Compressive Behavior of GFRP Tubes Filled with Self-Compacting Concrete

Abstract

Self-compacting concrete (SCC) features excellent flow ability without the need of vibration for compaction during casting. This makes it particularly suitable for application in hybrid fiber-reinforced polymer (FRP)-concrete–steel double-skin tubular columns (DSTCs), a high-performance structural form evolved from concrete-filled FRP tubes (CFFTs). In a DSTC, the space between the inner steel tube and the outer FRP tube for filling concrete may be narrow and the application of vibration may be difficult. However, because of the large shrinkage of SCC compared to traditional concrete of normal flow ability, the integrity and composite action of DSTCs with SCC become a major concern. To clarify this issue, an understanding of the behavior of CFFTs filled with SCC is an essential prerequisite. While a large number of studies have been published on CFFTs with normal concrete (NC), only limited studies have been carried out on CFFTs with SCC. This paper presents a comprehensive investigation on the effect of SCC on the behavior of large-scale CFFTs. Axial compression tests were carried out on concrete-filled glass FRP (GFRP) tubes with diameters of 150, 200, 300, and 400 mm. The compressive behavior of the CFFT specimens filled with NC, a nonexpansive SCC, and an expansive SCC (ESCC) was compared and discussed. The results showed that the specimens with nonexpansive SCC behaved differently compared to those with NC as a result of larger shrinkage, especially for large specimens for which the confinement level was lower. This situation, however, improved in specimens where ESCC was used. Finally, the test results were further analyzed using a theoretical model recently proposed by the authors’ group. This paper investigates the compressive behavior of glass fiber–reinforced polymer (GFRP) tubes filled with self-compacting concrete (SCC). SCC is a type of concrete featuring excellent flow ability and larger shrinkage than normal concrete (NC). The detrimental effect of shrinkage can be counterbalanced by using expansive cement to form expansive SCC (ESCC). Compression tests were conducted on SCC-, NC-, and ESCC-filled GFRP tubes. Their compressive behavior was compared and analyzed. It was found that the NC- and ESCC-filled specimens behaved similarly, while the SCC-filled specimens showed a stronger dilation tendency under axial compression and less satisfactory performance than their NC- and ESCC-filled counterparts when the confinement level was relatively weak. Therefore, the use of an appropriate amount of expansive cement or a strong level of confinement is recommended when SCC is used as the concrete infill in practical confinement applications. The findings of this study are useful for applications of SCC in composite columns, especially in situations where only a narrow space is available for concrete casting, such as casting composite columns with a narrow ring section.