Department of Civil & Infrastructure Engineering

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This paper describes experimental and numerical investigations conducted to characterize the basic material properties and design of YSt–310 cold–formed structural steel sections at Indian Institute of Technology, Guwahati. Square (SHS) and rectangular (RHS) hollow sections with minimum yield strength of 310 MPa manufactured by Tata Steel India, were considered in the study. Initially, results from elemental analysis via optical emission spectrometer (OES) investigation and metallographic examination using optical microscope are presented. Key stress–strain parameters viz., Young's modulus, proof stress, ultimate strength, percentage elongation, strain hardening exponent etc. were generated based on flat, corner and weld coupon tests data. Extent of corner strength enhancement due to cold – forming determined using Vickers's microhardness test are reported. Additionally, cross – section capacity of the stub columns were also investigated experimentally and numerically. The column capacities generated from test and finite element study are compared with the existing design code – EN 1993–1–1 (EN 1993-1-1, 2005) [1] and design rules – continuous strength method (CSM) (Zhao et al., 2017) [2] and direct strength method (DSM) (North American Specifification for the Design of Cold-Formed Steel Structural Members, 2016; Arrayago et al., 2017) [3,4]. Based on the comparison, modifications on the existing design code and rules are suggested to provide a more accurate and reliable compressive design prediction. © 2017 Elsevier Ltd

World University root node

Thin-Walled Structures

Structural performance of YSt–310 cold–formed tubular steel stub columns

In this paper, a computationally efficient integrated frame-work is developed for coupled thermo-mechanical analysis of 3D frames. It can account for physical phenomena like large deformations, temperature dependent material degradation, permanent plastic deformations and fire induced spalling which are prevalent at elevated temperatures. The developed frame-work utilizes three way sequential coupling between thermal, mass transport and structural analysis. A two level discretization scheme is incorporated where 1D beam column elements are utilized for structural analysis, the cross-section of these beam-column elements are further discretized into matrix of segments. Aforementioned strategy entails sequential coupling of effects of non-uniform temperature and pore pressure across the cross-section into structural analysis. Subsequently structural analysis is performed with an updated Lagrangean based formulation with force deformation relationships deduced form classical Euler-Bernoulli beam column theory. Critical physical phenomena like cracking, crushing, spalling and transient states of strain in case of concrete and yielding in case of steel are duly accounted. Cross-sectional reduction due to spalling are accounted for by replacing the spalled segments with void segments in the subsequent time steps. Numerical examples of steel and concrete structures subjected to various fire scenarios are presented to demonstrate the accuracy of developed framework. Furthermore, progressive collapse analysis is carried out for concrete and steel 3D subjected to fire. © 2017 The Authors. Published by Elsevier Ltd.

Fulltext

Procedia Engineering

Efficient Three Dimensional Nonlinear Thermo-Mechanical Analysis of Structures Subjected to Fire

Water Science and Technology: Water Supply

Performance evaluation of metal impregnated activated carbon composite for removal of fluoride under different solution chemistry

Results of an experimental study on the countermeasure of scour depth at circular piers are presented. Experiments were conducted for pier scour with and without a splitter plate under a steady, uniform clear-water flow condition. The results of pier scour without splitter plate were used as a reference. Different combinations of lengths and thicknesses of splitter plates were tested attaching each of them to a pier at the upstream vertical plane of symmetry. Two different median sediment sizes (d 50 = 0.96 and 1.8 mm) were considered as bed sediment. The experimental results show that the scour depth consistently decreases with an increase in splitter plate length, while the scour depth remains independent of splitter plate thickness. In addition, temporal evolution of scour depth at piers with and without a splitter plate is observed. The best combination is found to be with a splitter plate thickness of b/5 and a length of 2b. Here, b denotes the pier diameter. An empirical formula for the estimation of equilibrium scour depth at piers with splitter plates is obtained from a multiple linear regression analysis of the experimental data. The flow fields for various combinations of circular piers with and without splitter plate including plain bed and equilibrium scour conditions were measured by using an acoustic Doppler velocimeter. The turbulent flow fields for various configurations are investigated by plotting the velocity vectors and the turbulent kinetic energy contours on vertical and horizontal planes. The splitter plate attached to the pier deflects the approach flow and thus weakens the strength of the downflow and the horseshoe vortex, being instrumental in reducing the equilibrium scour depth at piers. The proposed method of pier scour countermeasure is easy to install and cost effective as well. © 2017 Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences.

Acta Geophysica

Splitter plate as a flow-altering pier scour countermeasure

In a turbulentwall shear flow, we explore, for the first time, the stochastic mechanics of loose boundary particle transport, having variable particle protrusions due to various cohesionless particle packing densities. The mean transport probabilities in contact and detachment modes are obtained. The mean transport probabilities in these modes as a function of Shields number (nondimensional fluid induced shear stress at the boundary) for different relative particle sizes (ratio of boundary roughness height to target particle diameter) and shear Reynolds numbers (ratio of fluid inertia to viscous damping) are presented. The transport probability in contact mode increases with an increase in Shields number attaining a peak and then decreases, while that in detachment mode increases monotonically. For the hydraulically transitional and rough flow regimes, the transport probability curves in contact mode for a given relative particle size of greater than or equal to unity attain their peaks corresponding to the averaged critical Shields numbers, from where the transport probability curves in detachment mode initiate. At an inception of particle transport, the mean probabilities in both the modes increase feebly with an increase in shear Reynolds number. Further, for a given particle size, the mean probability in contact mode increases with a decrease in critical Shields number attaining a critical value and then increases. However, the mean probability in detachment mode increases with a decrease in critical Shields number. © 2017 Author(s).

Physics of Fluids

Stochastic mechanics of loose boundary particle transport in turbulent flow

The bedforms on a biofilm-coated sediment (biosediment) bed are different from those on a noncohesive sediment bed under an identical flow condition and sediment particle size without biofilm. Bedforms on biosediment beds can therefore modify the resistance to flow. In this study, experiments were conducted for the bedforms on both cohesive and biosediment beds. The biofilm coat around the fine cohesive sediment particles of a median size less than 0.1 mm was cultivated within a laboratory flume. The bedforms on biosediment beds are identified as dunes by comparing the Froude number and the Shields parameter. The equations of bedform steepness, bedform height, and equivalent roughness for biosediment beds are empirically derived. The maximum variations of equivalent roughness, Chézy coefficient, and Manning coefficient for a biosediment bed are 96.7, 60.5, and 44.3%, respectively, as compared to those for a noncohesive sediment bed under an identical flow condition and sediment size without biofilm. © 2017 American Society of Civil Engineers.

Journal of Hydraulic Engineering

Bedforms and flow resistance of cohesive beds with and without biofilm coating

Fracture and mechanical properties of the water saturated sedimentary rocks have been experimentally investigated in the present paper. Three types of sandstones and one type of shale were saturated in water for different periods of time. They were then tested for their index geomechanical properties such as Brazilian tensile strength (BTS), Young’s modulus (YM), P-wave velocity and all pure and mixed-mode fracture toughness (FT). FT was measured using semicircular bend specimens in a three-point bend set-up. All the geomechanical and fracture properties of the saturated rocks were compared together to investigate their interrelations. Further, statistical methods were employed to measure the statistical significance of such relationships. Next, three types of fracture criteria were compared with the present experimental results. Results show that degree of saturation has significant effect on both the strength and fracture properties of sedimentary rock. A general decrease in the mechanical and fracture toughness was noticed with increasing saturation levels. But, t-test confirmed that FT, BTS, P-wave velocity and YM are strongly dependent on each other and linear relationships exist across all the saturation values. Calculation of the ‘degradation degree’ (DD) appeared to be a difficult task for all types of sedimentary rocks. While in sandstone, both the BTS and mode-I FT overestimated the DD calculated by YM method, in shale BTS was found to give a closure value. © 2017, Springer-Verlag GmbH Austria.

Rock Mechanics and Rock Engineering

Effect of Water Saturation on the Fracture and Mechanical Properties of Sedimentary Rocks

Modelling heterogeneous traffic flow lacking in lane discipline is one of the emerging research areas in the past few years. The two main challenges in modelling are: capturing the effect of varying size of vehicles, and the lack in lane discipline, both of which together lead to the ‘gap filling’ behaviour of vehicles. The same section length of the road can be occupied by different types of vehicles at the same time, and the conventional measure of traffic concentration, density (vehicles per lane per unit length), is not a good measure for heterogeneous traffic modelling. First aim of this paper is to have a parsimonious model of heterogeneous traffic that can capture the unique phenomena of gap filling. Second aim is to emphasize the suitability of higher-order models for modelling heterogeneous traffic. Third, the paper aims to suggest area occupancy as concentration measure of heterogeneous traffic lacking in lane discipline. The above mentioned two main challenges of heterogeneous traffic flow are addressed by extending an existing second-order continuum model of traffic flow, using area occupancy for traffic concentration instead of density. The extended model is calibrated and validated with field data from an arterial road in Chennai city, and the results are compared with those from few existing generalized multi-class models. © 2016 Elsevier B.V.

Physics Letters, Section A: General, Atomic and Solid State Physics

Heterogeneous traffic flow modelling using second-order macroscopic continuum model

A novel coupled framework for analysis of reinforced concrete (RC) and steel planar frames subjected to fire is developed with three-way coupling between heat transfer, mechanical deformations and pore pressure build-up. Structural members are discretized in space using a two-level scheme where the mechanical solver utilizes 1D line elements, and the thermal and the pore pressure solvers work on 2D finite element (FE) meshes for each sub-span used by the mechanical solver. Such a strategy enables consideration of effects of large deformations, temperature-dependent material properties (thermal, moisture transport and mechanical), and spalling. None of the earlier developed frameworks considered a three-way coupling between mechanical, thermal and pore pressure solvers without employing a full-fledged 3D FE scheme. A matrix method type approach, developed herein, enables modeling of the three main physical processes taking place in RC members during fire without the need to consider full-fidelity 3D FEM. Several numerical examples are presented to demonstrate the accuracy and applicability of the developed framework in fire analysis of normal and high strength RC and steel structures. © 2017 Elsevier Ltd

Computers and Structures

An integrated framework for nonlinear analysis of plane frames exposed to fire using the direct stiffness method

This study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses. We explore the relationship between the two regimes in a representative, US Midwestern stream with semi-cohesive bank soils, namely Clear Creek, IA. Photo-Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion. We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt-sized particles at low shear stresses over sand-sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several-fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows. The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.