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\begin_body

\begin_layout Title
Structural Design of AguaClara Plants
\end_layout

\begin_layout Abstract
The AguaClara team at Cornell has focused on the unit process and hydraulic
 design of municipal drinking water treatment plants and has left the structural
 design to the Honduran engineers who are also responsible for site surveys
 and construction supervision.
 There are many opportunities for structural design work and research at
 Cornell that could significantly improve the design and reduce the construction
 costs.
 Although the structural design based on locally manufactured brick, re-bar,
 mortar and poured concrete columns is a common construction technique in
 Honduras, there may be opportunities to further optimize this construction
 technique and there may be alternate construction techniques that would
 be more cost effective.
 As a first step it would be beneficial to evaluate the current construction
 techniques using modern tools of structural analysis.
 A second opportunity is to design a more cost effective foundation for
 the plants.
 A third opportunity is to begin to automate the structural design.
 A fourth opportunity for research would be to develop a set of material
 strength tests that could be used at AguaClara construction sites for quality
 control.
 
\end_layout

\begin_layout Labeling
\labelwidthstring 00.00.0000
Students 4
\end_layout

\begin_layout Labeling
\labelwidthstring 00.00.0000
Skills Structural engineering (preferably senior level or M.Eng.)
\end_layout

\begin_layout Section
Geotech-Structure interactions and the slab design
\end_layout

\begin_layout Standard
The design for AguaClara tanks begins with a 60 cm rock/concrete layer (See
 Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Slab"

\end_inset

).
 The rock/concrete layer is created by first carefully placing large rocks
 and then pouring a thin mixture of concrete into the voids.
 The purpose of this layer is apparently to provide a thick slab that acts
 like a beam and that will be strong enough to resist cracking from moments
 or shear due to uneven settling of the soil.
 It is not clear if this layer is necessary for AguaClara plants.
 Elimination of this layer would significantly reduce excavation and the
 labor of placing the rocks.
 The rock layer might be more necessary for water storage tanks that don't
 contain interior walls.
 In the case of the AguaClara plant, the reinforced walls that are connected
 with rear to the slab form a monolithic unit.
 The reinforced walls act like very large beams that prevent the slab from
 bending.
 Analyze the effects of shear and loading conditions for the slab.
 What happens if floc tank is full and the sedimentation tank is empty?
 Does the rock base provide any advantage? What alternative foundation designs
 could be used to reduce construction costs?
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename AlaucaRockFoundation.JPG
	width 6cm

\end_inset

 
\begin_inset Graphics
	filename AlaucaRocksWithConcrete.JPG
	width 6cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Graphics
	filename AlaucaSlabRebar.JPG
	width 6cm

\end_inset

 
\begin_inset Graphics
	filename AlaucaSlabConcrete.JPG
	width 6cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Slab"

\end_inset

Construction technique for the slab at a 12 L/s plant at Alauca, El Paraiso,
 Honduras during the summer of 2011.
 The section of the slab with few vertical re-bars will support the sedimentatio
n tanks.
 The vertical re-bars will support the channel walls for the flocculator.
 
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The structural engineer designs the plant assuming the soil supports 0.5
\begin_inset Formula $\,\frac{kg}{cm^{2}}$
\end_inset

 (49 kPa).
 This is equivalent to a column of water 5 m deep.
 Thus it appears that the pressure applied by AguaClara plants is smaller
 than even a relatively low strength soil.
 Some soils resist up to 3-4
\begin_inset Formula $\,\frac{kg}{cm^{2}}$
\end_inset

.
 
\end_layout

\begin_layout Section
Structural Analysis of AguaClara Tank Walls
\end_layout

\begin_layout Standard
AguaClara plants use a poured concrete slab and stacks of bricks (see Figure
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Poured-slab-reinforced"

\end_inset

) with both horizontal and vertical re-bar for reinforcement.
 The relatively shallow tanks are approximately 1.6
\begin_inset space \thinspace{}
\end_inset

m to 2
\begin_inset space \thinspace{}
\end_inset

m deep and thus the hydrostatic forces are relatively small.
 This has made it possible to construct walls that are only 15 cm thick
 when finished.
 
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename slabandrebar.png

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Poured-slab-reinforced"

\end_inset

Poured slab reinforced foundation and bricks with both horizontal and vertical
 re-bar at the Agalteca water treatment plant.
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The structural analysis of AguaClara plants should begin with an overview
 of structural analysis methods that could be applied to these tank walls.
 The methods should include both approximate analytical approaches and more
 sophisticated analytical methods that facilitate analysis of the entire
 structure.
 After the available tools are identified the structural design should be
 evaluated using one or more approaches.
 The failure modes need to be characterized with special attention to the
 need of the tanks to be waterproof and thus to have minimal cracking.
 After the structural design is evaluated, opportunities for improving the
 current design can be explored.
 For example, could the addition of a steel mesh on the outside of the brick
 that would be embedded in the plaster improve the strength of the walls?
 Could the amount of re-bar used in the walls be safely reduced?
\end_layout

\begin_layout Standard
There is some indication that reinforced masonry unit walls are sufficiently
 complex that they are beyond the computational scope of commercial structural
 design software.
 This assessment needs to be corroborated and if it is the case, then a
 strategy for design needs to be developed.
\end_layout

\begin_layout Standard
Another strategy would be to propose a different construction technique.
\end_layout

\begin_layout Section
Automate Structural Design
\end_layout

\begin_layout Standard
A key innovation of the Cornell AguaClara team is the online AguaClara design
 tool that creates the unit process and hydraulic design for AguaClara facilitie
s.
 The same scalable design approach could be used for the structural design
 as well.
 It is not yet clear if it is appropriate for the Cornell AguaClara team
 to design the structure.
 We will need to carefully address issues of liability if we provide structural
 design guidance.
 It should be possible to have the structural design reviewed by professional
 engineers prior to inclusion in the design tool to ensure that the structural
 designs are robust.
 The rational for adding structural design to the online design tool is
 that it will further reduce implementation costs.
 
\end_layout

\begin_layout Standard
The structural design will need to be varied based on the availability of
 materials.
 This added complexity needs to be carefully assessed to create a design
 methodology that can scale globally.
 
\end_layout

\begin_layout Section
Site Evaluation of Material Properties
\end_layout

\begin_layout Standard
The use of locally available materials often means that the strength of
 the materials is unknown or poorly characterized.
 This leads to uncertainty in the structural design and a need to include
 large factors of safety.
 It would be very useful to develop test methods that could be implemented
 at the construction site to evaluate the strength of the material as well
 as to maintain quality control of construction.
 The test methods could be evaluated relative to laboratory test methods
 used in the Bovay test facility at Cornell.
\end_layout

\begin_layout Section
Alternative Construction Methods
\end_layout

\begin_layout Standard
Scaling up AguaClara implementation would benefit significantly from improved
 construction methodologies.
 The construction techniques that rely on bricks/re-bar/mortar are time
 consuming to assemble.
 Are there alternative construction methods that would be consistent with
 the AguaClara philosophies (local labor, locally available materials) that
 could reduce construction costs and construction time? Possibilities include
 using 
\end_layout

\begin_layout Enumerate
reusable forms
\end_layout

\begin_layout Enumerate
prefabricated wall panels
\end_layout

\begin_layout Enumerate
bricks that are perforated so that the bricks can be interlaced and have
 re-bar connecting them
\end_layout

\begin_layout Section
Stacked Rapid Sand Filter Construction
\end_layout

\begin_layout Standard
The stacked rapid sand filter (SRSF) at Tamara, Honduras is approximately
 3.8 m deep, 1 m wide, and 1.4 m long (see Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:SRSF"

\end_inset

).
 The SRSF box experiences significantly higher hydrostatic pressure than
 the sedimentation and flocculation tanks.
 The SRSF box at Tamara was constructed using stacks of bricks oriented
 the long way to make thick walls.
 The 25 to 30
\begin_inset Formula $\,$
\end_inset

cm thick walls may be over designed given the dimensions of the filter box.
 The wall design for the filter box must account for this pressure and the
 foundation must accommodate the higher loading on the soil.
 The relatively short walls of the filter box suggest that the moments from
 the hydrostatic pressure can be transferred to the adjoining walls and
 that the walls must be designed to withstand the bending moment at the
 corners.
 Alternately, the bending moment could be transferred to the slab, but this
 is inefficient given the much larger moment that would need to be resisted.
 
\end_layout

\begin_layout Standard
The SRSF includes a rock base similar to the foundation at Alauca (see figure
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Slab"

\end_inset

).
 Evaluate the function of the rock slab and the possibility of eliminating
 it in future construction projects.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename SRSFoverview.JPG
	width 8cm

\end_inset

 
\begin_inset Graphics
	filename SRSFBrickRebarWalls.JPG
	width 8cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:SRSF"

\end_inset

Re-bar and brick placement for the first stacked rapid sand filter at Tamara,
 Honduras.
 The concrete ledger is also visible.
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
Devise improved structural designs for the filter.
 
\end_layout

\begin_layout Standard
It is very likely that the filter design will be included in new plants
 beginning in October of 2011.
 The filter box location in the plant is an important design consideration.
 We are currently assuming that the filter box will go next to the sedimentation
 tank (see figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:ACPlantCrossSection"

\end_inset

).
 From a structural perspective it might be easier to build the filter as
 a separate unit from the sedimentation tank.
 We need to evaluate the optimal layout of the filter relative to the rest
 of the plant from both a structural and a hydraulics perspective.
 
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename ACPlantLayout.png
	width 12cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Graphics
	filename ACLayoutSection2.png
	width 12cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:ACPlantCrossSection"

\end_inset

AguaClara plant cross section showing the much deeper filter box.
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\end_body
\end_document
