Damage model for FRP-confined concrete columns under cyclic loading

International audienceIn structural engineering, seismic vulnerability reduction of existing structures is a crucial issue. External reinforcement with fiber-reinforced polymer (FRP) holds interest in achieving this aim. Its use as a retrofitting method is limited, however, for a number of reasons, including the lack of numerical tools for predicting cyclic loading. This paper presents a simplified stress-strain model suitable for monotonic and cycling loading capable of predicting the FRP's effect on reinforced-concrete columns. The model was inspired by two well-known concrete constitutive laws: one based on damage mechanics (La Borderie's concrete-damage model, 1991); the other on extensive experimental studies (Eid and Paultre's confined-concrete model, 2008). Validation is provided using experimental results on reinforced concrete columns subjected to axial and flexural cyclic loading. The proposed approach also deals with steel-bar rupture, considering low-cycle fatigue effects. All the simulations were conducted with multifiber Timoshenko beam elements

Stress-strain model for FRP-confined concrete columns under cyclic and seismic loading

In structural engineering, seismic vulnerability reduction of existing structures is a crucial issue. External reinforcement with fiber-reinforced polymer (FRP) holds interest in achieving this aim. Its use as a retrofitting method is limited, however, for a number of reasons, including the lack of numerical tools for predicting cyclic loading. This paper presents a simplified stress-strain model suitable for monotonic and cycling loading capable of predicting the FRP's effect on reinforced-concrete col umns. The model is inspired by two well-known concrete constitutive laws: one based on damage mechanics (La Borderie's concrete-damage model, 1991); the other on extensive experimental studies (Eid & Paultre's confined-concrete model, 2008). Validation is provided using experimental results on reinforced concrete columns subjected to axial and flexural cyclic loading. All the simulations were conducted with multifiber Timoshenko beam elements

Retrofitting reinforced concrete structures with FRP: Numerical simulations using multifiber beam elements

In structural engineering, seismic vulnerability reduction of existing structures is a crucial issue. External reinforcement by Polymer Reinforced Fibers (FRP) is an interesting tool in order to fulfill this aim. However, the use of FRP reinforcement as a retrofitting method is limited, one of the reasons being the lack of predicting numerical tools for cyclic loading. This paper presents a method to predict the behavior of beam-column structures considering the FRP reinforcement effect. It describes the construction of a 1D concrete constitutive model suitable for monotonic and cycling loadings. The model is inspired on two well-known concrete models, the first one based on the damage mechanics theory (La Borderie concrete damage model), and the second one based on experimental studies (Eid & Paultre's confined concrete model). Validation of the approach is done using experimental results on reinforced concrete beam and columns submitted to axial and flexural cyclic loading. The proposed method deals also with steel bar rupture considering low cycle fatigue effects. All the simulations are done using multifiber Timoshenko beam elements

Wòch nan solèy

41 pages ; 22 c

Traka yon kretyen pandan vwayaj li : adaptasyon liv “Pilgrim’s Progress" / John Bunyan

91 pages : illustrations ; 22 c

Mwen renmen yon jenn gason : yon korespondans konfidansyèl

Twazyèm parèt 73 p. : ill. ; 22 c

Lipids and carotid plaque in the Northern Manhattan Study (NOMAS)

<p>Abstract</p> <p>Background</p> <p>Lipids, particularly low-density (LDL) and high-density (HDL) lipoproteins, are associated with increased risk of stroke and cardiovascular disease, probably due to atherosclerosis. The objective of this cross-sectional analysis was to investigate the relation between blood lipids and carotid plaque.</p> <p>Methods</p> <p>As part of a prospective population-based study to determine the incidence and risk factors of stroke in a multiethnic population, we evaluated 1804 participants with lipid measurements and B-mode ultrasound of carotid arteries (mean age 69 +/- 10 years; 40% men; 51% Hispanic, 26% black, 23% white). The association between lipid parameters and carotid plaque was analyzed by multiple logistic regression.</p> <p>Results</p> <p>Plaque was present in 61% of participants. Mean total cholesterol was 202 +/- 41 mg/dl. After controlling for other lipid parameters, demographics, and risk factors, the only cholesterol subfraction associated with carotid plaque was LDL (OR per standard deviation (SD) = 1.14, 95% CI 1.02-1.27). Neither HDL nor triglycerides independently predicted carotid plaque. Apolipoprotein B (ApoB) was also associated with risk of plaque (OR per SD = 1.29, 95% CI 1.03-1.60). Apolipoprotein A-I (apoA-1) was associated with a decrease in multiple plaques (OR per SD = 0.76, 95% CI 0.60-0.97), while lipoprotein a was associated with an increased risk of multiple plaques (OR per SD = 1.31, 95% CI 1.03-1.66). ApoB:ApoA-I had the strongest relation with carotid plaque (OR per SD = 1.35, 95% CI 1.08-1.69).</p> <p>Conclusions</p> <p>Among the common lipid parameters, LDL has the strongest relation with carotid plaque. Other lipid precursor proteins such as ApoB and ApoA-I may be stronger predictors of subclinical atherosclerosis, however, and better targets for treatment to reduce plaque formation and risk of cerebrovascular disease.</p