MOMENTUM INTEGRAL METHOD FOR FORCED CONVECTION IN THERMAL NONEQUILIBRIUM POWER-LAW FLUID-SATURATED POROUS MEDIA

Forced convection heat transfer for power-law fluid flow in porous media was studied analytically. The analytical solutions were obtained based on the Brinkman-extended Darcy model for fluid flow and the two-equation model for forced convection heat transfer. As a closed-form exact velocity profile is unobtainable for the general power-law index, an approximate velocity profile based on the parabolic model is proposed by subscribing to the momentum boundary layer integral method. Heat transfer analysis is based on the two-equation model by considering local thermal nonequilibrium between fluid and solid phases and constant heat flux boundary conditions. The velocity and temperature distributions obtained based on the parabolic model were verified to be reasonably accurate and improvement is justified compared to the linear model. The expression for the overall Nusselt number was derived based on the proposed parabolic model. The effects of the governing parameters of engineering importance such as Darcy number, power-law index, nondimensional interfacial heat transfer coefficient, and effective thermal conductivity ratio on the convective heat transfer characteristics of non-Newtonian fluids in porous media are analyzed and discussed.     

Theoretical study on concrete-filled steel tubes under static and variable repeated loadings

This paper presents an analytical study for modelling the behaviour of concrete-filled steel tubular (CFST) columns subjected to Static Loading (SL) and Variable Repeated Loading (VRL). The variables considered in this study are concrete strength and load eccentricity. Simple mathematical models are developed and used in the analysis. The analytical results show that the incremental collapse (IC) occurs in high load ranges in CFST columns under VRL and instability failure occurs under SL. The CFST columns with large end load eccentricity were found to fail at a low upper limit load level than that with small eccentricity of loading. The IC failure was found to be unaffected by the strength of concrete infill. The hollow steel tubular (HST) columns showed similar behaviour under SL and VRL protocols. The study showed that the theoretical analyses satisfactorily model the actual behaviour of the columns under SL and VRL protocols.     

Behaviour of concrete-filled steel tubes under static and variable repeated loading

This paper presents the results of static loading (SL) and variable repeated loading (VRL) tests on concrete filled steel tubular (CFST) columns. Assessment of the columns was based on its length, concrete strength and load eccentricity. The column behaviour (with and without filling) from the tests was studied. The ultimate strength of the columns subjected to VRL reduced by up to 16% after undergoing a number of load cycles. The incremental collapse (IC) limit was found to lie between 70% and 88% of the static collapse load for CFST columns. The deformations at IC limit were significant and could affect practical designs. The theoretical strengths of the stub and long columns tested are determined on the basis of building code 318 of the American Concrete Institute, and compared with the test results. The squash load equation of the code was found to underestimate the nominal strength of short composite columns.     

Incremental collapse threshold for pushout resistance of circular concrete filled steel tubular columns

This paper presents the results of a series of pushout tests using static loading (SL) and variable repeated loading (VRL) on concrete filled steel tubular (CFT) circular stub columns. The main parameters examined in this paper were the strength and age of concrete and the loading protocol. Under SL tests, the interface bond strength in CFT columns filled with normal strength concrete was found to be higher than that with high strength concrete. The SL test results showed that the interface bond strength varied from 0.41 to 0.85 MPa but from 0.33 to 0.66 MPa under VRL tests. A lower bound for the incremental collapse threshold of the pushout resistance of 70% of the static collapse load was empirically derived. Also an expression of the average growth of slip per loading cycle was empirically derived and recommended for design purposes. A comparison between the bond strength of the columns obtained from the present and previous test results, and available design codes is presented. Two newly derived bond strength limits were experimentally obtained and proposed for the design of structures subjected to either predominantly static or predominantly cyclic loading.