International Concrete Abstracts Portal

In this study, the seismic performance of reinforced concrete beam-column joint subassemblies reinforced with steel fiber was evaluated through experiments. A total of seven specimens were used, and four steel fiber-reinforced specimens were planned based on the amount of steel fiber, the presence or absence of hoops of joints, and the spacing of hoops arranged in the beam. The steel fibers used were determined to have properties that could be used to replace the minimum shear reinforcement in beams proposed by ACI 318. To evaluate the seismic performance quantitatively, a loading protocol was applied based on the displacement control protocol of ACI 374. Experimental results showed that reinforcement of steel fiber improves the shear strength of the joint itself. The shear strength of the joint increased as the amount of steel fiber was increased. However, the increase rate of the shear strength of the joint decreased with increasing steel fiber content. A large seismic performance improvement was confirmed when the hoop spacing on the beam was widened and the steel fiber was used with the hoop of the joint. Simultaneous reinforcement of steel fiber and the hoop with increased hoop spacing on the beam caused more damage on the beam and reduced the joint shear strength. Seismic performance evaluations according to ACI 374 showed that performance similar to that of the hoop reinforced joint can be expected when steel fiber with 2% volume fraction is used instead of the hoop in the joint region.

This paper presents the experimental results of two reinforced concrete (RC) frames subject to column loss scenario to investigate the development of membrane action and progressive collapse resistance. Two two-fifths-scale RC frames with three bays and two stories were built and tested under displacement-controlled push-down loading at the top of the missing column. The same geometry and longitudinal reinforcing ratio were used in each frame; however, the type of concrete (conventional and steel fiber-reinforced) and spacing of stirrups in the beams were different to assess the replacement of shear reinforcement with steel fibers. It was concluded that using discrete steel fibers in conjunction with reducing the number of beam stirrups does not significantly change the membrane behavior following column loss. However, there was better localized performance of the concrete for the case of steel fiber concrete, with fewer cracks within the joint zones and no spalling of concrete cover

A rational approach is developed to link standard drying shrinkage values and environmental parameters to control-joint spacing for slabs-on-ground. The analysis includes the combined effects of shrinkage, tensile creep, reinforcement, and subgrade friction. The result of the analysis is a set of equations to calculate the control-joint spacing, establishing a rational framework for shrinkage performance specifications. Thermal effects are not included in the model, thus limiting the applicability of the equations to slabs-on-ground in an environment where thermal gradients are minimized. The calculated control-joint spacing values for plain concrete compare favorably with the commonly used empirical PCA recommendations. Reduction in drying shrinkage is shown to increase control-joint spacing. The examples provided show that reinforcement provides marginal increases in control-joint spacing if intermediate cracks are not allowed. When tight intermediate cracks are allowed, reinforcement and low-shrinkage concrete are shown to have a synergistic effect and can provide significant increases in joint spacing.

The present work studies the problem of cracking due to volume change of base-restrained reinforced concrete walls. The cracking behavior of some 61 full-size walls and 14 experimental walls was investigated. The observed primary and secondary crack spacings and widths were compared with the values obtained using recently developed formulas and previous formulas developed by other researchers. A good agreement was found between the observed values and those predicted using the developed formulas. On the practical side, the results clearly showed that crack spacing and, consequently, the crack width, increased with the increase of the wall height and, therefore, a higher percentage of reinforcement or closer joints is required for their control. Furthermore, crack width was not uniform with the wall height, but varied according to the change of restraint associated with cracking and, therefore, the percentage of reinforcement may be varied with the wall height to obtain approximately uniform crack widths. This may lead to savings in reinforcement cost.

Wire bed-joint reinforcement has been used widely over the years for control of cracks due to temperature and shrinkage, for continuity in multiple wythe walls, and to satisfy arbitrary minimum code requirements in the horizontal direction. However, the structural significance of joint reinforcement in block masonry walls is not well established. This paper presents an experimental study of the behavior of horizontally spanning joint reinforced block masonry walls under out-of-plane monotonic lateral loading. Five full-scale wall panels were tested to determine the effect of amount and type of horizontal steel and bond pattern (running versus stack bond) on wall behavior including cracking moment, load-deflection relationships, and flexural strength. Correlation between flexural strength test results and the UBC-88 code strength design method is presented. The results showed that the shape of the load-deflection curve was a function of the spacing and type of reinforcement. The walls exhibited very little post-peak inelastic deformation due to the limited inelastic strain of the cold-drawn joint reinforcement. Joint reinforcement did not influence the cracking load significantly; however, the flexural strength was increased significantly. Bond pattern did not affect the ultimate moment carrying capacity of the walls but significantly affected the cracking moment. It is concluded that as the UBC strength design method gives a reasonable estimate of wall flexural strength, a method based on strain compatibility would provide more accurate results.