Thomas Neitzert

Pull-out behavior of galvanized steel strip in foam concrete

The interface and bond between concrete and reinforcing steel are the most fundamental problems of reinforced concrete structures. In this paper, the pull-out strength of galvanized steel strips with different geometries and hole patterns in foam concrete blocks are investigated experimentally and numerically. Foam concrete mixtures of 1,200-kg/m3 density were obtained by mixing cement and water in a mortar mixer together with ultrafoam as the foaming agent and Quick-Gel as the viscosifier. A theoretical model is developed to predict the bond-slip relationship between the strip and the concrete. This model is further implemented in a finite element simulation of the pull-out tests through the ABAQUS user subroutine. The results show good correlation between experimental, theoretical, and finite element simulation analyses. The influence of the steel strip geometries on the maximum pull-out force is also studied, and it was found that the strips with the greatest hole area, hole diameter, and circumference areas have higher pull-out forces and the increase is nearly linear.

An Analysis of the Bonding Energy through Pull-Out Tests for Aerated Concrete with Various Steel Strip Geometries

The relationship between various steel strip geometries and the bonding energy through pull-out tests of aerated concrete specimens is investigated. Prismatic concrete samples containing embedded steel strips with and without holes of differing sizes and quantities were analysed. Improvements of the bonding energy through pull-out tests by 70% are possible by increasing the number of holes on a steel strip from one to four while maintaining a constant surface area. The energy increased even up to 130% for strips containing holes compared to strips without. In addition, the tests have been carried out with a novel easy to assemble set-up containing a freely adjustable ball-joint and a plate with embedded bolts to avoid eccentricity during pull-out tests.

Rapid casting: a critical analysis of mould and casting characteristics

Abstract The use of rapid prototyping technologies for the production of sacrificial sand moulds for the foundry industry has been previously researched, but with selective laser sintering as the main technology, and with different methods of processing and materials as critical variables. With the proliferation of 3D printers and the relatively easy and economical production of moulds with special sands supplied by Z-Corporation, it is time that direct metal casting through 3D printing is scientifically investigated. Knowledge of the influence of various process parameters on the quality of moulds and subsequent castings is essential in effectively employing direct metal casting in real-world applications. This paper presents results of experimental investigations carried out to establish the influences of critical factors, such as curing times and temperatures, on mechanical characteristics, such as strength and permeability, of sand moulds produced by 3D printing. The dimensional and surface qualities of castings produced using the casting grade aluminium, A356, and the effectiveness of various mould surface coatings, and causes of casting defects, are also investigated. Statistically-designed experiments are employed for the systematic analysis of the individual roles of direct metal casting parameters, as well as their combined effects.

Developing and evaluating a framework for process improvement in an alliance project: a New Zealand case study

‘Lean thinking’ holds out the promise of dramatic improvements in construction production processes, especially in waste minimization. While there exist empirical studies of ‘leanness’ with regard to non-relational-type projects, there is a need to analyse its applicability in relational contexts, such as an alliance. The application of ‘lean’ to a project alliance in a viaduct replacement in New Zealand is investigated here. The primary objective is to define a framework to streamline improvements in processes and to verify the applicability of the defined framework to a real construction alliance project. Participant observations, project documentation and action research meetings were used to collect data on the waste identification and elimination processes. The findings indicate that the construction work in a project alliance can be improved considerably by eliminating or reducing waste. Moreover, the savings are substantial, as the processes investigated were cyclic and repetitive. This framework is equally suited to waste detection and improvements at the site level. Project organizations should detect needs and opportunities for process change and transform processes accordingly. The current lack of any waste elimination technique, which could provide a significant competitive advantage for industry participants, has been established. Organizational conditions exist in project alliances that help to disseminate and sustain the lean concept.

Correlation between Construction Procurement Methods and Lean Principles

Abstract Different procurement methods have been developed and applied in the construction industry for improving performance. At the same time, novel management concepts have been adopted for performance improvement based on new production methodologies. The lean principle is one such methodology being applied in the construction industry. This paper proposes that with the right combination of objectives, principles and techniques, this can form the basis for a new project delivery system. The paper has as its objective the identification of an appropriate procurement method that incorporates lean principles. It reviews extant literature on the lean concept and its application in the construction industry, as well as construction procurement methods, and their individual characteristics. The study finds that partnership arrangements have a higher correlation with lean principles compared to other procurement methods because of the emphasis on collaboration and teamwork through construction partnerships.

EFFECT OF STEEL STRIP GEOMETRY ON PULL-OUT STRENGTH OF AERATED CONCRETE

An investigation of shearing strength between steel strips and concrete specimens is presented in this paper. Pull-out tests were carried out to check the influence of various geometrical parameters of steel strips on the shearing strength in aerated concrete. The size-effect of the various strip widths with and without holes, area of holes and circumference area of holes were analysed. All these parameters were compared to a total area of the strip among different sets and ratio/coefficients were proposed. The tests were performed on aerated concrete cubes with galvanized steel strips of 0.75mm thickness.

Optimization of pocket design to produce a thin shape complex profile

In extrusion practice surface quality problems like flow lines with thin and varying thicknesses of complex profiles are experienced. Minimization of temperature variance inside the forming zone and velocity variation across the face of the die are particularly important during the metal flow in order to maintain a good quality finish. Several parameters such as shape, depth of pocket, location of die hole and local bearing lengths can be altered to minimize these effects, but fundamental understanding between these parameters and homogeneity of metal flow are very limited in the literature. This study investigates the influence of above-mentioned parameters on the flow behaviour during extrusion for simple and more complex geometries.

Reciprocating Sliding Wear Behavior of 60NiTi As Compared to 440C Steel under Lubricated and Unlubricated Conditions

ABSTRACT 60NiTi is a hard (∼60 HRC) and highly corrosion-resistant intermetallic with a relatively low elastic modulus (∼100 GPa). In addition, this alloy exhibits a high compressive strength (∼2,500 MPa) and a high elastic compressive strain of over 5%. These attributes make this alloy an attractive candidate to be employed in structural and mechanical component applications. However, sliding wear behavior of this intermetallic has not yet been studied in a systematic way. In this study, lubricated and unlubricated reciprocating sliding wear behavior of 60NiTi is compared to 440 C steel as a conventional bearing and wear-resistant alloy. Results of experiments carried out under different loads show that 60NiTi, despite having a higher hardness, exhibits a significantly inferior wear behavior under dry conditions in comparison to 440 C steel. These unexpected results indicate that 60NiTi does not follow conventional wear theories where the wear of materials has an inverse relationship to their hardness. On the other hand, under lubricated conditions with castor oil and a synthetic gear oil, 60NiTi exhibits low specific wear rates. These results exhibit the importance of proper lubrication in sliding mode applications where 60NiTi is exploited as a wear-resistant alloy.

High Strain Rate Compressive Behaviour of Selective Laser Melted Ti-6Al-4V

Ti-6Al-4V alloy is one of the most important engineering alloys, combining attractive properties with inherent workability. The aim of this study is to investigate the effect of strain rate on the compressive mechanical properties of Ti6Al4V alloy manufactured by a selective laser melting process. The mechanical tests were performed by means of a compression split Hopkinson pressure bar apparatus under high strain rate ranging from 1400 s-1 to 4500 s-1. The true stress-strain curves obtained from static and dynamic compressive tests show strain rate sensitivity from quasi-static (peak strength 1300MPa) to high strain rate (peak 1500 MPa). Within the high strain rate range tested, the strain rate sensitivity is not remarkable. The fractographic analysis shows a relatively smooth and smeared fractured surface along with a dimple like structure. The observation of elongated dimples confirms the operation of a dynamic shear failure mechanism for the additively manufactured Ti-6Al-4V parts.

Experimental and numerical analysis pull-out strength of steel strip in foam concrete

The structural performance of a reinforced concrete is influenced by the properties of the reinforcing element and the concrete interface. Therefore, investigating the pull-out strength and bond stress vs. slip relationship between components of the reinforced concrete are very important. This paper presents a numerical method to study the pull-out behaviour of galvanised steel strips in aerated concrete. A local bond-slip relationship is determined using experimental and theoretical analyses and is then implemented to the finite element simulation through the user-defined subroutine of ABAQUS software. The effect of strip geometry and mechanical properties of the aerated concrete on the pull-out force is also investigated. Comparison between the experimental, theoretical and FE simulation results shows very good agreement. It was shown that a trilinear bond-slip model is suitable for the modelling of steel strip and concrete interface.