Corner Walls Research Articles

Geogrid reinforced brick buildings for earthquake disaster mitigations

In a severe earthquake, the walls of brick buildings experience in-plane shear and out-of-plane bending, leading to diagonal crack and corner failure, respectively. In this study, an experimental investigation was carried out to observe the above damages on brick masonry buildings reinforced with geogrid embedded in bed joint mortar of the walls. It was observed that the geogrid reinforced brick panels showed better shear strength, lateral strength, ductility, etc. A qualitative comparison was made using a sinusoidal shake table test on a one-fourth single-room building model consisting of two sets of corner walls with and without geogrid reinforcement. It was observed that the corner wall without reinforcement showed crack initiation at 0.45 g and complete collapse with over toppling of the transverse wall at 0.90 g. In contrast, no sign of damages for the corner walls strengthened with geogrid reinforcement for any level of shaking.

Modeling of hydrogen dispersion from hydrogen fuel cell vehicles in an underground parking garage

Hydrogen is a promising energy carrier that will become competitive in the near future. The present study modeled hydrogen leaks and diffusion in an actual size underground parking garage with the numerical model validated by scale experimental data. The results show that the hydrogen concentration distributions are not uniform in the gas mixture layer along the ceiling and the initial front velocity of the gas mixture layer decays with horizontal distance from the leaking car. The vertical filling front velocity for times after 600 s remain constant in the near field but increases linearly with distance in the far field. The corner walls did not significantly affect the far-field concentration distributions and the ventilation layout with vents in the garage corners provided better hydrogen removal. These results can be used to predict the hydrogen concentration buildup in large confined spaces and to help design underground parking garage ventilation systems.

Experimental study of corner wall fires with one or two combustible walls

The corner fire characteristics with two inert walls are compared against those with one or two combustible corner walls through a set of standard Single Burning Item (SBI) tests. The study examines how the corner fire behavior is affected by flame spread over one or two walls. In the case of flame spread over one corner wall, the inert side is a Calcium Silicate (CS) panel. As for the combustible wall, two different materials have been tested, namely, plywood and Medium-Density Fiberboard (MDF) panels. The results indicate that the simultaneous burning of two panels in the corner geometry increases the Heat Release Rate (HRR) contribution of each panel by 45–50%. This is because the burning of one corner wall increases the temperatures on the adjacent wall significantly, occasionally by more than 200 °C, and increases the heat fluxes on both corner walls at the same time, sometimes by nearly 20%. The results of HRR, Smoke Production Rate (SPR), flame heights, pyrolysis front propagation, panel temperatures, and total heat fluxes at several characteristic locations are presented.

Out‐of‐plane shaking table tests of full‐scale historic adobe corner walls retrofitted with timber elements

SummaryHistoric adobe structures pose a high seismic risk mainly because of the poor out‐of‐plane bending response of their walls that may produce fatalities and significant economic, cultural, and heritage losses. In this paper, we propose a retrofitting technique that increases the wall strength for both in‐plane and out‐of‐plane directions. This technique consists of vertical and horizontal timber elements symmetrically installed on each face of the wall to form a confining wood frame, supplemented with vertical tensors that pre‐compress the wall. This study evaluates the performance of this retrofitting technique with a two‐set experimental program on full‐scale historic adobe walls. On the first set, four specimens were subjected to a static overturning test with boundary conditions representing the confinement effect at both ends by orthogonal walls. On the second set, three full‐scale specimens, one unretrofitted and two retrofitted, were subjected to four ground motion records on a shaking table to assess the out‐of‐plane dynamic behavior of typical corner walls. The unretrofitted specimen collapsed during the second motion (peak ground acceleration [PGA] = 0.39 g), while both retrofitted walls survived all four motions (maximum PGA of 0.75 g) proving the high effectiveness of the proposed retrofitting. The addition of base anchors as a variation of the retrofitting technique significantly reduced the rocking effects and the residual drifts of the system, thus improving its overall seismic performance. Further research is needed to develop guidelines for seismic retrofit of heritage buildings including multistory full‐scale tests of specimens with various types of openings and retrofitting strategies that minimize their architectural impact.

Hydrodynamics of octagonal culture tanks with Cornell-type dual-drain system

Large culture tanks of several hundred or thousand m3 size are generally encouraged for economic advantages in Recirculating Aquaculture Systems (RAS). Out of numerous possibilities in designing the inlet and outlet configurations in octagonal culture tanks, the inlet pipes near the corner walls and the outlets at the tank’s center and/or on side wall are some of the widely-used configurations. The use of wall drain to achieve a controlled flow pattern in the tank, however, influences distinct flow features such as pressure, velocity, uniformity and turbulence in the tank, which are of theoretical interest as well as practical importance. A finite volume description of the flow in an octagonal culture tank at full-scale was therefore developed using Realizable turbulence model with second order accuracy in space and time. The tank was equipped with an inlet pipe near the corner wall and dual-drain outlet system of Cornell-type. The base case had a flow configuration of 45% of flow through central bottom drain, and the rest through the wall drain. Model verification was performed using grid convergence tests, and validation was conducted using Acoustic Doppler velocimetry (ADV) based velocity measurements. The effect of wall drain on the large-scale and small-scale turbulent structures was studied using the distribution of turbulent kinetic energy and vorticity respectively. The parametric study on the flow-split between the two outlets was analyzed using different flowfield indicators, such as flow velocity, uniformity, vorticity strength, maximum absolute vorticity and swirl number. Such an inclusive analysis not only explores the hydrodynamics in the commercial culture tanks with Cornell-type dual-drain but also recommends the farmers with the suitable flow-split between such outlet systems.

Experimental study on flame spread behavior along poly(methyl methacrylate) corner walls at different altitudes

The effects of altitude and intersection angle on the flame spread behavior and pyrolysis front characteristics along corner walls were experimentally studied. The experiments were conducted using mock corners made of poly(methyl methacrylate) slabs with intersection angles varying from 60° to 120° at two altitudes of 29.8 and 3658.0 m. Measurements were taken for the upward and lateral flame spread rates, the flame heights, the flame heat flux to the fuel surface, and the mass loss rates of the tested slabs. An “M”-shaped pyrolysis front was observed for all the intersection angles examined at both altitudes. The upward flame spread rate increases with decreasing intersection angles while no obvious trend was found for lateral spread rate when the intersection angle is varied. The high altitude leads to a spread rate about half of that at the lower altitude both for upward and lateral spread irrespective of the intersection angle. The measured mass loss rates are significantly higher than twice of that over a flat vertical slab.

Application of a Statistical Narrow Band Model to CFD Modelling of Upward Flame Spread Over PMMA Walls

A statistical narrow band (SNB) radiation gas model has been incorporated into a Reynolds-averaged Navier-Stoke (RANS) based computational fluid dynamics (CFD) code. The coupled CFD code is used in this work to simulate two upward flame spread scenarios: the first one concerns flame spread over a vertical PMMA wall, while the other represents flame spread along vertical corner walls. For comparison purpose, the weighted-sum-of-greygases (WSGG) model was also used. Simulation results indicate that the CFD model is capable of predicting reasonably the flame spread phenomenon over simple materials such as PMMA. Compared to the WSGG approach, the SNB model generally yields more accurate results thanks to a better predicted gas flow field which in turn improves the prediction of the radiative heat fluxes imposed on solid surfaces and consequently that of the flame spread rate and heat release rate.

Effect Of Radiation Models On Cfd Simulations Of Upward Flame Spread

In combustion applications, the weighted-sum-of-grey-gases (WSGG) model is widely used because it is computationally efficient, but it often yields relatively large errors. The objective of this study is to examine the effect of radiation models on CFD predictions of flame spread. To this end, a statistical narrow band (SNB) model and the WSGG model are employed for the simulation of two upward flame spread scenarios, one being a largescale flame spread over a vertical PMMA wall while the other representing flame spread along vertical corner walls. The entire flame spread model also consists of a four equation turbulence model, an eddy-break-up (EBU) combustion model, a discrete transfer (DT) radiation model, a simple soot model and a non-charring pyrolysis model. Quantitative comparison is made between the prediction results obtained with the SNB model and the WSGG model as well as the experimental data. Results clearly show that the SNB model yields more accurate results than the WSGG approach. However, the SNB model is about four to five times more time consuming than the WSGG model. Therefore, for simulations of complex engineering applications a compromise between accuracy and numerical efficiency should be taken into account.

Thermal characteristics of fires in a noncombustible corner

A series of fire tests were conducted in a full-scale open corner with a ceiling to measure the thermal field generated by fires located in a corner. Fires were produced using different size (0.17, 0.30, and 0.50 m) square and line propane burners with heat release rates ranging from 25 to 300 kW. Burner distance below the ceiling was also considered. Measurements included flame length, gas temperatures, and total incident heat flux onto the noncombustible corner boundaries. Flame lengths were related to Q*, with the burner dimension as the length scale, and were found to be similar to those measured in studies with no ceiling. By dividing the corner into three regions (corner walls ( z/ H<0.8), top of the walls ( z/ H>0.8), and ceiling, empirical relations for estimating the gas temperatures and incident heat fluxes were developed. Incident heat fluxes on the corner walls were measured to be similar to those in other studies.

L-, T-, AND CROSS-JOINTS OF LINED DUCTS

Much effort has been spent to increase the attenuation of lined ducts at low frequencies with only a minor increase of the blocking of the duct by thick silencers, in order to keep the stationary flow of the resistance of the silencer at low values. There exists a similar problem at high frequencies, where the attenuation goes down at about the square of the inverse frequency as soon as the frequency limit of ray formation is exceeded at which the free duct is about half a wavelength wide. The principal remedy of the problem, to choose narrow ducts, would increase the aerodynamic resistance. The ray-acoustical background of the low attenuation at high frequency suggests using the existing corners of the ductwork into which the silencer is inserted for the generation of high-frequency attenuation. A naı̈ve idea is to assume that the exciting sound ray of the inlet duct should be absorbed by an absorber on the corner wall opposite this duct, thereby avoiding the excitation of the outlet branch of the duct. Such a corner absorber could be applied in wide ducts also. This paper presents theories of joints of acoustically lined ducts with separate sound absorbers at the corner walls. The numerical results will show that high transmission losses can indeed be achieved at high frequencies, but the mechanism of the corner attenuation is not so much the absorption by the corner absorber, but more the (cut-off) attenuation of higher modes in the lined outlet branch of the duct.

Changes in the Three Dimensional Architecture of the Cell Wall During Lignification of Xylem Cells inEucalyptus tereticornis

The three dimensional architecture of the cell wall during differentiation of xylem cells in Eucalyptus terericornis was visualizes by rapid-freezing and deep-etching electron microscopy. A highly porous structure was demonstrated in cell corner, middle lamellar and primary walls of both cambium and enlarging xylem cells, but disappeared after lignification of the xylem cells. The porosity of the structure was abruptly diminished by the incrustation of lignin as well as dense deposition of cellulose microfibrils in differentiating xylem cells. This study is the first to detect rosettes, cellulose synthesising enzyme complexes, in the differentiating xylem cells of a woody plant, and provides the first account of the visualization of the three dimensional architecture of xylem cell walls before and after lignification.

95/02097 Upward flame spread along PMMA vertical corner walls. Part II. Mechanism of ‘M’ shape pyrolysis front formation

95/02097 Upward flame spread along PMMA vertical corner walls. Part II. Mechanism of ‘M’ shape pyrolysis front formation

Toxicity of Gases from Full-Scale Room Fires Involving Fire Retardant Contents

Fire experiments were conducted in a 2-story fire resistant house using one of the first floor rooms as the burn room with various fire retardant or non-fire retardant items. The toxicity of the fire effluents was determined both by chemical analysis and bioassay techniques. Plywood boards arranged as corner walls and crumpled newsprint in a corrugated cardboard box were used as fire initiators. HCN and CO were the two major toxicants. The HCl level was generally and unexpectedly low in terms of toxicity. There was no case where fires involving fire retardant materials were more dangerous in tox icity than those of non-fire retardant ones. Calculated incapacitation times were in roughly good agreement with the actual incapacitation times for rab bits when the toxicants were limited to HCN and CO.

Upward flame spread along PMMA vertical corner walls Part II: Mechanism of “M” shape pyrolysis front formation

Flame spread behavior and the pyrolysis region spread characteristics along polymethylmethacrylate (PMMA) vertical corner walls were studied in detail with an automated infrared (IR) imaging temperature measurement technique. The technique was recently developed for the measurement of transient pyrolysis temperature on both charring and noncharring materials. Temporal isotherms on large PMMA samples were successfully obtained, from which the progress rate of the pyrolysis front was automatically deduced. It was found that the pyrolysis front shape was always M shaped, i.e., no spread along the corner, and the maximum spread is within a few centimeters of the corner. Understanding of the mechanism of the M-shape formation is important in developing a prediction model of the spread rate. Four possible mechanisms, effect of ignition mode, effect of solid phase conduction heat loss, fire-induced flow cooling, and flame displacement effect, were identified. Four different experiments were designed to test each mechanism, among them the flame displacement effect, which causes a large heat loss in a nonflammable gas layer due to a poor mixing of pyrolysis products and air was found to be the principal mechanism. For an upwardly spreading fire, total heat flux distributions above the M-shape pyrolysis peak were measured by a Gardon-gauge heat flux meter, and visible flame height and pyrolysis front height were respectively measured by a video camera and the IR technique.

Automated infrared imaging temperature measurement with application to upward flame spread studies. Part I

This article describes a new experimental technique with wide application that has been proven for wall fires. To measure the spread rate of the pyrolysis front along vertically oriented flat and corner walls, it may be necessary to measure transient temperature profiles on the walls. Conventional thermocouple and visual observation methods, however, have limitations due to complexity of implementation and the inherent ambiguity of visual observations due to interference from flames. To overcome these limitations, an automated infrared imaging system was applied to obtain two-dimensional wall surface temperature data in a relatively large area. In addition, upward flame spread experiments were conducted over vertically oriented PMMA flat and color board corner walls; and surface thermocouple and infrared imaging temperature data were compared in the PMMA wall fires. All the results indicate that the infrared system with a (10.6 ± 0.5 μm) bandpass filter successfully avoids interferences from the flame allowing measurements of temperature distribution on the fire-heated wall, from which the spread rate in any direction can be deduced. However, this technique will fail for flames whose emissivity is greater than 0.1.

Optimum attenuation of gas turbine noise by acoustical corner treatment

In this paper two materials, placed over the corner walls surrounding a gas turbine unit in five different geometric configurations, are tested to establish their effectiveness on the noise field of a 45 kW gas turbine unit. The measured noise without wall treatment reveals that about 46% of the noise radiated acoustic power of the unit is in the 1 3 octave band of 12 500 Hz central frequency. The results of this research show that the sound absorber comprised of plastic sponges of irregular shapes of an average linear dimension of 7 cm formed in strings 2 m high and suspended 15 cm from the solid walls is considerably more effective than the traditionally used fiber glass panels also suspended 15 cm from the solid walls. The optimum configuration of the plastic sponges attenuated the dominant pure tone band by about 78% of its original power. Similar reductions took place in the other twenty 1 3 octave bands. The overall broadband attenuation of the measured noise amounts to 71% of the original acoustic power of the noise field of the unit.

Comparative localization of three classes of cell wall proteins

The localization of the cell wall proline-rich proteins (PRPs), and the gene expression of the cell wall glycine-rich proteins (GRPs) and the hydroxyproline-rich glycoproteins (HRGPs) were examined in several dicot species. The PRPs are accumulated in the corner walls of the cortex where several cells are joined together and in the protoxylem cell walls of 3-day-old soybean root. In 1-month-old soybean plants, the PRPs are specifically deposited in xylem vessel elements of the young stem, and they are accumulated in both phloem fibers and xylem vessel elements and fibers of the older stem. Likewise, the PRPs are localized in xylem vessel elements and fibers in tomato, petunia, potato and tobacco stems. They are also found in outer and inner phloem fiber cell walls of tomato stem and in outer phloem fiber cell walls of petunia stem. The gene expression of the HRGPs and the GRPs is developmentally regulated in tomato, petunia and tobacco stems. HRGP mRNAs are abundant in outer and inner phloem regions, while GRP mRNAs are present mostly in primary xylem and in the cambium region. Immunocytochemical localization showed that the GRPs have a localization pattern similar to that of the PRPs in tomato, petunia and tobacco stems.

Comparative localization of three classes of cell wall proteins

The localization of the cell wall proline-rich proteins (PRPs), and the gene expression of the cell wall glycine-rich proteins (GRPs) and the hydroxyproline-rich glycoproteins (HRGPs) were examined in several dicot species. The PRPs are accumulated in the corner walls of the cortex where several cells are joined together and in the protoxylem cell walls of 3-day-old soybean root. In 1-month-old soybean plants, the PRPs are specifically deposited in xylem vessel elements of the young stem, and they are accumulated in both phloem fibers and xylem vessel elements and fibers of the older stem. Likewise, the PRPs are localized in xylem vessel elements and fibers in tomato, petunia, potato and tobacco stems. They are also found in outer and inner phloem fiber cell walls of tomato stem and in outer phloem fiber cell walls of petunia stem. The gene expression of the HRGPs and the GRPs is develop-mentally regulated in tomato, petunia and tobacco stems. HRGP mRNAs are abundant in outer and inner phloem regions, while GRP mRNAs are present mostly in primary xylem and in the cambium region. Immunocytochemical localization showed that the GRPs have a localization pattern similar to that of the PRPs in tomato, petunia and tobacco stems.

Natural convection in a differentially heated corner region

This is a fundamental study of the phenomenon of natural convection in the region formed by a vertical warm wall rising above a cold horizontal wall, or in the region between a cold vertical wall extending downward from a warm horizontal surface. The study consists of scale analysis, numerical simulations, and an asymptotic solution of the low Rayleigh number limit. The scale analysis predicts the persistence of a single cell in the corner region, regardless of Rayleigh number. The cell migrates toward the corner as the Rayleigh number RaH increases: the flow rate and the net heat transfer rate vary as Ra1/7H. The scale analysis is verified qualitatively and quantitatively by means of numerical experiments in the range RaH =103–107, Pr=0.7–7, H/L=1–4, where Pr is the Prandtl number and H/L is the height/length ratio of the corner region. Additional numerical simulations are presented for cases where one or both walls have uniform heat flux; in these cases, the heat transfer rate shows nearly the same behavior as when the corner walls are both isothermal. The asymptotic solution for the RaH→0 limit shows that the flow field is relatively insensitive to whether the wall temperature varies continuously or discontinuously through the corner point.

Analysis and Asymptotic Solutions of Compressible Turbulent Corner Flow

The turbulent compressible flow along an unbounded 90 deg axial corner has been analyzed. The limiting equations for the far-field boundary, simulating a two-dimensional boundary layer with crossflow, have been obtained appropriately. This latter set of equations have been solved using a semi-implicit second-order accurate numerical marching scheme. The turbulent stresses have been modeled first using a Cebeci-Smith type two-layer algebraic model in which isotropy is assumed. The turbulence stresses were also modeled using a modified form of the Gessner-Emery anisotropic model. Results have been presented for a range of Mach numbers between 0 and 2.0 with adiabatic as well as heat transfer boundary conditions at the corner walls. Effect of suction and injection have also been included. The anisotropy in the turbulence modeling showed insignificant effect on the flow field at far-field boundary, but it is believed to be essential in the inner corner region. The analysis presented recovers all previously available results for the simplified cases of this corner configuration.