ICE - Institution of Civil Engineers - Virtual Library

The work described in this paper is concerned with the application of the method of the compressive force path (CFP) to the strengthening of reinforced concrete (RC) structures designed for seismic action (the initial design of the member(s) covers both CFP design and design to current Eurocodes). Carbon fibre-reinforced polymer sheets are used for this purpose. Eight column specimens were tested under the combined action of a constant axial force and monotonic or cyclic lateral displacement. The eight columns were tested in groups of two, each group having one specimen strengthened initially and then tested to failure, while the second specimen was tested without strengthening, and was repaired and strengthened before testing it to failure. The tests showed that the strengthening procedure based on the CFP fully satisfied the performance requirements of current code provisions for strength and ductility irrespective of whether the initial design followed Eurocodes or the CFP methodology. Moreover, all strengthened (or repaired and strengthened) specimens had stiffnesses similar to those of their virgin counterparts.

This paper evaluates the ultimate strength of high-strength concrete (HSC) columns subjected to both axial load and biaxial bending. Fifteen square section (200 × 200 mm) columns with concrete compressive strength of 34, 57 and 64 MPa, respectively, were axially loaded with bi-directional eccentricities. The loading point was at an angle of 0°, 22·5° and 45° and the distances of eccentricity were determined to induce tension, balanced and compression failures, respectively. Test results were compared with the results of nonlinear analysis on P–M interaction curves and load contours. It was observed that, as concrete strength increases from 34 to 57 MPa, the concrete strength has a minor effect on the biaxial moment strength of reinforced columns, but as concrete strength increases up to 64 MPa, the concrete strength has a significant influence on biaxial flexural strength. This observed result is complementary when compared with the load contour method of ACI, in which biaxial bending design constants of columns are limited to concrete compressive strength of 41 MPa and estimate the effect of concrete strength to be minor.

Based on a multi-species approach, a new model for evaluating free chloride content in cementitious materials is proposed. To validate the model, migration tests were carried out on cement mortars with several NaCl concentrations. The total chloride was measured with the potentiometric method. The subtraction of the free chloride from total chloride results in bound chloride. Thus, a chloride-binding isotherm is obtained. First, it is shown that free chloride depends on the concentration of anions and cations contained in the pore solution. Second, the chloride-binding isotherm obtained (linear isotherm) shows that the interactions between chloride and hydrated products of the tested mortars are stronger than those (non-linear isotherm) quantified by the method based on water extracting. Finally, the electrical current is shown to be dependent on the binding phenomenon during the unsteady state. In fact, in a steady state, the sites that can react with chlorides are saturated; hence the binding isotherms do not affect the transport process.

Available test results and stress–strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than 2·0%, are scarce. This paper presents test results loaded in the axial direction for square reinforced concrete (RC) columns confined by various volumetric ratio lateral ties including low volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type and tie volumetric ratio. Local strains are measured using strain gauges bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was improved by changing tie arrangement type from type A to type B. A method to compute the stress in lateral ties at the concrete peak strength is proposed, as well as a new stress–strain model for the confined concrete. The model shows good agreement with stress–strain relationships established experimentally over a wide range of confinement parameters.

Cores measuring 94 mm and 144 mm in diameter and having length-to-diameter ratios of 2·0, 1·0 and 0·75 were removed from beam specimens produced from different concrete mixtures. Standard cubes and cylinders were also produced from the same mixtures. Compressive strength tests were conducted on 216 standard and 530 core specimens. The test results obtained from core specimens were compared with those of standard specimens. The effects of maximum aggregate size in concrete mixture, core diameter and type and size of the standard specimens on the interpretation of the core test results were examined. The test results showed that the maximum size of the aggregate affects the strength of the cores even when the diameter of the core is larger than three times the maximum size of the aggregates. The age of the concrete was found to be an important factor in the interpretation of the core strength results. Although the cores with a length-to-diameter ratio of 0·75 gave higher strength values, they may be used for the evaluation of the core strength results.