Stijn Matthys

fib model code for concrete structures 2010

The fib Model Code 2010 is the most comprehensive code on concrete structures, including their complete life cycle: conceptual design, dimensioning, construction, conservation and dismantlement. It is expected to become an important document for both national and international code committees, practitioners and researchers.

Axial load behavior of large-scale columns confined with fiber-reinforced polymer composites

Confinement of concrete is an efficient technique used to increase the load-carrying capacity and ductility of concrete columns and is of interest for upgrading columns, piers, and chimneys. This article reports on an experimental and analytical study of axially-loaded large-scale columns confined with fiber-reinforced polymer (FRP) wrapping reinforcement; this work updates previous studies on smaller-scale columns. The effective circumferential FRP failure strain and the effect of increasing confining action were investigated. The authors compared the different existing compressive strength models to their study results. The authors then present a revision of an existing model developed previously by the second author. This revised model addresses the effective FRP failure strain that is attributed to localized stress concentrations near failure due to nonhomogenous deformations of the damaged concrete. The authors note that the wrapping configuration of the confinement has a considerable influence on the effectiveness of the FRP wrapping. The authors conclude that although the available models were developed based on small-size cylinders, four models seem to predict the ultimate strength of large-scale columns fairly accurately (Miyauchi et al, Saafi et al, Samaan et al, and Toutanji Revised).

TESTS ON AXIALLY LOADED CONCRETE COLUMNS CONFINED BY FIBER REINFORCED POLYMER SHEET WRAPPING

Wrapping of columns by means of FRP (Fiber Reinforced Polymer) reinforcement enhances the structural behavior of concrete columns considerably. At the Magnel Laboratory for Concrete Research a test program is set-up to evaluate some specific problems in the modeling of FRP confined concrete, i.e., effective circumferential FRP failure strain and effect of increasing confining action. Parameters studies are FRP type, bonded or unbonded wrapping application, column shape and strengthening lay-out. Both wrapped cylinders and wrapped columns are investigated. An analytical verification of the test results is performed according to different models. From the test results obtained so far, the efficiency of this strengthening technique has been demonstrated, both in terms of structural performance and ease-of-application. Quality of the application (voids, protrusion, etc.) and the wrapping concept (bonded or unbonded, partial wrapping, etc.) influence the strengthening effect.

Behavior of Large-Scale Rectangular Columns Confined with FRP Composites

This paper focuses on axially loaded, large-scale rectangular RC columns confined with fiber-reinforced polymer (FRP) wrapping. Experimental tests are conducted to obtain the stress-strain response and ultimate load for three field-size columns having different aspect ratios and/or corner radii. Effective transverse FRP failure strain and the effect of increasing confining action on the stress-strain behavior are examined. Existing strength models, the majority of which were developed for small-scale specimens, are applied to predict the structural response. Since some of them fail to adequately characterize the test data and others are complex and require significant calculation, a simple design-oriented model is developed. The new model is based on the confinement effectiveness coefficient, an aspect ratio coefficient, and a corner radius coefficient. It accurately predicts the axial ultimate strength of the large-scale columns at hand and, when applied to the small-scale columns studied by other investigators, produces reasonable results.

Relationship between sports participation and the level of motor coordination in childhood: A longitudinal approach

OBJECTIVES This study examined the stability of motor coordination and the relationship between motor coordination and organized sports participation over time. DESIGN Longitudinal design. METHODS A total of 371 children between six and nine years of age at initial testing completed a test battery measuring motor coordination in three consecutive years and a questionnaire on their club sports participation in year 1 and year 3 of testing. RESULTS Correlation coefficients revealed the motor coordination of children to be a highly stable factor, ranging from 0.662 (6-8 years) to 0.873 (7-9 years). Results of the Repeated Measures ANOVA indicated that children who consistently practiced sports in a club environment over the three years of testing displayed better coordination levels than children who only partially participated or did not participate in a club environment at all. Moreover, stability was further indicated as consistent sports participation over time and changes or lack thereof did not substantially influence the development of motor coordination over time. In addition, the basic level of motor coordination and the amount of club sports participation significantly predicted sports participation two years later. CONCLUSION The importance of the stability of motor coordination levels in childhood and its role in determining organized sports participation may have implications for talent identification purposes as well as potential health-related benefits in childhood and throughout the lifespan.

Influence of High Temperature on Bond between NSM FRP Bars/Strips and Concrete

The use of near surface mounted (NSM) fiber reinforced polymers (FRPs) is being increasingly recognized as a valid technique strengthening of concrete members. In case of elevated temperature or fire exposure however, the bond between the bars and the concrete will be lost very quickly due to the adhesives low glass transition temperature. Although recent studies have shown that the fire endurance of appropriately designed and insulated FRP strengthened RC members is satisfactory, the performance of FRP strengthening systems at high temperature remains largely unknown. To study the bond behaviour at elevated temperature between the NSM FRP bars and concrete a series of 18 double bond shear tests were performed at Ghent University. Results show that the failure load of NSM FRP strengthened concrete structures and the bond strength are influenced at values of temperature equal to or beyond the glass transition temperature. Failure mode changed by increasing the temperature.

Fire testing of RC beams strengthened with NSM reinforcement

The weak performance of fibre reinforced polymer (FRP) strengthened members in fire is a primary factor hindering the widespread implementation of FRP strengthening technology in the construction industry. An investigation was undertaken to examine and document the performance of NSM FRP strengthened concrete beams under fire conditions. Six reinforced concrete beams were strengthened in flexure with NSM FRP bars and insulated with different insulation systems. The specimens were subsequently exposed to a standard fire under service load. The testing parameters of these elements include the use of different thermal protections (including different materials and geometric layouts of the protection) of the glued reinforcement. Member deflections and temperatures throughout the section were measured during fire testing. Tests results indicated that insulated NSM FRP strengthened beams can achieve a fire endurance of at least of two hours.

Basis of a Finite-Element Simulation Tool to Predict the Flexural Behavior of SFRC Prisms

The fiber pull-out response of a steel fiber, both straight and end-hooked, embedded in a concrete matrix has been widely investigated in the past. Attention was given to the influence of the type of fiber, the concrete strength and the inclination of the pull-out force. Hooked-end fibers need more energy to be pulled out of the concrete and thus are preferably used in steel fiber reinforced concrete (SFRC) for structural purposes.

Deflection and cracking behavior of RC beams strengthened in flexure

This paper will discuss that in order to understand and predict the effect of externally bonded reinforcement (EBR) on the serviceability behavior of FRP (fiber-reinforced polymer) strengthened members, four-point bending tests have been executed on reinforced concrete (RC) beams with span length 3.8 m (150 in.). This experimental campaign was further complemented with tests on strengthened tensile members. These so-called ‘tension stiffening’ tests typically consist of a tensile test on a reinforcing bar embedded in a FRP strengthened concrete prism. As the FRP EBR increases the stiffness of the beams and as a denser crack pattern with smaller crack widths is obtained, the serviceability limit state (SLS) of the strengthened members is positively influenced. Hereby, the behavior in terms of deflection and crack widths can be predicted in a fairly accurate way.

COMPARISON OF CONCRETE SLABS PRETENSIONED WITH COMPOSITE BARS AND STEEL WIRES

A test program was set up to study AFRP as prestressing reinforcement for concrete slabs. The paper describes short-term, long-term and cyclic loading tests on ten slabs. The structural behavior of the pretensioned slabs, under these loading conditions, is investigated. Finally, it is concluded that the use of AFRP as prestressing reinforcement can offer promising perspectives.