Strengthening reinforced concrete structures with FRP composites

Civil infrastructures made of reinforced concrete (RC) play an important role in the economic activities and services of society. However, signs of deterioration and functional deficiency are commonly found in existing RC structures. Thus, there is a great demand for upgrading the capacity and performance of existing concrete structures. Fibre reinforced polymer (FRP) composites have been widely used as externally bonded reinforcement (EBR) for strengthening RC structures since the 1990s. The work of this thesis aimed to investigate robust and efficient FRP-strengthening systems for structural strengthening of existing RC structures with a focus on RC bridge superstructures. Three different strengthening techniques were investigated.A recently developed technique, namely the stepwise prestressing method, was studied in the current work to eliminate the need for mechanical anchors when using prestressed carbon-FRP (CFRP) plate as EBR for strengthening RC beams. Experiments showed that this method could realise the self-anchorage of prestressed CFRP plates on the surface of concrete beams given prestressing levels of 25-30% (of the CFRP tensile capacity). Despite no installation of mechanical anchors, the self-anchored prestressed plates were demonstrated to be efficient in reducing crack widths and improving the flexural capacity of the strengthened RC beams. At the debonding of the CFRP plates, the utilization ratios were in the range of 81-86% (of the CFRP tensile capacity) indicating significantly improved utilisation of the plates compared with equivalent non-prestressed plates.A practical modelling strategy was also developed to enable nonlinear FEA of the CFRP-strengthened RC beam. Using the FEA, parametric studies on the self-anchored plates indicated an optimal prestressing level of 40% (specifically for the investigated specimen), above which both load-carrying and deflection capacities of the strengthened beam would decrease due to CFRP debonding before yielding of steel reinforcement. A hybrid FRP system for strengthening RC beams with a T-shaped cross-section, representing the deck and girder system of RC bridge superstructures, was also investigated. The hybrid system included self-anchored prestressed CFRP plates applied to the soffit of the T-beams and prefabricated glass-FRP (GFRP) panels installed on the top of the T-beam flanges. In the strengthened RC T-beams subjected to bending, the CFRP plate acted as tensile reinforcement and the GFRP panel took most of the compressive force. Flexural tests showed that the applied hybrid FRP strengthening system was robust and efficient in improving the flexural stiffness and capacity. The tests also highlighted substantial residual capacity after the CFRP debonding, as the compressive zone shifted to the GFRP panel and concrete crushing at the top of the T-beam was prevented. The current work also investigated effective FRP strengthening systems for deteriorated concrete beams with highly corroded steel reinforcement. The system included externally bonded FRP reinforcement on the beam soffit and CFRP U-jackets along the span. Flexural tests showed that the system was efficient in upgrading the flexural capacity of deteriorated concrete beams, despite local corrosion levels of steel reinforcement up to 57% and unrepaired concrete cover with up to 2 mm wide corrosion-induced cracks. The U-jackets effectively suppressed spalling of the concrete cover and thus enabled improved utilisation of the bonded FRP reinforcement on the beam soffits, with a utilisation ratio of CFRP plates up to 64% and even rupture of GFRP laminates.In summary, the FRP-strengthening systems investigated in the current work were demonstrated to be robust and efficient in strengthening RC members subjected to bending

Vorticity interior trace estimates and higher derivative estimates via blow-up method

We derive several nonlinear a priori trace estimates for the 3D incompressible Navier-Stokes equation, which extend the current picture of higher derivative estimates in the mixed norm. The main ingredient is the blow-up method and a novel averaging operator, which could apply to PDEs with scaling invariance and $\varepsilon$-regularity, possibly with a drift.Comment: 34 pages, 2 figures, comments are welcom

Blood glucose related adverse drug reaction of antitumor monoclonal antibodies: a retrospective analysis using Vigibase

On the increasing prevalence of using mAbs (monoclonal antibodies) in cancer therapy and the severe risk of hyperglycemia, we aimed to analyze the main clinical ADRs of mAbs, with a focus on adverse hyperglycemic events associated with currently clinically used mAbs. mAbs as well as target information were selected from Martinadale book and published articles. Drug approving information was collected from each government website, and ADR statistic data were collected from VigibaseR, comparing with Adverse Event Reporting System of US FDA. Top 10 mAbs were classified within listing in total ADR records, ADRs per year, hyperglycemic ADR records. Vigibase data were updated onto 15 Feb 2019. 20 mAbs were analyzed with 263217 ADR reports, wherein 16751 records on Metabolism and nutrition disorders and 1444 records on Glucose metabolism disorders. The geographic, age, gender distributions and annual ADR report numbers were listed respectively. Of the top 10, Rituximab, Bevacizumab and Nivolumab were on the top 3 in total ADR record and hyperglycemic record. Top 3 record results were similar in Vigibase and FDA database. It is of increasing importance for clinicians to be aware of early detection, patient management, or drug selection strategies when using mAbs, particularly within the high glycemic risk-reported mAbs, to improve the efficacy and tolerability of mAbs regiment and optimize patient outcomes

A practical finite element modeling strategy to capture cracking and crushing behavior of reinforced concrete structures

Nonlinear finite element (FE) analysis of reinforced concrete (RC) structures is characterized by numerous modeling options and input parameters. To accurately model the nonlinear RC behavior involving concrete cracking in tension and crushing in compression, practitioners make different choices regarding the critical modeling issues, e.g., defining the concrete constitutive relations, assigning the bond between the concrete and the steel reinforcement, and solving problems related to convergence difficulties and mesh sensitivities. Thus, it is imperative to review the common modeling choices critically and develop a robust modeling strategy with consistency, reliability, and comparability. This paper proposes a modeling strategy and practical recommendations for the nonlinear FE analysis of RC structures based on parametric studies of critical modeling choices. The proposed modeling strategy aims at providing reliable predictions of flexural responses of RC members with a focus on concrete cracking behavior and crushing failure, which serve as the foundation for more complex modeling cases, e.g., RC beams bonded with fiber reinforced polymer (FRP) laminates. Additionally, herein, the implementation procedure for the proposed modeling strategy is comprehensively described with a focus on the critical modeling issues for RC structures. The proposed strategy is demonstrated through FE analyses of RC beams tested in four-point bending—one RC beam as reference and one beam externally bonded with a carbon-FRP (CFRP) laminate in its soffit. The simulated results agree well with experimental measurements regarding load-deformation relationship, cracking, flexural failure due to concrete crushing, and CFRP debonding initiated by intermediate cracks. The modeling strategy and recommendations presented herein are applicable to the nonlinear FE analysis of RC structures in general

Boundary Vorticity Estimates for Navier-Stokes and Application to the Inviscid Limit

Consider the steady solution to the incompressible Euler equation $\bar u=Ae_1$ in the periodic tunnel $\Omega=\mathbb T^{d-1}\times(0,1)$ in dimension $d=2,3$. Consider now the family of solutions $u^\nu$ to the associated Navier-Stokes equation with the no-slip condition on the flat boundaries, for small viscosities $\nu=A/\mathsf{Re}$, and initial values in $L^2$. We are interested in the weak inviscid limits up to subsequences $u^\nu\rightharpoonup u^\infty$ when both the viscosity $\nu$ converges to 0, and the initial value $u^\nu_0$ converges to $Ae_1$ in $L^2$. Under a conditional assumption on the energy dissipation close to the boundary, Kato showed in 1984 that $u^\nu$ converges to $Ae_1$ strongly in $L^2$ uniformly in time under this double limit. It is still unknown whether this inviscid limit is unconditionally true. The convex integration method produces solutions $u _E$ to the Euler equation with the same initial values $Ae_1$ which verify at time $0<T<T_0$: $\|u_E(T)-Ae_1\|_{L^2(\Omega)}^2\approx A^3T$. This predicts the possibility of a layer separation with an energy of order $A^3 T$. We show in this paper that the energy of layer separation associated with any asymptotic $u^\infty$ obtained via double limits cannot be more than $\|u^\infty(T)-Ae_1\|_{L^2 (\Omega)}^2\lesssim A^3T$. This result holds unconditionally for any weak limit of Leray-Hopf solutions of the Navier-Stokes equation. Especially, it shows that, even if the limit is not unique, the shear flow pattern is observable up to time $1/A$. This provides a notion of stability despite the possible non-uniqueness of the limit predicted by the convex integration theory. The result relies on a new boundary vorticity estimate for the Navier-Stokes equation. This new estimate, inspired by previous work on higher regularity estimates for Navier-Stokes, provides a nonlinear control scalable through the inviscid limit.Comment: 29 pages, 5 figures. We improved our conclusion and estimated the layer separation of any weak inviscid limi