Ceiling Surfaces Research Articles

Assessment of Acoustic Properties of Lecture Theatres in Ladoke Akintola University of Technology, Ogbomoso, Nigeria

Acoustic design is an important consideration in the design of lecture theaters (LTs); it has a significant impact on communication between students and instructors, their hearing comfort levels, lecture outputs and their overall performance. However, despite the significant role acoustic design plays in LTs, it has not received a significant attention both in design and literature in the developing countries especially Nigeria. This study is hence aimed at assessing the acoustic properties of lecture theaters in Ladoke Akintola University of Technology (LAUTECH) Ogbomoso with a view to establishing the design requirements for effective acoustic comfort in lecture theatres in Nigeria. Seven (58.33%) lecture theaters were randomly selected out of a total of 12 available in the study area and were objectively analysed. Shape of the lecture theaters, wall, floor, ceiling and furniture surface finishes were physically observed and their sound absorbing coefficients were evaluated and compared with data obtained from the Bureau of standards for the sound absorption coefficients, ISO 354 and literature. The total surface absorption coefficients of materials and surface area were used to calculate the Reverberation Time (RT) using Wallace Sabine model and results was compared with RT standard of between 0.5 and 1.0s recommended by scholars Odoh and Urenyang for LTs in Nigeria. The study observed that walls, floor and ceiling surfaces were treated with materials of low sound absorbing coefficients while only the ceilings were treated with high coefficient materials, the effect was observed in the RT values obtained. It was observed that only 3 (42.86%) LTs have their RTs within the recommended standards and hence are capable of providing good acoustic comfort for users while 4 (57.14%) LTs have excessive RT implying likely acoustic discomfort. The study recommended that materials with high sound absorbing coefficients be used for building component finishes and acoustic decisions should be taken right from design inception stage.

ENGINEERING METHOD FOR CALCULATING THE TEMPERATURE ON THE INNER SURFACE OF THE OUTER CORNER OF A BUILDING

Statement of the problem. The temperature on the inner surface of the outer corner is always lower than on the inner surface of the outer wall. This temperature difference might lead to the formation of condensation on the inner surface of the wall at low outdoor temperatures. Therefore the problem of developing an engineering method for calculating the temperature in the outer corner to exclude the possibility of condensation on the inner surface in the design process of the outer wall structures is extremely relevant. Results. To address this problem, based on solving the heat balance equation, taking into account the amplitude of air temperature fluctuations in the room and heat absorption of the inner surfaces of walls, intermediate bottoms (ceiling and floor surfaces), parting walls, a formula was obtained to calculate the temperature on the inner surface of the outer corner. Also, during the study, natural tests of the wall structure with an outer corner were carried out and the temperatures on the inner and outer surfaces were obtained.Conclusions. Comparison of the calculation results using the developed engineering calculation method and experimental data showed that the temperatures on the inner surface of the outer corner almost coincided. This makes it possible to use the suggested engineering method for calculating the temperature on the inner surface of the outer wall corner in the design of enclosing structures to exclude the appearance of condensation.

Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards

Evidence suggests that SARS-CoV-2, as well as other coronaviruses, can be dispersed and potentially transmitted by aerosols directly or via ventilation systems. We therefore investigated ventilation openings in one COVID-19 ward and central ducts that expel indoor air from three COVID-19 wards at Uppsala University Hospital, Sweden, during April and May 2020. Swab samples were taken from individual ceiling ventilation openings and surfaces in central ducts. Samples were subsequently subjected to rRT-PCR targeting the N and E genes of SARS-CoV-2. Central ventilation HEPA filters, located several stories above the wards, were removed and portions analyzed in the same manner. In two subsequent samplings, SARS-CoV-2 N and E genes were detected in seven and four out of 19 room vents, respectively. Central ventilation HEPA exhaust filters from the ward were found positive for both genes in three samples. Corresponding filters from two other, adjacent COVID-19 wards were also found positive. Infective ability of the samples was assessed by inoculation of susceptible cell cultures but could not be determined in these experiments. Detection of SARS-CoV-2 in central ventilation systems, distant from patient areas, indicate that virus can be transported long distances and that droplet transmission alone cannot reasonably explain this, especially considering the relatively low air change rates in these wards. Airborne transmission of SARS-CoV-2 must be taken into consideration for preventive measures.

Discussion on the Reinforcement of Reinforced Concrete Slab Structures

Because of global environmental changes and the continued warming of the planet, the increase in carbon dioxide emissions has had a major impact on the environment. The development of zero-carbon buildings, the promotion of energy conservation and carbon reduction, and the concept of green environmental protection are regarded as important issues for humanity to achieve sustainable development. In Taiwan, the combination of moisture and high salt content in the environment, corrosion caused by chloride ions, and earthquakes often lead to the formation of crevices in buildings. These crevices can cause rebar oxidation and corrosion and even concrete structure damage or spalling. Conventional structural damages can be repaired with epoxy resin grout. However, such practices are incapable of removing the rusted components of the rebars inside the structures and thus subject the internal rebars to continuous oxidation in the original rust-covered environment. Components located deep within the structures would still swell as a result of continuous rebar oxidation and cause concrete breaking and spalling, making previous repair efforts ineffective. This study proposes an improved repair and retrofit technique that includes the removal of rust from oxidated rebar parts, by applying low viscosity epoxy resin to the slab base and allowing it to fully penetrate the concrete cracks and surface of the rebars inside, thus producing a protective layer and repairing the bond. Additionally, carbon-fiber reinforced plastic (CFRP) patches were adopted as repair materials and attached to the beams and slab (ceiling) surfaces. Angle steels were used at the edges and installed to connect the beams to the slab with chemical anchors. The gaps between the angle steels and the slab were filled with epoxy resin grouts. On the short side of the slab, small steel H-beams were installed 1 m apart as a means of retrofit. Because the epoxy resin expands by 8% after undergoing chemical reactions, it bonds perfectly with concrete, CFRP patches, and steel materials. Approximately 10 years have elapsed since the case-study was repaired using the proposed technique, and the retrofit effect has yielded excellent results to the present day, with no occurrence of internal swelling or spalling from rebar oxidation. The proposed retrofit technique can reduce construction costs, while ensuring effective repair and maintenance of structural safety, and extend the service life of structures.

The soundscape of music education

Research on acoustical qualities of music education spaces based in soundscape theory provides a method to link the acoustical performance of a space with the instructional tasks that occur in the space with the architectural design features of the rooms. There has been limited study of the acoustical needs of teachers and students in music education spaces. Pirn (1978) showed that music practice rooms can become too loud as multiple musicians are placed in a closed and limited room volume without sufficient sound absorbing materials. Gade (1988) defined the characteristic of Support to measure cross room reflections from ceiling and wall surfaces to allow the musicians to hear each other. Tsaih (2011) found that the soundscape of music education was based on the ability of the students and teacher to be able to clearly understand spoken instruction and for students to hear each other and for the instructor to hear students playing in time, in tune and in dynamic. Case studies of music education spaces will illustrate how these concepts are integrated within the architectural design and acoustical analysis of the spaces.

Theoretical and experimental study of departure duration of condensate droplets from radiant cooling ceiling surfaces

In this paper, a mathematical model for predicting the departure duration of the first condensate droplet from a radiant ceiling surface was proposed on the basis of the condensation water mass. The simulation results indicate a dependence of condensation water mass on the apparent contact angle of the substrate, but almost in no relation with the surface temperature. The condensation water mass firstly increases with the increase of the apparent contact angle. It reaches a maximum weight of 522 g/m2 at an apparent contact angle of 110°, and then decreases. A visualization experiment of condensation on a radiant ceiling panel with a conventional aluminum alloy surface was performed in a climate chamber to measure the departure duration of the droplet. The measured departure duration fluctuates due to the variance of apparent contact angle and the randomness of condensation process, but it decreases sharply with the sub-cooled degree (air dew point minus surface temperature). And the average departure duration is 10 h with a sub-cooled degree of 5 °C. The theoretical model is validated as the average relative biases between the experimental and theoretical results are within 25%.

Acoustic performance of balconies having inhomogeneous ceiling surfaces on a roadside building facade

Balconies provide noise screening effects in residential buildings even with the balcony door opened for natural ventilation. However, the screening effect of a balcony was found to be canceled due to the reflection from the ceiling. This paper describes a balcony whose ceiling is made from materials of inhomogeneous impedance which eliminates this drawback. The nonuniform impedance affects wave behavior by altering the direction of energy flux away from the region of a balcony as it reflects on the ceiling. A proposed realization of the balcony ceiling comprises a closely spaced array of progressively tuned hollow narrow tubes which create a phase gradient. The acoustic performance of a balcony with an inhomogeneous ceiling surface is examined theoretically by a ray-based model. All of the results predicted by the theory fit well with numerical simulations using a two-dimensional finite element method. Balconies with the proposed ceilings have the potential to be widely used in a roadside multi-residential building against the exterior traffic noise.

COLOUR CULTURE AND IDENTITY: INFLUENCE OF COLOURS ON KERALA MURAL ART

The word ‘mural’ is derived from the Latin word ‘murus’, meaning ‘wall’. Murals refer to paintings embellished on visual components like the wall, ceiling, or other huge lasting surfaces. The murals of Kerala unfathomably stand out for their prominence in beauty, clarity and symmetry with unmatchable linear accuracy. The tradition of mural painting in Kerala is unique in the world, and it is extremely rich with symbolism. Made only with natural mineral pigments, the colours represent the qualities of the three gunas- sattva, rajas and tamas. Sattva is purity, which is usually represented by the colour green; the figures painted with green are those for whom knowledge is the chief characteristic. Those in whom rajas, the spur to activity, is predominant, are painted in golden yellow. Tamas, inertia, the least pure is, curiously, represented by white. The traditional colours used in this art are red ochre, yellow, green, blue, white and black. Sometimes blue is also used. This traditional style mural art form uses natural pigments and vegetable colours. The subjects for the painting, derived from various Vedic texts, are not a fanciful representation but drawn from the description in the invocatory verses or dhyana slokas. Flora and fauna and other aspects of nature are pictured as backdrops, in highly stylized manners. Keywords : Mural, Painting, Natural, Style, Vegetable colour, Vedic Texts

Optimizing the signal to noise ratio in speech rooms using passive acoustics

Adults with normal hearing require roughly a 0 dB signal-to-noise ratio for good speech intelligibility. However, significantly higher values may be needed to compensate for neurological immaturity, sensorineural and conductive hearing losses, language proficiency and excessive reverberation. ANSI 12.60 addresses ways to lower the noise interference due to background levels and reverberation time. However, it is also possible to increase the signal, by reflecting or diffusing early reflections. Speech intelligibility is delivered in the consonants, which occur in the 2–6 kHz frequency range. Therefore, intelligibility can be enhanced by incorporating scattering surfaces, rather than solely surfaces that absorb sound in the 2–6 kHz region, on the front wall, lower side walls, and central ceiling areas, to increase the speech signal by temporal fusion. The decay time can be controlled with broadband absorption on the perimeter of the ceiling and upper wall surfaces. Since ceiling diffusion is an important design ingredient and the ceiling plane is coveted by many trades, including lighting, HVAC, speakers, sprinklers, etc., we will describe a 24 VDC combined LED lighting and sound diffusor, with a 24 VDC emergency lighting central battery system, dynamic lighting capability, and the ability to incorporate sonic actuators for announcements.

Effectiveness of the total absorption on noise reduction in industrial plants

This study investigates the noise reduction levels on acoustical models of an existing production plant due to the total absorption. Noise measurements have been carried out in this plant in order to determine the actual noise levels emitted by different types of machinery and the workers' noise exposure. The production plant has been acoustically simulated in order to evaluate the noise attenuations for various absorption configurations comprising low (actual situation), medium and high absorptive states of wall, ceiling and wall-ceiling surfaces together. The effectiveness of each absorption configuration has been evaluated regarding the amount of the assigned absorption and achieved noise reduction for the workers' positions and also for the entire production area. It can be clearly stated that the choice of the absorptive material and the place of the absorptive surface inside the production plant are both significant factors to obtain the desired reduction in noise levels and an acceptable distribution of the noise levels in the production plant. As the result of the study an equation is proposed, which gives the possibility to determine the effectiveness of the used absorption by considering the noise reduction gain compared to the used amount of absorption.

The ground is dominant in infants’ perception of relative distance

When making relative distance judgments, adults attend to information provided by the ground surface and generally ignore information provided by ceiling surfaces. In the present study, we asked whether this ground dominance effect is present in infancy. Groups of 5- and 7-month-old infants viewed a display depicting textured ground and ceiling surfaces. Two toys, which were attached to vertical rods, were affixed to the display. The toys/rods were positioned so that one toy was specified as being nearer by the ground surface but farther away by the ceiling surface, while the other toy was specified as being farther away by the ground surface but nearer by the ceiling surface. Under monocular viewing conditions, the infants in both age groups reached preferentially for the toy that was specified as being nearer by the ground surface. This effect was significantly stronger than that observed under binocular viewing conditions. The findings indicate that the infants responded to the distance information provided by the ground surface to a greater extent than to information provided by the ceiling.

Environmental surfaces and the compression of perceived visual space.

The present study examined whether the compression of perceived visual space varies according to the type of environmental surface being viewed. To examine this issue, observers made exocentric distance judgments when viewing simulated 3D scenes. In 4 experiments, observers viewed ground and ceiling surfaces and performed either an L-shaped matching task (Experiments 1, 3, and 4) or a bisection task (Experiment 2). Overall, we found considerable compression of perceived exocentric distance on both ground and ceiling surfaces. However, the perceived exocentric distance was less compressed on a ground surface than on a ceiling surface. In addition, this ground surface advantage did not vary systematically as a function of the distance in the scene. These results suggest that the perceived visual space when viewing a ground surface is less compressed than the perceived visual space when viewing a ceiling surface and that the perceived layout of a surface varies as a function of the type of the surface.

Application of 3D Terrestrial Laser Scanning to Map Building Surfaces

High definition laser scanning is a non-invasive, non-destructive method for recording a 3D digital image of a building. This technology has seen an exponential increase in its accuracy, speed and data collecting capacity over the past five years. Difficulties in processing the large files created from point cloud scanning have been reduced with advances in computer technology such as 64-bit processing and mega-gig video cards. Programs have been developed which allow the utilization of the data within CAD programs typically used in the design industry.Through case studies and examples, this paper illustrates how 3D laser scanning technology can be used to map planar variations in ceiling and floor surfaces, and masonry façades, and provide evidence of possible structural shifts or deterioration not apparent through traditional visual inspection and measurement methods.

Investigating the absorption characteristics of open ceilings in multi-purpose halls using a 1:25 scale model

This paper investigated the absorption coefficients of acoustically transparent ceilings using 1:25 scale models. From a field survey of 18 existing halls, it was found that the open ceilings were equipped with steel truss structures, ducts, catwalks and ceiling surfaces. In order to investigate the absorption characteristics of the equipped ceilings, measurements were made using a 1:25 reverberation chamber based on ISO 354. Results showed that for an empty ceiling with a depth of 6 m, the absorption coefficient with a 50%-perforated ceiling surface is 0.2–0.3 above 500 Hz. If there were steel structures inside the ceiling, the absorption coefficient increased by 0.1 at 125 Hz to 2 kHz. Adding ducts and catwalks increased the absorption by 1–2 kHz. The absorption coefficients of the equipped ceilings ranged from 0.19 to 0.61 and the absorption characteristics were mainly found at high frequencies. Maximum absorption was observed in heavily equipped ceiling structures.

Predominance of ground over ceiling surfaces in binocular rivalry

The superiority of ground surfaces over ceiling surfaces in determining the representation of the visual world, demonstrated in several studies of visual perception and visual search, has been attributed to a preference for top-away projections resulting from ecological constraints. Recent research on binocular rivalry indicates that ecological constraints affect predominance relations. The present study considered whether there is a difference in predominance between ground and ceiling surfaces. In Experiment 1, we examined whether a ground surface would dominate a ceiling surface when one surface was presented to each eye. In Experiment 2, we used an eye-swapping paradigm to determine whether a ground surface would come to dominance faster than a ceiling surface when presented to the suppressed eye. The eye-swapping paradigm was used again in Experiment 3, but the ground and ceiling planes were replaced with frontal planes with similar variations in texture density. The results of these experiments indicate that ground surfaces are predominant over ceiling surfaces, with this predominance affecting both the dominance and suppression phases of binocular rivalry. This superiority of ground planes is independent of image properties such as the increase or decrease in texture density from the lower half to the upper half of the images.

Optimizing the signal-to-noise ratio in speech rooms using passsive acoustics.

Adults with normal hearing require a roughly 0‐dB signal‐to‐noise ratio for good speech intelligibility in classrooms and lecture halls. However, significantly higher values may be needed to compensate for neurological immaturity, sensorineural and conductive hearing losses, language proficiency, and excessive reverberation. ANSI 12.60 addresses ways to lower the noise interference due to background levels and reverberation time. However, it is also possible to increase the signal, by reflecting or diffusing early reflection. While speech power is delivered in the vowels which are predominately in the 250–500‐Hz frequency range, speech intelligibility is delivered in the consonants, which occur in the 2–4‐kHz frequency range. Therefore, effective core learning designs can incorporate scattering surfaces, rather than surfaces that absorb in the 2–4‐kHz region, on the front wall, lower side walls, and central ceiling areas, to increase the speech signal. The decay time can be controlled with broadband absorption on the perimeter of the ceiling and upper wall surfaces. A computer model analysis of various speech environments will be presented.

The ground dominance effect in the perception of relative distance in 3-D scenes is mainly due to characteristics of the ground surface

Previously, we (Bian, Braunstein, and& Andersen, 2005) reported a dominance effect of the ground plane over other environmental surfaces in determining the perceived relative distance of objects in 3-D scenes. In the present study, we conducted three experiments to investigate whether this ground dominance is due to inherent differences between ground and ceiling surfaces, or to the locations of these surfaces in the visual field. In Experiment 1, two vertical posts were positioned between a ground surface and a ceiling surface, and optical contact was manipulated so that the two surfaces provided contradictory information about the relative distances of the posts from the participant. The two surfaces were either both above, both below, or one above and one below fixation. In Experiment 2, only one surface was presented, either above, below, or at fixation. In Experiment 3, the posts were replaced by two red dots, and the eccentricity of the optical contact on the two surfaces was equated in each of five locations in the visual field. In all three experiments, participants judged which of the two objects appeared to be closer. Overall, we found a higher proportion of judgments consistent with a ground surface than with a ceiling surface in all locations, indicating that the ground dominance effect is mainly due to characteristics of the ground surface, with location in the visual field having only a minor effect.

Radioisotope Deposition on Interior Building Surfaces: Air Flow and Surface Roughness Influences

Interior surface deposition effects of vaporized radioactive aerosols are important in understanding their behavior in accident conditions such as the Japanese nuclear laboratory accident in 1999 and the Chernobyl nuclear power plant accident in 1986, where entire communities had to be abandoned because of surface contamination, and the hopefully unlikelihood of a terrorist dirty nuclear bomb attack. Airborne radon progeny offers an opportunity to study radioisotope surface deposition. A significant annual lung cancer rate is also attributed to airborne radon progeny in the interior domestic environment. Surface deposition rates influence the airborne progeny levels. Here, we report extensive 218Po deposition rates over typical air change rates (ACHs) from 0.02 to 1.0 h-1 for interior furnishings surfaces in a 0.283-m3 test chamber to supplement earlier reported deposition rates for interior wall, ceiling, and floor surfaces. In analyzing the deposition results from the different materials, it is found that they correlate in terms of roughness with relative static friction and aerodynamic shear stress. Extrapolation to perfectly smooth surfaces provides a good estimate of the Fick’s law value. Contrary to prior radon analysis at higher air flow, where the Crump and Seinfeld (CS) turbulent deposition models seemed to fit, at low ACH below 0.5 h-1 the deposition data found excellent agreement with a new Brownian diffusive deposition model for laminar flow. A composite model using the Brownian diffusive laminar flow and the CS turbulent flow models provides an excellent fit to all data. These results provide insight into contamination issues relative to other airborne radioisotopes, with the relative effects being dependent on the airborne contaminant particle sizes and their respective diffusion coefficients as seen in the two deposition models.

Fire-Plume-Generated Ceiling Jet Characteristics and Convective Heat Transfer to Ceiling and Wall Surfaces in a Two-Layer Fire Environment: Uniform Temperature Geiling and Walls

This work presents a model to predict the instantaneous rate of convective heat transfer from fire plume gases to the overhead ceiling surface in a room of fire origin. The room is assumed to be a rectangular parallelepiped and, at times of interest, ceiling temperatures are simulated as being uniform. Also presented is an estimate of the convective heat transfer, due to ceiling-jet-driven wall flows, to both the upper and lower portions of the walls. The effect on the heat transfer of the location of the fire within the room is taken into account. Finally presented is a model of the velocity and temperature distributions in the ceiling jet.The model equations were used to develop an algorithm and associated modular computer subroutine to carry out the indicated heat transfer calculations. The subroutine is written in FORTRAN 77 and called CEILHT. The algorithm and subroutine are suitable for use in two-layer zone-type compartment fire model computer codes. The subroutine was tested for a variety of fire environments involving a 107 W fire in a 8m × 8m × 4m high enclosure. While the calculated results were plausible, it is important to point out that CEILHT simulations have not been exprerimentally validated.

The acoustics of small rooms for music practice and teaching

At best, the small rooms typical for music teaching and practice are unnatural environments for music production. Given the usual constraints of budget and practicality, a small room cannot be made to approximate the acoustics of a fine concert hall. If all normal modes are suppressed completely by sound-absorbing treatment, the room will be unnaturally dead or anechoic, and will be disliked by students and instructors. Yet, if normal modes are not controlled and the small room left “live,” it will not sound like a normal concert hall but be “boxy,” with a very uneven frequency response, and will be equally disliked. Compromise solutions involving fixed treatment on one wall or two adjacent walls, or adjustable treatment, with varying degrees of room irregularity and splaying, which have provided satisfaction in music teaching buildings, will be discussed. Organ practice rooms pose a separate problem, and solutions involving no applied sound-absorbing treatment, but considerable splaying or irregularities in ceiling and wall surfaces appear best. Some discussion of sound isolation will be presented.