Nonlinear analysis and reliability of metallic truss structures

The present study goes into the search for the safety domain of civil engineering structures. The objective is to show how a reliability-evaluation brought by a mechanical sizing can be obtained. For that purpose, it is necessary to have a mechanical model and a reliability model representing correctly the behavior of this type of structure.It is a question on one hand, to propose a formulation for the nonlinear calculation (mechanical nonlinearity) of the spatial structures in trusses, and on the other hand, to propose or to adapt a formulation and a modeling of the reliability. The principle of Hasofer-Lind can be applied, in first approach, for the reliability index estimation, scenarios and the probability of failure.The made check concerned metallic in truss structures. Finally, some structures are calculated using the method adapted by Hasofer-Lind to validate the probability approach of the reliability analysis.     

Non linear modeling of three-dimensional reinforced and fiber concrete structures

Under the effect of the ascending loading, the behavior of reinforced concrete structures is rather non linear. Research in industry and science aims to extend forward the use of non-linear calculation of fiber concrete for structural parts such as columns, veils and pious, as the fiber concrete is more ductile behavior then the classical concrete behavior. The formulation of the element has been established for modeling the nonlinear behavior of elastic structures in three dimensions, based on the displacement method. For the behavior of concrete and fiber concrete compressive and tensile strength (stress-strain) the uniaxial formulation is used. For steel bi-linear relationship is used. The approach is based on the discretization of the cross section trapezoidal tables. Forming the stiffness matrix of the section, the integral of the surface is calculated as the sum of the integrals on each of the cutting trapezoids. To integrate on the trapeze we have adopted the type of Simpson integration scheme.     

Control for PWM ac chopper feeding nonlinear loads

This paper presents a novel robust control technique for PWM ac choppers with the ability to generate high quality sinusoidal waveforms with adjustable amplitudes over a wide range control. For this purpose a deadbeat-based digital controller has been developed to perform tight closed-loop control of the ac chopper. This controller is based on a generalized predictive control (GPC) approach. A dedicated control algorithm has been developed and implemented. The proposed controller presents the advantages of allowing a very fast transient response and compensating effectively for load disturbance and the effects of nonlinear loads. Computer simulations are performed to investigate the proposed controller performance. The simulation results show that the designed controller has a good dynamic behaviour, a good rejection of impact load disturbance, and is ;very robust. To evaluate the proposed approach an experimental prototype has been constructed. Experimental results under various loading conditions have demonstrated that the system performs well.     

Bond-slip law and short tie behavior without main cracks

The aim of this paper is to study the reinforced concrete short tie-rods behavior using the adhesion-slip curve shape between steel and concrete adopted by the European Concrete Committee. We are interested here in short tie-rods without main cracks for which we calculate and measure the maximum mobilization state of steel-concrete adhesion, and beyond the decrease mode of this bond. For this, tests of short tie-rods, with different high adhesion rebar diameters have been carried out. To characterize the first phase of the adhesion-slip behavior law (τ?g), pull out tests have been carried out with the same concrete, the same reinforcement and the same cross-section such as the tie-rod tests, with a proposed method to estimate the adhesion peak and the corresponding slip. For this adhesion peak value, slightly underestimated by the conventional curve of the European Concrete Committee, a new expression is suggested. A numerical model with theoretical relations of the behavior of such tie-rods is proposed. The comparison of this model with the obtained test curves of the short tie-rods shows a suitable approach. Also, we deduce that the steel (coated with concrete) fictitious module slope is even higher than the percentage of reinforcement is low. These results may help to understand the tie-rods behavior generally, in the phase of cracks stabilization, during which the tie-rod is composed of short tie-rods without main cracks.     

Frequency and significance of anemia in non-Hodgkin's lymphoma patients

OBJECTIVES: Retrospective evaluation of anemia frequency and its prognostic value in patients with different subtypes of non-Hodgkin's lymphoma and comparison with other clinical characteristics. PATIENTS AND METHODS: Anemia was defined as a hemoglobin value less than or equal to 12 g/dl for all men and women over 50 years of age, and less than or equal to 11 g/dl for women under 50 years of age. The study included 1077 adult lymphoma patients treated between 1980 and 1995 with the following histologic subtypes: 127 patients with small lymphocytic or lymphoplasmacytoid, 62 with marginal zone, 50 with mantle-cell, 208 with follicular, 104 with T-cell lymphoma, 426 with diffuse large-cell and, finally, 73 patients with other high-grade lymphomas. RESULTS: Anemia was present in 341 patients (32%). It was an adverse prognostic factor (P < 0.0001) for overall survival (OS) and progression-free survival (PFS) but not for relapse-free survival (RFS). When patients with and those without bone marrow involvement were considered separately, anemia remained an adverse factor. Anemia was significantly associated with shorter PFS in small lymphocytic or lymphoplasmacytoid, mantle cell, diffuse large cell and high-grade lymphomas and with shorter OS in all histologic subgroups except marginal zone lymphoma. In multivariate analysis, anemia was a significant prognostic factor for OS and PFS for the population as a whole (P = 0.0001 and P = 0.0048, respectively) and in patients with bone marrow involvement (P = 0.007 and P = 0.005, respectively) but not in patients without bone marrow involvement. Finally, the addition of anemia to the International Prognostic Index led to an improvement for OS (P = 0.0004) and PFS (P = 0.0004). CONCLUSIONS: Anemia is an important adverse prognostic factor for the outcome of lymphoma patients, particularly in some histologic subgroups and in patients with bone marrow involvement.     

High CD34(+) cell counts decrease hematologic toxicity of autologous peripheral blood progenitor cell transplantation

Optimal numbers of CD34(+) cells to be reinfused in patients undergoing peripheral blood progenitor cell (PBPC) transplantation after high-dose chemotherapy are still unknown. Hematologic reconstitution of 168 transplantations performed in patients with lymphoproliferative diseases was analyzed according to the number of CD34(+) cells reinfused. The number of days from PBPC reinfusion until neutrophil recovery (>1.0 x 10(9)/L) and unsustained platelet recovery (>50 x 10(9)/L) were analyzed in three groups defined by the number of CD34(+) cells reinfused: a low group with less than or equal to 2.5 x 10(6) CD34(+) cells/kg, a high group with greater than 15 x 10(6) CD34(+) cells/kg, and an intermediate group to which the former two groups were compared. The 22 low-group patients had a significantly delayed neutrophil (P < .0001) and platelet recovery (P < .0001). The 41 high-group patients experienced significantly shorter engraftment compared with the intermediate group with a median of 11 (range, 8 to 16) versus 12 (range, 7 to 17) days for neutrophil recovery (P = .003), and a median of 11 (range, 7 to 24) versus 14 (range, 8 to 180+) days for platelet recovery (P < .0001). These patients required significantly less platelet transfusions (P = .002). In a multivariate analysis, the amount of CD34(+) cells reinfused was the only variable showing significance for neutrophil and platelet recovery. High-group patients had a shorter hospital stay (P = .01) and tended to need fewer days of antibotic administration (P = .12). In conclusion, these results suggest that reinfusion of greater than 15 x 10(6) CD34(+) cells/kg after high-dose chemotherapy for lymphoproliferative diseases further shortens hematopoietic reconstitution, reduces platelet requirements, and may improve patients' quality of life.     

Intensive therapy with peripheral stem cell transplantation in 16 patients with mantle cell lymphoma

BACKGROUND: Despite improved detection of mantle cell lymphoma (MCL), results of its treatment with conventional therapies remain disappointing and the survival rate poor. The role of high-dose chemotherapy has recently been investigated but no potential benefit has been clearly established. We report here our experience with MCL patients treated with intensive chemotherapy and autologous stem cell transplantation (ASCT). PATIENTS AND METHODS: Of the 16 MCL patients who received high-dose chemotherapy and ASCT beginning in 1989, six were treated in first-line and 10 in sensitive relapse. Twelve of 16 patients received regimens which included total body irradiation. All patients received peripheral blood stem cells (PBSC) with the exception of one, who underwent bone marrow transplantation. RESULTS: Three patients died of toxic effects of treatment, Three months after transplant, seven achieved complete response, (CR) and two partial responses (PR), two were stable and two had progressed. With a median follow-up after transplant of 22 months, five of the six surviving patients were without progression, and three were in CR. The median times for event-free survival (EFS) and overall survival (OS) were, respectively, 249 and 317 days. The expected three-year EFS and OS were 24%. The median survival after diagnosis was only 29 months. None of the criteria appeared to be significantly associated with a better outcome, but first-line intensification and a short delay after initial diagnosis may be favorable. CONCLUSION: In this study we were not able to confirm the hypothetical benefit of high-dose chemotherapy and PBSC transplantation in mantle cell lymphoma, even though this approach may be promising in a subgroup of patient.     

Numerical analysis of the effect of pore on local stresses in spot welds

In this investigation, the finite element analysis has been employed to study the distribution and the level of stress induced in a ferritic matrix by pores resulting from the process of welding. The effect of pore inter-distance and the interaction between pore and different weld imperfections in a spot weld (pore–pore, pore–precipitate and pore-micro-crack) on the stresses level were highlighted. The results showed that the distribution of the pores and the interaction between pores and different weld imperfections have a significant influence on the level of the developed stresses.