International Concrete Abstracts Portal

The benefits derived from the ability of the fibers to control crack propagation have been recognized for many years. In addition, the development of high-perfurmance concretes has enhanced this situation as the increases in strength lead to a more brittle behavior of the material. The introduction of steel-fiber rein- forcement in these concretes is probably the best way to improve the performance of concrete when higher tenacity is required. This paper shows the contribution of fiber reinforcement in both conventional and high-strength concretes exposed to temperatures up to 500°C. Conuutes with diffemnt types and content of fibers are analyzed, mainly regarding the failure mechanism and tenacity. The post-peak behavior under conpressive and flexural loads is studied using a close loop system. NDT was also used to evaluate the damage. The residual mechanical properties of fiber-reinforced concretes qre affected in a similar way thau those corresponding to plain concrete. Nevertheless, it can be seen that the residual parmeters tend to increase as the strength increases when high carbon-steel fibers bstead of low carbon-steel fibers are used, and when fiber reinforcement is introduced.

The basic problem in beam-column design is to establish the proportions of a reinforced concrete cross-section whose design strength is just adequate enough to support the factored axial load and moments. Since the stress distribution due to the axial load and moment depends on the cross-section’s proportions, which are initially unknown, column design cannot be carried out directly. Instead, the proportions of a cross-section must be estimated and then investigated to determine whether its design capacity is adequate for the factored loads and moments. The dimensions of a beam-column cross-section and the area of reinforcing steel required to support a specific combination of axial load and moment can be established by using the column design interaction curves, where an interaction curve represents all possible combinations of axial load and moment that produce failure of the cross-section. The bending resistance of an axially loaded column about a particular skewed axis due to biaxial moments can be determined through itera- tions and lengthy calculations. These extensive calculations are multiplied when optimization of the reinforcing steel or column cross-section is required. This pa- per investigated the suitability of an Artificial Neural Network (ANN) for model- ing a preliminary design of reinforced concrete beam-column. An ANN back- propagation model has been developed to design a beam-column which predicts column cross-section and reinforcing steel requirements for a given set of inputs which are concrete compressive strength, reinforcing steel strength, factored axial load and moment. The trained ANN back-propagation model has been tested with several actual design data, and a comparative evaluation between the ANN model predictions and the actual design has been presented.

Performance evaluation of sacrificial exterior shear keys under simulated seismic loading is presented in this paper. The performance evaluation was conducted in terms of damage levels observed during testing. The experimental program consisted of six experiments, and the variables investigated during testing were; (1) inclusion and exclusion of back and wing walls to determine influence of these walls in the seismic response of the shear keys, (2) adoption of different design details such as the use of sacrificial flexural keys, and (3) prestressing of the abutments with the main objective of decreasing damage propagation into the abutment walls. These experiments provided results that were used to make realistic assumptions of the load-deformation response of sacrificial exterior shear keys as well as their post-peak performance under cyclic loads. Experimental and analytical results were also used to develop a hysteretic model for exterior sacrificial shear keys at the abutments. The development of this hysteretic model is also discussed in the paper.

Corrosion of reinforcing steel in concrete usually initiates from chloride ingress. The temperiiture of thd service environment and cementitious material blends influence chloride ingress. This paper presents data from a multi-year experiment designed to illustrate the effects of temperature and supplementary cementing materials on chloride diffusion in concrete. This experiment consists of six concrete mixtures, five of which contained different supplementary cementing materials. Test specimens were submerged in 6% sodium chloride solution, and stored at a temperature of 10, 23, and 32 C for approximately three and one-half years. The chloride ingress data are presented, and the impact of temperature on chloride diffusion coefficients along with its implications for corrosion service life modeling am discussed presently, most service life prediction models adjust for the service temperature of a structure by using the Arrhenius Equation. The time-to-cormsion data obtained in this study suggests that the net result of temperature related effects does not match the predictions based on the Arrhenius Equation.

Imaging and non-imaging sensors that collect spectral data of surface materials are rapidly becoming available to engineers due to advances in electrooptics and sensor technology. Applications of remote sensing for the identification of surface materials and determination of some of their characteristics have been developed in the geological sciences. Transportation research systems are moving aggressively towards using these types of technologies for materials such as soil subgrades, concrete, asphalt, and, to a lesser extent, steel. A series of experiments were identified to analyze the spectral response of laboratory prepared surfaces, primarily of materials with a mineralogical origin, including soil, aggregate, and concrete. This paper presents the experimental procedure and results of a series of tests performed on a mortar mixture. Temperature, strength, and spectral reflectance were measured for a period of time during curing of the mortar. Results revealed apparent correlations between temperature, water content (curing rate), and spectral response.