Influence of Context on Item Parameters in Forced-Choice Personality Assessments

A fundamental assumption in computerized adaptive testing (CAT) is that item parameters are invariant with respect to context – items surrounding the administered item. This assumption, however, may not hold in forced-choice (FC) assessments, where explicit comparisons are made between items included in the same block. We empirically examined the influence of context on item parameters by comparing parameter estimates from two FC instruments. The first instrument was compiled of blocks of three items, whereas in the second, the context was manipulated by adding one item to each block, resulting in blocks of four. The item parameter estimates were highly similar. However, a small number of significant deviations were observed, confirming the importance of context when designing adaptive FC assessments. Two patterns of such deviations were identified, and methods to reduce their occurrences in a FC CAT setting were proposed. It was shown that with a small proportion of violations of the parameter invariance assumption, score estimation remained stable

On the identity and typification of Solanum brasilianum Dunal (Solanaceae)

The file attached is the published version of the article.NHM Repositor

Micromechanical modeling of tension stiffening in FRP-strengthened concrete elements

This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymer–strengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for concrete tension stiffening and average response of steel reinforcing bars in fiber reinforced polymer–strengthened members as the main inputs of smeared crack modeling approaches

Chaos in Anisotropic Pre-Inflationary Universes

We study the dynamics of anisotropic Bianchi type-IX models with matter and cosmological constant. The models can be thought as describing the role of anisotropy in the early stages of inflation. The concurrence of the cosmological constant and anisotropy are sufficient to produce a chaotic dynamics in the gravitational degrees of freedom, connected to the presence of a critical point of saddle-center type in the phase space of the system. The invariant character of chaos is guaranteed by the topology of the cylinders emanating from unstable periodic orbits in the neighborhood of the saddle-center. We discuss a possible mechanism for amplification of specific wavelengths of inhomogeneous fluctuations in the models. A geometrical interpretation is given for Wald's inequality in terms of invariant tori and their destruction by increasing values of the cosmological constant.Comment: 14 pages, figures available under request. submitted to Physical Review

CFRP flexural and shear strengthening technique for RC beams : experimental and numerical research

Near surface mounted (NSM) technique has proved to be a very effective technique for the flexural strengthening of RC beams. Due to the relatively small thickness of the concrete cover that several beams present, cutting the bottom arm of steel stirrups for the installation of NSM laminates might be a possible strategy, whose implications on the beam’s load carrying capacity need to be assessed. When steel stirrups are cut, however, the shear resistance can be a concern. This also happens when a strengthening intervention is carried out to increase the flexural resistance of a beam, since in certain cases it is also necessary to increase the shear resistance in order to avoid the occurrence of brittle shear failure. The present work assesses the effectiveness of a technique that aims to increase both the flexural and shear resistance of RC beams that have the bottom arm of the steel stirrups cut for the application of NSM laminates. This assessment is performed by experimental and numerical research. The main results of the experimental program are presented and analyzed, and the innovative aspects of a constitutive model implemented in a computer program are described, being their virtues and deficiencies discussed.The study reported in this paper forms a part of the research program "CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures" supported by FCT, PTDC/ECM/73099/2006. The authors wish to acknowledge the support also provided by the S&P, Casais and Artecanter Companies. The second Author acknowledges the grant under the aforementioned research project. The third author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005

Numerical modelling of composite floor slabs subject to large defections

This paper is concernedwith the ultimate behaviour of composite floor slabs. Steel/concrete composite structures are increasingly common in the UK and worldwide, particularly for multi-storey construction. The popularity of this construction formis mainly due to the excellent efficiency offered in terms of structural behaviour, construction time and material usage all of which are particularly attractive given the ever-increasing demands for improved sustainability in construction. In this context, the engineering research community has focused considerable effort in recent years towards understanding the response of composite structures during extreme events, such as fires. In particular, the contribution made by the floor slab system is of crucial importance as its ability to undergo secondary load-carrying mechanisms (e.g. membrane action) once conventional strength limits have been reached may prevent overall collapse of the structure. Researchers have focused on developing the fundamental understanding of the complex behaviour of floor slabs and also improving themethods of analysis. Building on thiswork, the current paper describes the development and validation of a finite element model which can simulate the response of floor slab systems until failure, both at ambient and elevated temperature. The model can represent the complexities of the behaviour including the temperature-dependent material and geometric nonlinearities. It is first developed at ambient temperature and validated using a series of experiments on isolated slab elements. The most salient parameters are identified and studied. Thereafter, the model is extended to include the effects of elevated temperature so it can be employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed

Reliability analysis of moment redistribution in reinforced concrete beams

Design codes allow a limited amount of moment redistribution in continuous reinforced concrete beams and often make use of lower bound values in the procedure for estimating the moment redistribution factors. Here, based on the concept of demand and capacity rotation, and by means of Monte Carlo simulation, a probabilistic model is derived for the evaluation of moment redistribution factors. Results show that in all considered cases, the evaluated mean and nominal values of moment redistribution factor are greater than the values provided by the ACI code. On the other hand, the 5th percentile value of moment redistribution factor could be lower than those specified by the code. Although the reduction of strength limit state reliability index attributable to uncertainty in moment redistribution factors is not large, it is comparable to the reduction in reliability index resulting from increasing the ratio of live to dead load

Time-dependent fibre pull-out behaviour in self-compacting concrete

In the present study, the effectiveness of a fibre as an element for transferring stresses across cracks under a sustained load was assessed. Single fibre pull-out creep tests were performed, in which fibre slip was monitored as a function of the time. The influence of the fibre orientation angle (0, 30 and 60 degrees), as well as pre-imposed fibre slip levels, spr, 0.3 and 0.5 mm on the creep response was investigated. Additionally, instantaneous fibre pull-out tests were carried out on undamaged-bond specimens in order to quantify the effects of the pull-out creep behaviour. The damage introduced by the pre-slip levels in the bond of the fibre/matrix interface influenced the long-term fibre pull-out behaviour and, consequently, accelerated the creep rate. However, the assembled pull-out creep behaviour did not differ considerably from the instantaneous pull-out behaviour for the adopted pre-imposed fibre slip levels.This work is supported by the FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project 18 SlabSys-HFRC-PTDC/ECM/120394/2010. The authors would like to acknowledge the materials supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash).info:eu-repo/semantics/publishedVersio

Analytical model for residual bond strength of corroded reinforcement in concrete structures

Bond strength deterioration in corrosion-damaged reinforced concrete structures significantly affects serviceability and load-carrying capacity in their remaining service life. This paper presents a new analytical model for predicting the cracking development in the surrounding concrete and the residual bond strength of rebar in concrete structures due to reinforcement corrosion. The proposed analytical method adopts the thick-walled cylinder model for the cover concrete and considers the realistic properties of the corrosion-induced cracked concrete such as anisotropic behavior, residual tensile strength, and reduced tensile stiffness. As corrosion progresses, three phases for bond strength evolution associated with concrete cracking development are defined and the corresponding corrosion levels in each phase are determined. By using the constructed new governing equation, the crack width growth in the concrete cover and the radial bursting pressure at the bond interface are evaluated. The ultimate bond strength is then estimated from the contributions of adhesion, confinement, and corrosion pressure as a function of corrosion level. Finally, the effectiveness of the proposed analytical model is demonstrated by comparing the predicted results with experimental data available, and the results show that the proposed model is useful for predicting the bond strength evolution of the corroded rebar in concrete structures