Large Rupture Strain Research Articles

Experimental investigation on the dynamic mechanical response of polyethylene terephthalate fiber-reinforced polymer confined pre-flawed concrete under impact loading

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) is expected to remarkably improve the impact resistance and bearing capacity of reinforced concrete due to its excellent mechanical characteristics of large rupture strain. The dynamic mechanical properties and damage evolution characteristics of internal pre-flawed concrete confined with the different layers of PET FRP are studied by adopting a split Hopkinson pressure bar (SHPB) apparatus at a large strain rate range of 83 s−1 to 503 s−1. It was found that damage to the specimens was strictly restricted by the PET FRP jacket, while the corresponding responses of the unconfined specimens were closely related to the strain rate. Some linear correlations can also be outlined between dynamic mechanical properties (e.g., dynamic compressive strength, toughness, and ultimate compressive strain) and strain rate, as well as the layers of PET FRP. To investigate the damage evolution characteristics further, the specimens confined with PET FRP were subjected to SHPB multiple impacts under the same launch energy level. In addition, the impact times of SHPB do affect the dynamic properties of the PET FRP-confined specimens. A linear relation holds for the ultimate compressive strain, while the effect of impact times on the strength decaying factor tends to increase and decrease at relatively low impact energies.

Experimental study on the mechanical properties of corroded RC columns repaired with large rupture strain FRP

This paper presents experimental results of the mechanical properties of corroded reinforced concrete (RC) columns repaired with large rupture strain (LRS) fiber-reinforced polymer (FRP). This work seeks to evaluate the effects of corrosion-induced damage, including concrete cracks and rebar buckling, on the confinement effectiveness of LRS-FRP. A total of sixteen RC columns were corroded to different extents by an electrochemical method and then repaired by wrapping them with FRP. A series of monotonic axial compression tests were conducted on these repaired specimens that were characterized by their corrosion conditions and FRP confinement rigidities. The test results show that LRS-FRP confinement effectively enhanced the mechanical properties of corroded RC columns. However, the existence of corrosion weakened the rebar cross-sections and further damaged the confined inner concrete, significantly influencing the compressive strength and ductility of the repaired RC columns. In addition, rebar buckling was more pronounced at higher corrosion rates, which affected the hoop strain distribution of the FRP and further reduced its confinement effectiveness. The existing ultimate condition models for confined concrete are also validated by the current test results, indicating that satisfied predictions can be made as the corrosion effects on confinement effectiveness are properly considered in these models.

Compressive behavior of double-skin tubular stub columns with recycled aggregate concrete and a PET FRP jacket

This paper presents an experimental study on the compressive behavior of hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular stub columns (DSTSCs) with recycled aggregate concrete (RAC) and a polyethylene terephthalate (PET) FRP jacket. RAC is a green, sustainable alternative to natural aggregate concrete (NAC), while its mechanical properties are generally inferior to NAC. Polyethylene terephthalate (PET) FRP is manufactured from recycled plastics and has a large rupture strain (LRS) value of more than 7% compared to pure polyethylene FRP. In this study, a total of 20 DSTSC specimens were tested under axial compression. The main parameters studied were the RAC replacement percent (0, 50 and 100%), the FRP jacket thickness, and steel tube thicknesses (3 and 5 mm). Test results indicated that the compressive behavior of DSTSC specimens with RAC and PET FRP is similar to that of specimens with NAC and PET FRP, and both types of columns exhibit highly ductile compressive behavior. It is also observed that the compressive behavior of DSTSCs is primarily influenced by the confinement stiffness of the FRP jacket and the steel tube, and the replacement percent of RAC has marginal effect. The increase of the FRP jacket or steel tube stiffness can counterbalance the replacement percent effect of RAC on the axial compressive behavior of DSTSCs. Finally, the suitability of the existing ultimate condition models of different types of DSTSCs was investigated based on the experimental results of this study.

Durability assessment of PEN/PET FRP composites based on accelerated aging in alkaline solution/seawater with different temperatures

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, including polyethylene naphthalate (PEN) FRP and polyethylene terephthalate (PET) FRP composites, have become increasing popular in civil construction. PET FRP and PEN FRP can be recyclable and thus they are environmentally friendly. However, the durability of LRS FRP composites under extreme environmental conditions (e.g., marine environment and high temperature) has not been understood. To this end, durability tests on 282 LRS FRP sheets after aging in alkaline/seawater solution with different temperatures (25℃, 40℃, 60℃) were conducted in this study. The microstructure of PEN FRP sheets was also analyzed using scanning electron microscope (SEM). The results show that the changes of the elastic modulus of the first linear portion and the elastic modulus of the second linear portion of PEN FRP sheets after aging in different aging temperatures are slight. For PEN FRP sheets with an aging period of 365 days in 60 °C solutions, the degradation rate of the tensile strength is around 10% for both alkaline (pH = 13.2) and seawater solutions, and the degradation rate of the tensile rupture strain is around 12.5%. Additionally, under a higher exposure temperature, there is a significant decrease in the tensile strength of LRS FRP composites. Furthermore, it shows that the durability of PEN FRP sheets was significantly affected in the alkaline environment compared to that in the seawater environment, and the alkaline resistance of PEN FRP composites is better than that of PET FRP composites.

Large-rupture-strain (LRS) FRP-confined concrete in square stub columns: Effects of specimen size and assessments of existing models

As an environmental-friendly material with high rupture strain capacity, polyethylene terephthalate (PET) fiber reinforced polymer (FRP) has promising industry applications. Previous studies mainly focused on the application of PET FRP-confined concrete in circular columns, while investigations on PET FRP-confined concrete in square columns are rather limited. The purpose of this study is to fundamentally understand the confinement mechanism of PET FRP-confinede concrete in square stub columns by conducting axial compression tests. Particularly, the influences of confinement thickness, corner radius and specimen size were investigated. Test results reveal that the specimen size is not significant for small- and medium-sized stub columns with a similar confinement level. The minimum confinement stiffness ratio and modified confinement ratio for achieving a sufficient confinement are 0.0036 and 0.13 respectively. Additionally, assessments of existing confinement models for PET FRP-confined concrete are conducted.

Flexural behavior of RC beams externally bonded with polyethylene terephthalate (PET) fiber reinforced polymer (FRP) laminates

This paper presents an experimental study on the flexural behavior of reinforced concrete (RC) beams externally strengthened with a unique and sustainable type of fiber reinforced polymer (FRP), named polyethylene terephthalate (PET). Compared to conventional FRPs, PET-FRP is characterized by its large rupture strain and low elastic modulus. The flexural behavior of RC beams strengthened with one and two layers of PET-FRP was compared to that strengthened with one carbon FRP (CFRP) layer and an unstrengthened beam specimen. Test results showed that the specimens strengthened with two PET-FRP layers and one CFRP layer displayed equal and significant strength enhancement of 47% compared to the unstrengthened beam. However, the former exhibited higher ductility than the latter by 33%. Lower strength enhancement was depicted in the specimen strengthened with one PET-FRP layer. Despite that, the ductility of the PET-strengthened beam was substantial, which even outweighed that of the unstrengthened beam by 9%. The results of this study showed that PET-FRP is a promising strengthening material that improves structural performance and provides a sustainable alternative to conventional FRP strengthening systems.

A unified stress-strain model for LRS FRP-confined concrete columns with square and circular cross-sections

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites with an ultimate elongation of greater than 5% offer superior deformation and energy dissipation abilities over traditional carbon or glass FRP when used them in lateral confinement of concrete under the same confinement level. However, a flexible model for predicting the stress-strain relationship of concrete columns confined with LRS FRP is not yet perfectly developed, especially for noncircular columns experiencing nonuniform confining stress. Accordingly, an extensive database of LRS FRP-confined square and circular concrete columns with corner radius ratios varying from 0 to 1 was employed to establish a unified stress-strain model. This model not only includes the determinations of key points, but also attempts to define the threshold confinement level to distinguish the post-peak strain-hardening and strain-softening behaviors. The mathematical expression of the model is simple; it also avoids discontinuities in the prediction of different cross-sections. The proposed model is verified to be accurate in predicting the complete stress-strain curves of LRS FRP-confined square and circular concrete columns with hardening and softening behaviors. In addition, it outperforms the existing theoretical models in predicting the ultimate strength and the ultimate axial strain.

FE modeling of Non-circular LRS FRP-confined concrete columns

In concrete columns confined with large rupture strain (LRS) fiber-reinforced polymers (FRPs), the LRS FRPs enhance the strength and ductility of concrete columns with the same mechanism as conventional FRPs by rendering passive lateral confinement pressure. However, LRS FRPs exhibit a strain capacity much larger than that of conventional FRPs. Notably, LRS FRPs have a bilinear material stiffness instead of the linear stiffness in conventional FRPs. Therefore, under axial compression, concrete confined by LRS FRPs will bear a different load path compared to that confined by conventional FRPs. This difference must be considered for finite element analysis (FEA) of LRS FRP-confined columns especially when the confinement pressure is non-uniform. To this aim, 23 samples of non-circular LRS FRP-confined concrete columns under axial monotonic compression were tested and analyzed. The variable test parameters are the aspect ratio (i.e., the depth (longer side) and width (shorter side) of the cross-sections）, the number of LRS FRP layers, and the type of LRS FRPs. For FEA, the concrete damage plasticity module (CDPM) was calibrated by both the active confinement pressure approach and the confinement stiffness approach. The active confinement pressure approach shows that the concrete plastic flow of LRS FRP-confined concrete is dominated by the secondary stiffness of the LRS FRP jacket. For the confinement stiffness approach, the concrete plastic flow is deduced from the compressive cyclic tests of cylindrical columns confined by LRS FRP jackets as a function of confinement stiffness. Results showed that the plastic dilation angle of concrete confined by LRS FRPs changes almost three times faster than that for concrete confined by conventional FRPs. The geometrical effects are included in the obtained plastic dilation angle so that a new plastic dilation angle model becomes feasible for the FEA of non-circular LRS FRP-confined concrete columns. Utilizing this new plastic dilation angle model enables the proposed plastic damage model to capture the stress strain behavior of the non-circular columns. Moreover, the non-uniformity of plastic flow on sections is captured reasonably.

Performance of RC beams externally strengthened with hybrid CFRP and PET-FRP laminates

The use of fiber-reinforced polymers (FRP) composite materials in strengthening applications of reinforced concrete (RC) structures has been gaining wide popularity in recent decades. This is due to its superior properties such as high strength to weight ratio, durability, and versatility. In fact, it is well established that bonding FRP materials to the soffit of RC beams enhances the flexural capacity of such beams. However, the non-yielding characteristic of FRP materials is a major concern, and often results in sudden and brittle failure mode of the strengthened member. To encounter this issue, a new type of FRP materials composed from polyethylene terephthalate (PET) fibers have been developed. Compared to conventional FRPs, PET-FRP have large deformability and possess a nonlinear stress-strain relationship. Employing PET-FRP in the retrofitting industry reduces construction waste, enhances the capacity of structures and provides a solution that encourages the concept of sustainability. However, these types of large rupture strain (LRS) FRPs have lower stiffness and tensile strengths than conventional FRPs. Therefore, the main aim of this study is to combine the lower stiffness and large rupture strain of PET-FRP sheets with that of the higher stiffness and strength of carbon FRP (CFRP) sheets resulting in a new hybrid composite system. The research program consists of four RC beams externally strengthened with CFRP, PET-FRP, and their hybrid combinations, in addition to a control unstrengthened beam specimen. The beams are tested under four-point bending and load-displacement curves along with the failure modes, strength, strain in the FRP, and ductility of the beam specimens are examined. Test results indicate that strengthening with PET-FRP laminates significantly enhances the deformation capacity of the strengthened specimens compared to that with CFRP. In addition, the hybrid mix between CFRP and PET-FRPs resulted in 46-48% strength improvement compared to the unstrengthened control beam. However, the effectiveness of the hybrid system was not pronounced in terms of ductility due to the premature debonding of the concrete cover that occurred before utilizing the full strain of the hybrid system. Hence, it is advised for future research studies to anchor the hybrid sheets by means of end U-wraps or FRP spike anchors to delay the debonding failure and to exploit the benefits of the proposed hybrid system.

Simplified plasticity damage model for large rupture strain (LRS) FRP-confined concrete

Large rupture strain (LRS) fiber-reinforced polymers (FRP) composites with an elongation greater than 5% offer an attractive solution for seismic strengthening of reinforced concrete (RC) columns. For a quick and reliable design of LRS FRP-strengthened RC columns, this paper presents a simplified plasticity damage model for LRS FRP-confined concrete under cyclic axial compression. This model consists of two parts: (a) a recent monotonic LRS FRP-confined concrete model developed by the authors’ group as an envelope curve and (b) a simplified linear plasticity damage cyclic rule for predicting unloading and reloading paths. To solve the cyclic model deviation induced by concrete softening under a large axial strain, a pseudo-plastic strain was proposed, based on which the damage degradation of FRP-confined concrete can be quantified. The model comparisons show that although the proposed model sacrificed some precision when directly applied for the cyclic axial compressive behavior of FRP-confined concrete, it can give similarly accurate predictions as a complex model does for the behavior of conventional or LRS FRP-jacketed RC columns under a combined axial load and cyclic lateral load. Thus, this simplified plasticity damage model serves as a promising basic model for simulation of the seismic performance of FRP-strengthened structures.

Confinement model for LRS FRP-confined concrete using conventional regression and artificial neural network techniques

Concrete confined using fiber-reinforced polymer (FRP) composites experience significant enhancements in strength and strain. For the seismic retrofitting of existing reinforced concrete (RC) structures, a large rupture strain (LRS) FRP (i.e., polyethylene terephthalate and naphthalate, denoted as PET and PEN respectively), with a larger rupture strain of more than 5%, is a promising alternative to conventional FRPs with a rupture strain of less than 3%. The majority of analytical models on the stress–strain behavior of FRP-confined concrete under axial compression have focused largely on concrete confined with the traditional FRP material. Analytical research on LRS FRP-confined concrete is, however, limited. Moreover, all existed stress–strain models were determined based on theoretical analysis and test data fitting. In this paper, the artificial neural networks (ANN) method is employed to build a confinement model directly from experimental data to predict the different components of the stress–strain response. A test database consisting of 226 axial compression tests on LRS FRP-confined concrete specimens is used. The test results, in terms of full confined stress–strain response, strength, strain, FRP rupture strain, and dilation response were investigated. Predictive expressions and practical ANN models for the strength, strain, and shape of an axial stress–strain response are provided. Existing models for LRS FRP-confined concrete were also evaluated. The results of the existing and proposed models report that the proposed methods achieve significantly better results.

Axial impact behavior of Large-Rupture-Strain (LRS) fiber reinforced polymer (FRP)-confined concrete cylinders

This paper presents an experimental study on the impact performance of concrete columns confined with large-rupture-strain (LRS, tensile rupture strain ≥ 5%) fiber reinforced polymer (FRP) jackets. A total of 32 concrete specimens were prepared and tested using large-capacity drop-weight equipment. The test variables included four impact heights (2, 3, 4 and 5 m), three types of FRP, i.e., aramid FRP (AFRP), polyethylene naphthalate (PEN) FRP and polyethylene terephthalate (PET) FRP and two layers of FRP jackets (1 and 2). The time histories of impact force and FRP rupture strain as well as failure modes were obtained from the test. Compared to the AFRP-confined concrete specimen with similar jacket stiffness, the core concrete of the LRS FRP-confined specimen was less damaged due to the large-rupture-strain characteristic. The impact force increased and the impact duration decreased with increasing impact height. The impact duration of concrete specimens confined with LRS FRP was longer than that of the AFRP-confined concrete column. Results showed that the impact-resistance behaviours of LRS FRP-confined concrete column outperformed its companion column confined with AFRP. Besides, increasing the thickness of FRP jacket can enhance the impact resistance capacity. These findings may facilitate the impact resistance strengthening/retrofitting of RC structures with the application of LRS FRP composites.

Comparison of monotonic axial compressive behavior of rectangular concrete confined by FRP with different rupture strains

Axial compressive behavior of rectangular concrete might differ greatly when it is confined by fiber reinforced polymer (FRP) with different rupture strains. To address this issue, this study experimentally investigated and compared the monotonic axial compressive behavior of rectangular concrete confined by FRP with three rupture strains. Axial compression experiments of 28 rectangular concrete stub columns confined by FRP were carried out. The FRP utilized in this study included conventional FRP with small rupture strain, i.e., carbon FRP (CFRP) and glass FRP (GFRP), and large rupture strain FRP (LRS-FRP), i.e., polyethylene terephthalate (PET) FRP. The key test parameters were the rupture strain of FRP, the FRP thickness, and the cross-sectional aspect ratio. Failure modes, stress vs. strain behavior, axial stress and strain relationship, hoop rupture strain, the effect of FRP confinement stiffness ratio, and the effect of cross-sectional aspect ratio were analyzed, respectively. Results of this research showed that the rupture strain of FRP exhibited significant influence on the failure mode and the axial deformation of rectangular concrete confined by FRP. FRP strain reduction factors were decreased with the increasing rupture strains of FRP. This is because the rectangular concrete confined by FRP with larger rupture strains dilated more non-uniformly than its counterpart using smaller rupture strain FRP. In addition, based on the transition point and the ultimate condition, the axial stress vs. strain curves of rectangular concrete confined by FRP could be categorized into three types, including sufficient, moderate, and insufficient FRP confinement, respectively.

An Innovative Tubular Standing Support Incorporating PVC and FRP Composites: Laboratory Tests

The importance of developing innovative support structure for underground mines has drawn much attention with the depletion of shallow resources. This paper presents a hybrid tubular standing support consisting of an exterior container made of the polyvinyl chloride (PVC) and fibre-reinforced polymer (FRP) while the infill is the coal rejects based backfill material. The FRP jacket featured with the high strength-to-weight ratio is attached on the exterior surface of the PVC tube with the large rupture strain to provide confinement to infilled backfill material. A series of laboratory tests were conducted on this FRP-PVC tubular standing support (FPTSS) with different FRP thickness. Meanwhile, the FRP tubular standing support and the PVC tubular standing support with the sole confining material were also prepared and tested. Tests results showed that the FPTSS specimen exhibited the typical strain hardening behaviour attributed to the effective confinement provided by the combined container. It is also indicated that the enhancement of either the compressive strength or the axial deformation ability is closely related to FRP thickness. The other comparative advantage of FPTSS obtained from this research is its ductile post-peak behaviour after the rupture of the exterior FRP jacket, indicating the importance of using PVC tube in FPTSS. Except for its superior compressive behaviour, the cost effectiveness and ease of construction of FPTSS are also attractive from the design aspect.

Mechanical behavior of large-rupture-strain (LRS) polyethylene naphthalene fiber bundles at different strain rates and temperatures

This paper presents the results of an experimental study aimed at investigating the effects of strain rate and temperature on the tensile mechanical properties of polyethylene naphthalene (PEN) fiber bundles by using a drop-weight impact system. A total of 65 specimens with a gauge length of 25 mm were prepared and tested. The test variables included five different strain rates (1/600, 40, 80, 120 and 160 s−1) and five different temperatures (−50, −25, 0, 25 and 50 °C). The results indicated that the tensile strengths and elastic moduli of the specimens increased with the strain rate, whereas the failure strain decreased and the toughness remained almost unchanged with the increase of the strain rate. The tensile strength, toughness and failure strain initially improved and then reduced with an increasing temperature from − 50 °C to 50 °C. A Weibull distribution model was implemented to describe the degree of variability in the tensile strength of PEN fiber bundles for future use.

Compressive behavior and modelling of engineered cementitious composite (ECC) confined with LRS FRP and conventional FRP

A combination of core engineered cementitious composite (ECC) and external fiber-reinforced polymer (FRP) composites can solve the problems of insufficient ductility and durability of normal concrete (NC) in adverse environments and improve bearing capacity. However, existing studies on the performance of ECC strengthened by FRP are very limited—particularly the research on large rupture strain (LRS) FRP-confined ECC. In this study, an experimental investigation of LRS FRP and conventional glass FRP-confined ECC cylinders with different confinement levels under axial compression is presented. It is found that the application of external FRP jackets leads to a significant improvement in the compressive strength and deformation of the core ECC. LRS FRP-confined ECC exhibits a higher ultimate deformation than conventional FRP-confined ECC. The dilation behavior, axial stress–strain behavior, and energy dissipation capacity between FRP-confined ECC and FRP-confined NC under the same confinement level are compared, and the former exhibits a significantly larger ductility and energy dissipation capacity than the latter. The results also indicate that most existing models are unable to accurately predict the compressive behavior of FRP-confined ECC. To address this, a dilation model and an axial stress–strain model of FRP-confined NC are modified to extend their application to FRP-confined ECC.

Rate-dependent compressive behavior of concrete confined with Large-Rupture-Strain (LRS) FRP

The polyethylene naphthalene (PEN) and polyethylene terephthalate (PET) fibers have a tensile rupture strain of over 5%, and hence they are referred to as large-rupture-strain (LRS) fiber reinforced polymer (FRP) materials. Their large rupture strain characteristics may contribute to significant improvement of the impact resistance of reinforced concrete (RC) structures. This study investigates the strain rate effect on LRS FRP-confined concrete through Split Hopkinson Pressure Bar (SHPB) test. Results revealed that LRS FRP-confined concrete specimens exhibited superior impact resistance behaviors compared to the counterpart confined with CFRP composites when subjected to a single impact. The critical strain, compressive strength and toughness of the LRS FRP-confined concrete specimen increased with increasing strain rate. Due to the large rupture strain characteristics, the LRS FRP-confined concrete specimen virtually had no visible damage after a single impact. To study the damage evolution mechanism of concrete, the specimens were impacted for multiple times with the same energy until the failure of the specimen. Due to progressive concrete damage, the dynamic compressive strength and toughness experienced a decrease during multiple impacts. These findings might promote the application of LRS FRP materials in the field of impact resistance design of RC structures as a promising external jacketing material.

Experimental Study on the Confinement of Concrete Cylinders with Large Rupture-Strain FRP Composites

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, typically formed from polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fibers, generally exhibit ultimate rupture strains >5%. Such fibers are particularly suited to the confinement of concrete columns on account of their LRS and sufficient elastic modulus. There are currently a limited number of studies on LRS FRP-confined concrete, particularly with high- and ultrahigh-strength concrete, so their behavior across a range of variables is still unknown. To improve this understanding, this paper systematically investigates the influence of fiber type, fiber thickness, and concrete strength on the behavior of FRP-confined concrete. To achieve this objective, the current investigation presents the results of 66 circular FRP-confined cylinders that are loaded concentrically. Three main parameters are investigated, namely, fiber type (i.e., PEN, PET, carbon, glass, and aramid), concrete strength (i.e., normal, high, and ultrahigh strength), and fiber thickness. The results show that regardless of fiber type, the stress–strain response is bilinear when the concrete is sufficiently confined. However, when there is insufficient confinement provided to the concrete core, the stress–strain response becomes trilinear. This trilinear response is more pronounced for LRS FRP-confined specimens because the confinement stiffness of the LRS FRP jacket is lower than that of a traditional FRP-confined specimen with an equivalent confinement ratio. Increasing the confining hoop stiffness (i.e., increasing FRP layers) reduces the magnitude of strength reduction after initial concrete cracking. It is also evident that as the unconfined concrete strength increases, the minimum confinement stiffness ratio necessary to prevent strength reduction after initial concrete cracking increases.

Seismic Performance of LRS-FRP–Concrete–Steel Tubular Double Coupling Beam

To improve the ductility and seismic performance of a double coupling beam, the authors applied a polyethylene terephthalate (PET) sheet and steel tube to form fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular (DST) composite coupling beams. A low-cyclic reversed experimental program was carried out which factored in the member form, steel tube diameter, and construction methods. The results indicate that the ductility and energy dissipation performance of double coupling beams—whether wrapped with a PET-FRP sheet or surrounded by an FRP–concrete–steel DST composite system—is a substantial improvement over the traditional reinforced-concrete double coupling beam (RC-DCB). The ductility coefficient and accumulated energy dissipation of the DST-DCB members improved above 170% and 2300%, respectively. These percentages compare to the RC-DCB and are based on the rupture of a PET-FRP sheet. The results are similar to those of the large rupture strain double coupling beam (LRS-DCB). Meanwhile, the external wrapped PET-FRP sheet does not affect the initial stiffness and peak strength of the RC-DCB. Relatively, the inner steel tube will improve the initial stiffness, yielding strength, and peak strength. DST-DCB members still have considerable deformability after 85% of peak strength since the external PET-FRP sheet provided an effective constraint effect on the core concrete and the inner steel tube could bear excellent shear deformation.

A hybrid tubular standing support for underground mines: Compressive behaviour

This paper presents the development of an innovative standing support for underground mines. The main feature of this standing support is its exterior container, a combination of polyvinyl chloride (PVC) with large rupture strain and fibre-reinforced polymer (FRP) with high strength-to-weight ratio. To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular (PFT) standing support, a series of compression tests were conducted. Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket. Compression tests were also conducted on cementitious grout-filled PVC tubular (PT) support and cementitious grout-filled FRP tubular (FT) support. These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability (>20% of the overall height of the support). In addition, the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support. Furthermore, using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support. These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents (i.e. PVC and FRP) and infill material.