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Grout injection is a widely used technique for consolidation of multi-leaves masonries, aimed at increasing the compactness and to create links between the internal and external leaves that will improve shear, flexural and compressive resistances. Grouts can be seen as mixtures of binder with water, admixtures and/or additives, which should present low viscosity and high penetrability. The definition of a grout composition should involve the knowledge of the injection capacity within a specific type of masonry and good physical and chemical compatibility with the original materials present in the historic structures. The flow of the grout through the masonry depends on the fresh grout properties, such as stability, water retention and rheological behaviour. Thus, the evaluation of the performance of the grout as function of a porous medium is firstly started by checking the intrinsic properties of the grout (namely rheological and stability) and then by controlling the injectability of masonry by injection tests on cylinders. Since it is difficult to reproduce a real masonry and to visualize what is happening inside the porous medium being injected, masonry samples were created by filling plexiglass cylinders with a fraction of limestone sands and crushed brick. These materials are sieved to obtain different grain size distributions to enable the simulation of different permeabilities and internal structures for the masonry. The lack of information about the performance of hydraulic lime based grouts as a function of the properties of the porous medium to be injected enhances the need of a detailed research on the subject.

Systems externally reinforced by bonded fibre reinforced polymers (FRP) are widely used in the retrofitting and strengthening of reinforced concrete (RC) structures. A drawback of the usage of this technique lies on the uncertainty of the long term behaviour of those reinforcements. Researchers have paid heed to this aspect and a number of tests and alternative techniques have recently been described. An experimental programme developed to supplement work of the authors recently published and which focused on specimens not submitted to aggressive environments is described. The specimens used have the same geometry as in the previous paper, but they were exposed to salt fog cycles and dry/wet cycles with salt water for periods of 3000 h, 5000 h and 10,000 h. The interface of the glass fiber polymeric composite (GFRP)-to-concrete was characterized after the systems underwent such aggressive conditions. The GFRP wrap comprised of two layers and wet lay-up technique was used on its preparation and application. The cohesion and friction angle for GFRP-to-concrete interfaces were measured tat selected stages of ageing process and envelope failure laws were obtained based on the Mohr–Coulomb failure criterion. Changes of 27% in cohesion and 8% in the friction angle were found due to the attack of the interface and consequences of the changes are examined.

During the last years several projects and studies have improved the knowledge about textile reinforced mortar (TRM) technology. TRM has already been used in strengthening masonry and reinforced concrete structural elements such as walls, arches, columns and beams. This material is presented as a real alternative to the use of fiber-reinforced polymers (FRP) in situations where these composites have presented some drawbacks or their use is banned. Textile reinforced mortar show a complex mechanical behavior derived from the heterogeneity of the constituent materials. This paper aims to deepen the knowledge of this composite material in terms of tensile behavior. Following this scope, this paper presents an experimental campaign focused on thirty-one TRM specimens reinforced with four different reinforcing ratios. The results are analyzed and contrasted with two distinct models. (i) The Aveston–Cooper–Kelly theory (ACK) which is based on a tri-linear analytical approach; and (ii) a non-linear numerical simulation with a 3D finite element code. The finite element analysis (FEA) of the TRM tensile tests also showed no significant dependence on the basalt-to-mortar interface, i.e., the choice of a bond-slip curve in order to reproduce the bond stresses and slippages along the interface is irrelevant and it can be simply considered as rigid interface.

Grouting is a current repair technique for consolidating and strengthening old masonry buildings. Grouts can be seen as mixtures of binder with water, admixtures and/or additives, which should present low viscosity and high penetrability. The grout specification involves the knowledge of the flow capacity within the masonry inner core and physic-chemical compatibility with the original materials. Nevertheless, the grout properties are affected by a large number of parameters, including binder type and composition, mixing procedure, type and dosage of admixture, environmental conditions such as temperature that may lead to different grout injection capacities, as reported by several authors. This paper deals with the effect of environmental temperature over superplasticized hydraulic lime-based grouts with partial replacement of lime by silica fume. Grout performance was analysed in fresh and hardened state by testing its rheological behaviour, injectability as well as its hydration reactions kinetics. In spite of the considerable amount of information that exists for cement based mixtures with superplasticizers, there is little information about the effects of superplasticizers when used in natural hydraulic lime mixtures proportioned with silica fume. This study aims to contribute to a better understanding of the behaviour that superplasticized hydraulic lime grouts present under different temperatures. The results showed that hydraulic lime grouts performance could be improved, regarding rheological parameters and strength capacity if they are properly design and a suitable processing temperature were ensured.

In a recent paper (Goncalves and Camotim, 2013 [1] ), the authors presented an investigation concerning the buckling (bifurcation) behaviour of uniformly compressed thin-walled tubes with regular polygonal cross-sections (RCPS). The present paper complements the previous work by addressing the local and distortional buckling behaviour of RCPS members subjected to bending or torsion and aims at providing a novel insight into these phenomena. In particular, the specialization of Generalized Beam Theory (GBT) for RCPS, as recently proposed in Goncalves and Camotim (2013) [2] , is employed to obtain closed-form analytical solutions and also to carry out parametric studies by means of numerical analyses which are both computationally efficient (due to the small number of d.o.f. involved) and clarifying (due to the modal decomposition features of GBT). For validation purposes, solutions taken from the literature and also standard shell finite element model results are employed.

The recent development of inorganic based composites as low-cost materials in reinforced concrete structural strengthening and precast thin-walled components, requires the creation of models that predict the mechanical behaviour of these materials. Textile Reinforced Mortar (TRM) shows complex stress–strain behaviour in tension derived from the heterogeneity of its constituent materials. This complexity is mainly caused by the formation of several cracks in the inorganic matrix. The multiple cracking leads to a decrease in structural stiffness. Due to the severe conditions of the serviceability limit state in structural elements, the prediction of the stress–strain curve is essential for design and calculation purposes. After checking other models, an empirical nonlinear approach, which is based on the crack control expression included in the Eurocode 2, is proposed in this paper. Following this scope, this paper presents an experimental campaign focused on 31 TRM specimens reinforced with four different reinforcing ratios. The results are analysed and satisfactorily contrasted with the presented non-linear approach.

Research on bond between composite and concrete on beams externally reinforced with fiber reinforced polymers (ERBs) has generated many publications, but uncertainties remain. The issue of the long term behavior of those joints, especially the effect that severe and prolonged environmental actions may induce, justifies the search for additional data and recommendations to avoid premature debonding and failures. The present paper devotes attention to the effects of environmental aging on the constitutive bond-slip curves. Aging was imposed on an accelerated manner and several actions used to degrade the behavior of the joints evaluated by mechanical testing. Prismatic blocks of reinforced concrete linked on the upper side by a stainless steel hinge and externally bonded by a continuous strip of carbon or glass fiber reinforced polymer (CFRP or GFRP) adherent to the soffit were made so as to fit in commercially available laboratory climatic chambers. After aging, they were tested till failure under four point loading. Aging conditions imposed on the CFRP beams were (i) cycles of high-low relative humidity, (ii) salt fog cycles, and, on the GFRP beams, (iii) salt fog cycles, (iv) dry/wet cycles (water with 5.0% weight of NaCl), (v) total immersion in salt water, and (vi) freeze/thaw cycles. The results of the experimental program enabled the proposal of bond-slip laws that take into account the aging of the beams. They also showed that salt fog cycles were more severe in the case of CFRP, while freeze/thaw cycles were more degrading on bond of GFRP-to-concrete. The salt water effects on the GFRP beams appeared to be beneficial, most likely by improving the tensile strength of concrete. Numerical modeling certified by the obtained experimental data is presented that allows more general estimates of the environmental effects.

This paper presents and discusses the results of a GBT-based numerical investigation concerning the local, distortional and global buckling behaviour of lipped channel and zed-section cold-formed steel purlins restrained by steel sheeting and subjected to an uplift loading. Strengthened (lapped) joints, commonly employed at internal supports to preclude the occurrence of local/distortional buckling phenomena, are also investigated and an illustrative application of the use of GBT to determine strengthening lengths is also presented. The sheeting restraint is modelled by means of elastic translational and rotational springs, located at the purlin upper flange, and the joint strengthening is modelled by doubling the cross-section wall thickness. For validation, the GBT-based results are compared with values yielded by A nsys shell finite element analyses.

The strengthening of reinforced concrete structures with laminates of fibre reinforced polymeric (FRP) matrix has received considerable attention, although there still is lack of information on the more adequate modelling of the interface between FRP composites and concrete. An experimental programme is described and was designed to: (i) characterise glass FRP-to-concrete interface by shear tests; (ii) analyse reinforced concrete T-beams with external GFRP plates. Double shear tests were carried out based on 15 cm cubes with GFRP bonded to two opposite faces. The concrete T-beams were 3.0 m long and 0.28 m high and were loaded till rupture in 4-point bending tests. The external reinforcement system showed great strength increment in relation to the non retrofitted T-beam, confirming to be an effective approach to the flexural strengthening of RC beams. The computational analysis was based on a three dimensional smeared crack model. In total, 22 computational analyses were made. Models with and without interface FE associated with Mohr–Coulomb failure criterion for the FRP-to-concrete interface were defined and different strength types of concrete were considered. The rigid interface does not predict the rupture of the T-beam with precision; however, the results obtained for low concrete strengths revealed that rigid interfaces can be assumed when conjugated with the fixed crack approach. Consequently, a slightly stiffer response of the beam is obtained. The maximum bond stresses obtained from Finite Element Analysis (FEA) revealed that the models with rigid interfaces developed lower bond stresses due to the lack of relative displacements between both materials. The effects of assuming either fixed or rotated crack approaches were also compared. The rotated crack conjugated to a fine mesh in the vicinity of the GFRP-to-concrete stress led to a very good estimation of the bond stresses along the interface. The prediction of the T-beam rupture was also estimated with better results when the rotated crack was used in the model. In general, the FEA predicted with very good results the de-bonding of the GFRP-to-concrete interface of T-beams externally bonded with GFRP composites.

Unstabilised rammed earth is a recyclable, economical and eco-friendly building material, used in the past and still applied today. Traditionally, its use was based on a long empirical knowledge of the local materials. Because this knowledge was mostly lost or is no longer sufficient, in many countries normative documents have been produced to allow the assessment of rammed earth soils. With the aim of contributing for a refining of these normative requirements, this article presents a research work that included: (i) collection of unstabilised rammed earth samples from six constructions in Portugal; (ii) a literature survey of normative and complementary documents to identify the most mentioned key-properties, the test procedures and the corresponding threshold limits; (iii) a discussion of the test procedures and of the thresholds limits in the light of the experimental results. The analyzed properties are the particle size distribution, maximum particle size, plasticity, compaction, linear shrinkage, organic content and salt content. The work highlights the advantages of taking into account the characteristics of existing constructions as a basis for the establishment and further refining of consistent threshold values. In particular, it shows that it is essential to adjust the requirements to the specificities of local materials. This work was carried out at the National Laboratory for Civil Engineering (LNEC), in Lisbon. M. I. Gomes was supported by a doctoral grant from the Portuguese Foundation for Science and Technology (FCT). 7 12 25p We are grateful to many people from the Geotechnics and the Materials Departments of LNEC who collaborated in the experimental work. We would like to thank, in particular, José Costa, João Júnior and João Ribeiro. We are also thankful to the owners of all buildings that allowed the collection of material. To Raul Almeida and the architects Ines Fonseca and Florbela Vitorino who helped in the search of suitable buildings in Odemira, Avis and Arraiolos. DOI:10.1080/15583058.2012.683133M DM/NPC International Journal of Architectural Heritage

The strengthening of reinforced concrete structures by means of externally bonded fibre reinforced polymers (FRPs) is now routinely considered and applied in the retrofit or strengthening of structures. FRP composites have received a considerable attention from civil engineers in recent years due to the high strength-weight and stiffness/weight ratios when compared to other materials. However, when FRP composites are bonded to a concrete surface, there is a persistent potential problem that the FRP plates may debond prematurely from the concrete. This is a very important issue for the engineers who have to focus on the computational modelling of this phenomenon. Some studies can be found in literature on computational modelling. However, there is very little information about the best modelling of the interface between FRP composites and concrete and this work is intended to help bridge this gap. The computational analysis presented here is based on three-dimensional software which assumes the smeared crack model, and the interface finite elements (FEs) used have a rupture criteria based on the Mohr-Coulomb criterion with tension cut-off. The definition of these FEs was based on double shear tests that were performed specifically for this purpose and they have shown that the debonding phenomenon can be predicted with some accuracy. In total, 10 double shear models were studied and the results were compared with the 21 experimental tests performed. The double shear tests consisted of applying loads to 2 layered GFRP laminates bonded to a 150 mm concrete cube with a bonded area of 150 × 80 mm (length × width). Double shear models with and without a gap interface were considered in order to emphasize the importance of modelling the GFRP-to-concrete interface with interface finite elements. The effect of the concrete strength on the interface performance was also considered. An externally bonded reinforcement (EBR) concrete T-beam strengthened with 2 GFRP layers is presented to illustrate the application of the method. The wet lay-up technique was used for the external reinforcement of a reinforced concrete T-beam and then tested under a four point bending test until rupture. The results are reported and differences between the numerical and the experimental results are discussed.

This paper investigates the elastic buckling (bifurcation) behaviour of uniformly compressed thin-walled tubular members with single-cell regular polygonal cross-sections (RCPS), such as those employed to build transmission line structures, towers, antennas and masts. A specialisation of Generalised Beam Theory (GBT) for RCPS, reported in a recent paper (Goncalves and Camotim, 2013) [1] , is used to obtain both analytical and numerical results concerning the most relevant buckling modes and provide novel and broad conclusions on the structural behaviour of this type of members. In particular, local, cross-section extensional, distortional and multi-mode (including global flexural) buckling phenomena are addressed. For validation purposes, the GBT-based results are compared with solutions taken from the literature and also with numerical values obtained from finite strip analyses.

The paper analyses numerical solutions for the process leading to debonding failure of fibre reinforced polymers (FRP)-to-concrete interfaces in shear tests with the FRP plate subjected to a tensile load at one end. Any realistic local nonlinear bond–slip law can be used in the numerical analysis proposed in the present study. However, only a Popovics’ type expression is employed in the numerical process due to its use in different studies found in the literature. Effective bond length ( L eff ) is discussed and an expression depending on the Popovics’ constant ( n P ) is proposed to calculate it. Assuming a fracture in pure Mode II, the debonding process is analysed in detail and distributions of bond stresses and strains in the FRP plate along the interface are presented. The load–displacement behaviour is also presented and the influence of the local bond–slip law on the debonding process is discussed.

This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening. The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0%, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0%, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCEs) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35 °C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 min. In the hardened state, silica fumes increased not only the grout’s porosity but also the grout’s compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 d and beyond.

The paper analyses different analytical and numerical solutions for the debonding process of the FRP-to-concrete interface on shear tests with the FRP plate submitted to a tensile load in one of its ends. From the point of view of the state of the art, two different ways of finding the bond-slip curve from experiments are discussed and analysed. Essentially, three different linear bond-slip models, one exponential model and another power based function are employed in the numerical process. The results are analysed and compared. The differences found in the stress field along the interface, maximum load, maximum slip, ultimate slip, fracture energy and effective bond length are reported. The load-slip behaviour is also presented for the linear and non-linear models herein studied and the influence of the local bond-slip model on the debonding process is discussed. The numerical integration process used on the present study proved to be coherent with the analytical expressions determined for the linear bond-slip models and allowed to verify that maximum load transmittable to the FRP plate is influenced by the square root of the FRP stiffness and fracture energy even when nonlinear bond-slip models are assumed.

The injection of grouts inside multi-leaf stone masonries is a technique widely used for structural consolidation. To ensure an adequate flow of the grout inside the masonry, it is crucial to assure good fresh grout properties, such as good rheological behaviour. The scope of this paper is to provide preliminary indications and valuable data about the effects of specific hydraulic lime grout composition on their rheological behaviour with the purpose of a successful injection process. Through the use of rotational rheometer together with the Taguchi method, it was possible to study the influence of water/binder ratio, the type and dosage of superplasticizer and the partial replacement of hydraulic lime by silica fume, upon the grout rheological properties. The study leads to the conclusion that polycarboxylate-based superplasticizers present better performance from a rheological point of view than the naphthalene-based superplasticizer and that the water/binder ratio and superplasticizer dosage are the most determinant factors in the fresh grout rheological behaviour. On the other hand, silica fume dosage turned out to be the factor with the least contribution to improve the grout rheological behaviour compared to the other two factors reported in this study. The results summarised in this paper are part of a larger study and precede the analysis of the performance of those grouts when injected into different porous media that simulate old masonries.

This paper presents an investigation concerning the mechanics of deformation of thin-walled steel tubular members with single-cell regular polygonal cross-sections, such as those employed to build transmission line structures, towers, antennas and masts. This type of cross-sections exhibit rotational symmetry of order equal to the number of walls, which leads to remarkable peculiarities concerning the cross-section in-plane and out-of-plane (warping) deformation. The investigation is based on a specialization of Generalised Beam Theory (GBT), aiming at fully uncoupling the main cross-section deformation mode sets, which makes it possible to obtain analytical results and thus extract in-depth information concerning the structural behaviour of this type of members. Several illustrative examples, employing both analytical and numerical (using GBT-based beam finite elements) strategies, are presented throughout the text. For validation and comparison purposes, results obtained with standard shell finite element models are also provided.

The present work reports the experimental research carried out to study a strengthening method for flat slabs under punching by introduction of new shear reinforcement. Eight specimens were strengthened with the introduction of prestressed vertical bolts, using different anchorage approaches: large anchorage on surface, small anchorage on surface and small embedded anchorage. A reference specimen, unstrengthened, was also tested. The experimental punching loads, failure modes and shear reinforcement contribution are compared with the provisions of EC2, ACI 318-11 and MC2010. The tests results show that using small embedded anchorage plates is viable and efficient method for punching capacity improvement. Additionally is a method also with advantages of better aesthetics for the final strengthened structure.

One of the techniques of old masonry consolidation is the injection of grouts. For a successful injection it is necessary to ensure an adequate flow of the grout inside the porous media, for which it becomes essential to control the grout rheological behaviour and stability. This paper analyses the influence of grout mixing procedures on rheological behaviour, water retention and stability of hydraulic lime grouts with superplasticizer. This research has particular relevance due to lack of information about the use of superplasticizers in hydraulic lime grouts, compared to the amount of information that exists in the case of Portland cement based mixtures. The research showed that fresh grout behaviour can be improved using an appropriate mixing procedure, optimised with the Taguchi method.

In this paper, a new geometrically exact beam formulation is presented, aiming at calculating buckling (bifurcation) loads of Euler-Bernoulli/Vlasov thin-walled beams with deformable cross-section. The resulting finite element is particularly efficient for problems involving coupling between lateral-torsional buckling and cross-section distortion/local-plate buckling. The kinematic description of the beam is geometrically exact and employs rotation tensors associated with both cross-section rotation and the relative rotations of the cross-section walls in the cross-section plane. Moreover, arbitrary deformation modes, complying with Kirchhoff's assumption, are also included, which makes it possible to capture local/distortional/global buckling phenomena. Load height effects associated with cross-section rotation/deformation are also included. The examples presented throughout the paper show that the proposed beam finite element leads to accurate solutions with a relatively small number of degrees-of-freedom (deformation modes and finite elements).

This work presents an experimental study concerning the post-punching behaviour of flat slabs strengthened with a new technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. This strengthening technique proved efficient with respect to ultimate and serviceability states. Five slab specimens were tested in the post-punching range and it was found that the post-punching resistance was on average 78% of the punching resistance. This paper reports the development of strand forces and slab displacements from the beginning of the tests, including the bond stresses developed at several stages of the loading process. It was observed that top reinforcement bars were capable of transmitting post-punching loads to the prestressing strands. Taking this into account and based on the load bath envisaged from the column to the slab, expressions for the vertical load capacities corresponding to the parts of the load path are presented and compared with the experimental results, showing their ability to predict both ultimate loads and modes of failure. Compared with other strengthening techniques, the one proposed here not only upgrades ultimate and serviceability behaviour but also adds post-punching resistance, which is a great advantage in the event of progressive collapse, since it may avoid the collapse of an entire structure, thus reducing the risk of material and human losses.

SUMMARY The present paper presents a physical prototype that simulates the response of a single degree of freedom dynamic system, equipped with a novel semi-active vibration control device. This device comprises two superelastic NiTi elements working in phase opposition and aims to prevent deck unseating in simply supported bridges, during a seismic excitation. The special design of this device allows to avoid problems related to stress–relaxation phenomena and material degradation because of cyclic loading that have been observed in similar passive dissipation devices. The proposed design uses a strategy that permits the continuous adapting of the accumulated stress in the NiTi wires, on the basis of the response of the device to external excitations. Although unloaded, the NiTi elements remain strain/stress free, preventing stress–relaxation phenomena. With the occurrence of a dynamic excitation, a cumulative strain/stress process in the superelastic wires is initiated, enabling higher martensite transformation ratios and therefore increasing the damping capacities of the system while keeping the stresses in the wires inside a narrower superelastic window. The strain/stress accumulation in the superelastic wires is a direct result of the motion of the structure itself, with no need for external energy input. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents the formulation and validation of a geometrically and physically (J2 plasticity) non-linear Generalised Beam Theory formulation, intended to calculate accurate non-linear elastoplastic equilibrium paths of thin-walled metal bars and associated collapse loads. This formulation extends previous work (Goncalves and Camotim, 2011) [1] by including the geometrically non-linear effects. The plate-like bending strains are assumed to be small (as in all GBT formulations), but the membrane strains are calculated exactly. Both stress-based and stress resultant-based GBT approaches are developed and implemented in a 3-node beam finite element. The stress-based formulation is generally more accurate, but the stress resultant-based formulation makes it possible to avoid numeric integration in the through-thickness direction of the walls. In order to show the potential of the proposed formulation and resulting finite element, several numerical results are presented and discussed. For validation purposes, these results are compared with those obtained with standard 2D-solid and shell finite element analyses.

Externally bonded reinforced systems have been widely used in civil engineering. However, the problems associated with bond between structural elements are not yet fully solved. As a consequence, many researchers have been proposing tests and techniques to standardize procedures and reach better agreement for design purposes. In the present paper, an experimental program is described that was developed to characterize the glass FRP/concrete interface by double shear tests made on 15 cm side cubes with GFRP bonded on two opposite faces. The GFRP wrap had two layers applied by the wet lay-up technique and three classes of concrete were considered. With the support of the experimental program, cohesion and friction angle for GFRP–concrete interfaces were found leading to different envelope failure laws, based on the Mohr–Coulomb failure criterion for each concrete class, capable of predicting GFRP debonding. Results are discussed.

SUMMARY This paper describes a novel upper-bound formulation of limit analysis. This formulation is an innovative variant of an existing two-field mixed formulation based on the augmented Lagrangian method also developed by the authors. A natural approach is used to describe the deformation of each finite element. Furthermore, and in contrast to the previous formulation, two independent field approximations are now both used to define the velocity field, defined globally and at element level. It is shown that this feature allows a governing system of uncoupled linear equations to be obtained. Some numerical examples in plane strain conditions are presented in order to illustrate the current model performance. In conclusion, the potential and advantages of this new approach are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

This paper addresses the formulation and validation of GBT-based beam finite elements, intended to analyse the physically non-linear (plastic zone) behaviour of thin-walled metal members. Both stress-based and stress resultant-based elastoplastic formulations are developed. The stress-based formulation is generally more accurate, but the stress resultant-based formulation, which employs the Ilyushin yield function, leads to significant computational savings, namely (i) numeric integration in the through-thickness direction is not required and (ii) constraints to the stress resultant and work-conjugate strain field, typical of linear elastic GBT-type formulations, are straightforwardly enforced. The choice of interpolation functions and the cross-section discretization procedure are also discussed. In order to illustrate the application, provide validation and demonstrate the capabilities of the proposed finite elements, several numerical results are presented and discussed. These results are compared with those obtained with standard 2D-solid and shell finite element analyses.

The objective of this study was to analyse the behaviour of prestress strand anchorages by bonding with an epoxy adhesive for structural strengthening use. Pull-out and push-in tests were carried out on 15·2 mm diameter prestress steel strands sealed in 18 mm diameter holes with several embedment lengths, complemented by long-term tests. Experimental results are presented and compared with theoretical results regarding maximum pull-out and transmittable loads and also draw-in results. Theoretical results are obtained by solving the governing equation of the bond phenomenon adopting a non-linear local bond/slip law derived from pull-out tests with short embedment length. The study shows that it is reasonable to assume an average constant bond stress for anchorage design with the studied epoxy adhesive in the range of the studied values of anchor embedment length and diameter. The average values for bond stress to be used for determining the maximum pull-out and transmittable loads were found to be 12·0 and 5·2 MPa, respectively. Experimental draw-in values show a great variability, and so determining transmission length based on draw-in values may lead to a false perception that the transmission length is very variable.

The confinement of reinforced concrete (RC) columns with transverse reinforcement has been extensively studied and it is known that the response of concrete cylinders subjected to equivalent levels of pressure depends on how that lateral pressure is transmitted, and not on its magnitude alone. When confinement is, additionally to that given by steel stirrups, provided by external jackets of fiber reinforced polymers (FRP) the complexity and the scarcity of experimental data increase and tests to gain insight into the structural behavior and consequent design procedures are still required. The present study reports tests performed on axially loaded RC columns, with and without jackets. The FRP tested were made either of carbon fibers reinforced polymers (CFRP) or aramidic (AFRP) wraps and the geometry of the specimens included square and circular cross-sections. Comparison of gains of axial strength and ductility are presented and aspects of the variation of the lateral pressure and rupture of FRP jackets are examined.

The elastodynamic response of saturated poroelastic media is modelled approximating independently the solid and seepage displacements in the domain and the force and pressure components on the boundary of the element. The domain and boundary approximation bases are used to enforce on average the dynamic equilibrium and the displacement continuity conditions, respectively. The resulting solving system is Hermitian, except for the damping term, and its coefficients are defined by boundary integral expressions as a Trefftz basis is used to set up the domain approximation. This basis is taken from the solution set of the governing differential equation and models the free-field elastodynamic response of the medium. This option justifies the relatively high levels of performance that are illustrated with the time domain analysis of unbounded domains.

This work aims to study a new flat slab strengthening technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. The main advantages of this technique over the traditional prestress strengthening systems that use mechanical anchorages are that it does not need external permanent anchorages, meaning that the forces are introduced into the concrete gradually instead of being localized, thereby preserving aesthetics and useable space. The seven tested slab models show that this technique meets its objective as it is able to reduce reinforcement strains at service loads by up to 80% if the strengthening technique is applied in two directions and slab deformations by up to 70%, consequently making crack widths smaller. It can also increase punching load capacity by as much as 51% when compared to non-strengthened slabs. The results are compared with the EC2 (2004) [20], ACI 318-08 (2008) [23] and MC2010 (2010) [21] provisions. The main conclusions are that this strengthening technique is effective regarding ultimate and serviceability states and that it represents an advance in RC slab strengthening techniques.

In this paper, a large displacement and finite rotation thin-walled beam element previously developed by the authors, which accounts for cross-section deformation, is extended by including finite relative rotations of the beam walls in the in-plane kinematic description of the cross-sections. The inclusion of these relative rotations is motivated by the fact that it enables a simple and meaningful representation of the cross-section in-plane distortion and allows for a co-rotational description of the wall "local-plate" behavior, which leads to a computationally efficient numerical implementation. The present extension preserves all features of the original formulation, namely the geometrically exact description of the beam mid-surface and the allowance for arbitrary cross-section deformation modes complying with Kirchhoff's assumption. The efficiency of the resulting beam finite element is demonstrated by means of numerical examples, which include comparisons with solutions obtained by means of the previous beam finite element and standard shell finite elements.

Based on extensive experimental program on effects of artificial environmental aging, its effects on strength and bond between outer GFRP reinforcement of RC beams and concrete are described and interpreted. Artificial aging of beams consisted of saline water immersion, salt fogging and cyclic tidal-like action causing degradation on mechanical properties that are reported and examined. Computational modeling of these effects is also preliminarily described, considering post-aged constitutive properties of the component materials and relevant non-linear material properties, to study bond-slip and beam response. Tests to develop a shear Mohr–Coulomb envelope as a rupture criterion on the layers adjacent to the interface are also presented.

This work presents a procedure for the use of probabilistic modelling techniques in the assessment of safety parameters of existing timber structures, when influenced by two types of actions. The parameters of the models have been defined as probabilistic variables, and Monte Carlo simulation technique was taken into account for safety evaluation. The case study here examined concerns four king post trusses on which a safety evaluation method was conducted to determine a target reliability index. Since the structures presented a high level of deterioration, a model considering the variation of the residual cross-section and the influence of environment in resistance was taken into account. Time dependent deterioration models have also been considered. With the results given by the different used models, it was possible to obtain probabilities of failure and respective reliability indices, as well as time evolution deterioration curves for a deteriorated historical structure.

The retrofit of reinforced concrete columns with FRP jackets has received considerable attention in recent years. The advantages of this technique compared to other similar techniques include the high strength-weight and stiffness-weight ratios of FRP (Fibre Reinforced Plastics), the strength and ductility increase of RC columns confined with FRP jackets as well as the fact that FRP external shells prevent or mitigate environmental degradation of the concrete and consequent corrosion of the steel reinforcement. Furthermore, this method also reduces the column transversal deformation and prevents the buckling of longitudinal reinforcement. Twenty five experimental tests were carried out on reinforced concrete columns confined with CFRP composites, and subjected to axial monotonic compression. In order to evaluate the influence of several parameters on the mechanical behavior of the columns, the height of the columns was maintained, while changing other parameters: the diameter of the columns, the type of material (plain or reinforced concrete), the steel hoop spacing of the RC columns and the number of CFRP layers. Predictive equations, based on the experimental analysis, are proposed to estimate the compressive strength of the confined concrete, the maximum axial load and the axial or the lateral failure strain of circular RC columns jacketed with CFRP. A stress–strain model for CFRP confined concrete in compression, which considers the effect of the CFRP and the transversal reinforcement on the confined compressive strength of the column is also proposed. The curves, axial load versus axial or lateral strain of the RC column, are simulated based on the stress–strain model and include the longitudinal reinforcement effect. The results demonstrate that the model and the predictive equations represent very well the axial compression behavior of RC circular columns confined with CFRP. The applicability of this model to a large spectrum of RC column dimensions is its main advantage.

The purpose of grout injection is to increase the compactness of the masonry and its injection optimization is a task of major importance for masonry consolidation. Fresh grout properties seem to be as important as the ones in the hardened state since grout consistency is an essential characteristic to allow the filling of voids. Since the grout rheological behaviour is associated with its fresh properties, they should be well understood and controlled so that the fluid may be pumped and flow correctly inside the porous media. This paper analyses some relevant rheological properties for natural hydraulic lime grouts, such as yield stress, plastic viscosity, consistency and power-law index. The study envisage to increase the understanding of the influence of environmental temperature and of the addition of fly ash in fresh grouts behaviour. An attempt was made to achieve an optimal grout composition by using the Taguchi method. The paper shows that fly ash is capable of substantially changing the grout rheological parameters, while the effect of temperature is negligible for the parameters tested.

This paper presents a new and general approach for the calculation of cross-section deformation modes in thin-walled beams, to be used in the framework of generalized beam theory (GBT). The proposed approach subdivides and hierarchizes the cross-section deformation modes by employing several kinematic hypotheses. This makes it possible to discard a priori specific types of deformation modes and consequently reduce the number of cross-section degrees-of-freedom. The approach is applicable to arbitrary (with open and closed parts) polygonal cross-sections with external and internal constraints and allows for the a posteriori inclusion of particular deformation modes (e.g., shear deformation modes in a part of the cross-section). Although only GBT applications are dealt with, the deformation modes obtained may be straightforwardly incorporated in other thin-walled beam formulations that include cross-section deformation.

This paper presents a new formulation for thin-walled beams that includes cross-section deformation. The kinematic description of the beam emanates from the geometrically exact Reissner–Simo beam theory and is enriched with arbitrary cross-section deformation modes complying with Kirchhoff’s assumption. The inclusion of these deformation modes makes it possible to capture the cross-section in-plane distortion, wall (plate) transverse bending and out-of-plane (warping), which leads to a computationally efficient numerical implementation. Several illustrative numerical examples are presented and discussed, showing that the resulting beam finite element leads to solutions that are in very good agreement with those obtained with standard shell finite elements, albeit involving much less degrees-of-freedom.

This paper analyses and compares the dynamic behavior of superelastic shape memory alloy (SMA) systems based on two different constitutive models. The first model, although being able to describe the response of the material to complex uniaxial loading histories, is temperature and rate independent. The second model couples the mechanical and kinetic laws of the material with a balance equation considering the thermal effects. After numerical validation and calibration, the behavior of these two models is tested in single degree of freedom dynamic systems, with SMAs acting as restoring elements. Different dynamic loads are considered, including artificially generated seismic actions, in a numerical model of a railway viaduct. Finally, it is shown that, in spite of its simplicity, the temperature- and rate-independent model produces a set of very satisfying results. This, together with its robustness and straightforward computational implementation, yields a very appealing numerical tool to simulate superelastic passive control applications.

The transient dynamic response of a beam supported on a foundation with sudden stiffness change and subjected to a force moving with constant velocity is analysed. The abrupt change is located at the mid-section of the beam of finite length. Two analytical approaches are implemented. In the first one, the response is obtained by finite integral transformations incorporating global modes of vibration, while in the second the analytical responses of each half of the beam are linked by continuity conditions. The values obtained are used to study the influence of the abrupt change on the critical velocities. The analyses carried out enable to reach results and draw conclusions directly related to the knowledge of ground vibrations induced by high-speed trains.

This paper presents the derivation, validation and illustration of a generalised beam theory (GBT) formulation intended to perform first-order and buckling analyses of arbitrary thin-walled members, namely members with cross-sections that combine closed cells with open branches. Following a brief overview of the so-called “conventional GBT formulation”, as well as of the available extensions for different specific cross-section types, the paper addresses in detail the modifications that must be incorporated into the GBT cross-section analysis procedure to handle the simultaneous presence of closed cells and open branches. The proposed formulation is then employed to analyse the first-order and buckling behaviours of thin-walled members (mostly beams) with complex cross-sections. For validation purposes, the GBT-based numerical results are compared with values yielded by shell finite element and finite strip analyses.

The purpose of a grout injection technique applied in a multiple leaf wall is to increase the compactness and create links between the internal and external leaves. The correct grout selection should take into account many characteristics, in particular injectability and stability. This paper analyses the variations of some fresh grout properties that may affect injectability and stability—water retention, rheological behaviour and bleeding. The study has sought to increase the understanding of the influence of the mixing procedure in grout behaviour and how it may improve some essential injection characteristics. For this purpose, a natural hydraulic lime grout has been considered. The paper shows that there are differences in the grout behaviour when different mixing procedures are used and that fresh grout properties may be optimized if a proper mixing procedure is chosen.

This paper addresses an implementation of the upper bound limit analysis theorem using a parallel mixed finite element formulation. The intrinsic characteristics of the adopted upper bound formulation proved to be suitable to adapt it to an efficient parallelization scheme. In order to illustrate the computational power provided by the new parallel processing method, accurate upper bound collapse load estimates, for 3D problems, are produced using a cluster of common PC machines.

Beams and slabs externally reinforced with FRP are often in contact with moisture and temperature cycles that reduce the expected durability of the system. Bond degradation is a frequent cause of premature failure of structural elements and environmental conditions are known to relate to such failures. The study shows the effects of cycles of salt fog, temperature and moisture as well as immersion in salt water on the bending response of beams externally reinforced with GFRP or CFRP, especially on bond between FRP reinforcement and concrete. Temperature cycles (−10 °C; 10 °C) and moisture cycles were associated with failure in the concrete substrate, while salt fog cycles originated failure at the interface concrete–adhesive. Immersion in salt water and salt fog caused considerable degradation of bond between the GFRP strips and concrete. However, immersion did not lower the load carrying capacity of beams, unlike temperature cycles (−10 °C; 10 °C) that caused considerable loss. No significant differences were detected on the behavior of the systems strengthened with GFRP and CFRP, perhaps because the design of the tests impeded failure of the fibres.

International bibliography on conservation usually refers that mortars made with lime putty with long extinction periods behave better than others made with the current dry hydrated limes. In order to evaluate this assess, an experimental study of lime mortars was carried out, using dry hydrated lime and two lime putties. It becomes clear that the use of lime putties with long extinction periods in mortars allow better performances, particularly in applicability and resistance to sulphates.

This paper examines a methodology for computing the probability of structural failure by combining neural networks (NN) and Monte Carlo simulation (MCS). MCS is a powerful tool, simple to implement and capable of solving a broad range of reliability problems. However, its use for evaluation of very low probabilities of failure implies a great number of structural analyses, which can become excessively time consuming. The proposed methodology makes use of the capability of a NN to approximate a function for reproducing structural behavior, allowing the computation of performance measures at a much lower cost. This approach seems very attractive, and its main challenge lies in the ability of a NN to approximate accurately complex structural response. In order to assess the validity of this methodology, a test function and two structural examples are presented and discussed. The second example is also used to show how this methodology can be used to perform reliability-based structural optimization.

The progressive collapse of structures generally results in the loss of human lives. Experience shows that flat slab structures are very sensitive to progressive collapse, which may cause serious accidents if special detailing is not provided. The post-punching behaviour of a column-supported slab is decisive in the progressive collapse development. This work presents the experimental research carried out to study the post-punching behaviour of prestressed concrete flat slabs. Six reduced-scale prestressed concrete flat slab models were tested. The tests were carried out in two different phases. In the first phase the models were loaded up to failure by punching. Afterwards, the models were loaded again to study the post-punching behaviour changes caused by the presence of unbonded, prestressed tendons and the influences of their distance to the column.

The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous media adopting circular or spherical particles. A 2D circular rigid DEM formulation developed with the purpose of modelling concrete is described and evaluated in uniaxial tensile and compression tests. According to this model, the aggregate can be modelled either as a rigid macro-particle or as a deformable group of particles. The inter-particle contacts can either be assumed as brittle or follow a given bilinear softening curve. It is shown that aggregate deformability, together with the consideration of pure friction contacts working under compression, increases the fracture energy in compression, leading to a better agreement with concrete tests. The softening contact model, by adding a higher capability of load redistribution, is shown to give a better agreement than the brittle model under tensile loading. The recognized crack mechanisms of the brittle model (tensile splitting, branching, bridging) are also present with softening.

The main sources of moisture on building facades are rain and condensation. Being moisture a prerequisite for the development of microbial growth it is of great interest to identify and analyse the factors responsible for these wetting mechanisms. The development of the microbial vegetation, in addition of being potentially damaging to the building envelope, creates a visual nuisance. This work aims to study the external environment conditions favourable for exterior surface condensation of buildings. The risk for occurrence of surface condensation depends mainly on the surface energy balance and on the moisture content of the ambient air. Because external surface temperature of buildings are very sensitive to convective and radiative exchanges, the investigation has been conducted analysing both convective and radiative heat transfer coefficients for a wide range of scenarios covering different climate sensitivities and building envelope qualities. The analysis has shown that convection and the moisture content of the air play a key role in the occurrence of surface condensations on building facades.

A class of specialised data structures designed for the distributed solution of non-conventional finite element formulations, which are equally effective when used in conjunction with conventional formulations, is presented. We begin by briefly discussing how the non-conventional finite element formulations being developed within the structural analysis group at IST [Freitas JAT, Almeida JPM, Pereira EMBR. Non-conventional formulations for the finite element method. Comput Mech 1999;23(5-6):488-501] lead to systems of equations that appear to be naturally suited for parallel processing, but we also recognise that to take full advantage of the characteristics of these systems - large dimension, non-overlapping block structure and sparsity - it is necessary to use appropriate data structures. The approach presented, which references the logical subdivisions of the system matrices, was designed to fulfil these objectives. Examples of parallel performance and efficiency on an homogeneous distributed platform are presented.

This paper presents the formulation and illustrates the application of a non-linear Generalised Beam Theory (GBT), which makes it possible to calculate bifurcation load factors of thin-walled members made of non-linear elastic-plastic materials and subjected to general loading conditions. This formulation is an extension of the non-linear GBT recently derived by the authors, which was valid for uniformly compressed members only. In order to illustrate the application of the proposed non-linear GBT, a beam finite element is formulated and some numerical results are presented and discussed. These results concern rectangular plates and thin-walled hat-section beams. The material instantaneous elastic moduli are determined on the basis of both the well known J"2-flow and J"2-deformation small strain plasticity theories.