Papers

In the early nineties, the Performance-Based Seismic Engineering (PBSE) principles have been introduced in the seismic design of structures. Several authors have identified the limitations of traditional force-based design (FBD) procedures widespread in most of the design codes to accomplish the PBSE requirements. Therefore, various contributions were made towards the development of displacement-based seismic design methodologies, in particularly the one proposed by Priestley, known as "Direct Displacement-Based Design" (DDBD). The purpose of this work is to investigate the DDBD approach in its entirety. In particular, the emphasis is set herein on the definition of the equivalent viscous damping and on the concrete impact of choosing one or another expression. Then, the efficiency of applying DDBD to reinforced concrete (RC) plane frames and dual frame-wall structures is assessed and the consequences of using the linear response spectrum suggested in the Eurocode 8 as input data is investigated.

Detailed models of concrete mesostructure can be used to understand the interactions between its components and predict complex deterioration scenarios. The discrete or distinct element method (DEM) is currently being used for modeling the fracture process of quasibrittle materials, such as rock and concrete. An explicit formulation of a DEM contact model that includes aging viscoelastic behavior based on the solidification theory is proposed, allowing the DEM particle model to be applied to delayed concrete analysis. Because of thetimestep constraints of the DEM, a fast numerical procedure for the analysis of long-term aging viscoelastic behavior of concrete is also proposed. A calibration procedure for the aging viscoelastic contact model parameters is presented, including new expressions for the delayed deformability macro properties. The presented validation tests using a one-contact particle assembly show good agreement between the fast numerical procedure, the fully explicit DEM procedure with small timestep, and the creep compliance analytical solution. The contact aging model validation tests using larger regular and random particle assemblies show that the fast numerical procedure significantly reduces the computational costs by introducing large timesteps in which the solution is computed while giving the same accuracy as the fully explicit procedure. The DEM aging concrete model is validated using a B3 model fit to Ward et al.

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In order to fully perform their functions and be durable, mortars for renders and plastersare requested to have a set of characteristics that can vary with the type of exposure to externalenvironmental actions and the type of substrate. Generally, they need moderate strength, highdeformability, some water protection capability, good adhesion to the substrate and compatibilitywith the pre-existent materials. The presence of water and its movement inside the pore structureof the mortars are among the most significant causes of degradation. Moreover, several authorsconsider that the main factors for durability and good performance of lime-based mortars are mostlyrelated with the good quality of the binder and the use of adequate aggregates. This paper intends tostudy the effect of ageing on the properties and durability of air lime mortars, using aggregates ofdifferent mineralogy. For this purpose, different mortars compositions are exposed to an acceleratedweathering test under defined conditions. The obtained characteristics are discussed and comparedwith the results obtained with the same mortars tested in laboratory conditions. The effects ofthe aggregate type on the durability of mortars seem to be linked to their effects on the mortarsporous structure.

This paper presents an experimental and numerical study about the durability of adhesively bonded joints between pultruded glass fibre reinforced polymer (GFRP) adherends for civil engineering applications. Single lap joint (SLJ) specimens were manufactured using either epoxy (EP) or polyurethane (PUR) adhesive and exposed to the following hygrothermal and outdoor ageing conditions for up to 730 days: water and salt water immersion at 20 °C and 40 °C, continuous condensation at 40 °C, salt fog spray at 35 ºC, and outdoor ageing in Lisbon, Portugal. At predetermined times, the mechanical behaviour of the SLJs was assessed through shear tests, in a dry condition. Results obtained show that hygrothermal ageing detrimentally affected the failure load and stiffness of the SLJs made with both adhesives, although this degradation was balanced to some extent by post-curing effects and the desorption period. The magnitude of such degradation was not significantly influenced by the immersion media, but was largely affected by temperature. Outdoor ageing did not cause significant changes in terms of stiffness; for both adhesives, ultimate load presented a moderate increasing trend, with cyclic pattern, reflecting the effects of seasonal changes in weather. For both adhesives, failure always initiated in one of the GFRP adherends, regardless of the ageing process. However, ageing seemed to affect the portion of bond area with either (light) fibre-tear or adhesive failure: in EP-GFRP specimens, the area with adhesive failure (initially null) increased due to ageing, while in PUR-GFRP specimens (significant in unaged joints) it decreased. The final part of the paper presents non-linear finite element (FE) models of the SLJs; these models were developed to numerically simulate the mechanical performance of the joints and to estimate the influence of ageing on the bond vs. slip laws that describe the interaction between the GFRP adherends.

Fibre Reinforced Polymer (FRP) composites have been the source of an increasing interest in the field of rehabilitation, namely for repair and strengthening of reinforced concrete (RC) structures. One of the most effective techniques comprises externally bonded FRP composites, in which the efficacy of rehabilitation depends considerably on the integrity and durability of the bond established between the FRP and the substrate, which is provided by a structural adhesive. This paper presents a concise review of critical durability issues associated with the structural bond between FRP and concrete for rehabilitation purposes. A number of factors determining the durability of FRP-concrete bonded joints have been identified and grouped into the following categories: materials – adhesive and adherends, joint characteristics and in-service conditions. For each of those factors, the main findings obtained in previous studies are summarized and the aspects that need fuarther investigation are outlined.

This paper presents an experimental study about the effects of thermal cycles on adhesively bonded joints between pultruded glass fibre reinforced polyester (GFRP) adherends used in civil engineering structural applications. Single lap bonded joints were produced with two commercial polymeric adhesives - epoxy (EP) and polyurethane (PUR) - and exposed to a mild (Mediterranean) range of thermal variations (-5 °C to 40 °C) for up to 350 cycles in a dry condition. The mechanical performance of the adhesively bonded joints was assessed by means of single lap shear tests. Regardless of the inherent differences between both adhesives, results obtained show that the global effect of thermal cycles on the load vs. displacement response of EP-GFRP and PUR-GFRP joints was similar. For both adhesives, thermal cycles caused considerable reduction of joint stiffness and strength, with maximum reductions of 18% and 22% for EP-GFRP joints, respectively, and 19% and 11% for PUR GFRP joints. The degradation of performance was influenced by post-curing effects, more relevant in the PUR adhesive. Before exposure to thermal cycles, both types of specimens exhibited similar failure mechanisms, which generally (80-90% of cases) involved light fibre tear and fibre tear modes, attesting the effectiveness of the adhesion process and material compatibility. Exposure to thermal cycles did not influence the failure modes of the PUR-GFRP joints; however, EP-GFRP joints became more prone to adhesive failure after being subjected to thermal cycles. Overall, the results obtained indicate that thermal cycles degrade bonded joints between pultruded GFRP adherends; however, for the conditions used in this study, this degradation seems to be compatible with the structural use of this type of joints in civil infrastructure.

This paper presents a novel methodology for assessing the overall efficiency of indoor water uses in the household. The methodology comprises three main components of assessment: the evaluation based onefficient patterns, the comparison with peers grouped by clustering techniques and the performance of water use devices based on penalty functions. A water use index is calculated for individual households for each component; this index can be used to compare and to rank the performance of different households. The most representative results from a real life case study composed of 43 households are presented herein. The proposed methodology can support urban demand managers to identify low efficiencies, to set viable water efficiency targets, to calculate potential water savings and, subsequently, to implement water demand management strategies customized to less-efficient water use devices and to groups of consumers with specific socio-demographic characteristics.

Most office buildings are designed to be ventilated and cooled using mechanical systems. However, in a temperate climate, passive ventilation and cooling techniques can reduce energy consumption when the outdoor temperatures are favourable, e.g., at night. Nevertheless, decorative components like the suspended ceiling (SC) contribute to insulation, preventing the desired thermal exchange with the slab. This work investigates an innovative solution to the optimization of the night cooling phenomenon by using a SC with a peripheral gap and taking advantage of the plenum formed by the space between the slab and the SC for cooling purposes. The experiments were carried out on a reduced scale model. It was found that a SC with a gap allows part of the heat dissipated in the room during the occupation period to be used to heat the slab, thus reducing the air temperature during the day, in comparison with a conventional SC with no gap. Moreover, a SC with a gap, and with supply and extraction slots placed above it, improves the air cooling during the night, and reduces the temperatures in the occupation zone during the following day, in comparison with a conventional SC with no gap, and with the ventilation slots located below it.