Behaviour of steel and composite beam-column connections in fire
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Experimental and numerical study on behaviour of extended end-plate connections with Q960 steel at elevated temperature
2024, Journal of Constructional Steel ResearchThis paper presented a series of tests to investigate the behaviour of the extended end-plate connection utilizing high strength Q960 steel. A total of 8 specimens were tested, including two under ambient temperature and three under high temperature. The results of the tests indicated that increasing the end-plate thickness from 8 mm to 12 mm significantly enhances the flexural capacity and initial rotational stiffness of the connections but reduces the critical temperature and ultimate rotation. In addition, a higher beam bending moment ratio was found to increase the ultimate rotation of the connections while having minimal impact on the critical temperature. Then, the finite element model of the connections was established to investigate the parametric effect, including column axial pressure ratio, beam bending moment ratio, and end-plate thickness on fire resistance. The numerical analysis indicated that increased column axial pressure ratio and end-plate thickness decreased fire endurance, critical temperature, and ultimate rotation of the connections. On the other hand, increasing the beam-bending moment ratio enhanced the ultimate rotation of the connections. Lastly, a rotation-temperature relationship model was proposed to accurately predict the temperature-rotation curve of high-strength steel Q960 end-plate connections, which was validated with experimental data.
Experimental study on flexural capacity and fire resistance of high strength Q690 steel flush end-plate connections
2023, Thin-Walled StructuresHigh-strength steel is widely used in building structures, but fire-induced damage and collapse of high-strength steel structures cause huge economic losses. As a primary part of the structure, the reliability of beam–column joints is essential for the structure’s fire safety. This paper presents an experimental study on high-strength Q690 steel flush end-plate connections (Q690-FEC) at ambient and elevated temperatures. Ultimate bending capacity tests were conducted at ambient temperature to investigate its structural performance, where initial rotational stiffness, bending capacity, and ultimate rotation were obtained. Numerical models were developed to reproduce the tests, and parametric analyses were performed to investigate the influence of load ratio, end-plate thickness, and bolt diameter. Transient fire-resistance tests were performed on specimens with different end-plate thicknesses, where specimen temperature, furnace temperature, and joint rotation were measured. The test results indicate that increasing end-plate thickness has little influence on the critical temperature and fire resistance. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of Q690-FEC and validated against the experimental data.
Experimental study on high-strength Q460 steel extended end-plate connections at elevated temperatures
2023, Journal of Constructional Steel ResearchThis paper presents an experimental study on high-strength Q460 steel extended end-plate connections at ambient and elevated temperatures. Ambient temperature tests were conducted on connections with 8 and 12 mm end-plates to investigate the ambient temperature structural response, including the initial rotational stiffness, plastic flexural resistance and ultimate rotation. The results show that high-strength steel connection with 12 mm end-plates significantly improves mechanical properties compared to that with 8 mm end-plate with an increase of 22% at least while not influencing the failure modes. Then, the experimental results were compared with the theoretical predictions of Eurocode 3. There are reasonable agreements between these two methods on plastic resistance, while the calculation by Eurocode 3 on initial rotational stiffness exhibits much higher results. In addition, the temperature distribution of the connection specimens and furnace air, rotation-temperature characteristics, and failure modes of the connections in transient tests were obtained to study the influence of different end-plate thicknesses. The 12 mm end-plate effectively improves the connection's rotation capacity at elevated temperatures with an increase of 29% compared to 8 mm end-plate while influencing the critical temperature and fire endurance lightly. Besides, the fire performance results were compared and discussed between mild steel and high-strength steel connections. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of high-strength steel end-plate connections under transient conditions and validated against the experimental data with considerable accuracy.
The influence of loading rate on the ultimate capacity of bolted T-stubs at ambient and high temperature
2021, Fire Safety JournalIn case of accidental actions, the robustness of multi-storey steel frame buildings depends to a large extent to the performance of the beam-to-column joints. For an extreme scenario that involves a column loss under fire, the dynamic process can induce high strain rates and therefore needs to be considered when evaluating the resistance and ductility of the beam-to-column connections. End plate bolted connections are widely used in the steel framed constructions. The simple macro-component through which the response of such a connection is assessed, consists in the T-stub model included in EN1993-1-8.
The paper presents the results of an experimental program on T-stubs subjected to normal and high temperatures, in both quasi-static and high loading rate conditions. While under normal temperature the response of the T-stubs are not significantly influenced by the strain rate, at high temperatures the strain rate determines a change in the failure mode and in the ultimate resistance and deformation. The experimental study highlights the necessity of assessing the strength reduction factors of bolts function of both temperature and strain rate, a critical information in the progressive collapse assessment of structures under fire, in order to obtain realistic results.
Predicting post-fire mechanical properties of grade 8.8 and 10.9 steel bolts
2019, Journal of Constructional Steel ResearchStructural fire safety is one of the primary considerations in the design of high-rise buildings where steel is often a popular material for structural members selection. Therefore, predicting post-fire mechanical properties of steel bolts as a crucial element in steel structures is highly valuable. In this paper, the behavior of the High-Strength Steel Bolts (HSSB), after exposing to fire, is investigated and practical equations for the mechanical properties, including the ultimate strength, the yield strength, and the modulus of elasticity, are proposed as well. Accordingly, Grade 8.8 and Grade 10.9 steel bolts are employed in a variety of sizes, from M6 to M24, experiencing six different target temperatures. After natural cooling, a tensile test is applied to all the bolts, the corresponding stress-strain curves are derived, and finally all required data for each specimen are obtained by means of these curves. Results from these curves indicate that at 400 °C or fewer temperatures, more than 80% of the mechanical properties are recovered. Between 400 °C and 500 °C, the features began to reduce, however, above 500 °C, a sudden drop was noticeable. Besides, by using both the obtained data and the Gene Expression Programming (GEP) as a branch of Genetic Algorithm, equations for mechanical properties of HSSB are derived. The validation results indicate that the relative error of GEP-based models is less than 10%. All in all, the minimum error in the GEP-based models demonstrates favorable equations for post-fire mechanical properties of HSSB and also better predictions than the traditional models.
Modeling of composite beam-column flexible endplate joints at elevated temperature
2016, Composite StructuresThe paper presents a numerical study on two composite cruciform beam–column joints with flexible endplates subjected to elevated temperature. A two 356 × 171 × 51 UB connected to a 254 × 254 × 89 UC labeled Joint-A and two 610 × 229 × 101 UB connected to 305 × 305 × 137 UC labeled Joint-B. Numerical experiments were performed to estimate moment capacity of the joints at ambient temperature. Four fire tests for Joint-A and two for Joint-B were investigated with applied moment varying between 30%–70% of the joint capacity. Heating was applied linearly at a rate of 10 °C/min. Utilizing biaxial symmetry, only one fourth of joint configuration was modeled in ABAQUS. The bare steel and concrete slab components of the joints were modeled using a four-noded tetrahedral element capable of coupled thermal displacement analysis. EC3 recommendations for degradation in strength and stiffness were employed to model steel behavior. The concrete slab was modeled using damaged plasticity. Based on temperature–rotation relationship, the predicted results showed good agreement with experiment data in the elastic range while slight overestimates were observed in the plastic region. The results indicated high stress concentration in the top end of the endplate, top bolts and lower portion of the beam web close to bottom of the endplate. It was also observed that base of the embedded shear studs were heavily stressed. The failure modes of both joints in all loading cases were well predicted in simulation.