Ultimate Deformation Research Articles

Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panel reinforced with FRP bar/grid: Development and flexural performance

In this study, Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panels with Fiber-Reinforced Polymer (FRP) reinforcement (i.e., FRP bars and girds) were proposed for the construction of sustainable marine structures. Based on four-pointed bending tests, the mechanical performance of FRP-reinforced UHS-ECC [with 2% polyethylene (PE) fibers] and FRP-reinforced ultra-high-strength concrete (UHSC, without fibers) panels were investigated and compared to understand the composite action between UHS-ECC and FRP. Compared with the FRP-reinforced UHSC panel, the FRP-reinforced UHS-ECC panel showed significantly higher ultimate load (139-173% higher), stiffness, and deformation capacity. It was also found that the use of seawater as the raw material had almost no effect on the mechanical performance of FRP-reinforced UHS-ECC (UHSC) panels. An analytical investigation was conducted to predict the load capacities of the tested panels, and the prediction error was acceptable. For FRP-reinforced UHS-ECC (UHSC) panels, it was revealed that using UHS-ECC to replace UHSC improved the stress transfer and deformation compatibility with FRP because the multiple cracking behavior of UHS-ECC lowered the crack-induced shear stress concentration along the FRP reinforcement. The developed FRP-reinforced UHS-ECC system showed great potential in the construction of durable and sustainable marine infrastructure.

In Vitro Characterisation of 3D Printable Filaments Subjected to Edible Liquids: An Analysis of Fused Deposition Modelling for Intraoral Applicability.

To evaluate the influence of edible liquids on the characteristic properties of 3D printable materials compared to conventionally used dental resin acrylic. Dental polymethyl methacrylate (PMMA) specimens were fabricated from preformed molds while polylactic acid (PLA) and polyethylene terephthalate glycol (PETG) specimens were 3D printed using fused deposition modelling at 0.1 mm layer thickness. All specimen forms adhered to ISO 37:2017 and ISO 604:2002 specifications. Specimens underwent controlled immersion for 180 hr into different media (no immersion (control), oil, soda, milk, and caffeine). Changes in mass (g), plastic deformity (N/mm2), ultimate tensile stress (N), flexural deformity (N/mm2), and break force (N) were evaluated using analysis of variance. There was an increase in mass for all specimens following immersion with significant interactions between immersion media and the materials. The materials exhibited significant differences in plastic deformity (F (df) = 156.632(2), P < 0.001), ultimate tensile stress (F (df) = 109.521(2), P < 0.001), and break force (F (df) = 319.785 (2), P < 0.001) with no significant interactions with immersion media (P > 0.05) on both accounts. Materials showed no significant differences in flexural deformity (F (df) = 2.693(2), P = 0.074) but with significant interactions (F (df) = 4.984(8), P < 0.001) between acrylic and immersion media. Commercially available 3D printable PLA and PETG filaments printed at 0.1 mm thickness possess approximately half the mechanical resilience as dental PMMA with comparable flexural deformity after exposure to edible liquids.

Experimental Study on the Bending Performance of GFRP‐Concrete‐Steel Double‐Skin Tubular Beams with Different Fiber Angles

Glass fiber‐reinforced plastics (GFRP) tube‐concrete‐steel tube double‐skin tubular beam (DSTB) is composed of an outer GFRP tube and an inner steel tube, with concrete sandwiched between two tubes. It possesses numerous advantages, including excellent ductility and corrosion resistance, lightweight, and convenient construction. Current research on DSTBs is primarily focused on the GFRP tube with an approximate ±90° fiber angle (the angle between the fiber direction and the longitudinal axis of DSTB). An experimental study on DSTBs with ±45°, ±56°, ±68°, and ±80° fiber angles was conducted under bending load. Experimental results show that the ultimate bearing capacity and deformation ability of DSTBs increases with the increase of fiber angle, the ultimate moment capacity of DSTBs with ±56°, ±68°, and ±80° fiber angles were 2.61%, 6.69%, and 6.74% higher than that of DSTB with ±45° fiber angle, respectively, the deformation ability of DSTBs with ±56°, ±68°, and ±80° fiber angles were 23.03%, 32.04%, and 38.48% higher than that of DSTB with ±45° fiber angle, respectively. However, the cracking strain decreases with the increase of fiber angle.

Evaluation of Ultimate Axial Strain Models for Fiber-Reinforced Polymer-Confined Concrete Cylinders

Fiber-reinforced polymer (FRP) composite has been widely applied to reinforce and rehabilitate concrete columns in civil engineering. It is necessary to deeply understand the ultimate deformation (i.e., the ultimate axial strain εcc ) of FRP-confined concrete columns. A large database including different types of FRP (conventional FRP and large-rupture-strain FRP), concrete compressive strengths (19.4 MPa-169.7 MPa), and cylinder sizes (51 mm-508 mm), as well as various concrete types, is collected in this study. For this reason, several existing ultimate axial strain modes for FRP-confined cylinders have been evaluated via some statistical parameters based on the database. The verification results illustrate that the prediction accuracy of axial strain models is not good enough due to the intrinsic difficulty in predicting deformation and variability of data source, although the available models with better performance can achieve the average ratio between experimental and predicted strain value ( εccexpe/εccpred ) below 10%.

Effect of Denim Waste Fibres on Technical Properties of Cementitious Lightweight Composite Mortars

The aim of this study was to investigate the utilization of recycled denim waste fibers (DWF) for reinforcing cementitious lightweight composite mortar (CLCM). The research focused on evaluating how the addition of DWF affected various aspects of CLCMs, such as flowability, fresh and hardened unit weight, porosity, water absorption, flexural strength, compressive strength, and load-deformation characteristics. Different proportions of fibers (0, 0.25, 0.50, 0.75, 1.00, 1.25, and 1.50 wt.% of cement) were incorporated into the CLCM. The results showed a slight decrease in both fresh and hardened unit weights compared to the reference. It was noted that the consistency of the mortars declined with the increasing addition of fibers. Additionally, the inclusion of any amount of fiber led to an enhancement in the mechanical properties of the lightweight mortars. Furthermore, the reference mortar exhibited less deformation under load, indicating its higher brittleness. Moreover, the study observed that the incorporation of DWFs had the ability to simultaneously improve both the ultimate load-bearing capacity and deformation of the mortars.

РАСЧЕТ ЭЛЕМЕНТОВ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ НА ОГНЕСТОЙКОСТЬ И ОГНЕСОХРАННОСТЬ В ПРОГРАММНОМ КОМПЛЕКСЕ СТАРКОН.

RCDiagra software as a part of the domestic STARKON software is presented. The software is designed to perform fire resistance and fire safety analysis of reinforced concrete beams and columns. The strength analysis is based on the nonlinear deformation theory and enables to take into account non-stationary thermal effects changing the concrete and reinforcement properties. To determine the ultimate strength, elastic modulus for concrete and reinforcement, ultimate relative deformations, a thermal analysis is performed in accordance with SP 468.1325800.2019 and MDS 21-2.2000. The thermal engineering analysis solve the problem of determining the temperature field in the beam cross-section under non-stationary thermal action, depending on the boundary conditions and thermophysical parameters of the material. It is assumed that the coefficients of thermal conductivity and specific heat capacity of concrete depend on the current temperature at the crosssection points.

Bearing capacity of bolted longitudinal seams of corrugated steel structures under compression

This study investigates the bearing performance of the longitudinal seams of corrugated steel plate structures with high-strength bolted connections. Axial compression testing and finite element simulation analysis were performed, considering factors such as the strengths of the corrugated steel plates and the grade and number of bolts. We found that the torque coefficient and standard deviation of hot-dip galvanised high-strength bolts were higher than the specification requirements and that the bolts had to be reasonably screwed according to the measured torque coefficient to ensure seam reliability. Seams with plate bearing failure could entirely utilise the strength of the corrugated steel plate and exhibit better ductility than those with bolt shear failure. Under the bolt shear failure mode, increasing the strength of the steel plate reduced the ultimate bearing capacity of the seam. Therefore, the strength of the corrugated steel plate and specifications of the bolts had to match to leverage the synergy between them. In the bolt shear failure mode, an increase in the number of high-strength bolts in the seam could proportionally increase the slip platform load and ultimate bearing capacity of the specimen. Owing to the geometry, the ultimate strain and deformation of the plate at the crest of the corrugation were considerably greater than those at the trough. Equations for calculating the bearing capacities of high-strength bolted connections of corrugated steel plates were established, enabling accurate predictions of the seam failure mode and strength. The obtained strengths were approximately 98% of the measured seam strength.

Performance analysis of novel double web V-bending angle-steel connections against progressive collapse

This study introduces a double web V-bending angle-steel connection (DWVAC) as a novel solution to overcome the ductility limitations of traditional double web angle-steel connections, specifically catering to the requirements of the tying force strategy. The DWVAC's anti-progressive collapse performance is analyzed using validated numerical models, and its working mechanism during progressive collapse conditions is revealed through theoretical analysis. The design process for the DWVAC is also presented, providing a comprehensive understanding of its structural performance. The study reveals that the DWVAC operates in two stages: the micro-bending stage and the catenary stage. During the micro-bending stage, the DWVAC exhibits minimal load-bearing capacity, relying primarily on axial forces in the subsequent catenary stage. Ultimately, the DWVAC fails due to rupture of web V-bending angle-steels. By understanding the DWVAC mechanism, the geometrical parameters of the V-bending angle-steel can be customized to achieve the recommended 0.20 rad ultimate rotation while satisfying various deformation requirements within a 0.30 rad ultimate rotation. The study further investigates six key parameters of the V-bending angle-steel, providing a calculation formula for its ultimate deformation based on multiple nonlinear fitting of numerical simulation analysis results. Notably, the numerical simulation analysis recommends that parameter g should not exceed 3.5 times the bolt hole diameter, and the recommended range for beam length is between 8 and 20 times the beam depth. The theoretical design process for the DWVAC is proposed, and numerical examples considering different beam and column sections are analyzed to demonstrate the rationality of the DWVAC's design process.

RESISTANCE OF COMPRESSED CONCRETE TO LONG-TERM LOADS

This article deals with the main regularities and features of compressed concrete deformation under the action of long-term loads. The main efforts are aimed at establishing an analytical dependence on determining the long-term strength level of compressed concrete. A critical analysis of the currently existing dependencies based on its calculation was carried out. These studies are based on the general provisions and hypotheses of the previously developed energy model of concrete and reinforced concrete deformation.The defining hypothesis of the specific potential energy invariance of the concrete ultimate deformation (destruction) and its independence from the loading mode of the concrete itself was used. The specific potential energy of compressed concrete deformation at the moment of its destruction under three loading modes is considered: instantaneous dynamic, standardized short-term and long-term. The level of compressed concrete long-term strength is related to the dynamic increase factor limit values (DIFu) under the instantaneous loading mode. In turn, the compressed concrete dynamic increase factor is functionally related to the generally recognized coefficient of compressed concrete standardized elastic-plastic properties under a short-term loading regime. In this way, the functional dependence of the level of compressed concrete long-term strength was obtained not only on its standardized elastic-plastic characteristics, but also on the rate of concrete deformation or on the rate of its loading. The evaluation of the proposed methodology for determining the level of compressed concrete long-term strength is reduced to a comparison of the relevant theoretical calculations results with the various researchers’ published experimental data.

Synergistic effects of web reinforcement and hybrid fibres on shear performance of continuous deep beams with unsymmetrical web openings

Application of fibre-reinforced concrete or novel web reinforcement detailing could be an effective way to enhance structural behaviour of continuous deep beams with web openings. However, there are very few experimental works studying the synergistic effects of these two methods. Therefore, an experimental programme is introduced in this paper to study synergistic effects of shear reinforcement and hybrid fibres on shear strength of nine double-span deep beams with unsymmetrical web openings (denoted as pierced span). The test specimens were designed to consist of a pierced beam span with a web opening and an adjacent solid beam span. The spans with openings were designed with different shear reinforcement configurations. It was experimentally shown that provision of sufficient web steels above and below web openings has the most important and beneficial effect on ultimate shear strength of the pierced spans. Besides, a tailored steel reinforcing method was also proposed that is capable of improving strut capacity near the web opening. In addition, adoption of hybrid fibre reinforcement led to enhanced crack-opening resistance, ultimate shear strength and shear deformation. Based on the research outcomes, it was recommended to adopt the proposed detailing method or fibre reinforcement dosage for shear strength enhancement of continuous deep beams with web openings. Furthermore, an analytical model was adopted to the shear strength of continuous deep beams accounting for web openings, steel stirrups, and hybrid fibres, which yielded safe predictions.

Collapse-resistant mechanism of RC beam-slab substructures using kinked steel plates under two-adjacent-edge-columns removal scenario

To improve the progressive collapse resistance of reinforced concrete (RC) frame structures without basically affecting their seismic performance, the authors have proposed a novel method of adding locally debonded kinked steel plates (KPs) at the beam-ends of the RC frames. This method has been verified through quasi-static tests on the RC beam-column assemblies. Considering the presence of slabs, this paper investigated the collapse-resistant mechanism and resistance improvement for the RC beam-slab substructures using locally debonded KPs. First, quasi-static tests were conducted on two RC beam-slab substructures under the scenario of removing two-adjacent-edge-columns. One substructure was configurated with the KPs and the other without the KPs for comparison. Test results demonstrated that, by adding the KPs, the ultimate resistance and deformability of the beam-slab substructure improved by 76% and 40%, respectively. Second, the high-fidelity finite element (FE) models were created to analyze the load transfer path of the substructure and the resistance contribution at the stage of catenary mechanism. Combining the test and FE analysis results, the collapse-resistant mechanism was revealed, i.e., the KPs could fully mobilize and develop the catenary action in the edge-beams and the tensile membrane action in the slabs along the edge direction. Finally, an analytical model was developed for predicting the ultimate resistance of the RC beam-slab substructures with or without the KPs under the scenario of removing two-adjacent-edge-columns.

Measurement of Temperature and Load Versus Bearing Displacement in a Thrust Foil Bearing: Differences Between Light Load and High Load Operation

Abstract This paper presents a test rig for evaluation of gas thrust foil bearings (GTFBs) and details measurements of load capacity conducted with a commercial GTFB comprising a single 360 deg, 0.127 mm thick top foil divided into six continuous arc segments with a formed taper of 0.102 mm. Coated with Teflon®, the top foil rests on a stack of shims above six underspring structures, each comprising three strips of bump foils, 0.102 mm thick. Measurements include the applied static load and break-away torque, rotor speed, bearing axial displacements at three locations 120 deg apart, the flow of a cooling stream, and temperatures in and out of the bearing. Static load tests produce the underspring deformation and a dry-sliding friction coefficient f ∼ 0.12. The underspring is rather flexible though quickly hardening for specific load (P*) &amp;gt; 25 kN/m2 to reach an ultimate deformation of ∼0.320 mm. Measurements at 30 krpm (OD surface speed = 111 m/s) and increasing static loads produce bearing displacements that parallel the displacements without shaft rotation. Most importantly, the difference between displacements approaches ∼0.060 mm for P* &amp;gt; 45 kN/m2. The test bearing operated safely to P* = 90 kN/m2 and failed at P* = 120 kN/m2. When heavily loaded, the GTFB is significantly stiffer than when lightly loaded. Designed for easiness of installation and operation, the test bearing demonstrated a stable and repeatable performance with likely a uniform gap or film thickness even for the largest loads applied.

Experimental and Theoretical Justification of the Foam Fiber-Reinforced Concrete Application Expediency in Earthquake-Resistant Construction

Introduction. Based on the evolutionary approach to the analysis of the lightweight concrete application expediency in earthquake-resistant construction it has been revealed that development of the above mentioned technologies fosters the reduced material consumption in construction and the increased durability of buildings under the seismic loads. The efficient solutions for constructing the earthquake-resistant buildings are constantly searched for, and the reasons for reducing the range of energy-efficient products made of the autoclaved aerated concrete are noticed. The research is aimed at compiling an inventory of modern technological methods of increasing the buildings seismic resistance.Materials and Methods. The list and properties of raw materials used for single-stage technology manufacture of the foam concrete mixtures have been provided. The list of equipment used for assessing the studied materials’ mechanical properties has been defined.Results. The new experimental data confirming the significant influence of the individual properties of fiber on the value of the dispersedly reinforced foam concrete ultimate deformability and bending tensile strength has been obtained. The positive effect of the length of fiber on the foam concrete mechanical properties has been confirmed. The considerably positive effect of the dispersed reinforcement on the homogeneity of mechanical properties observed in the foam concrete mass has been distinguished.Discussion and Conclusions. The work performed has elucidated the importance of the individual properties of fiber as a tool for managing the operational properties of foam concrete. The ultimate properties of the aerated rock material are influenced by the length of fibers and their ultimate deformability. The length of fiber is important for the bending tensile strength, whereas the values of this parameter in the composite material are regulated by the ultimate extensibility.

Influence of Steel and Polypropylene Fibers on the Structural Behavior of Sustainable Reinforced Lightweight Concrete Beams Made from Crushed Clay Bricks

Structural lightweight concrete is preferred over traditional concrete due to its ability to reduce the dead load, minimize the size of load-bearing structural members, and provide more economical solutions for foundation deteriorations. This research sheds light on sustainable lightweight concrete using waste crushed clay bricks (CCB) as a lightweight aggregate. To reduce micro-crack propagation of the developed concrete, two types of fiber were implemented and investigated. Steel fibers (SF) with amounts of 0.5% and 1.0% by volume of concrete, and polypropylene fibers (PPF) with amounts of 0.1% and 0.2% by volume of concrete, were employed. Five reinforced concrete beams were made and tested in order to precisely evaluate the structural behavior of the proposed lightweight CCB concrete. Additionally, ABAQUS software for nonlinear finite element analysis has been utilized to simulate the tested beams and compare the numerical model predictions with the experimental findings. The findings revealed that the addition of SF and PPF exhibited a notable influence on enhancing the mechanical characteristics of lightweight CCB concrete. Adding 0.2% PPF increased the ultimate load and deformation capacity at failure by approximately 16% and 24%, respectively. Furthermore, after 28 days, the addition of 0.5% and 1.0% SF enhanced the compressive strength by around 11.7% and 17.6%, respectively. Moreover, a significant level of consistency between the results obtained from the numerical model and the experimental findings was observed. In general, the use of SF and PPF in CCB concrete successfully produced high-quality lightweight concrete with interesting results for use in reinforced concrete beams.

MAIN FEATURES OF CONCRETE DEFORMATION UNDER THE ACTION OF DYNAMIC LOADS

This article is devoted to the features of the general model of compressed concrete deformation in concrete and reinforced concrete elements and structures under the dynamic loads action. The proposed model is a further in-depth development of the previously developed generalized deformation and force model of concrete and reinforced concrete resistance to force effects. It is based on the hypothesis of invariability and independence from the loading mode of the specific potential energy of concrete ultimate deformation (destruction) in a standard sample. A critical analysis of the research results by other authors published today on the above-mentioned subject has been performed. The main attention is paid to the well-known dynamic increase factor (DIF). The main advantages and disadvantages of the currently existing methods and ways of its determination have been classified and analyzed. An analytically justified function of its maximum possible values under the dynamic loads action was obtained. The various factors influence on the DIFu limit values for compressed concrete is taken into account using an integrated parameter – the well-known coefficient of elastic-plastic concrete properties k. The dependence of intermediate DIF values on the compressed concrete deformation rate under the different intensity dynamic loads action is proposed. The effectiveness of the developed method of determining the DIF coefficient for compressed concrete according to the proposed dependence was evaluated by comparing the theoretical calculations results with individual researchers experimental data. Similar comparisons were also made with the calculations results performed according to well-known European methods of the CEB FIB.

Study on seismic behavior of steel frame joint with external arc diaphragm

The application of External Diaphragm (ED) in steel frame system is able to reinforce the stiffness of joint and provide efficient protection for the critical part of joint. However, due to the limitation of the existing design codes, the inside space of building is affected frequently by the excessive size of the ED. To reduce the size effect of ED, a hysteretic experiment on four steel joint specimens is first carried out in this paper, the effects of the width ratio (the ratio of ED width to beam flange width) and connection type (Bolted web-Welded flange (BW) connection and Full Bolted (FB) connection) are investigated. Then, a numerical analysis is conducted to further explore the influence of the width ratio and the thickness ratio (the ratio of ED thickness to beam flange thickness). The results indicate that the specimen with BW connection exhibits larger stiffness and bearing capacity, but the specimen with FB connection has obvious ascendancy on the ultimate deformation capacity and ductility. Moreover, Changing the width ratio and thickness ratio are unable to cause significant variation on the seismic performance of steel joint if the thickness ratio is larger than 1.25. Therefore, the thickness of the ED is more critical than width to the seismic performance of steel joint. Meanwhile, in the circumstance of the thickness ratio is equal to 1, the width ratio of 0.1 is recommended for the minimum limited value in structure design.

Experimental study and numerical simulation on shear behavior of steel and concrete composite beam with molybdenum tailing

To improve the flexural performance of steel–concrete composite beams and alleviate the problem of sand depletion caused by the application of concrete structures, this paper proposes a new type of steel-molybdenum tailings concrete composite beam. In order to further study the shear performance of the new type of steel-molybdenum tailings concrete composite beam, this paper couples molybdenum tailings replacement ratio (0%, 50%, and 100%) and shear span ratio (1 and 2) as research parameters, designs a total of six 1:2 scaled composite beam models, and conducts monotonic loading tests to study the failure process, failure mode, ultimate bearing capacity, deformation, and local strain of some typical measuring points of the new composite beam. The steel and concrete composite beam with the molybdenum tailing has the similar mechanical behavior for each ratio of the shear span to the effective depth with that of the steel and concrete composite beam. In addition, they have a little difference in the failure processes for each ratio of the shear span to the effective depth, whereas they show typical diagonal compression failure mode for the ratio of the shear span to the effective depth is equal to 1 and the representative shear-compression failure mode for the ratio of shear span to effective depth is 2, and have no obvious difference in failure mode for each ratio of the shear span to the effective depth. Their shear resistance mechanism is basically the same. Furthermore, based on the validated finite element model, this paper conducted a parameter extension analysis. The finite element results show that: The ultimate load bearing capacity of the steel and concrete composite beam with molybdenum tailing varies significantly with the beam section size (beam section width and beam depth), reinforcement ratio, and the ratio of the shear span to the effective depth; Whereas it has little relation to the steel plate thickness. This provides the necessity and feasibility to use the steel and concrete composite beam with the molybdenum tailing in engineering practice. The proposed equation in this study is based on the previous researches and the simulated and test results. The proposed equation is rigorous and thorough and the predicted results are highly accurate and effective.

Development of an empirical model for damage degree assessment of steel specimens based on the results of acoustic emission signal flow statistical processing

The study is devoted to acoustic emission (AE) method application for monitoring the state of structural materials at the inelastic and ultimate deformation stages. The possibilities of using the standard AE signal parameters recorded at the inelastic and ultimate deformation stages to assess the damage degree of steel specimens were investigated. It was shown that such parameters as the maximum amplitude of the recorded AE signals and their AE activity did not have a clear correlation with the damage degree of products made of structural steel and alloys. This makes it difficult to apply standard methods for assessing the damage degree of structural steels. The feasibility of monitoring the state of damage of 30KhGSA alloyed steel at the inelastic and ultimate stages by the evaluation of partial activity of the high-energy AE signals weight content was presented. The Kolmogorov-Smirnov criterion was used to separate the processes of ductile and brittle fracture.

Behavior of large-scale concrete columns reinforced with high-strength and high-toughness steel bars under axial and eccentric compression

In this paper, combined with the current era background of energy saving and emission reduction, low carbon and environmental protection, the mechanical performance of new high-strength and high-toughness steel bars (HSHTSB) in concrete structural members is studied, and HSHTSB is expected to be popularized. To investigate the compression behavior of large-scale concrete columns reinforced with HSHTSB under axial and eccentric compression, thirteen reinforced concrete (RC) columns were designed in this paper, including the five columns under axial compression and the eight columns under eccentric compression. The effects of different types of steel bars, transverse steel bar spacing, the configuration of transverse steel bars, and eccentricity on failure modes, load-deformation curves, load-strain curves, ultimate bearing capacity, deformation capacity, and energy absorption capacity were studied in detail. The results show that the cracks are more uniform for concrete columns reinforced with HSHTSB. When the transverse steel bar spacing is less than 80 mm, concrete columns reinforced with HSHTSB with eccentricity ≤200 mm (including eccentricity = 0) have obvious secondary bearing phenomenon, and significantly improve ductility and energy absorption capacity; HSHTSB as longitudinal steel bars can reach yield strength for RC columns under axial compression. For RC columns under eccentric compression, HSHTSB could not reach yield strength on both the tensile and compression side. For the RC columns of Group II, III, and IV, when the eccentricity increases from 100 mm to 400 mm, the ultimate bearing capacity decreases by 76.1%, 75.2%, and 75.1%, respectively. Different from the ordinary RC columns, the ductility decreases with the increase of eccentricity for concrete columns reinforced with HSHTSB. Compared with ordinary RC columns, the energy absorption capacity and deformation capacity of concrete columns reinforced with HSHTSB under axial compression are increased by 120.9% and 116.9%, respectively. Compared with RC columns using transverse steel bars with single-leg, the energy absorption capacity and ductility for multiple-leg can be increased by 111.5% and 103.2%, respectively. When the eccentricity increases from 100 mm to 400 mm, the ductility for columns of Group II and III decreases by 73.5% and 65.9%, respectively. The use of HSHTSB can save the number of longitudinal steel bars and the transverse steel bar spacing while maintaining the bearing capacity, and further improve the deformation capacity. Based on the section strain analysis, the analytical models of the ultimate bearing capacity for the concrete columns reinforced with HSHTSB were established with high accuracy.

Progressive collapse resistance of RC frames subjected to localized fire

Fire is one of the accidental loads that can cause progressive collapse of buildings. However, the behavior of fire-exposed reinforced concrete (RC) frames to resist progressive collapse are still unclear. Therefore, a numerical study on the RC assembly based on the sequential thermal-mechanical coupling method is conducted. Fire effects on the failure mode, load-resistant capacity, and the evolution of load-resistant mechanisms of the RC frame are captured. The numerical results show that compressive arch action (CAA) and catenary action (CA) can develop in sequence for the specimens exposed to fire within a short fire duration of 30 min. The failure of the specimen is controlled by the fracture of beam rebars near the removed column. However, when the fire duration exceeds 60 min, the specimen is difficult to develop effective CA due to a decrease of over 80% in the tensile strength of the bottom reinforcement. The failure of the specimen is dominated by the fracture of the rebar at the cut-off point of the beam top rebar. Fire lasting for 30 min, 60 min, 90 min and 120 min results in a decrease of 41%, 72%, 77% and 78% in ultimate load, respectively. Increasing the span-depth ratio can upgrade the deformation capacity of the specimen, but it is adverse to the development of CAA. The effects of the reinforcement ratio on the failure mode, the ultimate load and deformation capacity are mild as the fire exposure duration increases.