Analytical Behavior of Eccentrically Loaded Concrete Encased Steel Columns Subjected to Standard Fire including Cooling Phase

Er-Feng Du,Gan-Ping Shu,Xiao-Yong Mao 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.1

A nonlinear 3-D finite element analysis (FEA) model was developed to predict the behavior of eccentrically loaded concrete encased steel (CES) columns subjected to ISO-834 standard fire including heating and cooling phases. The finite element model has been validated against published tests conducted at elevated temperatures. Comparisons between the predicted results and the test results show that this model can accurately predict the behavior of CES columns under fire. The FEA model was then used to investigate the typical temperature-time curve and mid-height lateral deformation-time curve of eccentric compression CES columns in a complete loading history including initial loading, heating and cooling. It is shown that the temperature delay is obvious at the inner layers of concrete. The fire resistance of a CES column should be checked for the full process of fire exposure until temperatures everywhere in the column start to decrease. The lateral deformation of the column still gradually increases during the cooling phase and the column may fail during that phase. There is a large residual deformation after the fire exposure. Furthermore, the variables that influence the behavior of the CES columns under fire were investigated in parametric studies. It is found that the main parameters which influence the lateral deformation-time curve of the column during the full process of fire exposure are load ratio, slenderness ratio, duration time, depth to width ratio and steel ratio, and the main parameters which influence the residual deformation ratio of the column after fire are load ratio, duration time, cross-sectional depth and steel ratio.

Parameters Effect on Predicting Fire Resistance of Ultra-high Strength Concrete Filled Protected Square Steel Tubular Columns

Xiao Lyu,Gan-Ping Shu,Er-Feng Du 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.5

Ultra-high strength concrete (UHSC) with compressive strength greater than 100 MPa at room temperature has been developed for concrete fi lled square steel tubular column for use in high-rise buildings. The fi re resistance of UHSC fi lled protected square steel tubular columns exposed to the standard ISO fi re is investigated in this paper. For this purpose, numerical heat transfer analysis and nonlinear thermal stress analysis were conducted by taking into account the existing material properties, such as the thermal and mechanical properties of UHSC and high strength steel. The numerical analyses were carried out and the results were validated against the test results in terms of heat distribution and mechanical behavior. Comparison with the test results showed a reasonable agreement with fi nite element results in terms of temperature fi eld prediction and load displacement behavior during the fi re. Finally, based on the validated fi nite element model, the eff ects of fi re protection thickness, load ratio, the strengths of concrete and steel, steel contribution ratio, and relative slenderness ratio on the fi re resistance of UHSC fi lled square steel tubular columns were carried out and discussed.

Buckling analysis of elastically-restrained steel plates under eccentric compression

Ying Qin,Gan-Ping Shu,Er-Feng Du,Rui-Hua Lu 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.3

In this research, the explicit closed-form local buckling solution of steel plates in contact with concrete, with both loaded and unloaded edges elastically restrained against rotation and subjected to eccentric compression is presented. The Rayleigh-Rize approach is applied to establish the eigenvalue problem for the local buckling performance. Buckling shape which combines trigonometric and biquadratic functions is introduced according to that used by Qin <i>et al</i>. (2017) on steel plate buckling under uniform compression. Explicit solutions for predicting the local buckling stress of steel plate are obtained in terms of the rotational stiffness. Based on different boundary conditions, simply yet explicit local buckling solutions are discussed in details. The proposed formulas are validated against previous research and finite element results. The influences of the loading stress gradient parameter, the aspect ratio, and the rotational stiffness on the local buckling stress resultants of steel plates with different boundary conditions were evaluated. This work can be considered as an alternative to apply a different buckling shape function to study the buckling problem of steel plate under eccentric compression comparing to the work by Qin <i>et al</i>. (2018), and the results are found to be in consistent with those in Qin <i>et al</i>. (2018).

Post-fire Study on Mechanical Properties of Damaged Ultra-high Strength Concrete

Xiao Lyu,Guang-Hao Jia,Gan-Ping Shu,Xin Zhang,Er-Feng Du,Wen-Ming Wang 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.6

In order to study the eff ect of steel tube, pre-load and temperature on residual performance of heated ultra-high strength concrete (UHSC), an experimental program was carried out to investigate the physical and mechanical properties of UHSC post-fi re in room temperature. With total of 54 standard cylindrical concrete specimens subjected to various temperatures ranging from 62 °C to 496 °C, their residual compressive strength, elastic modulus, peak strain was measured after natural cooling down. By comparing the test results of standard cylindrical concrete specimens with the results of the bare specimens in and after fi re, it is known that the residual compressive strength of standard cylindrical concrete specimens decayed more serious after exposing to same temperature. Seen from the results, the temperature which the specimens suff ered was found to be responsibility to the reduction of the compressive strength, elastic modulus, peak strain. As the temperature up to 300 °C, the strength reduction coeffi cient of UHSC was 0.67 ~ 0.68 and the elastic modulus reduction coeffi cient of UHSC was 0.41 ~ 0.51 with peak strain coeffi cient ε cr ( T ) /ε 0 1.57 ~ 1.67. Finally, based on the analysis of test results, simple formulae were proposed to describe the eff ect of temperature on residual performance of heated UHSC which infi lled the steel tube.

Innovative displacement-based beam-column element with shear deformation and imperfection

Yi-Qun Tang,Yue-Yang Ding,Yao-Peng Liu,Siu-Lai Chan,Er-Feng Du 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.1

The pointwise equilibrium polynomial (PEP) element considering local second-order effect has been widely used in direct analysis of many practical engineering structures. However, it was derived according to Euler-Bernoulli beam theory and therefore it cannot consider shear deformation, which may lead to inaccurate prediction for deep beams. In this paper, a novel beam-column element based on Timoshenko beam theory is proposed to overcome the drawback of PEP element. A fifth-order polynomial is adopted for the lateral deflection of the proposed element, while a quadric shear strain field based on equilibrium equation is assumed for transverse shear deformation. Further, an additional quadric function is adopted in this new element to account for member initial geometrical imperfection. In conjunction with a reliable and effective three-dimensional (3D) corotational technique, the proposed element can consider both member initial imperfection and transverse shear deformation for second-order direct analysis of frame structures. Some benchmark problems are provided to demonstrate the accuracy and high performance of the proposed element. The significant adverse influence on structural behaviors due to shear deformation and initial imperfection is also discussed.