The main objective of this work is to study the performance of prestressing steel (PS) bars as reinforcements in the reinforced concrete (RC) elements strengthened by the near-surface mounted method ...(NSM). The work includes two parts. In the first part, direct pull-out tests are performed in order to study the bond performance between PS reinforcement and concrete. The influences of groove sizes and PS surface conditions (smooth and sand coated) are evaluated. The results show that the sand coated PS (PS-Sc) reinforcement has the best adhesion behavior compared with the smooth bar, and its pull-out force is increased by 48%. For this reason, the PS-Sc bars are used in the second part of this work as NSM reinforcement to strengthen RC beams subjected to bending forces. Then, four-point bending tests are carried out to understand the flexural behavior of strengthened RC beams with PS-Sc reinforcements of different lengths and ratios. The obtained results demonstrate that the use of NSM-PS-Sc bars strengthening technique leads to important enhancement in the load carrying capacity of the RC beams. The first crack load and ultimate load of the strengthened RC beams attain 71.41 and 65.67%, respectively, which are higher than those of the control beam. Furthermore, the experimental values show a good agreement with the analytical values in both the ultimate deflection and the ultimate load. This proves that the NSM-PS-Sc bars studied in this work are promising reinforcement of the RC beams.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper presents an investigation of the bond mechanism between carbon fibre reinforced polymer (CFRP) laminates, concrete and steel in the near-surface mounted (NSM) CFRP-strengthened reinforced ...concrete (RC) beam-bond tests. The experimental program consisting of thirty modified concrete beams flexurally strengthened with NSM CFRP strips was published in. The effects of five parameters and their interactions on the ultimate load carrying capacities and the associated bond mechanisms of the beams are investigated in this paper with consideration of the following investigated parameters: beam span, beam depth, longitudinal tensile steel reinforcement ratio, the bond length of the CFRP strips and compressive concrete strength. The longitudinal steel reinforcement was cut at the beam mid-span in four beams to investigate a better assessment of the influence of the steel reinforcement ratio on the bond behaviour of CFRP to concrete bond behaviour. The numerical analysis implemented in this paper is based on a nonlinear micromechanical finite element model (FEM) that was used for investigation of the flexural behaviour of NSM CFRP-strengthened members. The 3D model based on advanced CFRP to concrete bond responses was introduced to modelling of tested specimens. The FEM procedure presents the orthotropic behaviour of the CFRP strips and the bond response between the CFRP and concrete. Comparison of the experimental and numerical results revealed an excellent agreement that confirms the suitability of the proposed FE model.
AbstractExternally bonded (EB) reinforcement and near surface–mounted (NSM) reinforcement were extensively studied to strengthen reinforced concrete beams in the last decades. However, few studies ...compare their effectiveness. This paper aims to study the effectiveness of EB and NSM strengthening techniques using carbon fiber–reinforced polymer (CFRP) strips in strengthening RC beams. In this study, three different parameters were studied, including the strengthening technique (i.e., NSM, EB), CFRP quantity, and NSM-CFRP distribution. In addition, two different bond behaviors were investigated, including perfect and cohesive models. A total of twelve beams were modeled, including six beams with perfect bond behavior and six beams with cohesive bond behavior. Each six tested beams include one control beam, two strengthened beams with EB-CFRP, and three strengthened beams with NSM-CFRP. All beams have the same cross-section dimensions, material properties, and steel reinforcement. The finite-element (FE) models were analyzed using a nonlinear FE analysis by ABAQUS software, and the results were validated with experimental works obtained from literature. In general, the developed FE models accurately predicted the ultimate strengths, strains, maximum deflections, and failure mode when compared to analytical and experimental results. For the same area of CFRP laminates, beams strengthened with the NSM system achieved higher ultimate strength but relatively lower stiffness when compared to beams strengthened with the EB system.
•Introduced the analytical approach to calculate the γ–γ coincidence summing correction factors.•The approach depends on the calculation of the full-energy peak and total efficiency.•The effective ...solid angle between the source-to-detector was calculated.•The coincidence summing correction factors are used to correct the measured efficiency curves.•The results show a good agreement between the ETNA and EFFTRAN programs values.
The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ–γ coincidence summing correction factors (CSCF) for a 3″× 3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ–γ CSCF were calculated for 60Co, 133Ba and 152Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (εT), the full-energy peak efficiency (εP) and the effective solid angle (Ωeff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances.
Background
Nipple-sparing mastectomy (NSM) is an advantageous treatment option, providing a complete cure and good cosmetic results. We tested whether NSM is a surgically and oncologically safe ...technique.
Methods
We evaluated the oncological outcome of 425 breasts in 413 patients who underwent NSM between January 2000 and March 2013. We retrospectively reviewed patient data and analyzed all patient characteristics as potential risk factors of recurrence at the nipple–areola complex (NAC). To confirm the oncological safety of NSM, we compared outcomes of NSM and conventional total mastectomy.
Results
The median follow-up time after surgery was 46.8 months (range 6–158 months). Nipple necrosis was observed in 6 cases (1.4 %). The cumulative local recurrence rate after NSM was 5.8 % (25/425 cases), similar to that of conventional total mastectomy in the same period (5.6 %, 49/878 cases). Furthermore, the cumulative local recurrence rate at the NAC was 2.3 % (10 cases). HER2-enriched tumors and young age (<40 years) were significant risk factors for recurrence at the NAC. In patients with recurrence, the site of recurrence was easily excised, and good cosmetic results were achieved in breast reconstruction cases.
Conclusion
NSM is safe with a low complication rate. No significant difference was observed in cumulative local recurrence rate, cumulative distant disease recurrence rate, and overall survival between patients who underwent NSM or conventional total mastectomy, confirming that NSM was surgically and oncologically safe.
•Analytical solution to interaction forces in NSM FRP round bar-strengthened beams.•Formulation of the tangential interfacial stiffness of adhesive layer.•Formulation of the normal interfacial ...stiffness of adhesive layer.•The proposed analytical solution gives accurate predictions.
The use of near-surface mounted (NSM) FRP composites for strengthening RC beams in flexure has become increasingly popular in the last decade. Compared to the externally bonded (EB) FRP strengthening method, the bond between FRP and concrete is much stronger when the NSM FRP strengthening method is used. However, debonding is still a likely failure mode in RC members strengthened with NSM FRP bars. The debonding in an NSM FRP-strengthened beam may initiate from either of the two ends of an NSM bar (i.e. end debonding) in the form of interfacial debonding or concrete cover separation, both of which are closely related to the existence of large localized interaction forces between the NSM bar and concrete near the bar ends in such beams. This paper presents an analytical solution for the interaction forces in RC beams strengthened with NSM FRP round bars, which are one of the most popular types of FRP bars used for NSM strengthening. The key elements of the proposed analytical solution are two interfacial stiffness parameters (i.e. tangential interfacial stiffness and normal interfacial stiffness). The validity of the proposed analytical solution is also verified using a sophisticated 3D FE model of a RC beam strengthened with a NSM round bar.
Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent ...years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars.
•Eleven slab strips flexurally strengthened with NSM CFRP laminates were tested.•Two different arrangements of CFRP laminates were applied in the slab strips.•The increase of the load carrying and ...moment redistribution capacities was analyzed.•The target increase of the load carrying capacity was attained for HS configurations.•Some strengthening configurations led to a decrease of the moment redistribution capacity.
This work presents and analysis the results of an ongoing research project on the use of the Near Surface Mounted (NSM) carbon fiber-reinforced polymer (CFRP) laminates for the increase of the load carrying capacity of statically indeterminate (two spans) reinforced concrete (RC) slabs. The test program consisted of seventeen slab strips, grouped in two series that are different on the adopted strengthening scheme: H series, where H is the notation to identify the slabs strengthened with NSM CFRP laminates exclusively applied in the hogging region; HS series, where HS is the notation to identify the slabs strengthened with NSM CFRP laminates applied in both hogging and sagging regions. The program includes six unstrengthened reference RC slab strips, and eleven strengthened with CFRP NSM configurations designed to increase in 25% or 50% the load carrying capacity of the corresponding reference RC slabs. An extensive monitoring system was applied in the constituent materials, in the critical regions of the tested slabs, in order to collect information for the discussion about the effectiveness of NSM technique in terms of load carrying and moment redistribution capacity. The strengthening procedures adopted in the laboratory tests followed, as much as possible, the real strengthening practice for this type of interventions. The obtained results show that the proposed technique is able to increase significantly the load carrying capacity of statically indeterminate RC slabs, even for those with relatively high steel reinforcement ratios. The load carrying capacity of the strengthened slabs was limited by its shear capacity or by the detachment of the strengthened concrete cover layer. At failure of the strengthened slabs, the longitudinal steel bars at intermediate support (hogging region) and at loaded sections (sagging regions) have already yielded, and the deflection was quite large. However, for some strengthening configurations, the CFRP laminates led to a decrease of the moment redistribution capacity of the slabs.
Nipple-sparing mastectomy (NSM) is increasingly performed for breast cancer (BC) treatment. To ensure local control with this procedure, it is important to obtain clear surgical margins. Here, we ...aimed to estimate the confidence in intraoperative evaluation of the retroareolar margin (IERM) and the necessity of removing the intra-nipple ducts.
In this retrospective cohort study, we evaluated 224 BC (infiltrating carcinoma 178, ductal carcinoma in situ 46) patients, who underwent NSM. IERM was determined via cytology and frozen sections. Following gland removal, the intra-nipple ducts were excised and embedded in paraffin for analysis. The retroareolar tissue was also paraffin-embedded and reanalyzed for definitive evaluation of retroareolar margins (DERM). The IERM predictive capacity in relation to DERM and the frequency of intra-nipple duct involvement were estimated.
IERM classified the sub-nipple areolar complex area as cancer-free in 219 cases (97.8%). The condition of clear retroareolar margin was confirmed by DERM in 216 cases (98.6%). The IERM accuracy was estimated as 98.6%. Ductal carcinoma
was detected in intra-nipple ducts using paraffin sections in 1.8% of the cases, despite clear IERM (4/219).
In conclusion, IERM affords high accuracy and its results are suitable to manage the nipple-areolar complex. Nevertheless, some patients may retain residual disease in the intra-nipple ducts; thus, these ducts should ideally be removed during NSM.
The repair and strengthening of concrete structures with composite material has become common during the last decade. Based on experimental results of specimens damaged by heating and subsequently ...repaired using CFRP laminate and epoxy adhesive, finite element analysis (FEA) was conducted to simulate the bond behaviour between NSM CFRP strips and heat-damaged concrete. The theoretical parameters included unheated and heat-damaged concrete and level of heat exposure. The finite element models (FEMs) showed reasonable agreement with the experimental results, and can therefore be used to predict the effects of high temperature on pull-out values after exposure to elevated temperatures.
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