1,721,020 research outputs found
EFFECTS OF CROSS-SECTION DEFORMATIONS ON THE DISPLACEMENTS OF A MULTIPLE-SHELL ROOF COMPOSED OF PI -SHAPED ELEMENTS
No full textUse of optical-interferometric method to analyze roof elements mutually connected by linear hinges is discussed. Both the warping of the section (due to combined bending and torsion) and plane cross-section deformations by two different theoretical approaches ('rigid section' and 'deformable section') are considered, so that experimental and theoretical results can be compared; a linear load is applied to each hinge in turn. The effects of diaphragm spacing on the section distortion are analyzed in the case of a single prismatic element
New Trends in Fracture Mechanics of Concrete
No full textFracture Mechanics of Concrete and Concrete Structures, Volume 1 of the Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, Catania, Italy, 17-22 June 2007, 3-Volumes
[101029.EG da
Correlazione tra curvatura media e curvatura locale di elementi monodimensionali in conglomerato armato
No full textCNR-Bollettino Ufficiale-Norme tecnich
Bending and shear behavior in one-way dapped-end reinforced concrete slabs
No full textSix one-way reinforced concrete slabs, simply supported along the short sides by means of corbels (dapped ends), were recently tested for bending and shear behavior in Milan under two different crosswise load distributions and with three partially different reinforcement layouts in the supporting corbels and in the main body (size 2200 x 1300 mm [7.22 x 4.27 ft]; thickness/length ratio close to 1/14; corbel depth and overhang/length ratio close to 1/23). The tests in bending under the service loads and in shear up to and beyond the peak load show that load crosswise-distribution plays a minor role. In shear, the quite complex crack patterns in the D-regions close to the dapped ends clearly indicate the formation of very effective strut-and-tie systems if the bottom bars of the main body are bent up, and of shallow arch-and-tie systems if the same bars are straight. In the former case, a proper introduction of the bond along the tension bars of the corbels is a must to define the position of bond-related joints and to make strut-and-tie models more reliable in predicting the bearing capacity, while in the latter case, the design equations provided by the codes for constant-section shear-unreinforced beams (ACI 318, EC2, and fib Model Code 2010) prove to be adequate also in the case of corbels
High-Performance Concrete, Brick-Masonry and Environmental Aspects
No full textFracture Mechanics of Concrete and Concrete Structures, Vol. 3 of the Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, Catania, Italy, 17-22 June 2007, 3-Volumes [101029.EG da <http://www.taylorandfrancis.com/books/details/9780415446174/>
Calcestruzzi Leggeri e Pesanti ad Alta Temperatura
No full textRecenti prove condotte al Politecnico di Milano sulla caratterizzazione termo-meccanica di calcestruzzi speciali hanno riguardato due mescole, l’una con aggregato a base di polistirene espanso sinterizzato – EPS e l’altra con aggregato baritico, maturata quest’ultima in due condizioni ambientali differenti. L’obiettivo è stato quello di rendere disponibili dati nuovi o aggiornati su due famiglie estreme di calcestruzzo strutturale (fc = 26-35 MPa). Una quarta mescola con aggregato ordinario è stata poi studiata per confronto. Circa 100 cilindri riscaldati a diverse temperature di riferimento fino a 700-750°C hanno permesso di valutare le resistenze in compressione ed in trazione indiretta per spacco, il modulo elastico, e la diffusività termica. L’introduzione di due indici di danno, basati rispettivamente sui decadimenti del modulo elastico e della velocità delle onde ultrasoniche, ha poi permesso di mettere in luce l’effetto che la temperatura ha sulla deviazione dalla linearità nei conglomerati studiati, il cui decadimento meccanico è risultato in linea con quello dei calcestruzzi ordinari. Tuttavia, il calcestruzzo baritico conserva più a lungo il proprio comportamento lineare, mentre il calcestruzzo con EPS richiede più cemento per garantire proprietà meccaniche accettabili
Bond shear modulus in reinforced concrete at high temperature: General trends from test results
No full textThe scanty attention devoted so far to bond shear modulus (secant or tangent slope of the loading branch of the bond-slip curve) limits the ability to numerically model such phenomena as tension stiffening, that controls the stiffness of cracked RC structures even past a fire. To improve the knowledge of bond shear modulus at high temperature, the bond stress-bar slip curves resulting from the tests of eleven selected experimental campaigns spanning a forty-year period are re-examined in this paper. Bond shear modulus is derived as the initial slope of the bond stress-bar slip curves of stressed or unstressed specimens in either hot or residual conditions. The criteria to compare the test results coming from very different experimental campaigns are discussed at length. Bond shear modulus is shown to be a decreasing function of the residual compressive strength of the concrete (at high temperature or past cooling). The envelopes of the test data allow to assess the roles of bar diameter and concrete grade. Trend curves are derived for normal-strength and high-strength/high-performance concretes, as a first necessary step for the formulation of parametric design-oriented laws, that may be useful to model tension stiffening and to describe the distribution of the bond stresses in long anchored bars. A numerical example is also developed and the consistency with EuroCode EC2 is checked
Indirectly-supported one-way R/C slabs: Durability and safety issues
No full textSimply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3×2.2×0.15 m [51×87×6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear - to the advantage of durability - while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown - once more - to markedly improve slab performance, with little or no extra cost
Proceedings of the 6th Intnl. Conf. on Fracture Mechanics of Concrete and Concrete Structures
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