434 research outputs found
Earthquake-resistant buildings with steel or composite columns: Comparative assessment using structural optimization
This work investigates and compares the cost-effectiveness of seismically designed buildings having either pure steel or steel-concrete composite columns. In order to ensure an objective comparison of these two design approaches, the assessed building designs are obtained by a structural optimization procedure. Thus, any bias that would result from a particular designer's capabilities, experience, and subjectivity is avoided. Hence, a discrete Evolution Strategies optimization algorithm is employed to minimize the total cost of materials (steel and concrete) used in a structure subject to constraints associated with: (a) Eurocode 4 provisions for safety of composite column-members, (b) Eurocode 3 provisions for safety of structural steel members, and (c) seismic system behaviour and resistance. Extensive assessments and comparisons are performed for a variety of seismic intensities, for a number of building heights and plan configurations, etc. Results obtained by conducting 154 structural design optimization runs provide insight into potential advantages attained by partially substituting steel (as a main structural material) with concrete when designing the columns of earthquake-resistant buildings
Seismic design optimization of multi–storey steel–concrete composite buildings
This work presents a structural optimization framework for the seismic design of multi–storey composite buildings, which have steel HEB-columns fully encased in concrete, steel IPE-beams and steel L-bracings. The objective function minimized is the total cost of materials (steel, concrete) used in the structure. Based on Eurocodes 3 and 4, capacity checks are specified for individual members. Seismic system behavior is controlled through lateral deflection and fundamental period constraints, which are evaluated using nonlinear pushover and eigenvalue analyses. The optimization problem is solved with a discrete Evolution Strategies algorithm, which delivers cost-effective solutions and reveals attributes of optimal structural designs
Experimental investigation of the structural response of adobe buildings to lateral loading before and after the implementation of compatible grout repairs
In the framework of this study, a 1:2 scaled replica of a traditional single-storey adobe building was constructed and tested at the laboratories of the University of Cyprus. The main objectives of the exper-imental program were to evaluate the structural performance of adobe buildings under horizontal loads (simulating seismic action) and to investigate the effectiveness of cracking repair by means of injection with a compatible grout. The model was initially subjected to a series of monotonic static lateral loading cycles that led to the development of extensive cracking damage and to significant reduction of the load-bearing capacity and overall stiffness. A compatible clay-based grout was then developed using the same soil as the one composing the model’s adobes. This material was injected into the cracked sec-tions of the masonry and the repaired model was re-tested. The clay-based grout successfully restored structural continuity, precluding the re-opening of injected cracks during subsequent loading cycles. The recorded load-deformation response revealed that the grout repair reinstated the original stiffness of the structure and recovered more than 90% of the initial lateral strength. The results indicate that clay-based grouts can be used for re-establishing the stability of adobe constructions under static loads.POCI-01-0145-FEDER-007633; POCI-01-0145-FEDER-016737; PTDC/ECM-EST/2777/201
Effects of Space Charge, Dopants, and Strain Fields on Surfaces and Grain Boundaries in YBCO Compounds
Statistical thermodynamical and kinetically-limited models are applied to
study the origin and evolution of space charges and band-bending effects at low
angle [001] tilt grain boundaries in YBaCuO and the effects of Ca
doping upon them. Atomistic simulations, using shell models of interatomic
forces, are used to calculate the energetics of various relevant point defects.
The intrinsic space charge profiles at ideal surfaces are calculated for two
limits of oxygen contents, i.e. YBaCuO and YBaCuO. At
one limit, O, the system is an insulator, while at O, a metal. This is
analogous to the intrinsic and doping cases of semiconductors. The site
selections for doping calcium and creating holes are also investigated by
calculating the heat of solution. In a continuum treatment, the volume of
formation of doping calcium at Y-sites is computed. It is then applied to study
the segregation of calcium ions to grain boundaries in the Y-123 compound. The
influences of the segregation of calcium ions on space charge profiles are
finally studied to provide one guide for understanding the improvement of
transport properties by doping calcium at grain boundaries in Y-123 compound.Comment: 13 pages, 5 figure
Inter- and intragrain currents in bulk melt-grown YBaCuO rings
A simple contactless method suitable to discern between the intergrain
(circular) current, which flows in the thin superconducting ring, and the
intragrain current, which does not cross the weakest link, has been proposed.
At first, we show that the intergrain current may directly be estimated from
the magnetic flux density measured by the Hall sensor positioned
in the special points above/below the ring center. The experimental
and the numerical techniques to determine the value are discussed. Being
very promising for characterization of a current flowing across the joints in
welded YBaCuO rings (its dependencies on the temperature and the external
magnetic field as well as the time dissipation), the approach has been applied
to study corresponding properties of the intra- and intergrain currents flowing
across the -twisted grain boundaries which are frequent in bulk
melt-textured YBaCuO samples. We present experimental data related to the flux
penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin
state and during the field reversal. The shielding properties and their
dependence on external magnetic fields are also studied. Besides, we consider
the flux creep effects and their influence on the current re-distribution
during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version,
corrections to perturbing effects near the weak links are introduced, one
more figure is added. lin
Theory of c-axis Josephson tunneling in d-wave superconductors
The temperature and angular dependence of the c-axis Josephson current and
the superfluid density in layered d-wave superconductors are studied within the
framework of an extended Ambegaokar-Baratoff formalism. In particular, the
effects of angle-dependent tunneling matrix elements and Andreev scattering at
grain boundaries are taken into account. These lead to strong corrections of
the low-temperature behavior of the plasma frequency and the Josephson current.
Recent c-axis measurements on the cuprate high-temperature superconductors
HgBa_2CaCu_{1+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} can therefore be
interpreted to be consistent with a d-wave order parameter.Comment: Revtex, 4 pages with 4 eps figures, to appear in PRB R
d-like Symmetry of the Order Parameter and Intrinsic Josephson Effects in Bi2212 Cross-Whisker Junctions
An intrinsic tunnel junction was made using two Bi-2212 single crystal
whiskers. The two whiskers with a cross-angle were overlaid at their c-planes
and connected by annealing. The angular dependence of the critical current
density along the c-axis is of the d-wave symmetry. However, the angular
dependence is much stronger than that of the conventional d-wave. Furthermore,
the current vs. voltage characteristics of the cross-whiskers junctions show a
multiple-branch structure at any cross-angle, indicating the formation of the
intrinsic Josephson junction array.Comment: 4 pages PDF fil
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