Concrete Block Wall Research Articles

Building damage in Rabaul, Papua New Guinea, 1994

Damage information on 173 buildings was collected in the immediate aftermath of the September 1994 eruption which destroyed large sections of Rabaul town, Papua New Guinea. The extent of damage is presented on a five-point scale and related to construction characteristics and tephra load. Total roof loads in Rabaul town ranged from 2 to 16 kN m–2 (about 100- to 950-mm tephra thickness). Most buildings which collapsed completely experienced loads >7.5 kN m–2, but many buildings sustained half this load with little more than cosmetic damage. Timber-framed buildings suffered more than buildings with at least some concrete block walls. However, some old, steel-framed buildings experienced severe damage with tephra loads as low as 2 kN m–2. Comparisons with tephra loads and building damage elsewhere are limited but suggest that Rabaul buildings experiencing roof loads of 2–5 kN m–2 generally survived reasonably well. However, the comparisons are unsatisfactory because of inadequate data on tephra unit weights, roof design, building ages, the quality of workmanship, and the natural variability of construction materials, particularly timber. The Rabaul data suggest that concrete block walls increase building resistance to tephra loads but it is doubtful that conventional residential buildings can be designed to sustain tephra loads exceeding 7 kN m–2. The Rabaul experience also indicates that building codes for volcanic areas need to consider mudfills and post-eruption corrosion of sheet metal roofs and wall cladding. Most importantly, had the majority of buildings in Rabaul survived the September 1994 tephra falls, wet season mudflows a few months later would still have made most of the town unsafe and uninhabitable.

Experiences with acoustical renovation of classrooms in a public school

The Harbor Science and Arts Charter School is a small, public elementary school with children in grades 1 through 7 located in the East Harlem section of New York City. A hallmark of our curriculum is that we encourage students to work on group projects and to make many oral presentations of the results of their work. We noticed that when children were engaged in group work and oral presentations, it was often difficult to understand everything that was said. One of our fourth grade teachers had a friend who was an acoustical designer who arranged a sound analysis of the teacher’s room that confirmed that our high ceilings, concrete block walls, and window air conditioners were creating some of the problems we were experiencing. Using the room as a test case, Armstrong Industries donated materials for modifications to the room. They subsidized lowering the ceiling with acoustical tiles. We installed new bulletin boards and purchased new air conditioners. The results were extraordinary. Students and teachers who used the classroom were amazed at the improvements. We have used what we have learned to modify all of the classrooms as well as the cafeteria. These relatively simple modifications have made a significant improvement in the quality of life in our school.

Model for Moisture-Content Evolution in Porous Building Elements with Hygro-Thermal Bridges and Air-Voids

Addressing the effects of moisture movement and residual moisture-con tents is becoming a recognized part of performance-based design of buildings. However, the multi-directional moisture-movement and subsequent moisture-content evolution in most common building elements with hygro-thermal bridges, without or with air-voids, has yet not been investigated. An integral presentation was utilized to establish the coupled heat and mass transfer field equations for these cases, and for their reduction to a discrete set of alge braic equations. An interactive converging numerical process solves the implicit set of alge braic non-linear equations. Results address some examples for verification of the computational procedure, and a symmetric drying process of an autoclaved-aerated- concrete block-wall with cementitious-mortar joints and renderings, with and without air- voids.

Antenna-sector time-division multiple access for broadband indoor wireless systems

This paper investigates a hybrid space-time-division multiple access (S-TDMA) for broadband indoor wireless systems using sectored antennas. It is shown that portables which are located in different sectors of an indoor microcell may be able to reuse the same frequency and the same time slot. However, this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. It is proposed that the scheduling be performed in the base station, i.e., a central control architecture. The optimum scheduling algorithm, the one that maximizes the number of packets transmitted per frame, may be in the NP-complete class of problems, so it cannot be solved in real time. Therefore, a suboptimum algorithm, called the first fit algorithm (FFA), is proposed for frame scheduling. It was found that the capacity gain achieved by the FFA is dependent on the capture threshold, which is defined as the minimum signal-to-interference ratio required in order to achieve a given packet error rate goal. The capture threshold depends on the modulation and coding schemes. This paper investigates the performance of the FFA operating with multicarrier trellis-coded modulation. An alternative multicarrier modulation is analyzed, and the FFA performance is investigated when operating with the alternative and with the conventional multicarrier through computer simulations based on measured data which were obtained with a sectorization level of ten (using ten antenna sectors in the base station). The simulations have shown that the FFA can provide a large capacity gain when operating with multicarrier trellis-coded modulation and using differential detection. For example, while previous schemes can transmit only one packet at a time, the proposed scheme can transmit, on average, more than four packets per time slot in an open indoor location, or close to three packets per time slot in a closed indoor location with internal walls of concrete blocks.

Broadband Indoor Wireless System with In-Cell Frequency Reuse Based on Sectored Antennas

This paper investigates a new multiple access system for broadband indoor wireless communications based on sectored antennas. Unlike previous sectored antenna indoor systems, this system incorporates the capability of reusing spectrum in different antenna sectors of the base station. It is shown that portable terminals located in different sectors of the indoor microcell may transmit/receive simultaneous data packets on the same frequency if their mutual interference is below a threshold level (or capture threshold) that guarantees an acceptable packet error rate. However, this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. When trying to transmit more than two packets per time slot, the optimum scheduling problem, the one that maximizes the number of packets transmitted per frame, is in the NP-complete class of problems, so it can not be solved in real time. Therefore, a sub-optimum algorithm named First Fit Algorighm is proposed for the frame scheduling problem. The problem is investigated experimentally for a sectorization level of ten (using ten antenna sectors in the base station). A statistical model of multipath propagation is used to extend the results to other levels of sectorization. The proposed system can significantly increase capacity when compared with systems that can transmit a single data packet per time slot. For example, while previous systems can transmit only one packet at a time, the proposed system can transmit on average close to three packets per time slot when operating with a capture threshold of 10 dB and ten antenna sectors in a closed indoor location with internal walls of concrete blocks.

The Location of Building Defects Using Structural Intensity

Many defects in the construction of buildings act as transmission paths across which unwanted sound can travel. The resulting increase in power flow can be measured using structural intensity techniques and the location of the source found from the intersection of two or more intensity vectors. This technique can be used to locate a source (or sometimes a sink) when the intensity being measured is above the residual or background intensity. Some applications of this technique are discussed and it is used to locate a point source on a concrete floor and a line source exciting a concrete block wall. The technique was found to work well for a point source but was less reliable for a line source. This was partly because a line source is less well spatially defined and partly because the damping of the wall was low, resulting in a high residual intensity.

Damage to River Levees and Revetments

ABSTRACT Levees with masonry and concrete-block walls underwent collapse and destortion between the central Kobe and Nishinomiya where the most severe damage was sustaind. In a coastal area, levees sustained characteristic deformation of the soft ground. In a reclaimed land liquefaction of the fill brought about excessive deformation in revetments of levees. Levees in the Muko River on the eastern foot of Mt. Rokko suffered from settlement, distortion and cracks. The Ina, Mo, Kanzaki, nakajima, Samondo, Aji and Shorenji Rivers were damaged where a thick soft sandy deposits underlay and old meanders were also found in some locations. In a port area, excessive distortion and cracks occurred in levees, while heavy concrete revetments supported by long piles which resist against the storm surge were little damaged. This paper outlines the structural, geological and geotechnical aspects of earthquake damage to levees in Hanshin region but damage to the Yodo River is excluded.

A New Subterranean Termite Introduced to Florida: Heterotermes Froggatt (Rhinotermitidae: Heterotermitinae) Established in Miami

On 3 January 1995, we were asked to identify termites collected on 30 December 1994 from a house in Miami. The sample, a termite-infested board and attached nest material (carton) contained thousands of workers and hundreds of soldiers and young brachypterous nymphs. We were struck by their small size and recognized the soldiers as Heterotermes which are characterized by their slender and straight mandibles in contrast to the relatively thick, curved mandibles of the native Reticulitermes spp. [Fig. 1; also see Mathews (1977) for character diagnosis of Heterotermes]. The specimens more or less fit the brief description of H. convexinotatus (Snyder 1924), a widely reported northern Neotropical species (Araujo 1977). However, the taxonomic status of Heterotermes in this region is vague and in need of revision, therefore, we have not as yet assigned a species name to this find. On 12 January 1995, we inspected the infested property, a small, older single-family house located 0.6 km east of Interstate Highway 95 and 0.3 km north of Interstate Highway 195 in the Little Haiti district of Miami. The Heterotermes infestation was centered in a room addition which was under construction on the north side of the house. The addition consisted of concrete-block walls opening without a ceiling to a covered wood-truss roof. We observed extensive drywood termite damage to the roof rafters of the original house. The floor area of the addition was unfinished, consisting of fill sand on bare soil. The sand completely or partially buried numerous plywood and solid lumber scraps. Additional scraps were scattered or stacked near the former north wall of the original house. Although conditions were dry, nearly all wood scraps were under some degree of Heterotermes attack. Foraging tubes criss-crossed the surfaces of some of the wood. Fist-size pieces of carton were attached to the older damaged wood. No foraging tubes were observed on any of the structure itself. The condition of the infestation and large numbers of brachypterous nymphs indicated that it had been active for years and had likely undergone one or more annual reproductive dispersal cycles. Our suspicion that additional colonies were established in the neighborhood were confirmed on 30 March 1995 when several soldiers and workers were collected by a pest control operator from a warehouse located about 300 m ENE from the original site. Unlike the original site, the warehouse showed many signs of above-ground for-

The Graphic Unconscious: A Response

The Graphic Unconscious: A Response Mark Seltzer (bio) Dorrit Cohn’s reading of “optics and power in the novel” largely devolves on a rehearsal of the argument of her Transparent Minds (1978), and that reading is largely premised on a repetition of exactly the simple opposition of art and power pressured, for example, in my Henry James and the Art of Power (1984). 1 Indeed, on these terms it’s tempting to describe Cohn’s rehearsals as uncanny—if the notion of the uncanny (the unhomelike) itself had not by now become an all too homey way of naming the defensive recapitulations, the belatedness, the uncertain attributions of cause and effect, that through and through mark that account. The uncanny has, as it were, been domesticated as yet another version of an “ethic” of better living through ambiguity, the ethic that of course continues to underwrite a wide range of literary studies. It is not hard to detect both the tendency to recapitulate and what might be called the recourse to complexity-as-such in this piece. But if something like the uncanny seems to surface here, it perhaps has more to do with another problem broached, but resolutely displaced, in the piece. The problem of seeing and power in the novel is of course most powerfully located in terms of the fantasy structure of the panopticon. But such a fantasmatics of seeing and power makes visible something more general: the seeing machine is also a personation machine. The seeing machine links processes of objectification, identification, and representation to what might be called the making of persons. What becomes visible then is the subject’s uncertain relation to processes of identification and representation: in short, the intricated matters of representation and self-representation, of seeing and seeing oneself. Hence the question of the subject as such is bound up with the order of representation: the status of the subject’s identity is inevitably bound up with the status of the subject’s processes of identification. 2 One might in fact locate the order of the subject in terms of the subject’s distance, or failure of distance, with respect to representation. Cohn’s account, utterly separating “real and fictional worlds,” posits something like the immunity of the subject to representation. What I mean to outline here is, rather, the contagious relation between the subject’s identity and his [End Page 21] identifications or representations. This, it will emerge, has to do precisely with the “fictional” status of transparent minds, albeit not at all in the sense that Cohn rehearses. In these pages then I want to take up, very briefly, such surfacings of the uncanny—repetition, ambiguation, and the subject’s intimacy with representation, focusing on the third as a way of specifying the effects generated by such haunted houses as panopticons and novels. The subject of vision has, of course, emerged as a centering topic in recent cultural and intellectual history. One might instance Martin Jay’s richly informed history of the vicissitudes of vision from the Enlightenment on, or Jonathan Crary’s more localized history of the shifts in technologies of visualization during the nineteenth century. 3 Correlatively, the status of “panoptic theory” has been clarified in recent work, in part through Gilles Deleuze’s reassessment of the mutation of the “disciplinary society” into the “control society,” or through Michel Serres’s related account of the displacement of networks of surveillance by the mode of information (“The informational world takes the place of the observed world”). 4 This is not to suggest, however, a simple withering away of panopticism. Consider, for example, the designs prepared in the early 1980s for a series of shopping complexes in Los Angeles: “The service area located at the rear of the property is enclosed with a six-foot-high concrete block wall; both service gates remain closed and are under closed-circuit video surveillance, equipped for two-way voice communications, and operated for deliveries by remote control from a security ‘observatory.’ Infra-red beams at the bases of light fixtures detect intruders who might circumvent video cameras by climbing over the wall.” 5 As Mike Davis points out, “the prototype plan for...

Comparison among Full-scale Failure Experiments of Geotextile Reinforced Soil Walls with Different Facing Types

To examine the effects of facing types upon stability and deformation of geotextile reinforced soil walls, failure experiments of full-scale models with different facings of 6m high were conducted. Findings from the experiments are as follows.(1) The horizontal displacement of EPS blocks was larger than that of concrete blocks during construction, showing that deformation during construction could be reduced by the weight effect of facing materials. For divided type concrete-panel wall, the horizontal displacement was larger than that of other type of panel wall.(2) In every case, the vertical pressure at the bottom of the facing was larger than the self dead weight.(3) Maximum tensile forces distributed on the reinforcements after the construction were nearly equal at upper 3m part of facing and were smaller at lower 3m part compared with the required tensile forces which the effects of facing was not taken into account. The greater the longitudinal rigidity of facing material became, the more salient this tendency was.(4) Tensile-force distribution similar to that on the main reinforcements was observed on sub-reinforcements suggesting that the sub-reinforcements were contributing to the stability.(5) The shape of the slipping surface of the EPS-block wall after the failure was most similar to that of slip circle by the current design method. The failure surface of slipping of the concrete-block wall was similar to that of slip circle analogous to Coulomb's active failure surface, and the slipping shape of the concrete-panel wall to that of two-part wedge type. In case of the facing material of low rigidity, the failure was progressed as the creep phenomenon

Transmission and reflection characteristics at concrete block walls in the UHF bands proposed for future PCS

Buildings such as warehouses, supermarkets and retail department stores typically have walls constructed from concrete (cinder) blocks. The web and void design of the individual blocks and their arrangement within a wall creates a periodic structure, which exhibits frequency dependent transmission and reflections characteristics in the UHF bands proposed for future Personal Communication Systems (PCS). For higher frequencies, higher order Floquet modes excited at the periodic structure can propagate away from the wall, suggesting that significant power can be carried away from the wall in non-specular directions. Indoor propagation prediction models must consider the non-specular paths exited by walls with a periodic nature in order to account for all of the scattered power. In this work, plane wave reflection and transmission characteristics for typical concrete block walls are examined theoretically and experimentally to determine the frequency dependence of the specularly and non-specularly transmitted and reflected fields. >

Sound transmission through slotted concrete blocks with attached gypsum board

Measurements of sound transmission loss through slotted concrete blocks with attached gypsum board showed that the cavity resonance of the blocks has an important beneficial effect. It counteracts the mass-air-mass resonance that occurs when gypsum board is added to the surface of a concrete block wall leaving an air space behind it. This significantly increases the sound transmission class rating relative to the same systems with normal-weight nonslotted blocks. The effects of the two resonances could be seen at different frequencies when there was no sound-absorbing material in the air space behind the gypsum board. When the air space was filled with sound-absorbing material, however, both resonances moved together and could not be separated, but the transmission losses and sound transmission class for the composite wall were still significantly greater than those for wall systems using nonresonant blocks. Sound absorption measurements for the slotted blocks showed the need for one-third octave band data in place of the octave band data often found in trade literature.

Models of Radon Entry

This paper reviews existing models of radon entry into houses. The primary mechanism of radon entry in houses with high indoor concentrations is, in most cases, convective entry of radon-bearing soil gas from the surrounding soil. The driving force for this convective entry is the small indoor-outdoor pressure difference arising from the stack effect and other causes. Entry points for the soil gas generally are the cracks or gaps in the basement sub-structure, or through other parts of the building shell directly in contact with the soil, although entry may also occur by means of flow through permeable concrete or cinder block walls of the sub-structure. Models using analytical solutions to idealised geometrical configurations with simplified boundary conditions obtain analytical tractability of equations to be solved at the cost of severe approximations; their strength is in the insights they offer with their solutions. Models based on lumped parameters attempt to characterise the significant physical behavioural characteristics of the soil gas and radon flow. When realistic approximations are desired for the boundary conditions and terms in the governing equations, numerical models must be used; these are usually based on finite difference or finite element solutions to the governing equations. Limited data are now available for experimental verification of model predictions. The models are briefly reviewed and their strengths and limitations are discussed.

Sound transmission through concrete blocks with attached drywall

The furring system for attaching drywall to concrete block walls must be chosen with care if sound transmission is not to be increased at low frequencies. Once drywall is attached to a normal-weight block wall, sound transmission loss is increased above a frequency fx given by fx=K/(Md)1/2 . (M is the surface mass of the drywall, kg/m2, and d is the depth of the cavity behind it, m. K is 108 for an empty cavity and 60 for a cavity filled with fibrous sound-absorbing material.) Sound transmission loss data measured for a number of 190-mm normal-weight concrete block wall systems are presented to support the above result. Walls were measured with drywall systems mounted on different furring types on one side and on both sides. The cavities behind the drywall were either empty or filled with glass fiber. A simple, limited prediction scheme that can be used to recreate the data is described. The measurements in this paper present a consistent picture of the influence of the depth of the air space between the drywall and the block, and the presence of sound-absorbing material in the cavity.

Radon-222, 222Rn Progeny, and 220Rn Progeny Levels in 70 Houses

A year-long, multipollutant, indoor air quality study involving 70 occupied houses in four states was completed in 1987. All of the houses included in the study had a partial or complete basement with a concrete slab floor and block walls. On an approximately quarterly schedule, integrating monitors for short-lived Rn progeny, nitrogen dioxide, formaldehyde, and water vapor were exposed for 1 wk in each house on both the basement and main floors. At the beginning of the study, a pair of alpha-track detectors were placed on top of the refrigerator in the kitchen (or some other sampling location on the main floor) and at a location in the basement. One detector at each location was left in place for a year while the other detector was retrieved and replaced once every 3-mo period. In addition, short-term measurements of Rn and 222Rn progeny were made at all sampling locations once per quarter. In this study, comparisons were made between: (1) seasonal and annual averages, (2) summer and winter averages, (3) living-area and basement results, (4) 222Rn and 220Rn progeny, and (5) short- and long-term measurements. The Rn and Rn progeny concentrations in houses near Huntsville, AL were found to be well above recommended action levels (150 Bq m-3). For houses near Birmingham, AL, summer Rn concentrations were found to exceed winter concentrations, whereas for the other houses in the study, winter concentrations exceeded summer concentrations. Potential alpha energy concentrations (PAEC) from 220Rn progeny were found to be generally less than PAEC from 222Rn.

A Comparison of Two Test Methods for Determining Transfer Function Coefficients for a Wall Using a Calibrated Hot Box

This paper experimentally verifies and compares two dynamic test methods for a calibrated hot box to characterize the transient thermal performance of complex walls. In these methods, a wall specimen is sandwiched between the two conditioning chambers of a calibrated hot box. The exterior surface of the wall specimen is subjected to a time-varying excitation function in air temperature. At the interior surface, the air temperature is maintained steady, and the heat transfer response is measured. Conduction transfer function coefficients that relate the measured heat transfer response to the excitation function are derived. The two dynamic test methods were applied to an insulated hollow concrete block wall that contained significant thermal bridges and lateral heat flows. Empirical transfer function coefficients derived by the test methods predicted with good agreement the heat transfer response of this wall specimen when its exterior surface was subjected to excitation functions that differed markedly from those used to derive the coefficients.

And the Wall came Tumbling Down - Analysis of Stucco Veneer Failure at Lee County Justice Center

The Lee County Justice Center is a five- and six-story masonry and concrete multi-sided building located in downtown Fort Myers, Florida. It is approximately 620 feet long by 250 feet deep at its extremities and covers a city block. The building contains courtrooms, offices and the Lee County jail (Figure 1). Pods A, B, C and the jail were constructed in 1983 and 1984 by one contractor. Pod D was constructed by a different contractor in 1984 and 1985. Construction costs were about $33 million. The architect and construction manager were the same throughout the entire construction. The building designers decided to insulate the building on the outside, because the jail required hard concrete block walls on the inside. The jail was only about one fourth of the entire building, but they let it dictate the wall design for the entire building.

Wind Damage to Masonry Buildings

An examination has been made of the methods of construction of masonry‐walled buildings, and their performance in severe windstorms. Particular emphasis was placed on low‐rise buildings using unreinforced concrete block walls and light roofs, which suffer the majority of wind damage. It is shown that traditionally built, nonengineered buildings have become more wind sensitive in recent years as the result of a reduction in the number of internal walls and a lowering of roof weights. Empirical design procedures regarding wall height‐to‐thickness ratios and roof anchorage have not changed to reflect this increased sensitivity, leaving many modern, nonengineered buildings with insufficient wind resistance. Professionally designed structures often have a similar structural form to traditionally built structures, since the same empirical design rules are often used to size walls and roof anchors. The longer roof spans in these buildings render them even more sensitive to wind uplift loads, and subject to progr...

Sound transmission measurements through concrete block walls with attached drywall layers

Sound transmission through a series of concrete block walls was measured in a reverberation room according to ASTM E90. The measurement frequency range was extended down to 63 Hz. The effects of the method of attaching the drywall and of adding sound absorbing material to the cavity were investigated during the series. The series produced a reasonably well-behaved set of data even at the lower frequencies. As expected, increasing the depth of the cavity and adding sound absorbing material moved the mass-air-mass resonance to lower frequencies and usually improved the sound transmission class rating. The highest sound transmission class measured was 73. Because of the extended range of the measurements, reductions in the low-frequency transmission loss values were quite evident. A simple method of predicting the results obtained will be presented and its extension to other cases discussed.

Out‐of‐Plane Bending of Concrete Block Walls

The test results for 21 full‐scale concrete block walls subjected to uniformly distributed loading normal to the surfaces of the walls are reported. The variables included in this experimental study include three wall lengths of 6.0 m (19 ft, 8 in.), 5.2 m (17 ft, 1 in.), and 3.6 m (11 ft, 10 in.) with a constant 2.8 m (9 ft, 2 in.) wall height. In addition, tests were performed with simple support conditions on all four boundaries, on the bottom and two sides, on only the two sides, and on only the top and bottom of the wall. Also, one series of tests was done with precompression loading in the vertical direction. Three repetitions for each combination of parameters were performed to provide a better statistical sample. The test results were compared with both elastic‐plate and yield‐line analyses. In these analyses, the bending strengths used were taken from tests of masonry assemblages constructed to allow testing of individual joints under bending normal to the bed joint and parallel to the bed joint....