International Concrete Abstracts Portal

Shape memory alloys (SMAs), with their unique ability to undergo large deformations and recover to their initial shapes through the removal of stress without significant residual strain, have become attractive materials in bridge engineering. In this study, nine samples of bridge piers are reinforced by two types of SMA (NiTi and Cu-Al-Mn) in plastic hinge regions where high-performance fiber-reinforced concrete (HPFRC) is additionally used to enhance the ductility of piers. To investigate the effects of SMAs and HPFRC on seismic performance of concrete bridge piers, 28 near-field ground-motion record pairs are selected. Then, the models are analyzed using the incremental dynamic analysis (IDA) method and fragility curves are derived. The results show that using SMAs leads to the reduction of residual drift. Also, using HPFRC increases the capacity of the models. Furthermore, the model with HPFRC and NiTi shows the best performance in terms of capacity and residual drift reduction.

Confinement enhances mechanical properties of concrete, especially the strain capacity. As a result, confined reinforced concrete (RC) members usually exhibit higher displacement capacities compared to unconfined members. Even though the behavior of concrete confined with external jackets has been extensively investigated in the past, confined properties of polyureajacketed concrete are largely unknown and were investigated in the present study. Thirty concrete cylinders were tested under slow uniaxial compression to investigate mechanical properties of polyurea-confined concrete and to establish stress-strain behavior. It was found that polyurea does not increase the strength of the confined sections under static loads. However, the compressive strain capacity of polyurea-confined concrete is more than 10%, equal to or higher than the reinforcing steel bar tensile strain capacity. Two uniaxial stress-strain models were developed for polyurea-confined concrete with circular sections under static loads. Analytical studies showed that the displacement ductility capacity of low-ductile bridge columns can be doubled using polyurea jackets. This unique property may make this type of confinement a viable retrofit or rehabilitation method to increase the displacement capacity of low-ductile members and structures in seismic regions.

Increasing cases of reinforcement corrosion in reinforced concrete (RC) elements raise serious concerns for achieving desired strength and ductility despite following the relevant seismic guidelines. The present study is an experimental attempt to evaluate the seismic behavior of corroded RC columns and thereby to examine the effectiveness of advanced composite materials in restoring the seismic behavior of such corroded columns. To this end, seven full-scale RC columns were cast and tested. Six column specimens were corroded using a precalibrated, accelerated corrosion regime, while one specimen acted as a control uncorroded column. Columns were corroded at two nominal degrees of corrosion: 10% and 20%. These corroded columns were then tested for evaluating their seismic behavior, while companion columns with the same degree of corrosion were retrofitted. Retrofitting was aimed at restoring the ductility and strength of corroded columns as well as to achieve increased durability against future corrosion. Advanced composite materials such as ultra-high-performance fiber-reinforced concrete (UHPFRC) and glass fiber-reinforced polymer (GFRP) were employed for retrofitting of columns. The results show an alarming reduction in seismic performance of columns due to corrosion of reinforcement. Corroded specimens when retrofitted with only UHPFRC jacket yielded satisfactory recovery of strength and ductility for 10% corrosion but showed insufficient improvement against 20% corrosion. For columns with 20% corrosion, a combination of UHPFRC and two layers of GFRP worked well in improving ductility and strength.

The fracture of longitudinal reinforcing steel causes the loss of load-carrying capacity in reinforced concrete (RC) members. Results of large-scale reverse cyclic column tests have indicated that the fracture of longitudinal reinforcement is influenced by the amount of buckling experienced by the reinforcing steel. Similar behavior was observed in a material test as reinforcing bars fractured in a brittle manner when pulled in tension after buckling. Brittle fracture occurred after the bending strain from buckling exceeded the critical bending strain. A material test was developed to quantify the critical bending strain, called the buckled bar tension test. The rib radius of the reinforcing bar was found to influence the magnitude of the critical bending strain. Additionally, the results of column tests indicated that the critical bending strain of the longitudinal reinforcement affected the column displacement capacity. Finally, a relationship between axial displacement and strain from bending was developed.

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.