Seismic Rehabilitation of Existing Buildings

Effect of cross-sectional aspect ratio on the strength of CFRP-confined rectangular concrete columns

Unified stress–strain model of concrete for FRP-confined columns

An important application of fiber-reinforced polymer (FRP) composites is as a confining material for concrete, both in the seismic retrofit of existing reinforced concrete columns and in the construction of concrete-filled FRP tubes as earthquake-resistant columns in new construction. The reliable design of these structural members against earthquake-induced forces necessitates a clear understanding of the stress-strain behavior of FRP-confined concrete under load cycles. This paper presents the results of an experimental study on the behavior of FRP-confined normal- and high-strength concrete under axial compression. A total of 24 aramid and carbon FRP-confined concrete cylinders with different concrete strengths and FRP jacket thicknesses were tested under monotonic and cyclic loading. Examination of the test results has led to a number of significant conclusions in regards to both the trend and ultimate condition of the axial stress-strain behavior of FRP-confined concrete. These results are presented, and a discussion is provided on the influence of the main test parameters in the observed behaviors. The results are also compared with two existing cyclic axial stress-strain models for FRP-confined concrete.

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/76703/3/hdl_76703.pdf

Behavior of FRP-Confined Normal- and High-Strength Concrete under Cyclic Axial Compression

This paper presents an experimental investigation on the effect of concrete compressive strength and confinement method on confined high and ultra high-strength concrete (HSC and UHSC) specimens. A total of 55 fiber reinforced polymer (FRP) confined concrete specimens were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and confined by carbon FRP (CFRP). Three different concrete mixes were examined, with average compressive strengths of 35, 65 and 100 MPa. The effect of the confinement method was also examined with FRP-wrapped specimens compared to FRP tube-encased specimens. Axial and lateral behavior was recorded to observe the axial stress–strain relationship and lateral strain behavior for concentric compression. Ultimate axial and lateral conditions are tabulated and the complete stress–strain curves have been provided. The experimental results presented in this paper provide a performance comparison between FRP-confined conventional normal-strength concrete (NSC) and the lesser understood area of FRP-confined HSC and UHSC. The results of this experimental study clearly indicate that above a certain confinement threshold, FRP-confined HSC and UHSC exhibits highly ductile behavior, however for the same normalized confinement pressures, axial performance of FRP-confined concrete reduces as concrete strength increases. The results also indicate that ultimate conditions of FRP-wrapped specimens are similar to those confined by FRP tubes, however a performance difference is evident at the transition region. The performance of 10 existing stress–strain models were assessed against the experimental datasets and the performance of these models discussed. The results of this model assessment revealed the need for further development for stress–strain models developed specifically for FRP-confined HSC or UHSC.

/pdf/influence-of-concrete-strength-and-confinement-method-on-3hbyyi9448.pdf

Influence of concrete strength and confinement method on axial compressive behavior of FRP confined high- and ultra high-strength concrete

In this study, 68 reinforced concrete columns were tested under uniaxial compression after being jacketed externally with carbon fiber-reinforced polymer (CFRP) sheets. Forty specimens were cast using low strength concrete and inadequate internal transverse reinforcement, while 28 specimens were cast with medium strength concrete and adequate internal transverse reinforcement. Thickness of the CFRP jacket, cross-section shape, concrete strength, amount of internal transverse reinforcement, corner radius, existence of predamage, loading type (monotonic or cyclic), and the bonding pattern (orientation, spacing, anchorage details, additional corner supports) of CFRP sheets were the main test parameters of this extensive experimental work. Test results showed that external confinement of columns with CFRP sheets resulted in an increase in ultimate strength and ductility. While the strength enhancement was more pronounced for specimens with circular cross section, specimens with square and rectangular cross sections exhibited larger ultimate axial deformations without a substantial loss in strength. The efficiency of retrofitting was much more pronounced in the case of relatively lower strength concrete. The proposed model, together with two other available models, were used for predicting the strength and corresponding axial deformations of more than 300 specimens tested by other researchers, as well as more than 100 specimens tested by the writers during this study and before. It was shown that the predicted results by the proposed model were in reasonable agreement with this extensive database of experimental studies.

FRP Retrofit of Low and Medium Strength Circular and Rectangular Reinforced Concrete Columns

Failures of structures during the October 23, 2011 Tabanlı (Van) and November 9, 2011 Edremit (Van) earthquakes in Turkey

The objective of this study is to investigate the seismic performance of reinforced concrete columns constructed with low quality of concrete and insufficient transverse reinforcement before and after retrofitting. Totally twenty nearly full size specimens with rectangular cross-section were tested under constant axial load and reversed cyclic lateral loads. Both longitudinal and transverse reinforcements were plain bars. Ten of the specimens had insufficient lap splice length of longitudinal reinforcement between stories as well. Both pre-damaged and undamaged columns with these deficiencies were retrofitted with FRP (fiber reinforced polymer) composite jackets or prefabricated HPFRCC (high performance fiber reinforced cementitious composite) panels. The test results showed that all reference specimens, which were not retrofitted, failed with a premature loss of performance either due to buckling of longitudinal reinforcement or loss of bond, while retrofitted ones exhibited a significantly superior perf...

Seismic Retrofit of Brittle and Low Strength RC Columns Using Fiber Reinforced Polymer and Cementitious Composites

Fifteen RC columns and one plain concrete column with inadequate transverse reinforcement were tested under uniaxial compression after being jacketed externally with carbon fiber reinforced polymer (CFRP) sheets. CFRP layer thickness, cross-section shapes and concrete strength were the test parameters. External confinement of columns with CFRP sheets resulted in an increase in the strength and ductility. The behavior of the CFRP jacketed columns was also predicted by the proposed stress-strain model. There was reasonable agreement between analytical behavior and experimental data.

Axial behavior of rc columns retrofitted with frp composites

Brittle behavior of substandard columns during earthquakes is among the most common reasons of structural failures. Because capacity design principles and ductile detailing concepts have no...

Cem Demir

Papers

FRP Retrofit of Low and Medium Strength Circular and Rectangular Reinforced Concrete Columns

Failures of structures during the October 23, 2011 Tabanlı (Van) and November 9, 2011 Edremit (Van) earthquakes in Turkey

Seismic Retrofit of Brittle and Low Strength RC Columns Using Fiber Reinforced Polymer and Cementitious Composites

Axial behavior of rc columns retrofitted with frp composites

Seismic Retrofit of Full-Scale Substandard Extended Rectangular RC Columns through CFRP Jacketing: Test Results and Design Recommendations