AbstractIn this study, a total of 16 reinforced concrete beams (dimensions of 203×305×3,861 mm) strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods and strips ...were tested under four-point bending fatigue loading. Monotonic loading was applied to their corresponding control specimens to obtain the static monotonic flexural strength. Fatigue loading with a range of 10% of the corresponding static strength to various upper limits was applied to determine the empirical relationship for each type of specimen. It was found that the dominating failure mode under fatigue was rebar rupture. Mixed failure modes of rebar rupture and unstable cracks in concrete were also observed in specimens with longer fatigue life. As the specimens underwent more fatigue cycles, an increase was observed in their tensile strains of CFRP and deflections due to accumulated damages and the losses of stiffness. A fatigue bond model was developed, which simulated the process of fatigue loading as fatigue crack growth at the NSM-epoxy interface. Based on the comparison with experimental data, the model predicts well the bond behavior and progression of the debonded length for most of the fatigue life.
The side near-surface mounted (SNSM) method is a new flexural strengthening method for reinforced concrete (RC) beams which was proposed to allow near-surface mounted (NSM) strengthening to be ...applied on beams with small width. As a relatively new strengthening method, further studies are needed to determine the effects of strengthening parameters on the flexural performance of RC beams. In response to that, this paper presents a parametric study on the concrete cover separation failure of SNSM strengthened beams using a simulation method based on the moment-rotation (M/θ) approach.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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.
This paper presents a finite element (FE) analysis for predicting the flexural behavior of reinforced concrete (RC) beams strengthened with Fe-based shape memory alloy (Fe-SMA) strips using a near ...surface mounted (NSM) method. Experimental results reported in the literature were used to verify the proposed FE model. FE analyses were conducted using OpenSees, a general-purpose structural FE analysis program. The RC beam specimens were modeled using a nonlinear beam-column element and a fiber element. The Concrete 02 model, Steel 01 model, and Pinching 04 model were applied to the concrete, steel reinforcement, and Fe-SMA strip in the fiber element, respectively, and the FE analysis was carried out in a displacement control method based on the Newton-Raphson method. The FE model of this study accurately predicted the initial crack load, yield load, and ultimate load. From parametric analyses, it was concluded that an increase in the compressive strength of the concrete increases the ductility of the specimen, and an increase in the level of recovery stress on the Fe-SMA strip increases the initial stiffness of the specimen.
Introduction:
Considering the promising results gained from several studies using cementitious composites with strain hardening behaviour (High Performance Fibre Reinforced Cementitious Composites, ...HPFRCC) for repair and retrofitting concrete flexural members, in this paper the possibility of using HPFRCC for retrofitting two-way RC slabs is investigated.
Methods:
A total of five two-way slabs were made and tested to failure. Three slabs were retrofitted with a variety of different types of retrofit configurations and two other slabs, having low and conventional reinforcement ratios, were used as control slabs. A novel technique of bonding, designated NSM-HPFRCC, is proposed. Flexural responses of all slabs are evaluated and the bonding behaviour and associated failure modes are investigated.
Results and Conclusion:
It is shown that the proposed retrofit configurations, especially when accompanied by the NSM-HPFRCC technique, can greatly improve the flexural performance of retrofitted slabs; hence, they can be used successfully to retrieve the flexural reinforcement deficiency of weak slabs.
This paper discusses the feasibility of using the impact–echo method (IE method) to assess the debonding flaws at the epoxy–concrete interfaces of near-surface mounted carbon fiber reinforced ...polymers (NSM CFRPs). The effectiveness of NSM CFRP strengthening is influenced by whether epoxy bonds CFRP bars and existing concrete structures effectively and thoroughly, thereby mutually transmitting the stress in the reinforced zones with CFRP bars. Because of poor construction quality, aging, and deterioration, debonding occurs between epoxy and concrete surfaces, severely inhibiting the reinforcement effectiveness of NSM CFRPs. The IE method is based on the principle of stress waves and was adopted in this study as the nondestructive debonding flaw assessment technique. To clarify the characteristics of the stress wave propagation caused by impact forces on NSM CFRP structures, numerical analysis and experimental test were performed on the bar-like epoxy specimens with a cross-sectional size of 13×13mm. The types of specimens used in this study included the bar-like pure epoxy specimen, bar-like epoxy specimens containing CFRP bars, and the concrete beams containing bar-like epoxy specimens with and without CFRP bars. For the concrete beams embedded with bar-like epoxy specimens, various debonding statuses at the epoxy–concrete surfaces were considered. The numerical analysis revealed that the impact responses in the bar-like pure epoxy specimen and bar-like epoxy specimens containing CFRP bars were dominated by the first few cross-sectional modes of vibration, and the IE test verified this result. The numerical and experimental results indicated that for the concrete beams containing bar-like epoxy specimens with and without CFRP bars and without debonding flaws, the impact response spectra each featured one high-amplitude peak at the fundamental mode frequency, referred to as the dominant frequency. When debonding occurred at the epoxy–concrete interfaces of the concrete beams containing bar-like epoxy specimens with and without CFRP bars, the impact responses showed that the dominant frequencies decreased significantly. When the dominant frequencies instead increased to levels nearly equal to those of the fundamental frequencies of the bar-like epoxy specimens, the epoxy thoroughly debonded from the concrete interfaces. According to the characteristics of the aforementioned impact responses, the IE method is capable of detecting the debonding flaws at epoxy–concrete interfaces in NSM CFRP strengthening.
AbstractThe large number of earthquake-prone vintage unreinforced masonry (URM) buildings in many seismically active parts of the world results in a need for minimally invasive and cost-effective ...strengthening techniques to enhance the poor earthquake performance of such buildings. The objective of the research reported here was to investigate the applicability of using near-surface-mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips as a retrofitting technique for improving the in-plane shear strength and displacement capacity of multi-leaf URM walls constructed using solid clay brick masonry. The use of this technique for repairing earthquake damaged URM walls was also investigated. Ten multileaf wall panels measuring approximately 1,200×1,200 mm were constructed using recycled vintage solid clay bricks and retrofitted using NSM CFRP strips with varying reinforcement ratios. These panels were loaded in diagonal compression, and the results were compared with those obtained from testing of nominally identical unretrofitted wall panels constructed using the same materials. In addition, four wall panels extracted from existing buildings were tested in an as-built condition and then later retested after being repaired using the NSM CFRP strip technique. Based on the experimental results it was established that the NSM CFRP strip technique provides a simple and cost effective method for substantially enhancing the shear strength and displacement capacity of understrength or damaged URM wall panels.
In this paper, unreinforced masonry (URM) and retrofitted masonry walls are modeled experimentally and computationally. The walls were subjected to in-plane loading to assess on the effectiveness of ...a retrofit solution that makes use of near surface mounted (NSM) reinforcing steel bars. A laboratory testing campaign was performed that included pull-out tests, diagonal compression tests, and in-plane cyclic tests of URM and NSM retrofitted physical models. The experimental results indicate that the NSM reinforcing steel bars are effective in improving the deformation capacity of the URM walls. A computational modeling approach that makes use of the applied element method is proposed and the computational results are validated using the experimental tests presented. Results from computational models indicate that a good correlation with the test results is achieved in terms of load-displacement response as well as failure mechanisms observed.
AbstractThis paper presents an analysis of the seismic performance of square RC bridge columns retrofitted with near-surface-mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars and/or BFRP ...sheet confinement based on fiber element modeling. An axial stress versus loaded-end displacement model of NSM FRP bars, including both elastic elongation and bond-slip effects, is proposed to account for the significant slippage of FRP bars in the plastic hinge region of strengthened columns. The simplified FRP bar model is then converted into the equivalent stress–strain relationship for easy implementation in fiber-based analysis. Moment-curvature analysis is performed based on the proposed FRP bar model, and the analytical moment versus fixed-end rotation relationship of a strengthened column is calculated and assigned to the rotational spring in the fiber element model. The proposed method avoids the nested iterations in sectional analysis that require force equilibrium and deformation compatibility. Comparisons between the numerical simulations and experimental results indicate that the proposed method is appropriate for predicting pushover curves and the hysteretic response of strengthened columns. Furthermore, the mechanism of the hybrid effect of combining NSM FRP bars with externally bonded FRP sheets can be interpreted after the analytical study; that is, confining the column with FRP sheets improves the bond conditions for NSM FRP bars, while the bond-slip effect mitigates the premature fracturing of the FRP bars, leading to more effective utilization of the NSM reinforcement and a more ductile column behavior.
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