International Concrete Abstracts Portal

Axial compression test results for square RC columns incorporation Taiwanese construction practice in the placement of stirrups and various kinds of jacketing schemes are presented. The jacketing schemes include circular, octagonal and square shapes. The jacketing materials vary from stell plate to carbon fiber reinforced polymer (CFRP) COMPOSITES. It is found from the monotonic axial load test results that the failure mode of the benchmark non-retrofitted specimen is identical to that observed in real damage cases subsequent to the 1999 Chi-Chi Taiwan earthquake. The benchmark specimen developed its design strength but a non-ductile failure mode occurred soon after the peak load was reached. Among the retrofitted specimens, the steel jacketed specimens exhibit not only greatly enhanced load carrying capacity but also excellent ductility performance. Test results show that CFRP sheets are effective in increasing the column axial strength, but the sheets could fracture suddenly in high strain conditions due to their brittle material characteristics. Test results indicate that CFRP sheet wrapping in general is not as effective as steel jacketing in improving the axial ductility capacity of RC columsn. However, the proposed octagon-shaped CFRP wrapping scheme exhibits an improved performance compared to rectangular-wrapped columns using the same layers of CFRP sheets. Tests confirm that all octagonal stell or CFRP jacketed specimens have axial load capacities more that 2 time the nominal capacity.

The structural behavior of reinforced concrete framed shear walls subjected to reversed cyclic lateral loading were studied by testing ten large-scale specimens, including high-, middle-, and low-rise shear walls. An analytical model was also proposed to predict the behavior of the tested specimens. The parameters of concrete strength and vertical stell ratio of walls were investigated. The predicted maximum load and corresponding displacement, and load-displacement curves satisfactorily agreed with the experimental results. In addition, the experimental results showed that the failure mode of high-rise shear walls was flexural; their ductility factors were greater than those of low-rise shear walls; their displacements were also greater. The mid-rise shear walls failed by a combination of both flexure and shear. The experimental results also showed that the maximum loads were greater for specimens with higher concrete strength or higher verical stell ratio. The vertical stell ratio of walls has more significant effect on flexure-predominant walls. However, it is insensitive to shear-critical walls. It was found that the simple model develped from previous small-scale tests could not closely reflect the experimental results of all specimens. This suggests that the size effect needs to be taken into account in the analytical model.

Full-scale dynamic tests provide valuable information on the characteristics of building structures that can be used to calibrate finite element models, to rate modeling techniques, to determine damage levels, and to evaluate design and detailing requirements for seismic loading. These tests usually provide the most complete information about the dynamic properties of a structure, I.e., mass, stiffness, and modal damping. In the paper, the dynamic behavior of a two-story reinforced high-performance concrete building is evaluated by repeated pseudo-dynamic tests, during which increasing seismic loads are applied and with resulting greater levels of permanent damage to the structure. In order to monitor the level of damage, a series of successive forced-vibration tests are also carried out at each step of the process and are used to track changes in the key dynamic properties of the building. The paper presents the design of the test structure, the series of forced vibration and pseudo-dynamic tests, the evaluation of the dynamic characteristics of te undamaged structure prior to and after pseudo-dynamic tests, and the evaluation of the damages to the building.

This paper reports on the experimentally and analytically observed behavior of unbounded post-tensioned precast concrete walls under static monotonic and cyclic lateral loads. Results show that the limit states that characterize that lateral load behavior of the walls occur as anticipated in the design of the walls and at force and drift levels predicted by the analytical model, except that the experimentally observed drift capacity exceeds the drift capacity predicted by the analytical model. Cyclic lateral load results how that unbonded post-tensioned precast walls can undergo significant nonlinear lateral drift without significant damage, and can maintain their ability to self-center, thus eliminating residual lateral drift.

This paper explores both flexural and shear behavior of carbon fiber-reinforced polymer (CFRP) strengthened reinforced concrete (RC) beams. For flexural strengthening of RC beams, a total of ten large-scale beams were tested to failure under monotonic and cyclic loads. The beams were originally designed as wither under-reinforced or almost over-reinforced concrete beams. The present experimental results show that externally bonded CFRP strips to the tension face of the beam is an effective technique for repair and retrofit of RC beams under various loads. This study also shows that ductility of CFRP strengthened beams, in particular for a shorter beam, is adequate if the beam is properly designed and the CFRP strips are properly anchored. Five RC beams without shear reinforcement were also cast for studying shear strengthening of RC beams. Results of test demonstrate the feasibility of using externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam, thus restoring beam shear strength using CFRP is also a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed as well.