El Cedro Bridge Project Overview

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El Cedro Bridge ProjectOverview

• Yoo Mi Hong

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What are we doing in this project?

• The proposed project in Canton El Cedro is to
  build a 40 meter pedestrian bridge to span the
  Quezalte river valley and to allow safe passage
  at all times of the year.

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The Community

• The community consists of about 450 families.
  Most of the residents were originally coffee
  plantation workers but the closure of many coffee
  plantations has devastated the local economy,
  leaving many without secure jobs. The dispersed
  nature of the community means that there are
  several groupings of dwellings on different
  nearby hillsides.

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The Community

• One such grouping, known as El Cedrito, consists
  of approximately 50 families who must cross the
  Quezalte River to access the main road, school,
  community center, mill, healthcare providers, and
  vocational/pediatric nutrition center. The river
  rises a meter and a half or more in the rainy
  months of May through October and becomes
  dangerously close to impassable. The tops of
  rocks appear and disappear as the water level
  rises and falls. There have been cases of people
  slipping and falling into the river only to drown
  when swept downstream.
• During these rainy months, children do not
  attend school. When the water level is too high
  to allow for safe passage, access to adult
  vocational training is curtailed, and the ability
  to travel to and from the market is also
  restricted.

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The Community

• The community has a labor force that has
  experience with community projects and
  construction. They have helped to construct many
  houses after the earthquakes in 2001 and some of
  the members of the community directive are
  experienced masons and worked on the local
  community center. They will be able to provide
• -Expertise masonry construction, material
  transportation and storage in the community
  
• -Organizational Support oversight on the
  project by master masons
  
• -Labor both skilled and unskilled

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What are the sites characteristics?

• Location
• Canton El Cedro, Morazan, El Salvador
• A community located near the city of Panchimalco,
  in the Morazan area
  
• 45 minute drive south from the capital city San
  Salvador
  
• 20-30 minute walk from nearest paved road 
• Topography is hilly ridges 
• Latitude (DMS) 13º 46' 0 N Longitude (DMS) 87º
  52' 0 W  

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What are the sites characteristics?

• Rainy season - May to October
• Dry season - November to April
• Warm climate all year, well forested with bushes,
  trees and other small vegetation.
  
• Steep ravines and trenches cause rapid floods.
• While the Quezalte river is easily passable
  during the dry months because of the low water
  level, the river rises a meter and a half or more
  in the rainy months of May through October and
  becomes dangerously close to impassable.
• Construction should take place during Dry season.

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What are the sites characteristics?
http//ewb.rice.edu/infodata/elcedro/summary.shtml
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Pictures
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Pictures
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Pictures
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Pictures
The top soil is scoured out really easily. In
this picture, what starts as a small ditch turns
into a trench above Renees head.
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Pictures
This is a picture of a bridge that they had built
across a crossing a little downstream from our
site, but that was knocked over by the flowing
water.
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Pictures
Soil in the stream bed
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Pictures
Showing water level
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Pictures
Large rock face (potential footing location)
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Pictures
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Pictures
A bridge that the team found in El Salvador
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Pictures
Another picture of the bridge that the team found
in El Salvador
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Pictures
Another bridge that the team found in El Salvador
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What has been done already?

• Topographic surveys survey data was taken from a
  100 ft length of the stream bed, centered on the
  path currently used by the people.
  
• Discussions with the town leaders were held
  concerning the nature and time scale of the
  project.

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What has been done already?
Transformed survey data into a 3D topographic
model in Arc-View.
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What has been done already?

• Looked at website of a company that specializes
  in building trail bridges in rural areas.  They
  have an amazing selection of designs, complete
  with photos documenting construction. http//www.s
  ahale.com/
• Started organizing calculation of forces in
  bridge for a given loading (excel spreadsheet)
  and researching different materials.

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Areas of Question

• Reasons for choosing to build a suspension bridge
  over a rigid bridge (steel/wood, truss/I-beam) or
  cable-stayed bridge or all-concrete bridge or
  just putting in giant stepping stones.
   Suspension bridges require less material.  One
  disadvantage is that a suspension bridge may sway
  and move more when people are on it, but there
  are ways to make it more stable. The people in
  the village prefer all-concrete bridges.

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Areas of Question

• Selecting Best Spot
• 1. The creek bed is wide and gradually sloped
  along the path used by the villagers, roughly 95
  feet.  Upstream and downstream it narrows to
  perhaps 33 feet, though one would expect floods
  to be deeper and stronger there.  This would
  necessitate a taller bridge resistant to faster
  flows. 
• 2. The reason the creek bed cross-section changes
  may be related to soil composition (perhaps loose
  soil was more easily washed away) or preferential
  flood erosion (a bend in the creek washing out
  one bank, as seems to be the case in the
  pictures).  A straight reach would be preferable
  to a bend due to erosion concerns.
• 3. The villagers may want the bridge in a certain
  spot, perhaps near the path visible in the
  pictures.
  
• 4. Coffee growers own the land on either side of
  the path.  We must discuss the construction of a
  bridge with them, especially if we're considering
  moving off the path.

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Areas of Question

• Load estimation- live load (people), dead load
  (deck, cable), factor of safety
  
• Deck- material (steel grating, concrete slab?),
  strength required (deck will experience bending
  between hangers), connection to towers cable,
  how many hangers are needed, how rigid/heavy
  should deck be?
• Footing- shape, material (concrete, rocks),
  interaction w/ soil, using large rock face as a
  footing, integrate with footing under tower?
  
• Cable- strength of material, methods of
  connecting, using chain
  

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Areas of Question

• Tower- material, design (truss, I-beam, frame),
  saddle for cable (pulley to allow motion of
  cable?), footing underneath
  
• General design- tower height vs. cable tension,
  stabilizing bridge (stay cables, rigid/heavy
  deck)