Effect of thermo-hygrometric exposure on FRP, natural stone and their adhesive interface

none3As well known, the performance of Fiber Reinforced Polymer (FRP) materials as external strengthening technique is strongly dependent on the bond behavior between FRP and substrate. Several experimental studies have been performed on this topic, however limited attention has still focused on the bond durability. In this paper, the effect of a thermo-hygrometric environment on the interface behavior FRP-calcareous natural stones is investigated. Each utilized materials (natural stone, adhesive, FRP sheets) was firstly exposed to the same thermo-hygrometric atmosphere; a relevant decay of mechanical properties has been found for the analyzed substrates (Lecce stone and Neapolitan tuff) while a negligible influence of the exposure has been observed for the composite reinforcements (CFRP and GFRP). The results regarding the variation of mechanical properties of the resins evidenced that the effect of the performed exposure is strictly correlated to the specific materials properties: a relevant degradation or even an improvement of mechanical performances has been,in fact, registered. The bond strength and the kind of failure were both analyzed as a function of the treatment used, as well as the strain and stress distribution at the interface. The kind of failure changed in some cases when passing from unconditioned to conditioned specimens; the bond strength, the maximum bond stress and the interface stiffness were affected by the treatment, manly depending on the adhesive resin deterioration. Finally, on the basis of the provisions given by the CNR-DT 200 R1/2013 document, the possibility of defining design relationships, able to take into account also durability aspects, is discussed.mixedM.S. Sciolti; M.A. Aiello; M. FrigioneSciolti, Margherita Stefania; Aiello, Maria Antonietta; Frigione, Mariaenric

In-situ procjena zidanih svodova: Dinamička ispitivanja i numerička analiza

This paper concerns the structural identification of historical masonry buildings with reference to a case study, which is discussed in detail. The building is located in Southern Italy (Lecce). It has an ancient vaulted roof that is complex and commonly found in old masonry structures. This study takes advantage of extensive historical and structural investigations of the building. Preliminary activities have been conducted to obtain information about the current state of the structure including the geometry, morphology, structural details, material properties, prior interventions, and existing damage. This process was supported by an historical investigation into the conceptual background and construction methods used to build the structure. After the historical investigation, a series of experiments, including dynamic tests, were conducted on a number of the vaults to determine their dynamic response characteristics under operational conditions. A numerical model was also determined. In this paper, the primary dynamic test results and modelling assumptions are reported. Comparisons between numerical and experimental results are discussed.U ovom se članku razmatra konstrukcija jedne kulturno-povijesne zidane zgrade, detaljno obrađena još u jednoj ranijoj studiji. Zgrada se nalazi u Južnoj Italiji (Lecce). Zgrada ima složenu konstrukciju krova, sa svodovima, kakva je česta kod starih zidanih zgrada. U članku se uzimaju u obzir ranija opsežna povijesna i statička istraživanja. Ta ranija istraživanja bila su usmjerena ka dobivanju informacija o prethodnim ispitivanjima te o sadašnjem stanju konstrukcije, uključujući geometrijske karakteristike, oblikovnost, konstruktivne detalje, svojstva materijala i oštećenja zgrade. Pri tome su pomogla i ranija istraživanja o koncepciji i načinu gradnje zgrade. Nakon ovih istraživanja, obavljene su serije ispitivanja, između ostalog i dinamički pokusi na mnogim svodovima da se ustanove svojstva njihovog dinamičkog odziva u uvjetima standardne uporabe. Postavljen je i numerički model. U ovom su članku prikazani rezultati prvih dinamičkih ispitivanja i svojstava modela. Diskutira se odnos rezultata dobivenih numerički i eksperimentalno

Brittle failure in RC masonry infilled frames:the role of infill overstrength

The interaction between an infill panel and a reinforced concrete (RC) column can lead to the brittle failure of the structural element. A novel combination of cutting-edge analytical modelling approaches for masonry infills and RC elements is employed to simulate five experimental tests (three infilled and two bare) characterized by brittle failure modes. The infill is modelled with a multi-strut idealisation, and the RC column is modelled using the recently developed PinchingLimitStateMaterial in OpenSees. The effects of the infill type (solid or hollow) and ductility characteristics of the RC elements on the optimal modelling parameters are investigated. The focus of this study is on the assumption of the overstrength ratio between the maximum and cracking strengths of the panel when brittle failure occurs. The preliminary assumption for this parameter is the widely accepted value of 1.3 suggested in the formulation by Panagiotakos and Fardis. This value is found to influence the shear failure simulation. To more accurately predict brittle failure, higher overstrength values of the infill are used in the numerical model to improve the matching between the numerical and experimental tests. These values are then compared with the approximate estimation of the overstrength ratio from a database of 98 experimental tests. The suggested estimation of the overstrength ratio is systematically greater than 1.3 and dependent on the infill type (i.e., 1.44 for hollow and 1.55 for solid infills). The proposed values can have a high impact on future code-compliant recommendations aimed at verifying the likelihood of the occurrence of brittle failure in columns due to their interaction with infill panels

Hybrid Micro-Modeling Approach for the Analysis of the Cyclic Behavior of RC Frames

The present study is aimed at developing a hybrid approach to consider the effect of concrete cracking on the hysteretic response of RC frames. The mechanical behavior of the concrete is defined according to the smeared cracking approach, while discrete cracking surfaces are included in the geometrical model. The interface behavior of the discrete cracking surfaces is defined by the combination of contact and cohesive elements. The proposed approach is adopted in ABAQUS to simulate an experimental test on a double cantilever column for the calibration of the numerical model. Therefore, a test conducted on a RC portal and modeled numerically for the first time is simulated. Numerical and experimental results are compared in terms of hysteretic force-displacement behavior and cumulative dissipated energy, in order to assess the reliability of the proposed model in simulating the energy dissipation capacity of RC members subjected to lateral cyclic loading. The hybrid modeling approach proposed allows an accurate description of the stress distribution and a fairly satisfactory matching of the hysteretic behavior with a reasonable compromise in terms of computational effort

Hybrid Micro-Modeling Approach for the Analysis of the Cyclic Behavior of RC Frames

The present study is aimed at developing a hybrid approach to consider the effect of concrete cracking on the hysteretic response of RC frames. The mechanical behavior of the concrete is defined according to the smeared cracking approach, while discrete cracking surfaces are included in the geometrical model. The interface behavior of the discrete cracking surfaces is defined by the combination of contact and cohesive elements. The proposed approach is adopted in ABAQUS to simulate an experimental test on a double cantilever column for the calibration of the numerical model. Therefore, a test conducted on a RC portal and modeled numerically for the first time is simulated. Numerical and experimental results are compared in terms of hysteretic force-displacement behavior and cumulative dissipated energy, in order to assess the reliability of the proposed model in simulating the energy dissipation capacity of RC members subjected to lateral cyclic loading. The hybrid modeling approach proposed allows an accurate description of the stress distribution and a fairly satisfactory matching of the hysteretic behavior with a reasonable compromise in terms of computational effort

Experimental Studies on Bond Performance of BFRP bars reinforced Coral Aggregate Concrete

As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section

Bond between glass fibre reinforced polymer bars and high - strength concrete

YesIn this study, bond properties of glass fibre reinforced polymer (GFRP) bars embedded in high-strength concrete (HSC) were experimentally investigated using a pull-out test. The experimental program consisted of testing 84 pull-out specimens prepared according to ACI 440.3R-12 standard. The testing of the specimens was carried out considering bar diameter (9.5, 12.7 and 15.9 mm), embedment length (2.5, 5, 7.5 and 10 times bar diameter) and surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) as the main parameters. Twelve pull-out specimens reinforced with 16 mm steel bar were also tested for comparison purposes. Most of the specimens failed by a pull-out mode. Visual inspection of the tested specimens reinforced with GFRP (HW-SC) bars showed that the pull-out failure was due to the damage of outer bar surface, whilst the detachment of the sand coating was responsible for the bond failure of GFRP (SC) reinforced specimens. The bond stress – slip behaviour of GFRP (HW-SC) bars is different from that of GFRP (SC) bars and it was also found that GFRP (SC) bars gave a better bond performance than GFRP (HW-SC) bars. It was observed that the reduction rate of bond strength of both GFRP types with increasing the bar diameter and the embedment length was reduced in the case of high-strength concrete. Bond strength predictions obtained from ACI-440.1R, CSAeS806, CSA-S6 and JSCE design codes were compared with the experimental results. Overall, all design guidelines were conservative in predicting bond strength of both GFRP bars in HSC and ACI predictions were closer to the tested results than other codes

Prospective validation of the CLIP score: a new prognostic system for patient with cirrhosis and hepatocellular carcinoma

Prognosis of patients with cirrhosis and hepatocellular carcinoma (HCC) depends on both residual liver function and tumor extension. The CLIP score includes Child-Pugh stage, tumor morphology and extension, serum alfa-fetoprotein (AFP) levels, and portal vein thrombosis. We externally validated the CLIP score and compared its discriminatory ability and predictive power with that of the Okuda staging system in 196 patients with cirrhosis and HCC prospectively enrolled in a randomized trial. No significant associations were found between the CLIP score and the age, sex, and pattern of viral infection. There was a strong correlation between the CLIP score and the Okuda stage, As of June 1999, 150 patients (76.5%) had died. Median survival time was 11 months, overall, and it was 36, 22, 9, 7, and 3 months for CLIP categories 0, 1, 2, 3, and 4 to 6, respectively. In multivariate analysis, the CLIP score had additional explanatory power above that of the Okuda stage. This was true for both patients treated with locoregional therapy or not. A quantitative estimation of 2-year survival predictive power showed that the CLIP score explained 37% of survival variability, compared with 21% explained by Okuda stage. In conclusion, the CLIP score, compared with the Okuda staging system, gives more accurate prognostic information, is statistically more efficient, and has a greater survival predictive power. It could be useful in treatment planning by improving baseline prognostic evaluation of patients with RCC, and could be used in prospective therapeutic trials as a stratification variable, reducing the variability of results owing to patient selection