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Plate reinforced concrete elements (beams)
- Thread starter elliottpj
- Start date
- Thread starter
- #4
I would like to thank RiBeneke and Austin for replying to my post. The project I have proposed is to reinforce concrete beams using internal plates in place of deformed bars. The beams will be reinforced with top and bottom plates. The plates will separated using a threaded bar system incorporating spacers.
When compared to a traditional reinforced concrete beam, the moment capacity of the member is increased, by positioning the centroid of the same area of steel reinforcement further away from the neutral axis of the beam.
The plate system should require less skill and time to put together on site, provided the majority of the system was prefabricated off site.
The problem with using the solid steel plates are:
1. Compacting the concrete.
2. Bond between the steel plates and the concrete.
3. Bond between the two layers of concrete separated by the steel Plates.
After considering these problems I intend to use steel plates with holes punched through them.
I have been unable the find research or information in this area. Am I barking up the wrong tree?
When compared to a traditional reinforced concrete beam, the moment capacity of the member is increased, by positioning the centroid of the same area of steel reinforcement further away from the neutral axis of the beam.
The plate system should require less skill and time to put together on site, provided the majority of the system was prefabricated off site.
The problem with using the solid steel plates are:
1. Compacting the concrete.
2. Bond between the steel plates and the concrete.
3. Bond between the two layers of concrete separated by the steel Plates.
After considering these problems I intend to use steel plates with holes punched through them.
I have been unable the find research or information in this area. Am I barking up the wrong tree?
flamby
Structural
- Feb 12, 2002
- 591
elliottpj,
What you are describing is generally described under the head of "Steel Beam Theory". When the area of steel is high, you can neglect the concrete area, and design the beam as if only composed of steel. The concrete filled there is only for aesthetic reasons and you dont have to worry about bond with steel etc. A fairly unusual detail this, but will work.
flame
What you are describing is generally described under the head of "Steel Beam Theory". When the area of steel is high, you can neglect the concrete area, and design the beam as if only composed of steel. The concrete filled there is only for aesthetic reasons and you dont have to worry about bond with steel etc. A fairly unusual detail this, but will work.
flame
- Thread starter
- #6
elloittpj,
Your proposal sounds like a very expensive way of providing reinforcement.
Firstly, all of the steel area in line with the holes does nothing except add weight and cost money. If you try to provide the same sort of 'openness' for concrete placement that you get with even the minimum bar spacings required by many design codes, at least half of the steel that you purchase will be wasted in this way.
Secondly, you will have to pay for the full mass of the original intact plates before you cut the holes. That is the holes will cost more than the steel you end up with - you will have to pay for the steel that was there before the holes, plus the cost of cutting the holes.
Thirdly, your threaded bar system will cost much more than 'standard' shear reinforcement, with the spacers contributing nothing towards shear capacity. Also your bars will need to be of larger diameter than normal shear reinforcement, due to the reduced tensile capacity at the threads.
Your proposal sounds like a very expensive way of providing reinforcement.
Firstly, all of the steel area in line with the holes does nothing except add weight and cost money. If you try to provide the same sort of 'openness' for concrete placement that you get with even the minimum bar spacings required by many design codes, at least half of the steel that you purchase will be wasted in this way.
Secondly, you will have to pay for the full mass of the original intact plates before you cut the holes. That is the holes will cost more than the steel you end up with - you will have to pay for the steel that was there before the holes, plus the cost of cutting the holes.
Thirdly, your threaded bar system will cost much more than 'standard' shear reinforcement, with the spacers contributing nothing towards shear capacity. Also your bars will need to be of larger diameter than normal shear reinforcement, due to the reduced tensile capacity at the threads.
to elliottpj
from "mapestru"
( 9/18/02)
(This is my first contribution to this excellent forum, so please forgive all glitches)
Re your steel plate reinforced concrete concept, I suggest that there is no apparent advantage, and there are many disadvantages,---most of which have been well discussed by Austim.
I do not understand the remarks of Flame (which could be dangerous, if applied, though misunderstood)
Modern standard rebars provide a very economical and efficient method of use of steel for reinforcement.
The use of exotic very strong plastics or carbon fibers, or fiberglass may eventually provide improvements, but there are many problems of cost, anchorage,etc, still to be solved.
(Some time back, I used an oriented fiberglass mat, epoxy glued to the exterior of a previously cast beam, to provide later additional reinforcement, but that was a special case which offered no great economy, except for being able to be done as an after-thought.)
In summary, though you have my best wishes, I must conclude that,-- as you surmised, --- you are "barking up the wrong tree".
from "mapestru" ( 9/18/02)(This is my first contribution to this excellent forum, so please forgive all glitches)
Re your steel plate reinforced concrete concept, I suggest that there is no apparent advantage, and there are many disadvantages,---most of which have been well discussed by Austim.
I do not understand the remarks of Flame (which could be dangerous, if applied, though misunderstood)
Modern standard rebars provide a very economical and efficient method of use of steel for reinforcement.
The use of exotic very strong plastics or carbon fibers, or fiberglass may eventually provide improvements, but there are many problems of cost, anchorage,etc, still to be solved.
(Some time back, I used an oriented fiberglass mat, epoxy glued to the exterior of a previously cast beam, to provide later additional reinforcement, but that was a special case which offered no great economy, except for being able to be done as an after-thought.)
In summary, though you have my best wishes, I must conclude that,-- as you surmised, --- you are "barking up the wrong tree".
- Thread starter
- #9
Firstly, I would like to thank Austim and Mapestru for your comments.
The system I have described above is understandably very crude. Please do not think of the system as a finished product, more the first stage of development. For the purpose of this project, I am using punched steel plates and threaded bar as my reinforcement members, these are being used to test the overall arrangement, a finished product would not use the above forms of fabrication and could very well use different materials altogether. My interest in the system is:
1. The system should require less skill and time to put together on site.
2. There might be a small increase in a the moment capacity
of the member.
3. It should be easier to predict the exact position of the reinforcement, therefore it might be possible to reduce factors of safety and or cover requirements.(Could it be said that rebar will always be parallel to the longitudinal axis of a member and that all bars will the same distance from the N.A.)
4. Reinforcement would be designed for a standard widths of beams, then its depth would be calculated for the required strength.
The system I have described above is understandably very crude. Please do not think of the system as a finished product, more the first stage of development. For the purpose of this project, I am using punched steel plates and threaded bar as my reinforcement members, these are being used to test the overall arrangement, a finished product would not use the above forms of fabrication and could very well use different materials altogether. My interest in the system is:
1. The system should require less skill and time to put together on site.
2. There might be a small increase in a the moment capacity
of the member.
3. It should be easier to predict the exact position of the reinforcement, therefore it might be possible to reduce factors of safety and or cover requirements.(Could it be said that rebar will always be parallel to the longitudinal axis of a member and that all bars will the same distance from the N.A.)
4. Reinforcement would be designed for a standard widths of beams, then its depth would be calculated for the required strength.
- Thread starter
- #11
I "think" you are barking up the wrong tree. Functionally, what you are describing sounds to me to be the same thing as a composite steel beam system with a concrete surface slab up top ( riding surface or floor ). Only... your system sounds like it is likely less stable and more expensive to make.
The concrete which encases your tension steel plates really only adds load to your system with no discernable strength benefits. Also... as you've already noted... bonding the concrete to the steel plates is not simple. I doubt that punched holes in the steel will do you much good. If you were going to do such a thing, I would think that steel studs attached to the plate would work better.
If the whole reason for your design concept is to obtain extra strength for the given beam depth which you have to work with... then I might suggest you look into either prestressed or poststressed concrete beams. My outfit does a LOT of poststressed continuous frame bridges. They work quite well at carrying large loads over long span lengths.
Dan
The concrete which encases your tension steel plates really only adds load to your system with no discernable strength benefits. Also... as you've already noted... bonding the concrete to the steel plates is not simple. I doubt that punched holes in the steel will do you much good. If you were going to do such a thing, I would think that steel studs attached to the plate would work better.
If the whole reason for your design concept is to obtain extra strength for the given beam depth which you have to work with... then I might suggest you look into either prestressed or poststressed concrete beams. My outfit does a LOT of poststressed continuous frame bridges. They work quite well at carrying large loads over long span lengths.
Dan
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