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

Modèle cyclique de béton confiné par TFC pour poteaux circulaires en béton armé

International audienceIn structural engineering, the seismic vulnerability reduction of existing structures is a crucial issue. External reinforcement using Fiber Reinforced Polymer (FRP) is an interesting tool in order to fulfill this aim.This paper presents a method to simulate the behavior of existing columns considering FRP reinforcement effect. It describes the construction of a 1D confined concrete behavior law suitable for monotonic and cycling loadings. The law is inspired on two well-known concrete laws, the first one based on damage mechanics theory (La Borderie concrete damage law) and the second one based on experimental studies (Eid & Paultre concrete monotonic law). Structures are discretized using multifiber beam elements. Validation of the approach is provided using experimental tests of RC columns under axial and flexural cyclic loading.En génie parasismique, la réduction de la vulnérabilité des structures existantes est un enjeux majeur. Le renforcement externe d'éléments par collage de Tissus de Fibre de Carbone (TFC) est une réponse intéressanteà cette problématique. Cet article présente la construction d'un modèle uniaxial de béton confiné adapté au cas des chargements monotones et cycliques. Ce modèle est fondé sur deux modèles bien connus, le premier basé sur la théorie de l'endommagement (La Borderie) et le second basé sur une série d'études expérimentales (Eid & Paultre). Le modèle est implanté dans un codé eléments finis multifibres. Une validation expérimentale de ce modèle est menée enétudiant le cas de poteaux en béton armé soumisà un chargement cyclique de flexion composée

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

Seismic behaviour of prestressed and normal reinforcement of communication tower with ultra-high performance concrete, high strength concrete and normal concrete materials

Nowadays, advances in telecommunications and broadcasting have led to the implementation of communication towers for installing network equipment. These towers are designed to go as high as possible in order to cover large area and avoid obstructions. However, there exist many challenges faced by engineers in relation to design of the tall and slender structures such as the complexity configuration of the structure. The nonlinear dynamic analysis is the only method that describes the actual behaviour of a structure during earthquake. Therefore, this study aims to investigate the behaviour of ultra-high performance concrete (UHPFC), high-strength concrete (HSC) and normal concrete communication tower with 30 m height located in Malaysia under seismic excitation. Also, to provide strength, stiffness and stability for the slender structures due to their sensitivity to dynamic load such as earthquake and vibration forces. For this propose, the finite element model of the tower is developed and time history analysis of communication tower under seismic load was conducted. In addition, the effect of using prestress instead of conventional reinforcement was investigated. The result indicated that prestressing of tower had lesser effect on the lateral displacement of tower under earthquake excitation. Although, the tower with UHPFC and HSC material shows lower lateral peak displacement against earthquake load compared to the normal concrete, which led to the increase in the use of these materials in lateral stiffness of the tower structure

Confinement reinforcement for bridges in medium to high seismicity zone based on new CSA A23.3-04 approach

Recent advances in confinement reinforcement of building columns have resulted in changes in Canadian code for Design of Concrete Structures CSA A23.3-04. Bridge columns and piers may also take advantage of these advances. The purpose of this paper is to use a comparable approach to propose new equations to be introduced in future Canadian bridge design code. The adopted approach for transverse reinforcement is based on the recently developed uniaxial confinement model for concrete column at Sherbrooke University. Parametric studies have been carried out on some typical bridge columns and piers to develop equations for confinement reinforcement. An intermediate level of ductility (moderate ductility) for bridge columns and piers has been introduced, similar to that in CSA A23.3-04 building design code. Confinement reinforcement for this level of ductility has been found to be less stringent than that for ductile level. This level of ductility is suitable for regions of low to medium seismicity. The adopted approach is supported by experimental results and will provide the designer more flexibility but economical and safer seismic design of bridge columns and piers

Stress-strain model for confined high-strength concrete

Peer reviewed: YesNRC publication: Ye