Finite element analysis of the flexural behavior of square CFST beams at ambient and elevated temperature

[EN] This paper presents the finite element (FE) analysis and modeling of square concrete-filled steel tube (CFST) members subjected to a flexural load at ambient and elevated temperature. The commercial FE tool ANSYS was used in the 3D modeling taking into consideration material and geometric non-linearities. The developed FE model can accurately predict the ultimate moment capacity of the square CFST members subjected to flexural loads and fire resistance time. A parametric study is conducted using the verified FE model to study the effect of the compressive strength of infilled concrete and the yield strength of the steel tube on the flexural behavior of the square CFST members. The ultimate bending capacity of the CFST members increases by up to 27% when the yield strength of the steel tube increases from 210 MPa to 400 MPa while its fire resistance time decreases. For a D/t ratio equal to 30, the flexural capacity increases by 20% when the compressive strength of the infilled concrete increases from 60 MPa to 100 MPa, while it shows increase in fire resistance time.This research was supported by University Malaya Postgraduate Research Fund (PPP –Project No. PG155–2015B).Javed, M.; Ramli Sulong, NH.; Khan, N.; Kashif, S. (2018). Finite element analysis of the flexural behavior of square CFST beams at ambient and elevated temperature. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 843-850. https://doi.org/10.4995/ASCCS2018.2018.7236OCS84385

Behaviour of steel connections under fire conditions

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On the behaviour of mid-connection in off-centre bracing system

This paper presents theoretical and experimental investigations on the behaviour of mid-connections in an off-centre bracing system. This braced system is preferred by architects because of the eccentricity introduced by the diagonal brace members, which allows a wider area of opening in the frame panel. Assumptions when designing the system in two dimensions has led to severe damage of structures based on observations of the recent Bam earthquake. In this regard, the assumption of mid-connection of the brace elements has a significant effect on the behaviour, stability and lateral buckling load resistance of the system. In order to investigate the effect of mid-connection types on the behaviour of the system, two possible implementations of this connection were considered. Based on the slope-deflection method and equilibrium equation at the connection point, the stiffness matrix was obtained to calculate the lateral buckling load of the system. In addition, to validate the theoretical calculation and practical consideration of the system, two frames of one-third scale were fabricated and tested. A good agreement between the experimental results and the theoretical calculations was obtained

Optimization of Off-Centre bracing system using Genetic Algorithm

In this paper, a method based on genetic algorithm is proposed for determining the optimum connection point with the highest lateral buckling load in the Off-Centre bracing system. This type of bracing system is mostly used in seismic areas and it allows architects to have more openings in the panel area. In this system, the non-straight diagonal member introduces eccentricity to the system and is connected to the corner of the frame by a third member. In designing this system, designers often use "trial and error" to locate the connection point of the brace elements considering various parameters affecting the design such as opening and frame dimensions, cross sectional areas of brace elements and the location of the brace element connection. Hence, finding the best connection point with maximum lateral buckling load can be problematic by the conventional methods. To demonstrate the effectiveness of the proposed GA method, examples with different frame specifications were presented. © 2011 Elsevier Ltd. All rights reserved

Effect of epoxy binder on fire protection and bonding strength of intumescent fire protective coatings for steel

This study focuses on the effect of epoxy emulsion, a binder for producing water-borne intumescent fire protective coating for steel structures. The influence of binder on the fire resistive performance, char formation, thermal stability and bonding strength of the coatings were investigated in detail by using Bunsen burner test, thermogravimetry analysis (TGA), field emission scanning electron microscopy (FESEM) and Instron microtester. It was found that the fire protection performance and foam structure of coating sample D2 was significantly improved by adding 10wt% of epoxy resin which produced the greatest thickness of char layer. In addition, TGA results showed that the residue weight of coating D2 was higher than coating sample D3 with 15wt% of epoxy. This indicated that sample D2 has better anti-oxidation and thermal stability. The results of Instron microtester indicated that the bonding strength of the coatings was improved with the increase of epoxy content

Stochastic response of intact and a removed tendon tension leg platform to random wave and current forces

This work analysed the dynamic response of intact and a removed tendon tension leg platform (TLP) in simultaneous action of random wave and current loads in normal and less severe environments. Two different sea states of extreme severe sea state but less probable and less severe state and most probable are considered in this study. The artificial random wave is simulated by Monte Carlo simulation using Pierson–Moskowitz spectrum. Wave diffraction effect is not considered since the ratio of characteristic dimension to wavelength is less than limit. The coupling in all degree of freedoms and various degrees of nonlinear effects is considered. The inertia, mass, damping matrices of equation of motion and hydrodynamic force vector are formulated and solved numerically using Newmark integration scheme. The statistical results show that removal of one tendon increases surge and tendon tension values, while heave and pitch are not adversely affected in both environments. The response values of the TLP in extreme severe sea state are quite higher compared to less severe sea state. The percentage increase in all degree of freedoms and tendon tension is <5 % when one tendon is removed as compared to intact tendon TLP. It could be concluded that maximum and minimum tension in tendon constraints is equally passed by the TLP tendons

New approach for developing soft computational prediction models for moment and rotation of boltless steel connections

This study aims to minimize the expensive experimental testing of unique boltless steel connections using the prediction power of several computational techniques. Thirty-two tests were conducted on boltless steel connections using double-cantilever test method and their results were compared with developed models using Artificial Intelligence (AI) techniques. Linear Genetic Programming (LGP), Artificial Neural Networks (ANNs) and Adaptive Neuro Fuzzy Inference System (ANFIS) were applied to predict the moment-rotation (M-θ) behavior of boltless steel connections. The predictive performance of the models was assessed by comparing the values of co-efficient of determination (R2), mean square error (MSE) and root-mean-square error (RMSE). The LGP model well predicted the M-θ behavior as compared to the other models. The robustness of the LGP model was further proved by performing different statistical tests