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The Qiqi structure design can automatically upset and spill its content once it arrives at limit capacity under vertical water flow excitation. Considering this function, the Qiqi structure has been utilized for small hydroelectric energy harvesting lately. To investigate the tradeoff between the Qiqi structure and the turbine structure for small hydroelectric energy harvesting, an energy harvester based on a hybrid Qiqi and turbine structure is proposed for vertical water flow hydroelectric applications. The hybrid structure is composed of a rectangular Qiqi structure, with two blades inserted on both sides. Self-tipping function of the hybrid Qiqi structure and working principle of the structure is investigated in detail. The proposed structure has both the advantages of low flow velocity energy harvesting of the Qiqi structure and high flow velocity energy harvesting of the turbine structure. A hydroelectric energy harvesting application using the hybrid structure is given to demonstrate that the hybrid structure had a higher rotational speed than the Qiqi structure under vertical low water flow excitation and was able to work at relatively high flow rates. Thus, the investigated hybrid structure can help small rotational hydropower achieve better energy harvesting performance and work at wide-range flow rates under vertical ultra-low water flow applications. At 600 mL/min, 902 μJ of electrical energy was charged by the investigated structure, which is six times higher than that using the Qiqi structure alone.

Rebar corrosion destroys the bond interface between concrete and the original rebar and, thus, affects their collaborative performance. External confinement, such as a concrete cover or fiber reinforced polymer (FRP) jackets, is a promising method to solve this problem since both can improve the bond properties between corroded rebars and concrete. However, existing tests results have shown the expected bond performance between rebars and its external concrete surroundings to be unstable for corrosion condition, and much of the bond strength data of corroded specimens is highly discrete. Traditional test methods such as cutting specimen are difficult to explain the instability of bonding phenomenon since it likely to destroy the rebar’s bonding interface during processing the specimen. In this study, X-ray microcomputed tomography (X-ray μCT), a new type of non-destructive testing method, was adopted to scan the inside of the corroded specimens and perform a three-dimensional reconstruction enabling a complete understanding of corrosion development. This paper also presents a thorough research analysis that focuses on the effects of variation in corrosion rates as well as the thickness of the concrete cover and FRP layers on the distribution of rust products and the volume change of rust products on the bond interface. Test results indicate that the distribution of corrosion products in 2D/3D is directly related to the location of cracks in the concrete cover, and increasing confinement (concrete cover thickness, FRP layer number) leads to a more uniform distribution of corrosion products. In addition, by using X-ray μCT, the “hollow volume,” defined as the volume between the surface of the uncorroded steel bar and the inside of the concrete cover, could be accurately obtained. Most importantly, this hollow volume was found to be the main factor affecting the bond performance of corroded reinforced concrete.

The development of cloud computing and big data results in a large amount of data transmitting and storing. In order to protect sensitive data from leakage and unauthorized access, many cryptographic file systems are proposed to transparently encrypt file contents before storing them on storage devices, such as eCryptfs. However, the time-consuming encryption operations cause serious performance degradation. We found that compared with non-crypto file system EXT4, the performance slowdown could be up to 58.53 and 86.89 percent respectively for read and write with eCryptfs. Although prior work has proposed techniques to improve the efficiency of cryptographic file system through computation acceleration, no solution focused on the inefficiency working flow, which is demonstrated to be a major factor affecting system performance. To address this open problem, we present NV-eCryptfs, an asynchronous software stack for eCryptfs, which utilizes NVM as a fast storage tier on top of slower block devices to fully parallelize encryption and data I/O. We design an efficient NVM management scheme to support the fast parallel cryptographic operations. Besides providing an address space that can be directly accessed by the hardware accelerators, our designed mechanism is able to record the memory allocation states, and supplies a backup plan to deal with the situation of NVM shortage. The additional index structure is built to accelerate lookup operations to determine if a given data block resides in NVM. Moreover, we integrate an adaptive scheduling in NV-eCryptfs to process I/O requests dynamically according to access pattern and request size, which is able to take full utilization of both software and hardware acceleration to boost crypto performance. Our evaluation shows the proposed NV-eCryptfs outperforms the original eCryptfs with software routine 23.41× and 5.82× respectively for read and write. This work is supported by National Natural Science Foundation of China: No.61502061, Chongqing application foundation and research in cutting-edge technologies: No. cstc2015jcyjA40016, the fundamental research funds for the central universities: 106112017CDJXY180004, and also the financial support from the program of China Scholarships Council No.201706055029.

Ultra-lightweight cement composite (ULCC) has low densities of less than 1400 kg/m3 with a compressive strength up to 60 MPa, making them ideal for use in structures where material weight is critical. However, these applications were limited by its brittleness and low ductility. Wrapping ULCC with fiber reinforced polymer (FRP) can enhance its ultimate strain and compressive strength. This premier study and model of FRP-confined ULCC under axial compression tested 21 FRP-confined ULCC cylinders. Strength and FRP thickness were the primary variables. Test results indicated that the bearing capacity and ductility of ULCC are considerably improved by FRP jackets, which is similar to FRP-confined normal concrete (NC). It also is shown that the lateral dilation behavior of FRP-confined ULCC differs significantly from that of FRP-confined NC because the former has lower elastic modulus and more brittle feature than the latter; this difference reveals the post-peak strain hardening-softening mechanism of confined concrete. In addition, this paper introduces a new strength model with an improved stress-strain relationship for FRP-confined ULCC columns. Compared with the existing models, the proposed model can predict the stress-strain behavior of FRP-confined ULCC with better accuracy.

Most existing stress-strain models for fiber reinforced polymer (FRP) confined concrete are applicable to monotonic loading or complete cyclic loading where unloading/reloading is a continuous process between envelope curve and zero stress. However, load cycling is mostly incomplete or partial in practical problems where reverse of loading occurs before the previous load cycle is completed, and this unloading and reloading process is random. Cyclic model allowing for random partial load cycling is rare, if any, due to the lack of experimental data, and the insufficient understanding on the behavior of confined concrete under partial cyclic loading. In this study, FRP confined concrete cylinders were tested under six typical cyclic load patterns. The test results reveal that the partial cyclic stress-strain behavior is different from that under full cyclic loading. The key parameters determining unloading/reloading curves, such as reloading modulus, plastic strain, and tangent unloading modulus are related to loading history and axial stress level. It is found that the key parameters will change, or accumulative damage to concrete will occur, only under certain condition which is defined as effective partial cyclic loading in this work. A simple method is proposed to define the effective partial cyclic loading. Based on an existing complete cyclic model, a stress-strain model for FRP confined concrete under random partial cyclic loading is developed in this work. The proposed model performs well under different load patterns.

Concrete production using recycled aggregates (RAs) from construction and demolition waste is known to have a lower strength performance than natural aggregate concrete. Many studies have been carried out to improve the strength properties of recycled aggregate concrete (RAC). One widely accepted strategy is to use fiber-reinforced polymer (FRP) jackets as external confinement material to enhance the compressive strength and ductility performance of RAC, especially in the seismic retrofit of RAC members. Most existing research has focused on normal strength concrete subjected to monotonic loading. However, retrofitting or repair work is more common for concrete structures with low concrete strength. In addition, cyclic behavior research focused on FRP-confined low-strength RAC is also rare due to the lack of sufficient experimental data. In this study, 29 concrete specimens were cast using varying proportions of RAs mixed with natural coarse aggregates. In this case, poor quality natural aggregates were selected to achieve a low concrete strength. Thickness of the carbon FRP (CFRP) jacket, loading types (monotonic or cyclic), and the RAs replacement ratio were the main test parameters of this experimental work. The mechanical properties of CFRP-confined RAC were analyzed and discussed from the failure mode perspective; these included peak strength, ultimate strain, and cyclic stress-strain relationships. Test results show that strength enhancement by FRP confinement was much more pronounced in lower strength RAC than in normal strength concrete, whereas the ductility improvement was almost consistent. Confinement rigidity and recycled aggregate replacement ratio had little effect on cyclic stress-strain behavior, in terms of unloading and reloading paths, as well as in plastic strain. The adhered cement mortar on RAs weakened the impact brought by confinement when repeated unloading and reloading were applied. This was especially true during cyclic loading, which generated a large deformation.

A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a new type of hybrid bar consisting of a steel core and an FRP shell coating. The advantages of the two materials are complementary. For example, the steel bar's good ductile properties and the FRP coating's corrosion resistance work together under tensile stress. This complementary combination provides better mechanical properties and durability than ordinary steel bars. This paper features the production of two different surface types of SFCBs, and these SFCBs' response to corrosion was accelerated by an electrochemical method encompassing three designed levels of corrosion at 5%, 15%, and 25%. The corrosion condition, including the thickness of the rust layer and the rust product distribution, was observed and qualitatively analyzed by environmental scanning electron microscopy (ESEM) and energy dispersive spectroscopy (EDS) techniques. Moreover, an X-ray microcomputed tomography (μCT) was used to investigate SFCBs corrosion, and the amount of corrosion product was quantitatively analyzed. The test results indicate that the fiber types, the micropore structure of the fiber coating layer, and the manufacturing process of the SFCBs are the main factors affecting SFCBs' corrosion resistance. The SFCBs show excellent corrosion resistance. The amount of corrosion product on the FRP coated-steel interface was much less than that of ordinary steel bars that experienced the same corrosion process. The actual corrosion rate of a carbon-type SFCB is less than 1/10 that of an ordinary steel bar, and the actual corrosion rate of a glass-type SFCB is less than 1/100 of an ordinary steel bar.

Surface characteristics of large-aperture potassium dihydrogen phosphate (KDP) frequency converter have direct and significant impacts on the performance of high-power solid-state laser in Inertial Confinement Fusion (ICF) facility. In this study, we analyze the close relationships between the phase gradient and the optical performances including type-I phase matching capacity and focusability of KDP frequency converter theoretically. Moreover, the influences of external forces are studied with field interferometry and finite element method (FEM). An edge-adaptive clamping apparatus with two-stage preload controllers (TSPCs) is proposed to mitigate the gravitational effect. With the proposed integrated optomechanical method and principle verification experiment, new clamping method is proved to be effective to perform offline precision calibration, improve frequency conversion efficiency and has potential for use in online surface control of this large-aperture transmission optics. The coupled effects of preload and gravity on optical performance are analyzed for identifying the characteristics of new clamping method, and the optimal preloads at typical installation attitudes are determined.

Using locally available raw materials for preparing concrete, such as coral reefs, seawater, and sea sand, is conducive to compensating for the shortage of construction materials used on remote islands. Jacketing fiber-reinforced polymer (FRP), as passive confinement, is a practical approach to enhance the strength, ductility, and durability of such coral aggregate concrete (CAC). Rational and economical CAC structural design requires understanding the interactions between the CAC fracture process and FRP confinement. The coral aggregate size is the critical parameter of their interaction since it affects the crack propagation of CAC and FRP confinement efficiency. This study conducted axial compression tests on FRP-confined CAC cylinders with varying coral aggregate sizes and FRP confinement levels. The test results indicate that the coral aggregate sizes affected the unconfined CAC strength. In addition, the dilation behavior of FRP-confined CAC varied with aggregate sizes, showing that CAC with smaller coral aggregate featured a more uniform hoop strain distribution and larger FRP rupture strain. These coupling effects are epitomized by the variation in the transition stress on the stress–strain curve, which makes the existing stress–strain models not applicable for FRP-confined CAC. A modified stress–strain model is subsequently proposed. Finally, the practical and environmental implications of the present study are discussed.

The stress–strain relationship of concrete is different under different boundary conditions, load paths, and environments. Identification of the stress–strain relationship of concrete for ...

The inherent defects of recycled aggregate concrete (RAC) include the complex interfacial transition zone (ITZ) and the many micro-cracks that appear during its producing process, which result in some inferior mechanical properties compared with natural aggregate concrete (NAC). This drawback usually prevents RAC from being selected for structural purposes. Existing research has shown that the strength and ductility of damaged concrete in compression members can be significantly enhanced through external confinement using fiber-reinforced polymer (FRP) wraps. This application has been widely used in concrete structural repair and retrofitting technology. However, research on the effects of RAC damage coupled with different load damage conditions is rare, as is information on the mechanical properties of RAC reinforced with FRP jackets. This paper presents the results of an experimental study on the behavior of pre-damaged recycled aggregate concrete cylinders that were repaired with carbon fiber-reinforced polymer (CFRP) or large rupture strain (LRS)-FRP jackets. Tests were conducted on 58 concrete cylinders with variations in the replacement ratio, damage levels, and FRP properties. Test results demonstrated that the ultimate strain and strength of damaged recycled aggregate concrete could be significantly enhanced by FRP jackets and that aggregate quality plays a vital role in the strength of confined concrete. Also, the energy absorption of CFRP- and LRS-FRP-confined RAC were evaluated. The analysis indicated that, compared with CFRP-confined RAC, LRS-FRP can greatly improve the energy absorption capacity of RAC; thus, LRS-FRP confined concrete has a good potential to achieve a ductile design for concrete columns, especially when used in seismic reinforcement.

Premature debonding failure of fiber-reinforced polymer (FRP) laminate is a primary reason for an accelerated onset of low working stress in the FRP of reinforced concrete (RC) structures strengthened with externally bonded (EB) FRP. Hybrid-bonded (HB) FRP can effectively prevent the debonding failure of FRP, leading to a significant enhancement in the ultimate strength of the HB-FRP system. The HB-FRP method mainly relies on external positive pressure provided by the anchoring device to improve the interfacial bond strength. Therefore, the magnitude of the positive pressure determines the strengthening effect of the anchoring system. This paper first optimizes the existing HB mechanical anchoring device. The positive pressure exerted on the FRP was adjusted by varying the torque to the anchoring device. The optimized anchoring device was used to study the bond behavior of the FRP-to-concrete interface under different torques. The test results showed that the debonding stress could be regulated by adjusting the torque, leading to a change in failure mode of the FRP-concrete interface. With the increase of torque, the utilization rate of FRP and ductility increased. When the torque was higher than a certain threshold, the FRP ruptured, after which, the continuously applied torque had no significant effect on the FRP-concrete interfacial bond behavior. Based on the experimental results, an ultimate bond strength model of the FRP-to-concrete interface under different torques was developed. Compared to the experimental results, the model showed satisfactory accuracy.

The majority of existing cyclic stress–strain models for fiber reinforced polymer (FRP) confined concrete are applicable only to cases where post-peak strain hardening occurs. Cyclic model catering for strain softening is rare due to the lack of sufficient experimental data. Recent experimental tests on FRP-confined concrete cylinders involving strain-softening have identified new factors that have a significant effect on the cyclic behavior. Through an analytical study, a newly defined parameter, the effective confinement rigidity, is found to be a key factor governing the cyclic softening and hardening. By including the additional key factors and using the latest database with more strain-softening cyclic stress–strain curves, a stress–strain model of FRP-confined concrete subjected to cyclic loading considering both post-peak hardening and softening is proposed. Compared with the existing models, the proposed model can predict the cyclic behavior of FRP-confined concrete with better accuracy.

This paper presents an analytical model to predict the bond behavior of hybrid bonded (HB) fiber reinforced polymer (FRP) strengthened concrete structures considering different confining effects. The bond strength of HB-strengthened concrete structures subjected to uniaxial loading is attributed to the friction-type bond from steel plate and the chemical bond provided by epoxy-based resin. The friction-type bond is assumed to develop before any interfacial slip occurs, and remain constant when the interfacial slip is nonzero; for the chemical bond between FRP and concrete, a tri-linear bond-slip relation is adopted. The loading process of HB-strengthened structures consists of three stages, and the stage-wise solution to slip, bond stress, and axial force of HB FRP are derived based on a governing ordinary differential equation (ODE). In this study, the experimental program includes twelve HB-strengthened concrete specimens, using different confining effects (twisting moments on the steel bolts). Test results indicated that the ultimate pullout strength increases and the failure mode switches from debonding to FRP rupture as the twisting moment increases. Moreover, by comparison to three series of experimental results, the proposed model can precisely predict failure mode, ultimate strength, load-slip relation and bond stress distribution. The twisting moment on bolts is found to have the most significant improvement on the ultimate tensile strength. Finally, the critical twisting moment without yielding FRP rupture is derived.

In the era of big data, the demand for secure data storage is rapidly increasing. To accelerate the complex encryption computation, both specific instructions and hardware accelerators are adopted in a large number of scenarios. However, the hardware accelerators are not so effective especially for small volume data due to the induced invocation costs, while the AES-NI (Intel®advanced encryption standard new instructions) is not so energy efficiency for big data. To satisfy the diversity performance/energy requirements for intensive data encryptions, a collaborative solution is proposed in this paper. We proposed a feasible hardware-software co-design methodology based on the stack file system eCryptfs, with quick assist technology, which is named adaptive crypto acceleration for secure data storage (ACA-SDS). ACA-SDS is able to choose the optimal encryption solution dynamically according to file operation modes and request characters. Adjustable parameters, such as $\alpha $ , $\beta $ , and M are provided in our scheme to provide a better adaptability and tradeoff choices for encryption computation. Our evaluation shows that ACA-SDS can get 15%–25% performance improvement for big-data blocks compared with only software or hardware accelerations. Furthermore, our methodology provides a wide range of practical design concepts for the further research in this field.

Externally bonded fiber-reinforced polymer (FRP) to a degraded reinforced concrete structure is currently a very popular strengthening technology; however, premature debonding mainly caused by concrete crack propagation leads to the underutilization of FRP. Engineered cementitious composite (ECC) has an excellent crack control capability. When used in combination with FRP, ECC can effectively delay the debonding of FRP and enhance the bearing capacity and ductility of FRP-strengthened structures. For the safe and economic strengthening design, the bond-slip relationship of FRP-ECC-concrete needs to be properly understood. This paper investigated the bond behavior of FRP–ECC–concrete interface through a series of simple shear tests. The effects of ECC thickness, concrete surface treatment, and construction method on the bond behavior were evaluated. The deformation and strain data of FRP were collected and analyzed using a noncontact full-field strain measurement system VIC-3D (three-dimensional video image correlation system). The experimental results show that the addition of an ECC layer delayed the debonding of FRP and significantly increased the maximum strain of FRP. The bearing capacity, the ultimate slip, and the interface energy consumption capacity also improved significantly.

This paper presents the results of an experimental investigation on mechanical properties of seawater sea-sand recycled aggregate concrete (SSRAC) filled double-skin tubular square columns (DSTCs). A total of 45 square DSTCs, included 12 fully-filled FRP confined SSRAC (fiber-reinforced polymer) columns, 21 FRP-SSRAC-aluminum tube columns, and 12 FRP-SSRAC-stainless steel tube columns, were tested under axial compression. The effects of the key parameters, including void ratio, recycled aggregate (RA) replacement ratio, and tube materials’ properties, on the structural behavior of SSRAC-filled square DSTCs are discussed. The test results indicate that mixing seawater and sea-sand with RAs could make up the early strength reduction caused by RA replacement. The void ratio significantly influences the stress–strain relationship of SSRAC filled in DSTCs due to the nonuniform hoop confinement pressure caused by the square cross-section. This nonuniform hoop confinement is also highly related to the inner tubes’ material properties due to their different local buckling behaviors. The test results are also used to assess the suitability of existing models proposed for different kinds of DSTCs. The evaluation results suggest that the models could provide satisfying predictions as long as the corner radius and void ratio’s coupling effects are reasonably considered.

Large-rupture strain (usually larger than 5%) fiber-reinforced polymer (LRS FRP) composites are attractive materials for the seismic retrofit of concrete structures. Jacketing LRS FRP on concrete columns can effectively improve the ultimate strength and deformation of a concrete structure and make the concrete structure have excellent ductility and superior energy absorption capacity . In comparison with conventional FRP, the concrete under LRS FRP confinement experiences a more severe damage process when it is under large deformation . The confining pressure at the large deformation can alter the concrete plastic flow and significantly affect the cyclic stress-strain path of LRS-FRP confined concrete. This study evaluates the performance of existing cyclic models (e.g., unloading path, reloading path, and plastic strain) using a database including both traditional and LRS FRP-confined concrete. Through an analytical study on the cyclic response of LRS FRP-confined concrete, two key parameters (plastic strain and stress degradation) were found to significantly influence the cyclic behavior of LRS FRP-confined concrete. By defining these two critical parameters, a new cyclic stress-strain model was developed for LRS FRP confined-concrete with good performance. The proposed cyclic model was also applicable in predicting both post-peak strain hardening and softening behavior when used in a stiffness-based envelope model.

This paper presents the results of an experimental study on the behavior of predamaged concrete prisms that were strengthened with fiber-reinforced polymer (FRP) jackets. Tests were conduct...

The objective of this paper is to introduce a modified local-to-global methodology to understand the effect of fiber reinforced polymer (FRP) confinement on square concrete section. Traditionally, the effect of confinement on square sections has been evaluated through the so-called “arching effect” developed for steel and FRP-confined sections. FRP-confined square section was characterized by a non-uniform confinement stress field, which makes concrete strength strongly position dependent. This novel concept resulted in the “arching effect” being re-examined, which led to a methodology to evaluate the stress-strain behavior of concrete subject to arbitrary FRP confinement stress ratio at a local level. Because of the conception and realization of an innovative true-triaxial testing machine, by the first authors of this paper, research could be extended thus allowing for new test results that form the base of 1) an improved local constitutive relationship and 2) a modified approach for the evaluation of axial stress-strain behavior of an FRP confined square concrete column. The proposed approach has been validated by a set of experimental results of square columns and gave a new perspective on FRP confinement efficiency for square section.

Background: Monocytes are critical components, not only for innate immunity, but also for the activation of the adaptive immune system. Many studies in animals and humans have demonstrated that monocytes may be closely associated with chronic inflammatory diseases and be proved to be pivotal in the association between high-intensity exercise and anti-inflammation response. However, the underlying molecular mechanisms driving this are barely understood. The present study aimed to screen for potential hub genes and candidate signaling pathways associated with the effects of high-intensity exercise on human monocytes through bioinformatics analysis. Materials and Methods: The GSE51835 gene expression dataset was downloaded from the Gene Expression Omnibus database. The dataset consists of 12 monocyte samples from two groups of pre-exercise and post-exercise individuals. Identifying differentially expressed genes (DEGs) with R software, and functional annotation and pathway analyses were then performed with related web databases. Subsequently, a protein–protein interaction (PPI) network which discovers key functional protein and a transcription factors-DEGs network which predicts upstream regulators were constructed. Results: A total of 146 differentially expressed genes were identified, including 95 upregulated and 51 downregulated genes. Gene Ontology analysis indicated that in the biological process functional group, these DEGs were mainly involved in cellular response to hydrogen peroxide, response to unfolded protein, negative regulation of cell proliferation, cellular response to laminar fluid shear stress, and positive regulation of protein metabolic process. The top five enrichment pathways in a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were the FoxO signaling pathway, protein processing in the endoplasmic reticulum, influenza A, the ErbB signaling pathway, and the MAPK signaling pathway. TNF, DUSP1, ATF3, CXCR4, NR4A1, BHLHE40, CDKN1B, SOCS3, TNFAIP3, and MCL1 were the top 10 potential hub genes. The most important modules obtained in the PPI network were performed KEGG pathway analysis, which showed that these genes were mainly involved in the MAPK signaling pathway, the IL-17 signaling pathway, the TNF signaling pathway, osteoclast differentiation, and apoptosis. A transcription factor (TF) target network illustrated that FOXJ2 was a critical regulatory factor. Conclusions: This study identified the essential genes and pathways associated with exercise and monocytes. Among these, four essential genes (TNF, DUSP1, CXCR4, and NR4A1) and the FoxO signaling pathway play vital roles in the immune function of monocytes. High-intensity exercise may improve the resistance of chronic inflammatory diseases by regulating the expression of these genes.

Double skin tubular columns (DSTCs) filled by ultra-lightweight cement composites (ULCCs), as primary load-bearing elements, are a practical and reasonable structural asset in lightweight civil infrastructure. This DSTC-ULCC system combines the advantages of three materials, 1) outer fiber-reinforced polymer (FRP) 1–3 ply jackets, 2) filled ULCCs, and 3) inner steel tubes to achieve lightweight, high strength and superior ductility. This article presents an experimental study on the mechanical behavior of DSTCs with FRP and ULCCs under axial compressive loading . The experiment designed a total of 26 DSTCs that were all filled with ULCCs. The key parameters were the number of FRP layers and the inner steel tube properties, (i.e., thickness and diameter of the steel tube). The test results indicate that the properties of the inner steel tube not only influences the effective FRP rupture strain ratio but also the ultimate axial strain of confined ULCCs. This calls attention to the inward buckling behavior for larger void ratios; moreover, thinner steel tubes result in more axial deformation of ULCC-filled DSTCs. In addition, ULCCs showed a much lower elastic modulus compared with normal concrete, which helped cause the change of transition stress of ULCCs in DSTCs, and FRP confinement can effectively increase the elastic length of the stress–strain curves for ULCCs. The experimental results are subsequently compared with predictions from an FRP-confined ULCC model, which led to a new ultimate strain model proposed herein for ULCC-filled DSTCs. The comparison demonstrates that the model can provide reasonably accurate predictions of the stress–strain curves of ULCCs in hollow DSTCs.