The effect of residual stresses on the strain evolution during welding of thin-walled tubes

In many applications, negative effects of residual stresses in the material stemming from the production process, are regularly encountered. These residual stresses in cold-rolled steel tubes are mainly due to two mechanisms: (i) the rolling of the flat plate into a circular cross-section and (ii) afterwards closing this section with a weld bead. This research focuses on the residual stresses due to the welding process. In an experimental setup abstraction is made of the real production process of the tube. A finite element model is built of this experimental setup. Validation of the welding simulations is done by comparing the strain evolution in both the experiment and the simulation. In this validation process, sometimes a discrepancy between the measured strain evolution and the one obtained from the numerical analysis is seen. In this contribution it is numerically investigated how initial residual stresses affect the thermal strain evolution in the tube during the welding process. This is done in two ways: firstly an initial stress field in hoop direction, based on the spring back of the tube when cut is taken as the reference state and secondly the stress/strain state after the first weld is used in stead of the virgin material state. The conclusion for both assumptions is that the strain evolution during the welding is affected by the initial stress/strain state of the material

Grouting as a repair/strengthening solution for earth constructions

Earth, as a building material, has been used since ancient times, and is still being used with that purpose. It was used for building shelters, houses, temples and even military constructions, like fortresses. As a consequence, currently, there is a great architectural heritage stock on this kind of constructions. Nevertheless, earthen materials are very sensitive when compared with modern materials, since they are more vulnerable to external aggressive agents, revealing most of the times a faster degradation rate. From a structural perspective they present a very low tensile strength, a low compressive strength and a fragile behaviour, making the earthen structures strongly vulnerable to earthquakes. The structural damage in this kind of structures manifests, in general, in the form of cracks or voids. Repairing these cracks is fundamental in order to obtain an improved structural behaviour, especially if the earth construction was built in a seismic zone. Injecting mud grouts may constitute a feasible and reliable solution for repair this kind of damage. Although, mud grouts experience many problems that hinder their application and the knowledge about them is still very limited. This requires that deep studies have to be carried out in order to solve their problems and to make this solution reliable. In this paper it is discussed the methodology that should be established for the design of mud grouts suitable for earth constructions. But first a summarized explanation about earth constructions and their problems is presented. This results from an ongoing PhD research that still is in an initial phase, and it aims, precisely, the development of grouts specifically to be applied in earth constructions.Fundação para a Ciência e a Tecnologia (FCT

Strengthening of masonry and earthen structures by means of grouting: design of grouts

Grout injection is a technique commonly used in the repair and strengthening of masonry, due to the simplicity in its execution. However, to design a suitable grout, a proper methodology must be followed. The grout must accomplish requirements that depend mainly on mechanical behaviour and durability features of the struc-tures. Grouting can be also applied to earthen structures, for repairing cracks and filling voids. The same methodology can be used to design grouts, but the requirements must be adapted. Therefore, this paper pre-sents a discussion concerning the repair and strengthening of masonry and earth constructions through grout injection. To emphasize the differences in the requirements, first a short characterization of earth as a building material is given. Subsequently, the main decay phenomena are identified. Finally, attention goes to the effect of shrinkage and swelling behaviour of earth and the design of an appropriate grout for injection.Fundação para a Ciência e a Tecnologia (FCT

Innovative Cross-section Shapes for Built-up CFS Columns. Experimental Investigation

Innovative cross-section shapes for built-up columns from cold-formed steel (CFS) profiles are evaluated experimentally. The goal is to obtain highly stable members with reduced sensitivity to bucking effects and initial imperfections, and therefore, higher strength-to-weight ratios. The columns have been designed following the principles of the direct strength method [1], with the ambition to exclude (or reduce) various buckling effects from the column response to compressive loads. Cross-section proportions and bolt spacing have been adapted, in order to interfere with the distortion of individual profiles and the overall buckling of the columns. Experiments show that, through proper design and insight into the behaviour of such members, columns with substantially increased overall capacity can be obtained. The good agreement between predicted and measured ultimate loads also indicates that such built-up assemblies could be integrated into everyday construction practice

Grouting as a mean for repairing earth constructions

A good condition of the structural elements of an earth construction is essential for a good global structural behaviour. Therefore, the absence of major cracks is essential. Repairing cracks by using traditional techniques, involving the partial or the total reconstructions of the structural elements, constitutes a very intrusive solution that must, necessarily, be avoided in the case of historical earth constructions. Grouting constitutes an alternative and more practical solution for solving this problem. However, the design of the grouts for earth constructions demands the implementation of a methodical process that accounts both for the structural and durability demands of the construction. Previous works showed that the injection of mud grouts is a reliable and feasible solution. However, the knowledge developed is still very limited, hindering the further development of a methodology for designing mud grouts for earth constructions. Therefore, in this paper an initial methodology proposal for the design of mud grouts is presented and discussed. This results from an ongoing research that aims at the development of suitable grouts for earth constructions.Fundação para a Ciência e a Tecnologia (FCT

Repair of earth masonry by means of grouting: importance of clay in the rheology of a mud grout

Building with earth is one of the most ancient and traditional ways of building. Consequently, many historic and new-built earthen buildings can be found all over the world. However, the specific characteristics of earthen materials make the earth constructions very sensitive to external damaging agents. In particular, the weakness and fragility extensively recognized on earthen materials make this type of constructions very vulnerable from a structural perspective. In general, the structural damage on earth constructions occurs in the form of cracks, which debilitate the structural behaviour and compromise the durability. Injection of mud grouts can be seen as a reliable and economic solution for repairing earth constructions. The success of such intervention on a historical construction requires following an appropriated design methodology. However, the knowledge about mud grouts is still limited, and thus research efforts are needed in order to develop such methodology and to surpass many of the difficulties that the restorers of earth constructions are currently facing. Understanding the rheology of the mud grouts is one of the key issues of the all process. Hence, this paper explains an initial proposal of methodology for the design of mud grouts and an experimental campaign that aimed to understand the role of the clay fraction in the rheology of mud grouts.Fundação para a Ciência e a Tecnologia (FCT

Modelling of rammed earth under shear loading

The intensive use of earth as a building material since ancient times resulted in an important and significant earthen built heritage currently existing worldwide spread. The rammed earth technique has a significant presence in this heritage, where it served to build from simple dwell-ings to fortresses. However, the high vulnerability of rammed earth constructions to decay agents and to seismic events puts in risk their further existence and the lives of millions of peo-ple. With respect to the seismic behaviour of rammed earth walls, the understanding and mod-elling of their shear behaviour are topics underdeveloped in the bibliography. Nevertheless, these topics are of extreme importance in the preservation and strengthening of rammed earth constructions. Therefore, this paper presents a numerical work aiming at modelling the non-linear behaviour of unstabilised rammed earth under shear loading, resorting to the finite ele-ments method (FEM). The models were used to simulate the behaviour of a set of rammed earth wallets tested under diagonal compression. Both macro- and micro-modelling approach-es were considered, where the objective of this last approach was to evaluate the influence of apparent weakness of the interfaces between layers on the shear behaviour. The total strain ro-tating crack model (TSCRM) was used to simulate the behaviour of the rammed earth material, while the Mohr-Coulomb failure criterion was used to simulate the behaviour of interfaces be-tween layers. Furthermore, uncertainties related to the definition of the input parameters re-quired performing a sensitivity analysis. The numerical models achieved good agreement with the experimental results and the compressive strength, the Poisson’s ratio, the tensile strength and the tensile fracture energy revealed to be the most important parameters in the analyses.Fundação para a Ciência e a Tecnologia (FC

A construção em taipa e os sismos

A reconhecida sustentabilidade da construção em taipa e o vasto património arquitectónico edificado segundo este processo construtivo são motivos, por si só suficientes, para justificar o crescente interesse pela construção taipa por parte das autoridades, investigadores, projectistas e empresas. Todavia, este tipo de construção apresenta tipicamente um deficiente desempenho sísmico, o que torna desaconselhada a adopção da taipa como solução estrutural em zonas de perigosidade sísmica não negligenciável. Neste contexto, o presente artigo descreve a construção em taipa bem como a sua importância cultural. Seguidamente, caracteriza-se o desempenho sísmico deste tipo de construções, com especial ênfase nos modos de rotura. Por fim, discutem-se possíveis modificações do processo construtivo para melhorar o desempenho sísmico das construções em taipa novas, bem como as técnicas de reforço sísmico e reparação para construções existentes