ISEL - Eng. Civil - Artigos
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- Experimental investigation of wave severity and mooring pretension on the operability of a moored tanker in a port terminalPublication . Abdelwahab, Hossam; Pinheiro, Liliana; Santos, João Alfredo; Fortes, Conceição; Guedes Soares, CarlosThis paper investigates the influence of sea severity and mooring line pretension configuration on the operability of a moored vessel at a modified berthing site inside a port. A physical model was constructed to replicate the new layout of the port of Leixo similar to es in Portugal, including bathymetry and a future 300 m extension of Leixo similar to es' north breakwater. A tanker ship model was tested with novel custom-made mooring system simulators for two fenders and four mooring lines under various offshore sea states and pretension configurations. The experiments focus on acquiring wave measurements at multiple spots within the port, ship motions, and loads on lines and fenders. The data is analysed in time and frequency domains to examine the relationship between waves, motions, and loads. The results are then compared to standard operational thresholds to estimate downtime and operability for cargo loading operations. The analysis of the results yields several conclusions. It is recommended to use the zero-peak amplitudes in conjunction with the maximum peak-to-peak amplitudes to ensure accurate operability analysis. The application of small-scale physical modelling for a moored tanker in Leixo similar to es port is a useful tool not only for investigating the feasibility of port modifications in the existing sheltering structures but also for analysing additional soft countermeasures to strengthen operational conditions at the berth. It also provides site-specific experimental data that may help to develop site-specific safety criteria. The applied mooring simulators help to reduce physical model costs.
- Mechanical and fracture properties of concrete with recycled concrete aggregates treated with acids and addition of aluminium sulphatePublication . Forero, J. A.; de Brito, J.; Evangelista, Luís; Pereira, C. H. F.The use of recycled aggregates, particularly concrete waste aggregate, has gained increasing popularity and has become current practice in day-to-day applications in many countries. Enhancing the physical and morphological characteristics of this type of aggregate is crucial to promote its widespread adoption. This study investigates the mechanical and fracture properties of concrete incorporating 100 % recycled concrete coarse aggregate (RCA), both untreated and treated with acid solutions of hydrochloric acid (HCl) and sulphuric acid (H2SO4), and addition to the addition of aluminium sulphate (AS). X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques were employed to characterize the cement and aluminium sulphate (AS). The performance of all mixes was evaluated in terms of mechanical properties, including compressive strength, tensile strength, and secant modulus of elasticity. Experimental fracture tests were conducted using the wedge splitting method on notched specimens aged for 28 days. The results demonstrate an improvement in the mechanical behaviour and fracture resistance of mixes incorporating RCA treated with acid solutions at concentrations of 0.3 M, 1 M, and 3 M for HCl, as well as at a concentration of 0.3 M for H2SO4. However, a decrease in properties was observed at higher concentrations of H2SO4 (1 M and 3 M). Furthermore, the addition of AS also resulted in improvements compared to mixes containing RCA.
- Improving indoor air quality in a higher-education institution through biophilic solutionsPublication . Idália da Gomes, Maria; Joanaz De Melo, Ana Maria Garcia Henriques Barreiros; Pinto, Iola; Rodrigues, AlexandraSchools are vital infrastructures where students acquire essential skills and foster social values. Indoor air quality (IAQ) is of paramount importance in schools, given that students spend a considerable amount of time indoors. This study examines the influence of a natural green structure (NGS) on IAQ in an Eco-Campus classroom. The IAQ of a classroom with an NGS was compared to that of an adjacent classroom without an NGS. The thermal conditions were monitored, including air temperature (T) and relative humidity (RH), as well as indoor pollutants, including carbon dioxide (CO2), volatile organic compounds (VOCs), and particulate matter (PM2.5 and PM10). The findings indicated a substantial improvement in indoor air quality in the classroom where the green structure was installed. This study lends support to the incorporation of biophilic solutions as sustainable approaches to fostering healthier learning environments, which in turn can lead to improvements in student performance and well-being.
- Experimental study of an onshore dual chamber oscillating water column devicePublication . Gadelho, Jorge; Rezanejad, Kourosh; Guedes Soares, Carlos; Santos, João Alfredo; Anastas, Gael; Fortes, ConceiçãoA wave flume is used to study a scaled model of a stepped bottom dual-chamber Oscillating Water Column (OWC) installed onshore. Compared to traditional single-chamber OWCs, the use of dual-chambers is expected to widen the range of sea states in which the OWC is more efficient, and the step, in front of the first chamber, boosts the capturing energy capacity of the device. The Power Take-Off (PTO) system is modelled as an air opening in the pneumatic chambers. Several experiments combining regular incident waves and PTO damping conditions are performed. Results of the amplitudes of the free surface elevations inside the chambers show that the device can amplify the incident wave amplitude up to 1.57 times in chamber 2. Results of the primary ef ficiency show that the device is highly dependent on the PTO damping characteristics and can reach around 40% for a wide range of wave periods. Results of the reflection analysis show that the reflection coefficient is also dependent on the PTO damping characteristics but remain lower than 0.6 for all the studied cases. Sloshing phenomenon (mostly in the cross-section direction) was observed for a wavelength close to the cross-section dimension, impacting negatively on the device pneumatic performance.
- Thermal performance of concrete with reactive magnesium oxide as an alternative binderPublication . Forero Valencia, Javier Andres; Bravo, Miguel; Pacheco, João; Brito, Jorge de; Evangelista, LuisThis study evaluates the thermal conductivity of concrete produced with reactive magnesium oxide (MgO) as a partial replacement for cement. MgO is a viable option for the concrete industry, mainly due to its benefits in sustainability and reducing CO2 emissions compared to cement emissions. Four different MgO's produced in Australia, Canada, and Spain were used in concrete mixes as a partial replacement of cement at 5%, 10%, and 20% by mass. The experimental results showed that the thermal conductivity is higher when MgO increases in mixes after 28 days of curing. With the incorporation of MgO, the thermal conductivity increased between 3.2% and 10.2%, and the mechanical properties declined: compressive strength between 12.7% to 26.2%, splitting tensile strength between 9.7% to 34.0%, and modulus of elasticity between -4.1% to 7.8%. Finally, it is important to highlight that the addition of different contents of MgO in the concrete mixes modified the microstructure of the cement matrix. As a result, there was an increase in porosity, which negatively influenced the mechanical properties and thermal conductivity. Therefore, the relationships between these properties were also analyzed.
- Energy assessment of potential locations for OWC instalation at the Portuguese coastPublication . Anastas, Gael; Santos, João Alfredo; Fortes, C. J. E. M.; Pinheiro, LilianaThis work aims to determine the exploitable wave energy resource at five potential sites close to harbour pro-tection facilities at the Portuguese coast, namely at the Azores archipelago, at Madeira Island and at Sines, on the coast of mainland Portugal. For that purpose, a third-generation wave model SWAN is used to transfer the offshore estimates of sea wave conditions to those points over the last 40 years. Sea states and wind fields are provided by the climate reanalysis datasets ERA5. Using sea states as boundary conditions and wind fields as forcings in the numerical domains of the SWAN model, the sea states were propagated shoreward, in order to estimate and analyse the wave conditions in the regions of interest. By combining the average energy flux per unit length of wave front and the probability of occurrence of each sea state, the average exploitable annual energy per unit length of wave crest can be computed. The variability of this energy flux is analysed since it is of paramount importance for the efficiency of Wave Energy Converters (WEC). This assessment showed that the best location for the installation of dual-chamber OWC devices is at the Azores archipelago.
- Seismic safety assessment of arch dams using an ETA-based method with control of tensile and compressive damagePublication . Alegre, André; Oliveira, Sérgio; MENDES, PAULO; Proença, Jorge; Ramos, Rafael; Carvalho, EzequielThe seismic safety assessment of large concrete dams remains a significant challenge in dam engineering, as it requires appropriate analysis methods, modern performance criteria, and advanced numerical models to simulate the dam seismic behavior. This paper presents a method for seismic safety assessment of arch dams based on Endurance Time Analysis (ETA), using tensile and compressive damage results from a robust formulation for seismic analysis considering joint opening/sliding and concrete non-linear behavior (finite element program DamDySSA, under development in LNEC). The seismic performance is evaluated by controlling the evolution of the damage state of the dam, according to predefined performance criteria, to estimate acceleration endurance limits for tensile and compressive damage. These acceleration limits are compared, respectively, with the peak ground accelerations prescribed for the Operating Basis Earthquake (OBE) and Safety Evaluation Earthquake (SEE), aiming to evaluate the dam seismic performance relative to both earthquake levels efficiently, using a single intensifying acceleration time history. The ETA-based method is applied to the cases of Cabril Dam (132 m-high) and Cahora Bassa Dam (170 m-high), confirming its usefulness for future seismic safety studies, while the potential of DamDySSA for non-linear seismic analysis of arch dams is highlighted.
- Crustal structure across the São Miguel Island (Azores, North Atlantic) and tectonic implicationsPublication . Batista, L.; Hübscher, C.; Terrinha, P.; Matias, L.; Afilhado, Alexandra; Loureiro, A.; Weiß, B.The crustal and uppermost lithospheric mantle of the São Miguel Island in the Azores Plateau was investigated using one 160 km long refraction and wide angle refection seismic profle across the island and the Terceira Rift along with multichan nel seismic refection profles on the top of it. P-wave velocity model shows that São Miguel Island is made up of 5 crustal layers. The sedimentary sequence varies between 150 and 1500 m of thickness and the upper and lower crusts vary from 6 km to maximum thickness of >10 km altogether. The Moho discontinuity lies at 15 km of depth underneath the island and at 11 km outside the island and rift. A 125 km-long layer with a maximum thickness of 2.5 km and Vp of 7.6 km/s is defned at the base of the crust. We speculate that this lens-shaped layer consists of gabbro cumulates formed by magmatic underplating. Extensional southwards directed simple shear across the whole crust and the Moho discontinuity – São Miguel Deep Ductile Deformation Zone – causes uplift, northwards tilting of the island and landslides. Decoupling between ductile deformation in depth and brittle deformation in the shallow levels caused the formation of a rift half-graben flled in with 1500 m of sediments and various mass transport deposits. The São Miguel Deep Ductile Deformation Zone is considered as a difuse plate boundary where deformation is accommodated by brittle mechanisms (seismicity) and plastic fow (lateral thickness variation of the lower crust).
- Ternary blends for self-compacting mortars production composed by electric arc furnace dust and other industrial by-productsPublication . Lopez-Uceda, Antonio; Cantador, David; Raposeiro Da Silva, Pedro; De Brito, Jorge; Fernandez Rodriguez, Jose Maria; Jimenez, Jose RamonThis study is framed within the circular economy model through the valorisation of industrial by-products. This research shows the results of producing self-compacting mortars (SCMs) with electric arc furnace dust (EAFD) and other industrial by-products such as fly ash, conforming (FA) or not conforming (NcFA), from coal-fired power plants, or recovery filler (RF) from hot-mix asphalt plants. Three batches of SCMs, each with one industrial-by product (FA, NcFA, or RF), and three levels of EAFD ratio incorporation (0%, 10%, 20%), were tested. An extra batch with a greater amount of FA was manufactured. When the incorporation ratio of EAFD rose, the mechanical strength decreased, due to the presence of a calcium zinc hydroxide dihydrate phase; nevertheless, this decrease diminished over time. All SCM mixes, except the 40C 40FA 20 EAFD mix, were above 20 MPa at 28 days. All mixes named 70C and 40C reached 40 and 30 MPa, respectively, at 90 days. Mixes with EAFD showed less capillarity and no difference in water absorption by immersion with respect to mixes without EAFD after 91 days. The SCMs designed proved to be stable in terms of leaching of the heavy metals contained in EAFD, where all the hardened SCMs were classified as inert.
- Improvement of the quality of recycled concrete aggregate subjected to chemical treatments: a reviewPublication . Forero, Javier A.; De Brito, Jorge; Evangelista, Luis; Pereira, CláudioThe main factor that alters the quality of recycled concrete aggregate (RCA) is the paste adhered to the natural aggregate (NA). Since it causes weakening of the interfacial transition zone (ITZ) between the aggregate and the cementitious paste, it becomes a determining factor for the mechanical behavior of concrete. It turns out that it is critical to enhance this interface by improving the surface of the aggregate or by removing the paste adhered to the NA. Considering the variety of methods for removing paste adhered to RCA-namely using acids such as hydrochloric acid (HCl), sulfuric acid (H2SO4), and phosphoric acid (H3PO4), among others-this paper presents a review of treatments for the removal of adhered paste using acidic solutions on the RCA, and their influence on the mechanical properties and durability of concrete produced with RCA. Pearson's correlation was used in the statistical analysis to determine the linear relationship of the main factors-for instance, immersion time, acidic solution, and aggregate size-involved in the removal of the paste in the RCA.