Ramo, a former journalist and the co-CEO and vice chairman of the consulting firm Kissinger Associates, applies network theory to international affairs. The fall of the Berlin Wall and the end of the Cold War helped usher in unfettered globalization, he argues, but now a backlash is underway. And separation is increasingly being achieved through physical barriers. The statistic Ramo cites about the spread of walls comes from a study by the political scientists Ron Hassner and Jason Wittenberg: Of the 51 fortified boundaries built between countries since the end of World War II, around half were constructed between and Hassner and Wittenberg found that such boundaries—structures like the existing U.
Recently, many of those fences have been appearing in Europe, as countries there struggle to process an influx of migrants and refugees. Hassner and Wittenberg theorize that the recent proliferation of wall-like structures is in part a function of countries copying one another. And yet, the evidence on whether these walls and fences achieve their goals—which these days often involve deterring immigration, terrorism, and smuggling— is mixed , especially when you factor in the expense and unintended consequences associated with the barriers.
One of the reasons these trends are important is that they reframe the election from a contest between the past and the future, as Bill Clinton and Barack Obama imply, to one between two plausible futures. The objective then is not to stem the tide of Mexican immigrants--or illegal immigrants in general--but to send a strong message to the rest of the world using Mexico as the example.
Mexico has distanced itself from the ideology of this particular wall. The truth is that walls are only as effective as the people living with them allow them to be. They require cultural and structural maintenance from both sides. And nations typically grow out of them. Have something to say? Comments have been disabled on Anthropology in Practice, but you can always join the community on Facebook. Alvarez, R. Annual Review of Anthropology, 24 , Earle, D.
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Identity, Biculturalism, and the Practice of Anthropology. Hingley, R. Understanding the presidency as a brand. A Nation Divided by Social Media. The views expressed are those of the author s and are not necessarily those of Scientific American. You can follow AiP on Facebook.
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You have free article s left. Already a subscriber? Sign in. See Subscription Options. Load comments. Get smart. Sign up for our email newsletter. Sign Up. Figure 1 is a schematic representation of how cladding, control layers and structure are arranged from outside to inside, respectively. Note that the control layers may actually be a single material that performs all control functions, or a number of materials with uni- or multi-functional control characteristics. Figure 1. The "Perfect Wall" is comprised of cladding rainwater control layer , control layers heat, air and moisture and structure dead and live load control system.
The interior finish and inboard integration of services is entirely optional.
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In the case of below grade walls, the same arrangement applies, except the cladding is replaced by a bulk water control layer drainage medium, mat, or membrane , which may also serve as a capillary break and thermal insulation. Alternatively, separate materials may address each of the required control functions.
In all cases, this arrangement of cladding, control layers, and structure maintains a controlled thermal environment for the structure thereby reducing stresses, and promoting thermal energy storage for improved passive survivability. The "perfect roof" is simply the "perfect wall" rotated 90 degrees such that the ballast and filter fabric serve the role of cladding. Control layers for heat, air, and moisture reside over top of the roof structure. Figure 2. Protected membrane roofs a. By situating critical control layers under the ballast and filter fabric cladding these are protected from ultraviolet degradation and mechanical damage to extend the service life.
Slabs-on-grade follow the same building science principles as the "perfect wall" except that the external environment is soil instead of the atmosphere.
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It should be recognized that for foundations and slab-on-grade floors, moisture management considerations extend outward to include the surrounding landscape, water features, parking areas, etc. Figure 3. Slabs-on-grade are simply upside down roofs. The control layers reside immediately below the slab structure and the gravel granular layer serves as a capillary break and drainage layer that may be vented to the outside in order to manage any soil gas. By adhering to this fundamental arrangement of materials and control functions, much of the enclosure design process is simplified and better performance is more practically and economically achieved.
It must be recognized other arrangements are technically possible, but they are almost always sub-optimal in terms of performance, often unreliable and much less durable. This underlying logic extends to all of the enclosure details and assembly transitions. There is an emerging discussion about what priorities should be given to control measures or functions that constitute the control layers when designing building enclosures.
Heat, air, and moisture must all be managed, but is there a more efficient way to address these in the design process? At present, it is generally acknowledged that moisture management takes priority because it influences the durability of the enclosure and its susceptibility to deterioration. By addressing the measures needed to effectively manage moisture, it is often the case that measures for managing air and heat flow will be largely resolved. For example, the amount of insulation may be determined by climate, energy efficiency requirements, and economy, but the type and position of the insulation should be governed by moisture management principles.
Moisture management is privileged in building enclosure design because it ultimately determines durability and to a large degree aesthetics, especially where rainwater staining of the facade is improperly managed. In most cases, these additional performance requirements will be satisfied when control functions for heat, air, and moisture have been achieved. The control of bulk water in building enclosure predominantly involves rain control theory, although in some cold regions, snow accumulations and wind-driven snow present special challenges.
Below-grade building enclosures basements, crawlspaces, and slabs-on-grade must manage precipitation that percolates through the soil as well as fluctuations in the local water table. For a simple building typology like housing, the basic strategies for managing bulk water are depicted in Figure 4.
Figure 4. The simple recipe for managing bulk water is to shed it from the roof and away from the building. Projections above walls, such as extended eaves, help deflect rain and minimize the amount striking the wall surfaces. Foundations are provided with a drainage system to remove percolating water that cannot be managed by the site grading. Guidelines on the design of basements to effectively manage moisture have been developed and are available online.
Looking at fundamental strategies for moisture management in exterior wall enclosures, the designer must select an appropriate typology suited to the climatic zone and precipitation exposure. Figure 5.
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The typology for exterior walls based on moisture management strategies reveals four basic types. The mass wall and barrier wall do not provide acceptable performance by contemporary standards, leaving the pressure-moderated and pressure-equalized rainscreen types as being the only practical and effective alternatives from a building science perspective. Selection of a suitable wall type corresponding to precipitation exposure is a necessary but insufficient condition for adequate moisture management.
The designer should attempt to observe the 4—Ds:. Figure 6. The profile of a building, including factors such as roof slope and eaves overhang, determines how much rain is deflected from the enclosure. In some climatic locations, wind-driven rain is so severe that the enclosure typology is much more significant than the building profile. Figure 7. The various mechanisms involved in drying are dependent on the selection and arrangement of materials in the enclosure assembly as well as the climate.
In some climate zones, drying potential by evaporation and ventilation is very low, at certain times negligible. This means positive drainage is critical along a drainage plane that is an effective water resistive barrier. Figure 8.
A typical residential enclosure depicts how the 4—Ds may be deployed. An important heuristic to observe is ensuring that it is easier for the water to get out than for it to get in—otherwise it will accumulate.
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Deflection, drainage, and drying are becoming increasingly important as materials become less robust because they are often thinner and less durable than their traditional counterparts. Contemporary building science has always advocated pressure-moderated and pressure-equalized rainscreens as the most effective wall enclosure typologies for acceptable rainwater control. Over the past several decades, a great deal of research and development has gone into materials comprising the drainage plane a. Figure 9. Wood-frame construction serves as a useful enclosure technology to demonstrate the principles of water resistive barriers.
The water resistive barrier may serve as the air barrier, in which case it should be fully structurally supported to adequately resist wind pressures. The drainage cavity is compartmentalized in pressure-equalized rainscreen walls, whereas in pressure-moderated rainscreen walls, it is usually left open top and bottom to enable ventilation drying.
go to link Figure Flashing and shingling are based on the concepts of layering and overlap. This is a proven approach to shedding water and is highly effective at transitions between materials and assemblies, and changes in the angle or geometry of drainage cavities and planes. Flashing bridges these transitions and accommodates building movements due to settlement, shifting, and dimensional changes expansion, contraction, swelling, shrinkage.
Most flashing design is based on successful precedents that have evolved over time. The minimum requirements for flashings have found their way into building codes and are a useful guide to designers. The number of layers of flashing and the overlap between the layers is also based on past experience. There are time and cost implications associated with the number of layers and overlap between layers that may be appreciated by considering cedar shake and shingle requirements found in many residential building codes. Figure 11 outlines the fundamental parameters and building physics involved in arriving at an acceptable overlap between shingles and shakes.
Before the mechanization of shake and shingle production, generous overlaps translated into a lot more time and labor, both fabricating the shakes and shingles, and then installing them.