Experimental evaluation of rectangular reinforced concrete column behaviour under biaxial cyclic loading     

Hugo Rodrigues  António Arêde  Humberto Varum  Aníbal G. Costa 《地震工程与结构动力学》2013,42(2):239-259

The cyclic behaviour of reinforced concrete columns has been the subject of many experimental studies in recent years. However, most of these studies have focused on the unidirectional loading of columns with square cross‐sections under constant axial loading conditions. In the present study, four types of full‐scale quadrangular building columns were tested under different types of loading, including uniaxial and biaxial loading conditions. The first two specimens of each column type were independently cyclically tested in the strong and weak directions. Bidirectional tests using different loading paths were performed on the other column specimens. All columns were tested under constant axial loading conditions. In this paper, the experimental results are presented, and the global behaviour of tested columns is discussed, particularly focusing on the stiffness and strength degradation because of the increasing cyclic demand. Finally, the deformation‐based performance limits proposed in Part 3 of Eurocode 8 were calculated and compared with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Damage evolution in reinforced concrete columns subjected to biaxial loading   总被引：1，自引：0，他引：1  

Hugo Rodrigues  António Arêde  Humberto Varum  Aníbal Costa 《Bulletin of Earthquake Engineering》2013,11(5):1517-1540

An analysis of the damage observed in 24 reinforced concrete (RC) columns tested under uniaxial and biaxial horizontal loading is presented. The test results show that for biaxial loading conditions specific damage occurs for lower drift demands when compared with the corresponding uniaxial demand (a reduction of 50–75 % was found). The damage distribution observed in each column is also analysed. No significant differences are found in the plastic hinge length for uniaxial and biaxial loading. The drift demands associated with each damage state are compared with reference values proposed in international guidelines. Finally, and based on the philosophy of the Park and Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. The results of the application of these expressions to the experimental results are discussed.  相似文献   

8- to 13-μm spectrophotometry of Comet IRAS-Araki-Alcock     

Michael A. Feierberg  Fred C. Witteborn  James R. Johnson  Humberto Campins 《Icarus》1984,60(3):449-454

We present spectrophotometry between 8.0 and 13.0 microns at 2% spectral resolution for areas in and near the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) on May 11 and 12, 1983. All the spectra can be fit very well by blackbody curves, and no 10 micron silicate emissions are seen. The temperature structure of the coma suggests the presence of small (radii <5 microns) dust particles within 150 km of the nucleus and larger ones further out. The change in the spatial distribution of the infrared flux between the two nights suggests that an outburst may have occurred sometime on May 11.  相似文献   

The differential system method for parameter identification; unconfined aquifer case     

Miguel Angel Moreles  Rogelio Vázquez  Fernando Avila 《Computational Geosciences》2005,8(3):235-253

We present the applicability of differential system (DS) method for identification of hydraulic conductivity and effective porosity in a phreatic aquifer. In the original setting, the first step of the DS system is to solve an overdetermined algebraic system in the least squares sense. A natural extension of the method is to pose a least squares problem in an appropriate functional space. We show an improvement of the identification by considering the least square problem in the space of square integrable functions in the time variable for a finite interval.  相似文献   

Surface lithogeochemical studies about a distal volcanogenic massive sulphide occurrence at Limerick,New South Wales     

A.C. Dunlop  E.P. Ambler  E.T. Avila 《Journal of Geochemical Exploration》1979,11(3):285-297

The results of a surface rock chip sampling study over a small distal volcanogenic massive sulphide deposit at Limerick, N.S.W., Australia are presented and compared with drill core and soil geochemical patterns. Major element halos are narrow in comparison to the pervasive patterns reported from major proximal deposits. Narrow zones of Mg and K enhancement are associated with sulphide mineralization. High levels of Na occur in these rocks in contrast to the regularly described pattern of Na depletion. Weathering, particularly in the presence of sulphides, has resulted in the leaching of Ca, Na and, to a lesser extent, K from surface rock chip samples, whereas Fe, Pb and Zn contents are enhanced compared to those in fresh rocks. Despite the problems of sample heterogeneity, variable weathering and the limited extent of alteration halos which exist in this environment, surface lithogeochemical methods in comparable situations may be useful in the confirmation and interpretation of soil geochemical anomalies.  相似文献   

Expected characteristics of cometary meteorites     

Humberto CAMPINS  Timothy D. SWINDLE 《Meteoritics & planetary science》1998,33(6):1201-1211

Abstract— Recent developments in our understanding of comets provide insights into the topic of cometary meteorites. These developments include the identification of comet-asteroid transition objects (such as 4015 Wilson-Harrington and 3200 Phaethon), information on the composition of cometary solids, and new ideas on the collisional history of Jupiter-family comets. In this work, we revisit this question, and we conclude that comets do indeed yield macroscopic meteorites, which either have not been found or have not been recognized. We also consider the expected characteristics of cometary meteorites, with an emphasis on those that may help identify and differentiate them from other types of meteorites. If cometary meteorites have preserved the main characteristics of cometary dust, the mineralogy would be dominated by highly unequilibrated anhydrous silicates, and the chemistry would be nearly chondritic but with a high abundance of C and N. On the other hand, if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites, they would resemble (or could even be) CI carbonaceous chondrites. We do not expect cometary meteorites to have chondrules. So far, no single meteorite looks unequivocally cometary. However, we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study.  相似文献   

Verification of a One-Dimensional Model of $$\hbox {CO}_{2}$$ Atmospheric Transport Inside and Above a Forest Canopy Using Observations at the Norunda Research Station     

Ivan Kovalets  Rodolfo Avila  Meelis Mölder  Sophia Kovalets  Anders Lindroth 《Boundary-Layer Meteorology》2018,168(1):103-126

A model of \(\hbox {CO}_{2}\) atmospheric transport in vegetated canopies is tested against measurements of the flow, as well as \(\hbox {CO}_{2}\) concentrations at the Norunda research station located inside a mixed pine–spruce forest. We present the results of simulations of wind-speed profiles and \(\hbox {CO}_{2}\) concentrations inside and above the forest canopy with a one-dimensional model of profiles of the turbulent diffusion coefficient above the canopy accounting for the influence of the roughness sub-layer on turbulent mixing according to Harman and Finnigan (Boundary-Layer Meteorol 129:323–351, 2008; hereafter HF08). Different modelling approaches are used to define the turbulent exchange coefficients for momentum and concentration inside the canopy: (1) the modified HF08 theory—numerical solution of the momentum and concentration equations with a non-constant distribution of leaf area per unit volume; (2) empirical parametrization of the turbulent diffusion coefficient using empirical data concerning the vertical profiles of the Lagrangian time scale and root-mean-square deviation of the vertical velocity component. For neutral, daytime conditions, the second-order turbulence model is also used. The flexibility of the empirical model enables the best fit of the simulated \(\hbox {CO}_{2}\) concentrations inside the canopy to the observations, with the results of simulations for daytime conditions inside the canopy layer only successful provided the respiration fluxes are properly considered. The application of the developed model for radiocarbon atmospheric transport released in the form of \(^{14}\hbox {CO}_{2}\) is presented and discussed.  相似文献   

Cyclic behaviour of interior beam–column joints reinforced with plain bars          下载免费PDF全文

José Melo  Humberto Varum  Tiziana Rossetto 《地震工程与结构动力学》2015,44(9):1351-1371

The seismic damages commonly observed on beam–column joints of old reinforced concrete structures, built with plain bars and without proper detailing, justifies the need to further study the behaviour of this type of structures. The response of these structures when loaded cyclically, as occurs during the earthquakes, is partially controlled by the bond properties between the reinforcing bars and the surrounding concrete. This paper presents the results of an experimental campaign of unidirectional cyclic tests carried out on six full‐scale beam–column joints built with plain bars. These joint specimens are representative of existing reinforced concrete structures, that is, built without adequate reinforcement detailing for seismic demands. For comparison, an additional specimen is built with deformed bars and tested. The seven specimens are designed and detailed to allow the investigation of the influence of bond properties, lapping of the longitudinal bars in columns and beams, bent‐up bars in the beams, slab contribution and concrete strength. The lateral force–drift relationships, global dissipated energy evolution, contribution of the joint, beams and columns to the global dissipated energy, ductility, equivalent damping, final damage observed, homogenized reinforced concrete damage index, displacement components, curvature evolutions and Eurocode requirements are presented and discussed. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Earthquake loss estimation for the Kathmandu Valley     

Hemchandra Chaulagain  Hugo Rodrigues  Vitor Silva  Enrico Spacone  Humberto Varum 《Bulletin of Earthquake Engineering》2016,14(1):59-88

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Seismic safety assessment of existing masonry infill structures in Nepal     

Hemchandra Chaulagain  Hugo Rodrigues  Enrico Spacone  Humberto Varum 《地震工程与工程振动(英文版)》2016,15(2):251-268

Reinforced concrete (RC) buildings in Nepal are constructed with RC frames and masonry infill panels. These structures exhibit a highly non-linear inelastic behavior resulting from the interaction between the panels and frames. This paper presents an extensive case study of existing RC buildings in Nepal. Non-linear analyses were performed on structural models of the buildings considered as a bare frame and with masonry infill, in order to evaluate the influence of infill walls on the failure mechanisms. Five three-storey buildings with different structural configurations and detailing were selected. The effect of masonry infill panels on structural response was delineated by comparing the bare-framed response with the infill response. Seismic performance is evaluated with regard to global strength, stiffness, energy dissipation, inter-storey drift, and total deflection of the structure. A parametric analysis of structures with masonry infill is also performed. For this, the influence of different material properties is studied, namely diagonal compressive stress, modulus of elasticity and tensile stress of masonry infill panels. Study results show that masonry infill increases the global strength and stiffness of the structures; it decreases the inter-storey drift and hence the total displacement of the structure. The results quantify the influence of the infill panels on structural response and, in particular, the effect of the diagonal compressive strength of the masonry wall.  相似文献