Appropedia needs your support - Please Donate Today

Las Malvinas community center shade/Literature Review

From Appropedia
Jump to: navigation, search

Literature Review[edit]

See Las Malvinas community center shade for the project that this research was completed for.

Client Information[edit]

Current Las Malvinas Community Center Shade Structure

The poverty­-stricken barrio of Las Malvinas is located in Santo Domingo Norte and consists of about 800 families. The community of Las Malvinas came together and decided what projects they thought were most urgent and important to their community. Among these projects was a new shade structure for their existing community center. The current shade structure was built with green bamboo, and is deteriorating quickly because of this. 

Weather[edit]

In designing a shade structure in Las Malvinas, it is necessary that the structure will remain physically sound and not deteriorate in a short amount of time. One of the main causes of deterioration is the harsh weather environment that is present in the Dominican Republic. From 1900-2009, the Dominican Republic has seen approximately 5 inches of average rainfall every month [1]. This value is the most varying weather condition, ranging from 2 inches per month in the dry season (December through April), to 10 inches per month in the rainy season (May through November) [1]. On average, the country encounters approximately 50-60 inches of rain each year [1]. While precipitation amounts vary, the temperature and wind conditions are relatively constant year round. The Dominican Republic experiences an average of 80 degree Fahrenheit temperatures and an average wind speed of 5 mph monthly each year [2]. While there is prevalent sun, rain, and wind exposure, there is also exposure to strong tropical storms and hurricanes. From 1944 to 1999, the probability of a tropical storm occurring and producing wind speeds greater than 40 mph is approximately 30% [3]. Once wind speeds increase over 74 mph, the Saffir-Simpson Wind Scale classifies the storm as a hurricane, the probability of which is 10% in the Dominican Republic from 1944 to 1999 [4]. Finally, once wind speeds reach 111 mph the storm is classified as a Category 3-5 hurricane, the probability of which is 3-4% over that time frame [3]. These intense seasonal weather conditions need to be considered when designing any architectural structures in the Dominican Republic.

Lean-to Roof[edit]

Lean-to roofs are a very common design in forming small canopies or ground floor extensions. Traditional or ‘cut’ roofs usually comprise a series of sloping timbers (rafters) fixed to a wall plate or support posts at their feet, and a ridge board or wall plate at their head [5]. “The wall plate is a strip of timber which is bedded on the top of the wall, and which evenly distributes the load from the roof and provides good fixing for the rafters” [6]. The depth of the rafter depends on its span and loading, and the width is primarily to prevent twisting and to provide a sufficiently wide surface on which to nail the battens supporting the roof [6]. A good practice is to notch the bottom of the rafter where it sits on the plate or posts as this gives a good bearing and aids alignment of the rafters [6].

Bamboo[edit]

Because of its rapid growth, abundance, and ability to contribute to both environmental protection and economic growth, the use of bamboo as an alternative building material is ideal in most tropical Latin American countries [7]. In the Caribbean, Bambusa vulgaris is the most cultivated exotic species of woody bamboo [7]. Timing is an important first step when considering when to harvest bamboo for use as a sound building material. In order to ensure optimum strength and to avoid pest invasion, it is advised to harvest bamboo during the dry season when starch content in the bamboo sap is low [8]. In addition, bamboo that is 3-5 years old is ideal as a construction material [8], although other sources argue that bamboo must be between 4-7 years before harvesting [9]. Nevertheless, bamboo older than five years (or seven years according to Schröder), becomes harder, drier, less permeable, and begins to deteriorate faster [8][9]. One can identify a mature bamboo stalk by its color and absence of rings around the stalk. An immature stalk will be shiny, bright green, and will have many white bands around the stalk; a mature stalk ready for harvest will be dark green to gray and the bands will be harder to see; an overly mature bamboo stalk will be white in color and the foliage will be less green than mature bamboos [9]. Harvesting bamboo mindfully will ensure both a better building product and will secure bamboo growth in the future. When felling bamboo, it is important to cut above the first or second node above ground level using a machete or saw; this way, rainwater is not able to collect in culm, which could cause rot and damage the bamboo plant system [9]. After harvesting, storage is the next most important step. The bamboo culms should be stood upright and placed on a stone, making sure that the bamboo stalks do not come in contact with the ground, as this can impact the drying process [9].

Bamboo Treatments[edit]

1. Non­chemical

  • Clump­curing: Bamboo is cut and left in a vertical position to dry out, reducing the starch content. This method effectively prevents attack by beetles, but not termites or rot [10].
  • Smoking: Cut bamboo is stored above a fireplace to blacken the culm. The bamboo could be cracked during this process [10].
  • Soaking: Directly after harvest, culms are soaked in water or mud with stones placed on top to keep them from floating. After a few weeks, the culms are removed and dried for a week in a shaded area [10].

2. Chemical

  • CCA or AsCu: A 3:1:4 composition of copper­chrome­arsenic can be used to treat bamboo and other types of timber, however it is highly toxic to people [10]. Chrome acts as a fixing agent, copper prevents attack from fungi, rot, and pests, and arsenic makes the solution appropriate for outdoor use [11]. The fixation process can take a few weeks using a soaking method, but can ensure the use of bamboo for up to 50 years [11]. Formula: 3 parts copper sulphate­1 part sodium dichromate­4 parts arsenic pentoxide [11].
    • Concentrations:
      • For outdoor structures not fixed to the ground: 6%
      • For outdoor structures fixed to the ground: 10% [11]
  • CCB: A 1.5:3:5 ratio of boric acid­copper sulphate­sodium dichromate is a non­toxic method of treating bamboo to prevent pests and rot [11]. However, it has a lower degree of fixation due to the boron in the solution and may not be appropriate for outdoor use if in an area with a high amount of rainfall [10].
    • Formula: 1.5 parts boric acid­3 parts copper sulphate­5 parts sodium dichromate Concentrations:
      • For indoor use not fixed to the ground: 6%
      • For outdoor use fixed to the ground: 8­10% [11]
  • Zinc Chrome: A 1:1 ratio of zinc­chrome can be used to treat bamboo. The mixture trends to absorb water from the air, The mixture tends to absorb water from the air, making it look wet in areas with high humidity and wet seasons.
    • Formula: 1 part zinc chloride­1 part sodium dichromate
    • Concentration: for structures outdoors and fixed to the ground: 10% [11]
  • Copper chrome acetic: A 5.6:5.6:0.25
    • Formula: 5.6 parts copper sulphate­5.6 parts sodium dichromate­0.25 acetic acid Concentration: for outdoor structures fixed to the ground: 8% [11]
  • Creosote: Coal tar and creosote are effective in preventing attack from fungi and insects. Due to its oily nature, it is water resistant and suitable for outdoor use. It is considered to be a cost effective material and primarily suitable for outdoor use due to its odor and color [11].
  • Light Organic Solvent­based Preservatives (LOSP): The organic solvents are more expensive than creosote. " The organic solvent acts as a carrier for toxic molecules and later evaporates, leaving the active ingredients behind" [11].

Treatment Methods[edit]

Butt Treatment: Place freshly cut bamboo culms with leaves in tact into a bucket containing preservatives or treatment chemicals. After a couple weeks, transpiration will occur and leaves will change color and indicate the preservatives have reached the top. Culms can be placed in empty buckets to gather left over preservatives during the drying phase [10].

Open tank: Place bamboo in an open tank filled with preservatives and leave for a week with a cover on it. After a week, dry the bamboo for a few days and collect leftover preservatives [10].

Pests[edit]

Untreated bamboo is more likely to attract unwanted pests, mainly termites and beetles. Powderpost beetles feed on the starch and sugars in the culm of the bamboo, and often leave a thin outer layer of bamboo once feeding is complete [12]. Subterranean termites infiltrate bamboo culms at the base of the plant, building colonies as they make their way up the culm. Infiltration can be prevented by using cement or other masonry at the base of construction projects [12]. Drywood termites often infiltrate higher on the bamboo culms and build their nests inside [12]. They can be prevented by using specific treatments. Other posts that are associated with bamboo are the: bamboo aphid, noxious bamboo mealybug, bamboo scale, bamboo spidef mite, persea mite, and the giant whitefly [13].

Bamboo Mechanical Properties[edit]

The cellulose fibers in bamboo act as reinforcement similar to reinforcing steel bars in concrete or glass-fiber in polyester-resin [14]. A bending force causes compression stresses on the upper part of the bamboo beam, parallel to the fibers, which does not pose a problem for the material. However, this compression causes strain perpendicular to the fibers, which occurs in between the fibers of the material, which is weak in taking strain. This, then, is the weak point in designing and building with bamboo for a beam; however, if the load is removed, the specimen will return to its original straight form, a definite advantage in the case of a hurricane or earthquake [14]. Compression force is another factor to take into consideration when designing the frame and foundation of a bamboo based structure, but is not easily evaluated. During longitudinal compression on bamboo, the bamboo becomes thicker in the middle and gives a false impression of compressive strength, when in reality, the friction at both ends of the culm are holding the material together, similar to a beer barrel [14]. Creep, or the increasing deformation under long-term loading, is negligible in bamboo. As stated earlier, bamboo structures are highly advantageous in the presence of an earthquake, it is lightweight and the hollow form gives much stiffness. While the material is great at reforming to its original state after a load is removed, such as a high wind load during a hurricane, it is very lightweight and easily blown away if not properly secured and jointed together.

Structural Integrity[edit]

“Next to the foundation and the roof covering, the basic frame is the part of a house most often made partly or wholly of materials other than bamboo” [15]. If the difference in cost can be accommodated, the use of more durable hardwood is preferred for the frame. This is because hardwoods make stiffer joints and more rigid construction than bamboo, partly because a greater load is placed on the frame and partly because certain hardwoods are naturally more resistant to rot fungi and wood-eating insects than untreated bamboo [15]. However, in locations such as the Dominican Republic where earthquakes occur frequently, a bamboo-framed structure may remain intact longer than any other type. Regardless of frame material, a cement foundation separating the frame and earth is desired in order to inhibit rot and insect infestation, as well as increase the strength of the design. The structural elements that compose the frame of a conventional all-bamboo structure are similar to those found in all timber frames: Corner posts, girders or plates, joists, studs, struts, tie beams, rafters, sheathing, etc. Because of their high strength-weight ratio, bamboo roofs carry excellent advantages for the structural integrity of the design [15]. Most bamboos have a tendency to split easily, a tendency the precludes the use of nails, while also limiting the range of techniques suitable for the framing and joining of structural units [15]. A remedy is to make end cuts just beyond a node where feasible as the nodes have a higher shear coefficient than the internodes and therefore have fewer tendencies to split, or by fastening joints using thongs or other lashing materials as opposed to nails or screws [15].

Coconut Palm Fronds[edit]

Palm Tree Fronds available in Las Malvinas

Palm fronds have been used as a traditional building material in tropical locations around the world. The time for which coconut frond thatch will last as a construction material depends on the palm species and how the thatch is harvested and woven [16] It is most ideal to choose a larger palm frond with long leaflets and it is advised to use only fresh palm fronds as opposed to dead palm fronds since fresh fronds will be less brittle and have more strength as a building material [16]. The basic process to create a coconut frond panel is as follows: the coconut frond will first need to be evenly divided from the spine of the palm frond with a machete [16]. The fifth leaflet is bent in the opposite direction of its natural growth and woven over the fourth leaflet, third leaflet, and so on using the formula (5+2+2) [16]. ‘Pegs’ should be created at intervals of 8-10 woven leaflets in order to create a hook to ensure the woven leaflets will be secured together [16]. To prevent water leakage, the leaflets must be well opened while weaving, and the woven palm frond at the end of the process must be tied together to make a complete woven panel of thatch [16]. One of the negative aspects of palm leaves is their durability. According to a thesis about construction in the Dominic Republic "There are still some houses that has roof made of palm leaves or yagua, this material is not very resistant to rain or sun so it needs to be replaced after just some years" [17]

Living Shade[edit]

Also called pergolas, living shade structures combine a structural frame made from wood or other strong material and climbing plants to create shade for an area. In the Dominican Republic, climbing plants such as Passionfruit Vine (P. edulis flavicarpa) naturally need the support of a wall or another plant for climbing in order to receive more sunlight [18]. Therefore, climbing plants could be an appropriate option to include in this shade structure.

Upcycled Industrial Materials (Plastic, Metal Roof Sheeting)[edit]

Materials such as plastic bottles and plastic containers flood the waste stream in Santo Domingo, most of which end up polluting nearby rivers and the ocean. In order to reduce the amount of plastic waste entering nearby waterways, the use of plastic bottles for a shade structure could serve as an appropriate technology. South African designer Heath Nash created shade structures from upcycled plastic bottles, with frames for the structure made from scrap metal and wood [19]. Metal roof sheeting is commonly found as scrap pieces in Santo Domingo. Durability, low maintenance, and high UV protection make metal roof sheeting a viable option as a material used in a shade structure [20].


References[edit]

  1. 1.0 1.1 1.2 "Climate Change Knowledge Portal 2.0." Climate Change Knowledge Portal 2.0. The World BanK Group, 2014. Web. 07 June 2014. <http://sdwebx.worldbank.org/climateportal/index.cfm?page=country_historical_climate&ThisRegion=North%20America&ThisCCode=DOM>
  2. "Average-monthly-Rainfall-Temperature-Sunshine,Santo-Domingo,Dominican-Republic." Weather and Climate. World Weather and Climate Information, 2014. Web. 7 June 2014. <http://www.weather-and-climate.com%2Faverage-monthly-Rainfall-Temperature-Sunshine%2CSanto-Domingo%2CDominican-Republic>
  3. 3.0 3.1 "What Is My Chance of Being Struck by a Tropical Storm or."What Is My Chance of Being Struck by a Tropical Storm or. National Weather Service, 2014. Web. 07 June 2014. <http://www.aoml.noaa.gov/hrd/tcfaq/G11.html>
  4. "Saffir-Simpson Hurricane Wind Scale." Saffir-Simpson Hurricane Wind Scale. National Weather Service, 24 May 2013. Web. 05 June 2014. <http://www.nhc.noaa.gov/aboutsshws.php>
  5. "Traditional (cut) Roofs." Traditional (cut) Roofs. University of Western England, Bristol, 2013. Web. 07 June 2014. <http://www.uwe.port.ac.uk/roof/cutroofs/print.htm>
  6. 6.0 6.1 6.2 BuildingRegs4Plans. "Guidance Pitched Roof Overview." Guidance Pitched Roof Overview. BuildingRegs4Plans, 2014. Web. 07 June 2014. <http://www.buildingregs4plans.co.uk/guidance_pitched_roof_overview.php>
  7. 7.0 7.1 Londono, Ximena. "Evaluation of Bamboo Resources in Latin America." A Summary of the Final Report of Project No. 96-8300-01-4 International Network for Bamboo and Rattan (n.d.): n. pag. Instituto Vallecaucano De Investigaciones Científicas. Web. 6 June 2014.
  8. 8.0 8.1 8.2 Environmental Bamboo Foundation. "Harvesting Bamboo." Harvesting Bamboo (n.d.): n. pag. Web. 6 June 2014<http://www.bamboocentral.org/PDF_files/page7-8.pdf>
  9. 9.0 9.1 9.2 9.3 9.4 Schröder, Stéphane. "When and How to Harvest Bamboo." Weblog post. RSS. Guadua Bamboo, 15 Nov. 2012. Web. 06 June 2014. <http://www.guaduabamboo.com/blog/when-and-how-to-harvest-bamboo>
  10. 10.0 10.1 10.2 10.3 10.4 10.5 10.6 "Bamboo Preservation." Appropriate Technology 37.1 (2010): 36­38. ProQuest. Web. 7 June 2014.
  11. 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 Schröder, Stéphane. "Chemical Bamboo Preservation." Guadua Bamboo, 12 Nov. 2012. Web. 07 June 2014
  12. 12.0 12.1 12.2 Schröder, Stéphane. "Bamboo Insect Infestation." Guadua Bamboo, 17 Nov. 2012. Web. 07 June 2014
  13. "Pests in Gardens and Landscapes: Bamboo." UC Davis Integrated Pest Management, 25 Apr. 2014. Web. 7 June 2014
  14. 14.0 14.1 14.2 Janssen, Jules J. A. Designing and Building with Bamboo. Beijing: International Network for Bamboo and Rattan, 2000. Print. ISBN 81-86247-46-7 <http://www.fundeguadua.org/imagenes/DESARROLLOS%20TECNOLOGICOS/ARTICULOS%20Y%20PUBLICACIONES/INBAR_Technical_Report_No20.pdf>
  15. 15.0 15.1 15.2 15.3 15.4 McClure, F. A. "Bamboo as a Building Material. Peace Corps. Appropriate Technologies for Development." (1981): 1-60. Department of Agriculture, Washington, D.C. Peace Corps. Information Collection and Exchange Div. Web. 7 June 2014. <http://files.eric.ed.gov/fulltext/ED242878.pdf>
  16. 16.0 16.1 16.2 16.3 16.4 16.5 Sokial, Richard Nelson. "The Sabah Architectural Heritage Blog: How to Weave a Thatch Roof from Coconut Palm Fronds." The Sabah Architectural Heritage Blog: How to Weave a Thatch Roof from Coconut Palm Fronds. N.p., 1 Sept. 2008. Web. 07 June 2014. <http://sabahwarriors.blogspot.com/2008/09/how-to-weave-thatch-roof-from-coconut.html>
  17. C. Knutson, K. Marburg. (2009) "A Study of Building Procedure in the Dominic Republic". Thesis. BSC
  18. Global Foundation for Democracy and Development. "Climbing Plant." Dominican Republic Encyclopedic Dictionary of the Environment. , n.d. Web. 07 June 2014.<http://www.diccionariomedioambiente.org/diccionariomedioambiente_en/en/definicionVer.asp?id=644>
  19. "S. African Designer Heath Nash Builds Shade Structure Out of Recycled Bottles." Inhabitat. Inhabitat, 27 July 2011. Web. 07 June 2014. <http://inhabitat.com/s-african-designer-heath-nash-builds-shade-structure-out-of-recycled-bottles/recycled-bottle-shades-heath-nash-8/>
  20. Cancer Council. "Qualities of Shade Materials." Sunsmart Information Sheet (2009): 1-17. Cancer Council, Jan. 2009. Web. 6 June 2014. <http://www.actcancer.org/downloads/File/Qualities%20of%20Shade%20Materials%20Information%20Sheet%2009.02.09.pdf>