Transient State Tests Research Articles

Experimental investigation combined with steady-state and transient-state tests on soot characteristics of hydrogenated catalytic biodiesel/n-butanol blends

The utilization of biodiesel and biobutanol offers a promising approach to achieve energy conservation and emission reduction in combustion engines. This study investigates the soot characteristics of hydrogenated catalytic biodiesel mixed with n-butanol (20% by volume) under steady-state and transient-state conditions using diffused background-illumination extinction imaging and two-color method, respectively. Both conditions in constant volume combustion chamber (steady-state) and optical engine (transient-state) exhibit similar soot stages, namely Formation Dominating and Oxidation Dominating. Between the above Dominating stages, the soot development under steady-state conditions is further segmented into Initial Oxidation and Secondary Oxidation, while a Stalemate stage manifests under transient-state conditions owing to wall impingement and strong turbulence. Under steady-state conditions, formation and oxidation processes are mainly controlled by the soot peak of spray head. By decreasing ambient temperature and increasing injection pressure, soot accumulation is notably diminished by 30.27% and 45.72% during the Formation Dominating stage, achieved through the deceleration of precursor reactions and enhancement of air-fuel mixing characteristics within the flame lift-off zone, respectively. Additionally, higher injection pressure notably amplifies the efficacy of the Initial Oxidation, primarily through the reduction of soot residence time. Under transient-state conditions, the Formation Dominating stage for SOI-25 and SOI-20 occur away from the early combustion, resulting in a reduction of 10.26% and 68.36% in soot compared to SOI-30. The Stalemate stage is characterized by a competition between the oxidation of high-temperature flames above 2000 K and the formation of low-temperature flames below 1800 K. A portion of soot originating from the high-temperature flames becomes integrated into the low-temperature flames after cooling, subsequently emerging as the primary hindrance to the ensuing oxidation process.

Intake pressure control based on improved super-twisting for altitude ground test facilities

This paper focuses on the problem of rapid tracking of engine transient pressure, an improved super twisting algorithm (STA) is adopted to control the intake pressure of the engine. The high altitude platform is analyzed systematically, the mathematical model is derived, and the system and control object model are established. It is improved on the basis of classical STA method and has better control effect than PID control methods and LADRC. Transient state tests of the engine under three different working conditions(acceleration/deceleration state of pushing/pulling accelerator lever, engine intake pressure changing from 50kPa to 60kPa, and engine intake pressure changing from 60kPa to 70kPa) are simulated and verified. The simulation results show that, compared with the traditional PID and active disturbance rejection control(LADRC)strategies, the method proposed in this paper can track the inlet pressure of the engine in transition state quickly, and can reach and stabilize the given set value accurately and quickly.

Tensile properties of carbon fabric-reinforced cementitious matrix (FRCM) at high temperatures

Despite many advantages of externally bonded FRP systems, the rapid loss of strength at high temperatures is a concern for fire scenarios. Fabric-reinforced cementitious matrix (FRCM) is deemed to perform superior at high temperatures. In this study, 84 carbon FRCM coupons were tested in tension at temperatures from 25 to 400 °C using both steady-state and transient-state test protocols. The main parameters considered in this study are the number of fabric layers and FRCM thickness, fabric orientation, target temperatures, and heating protocol. Results showed that at room temperature, the ultimate strength and cracked elastic modulus decreased by about 18% to 20% when the number of layers was increased from one to three. At 400 °C, the ultimate strength and cracked elastic modulus were reduced by up to 60 to 70% of their original values. The bidirectional FRCM specimens presented a slightly higher elastic modulus and strength than unidirectional specimens in most tests. In transient-state tests and under the same sustained load level, the failure temperature of 30 mm-thick specimens were approximately 100 °C higher than 20 mm-thick specimens. The test results showed that the carbon FRCM composites tested in this study were able to resist non-negligible tensile forces at elevated temperatures although they are significantly reduced.

Tensile strengths of super high-strength steel strand wire ropes and wire rope open swaged socket connections at fire and post fire

PurposeThe main purpose of this study was to evaluate the tensile strengths of JIS G3549 super high-strength steel strand wire ropes (1,570 MPa-class high-carbon steels) and wire rope open swaged socket connections at fire and post fire.Design/methodology/approachSteady-state tests from ambient temperature (20 °C) to 800 °C, transient-state tests under the allowable design tensile force and tensile tests in an ambient temperature environment after heating (heating temperatures of 200–800 °C) were conducted.FindingsThe tensile strengths of the wire rope and end-connection specimens at both fire and post fire were obtained. The steel wire rope specimens possessed larger reduction factors than general hot-rolled mild steels (JIS SS400) and high-strength steel bolts (JIS F10T). The end-connection specimens with sufficient socket lengths exhibited ductile fracture of the wire rope part at both fire and post fire; however, those with short socket lengths experienced a pull-out fracture at the socket.Originality/valueThe fundamental and important tensile test results of the super high-strength steel strand wire ropes (1,570 MPa-class high-carbon steels) and wire rope open swaged socket connections were accumulated at fire and post fire, and the fracture modes were clarified. The obtained test results contribute to fire resistance performance-based design of cable steel structures at fire and fire-damage investigations to consider their reusability post fire.

Improved fire design of steel I-sections under combined compression and bending

The fire resistance of hot-rolled and welded I-sections under combined compression and bending is numerically investigated in this study. Advanced non-linear shell models were developed and validated against existing experimental data on steady-state and transient-state tests. These models have been further used within parametric studies to gather a large cross-sectional resistance dataset. Various cross-section slenderness, section shapes, steel grades, fire temperatures and load combinations have been considered. The numerical results were used to evaluate the design rules suggested by current and upcoming European provisions, the EN 1993–1-2 and prEN 1993–1-2, respectively. It is observed that these two design recommendation sets usually lead to scattered and discontinuous resistance predictions, owing to the inappropriateness of the cross-sectional classification system and to inaccurate interaction equations. The Overall Interaction Concept (O.I.C.), which has been formerly proposed for the fire design of I-sections under axial compression or pure bending, is extended in this paper to combined compression and bending load cases and shown to yield more accurate, consistent and straightforward resistance predictions than EN 1993–1-2 and prEN 1993–1-2.

Influence of test parameters on the high-temperature material properties of G550 CFS

Cold-formed steel (CFS) members generally present rising and falling temperature periods during full-range compartment fires. This study conducted 78 experiments of 1.0 mm thick G550 CFS during rising and falling temperature periods and quantitatively estimated the influence of the holding time of peak temperature, cooling rate, temperature history, and test methods. The results show that the temperature history plays an important role in the steady-state results. If the G550 CFS members are exposed to fire multiple times, the maximum temperature and tensile temperature can be used to represent the influence of temperature histories on the material properties of G550 CFS. Additionally, the temperature history also has a significant influence on the transient-state test strains. Under the same tensile temperature, the relative deviation between transient-state test strains during rising and falling temperature periods can reach 99,642%. In addition, when the tensile temperature is not lower than 300 °C, the transient-state test strain is obviously higher than the steady-state test strain under the same tensile temperature and stress level. Therefore, the steady-state and transient-state test methods are not equivalent. After collecting approximately 250 groups of test data, a data-driven model of G550 CFS under full-range fires was developed based on the BP neural network. The peak temperature, tensile temperature, steel position and thickness were taken as input parameters, and typical expressions of stress-strain curves were taken as the output parameters. The proposed data-driven model could give an acceptable prediction of the material properties and stress-strain curves of G550 CFS during full-range fires.

Transient creep strain of fly ash concrete at elevated temperatures

Accurate modelling of transient creep strain (TRC) is crucial for reliable fire performance assessments of concrete structures, since it is the largest strain component for structural concrete subjected to thermal exposure. Nonetheless, the mechanism underlying TRC is still not fully understood and most of the available models were established based on ordinary Portland cement concrete. As the most widely used supplemental cementitious material, the effect of fly ash on the development of TRC still requires further study. For this paper, steady state tests and transient state tests were carried out on ordinary Portland cement concrete (CEM I 52.5 as per BS EN 197-1, water/cement = 0.5) and fly ash concrete (class F fly ash as per BS EN 450-1, 25% replacement percentage), respectively. It was found that replacing 25% ordinary Portland cement with class F fly ash in concrete can mitigate the development of TRC above 400°C. Based on the experimental results, one assumption of the influence mechanism of class F fly ash on TRC is made and a TRC model for fly ash concrete (class F, 25% replacement percentage) at elevated temperatures is proposed.

Fire behavior of novel Thread-anchored One-side bolted connection with internal component

Anchorage of the novel Thread-anchored One-side Bolt (TOB) is provided by the threads inside the bolt hole and the TOB could be installed from one side only, which provides an alternative way to install the connection of the Square Hollow Section (SHS) column. But the TOB might be pulled out from the threaded bolt hole when the SHS column wall is deformed, especially in fire conditions. The strengthening component could be installed inside the SHS column to restrict the deformation of the column wall and increase the depth of the threaded bolt hole. The tensile behavior of the TOB bolted SHS column connection and the influence of the internal strengthening component on the connection at fire scenario were studied and compared with Standard High-strength Bolted (SHB) connections by experimental method. Both steady-state fire test method and transient-state fire test method were used in the test. The TOB bolted SHS column connection had two typical failure modes, which were the yielding of the column wall (mode 1) and the yielding of the T-stub flange accompanied with the bolt failure (mode2), depending on the thickness of column wall. The internal strengthening component could change the failure mode from mode 1 to mode 2 and enhance the fire behavior of the SHS column connection when the thickness of the column wall was small. In the steady-state test, the resistance of the connection decreased obviously with the increase of the fire temperature. In transient-state test, the ductility and the failure temperature decreased obviously with the increase in load ratio. The internal component is an effective way to improve the fire behavior of the TOB bolted SHS column connection. The strengthened TOB bolted SHS column connection could replace SHB bolted connection with the same SHS column wall thickness under the same circumstance. Equations to calculate the yielding resistance of the TOB bolted SHS column connections at different temperatures were given. Comparison with test results showed the proposed equations could predict the failure mode of the TOB bolted connections precisely and predict the yielding load of the connections with acceptable accuracy.

Elevated temperature and post-fire stress-strain modeling of advanced high-strength cold-formed steel alloys

Advanced high-strength cold-formed steels (AHSS) have been developed with yield strengths up to 1250 MPa and ultimate strengths up to 1900 MPa. Accurate stress-strain modeling of these new steel alloys are required for eventual application of AHSS into the building construction industry, including the material behavior of AHSS subjected to elevated temperatures. A series of new constitutive material models are proposed based on the experimental AHSS stress-strain database at elevated temperatures (i.e., steady-state and transient-state test methods) and post-fire scenario (i.e., residual test method). The stress-strain curves from experiments on two families of AHSS, including dual phase steel with nominal yield strengths of 340 MPa and 700 MPa, and martensitic steel with nominal yield strengths of 1030 MPa and 1200 MPa, reported in a previous study are considered. Existing stress-strain models are investigated and fit to the AHSS database, in addition to the development of new material models. The required input parameters of the proposed stress-strain models are determined, and their corresponding predictive expressions are proposed. It is shown the stress-strain behaviors of AHSS could be accurately described by the proposed models. The data generated by this research addresses fire safety design and will be essential in supporting the adoption of these next-generation steels in future infrastructure.

Bending and flexural-buckling strength of steel members considering strain-rate-effects at elevated temperatures

PurposeIn this study, the bending strength, flexural buckling strength and collapse temperature of small steel specimens with rectangular cross-sections were examined by steady and transient state tests with various heating and deformation rates.Design/methodology/approachThe engineering stress and strain relationships for Japan industrial standard (JIS) SN400 B mild steels at elevated temperatures were obtained by coupon tests under three strain rates. A bending test using a simple supported small beam specimen was conducted to examine the effects of the deformation rates on the centre deflection under steady-state conditions and the heating rates under transient state conditions. Flexural buckling tests using the same cross-section specimen as that used in the bending test were conducted under steady-state and transient-state conditions.FindingsIt was clarified that the bending strength and collapse temperature are evaluated by the full plastic moment using the effective strength when the strain is equal to 0.01 or 0.02 under fast strain rates (0.03 and 0.07 min–1). In contrast, the flexural buckling strength and collapse temperature are approximately evaluated by the buckling strength using the 0.002 offset yield strength under a slow strain rate (0.003 min–1).Originality/valueRegarding both bending and flexural buckling strengths and collapse temperatures of steel members subjected to fire, the relationships among effects of steel strain rate for coupon test results, heating and deformation rates for the heated steel members were minutely investigated by the steady and transient-state tests at elevated temperatures.

Fire resistance of two types of composite beams constrained by rigid joint

To study the fire resistance of different types of composite beams in integral structures, transient state tests were performed on two-span composite beams (one span is a monolithic composite beam with a laminated slab and the other span is a composite beam with a cast-in-place slab) with rigid beam-to-column connections. The temperature distribution, displacement changes, and failure modes of the two types of composite beams were evaluated in tests mimicking the entire process of a real fire disaster. The following results were obtained in this study. Under the influence of fire, cracks of different patterns were formed on different types of composite beams. When the heating was stopped, the temperature of the steel beam experienced a sudden and sharp drop, whereas the temperature of the concrete slab rose within a short period of time. These behaviours cause the composite beam to undergo retraction in a reverse arch shape during deformation. Severe buckling occurred in the lower flange under the two ends of the steel beam as well as the web of the steel beam. During the test, the welds at both ends of the laminated-slab composite beam were cracked, whereas those at both ends of the composite beam with a cast-in-place slab remained undamaged. Finally, a method for calculating the axial force of the composite beam that considers the constraints at the beam ends is proposed in this study. The calculation results are in good agreement with the experimental test results.

Steady and transient state tests on local buckling of high strength Q690 steel stub columns

To investigate the local buckling behavior and obtain critical buckling stress of flange and web in Q690 steel stub columns at elevated temperatures, a total of 8 stub columns made of H-shape welded sections were tested under simultaneous axial compression and high temperatures. 2 stub columns were tested at ambient temperature and critical stress of flange and web were determined. 4 stub columns were tested in steady-state at 450°C and 600°C, respectively. 2 stub columns were tested in the transient state based on the critical stress of flange and web at 600°C. During the tests, temperature evolution, applied load, axial displacement, lateral deflection, failure modes of each specimen were recorded. The results showed that the critical buckling stress decreases significantly with the increase of temperature. At the same load level, the steady-state test’s critical temperature was lower than that obtained in the transient state test. In parallel with the tests, a finite element model was established using ABAQUS software under high temperatures to evaluate the effects of the temperature on local buckling stress, and the model was validated by the test results. A parametric study was carried out to investigate the effect of numerous factors, including width-to-thickness ratio, residual stresses, initial imperfection, and temperature. The simulation and test results were compared with the current design provisions in Eurocode 3, and the comparison showed that the Eurocode 3 design method could not be applied to the Design of the local buckling bearing capacity and ultimate stress, and it might not be precise enough at elevated temperatures.

Load and temperature influence on the post-fire mechanical properties of steel reinforcements

An experimental study was carried out to evaluate the residual mechanical properties of steel reinforcements after their exposure to elevated temperatures. In order to reproduce real loading conditions, specimens were simultaneously subjected to a load level and a thermal cycle consisting of heating up to a target temperature and cooling back to room temperature. The target temperature was a percentage of the critical temperature, i.e., the temperature at which a specimen breaks when it is subjected to a constant tensile load and an increasing temperature at a constant rate. After that, the residual mechanical properties were obtained submitting the specimens to tensile testing until failure. Critical temperatures for each load level were obtained by means of transient-state tests. In parallel, unloaded specimens were subjected to the same thermal cycle for comparison purposes, and for the same reason steady-state tests were also performed.Results indicated that the residual mechanical behaviour of reinforcing bars depended not only on the maximum temperature reached, but also on the load level that was bearing during the thermal cycle. Depending on this combination of variables, the code requirements for a given ductility class of a reinforcement may not be satisfied in a post-fire situation. Considering the lack of information in this issue, the obtained data can be helpful in the assessment of reinforced concrete structures after a fire.

A distinctive approach to testing and modeling thermal creep in ultra-high strength steel

The literature on the thermal creep of steels with nominal yield strengths greater than 700MPa is scarce. Conventionally, mathematical models simulating the thermal creep of steel are developed based on steady-state tests. Transient-state testing, however, replicates structural fire conditions more realistically, and consequently, yields more reliable results for the fire design of structures. Hence, in response to the existing knowledge gap, the thermal creep of Grade 1200 ultra-high strength steel (UHSS) is examined and modeled in this study using the transient-state testing approach. First, by performing transient-state tests at a 10°C/min heating rate, the stress-strain diagrams of the UHSS at elevated temperatures are obtained, in which thermal creep has been implicitly included. Thermal expansion, elastic modulus, and yield strength of the material are derived at temperatures up to 750°C and compared with the predictions given by three world-leading design codes of practice. Due to the distinct microstructure and chemical composition of the UHSS, a significant disparity is observed between the results obtained for the UHSS and specifications provided by the design codes for mild steel. Then, based on transient-state tests at the heating rates of 5 and 20°C/min, an analytical thermal creep model is developed for the UHSS. Exclusively tailored to the transient-state conditions such as real fires, the proposed creep model is capable of simulating tertiary creep, and hence, ideal for structural fire design applications. The model is validated against the experimental data obtained for the heating rate of 10°C/min, where the model predictions are found to be in very good agreement with experimental results. By the explicit inclusion of thermal creep using the creep model, it is then shown that under 5 and 20°C/min heating rates, the yield strength of the UHSS can experience a difference as great as 30% at fire temperatures; hence, the necessity of the explicit modeling of thermal creep for the safe and accurate fire design of UHSS components is concluded.

Experimental investigation on the creep behavior of G550 cold-formed steel at elevated temperatures

Creep behavior is an important parameter of the material properties of cold-formed steel (CFS) at elevated temperatures and the corresponding investigation is still very limited. In this paper, an experimental study with the creep duration of 4 h was performed for 1.0 mm thick G550 CFS. Forty-one test conditions were selected. The results showed that the creep curves of G550 CFS were distinctly different from that of Q550 and Q690 hot-rolled high-strength steel at elevated temperatures. In addition, the G550 CFS coupon specimens which demonstrated tertiary creep during the experiments would experience creep rupture. For the fire safety of steel structures, a critical temperature of G550 CFS which represented the onset of tertiary creep was given. When the stress ratio was less than 0.7, the critical temperature was lower than the temperature corresponding to the high-temperature yield strength of G550 CFS. Furthermore, a steady-state creep rate expression of G550 CFS was proposed. When the primary creep stage of G550 CFS was insignificant, the proposed expression could be used to give the estimation of the high-temperature creep curves of G550 CFS. Finally, the transient-state test strain of G550 CFS at 500 °C was predicted and compared with previous experimental results. It was shown that the creep strain was an essential part of the total strain of G550 CFS under transient-state conditions, and also a key factor leading to the difference of strain results between the transient-state and steady-state tests.

Elevated temperature material properties of advanced high strength steel alloys

Advanced High-Strength Steels (AHSS) have high potential to be adopted in future innovative infrastructure. However, the material properties of AHSS at elevated temperature, which are necessary for analysis and design in the fire situation, are not yet specified in design codes or literature. An experimental investigation is carried out on cold-formed steels with nominal yield stress ranging from 340 MPa to 1200 MPa. The tested materials include two types of advanced high-strength steels (dual-phase (DP) and martensitic (MS) steel) and two conventional steels (high-strength low-alloy (HSLA) and mild steel). 88 tensile specimens are tested in steady-state and transient-state conditions at temperatures up to 700 °C. Material properties are obtained from the tests including elastic modulus, 0.2% proof stress, yield stresses at strain levels of 0.5%, 1.5%, and 2%, ultimate stress, and elongation at fracture. The test results are compared with the design codes provisions in Eurocode 3 and AISC 360, and with data from existing literature. Comparisons show that cold-formed DP and MS steels exhibit relatively larger reduction in stiffness and strength than conventional cold-formed steels at elevated temperature, which warrant the development of specific provisions. It is also found that transient-state tests at 5 °C/min heating rate yield approximately similar yield stress retention factors as steady-state tests but yield lower values of elastic modulus retention factors. New predictive models are proposed to determine the mechanical properties at elevated temperature of the cold-formed advanced high-strength steels with nominal yield stress up to 1200 MPa.

Performance of an air membrane bioreactor for methanol removal under steady and transient state conditions

The main aim of this study was to evaluate the performance of an air membrane bioreactor (aMBR) for the treatment of gas-phase methanol. A laboratory-scale hollow fiber aMBR was operated for 150 days, at inlet methanol concentrations varying between 2 and 30 g m−3 and at empty bed residence times (EBRT) of 30, 10 and 5 s. Under steady-state conditions, a maximum methanol removal efficiency (RE) of 98% was obtained at an EBRT of 30 s and a decrease in RE of methanol was observed at lower EBRTs. On increasing the inlet loading rate, some portion of gas-phase MeOH was stripped into the liquid phase due to its solubility in water. Under transient conditions, the MeOH removal efficiency dropped from an average value of 95%–90% after 5 h of 10-fold shock load and dropped from an average value of 95%–88% under 5-fold increase in shock load. During transient-state tests, the aMBR performed well under different upset loading conditions and a drop in RE of ∼ 5–10% was observed. However, the aMBR performance was restored within 1–2 days when pre-shock conditions were restored. The results from microbial structure analysis revealed a big shift of the dominant methanol degrader, from Candida boidinii strain TBRC 217 to Xanthobacter sp. and Fusicolla sp., respectively.

Mechanical properties of pultruded high-temperature-resistant carbon-fiber-reinforced polymer tendons at elevated temperatures

Cable roof structures built with carbon-fiber-reinforced polymer (CFRP) cables instead of steel cables, which are called CFRP cable roofs, represent a new structure with great development potential. However, as one of the main stressed components of structures, CFRP cables are required to have better fire resistance. In this paper, the fire resistance of a type of high-temperature-resistant (HTR) CFRP tendon is studied. A total of 39 specimens with a diameter of 5 mm are performed in this study, among which 33 specimens are for steady-state tensile tests and 6 for transient state tests. Steady-state tensile tests are conducted over in the 20–600 °C range, and transient state tests are conducted for stress levels ranging from 0.19 to 0.57. The steady-state test results show that HTR CFRP tendons have excellent room-temperature and high-temperature mechanical properties. The strength remained 78% at 200 °C and the elastic modulus remained 82% at 300 °C, indicating the effectiveness of high-temperature resistant resin matrix. When the temperature reaches 600 °C, the strength remains 19%. The transient state test results show that the high initial stress (stress level of 0.57) can aggravate damage to CFRP tendons at high temperatures. Finally, a high-temperature equation is obtained for the temperature dependence of the strength and modulus of HTR CFRP tendons by developing a mathematical model that is fitted to the test data.

Experimental studies on thread-fixed one-side bolted T-stubs in tension at elevated temperatures

ABSTRACT Tests were carried out to investigate the tensile behavior of T-stubs connected by Thread-fixed One-side Bolts (TOB) at ambient and high temperatures. A total of 25 T-stub specimens with different bolt diameters and T-stub flange thicknesses were tested. In the high temperature tests, load ratios of 0.5 and 0.75 in transient-state tests and temperatures of 500 °C and 700 °C were selected in the steady-state tests. Totally four failure modes were observed in ambient and high temperature tests, which were the bolt failure, the flange yielding, flange yielding accompanied with bolts failure, as well as the flange yielding accompanied with threads failure. Results of high temperature tests showed that the failure modes of the same bolted T-stubs would be different at different temperatures in the steady-state tests or under different load ratios in the transient-state tests. However, the unfavorable failure modes integrating threads failure did not occur in high temperature tests, which demonstrated the good applicability of TOB in a fire. In transient-state tests, bolted T-stubs under the small load ratio had better ductility and higher failure temperature. In steady-state tests, the yielding strength, the ultimate strength as well as the initial stiffness decreased with the increase of temperature. The yield strength of bolted T-stubs could also be increased through the increase of bolt diameter and flange thickness of the target T-stub. Design equations for the yield strength of T-stubs connected using TOB at high temperatures were modified. The failure modes and yielding strength of TOB connected T-stubs at elevated temperatures predicted by modified design equations agreeed well with test results.

Behavior of thread-fixed one-side bolted T-stubs with backing plates at ambient and elevated temperatures

The tension behavior of Thread-fixed One-side Bolts (TOB) connected T-stubs at ambient and high temperatures was studied experimentally and theoretically. The anchorage force to TOB was provided by the threads on the bolt hole wall which was usually restrained by the limited thickness of the steel plate. The thread length and bending strength of the T-stub flange could be increased by adding backing plates. Two failure modes appeared in ambient temperature tests, which were completely flange yielding and flange yielding accompanied with threads failure. Both steady-state method and transient-state method were used in high temperature test. Test results showed that failure modes might be changed at high temperatures. However, the unfavorable threads failure did not appear at high temperatures which showed the good applicability of TOB. Backing plate was proved to be an effective way to strengthen the TOB connected T-stubs. Tension resistance and initial stiffness of strengthened T-stubs increased obviously while still keeping good ductility in both ambient and high-temperature circumstance. In transient-state test, the increase in load ratio would make the connection more fragile. The failure temperature and failure displacement decreased correspondingly. Design equations for predicting the failure mode and the tension strength of TOB connected T-stubs at high temperatures were proposed, considering effects of large deformation of the T-stub flange at high temperatures. Comparison with test results showed that the proposed design equations could precisely predict the failure mode and the yielding tension strength of strengthened or unstrengthened TOB connected T-stubs at both ambient and high temperatures.