This paper presents an experimental investigation on the behavior of six   reinforced concrete columns under elevated temperature. An expanded clay aggregate (LECA) was used in three reinforced concrete columns ,other three remain columns used natural aggregate .All RC columns have similar cross sectional dimensions of 150mm ×150 mm (width× height); and 1250mm total length. The columns were designed according to ACI Committee 318-2014 and exposed to different elevated temperatures of 400 oC and500 oC. After exposure to elevated temperature, the columns were axially loaded by compression force using an eccentricity ratio (e/h) equal to 0.5. The experimental test  results demonstrated a remarkable decrease in the ultimate carrying capacity of the columns when subjected to elevated temperature. The experimental test results have also revealed that the lightweight reinforced concrete columns have more fire resistance than the normal weight reinforced concrete columns under same elevated temperature. The ultimate load capacity of LWRC columns decreases by about 6.5 % ,and 14.286 %, at elevated temperature magnitude of 400 ºC, and 500 ºC respectively, compared with the control column at ambient temperature. However, the ultimate load capacity of NWRC columns decreases by about 14.15 %,and 28.571 %, at elevated temperature magnitude of 400 ºC, and 500 ºC respectively, compared with the control column at ambient temperature.

In this study a numerical simulation of the behaviour and failure modes of axially compressed steel column subjected to transverse impact by a rigid mass at different impact speeds and locations is presented. Firstly, the capability of the present numerical model to trace the response and to predict different failure modes of transversely impacted beams and columns with and without axial compressive force has been validated. These failure modes include plastic global failure, tensile tearing failure and transverse shear failure. The validation was performed by comparing simulation results in term of the contact force, deformation shape, failure mode and the maximum transverse displacement with available published experimental test results by others. The progressive damage and failure model available in ABAQUS/Explicit has been utilized in the present numerical models to account for material shear and tensile tearing failure under impact. Comparisons between the experimental and simulation results confirmed that the numerical models were able to accurately predict the aforementioned failure modes. Thereafter, a parametric study has been conducted to investigate the effects of several parameters on the response of axially loaded steel column, based on the results of which simplifying assumptions on column behaviour under impact can be made to develop appropriate design calculation methods for steel columns under such loading conditions.

The main objective of this study is to develop a simplified analytical approach to predict the critical velocity of vehicle impact on steel columns. This method utilizes the energy balance principle with a quasi-static approximation of the steel column response. Results of ABAQUS numerical simulations of the dynamic impact response of axially loaded steel columns under vehicle impact are used to validate the proposed method. To account for the effect of vehicle impact, a simplified numerical vehicle model has been adopted using a spring-mass system with a bilinear spring load-deformation relationship. The validation results show good agreement between the analytical method results and the numerical results with the analytical results tending to be on the safe side.

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