Experimental study on the spalling behaviour of ultra-high strength concrete in fire

High strength construction materials are now attractive owing to their economic and architectural advantages. The higher the material strength, the smaller member size is required. Ultra-high strength concrete (UHSC) encased columns are being developed for the erection of high-rise buildings due to their higher load bearing capacity and smaller cross section size compared to normal strength concrete encased columns. When the UHSC is subject to elevated temperature, explosive fire-induced spalling is more often observed than in normal strength concrete. The consequence of spalling could cause serious life loss and damage to the close key infrastructure. Spalling is mostly due to the UHSC increased density, lower permeability and brittleness. Most of the previous studies show that polypropylene fibres have been found effective in preventing fire spalling. The aim of this experimental study is to discover the minimum polypropylene fibre dosage to control the fire spalling of steel fibre reinforced concrete of 115-135 MPa strength. The experimental study was carried out on 15 concrete specimens with different parameters and two fibre-reinforced concrete encased columns exposed to ISO 834 fire. The study indicates that a polypropylene fibre dosage of 1.365 kg/m3 can prevent the 115-135 MPa ultra-high strength concrete from explosive fire spalling. This polypropylene fibre dosage is lower than that proposed in Eurocode 2, which is 2 kg/m3. The proposed lower polypropylene fibre dosage can potentially bring sustainability (use less polypropylene fibres that are made of crude oil) and economy, as well as improve constructability by improving the workability of fresh concrete. It is also found steel fibres may relieve the fire spalling but not adequate to prevent spalling. Moreover, there is no significant effect of the size and inner temperature of the centre of the concrete specimen on spallin

Numerical study of concrete-filled steel composite (CFSC) stub columns with steel stiffeners

Numerical study of concrete-filled steel composite (CFSC) stub columns with steel stiffeners is presented in this paper. The behaviour of the columns is examined by the use of the finite element software LUSAS. Results from nonlinear finite element analyses are compared with those from corresponding experimental tests which uncover the reasonable accuracy of the modelling. Novel steel stiffeners are used in the CFSC stub columns of this study. The columns are extensively developed considering three different special arrangements of the steel stiffeners with various number, spacing, and widths of the stiffeners. The main variables are: (1) arrangement of the steel stiffeners (C1, C2, and C3); (2) number of the steel stiffeners (2 and 3); (3) spacing of the steel stiffeners (50 mm and 100 mm); (4) width of the steel stiffeners (50 mm, 75 mm, and 100 mm); (5) steel thickness (2 mm, 2.5 mm, and 3 mm); (6) concrete compressive strength (30 MPa, 40 MPa, and 50.1 MPa); (7) steel yield stress ( 234.3 MPa, 350 MPa, and 450 MPa). Effects of the variables on the behaviour of the columns are assessed. Failure modes of the columns are also illustrated. It is concluded that the variables have considerable effects on the behaviour of the columns. Moreover, ultimate load capacities of the columns are predicted by the design code EC4, suggested equation of other researchers, and proposed equation of the authors of this paper. The obtained ultimate load capacities from the analyses are compared with the predicted values. It concludes that EC4 gives more conservative predictions than the equations

Ultra-high strength concrete filled composite columns for multi-storey building construction

10.1260/1369-4332.15.9.1487Advances in Structural Engineering1591487-1504ASED