Tools for assessing damage in concrete affected by AAR coming from fine and coarse aggregates
Over the last few years, comprehensive management programs for the diagnosis and prognosis of alkali-aggregate reaction (AAR) in aging concrete structures were developed in North America, based on a series of laboratory test procedures. Although promising, these lab-procedures presented several parameters whose impacts were not completely understood, which significantly reduced their applicability for the appraisal of deteriorated concrete structures in service. In this context, it has been suggested that two lab-tools, the Stiffness Damage Test (SDT) and the Damage Rating Index (DRI) could reliably assess the condition of concrete affected by AAR. This paper presents the condition assessment of 25, 35 and 45 MPa AAR affected concrete specimens incorporating fine and coarse reactive aggregates and presenting different distress degrees (i.e. expansion levels from 0.05 to 0.30%) through the use of an innovative multi-level approach. Results show that both SDT and DRI are suitable for assessing damage in AAR affected concrete through their output parameters. Yet, they present a complementary character, which illustrates the need for a multi-level approach.
Evaluation of the stiffness damage test (SDT) as a tool for assessing damage in concrete due to ASR: Test loading and output responses for concretes incorporating fine or coarse reactive aggregates
Abstract The stiffness damage test (SDT) is a powerful tool developed for the evaluation of the damage's degree of concrete affected by ASR. This paper presents the assessment of some parameters (test loading and output responses) on the efficiency of the method. The analyses were carried out with three types of concrete (25, 35 and 45 MPa) and two highly-reactive aggregates (New Mexico gravel and Texas sand). The diagnostic character of various output parameters was analyzed and the results showed that the SDT should be carried out with a percentage of the design strength (ideally 40%) instead of working with a fixed load. Parameters such as the hysteresis area and the plastic deformation over the five cycles of loading/unloading as well as the average modulus of elasticity of the second and the third cycles seem to give quite good correlations with the amount of expansion reached by the concrete.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.