CFRP-Steel hybrid retrofitting of steel-concrete composite structures

Carbon fiber reinforced polymer (CFRP) is found to be an effective material for the retrofitting of both reinforced concrete (RC) and steel structures. However, retrofitting such structures using CFRP alone is shown to exhibit a premature failure due to early de-bonding of the CFRP laminates from the hosting sur-faces. On the other hand, steel plates are also used separately for the steel and RC structures. However, steel plates usually add the self-weight to the structures whereas CFRP is known for its high strength to weight ra-tio. In the present study, the advantages of both steel plates and CFRP is used to form a hybrid retrofitting sys-tem that is able to withstand the existing load to prevent the failure of the structures. In order to improve the retrofitting efficiency of a steel-concrete composite structures, an experimental investigation is carried out to examine the use of effectiveness of CFRP-steel hybrid retrofitting system.

Database for structural steel experiments under a distributed collaboration environment

Due to the high requirements of civil infrastructures against the earthquake in Japan, a great number of research organizations have been conducting the structural steel experiments, in particular the seismic tests such as the cyclic loading test and the pseudo-dynamic test, for many years to determine the seismic performances of steel structures. However, the original test data gained by most research organizations are not well stored in an appropriate manner for distribution and possible usage of others. Although a Numerical Database of Steel Structures (NDSS) was developed some years ago to preserve and share experimental data of the ultimate strength tests acquired at Nagoya University, it was not easy to access this database from other computer platform due to the lack of the support of proper communication media. With the rapid development of information networks and their browsers, structural engineers and researchers are able to exchange various types of test data through Internet. This paper presents the development of a distributed collaborative database system for structural steel experiments. The database is made available on the World-Wide Web, and the Java language enables the interactive retrieval efficiently. The applications of the developed database system for the retrieval of experimental data and seismic numerical analysis are validated in the form of examples.

CAE crash analysis of structures in oblique loading

This work focussed on how tubular steel structures similar to that in frontal car frames deform under crash conditions. The novelty comes from finding three crash modes: axial crush, transitional and global bending. Each mode was categorised by reaction force and energy absorption, this allowing for better structural design practices.

Damage identification of steel beams using local and global methods

Structural condition monitoring methods can be generally classified as local and global. While the global method needs only a small number of sensors to measure the low-frequency structural vibration properties, the acquired information is often not sufficiently sensitive to minor damages in a structure. Local methods, on the other hand, could be very sensitive to minor damages but their detection range is usually small. To overcome the drawbacks and take advantage of both methods, an integrated condition monitoring system has been recently developed for structural damage detection, which combines guided wave and structural vibration tests. This study aims at finding a viable damage identification method for steel structures by using this system. First, a spectral element modelling method is developed, which can simulate both wave propagation and structural vibration properties. Then the model is used in updating analysis to identify crack damage. Extensive numerical simulations and model updating works are conducted. The experimental and numerical results suggest that simply combining the objective functions cannot provide better structural damage identification. A two-stage damage identification scheme is more suitable for identifying damage in steel beams.

Effect of strain ageing on the mechanical properties of partially damaged structural mild steel

ABSTRACT
This paper addresses the strain ageing effects on the mechanical properties of the partially damaged structural mild steel. Since repairing partly damaged structures may not occur immediately, the strain ageing effect can significantly influence the structural behaviour. The changes due to this effect have not so far been considered in the civil engineering design guidelines. In order to investigate strain ageing effects, two-stage experimental tests are carried out on the mild-steel specimens. In the first stage, partial damage is made using quasi-static loading. During the second stage, the strength and ductility of the specimens are examined after 2 and 7 days ‘ageing’ at room temperature and the results are compared with the corresponding no-age samples. The microstructure of the specimens is examined using scanning electron microscopy (SEM). To illustrate the effect of strain ageing on the global behaviour of steel structures, a numerical example is provided in which strain ageing impacts on loading capacity and deflection of a steel beam. Finally, the stress–strain relation of partially damaged mild-steel material incorporating strain ageing effects is expressed by calibrating the parameters of Ramberg–Osgood model.

Development and applications of an experimental database for structural engineering education

A great number of research organisations in Japan have been conducting structural steel experiments for many years, particularly seismic tests of steel structures like cyclic-loading and pseudo-dynamic tests, in order to determine their seismic performances. However, the original test data gained by most research organisations are not well stored in an appropriate manner for distribution and possible usage by others. With the rapid development of information networks, structural engineers and researchers are able to exchange various types of test data through the Internet. In this paper, the authors present the development of a distributed collaborative database system for structural steel experiments. The database is made available on the Internet, and the use of Java language enables efficient interactive retrieval. The potential applications of the developed database system for structural engineering education are validated for the retrieval of experimental data and seismic numerical analysis.

Study of the effect of grain size on the dynamic mechanical properties of microalloyed steels

In the present paper the effect of grain refinement on the dynamic response of ultra fine-grained (UFG) structures for C–Mn and HSLA steels is investigated. A physically based flow stress model (Khan-Huang-Liang, KHL) was used to predict the mechanical response of steel structures over a wide range of strain rates and grain sizes. However, the comparison was restricted to the bcc ferrite structures. In previous work [K. Muszka, P.D. Hodgson, J. Majta, A physical based modeling approach for the dynamic behavior of ultra fine-grained structures, J. Mater. Process. Technol. 177 (2006) 456–460] it was shown that the KHL model has better accuracy for structures with a higher level of refinement (below 1 μm) compared to other flow stress models (e.g. Zerrili-Armstrong model). In the present paper, simulation results using the KHL model were compared with experiments. To provide a wide range of the experimental data, a complex thermomechanical processing was applied. The mechanical behavior of the steels was examined utilizing quasi-static tension and dynamic compression tests. The application of the different deformation histories enabled to obtain complex microstructure evolution that was reflected in the level of ferrite refinement.

Implementing the international benchmarking labour productivity theoretical model

Purpose – Building upon the results of a critical review of previous studies, the purpose of this paper is to present a framework to enhance the reliability of the theoretical model for international benchmarking of labour productivity (TMIBLP) method for construction project activities. The next part of the paper presents the results of implementing the proposed framework for construction activities in the Iranian construction industry. Design/methodology/approach – This paper draws upon a critical review of the literature to highlight the drawbacks of the previous studies concerning implementing TMIBLP within the construction industry. Identifying these shortcomings, the authors propose a framework for construction projects, which presents the procedure for deploying TMIBLP for construction activities in a reliable manner. The final section of the paper demonstrates the empirical implementation of the proposed framework within the Iranian construction industry. Findings – The primary contributions of the paper include: identifying the drawbacks of previous studies within the construction context, the framework that would lead construction managers towards more reliable implementation of benchmarking for construction projects, and determining the baseline of erecting steel structures in a developing country. Practical implications – A practical implementation of the TMIBLP method was presented to address the lack of research in Iran and to show the feasibility of using the framework developed. The authors investigated the daily labour productivity for the activity of structural steel erection for six projects in Tehran in order to determine the values of the baseline productivity for each project. Accordingly, the disruption index, performance ratio and project management index as the project benchmarks were calculated for all six projects. Originality/value – Underlining the necessity of implementing methods such as TMIBLP, this study outlines the outcomes of the first study on the benchmarking of construction activities deploying the proposed framework and using the data on erecting steel structures from six construction projects in Iran. The discussions provide guidelines for construction project managers regarding benchmarking labour productivity. The paper concludes with suggestions for future research opportunities.

Generating misorientations in shear deformation structures

Of considerable importance to the generation of ultrafine microstructures is the development of high misorientations. The present work examines the effect of the crystallographic rotation field in simple shear upon the evolution of misorientation during plastic working. A series of Taylor simulations are presented and it is shown that the rotation field is such that small differences in orientation in the region of the main torsion texture components are considerably increased with the application of shear strain. This did not occur in simulations of rolling. The torsion simulations compare favourably with the nature of the misorientations evident in hot worked 1050 Al and Ti-IF steel. It is concluded that shear deformation, by its nature, facilitates the generation of higher misorientations.

Formation of ultrafine grained microstructures in steel through strain induced transformation during single pass hot rolling

In the present study, wedge-shape samples were used to study the effect of strain induced transformation on the formation of ultrafine grained structures in steel by single pass rolling. The results showed two different transition strains for bainite formation and ultrafine ferrite (UFF) formation in the surface layer of strip at reductions of 40% and 70%, respectively, in a plain carbon steel. The bainitic microstructure formed by strain induced bainitic transformation during single pass rolling was also very fine. The evolution of UFF formation in the surface layer showed that ferrite coarsening is significantly reduced through strain induced transformation combined with rapid cooling in comparison with the centre of the strip. In the surface, the ferrite coarsening mostly occurred for intragranular nucleated grains (IG) rather than grain boundary (GB) ferrite grains. The results suggest that normal grain growth occurred during overall transformation in the GB ferrite grains. In the centre of the strip, there was significantly more coarsening of ferrite grains nucleated on the prior austenite grain boundaries.

Characterization on ferrite microstructure evolution during large strain warm torsion testing of plain low carbon steel

Ferrite grain/subgrain structures evolution during the extended dynamic softening of a plain low carbon steel was investigated throughout the large strain warm deformation by hot torsion. Microstructural analysis with electron back-scattering diffraction (EBSD) scanning electron microscope (FEG/SEM) was carried out on the ferrite microstructural parameters. The results showed that the warm flow stress–strain curves are similar to those affected only by dynamic softening and an extended warm flow softening is seen during large strain deformation up to 30. Furthermore, with an increase in strain up to ~ vert, similar1 the grain size of ferrite, misorientation angle and fraction of high-angle boundaries gradually decrease and fraction of low-angle boundaries increases. With a further increase in the strain beyond ~, vert, similar2, these parameters remain approximately unchanged. No evidence of discontinuous dynamic recrystallisation involving nucleation and growth of new grains was found within ferrite. Therefore, the dynamic softening mechanism observed during large strain ferritic deformation is explained by continuous dynamic recrystallization (CDRX).

Magnesium alloy applications in automotive structures

The energy absorbed by magnesium alloys (high-pressure die-cast (HPDC) AM20, AM50, AM60, and extruded AZ31) in a buckling test was significantly greater than the aluminum alloy 6061 T6 and particularly mild steel of a similar weight, but was less than that of the aluminum alloy and steel for the same thickness (Figure 6).26 This indicates that mass savings can be achieved by the substitution with magnesium alloys to achieve similar energy-absorbing characteristics.

EBSD analysis of a Ti-IF steel subjected to hot torsion in the ferritic region

The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free steel was investigated using hot torsion. Tests were performed at temperatures between 765 °C and 850 °C at strain rates between 0.003 s−1 and 1 s−1 for samples with grain sizes of 25 μm, 75 μm and 150 μm. The structures were observed using EBSD analysis and are consistent with those expected for materials dominated by dynamic recovery. Some evidence was found for small amounts of thermally induced migration of pre-existing boundary (bulging) and for the generation of new segments of high angle boundaries by continuous dynamic recrystallization. The early onset of a steady-state flow stress in the finer grained samples is attributed to one or a combination of thermally induced boundary migration and enhanced rates of recovery near subgrain (and grain) boundaries.

Press forming performance of galvanneal coated steel

This project quantified the press formability of galvanneal coated steel. A coil of galvanneal coated steel was produced containing various coating structures. Using different lubricants, the powdering, friction and forming properties were determined. It was found that optimum formability was obtained by effective lubrication while galvanneal coating structure controlled powdering resistance.

Heterometallic CeIII–FeIII–salicylate networks : models for corrosion mitigation of steel surfaces by the ′Green′ inhibitor, Ce(salicylate)3

The syntheses and structures of the novel Ce–Fe bimetallic complexes [{Fe(sal)₂(bpy)}₂Ce(NO₃)(H₂O)₃]·EtOH and [{Fe(sal)₂(bpy)}₄Ce₂(H₂O)₁₁][salH]₂·EtOH·3H₂O (salH₂ = salicylic acid) suggest Fe³⁺–sal²⁻ units and Ce–OC(R)O–Fe bridging contribute to the formation of corrosion inhibitive layers on steel surfaces exposed to [Ce(salH)₃(H₂O)].