International Concrete Abstracts Portal

Corrosion of steel reinforcing bars in reinforced concrete (RC) structures is a matter of concern among practicing engineers and researchers are perpetually working over it. The development length of reinforcing bars at joints of RC structural frames are more prone to severe corrosion. Due to this, the design stress that needs to be developed in reinforcing bars is largely reduced. In addition, the development lengths of reinforcing bars create congestion at frame joints. This paper is an attempt to overcome these issues. In this paper, an epoxy-grouted nut coupler system is proposed that generates the required design stress in reinforcing bars with a very short development length at end anchorages, due to which congestion of the reinforcing bar at the joints can be avoided. The experimental investigation on the effect of corrosion on bond strength and development length of reinforcing bar in this epoxy-grouted nut coupler is also carried out by performing pullout tests. Statistical models are developed to predict the bond strength between the coupler and reinforcing bar corroded to different levels. This epoxy-grouted nut coupler is an effective tool for developing required stress in reinforcing bars by reducing the actual development length of reinforcing bars in the case of new structures. It is also useful and convenient in regeneration of stress in reinforcing bars at end anchorages that has been lost in corrosion-damaged structures.

The evaluation of the mechanical properties of steel fiber-reinforced concrete (SFRC) with different types of fibers and dosages endorses new design recommendations for using several types of construction materials for structural elements. The double-punch test (DPT) offers procedural and economic advantages for evaluating the indirect tensile strength of the SFRC. The objective of this paper is to show and discuss the results of the mechanical characterization obtained experimentally for SFRC using the DPT, with different types of anchorage and fiber dosages. The variables of the study were the dosage of steel fibers (20, 40, and 60 kg/m3) and the number of hooks at the ends of the fiber (1, 1.5, and 2 hooks). The paper develops empirical models for predicting the tensile strength, residual strength, and toughness of SFRC subjected to the DPT without resorting to experimental tests. The models were developed considering the trends of 385 results: 108 from 40 DPTs measured in this study, and 277 from 23 DPTs available in the literature.

The load transfer within joints of reinforced concrete elements can strongly influence the behavior of the structure. Additionally, cracks play an important role—they develop due to bending-induced tensile stresses in concrete and meander along the starter bars anchored in joints. The performance of joints becomes even more relevant under seismic loading conditions, whereby the reinforcing bars are subjected to cyclic loading and, at the same time, cyclic opening and closing of the cracks intercepting the starter bars. Such load and crack cycling may significantly influence the load and displacement capacity of starter bar anchorages. Experimental tests were carried out to verify a generic bond model to describe the bond stress-slip relationship under these seismic conditions. This seismic bond model should allow the realistic numerical simulation of seismically loaded reinforced concrete structures even if joints are designed with starter bars shorter than the development length.

Concrete screw anchors can be susceptible to stress-induced hydrogen embrittlement cracking because they are case hardened and often coated. Hydrogen attack can result in decreased tensile ductility and decreased fracture stress at the root, which is where the threads meet the core. Currently, Acceptance Criteria 193 (AC 193) requires that two types of tests are conducted to qualify screw fasteners for stress-induced hydrogen embrittlement cracking under service conditions: 1) Method A, which is a test subjecting a concrete screw installed in concrete to a sustained tensile load while in an aggressive environment; and 2) Method B, which is a bending test on the threaded portion of the fastener while in an aggressive environment. This study examines Method A and Method B qualification test data obtained from three manufacturers for five different diameters and 11 different lengths. The comparison of the test results for the two methods shows that Method B is a redundant test, resulting in no additional safety or information beyond that gained from Method A.

Anchors used in seismic applications have to resist cyclically pulsating loads and cyclically opening and closing cracks which potentially intersect the anchor location. In reality, cyclic load and cyclic crack phenomena act on anchors simultaneously; however, seismic tests in laboratories are carried out with either one of the two parameters kept constant. To investigate the effect of simultaneous load and crack cycling on anchor behavior, experimental tests with synchronized load and crack cycling protocols on headed bolts cast in special concrete specimens were carried out. The test results demonstrate that the anchor displacement depends on the phasing of load and crack cycling, and justify the reduction of the constant anchor load during simulated cyclic crack tests to compensate for disregarded load cycling effects. The influence of various phase lags and different frequencies on the relative anchor displacement is described by an analytical model based on the integrated cumulative damage regime.