This study examines Phase B of the GREENERGY project focusing on the seismic performance and structural health monitoring of a renovated single-story RC frame with brick masonry infills that received significant strategic structural interventions. The columns were confined with basalt fiber ropes (FR, 4 mm thickness, two layers) in critical regions, the vertical interfaces between infill and concrete were filled with polyurethane PM forming PUFJ (PolyUrethane Flexible Joints), and glass fiber mesh embedded in polyurethane PS was applied as FRPU (Fiber Reinforced PolyUrethane) jacket on the infills. Further, greenery renovations included the attachment of five double-stack concrete planters (each weighing 153 kg) with different support-anchoring configurations and of eight steel frame constructions (40 kg/m2) simulating vertical living walls (VLW) with eight different connection methods. The specimen was subjected to progressively increasing earthquake excitation based on the Thessaloniki 1978 earthquake record with peak ground acceleration ranging from EQ0.07 g to EQ1.40 g. Comprehensive instrumentation included twelve accelerometers, eight draw wire sensors, twenty-two strain gauges, and a network of sixty-one PZTs utilizing the EMI (Electromechanical Impedance) technique. Results demonstrated that the structure sustained extremely high displacement drift levels of 2.62% at EQ1.40 g while maintaining structural integrity and avoiding collapse. The PUFJ and FRPU systems maintained their integrity throughout all excitations, with limited FRPU fracture only locally at extreme crushing zones of two opposite bottom bricks. Columns' longitudinal reinforcement entered yielding and strain hardening at top and bottom critical regions provided the FR confinement. VLW frames exhibited equally remarkably resilient performance, avoiding collapse despite local anchor degradation in some investigated cases. The planter performance varied significantly, yet avoiding overturning in all cases. Steel rod anchored planter demonstrated superior performance while simply supported configurations on polyurethane pads exhibited significant rocking and base sliding displacement of ±4 cm at maximum intensity. PZT structural health monitoring (SHM) sensors successfully tracked damage progression. RMSD indices of PZT recordings provided quantifiable damage assessment. Elevated RMSD values corresponded well to visually observed local damages while lower RMSD values in columns 1 and 2 compared with columns 3 and 4 suggested that basalt rope wrapping together with PUFJ and FRPU jacketed infills in two directions could restrict concrete core disintegration more effectively. The experiments validate the advanced structural interventions and vertical forest renovations, ensuring human life protection during successive extreme EQ excitations of deficient existing building stock.

Existing Mediterranean reinforced concrete buildings with masonry infills exhibit critical seismic vulnerabilities, yet real-time damage detection capabilities remain limited. This study validates a novel dense piezoelectric transducer (PZT) network concept for early damage detection in deficient RC structures under progressive seismic loading. A three-dimensional single-story RC frame with brick infills, representative of pre-Eurocode Mediterranean construction (non-ductile detailing, inadequate transverse reinforcement), was tested at serviceability limit states (SLSs) (Phase A) using a dynamic pushover approach with the 1978 Thessaloniki earthquake record, progressively scaled from EQ0.1g to EQ1.1g within the GREENERGY vertical forest renovation project. The specimen featured 48 PZTs using electromechanical impedance (EMI) methodology, 12 accelerometers, 8 displacement sensors, and 20 strain gauges. Progressive infill deterioration initiated at EQ0.5g while steel reinforcement remained elastic (max 2350 μstrain < 2890 μstrain yield). Maximum inter-story drift reached 11.37‰ with negligible residual drift (0.204‰). The PZT network, analyzed through Root Mean Square Deviation (RMSD), successfully detected internal cracking and infill-frame debonding before visible manifestation, validating its early warning capability. Floor acceleration amplification increased from 1.26 to 1.57, quantifying structural stiffness degradation. These SLS results provide critical baseline data enabling the Phase B implementation of sustainable vertical forest retrofitting strategies for aging Mediterranean building stock.

Effective damage identification is paramount to evaluating safety conditions and preventing catastrophic failures of concrete structures. Although various methods have been introduced in the literature, developing robust and reliable structural health monitoring (SHM) procedures remains an open research challenge. This study proposes a new approach utilizing a 1-D convolution neural network to identify the formation of cracks from the raw electromechanical impedance (EMI) signature of externally bonded piezoelectric lead zirconate titanate (PZT) transducers. Externally bonded PZT transducers were used to determine the EMI signature of fiber-reinforced concrete specimens subjected to monotonous and repeatable compression loading. A leave-one-specimen-out cross-validation scenario was adopted for the proposed SHM approach for a stricter and more realistic validation procedure. The experimental study and the obtained results clearly demonstrate the capacity of the introduced approach to provide autonomous and reliable damage identification in a PZT-enabled SHM system, with a mean accuracy of 95.24% and a standard deviation of 5.64%.

The need for rehabilitation of Reinforced Concrete (RC) structures is highlighted by the increased requirements for adequate resistance to seismic actions. Recently, a novel Fiber Reinforced Polymer (FRP) -based strengthening approach utilizing FRP ropes has been introduced. The application of this new technique seems to have promising results when the ropes are anchored adequately. However, constructional restrictions may prevent the adequate FRP rope anchorage and lead eventually to the failure of the strengthening application. This study uses an innovative remotely controlled Electro-Mechanical Admittance (EMA) based SHM system to detect the structural damages that occurred in FRP-strengthened RC members due to the composite rope failure. The SHM approach employs custom-made devices that excite a network of intelligent Piezoelectric lead Zirconate Titanate (PZT) transducers/actuators by means of an amplified harmonic excitation voltage. Two test procedures are presented to verify the proposed SHM systems experimentally, including pullout tests of FRP ropes with different anchorage configurations and a large-scale shear-critical RC beam with a T-shaped cross-section. The installed PZT transducers showed promising damage indications demonstrating a direct correlation with the mechanical performance of FRF rope, composing an emerging tool for real-time identification of FRP failures.

Existing reinforced concrete buildings frequently require shear-strengthening to ensure structural integrity, and externally bonded carbon fiber-reinforced polymers (EB-CFRP) have become a wide-applicable approach. However, slabs and geometric restrictions impede wrapping the element, necessitating incomplete U-shaped applications vulnerable to debonding failures. This experimental study introduces a novel approach for shear-strengthening nine full-scale T-beams using near-surface mounted CFRP ropes forming closed stirrups. Their effectiveness as shear reinforcement is investigated compared to an alternative method incorporating EB-CFRP sheets with CFRP rope anchorage. Test results indicate that both techniques enhance the beams’ strength and performance. The load capacity increased 2 times for the reference specimen and 1.4-1.9 times for the strengthened beam with FRP sheets. The displacement at the maximum load increased 5.2-7.8 and 6.6-7.5 times, respectively. The rope stirrup arrangement outperforms the rope anchorage system in mechanical and construction efficiency. A thorough protocol for executing these processes to mitigate construction-related defects is introduced.

The need to strengthen the existing reinforced concrete (RC) elements is becoming increasingly crucial for modern cities as they strive to develop resilient and sustainable structures and infrastructures. In recent years, various solutions have been proposed to limit the undesirable effects of corrosion in RC elements. While C-FRP has shown promise in corrosion-prone environments, its use in structural applications is limited by cost, bonding, and anchorage challenges with concrete. To address these, the present research investigates the structural performance of RC beams reinforced with C-FRP bars under static loading using Structural Health Monitoring (SHM) with an Electro-Mechanical Impedance (EMI) system employing Lead Zirconate Titanate (PZT) piezoelectric transducers which are applied to detect damage development and enhance the protection of RC elements and overall, RC structures. This study underscores the potential of C-FRP bars for durable tensile reinforcement in RC structures, particularly in hybrid designs that leverage steel for compression strength. The study focuses on critical factors such as stiffness, maximum load capacity, deflection at each loading stage, and the development of crack widths, all analyzed through voltage responses recorded by the PZT sensors. Particular emphasis is placed on the bond conditions and anchorage lengths of the tensile C-FRP bars, exploring how local confinement conditions along the anchorage length influence the overall behavior of the beams.

Reinforced Concrete (RC) members in existing RC structures are susceptible to shear-critical due to their under-reinforced design. Thus, implementing a retrofitting technique is essential to eliminate the casualties that could arise from sudden and catastrophic collapses due to these members’ brittleness. Among other proposed techniques, using Carbon-Fiber Reinforced Polymers (C-FRP) ropes to increase the shear strength of RC structural elements has proved to be a promising reinforcement application. Moreover, an Electro-Mechanical Impedance (EMI-based) method using Lead Zirconate Titanate (PZT-enabled) was employed to assess the efficiency of the strengthening scheme. Initially, the proposed technique was applied to C-FRP rope under the subjection of pullout testing. Thus, a correlation of the rope’s tensile strength with the EMI responses of the PZT patch was achieved using the Root Mean Square Deviation (RMSD) metric index. Thereafter, the method was implemented to the experimentally acquired data of C-FRP ropes, used as shear reinforcement in a rectangular deep beam. The ropes were installed using the Embedded Through Section (ETS) scheme. Furthermore, an approach to evaluate the residual shear-bearing capacity based on the EMI responses acquired by being embedded in and bonded to the ropes’ PZTs was attempted, demonstrating promising results and good precision compared to the analytical prediction of the C-FRP ropes’ shear resistance contribution.

The present research delves into the experimental investigation of the mechanical properties of bee bricks, which serve as nesting habitats for solitary bees. The study aims to provide valuable insights into the efficacy of these bricks as eco-friendly alternatives emphasizing a low energy footprint. It is designed as a masonry unit to provide nest sites in urban or civil areas to order to protect and contribute to the reproduction of solitary (wild) bee pollinators. The invention concerns the solid structural and architectural material of masonry bricks, which have different sizes of cavities and constitute a natural habitat for various solitary bee species. It is an innovative material that can be used as a building material in both new constructions and existing masonry structures. At the same time, it can be used as a decorative material in gardens, nurseries, fields, the courtyards of houses, schools, and buildings in cities; it can even be used in “green” and sustainable buildings. To protect bees, it is necessary to address the threats mentioned above. The results indicate that the physical materials composed a high-performance product with a remarkable compressive strength of 12 MPa and 13 MPa in loading directions perpendicular and parallel to the bed joint, respectively. Simultaneously, despite the smooth surface, the bee brick presented respectable adhesive properties proving that this product is appropriate and can be proposed as a masonry unit for safe seismically designed structures. Furthermore, the direct shear results indicate that the low strength of the binder mortar as well as the bond strength of the masonry unit and the mortar play a significant role. Overall, this presents awareness about the reduction of biodiversity and, at the same time, a proposal of the dual use of the construction material for the construction of load-bearing masonry and a biotope needed for the reproduction and protection of pollinator bees.

Reinforced Concrete (RC) structures subjected to earthquakes can suffer from shear failure, which is often characterized by the formation of critical diagonal cracks and abrupt partial or total collapse. Externally Bonded Fiber-Reinforced Polymer (EB-FRP) sheets and laminates have been a popular method for strengthening shear-vulnerable RC structures. However, typical frame RC structures with non-rectangular cross-sectional shapes prevent the complete wrapping of EB-FRPs around them and in the transverse direction as shear reinforcement. Thus, most RC beams with L- or T-shaped cross-sections are retrofitted using EB-FRPs on three sides of the beam’s web, where brittle debonding failures predominate. This paper addresses these challenges by investigating the effectiveness of using Near Surface Mounted (NSM) carbon FRP ropes as a shear-strengthening technique in various RC structural members with shear problems. The experimental program presented includes three large-scale T-shaped beams and two full-scale external beam-column joints. The carbon FRP ropes were installed in the shear span of the T-beams and in the beam-column joints. The experimental results showed that the proposed FRP-strengthening technique improved the RC member’s structural performance and even altered the beam’s failure mode from shear and brittle to flexural and ductile.

The fiber-reinforced polymer (FRP) strengthening of reinforced concrete (RC) elements with torsional deficiencies has not yet been extensively studied. Existing studies have primarily focused on rectangular RC beams. The few studies on L or T-shaped beams have used open-form retrofitting methods. However, premature debonding of the retrofitting from concrete surfaces often leads to detachment before achieving enhanced torsional capacity. This study introduces an innovative application of closed-form FRP retrofitting for RC T-beams against torsion. Two novel closed-form torsional upgrading methods were proposed and investigated through a comprehensive experimental program involving eight large-scale T-beams. One method employs FRP ropes embedded in transverse grooves near the surface, while the other combines U-shaped EB-FRP strips with FRP ropes. Additionally, two configurations were examined replicating scenarios where the upper part of the slab is accessible or inaccessible. The results demonstrate that the closed-form methods improve torsional strength by 9% to 25% and twist at failure by 92% to 536% compared to unstrengthened beams, with beams retrofitting through the slab exhibiting superior performance. Step-by-step technical guidelines of the proposed methods are presented to minimize construction defects and ensure effective implementation in real RC structures.

Due to insufficient transverse reinforcement, the retrofitting of beam–column joints (BCJs) in existing reinforced concrete (RC) frame structures is commonly required to alter their brittle behavior. The construction industry has extensively embraced carbon-fiber-reinforced polymers (C-FRPs) as near-surface-mounted (NSM) reinforcement. Monitoring the performance of C-FRP retrofitting is crucial due to the wide range of factors influencing its effectiveness. A novel methodology has been implemented to assess the efficacy of the C-FRP retrofitting method in this study. This approach was validated through experimental investigation of full-scale BCJs, which were retrofitted with C-FRP ropes and subjected to cyclic loading. Furthermore, piezoelectric lead zirconate titanate (PZT) patches were placed on the NSM C-FRP ropes, and the electro-mechanical impedance (EMI) method was employed to monitor the retrofitting technique’s performance. A combination of the commonly used statistical damage index root mean squared deviation (RMSD) and a hierarchical clustering-based approach (HCA) was used to assess the performance of the C-FRP retrofitting technique. The experimental investigation results strongly indicate the proposed approach’s positive impact on the reliable assessment of C-FRP retrofitting performance. Thus, the proposed approach enhances the safety and resilience of retrofitted BCJs in RC structures.

Climate change induces extreme effects with lower-than-designed restoration periods, imposing the necessity of strengthening the structural integrity of existing and mainly older RC structures, which are often demonstrated to be under-reinforced in terms of the shear capacity, mainly due to outdated and old design codes/standards. Thus, finding cost-effective and feasible methods to strengthen RC elements is becoming increasingly important. Thin RC layers for jacketing represent a modern advancement in repairing and retrofitting RC members. In this context, U-shaped mortar jackets were employed to strengthen three shear-critical beams. In addition, a critical aspect in the success of any jacketing method is the degree of bonding and interaction between the original member and the new jacket. Additionally, the performance of these U-shaped jackets was assessed using an Electro-Mechanical-Impedance-based (EMI-based) method using a Piezoelectric-Transducer-enabled (PZT-enabled) technique. The integration of advanced monitoring technologies in retrofitting applications offers valuable insights into the performance and longevity of the retrofit system. Therefore, this study aims to experimentally investigate the cohesion between construction materials and assess the effectiveness of U-shaped jackets. Through the proposed Structural Health Monitoring (SHM) technique, any degradation at the interface or slippage of the retrofitting jacket can be promptly detected, restraining further damage development and potential failure of the structure.

This experimental study investigates the influence of synthetic macro-fibers added in fiber-reinforced concrete (FRC) prismatic specimens on their flexural response and overall cracking performance. Application of a novel structural health monitoring (SHM) system that implements the electromechanical impedance (EMI) technique and the use of piezoelectric lead zirconate titanate (PZT) transducers installed in the FRC prisms are also included. The applied PZT-enabled EMI-based monitoring system was developed to diagnose damage and the overall performance in reinforced concrete (RC) structural members subjected to cyclic repeated loading, simulating seismic excitations in existing RC buildings. The paper also aims to determine the sensitivity of the real-time, wireless, and portable monitoring technique corresponding to the location, the distance, the direction of polarization of the PZT transducers and the location and magnitude of damage due to flexural cracking. Further, the influence of the effect of stresses corresponding at various loading levels and the observed changes in the ΕΜΙ frequency response of the PZT transducers are also examined. Test results indicated that cracking detection is achieved using this SHM system by prompt damage level assessment due to the FRC’s flexural load at early seismic loading stages in existing RC buildings.

Traditional methods for estimating structural deterioration are generally costly and inefficient, especially for non-accessible structural members. However, recent research has demonstrated that electro-mechanical impedance (EMI) or its inverse electro-mechanical admittance (EMA) measurements can be used to continuously monitor the structural integrity of reinforced concrete (RC) civil infrastructures in real-time. In this work, three lead piezoelectric zirconate titanate (PZT) transducers were epoxy-bonded on the external surface of a real-scale RC beam-column joint (BCJ) specimen. An integrated wireless impedance/admittance monitoring system (WiAMS) excites and simultaneously measures the voltage signal response of the PZT transducers in various imminent damage states. Furthermore, a scalar statistical index is employed to quantify the structural damage based on the variation of the PZT output voltage signals between their response at different damage levels and a pristine, undamaged state (initial healthy). The results of this study indicate that through the EMI technique, external epoxy-bonded PZT transducers can reliably evaluate the structural integrity of BCJs.

Fiber Reinforced Concrete (FRC) has shown significant promise in enhancing the safety and reliability of civil infrastructures. Structural Health Monitoring (SHM) has recently become essential due to the increasing demand for the safety and sustainability of civil infrastructures. Thus, SHM provides critical benefits for future research to develop more advanced monitoring systems that effectively detect and diagnose the damage in FRC structures. This study investigates the potential of an Electro-Mechanical Impedance (EMI) based SHM system for detecting cracks in FRC prisms subjected to four-point repeated loading. For the needs of this research, an experimental investigation of three FRC specimens with the dimensions 150 × 150 × 450 (mm) were subjected to three different loading levels where no visual cracks formed on their surface. Next, prisms were subjected to reloading until they depleted their load-carrying capacity, resulting in pure bending fracture at the mid-span. A network of nine cement paste coated Piezoelectric lead Zirconate Titanate (PZT) transducers have been epoxy bonded to the surface of the FRC prisms, and their frequency signal measurements were utilized for quantitative damage assessment. The observed changes in the frequency response of each PZT sensor are evaluated as solid indications of potential damage presence, and the increasing trend connotes the severity of the damage. The well-known conventional static metric of the Root Mean Square Deviation (RMSD) was successfully used to quantify and evaluate the cracking in FRC specimens while improving the efficiency and accuracy of damage detection. Similarly, the dynamic metric of a new statistical index called “moving Root Mean Square Deviation” (mRMSD) was satisfactorily used and compared to achieve and enhance accuracy in the damage evaluation process.

The current paper presents the results of an experimental study of carbon nano-, micro-, and hybrid-modified cementitious mortar to evaluate mechanical performance, energy absorption, electrical conductivity, and piezoresistive sensibility. Three amounts of single-walled carbon nanotubes (SWCNTs), namely 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, and 0.3 wt.% of the cement mass, were used to prepare nano-modified cement-based specimens. In the microscale modification, 0.05 wt.%, 0.5 wt.%, 1.0 wt.% carbon fibers (CFs) were incorporated in the matrix. The hybrid-modified cementitious specimens were enhanced by adding optimized amounts of CFs and SWCNTs. The smartness of modified mortars, indicated by their piezoresistive behavior, was investigated by measuring the changes in electrical resistivity. The effective parameters that enhance the composites' mechanical and electrical performance are the different concentrations of reinforcement and the synergistic effect between the types of reinforcement used in the hybrid structure. Results reveal that all the strengthening types improved flexural strength, toughness, and electrical conductivity by about an order of magnitude compared to the reference specimens. Specifically, the hybrid-modified mortars presented a marginal reduction of 1.5% in compressive strength and an increase in flexural strength of 21%. The hybrid-modified mortar absorbed the most energy, 1509%, 921%, and 544% more than the reference mortar, nano-modified mortar, and micro-modified mortar, respectively. The change rate of impedance, capacitance, and resistivity in piezoresistive 28-day hybrid mortars improved the tree ratios by 289%, 324%, and 576%, respectively, for nano-modified mortars and by 64%, 93%, and 234%, respectively, for micro-modified mortars.

Deficient columns and joints of common reinforced concrete structures constructed according to old seismic regulations and practices or without seismic design often lead to local or even global failure. Easy-to-apply techniques based on Near Surface Methods (NSM) for the strengthening of columns have been recently proposed. The innovative material of Carbon-Fiber Reinforced Polymer (C-FRP) ropes is applied as external reinforcement for the strengthening of reinforced concrete columns and the body of the adjacent joint.A real-scale specimen externally strengthened with C-FRP ropes and a pilot specimen with the same geometrical and mechanical characteristics have been constructed and tested under the same cyclic loading sequence.All C-FRP ropes have been placed into notches curved on the concrete surface (NSM).The strengthened column compared to the unstrengthened pilot specimen exhibited improved hysteretic capacity in terms of maximum loads, stiffness and energy dissipation per 468

The favorable contribution of externally bonded fiber-reinforced polymer (EB-FRP) sheets to the shear strengthening of reinforced concrete (RC) beams is widely acknowledged. Nonetheless, the premature debonding of EB-FRP materials remains a limitation for widespread on-site application. Once debonding appears, it is highly likely that brittle failure will occur in the strengthened RC structural member; therefore, it is essential to be alerted of the debonding incident immediately and to intervene. This may not be always possible, particularly if the EB-FRP strengthened RC member is located in an inaccessible area for fast inspection, such as bridge piers. The ability to identify debonding immediately via remote control would contribute to the safer application of the technique by eliminating the negative outcomes of debonding. The current investigation involves the detection of EB-FRP sheet debonding using a remotely controlled electromechanical admittance (EMA)-based structural health monitoring (SHM) system that utilizes piezoelectric lead zirconate titanate (PZT) sensors. An experimental investigation on RC T-beams strengthened for shear with EB-FRP sheets has been performed. The PZT sensors are installed at various locations on the surface of the EB-FRP sheets to evaluate the SHM system’s ability to detect debonding. Additionally, strain gauges were attached on the surface of the EB-FRP sheets near the PZT sensors to monitor the deformation of the FRP and draw useful conclusions through comparison of the results to the wave-based data provided by the PZT sensors. The experimental results indicate that although EB-FRP sheets increase the shear resistance of the RC T-beams, premature failure occurs due to sheet debonding. The applied SHM system can sufficiently identify the debonding in real-time and appears to be feasible for on-site applications.

Microstructural characteristics and mechanical properties of nano-reinforced cementitious mortar using multi-walled carbon nanotubes (MWCNTs), dispersed in an aqueous solution by applying ultra-solicitation, were studied using X-ray microcomputed tomography (micro-CT), an innovative, non-destructive technique. This useful method was applied for characterizing the cementitious composites’ spatial micro-pore structure. The changes due to the MWCNTs’ integration into the mortar matrix and their effects were studied. The analysis revealed that the density and porosity values processed by micro-CT imaging are crucial parameters. They correlated with the mechanical strength of 2 × 2 × 8 prisms (in cm) in order to evaluate the dispersion effect of the different nanotube concentrations, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, and 0.5 wt.% by the mass of cement. The results highlight the linear correlation of the density, porosity, and spatial pores’ distribution obtained by the micro-CT 3D in vivo imaging of the microstructure, with the nanotubes’ concentration and flexural and compressive strengths. This investigation was achieved by proving that a deeper understanding of the complex nano- and microstructures can be utilized for the design of advanced cementitious composites at multiple scales.

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear failure mode from a brittle to a pseudo-ductile mode. Despite many guidelines for applying composite materials for retrofitting and predicting the performance of strengthened structures, the application of TRM systems in masonry walls is not extensively described. A thorough retrospect of the literature is presented, containing research results relating to different masonry walls, e.g., bricks, cement, and stone blocks strengthened with TRM jackets and subjected to diagonal compression loads. The critical issue of this study is the failure mode of the retrofitted masonry walls. Available prediction models are presented, and their predictions are compared to the experimental results based on their failure modes. The novelty of this study is the more accurate failure mode prediction of reinforced masonry with TRM and also of the shear strength with the proposed model, Thomoglou et al., 2020, at an optimal level compared to existing regulations and models. The novel prediction model estimates the shear failure mode of the strengthened wall while considering the contribution of all components, e.g., block, render mortar, strengthening textile, and cementitious matrix, by modifying the expressions of the Eurocode 8 provisions. The results have shown that the proposed model presents an optimum accuracy in predicting the failure mode of all different masonry walls strengthened with various TRM jackets and could be taken into account in the regulations for reliable forecasting.