4) climate changes causing rainstorms similar to tropical events. The failure of small bridges in road networks plays a key role in this sense. The present paper aims to analyse the behaviour of small bridges during rainfalls or floods. In particular, the recent case of Livorno is analysed. The Italian territory has about 460.000 small bridges, mostly designed without the support of technical codes or a proper interaction between the hydraulic and structural aspects. A large part of them can be submerged by water flows during rainfalls and pushed by unexpected actions. The failure scenarios allow identifying the hydraulic and structural vulnerabilities through a specific survey. A classification of small bridges on the basis of submergibility indexes is eventually proposed
On the Use of Vibro-Compressed Units with Bio-Natural Aggregate
No full textThe paper deals with the use of vibro-compressed units with bio-natural components on
construction. The proposed mix design of vibrated blocks consist of cork granules and/or hemp
shives, with the aim to substitute polymeric elements or expanded clay, together with the use of
natural hydraulic lime (NHL) as binder. An experimental campaign is presented, with mechanical
tests to evaluate the influence of each component on flexural and compression behavior. The proposal
is also investigated from a productive point of view, considering how it can be harmonized in the
productive process of lightweight aggregate concrete units without modifications in the productive
process. The tested elements could perform a certain reduction of the carbon impact, maintaining
interesting mechanical properties. The application of the proposed units in several contexts, as
separating elements joined with structural components, is considered to improve rehabilitation or to
obtain higher performances in buildings
Failure scenarios of small bridges in case of extreme rainstorms
No full textThis contribution comes from the investigations carried out on recent flooding events occurred in Italian suburban areas. Those events, regarding minor roads, cause unexpected failure modes of existing bridges with reduced span (less than 10 m), whose construction and maintenance are not properly covered by standards. Three failure scenarios are here considered: the dragging effect on vehicles when they are crossing bridges (A), the erosion effect due to the overtopping of the bridge (B), and the erosion and the floating effect caused by upward buoyant force from Archimedes’ principle on the bridge slab (C). The described mechanisms of failure are paradigmatic to identify not only the structural collapses but also the service failure. In this sense, the ‘resilience’ of the small bridge is defined, in view to propose technical indications for maintenance and consolidation activities
Seismic response of a stock of social housings in Italy with r.c. and masonry materials
No full textThe paper is based on a survey activity on a subset of 48 buildings for social housings. The structural materials are R.C. and Masonry. They are representative of about 9000 social ats on the district of Leghorn (Italy), built from early '900
up to 1981, date of adoption of seismic norms. The subset is divided into 15 masonry structures and 33 r.c. frames. Two different methods are adopted to classify the stock from seismic point of view. The stock has been classified in terms of Iv (Vulnerability Index) through GNDT 2ø level forms and PGA (Peak Ground Acceleration) from operation and collapse limit states (SLO and SLC), calculated by SAVE procedure. An example of classification, to establish priorities for further seismic investigations, is furnished. Main recurrent vulnerable details are highlighted, together with perspectives for more detailed seismic analysis
Recommended from our members
Analytical and experimental shear evaluation of GFRP-reinforced concrete beams
No full textReinforced Concrete (RC) technology is advancing towards new frontiers enhancing its sustainability and durability through innovative materials. In particular, the application of Glass Fiber Reinforced Polymer (GFRP) bars, in lieu of steel reinforcement, shows excellent performance, especially in aggressive environments. Nevertheless, current international design guidelines and standards tend to be rather conservative, especially concerning shear reinforcement. This element hinders the technology’s competitiveness, not only in terms of material consumption but also in construction efficiency. This research aims to conduct an analytical comparison and experimental validation of the formulations found in some international standards pertaining to shear capacity in a specific case. The focus is on scenarios involving reduced shear reinforcement and cases where the number of stirrups falls below the minimum recommended by these standards. In the sample beam tests, two distinct flexural GFRP reinforcement ratios were employed to evaluate their influence on shear capacity, leading to diverse failure mechanisms: rupture of longitudinal GFRP bars and concrete crushing. The experimental results were used to compare the North American ACI, French AFGC, and Italian CNR shear capacity design approaches in the case of reduced transversal reinforced ratio. Analytical capacity expressions of the standards above are discussed with some remarks aiming at structural optimization
Structural irregularity: the analysis of two reinforced concrete (r.c.) buildings
No full textStructural irregularity is a crucial issue in assessing seismic vulnerability of both new and existing
buildings. European technical codes provide simple criteria to define irregularities in plan and in
elevation, amplifying the seismic actions and/or introducing torsional effects. Nevertheless, this
approach only considers geometrical irregularity. For existing buildings, another source of
irregularity comes from the non-uniform distribution of the material strength. In particular, for
existing reinforced concrete (r.c.) structures, it is possible to detect significant spread of the
concrete compressive strength not only from different structural elements but also from different
parts of the same member. In this work, non-linear static analysis is performed on two case-studies
of r.c. buildings characterized by geometrical and mechanical irregularity. The resistance of each
column is determined with an extensive experimental campaign with in situ and laboratory test
(about 600 in situ tests). The results are analyzed considering both local and global effects in terms
of resistance of the single elements and of the entire buildings. In this sense, shear and bending
failure mechanism are taken into account. The effect of storey flexibility is also considered in the
models. Fragility curves are calculated for the buildings with random distribution of the
compressive strength of the columns. The results are then compared with the approaches proposed
by the Eurocodes evaluating in the standard approach proposed by technical codes is conservative
or not
- …
