The relation between the state indices and the characteristic features of undrained behaviour of silty sand

The characteristic features of a series of isotropically and K₀-consolidated undrained triaxial compression behaviour of a silty sand were investigated for a range of initial void ratio ($e)$ and mean effective confining stress ($p^{\prime }$). The silty sand used in this study contained about 10% natural fines. The critical state line (CSL) of K₀-consolidated specimens, K₀U was slightly lower than the CSL for isotropically consolidated specimens, CIU. The respective CSLs for K₀U and CIU were used to define state indices, such as state parameter ($\psi )$, state index ($I_s$), state pressure index ($I_p$) and modified state parameter (${\psi }_m$), within critical state soil mechanics (CSSM) framework. It was found that each state index exhibit a unique relation with liquefaction potential, irrespective of consolidation type, however different relationships were observed between state indices and the stress ratio at the triggering of liquefaction, ${\eta }_{\mathit{IS}}$ or the liquefaction resistance, $q_{\mathit{IS}}$. The correlation of characteristic features of undrained shearing (i.e., liquefaction potential, ${\eta }_{\mathit{IS}}$ and $q_{\mathit{IS}}$) and drained shearing (maximum rate of volume change, ${\left(d{\epsilon }_v/d{\epsilon }_a\right)}_{\mathit{m}\mathit{a}\mathit{x}}$) with state indices were compared statistically in terms of root mean square deviations (RMSD). All characteristic features of undrained shearing generally showed the best correlation with $I_p$ in term of RMSDs, however $\psi$ showed comparatively wider scatter for the specimens showing flow and limited flow behaviour.     

Effects of temperature on the shear strength of saturated sand

The effect of temperature on the shearing response of saturated, dense sand was investigated using a series of temperature-controlled, isotropically-consolidated, hollow cylinder triaxial compression tests, where specimens were heated in drained conditions followed by shearing in undrained conditions. As expected, the deviatoric stress at the peak state (i.e., the undrained shear strength) was observed to increase with increasing initial mean effective stress. However, it was observed to decrease linearly with increasing temperature. The effects of temperature on the deviatoric stress at the peak state were attributed to a linear increase in the magnitude of negative shear-induced pore water pressure at the peak state with temperature. The relationship between the undrained shear strength and the pore water pressure with changes in temperature was represented well by linear equations. When the shear strength was interpreted in terms of the critical state, no obvious changes in the critical state line in the $p^{\prime }-q$ plane were observed, and the critical state friction angle was unaffected by temperature. During drained heating, the dense sand specimens were observed to expand volumetrically, causing the normal consolidation line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane to shift upward with increasing temperature without a change in the slope. The negative pore water pressure during undrained shearing caused the state paths of the dense sand specimens to move to the right. As the magnitude of negative pore water pressure increased with increasing temperature, no obvious effects on the critical state line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane were observed.     

Window ejected flame width and depth evolution along facade from under-ventilated enclosure fires

This paper investigates window ejected flame width and depth evolutions along facade from under-ventilated enclosure fires. Experiments are carried out by 1:4 scale model. Two CCD cameras are employed to record the evolutions of flame depth and width. The flame base position (vertical height above the bottom of the opening), flame depth (width) along with their maximum values and corresponding positions (vertical height above the flame base position) are measured and analyzed by non-dimensional scaling. It is found that the flame base position is independent of fire heat release rate and its ratio to opening height is nearly the same. The flame depth for all heat release rates and the flame width for openings with aspect ratio in the range of $0.5\le W/H\le 1.5$ (the “(semi-) axi-symmetrical flame type”) first increases, reaching a maximum value and then decreases with height. However, for the opening with a relative larger aspect ratio ($W/H=2$) (“wall flame type”), the flame width decreases monotonously with height. The maximum flame width and its corresponding vertical position for “(semi-) axi-symmetrical flame type” are found to be well correlated by characteristic length scale ${\ell }_1$ [=${(A\sqrt{H})}^{2/5}$] non-dimensionally after normalized by the flame height. Meanwhile, the maximum flame depth for all conditions is found to be well correlated by characteristic length scale ${\ell }_2$ [=${(A{H}^2)}^{1/4}$] non-dimensionally after normalized by the flame height.     

Flexural strength of hollow tubular flange plate girders with slender stiffened webs under mid-span concentrated loads

A three-dimensional elastic finite element (FE) model, considering merely the geometric nonlinearity, is used in the first part of this paper to study the overall buckling resistance of hollow tubular flange plate girders (HTFPGs). Modeling is conducted using the general-purpose FE software package ABAQUS under mid-span concentrated loads. The developed model consists of the type and number of elements that allows capturing the different possible buckling mode patterns including local, interactive and lateral-torsional buckling. Finite element results revealed that, unlike the case of conventional beams with solid webs, the moment-gradient factor $C_b$ is significantly influenced by the girder geometry and slenderness. Hence, an equation representing the $C_b$ factor for the case of HTFPGs with slender stiffened webs is proposed. The paper extends to investigate the nonlinear flexural strengths of such girders. The results are compared to the AISC predictions. The original AISC predictions are found to be highly conservative using the code recommended $C_b$ value as well as the current proposed value. However, the suggested AISC strength (found in Hassanein et al., 2013 [1]) using $C_b=1.35$ is found to be the best among other values but it suffers from the discontinuity in the flexural strength-unbraced length relationship. Accordingly, a line representing the middle part of this relationship is currently assumed. Comparisons with FE results indicate that the currently proposed AISC method can fairly predict the flexural strength of the HTFPGs with slender stiffened webs.