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Design of Baffle Wall inside of an Inlet
3

Design of Baffle Wall inside of an Inlet

Design of Baffle Wall inside of an Inlet

(OP)
I seeking information on designing a baffle wall inside of an inlet.

My goal is to determine the required wall thickness and reinforcement for the baffle. My design intent is for the baffle wall to be a reinforced concrete wall.

Water needs to be able to go through the baffle wall, so an opening and sluice gate are required as well for the baffle wall.

Please see attachment for image of the preliminary configuration of the wall inside the inlet: https://files.engineering.com/getfile.aspx?folder=...

Comments/suggestion are appreciated.

RE: Design of Baffle Wall inside of an Inlet

One load case to consider would be water to the top of the wall, with gate closed.
A second load case, assuming it can happen, water flowing over the top of the wall at maximum flow rate with the gate closed. In that case, assume zero pressure on the backside and calculate pressures from Bernoulli's equation on the front side.
See the rectangular plate formulas in Roark's Formulas for Stress and Strain for one approach to bending in the plate part.
It may be equally reasonable to treat as just beams running across the well.
If that is drawn to scale, it may be difficult to fit a concrete wall in while retaining adequate cover (perhaps difficult to build it, too)- consider a stainless steel plate as another option in that case.

RE: Design of Baffle Wall inside of an Inlet

Depending on how the pipe slopes on the upstream side, and what the potential flow characteristics are, you may have to consider dynamic flow pressure. If it's only 0.26% for a long reach upstream, the velocity should be fairly low. If it's steeper upstream, you may need to get a calculated flow volume and velocity from someone with experience in hydraulics, so you can calculate the loading the sluice gate and baffle wall.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (BridgeSmith)

Depending on how the pipe slopes on the upstream side, and what the potential flow characteristics are, you may have to consider dynamic flow pressure. If it's only 0.26% for a long reach upstream, the velocity should be fairly low. If it's steeper upstream, you may need to get a calculated flow volume and velocity from someone with experience in hydraulics, so you can calculate the loading the sluice gate and baffle wall.

Would it be conservative to apply hydrostatic load to one side of the wall and design it that way?

Quote (JStephen)

A second load case, assuming it can happen, water flowing over the top of the wall at maximum flow rate with the gate closed. In that case, assume zero pressure on the backside and calculate pressures from Bernoulli's equation on the front side.

If the WSE = 147.0 and the top of the wall equals EL=147.0, would it be safe to say that the water elevation would not exceed the height of the wall? Would this be the reason for needing the opening and sluice gate?

RE: Design of Baffle Wall inside of an Inlet

Quote:

Would it be conservative to apply hydrostatic load to one side of the wall and design it that way?

I'm no expert on fluid dynamics, but I believe the dynamic pressure can exceed the hydrostatic if the velocity is sufficient.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Design of Baffle Wall inside of an Inlet

The thrust and overflow cases may not be necessary to be included in your design, however, it is prudent to keep them in mind when dealing with hydraulic structures. The gate might not open in time, or might not open at all, then what?

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (BridgeSmith)

I'm no expert on fluid dynamics, but I believe the dynamic pressure can exceed the hydrostatic if the velocity is sufficient.

Would you happen to be aware of any technical guides or textbooks that would be useful in addressing the types of loading you mentioned?

Quote (retired13)

The thrust and overflow cases may not be necessary to be included in your design, however, it is prudent to keep them in mind when dealing with hydraulic structures. The gate might not open in time, or might not open at all, then what?

Thank you for the input.

Are you aware of any technical literature that would be useful in designing a baffle wall with an opening and sluice gate?

@everyone
Does anyone have access to any example structural details for this type of situation?

RE: Design of Baffle Wall inside of an Inlet

Quote:

Would you happen to be aware of any technical guides or textbooks that would be useful in addressing the types of loading you mentioned?

No, not really. AASHTO has some equations for calculating stream pressure on a pier, but those are fairly specific to a totally different situation. Aside from that, I'm out of my depth, so to speak. I'm a structural guy who barely passed my fluid mechanics class nearly 20 years ago, and have avoided dealing with anything that flows as much as possible since.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Design of Baffle Wall inside of an Inlet

(OP)
Based on this website (see link: https://fabricsbuildhub.com/article/important-of-b... ) it appears that the design of a "baffle wall" would just be the design of reinforced concrete wall subjected to water pressure.

Does anyone have a different take on the design of this application?

RE: Design of Baffle Wall inside of an Inlet

Quote:

...it appears that the design of a "baffle wall" would just be the design of reinforced concrete wall subjected to water pressure.

That would seem to be pretty much it. The trick would seem to be figuring out the correct magnitude of water pressure to use.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (BridgeSmith)

That would seem to be pretty much it. The trick would seem to be figuring out the correct magnitude of water pressure to use.

It would appear that if the baffle wall can resist the forces of the water at the height of the Throat Elevation, that would be sufficient. My reasoning is because the Throat Elevation would surpass the WSE and that would be the greatest water head.

Does any one have information on providing a sluice gate within a baffle wall? Any available structural details?

RE: Design of Baffle Wall inside of an Inlet

Google the words "sluice gate" you will get a lot of results. Here are two, just to have a feel.





RE: Design of Baffle Wall inside of an Inlet

oengineer,

The structural aspect of baffle wall design is essentially the same as any concrete wall subject to hydrostatic pressure, but you need to pay attention to details around the opening, that will be abused by the water flow with abundant velocity head and turbulence; also, vibration from the sluice gate, albeit small, but repetitive. My only advice for you is "thickness is your friend" when dealing with hydraulic structures.

I wouldn't contemplate to design the sluice gate without consult a mechanical engineer. I think the best bet is to contact a supplier directly, if you do not have inhouse ME.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

The structural aspect of baffle wall design is essentially the same as any concrete wall subject to hydrostatic pressure, but you need to pay attention to details around the opening, that will be abused by the water flow with abundant velocity head and turbulence; also, vibration from the sluice gate, albeit small, but repetitive. My only advice for you is "thickness is your friend" when dealing with hydraulic structures.

Thank you for this input. This is what I came to the conclusion of regarding the structural design of the wall, based on my research & comments in this thread. So far, I have come up with a 10" thick wall (the wall is only 3'-2" tall, based on the sketch in the link) with vertical reinforcement of #5@ 12"o.c. At both faces of the wall.

You mentioned "thickness is your friend" when dealing with hydraulic structures. would you consider 10" thick concrete wall to be sufficient?

Would the following statement be correct:

Quote:

It would appear that if the baffle wall can resist the forces of the water at the height of the Throat Elevation, that would be sufficient. My reasoning is because the Throat Elevation would surpass the WSE and that would be the greatest water head.

The Throat Elevation is 7'-6" above the top of the wall.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

I wouldn't contemplate to design the sluice gate without consult a mechanical engineer. I think the best bet is to contact a supplier directly, if you do not have inhouse ME.

Thank you for this advice.

RE: Design of Baffle Wall inside of an Inlet

I would find out from the H&H people what the flow velocity will be. My guess is that it's low.

Your flowline is at ~144' and the top of baffle wall is at 147', so that's only 3ft extra. If the flow velocity was anything material, then your sluice gate wouldn't buy you much time. My gut tells me that the hydrostatic load will be the greatest. It's only 4ft of head, so still not that much.

For your wall, I think I would start at a 10" thickness, but maybe bump it to 12".
Here are the reasons:
1) The wall could see pressure from both sides, so you need 2 curtains of steel. That automatically means you need at least an 8" thick wall.

2) The sluice gate will have anchor bolts attaching it to the wall. These might have a 6" embedment. By going to a 10" thick wall, you will have at least 4" of concrete on the far side of the anchors, and the anchor tips should not be hitting the far side rebar cage.

Other things to think about:

Junction box/manhole size - There needs to be enough room to bolt up the sluice gate. If your opening is 24" in diameter, you need room on the left and right sides to mount the gate. Absolute bare minimum is 8" extra space on each side, but I would argue for more just to make sure they can get room to drill holes, etc. It's nice to have 12"+ inches of free space around your opening. You also want room to get some continuous rebar in the wall.

What type of sluice gate will you be installing? Is it a 'self contained gate' or a 'non-self contained gate' (you should google this). A 24" gate will not weigh much, but this becomes very important on larger gates. The stem carries the load of the gate when it's opened. For a 'non-self contained' gate, that load goes straight up the stem to the top of your man-hole. This means your steel grating/platform at the top needs to be stronger. A 'self-contained' gate has a steel frame with built in beam. The gate's self weight is carried by the beam and then sent into your concrete wall. The steel grating and platform at the top of the well does not have to carry the gate weight.

RE: Design of Baffle Wall inside of an Inlet

(OP)
The quote below is basically the method I used to determine the applied forces to the wall.

Quote (JStephen)

One load case to consider would be water to the top of the wall, with gate closed.
A second load case, assuming it can happen, water flowing over the top of the wall at maximum flow rate with the gate closed.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (JoelTXCive)

I would find out from the H&H people what the flow velocity will be. My guess is that it's low.

Your flowline is at ~144' and the top of baffle wall is at 147', so that's only 3ft extra. If the flow velocity was anything material, then your sluice gate wouldn't buy you much time. My gut tells me that the hydrostatic load will be the greatest. It's only 4ft of head, so still not that much.

For your wall, I think I would start at a 10" thickness, but maybe bump it to 12".
Here are the reasons:
1) The wall could see pressure from both sides, so you need 2 curtains of steel. That automatically means you need at least an 8" thick wall.

2) The sluice gate will have anchor bolts attaching it to the wall. These might have a 6" embedment. By going to a 10" thick wall, you will have at least 4" of concrete on the far side of the anchors, and the anchor tips should not be hitting the far side rebar cage.

Other things to think about:

Junction box/manhole size - There needs to be enough room to bolt up the sluice gate. If your opening is 24" in diameter, you need room on the left and right sides to mount the gate. Absolute bare minimum is 8" extra space on each side, but I would argue for more just to make sure they can get room to drill holes, etc. It's nice to have 12"+ inches of free space around your opening. You also want room to get some continuous rebar in the wall.

What type of sluice gate will you be installing? Is it a 'self contained gate' or a 'non-self contained gate' (you should google this). A 24" gate will not weigh much, but this becomes very important on larger gates. The stem carries the load of the gate when it's opened. For a 'non-self contained' gate, that load goes strait up the stem to the top of your man-hole. This means your steel grating/platform at the top needs to be stronger. A 'self-contained' gate has a steel frame with built in beam. The gate's self weight is carried by the beam and then sent into your concrete wall. The steel grating and platform at the top of the well does not have to carry the gate weight.

Based on your response, it appears I am on the right track. Thank you for your comments/suggestions. As I mentioned previously, based on my calculations I have come up with a 10" thick wall (the wall is only 3'-2" tall, based on the sketch in the link) with vertical reinforcement of #5@ 12"o.c. at both faces of the wall.

I have checked the wall for a total hydro-static head of 10'-6". The top of wall is 147 ft and the throat elev is 154.5 ft. This gave me 7'-6" of water above the baffle wall. Based on your comments, my analysis method appears to be conservative. The 10" thick concrete with #5 @ 12"o.c. (each face) is adequate, structurally.

Besides the advice of "thickness is your friend", I am not sure why a 12" wall would be required, given the applied loads.

Based on your comments, a 10" wall would suffice.

Please let me know if I am missing something.

RE: Design of Baffle Wall inside of an Inlet

JoelTACive covered the wall thickness well, I am in line with his suggestion.

To the design load, I don't understand how the throat elevation related to the pipe flow, and the abbreviation WSE, so no comment at this time. But are you sure there is no chance that "surge" will occur throughout its service life? A surge will increase the pressure on the wall, and the pressure head increase is usually furnished by the hydraulist, or the pipe designer.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

JoelTACive covered the wall thickness well, I am in line with his suggestion.

To the design load, I don't understand how the throat elevation related to the pipe flow, and the abbreviation WSE, so no comment at this time. But are you sure there is no chance that "surge" will occur throughout its service life? A surge will increase the pressure on the wall, and the pressure head increase is usually furnished by the hydraulist, or the pipe designer.

I am not sure I am clear on your statement in BOLD. Are you asking what the "WSE" abbreviation is? Or are you asking about its relationship to the throat elevation?

RE: Design of Baffle Wall inside of an Inlet

Yes, both, if you can explain. Thanks.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

Yes, both, if you can explain. Thanks.

WSE = Water Surface Elevation (WSE) means the height, in relation to mean sea level (existing grade in case of Zone AO), of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas.

I used the throat elevation as the highest point for my water head elevation when calculating my hydrostatic loads, since it was several feet higher than the WSE. Based on JoelTXCive's comments, this should be a pretty conservative design assumption.

RE: Design of Baffle Wall inside of an Inlet

All right then. I am very bad on abbreviations, it always make me nervous when guess. How about FEL (free water elevation), or MWEL (maximum water elevation) :) Just to make sure it is the maximum expected water elevation then.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

All right then. I am very bad on abbreviations, it always make me nervous when guess. How about FEL (free water elevation), or MWEL (maximum water elevation) :) Just to make sure it is the maximum expected water elevation then.

The section detail provided in the post was put together by the civil engineer. I did not set the abbreviations.

RE: Design of Baffle Wall inside of an Inlet

Oengineer. Yes, your water depth is conservative, but not crazy based on your geometry.

It doesn't really matter what the throat elevation is. Once water gets to the top of the baffle wall, it will flow over. Then you will have the same head on both sides. The throat could be 100ft up, and it wouldn't change the pressure on the wall. As long as water is on both sides, then it nets out to zero.

I'm with you on the 10" thick. I was just throwing out 12" in case you had super long anchors (i don't think this will be the case for a 24" gate.)

For gate structures like this, often times constructibility issues govern the design. You want to make sure there is room to get the gate in and out. Also, try and be nice to the engineer that has to replace or modify it 15 years down the road. Leave them some room to work.

RE: Design of Baffle Wall inside of an Inlet

I forgot. Do you have a preliminary gate schematic?

If not, you might want to have the contractor submit gate drawings prior to construction for your review. That way you can review the gate geometry and make sure it fits. Or put a comment that the contractor is responsible for making sure the gate works with your geometry.

RE: Design of Baffle Wall inside of an Inlet

That's okay, as long as the symbol indicating water is there, people will get it (not me though :). Another thing to keep in mind is the stainless steel for the gate framing should be ASTM 316, not 304, for better corrosion resistance.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (JoelTXCive)

I forgot. Do you have a preliminary gate schematic?

If not, you might want to have the contractor submit gate drawings prior to construction for your review. That way you can review the gate geometry and make sure it fits. Or put a comment that the contractor is responsible for making sure the gate works with your geometry.

I do not have a preliminary gate schematic. To be honest, I am not sure what that is. All I really have is the sketch contained in the link at the beginning of this post.

As of this point I am in the design phase, so I do not believe a contractor has been selected yet. The civil engineer has not made me aware if a contractor has been selected.

Would anyone please explain what does "MOC cast iron" mean? A vendor for a sluice gate that I reached out to mentioned this phrase.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

Another thing to keep in mind is the stainless steel for the gate framing should be ASTM 316, not 304, for better corrosion resistance.

Thank you for this advice.

RE: Design of Baffle Wall inside of an Inlet

I'm not sure what the "MOC" stands for.... "Material of Construction?"

These gates are often cast iron like a storm sewer cap. They can also be stainless steel (which is more expensive).

I think the cast iron is more common. Let me look through my files. I probably have some example drawings from Rodney Hunt (parent company is called Dash) or Waterman. They make a lot of these gates.

RE: Design of Baffle Wall inside of an Inlet

I apologize. I do not have any 24" diameter sluice gate drawings. I have some big square ones (10' x 10' or 12' x 12'), but I don't think that will help you.

Go to Rodney Hunts website and download their catalog:
https://www.rodneyhunt.com/cast-iron-sluice-gates/

Even though you do not know the brand or model of gate going in, the catalog has lots of photos and some geometry in it. On the projects I have worked on, I often do not know the make or model of gate going in on the front end; or the gate will get changed during the bidding process.

It's best to have your baffle wall (and junction box/manhole) setup in a way that will fit most gates. This means room to the left and right of the gate, along with above & below it for mounting a variety of gate frames.

RE: Design of Baffle Wall inside of an Inlet

I think you've already done a lot, including researches, up to this point. It should be a good time to talk to your civil engineer, I guess he is leading the effort, and can clear some of your questions and concerns. I believe this "regulator" is located in a flow channel, are there other functions/concerns beside control the pipe flow? Try to understand the project as much as you can get, some concerns may not have direct relevance to your task, but may be helpful down the road.

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (JoelTXCive)

I apologize. I do not have any 24" diameter sluice gate drawings. I have some big square ones (10' x 10' or 12' x 12'), but I don't think that will help you.

Go to Rodney Hunts website and download their catalog:
https://www.rodneyhunt.com/cast-iron-sluice-gates/

Even though you do not know the brand or model of gate going in, the catalog has lots of photos and some geometry in it. On the projects I have worked on, I often do not know the make or model of gate going in on the front end; or the gate will get changed during the bidding process.

It's best to have your baffle wall (and junction box/manhole) setup in a way that will fit most gates. This means room to the left and right of the gate, along with above & below it for mounting a variety of gate frames.

This is the vendor that I reach out to. Good to see that I am on the right path. I am new to baffle wall design.

Based on the picture that I provided, would it be correct to assume a manual operator for the sluice gate?

If so, what would be a reasonable top elevation level where the operator will be located?

Quote (retired13)

I think you've already done a lot, including researches, up to this point. It should be a good time to talk to your civil engineer, I guess he is leading the effort, and can clear some of your questions and concerns. I believe this "regulator" is located in a flow channel, are there other functions/concerns beside control the pipe flow? Try to understand the project as much as you can get, some concerns may not have direct relevance to your task, but may be helpful down the road.

Thank you.

I am wondering if i should ask the civil engineer the following questions or research it 1st:

  • Manual operated sluice gate?
  • Top elevation level where the operator will be located?

RE: Design of Baffle Wall inside of an Inlet

Talk to him, he's the boss, and its his call. Your job is to design the wall, and make sure it can easily accommodate the gate framing requirement (framing stud embedment). Get the type and size of the gate, which may affect your opening.

[ADD] If the structure is in a flow channel, what is the maximum flood elevation, and how the operator gets to it?

RE: Design of Baffle Wall inside of an Inlet

Waterman is another supplier of sluice gates.

RE: Design of Baffle Wall inside of an Inlet

(OP)
The vendor has recommended us to use a "self-contained" sluice gate for our application.

The vendor also mentioned "seated" and "unseated" head of water acting on the sluice gate.

Could anyone please explain what that actually means in relation to sluice gates?

RE: Design of Baffle Wall inside of an Inlet

See the sketches below. The self-contained gate has a closed frame, while un-contained gate does not have the header. The seated head is the operating head pushing the gate into the wall; the un-seated head is the operating head pushing the gate out of the wall. You shall let your civil engineer to provide these operating heads (simply the maximum backup water on each side of the wall while the gate is closed - one side with full head and the other side is empty as shown).

RE: Design of Baffle Wall inside of an Inlet

(OP)

Quote (retired13)

See the sketches below. The self-contained gate has a closed frame, while un-contained gate does not have the header. The seated head is the operating head pushing the gate into the wall; the un-seated head is the operating head pushing the gate out of the wall. You shall let your civil engineer to provide these operating heads (simply the maximum backup water on each side of the wall while the gate is closed - one side with full head and the other side is empty as shown).

Thank you for the explanation.

How about what "seated" and "unseated" head of water acting on the sluice gate means?

[ADD] - Sorry, I misread your explanation. You explained both concepts. Thank you again.

RE: Design of Baffle Wall inside of an Inlet

These the contractors terminology. See the sketch, I guess the left side is "seated head" situation (on-seating head), and the right hand side is "unseated head" (off-seating head). You can verify with the supplier. I general, I think you shall install the gate on the upstream side of the wall, and let the wall facing incoming flow, because the downstream side is likely to have minimal water remain,or empty while gate is closed, but the upstream side will be filled with backup water.

Pressure Head Push gate into wall - Seated Head (On-seating head)
Pressure Head Push gate out of wall - Unseated Head (Off-seating head)

RE: Design of Baffle Wall inside of an Inlet

There is usually a larger seated head capacity than an unseating head capacity.

For a seating head, your anchor bolts aren't doing much work. They carry the gate's self weight in shear only. The water pressure applied to the gate is transferred to the concrete through bearing pressure applied by the frame.

For an unseating head, your anchor bolts still carry the self weight, but are now in tension and working hard. The concrete breakout, tearout, pryout etc. limit states now apply.

It's easy to check these items though. You can come up with a shear and tension force per anchor bolt, and then plug into the free hilti or simpson software.

Most people make the assumption that all the shear loads are carried uniformly by all the anchors. Take the self weight of the gate and divide by the number of anchors.

For the tension load, Rodney Hunt (gate manufacturer) uses the water pressure at the gate centerline and applies it to the entire gate. For small gate like yours though, you can just take the water pressure at the bottom (flowline) since it's easier to calculate.

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