Integrated Buildings & Structures

Do you have a local steel fabricator available?  How do you plan to reinforce where the column lands on the girder?

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Chad Morrison P.E., M.ASCE
Professional Engineer
Greenville RI
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This is not an uncommon problem especially in Shopping/Office multi storey facilities.
Is the existing structure posttensioned concrete  construction. If so it is a little more difficult due to limitations in changing existing stress levels especially compression . Reinforced concrete allows more latitude. Deflection control and limiting its magnitude will be the prime design condition.

Several methods are available depending on the size relationship between existing column /beam/slab.
Fabricated steel channels (fire proofed) each side of the  existing transfer beams is a very good starting point. The balance of the modulus and strength requirement is then done above slab. Also steel plates epoxy grouted to under side of the beams is a useful strengthening measure. Work above the slab would be in reinforced concrete.
Another alterative would be reinforced concrete walls between columns. This solves the load transfer and deflection issues. These walls can have openings. This would be the ideal solution but may require a rethink on the architecture use-age/access at this level.

Have fun




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[Bruce [Montgomerie] M.ASCE
Design Engr
GLOUCESTER [AUSTRALIA]
Bruce
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Original Message:
Sent: 07-19-2017 15:50
From: Chad Morrison
Subject: Strengthening of transfer girders of a 22 story structure

Do you have a local steel fabricator available?  How do you plan to reinforce where the column lands on the girder?

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Chad Morrison P.E., M.ASCE
Professional Engineer
Greenville RI
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​Please describe briefly a change of use and a live load difference.
Also, what is a girder depth?

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Atul Patel P.E., M.ASCE
President
Faisant Assocs Inc
Baltimore MD
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​This seems like an ideal use for external post-tensioning. I know you said it wasn't locally available, but I wouldn't rule it out just for that reason. This is your building's critical link, and it has to work.

Is the failure mode flexure, shear, or both? If shear, perhaps you could add some steel side plates to the sides of the beam to reinforce for the load.

Adding a column in the middle of your transfer beam would work too, though that's probably not what the architect or owner wants!

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Brian Barna P.E., M.ASCE
Project Structural Engineer
Whitman, Requardt & Associates
Fairfax VA
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Box the beams in steel with flange extensions to get weld heat (use low heat skip weld pattern) away from concrete; apply a combined doweled and high-head adhesive bond at all faces.  A real time thermal measurement and dispersion protocol must be used during welding. Undertake a similar approach at the columns. As you iterate a  design, you will find the steel cladding will quickly pick up the lion's share of stresses, perhaps to the point where any allocation to the original conventional concrete beam/column is superfluous, especially if the building is in a high seismic location.
Fire rating is an issue, which, if you can not solve with cladding, and you do not already have a modifiable sprinkler system, you may have to retrofit a localized water or chemical fire suppressant system.
This type of design challenge is the rubber meeting the road of structural engineering.

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Robert Bullard P.E., M.ASCE
President
Ahimsa Technic Inc
Ponce Inlet FL
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The Suggestion offered by Robert, are seen as most appropriate, which can take care of supplementing the shortfall in either Moment or Shear Capacities.

However the option in place of welding could be use of Shear Connector Bolts Stitching to Webs and Flared additional steel Plates, with the stiffeners welded to the Web plates, which could in some way, eliminate the need for control of welding temperature at interface of Steel plates and Concrete.

Yet another option could be " Carbon Fibre Wrap " or Carbon Plates attachments, though this will need very very high care in effective bonding to concrete and Fire Protection, since any fire during lifetime of Building, can otherwise destruct this Wrapping, almost instantly, and thereby negating the very input for strengthening, which may lead to a catastrophe

Are the additional loads as envisaged, for change of " User" too significant ? If from Residential to Commercial, the reduction in Partition Wall Loads of Floors, ( designed for Residential Floor ), and NOT needed for a Commercial Offices Use, in such a Scenario, may Not be a major issue.

In my experience, these Transfer Girders' Design, would be more " Shear-Critical,  rather than Bending Moments





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Satish Dhupelia A.M.ASCE
Consulting Structural Engineer
Mumbai MH
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Original Message:
Sent: 07-20-2017 08:26
From: Robert Bullard
Subject: Strengthening of transfer girders of a 22 story structure

Box the beams in steel with flange extensions to get weld heat (use low heat skip weld pattern) away from concrete; apply a combined doweled and high-head adhesive bond at all faces.  A real time thermal measurement and dispersion protocol must be used during welding. Undertake a similar approach at the columns. As you iterate a  design, you will find the steel cladding will quickly pick up the lion's share of stresses, perhaps to the point where any allocation to the original conventional concrete beam/column is superfluous, especially if the building is in a high seismic location.
Fire rating is an issue, which, if you can not solve with cladding, and you do not already have a modifiable sprinkler system, you may have to retrofit a localized water or chemical fire suppressant system.
This type of design challenge is the rubber meeting the road of structural engineering.

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Robert Bullard P.E., M.ASCE
President
Ahimsa Technic Inc
Ponce Inlet FL
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------Original Message------

The Suggestion offered by Robert, are seen as most appropriate, which can take care of supplementing the shortfall in either Moment or Shear Capacities.

However the option in place of welding could be use of Shear Connector Bolts Stitching to Webs and Flared additional steel Plates, with the stiffeners welded to the Web plates, which could in some way, eliminate the need for control of welding temperature at interface of Steel plates and Concrete.

Yet another option could be " Carbon Fibre Wrap " or Carbon Plates attachments, though this will need very very high care in effective bonding to concrete and Fire Protection, since any fire during lifetime of Building, can otherwise destruct this Wrapping, almost instantly, and thereby negating the very input for strengthening, which may lead to a catastrophe

Are the additional loads as envisaged, for change of " User" too significant ? If from Residential to Commercial, the reduction in Partition Wall Loads of Floors, ( designed for Residential Floor ), and NOT needed for a Commercial Offices Use, in such a Scenario, may Not be a major issue.

In my experience, these Transfer Girders' Design, would be more " Shear-Critical,  rather than Bending Moments





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Satish Dhupelia A.M.ASCE
Consulting Structural Engineer
Mumbai MH
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Dear Shashank,

I am a bit intrigued, that you look forward to increasing the Depth of Existing Transfer Girder, by 30% to 40% as mentioned by you.

In that case , what is the Depth of existing RCC Transfer Girder ?

I think that achieving the required performance by mere Chemical bonding of New Reinforcement, sounds a bit dicy. The Best you can do, in my opinion, is  welding of New Stirrups, of additional depth being created by you,which could ensure positive connectivity, for composite behaviour.

You have mentioned about Autoclaved Cellular Concrete Blocks, like " Siporex" being to costly, there.

One option could be to try Gypsum Board Partitions, with sandwitched internal Al. Framiong stiffeners.


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Satish Dhupelia A.M.ASCE
Consulting Structural Engineer
Mumbai MH
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Original Message:
Sent: 07-22-2017 02:11
From: Shashank Pendharkar
Subject: Strengthening of transfer girders of a 22 story structure

Thanks Satish.

The use is changed from Commercial to Residential and therefore additional loads are mainly due to walls, part of wall load is offset by reduction in live load. We have adopted light weight walling to further reduce the load however, minimum wall weight we have achieved is 10kN/cu.m. Soporex imports from India were evaluated to be prohibitively expensive.

Structural steel also is prohibitively expensive as it is not manufactured locally, welding expertise is not available in this part of the world and bolting to concrete has been time consuming and difficult due to presence of large number of bars in tension and compression zones and links. 

We adopted additional concrete at top and have attempted to achieve composite action with existing concrete by removing cover concrete and anchoring links to existing top bars with chemicals. Same is done to the bars which are anchored to existing columns and floating column. Since depth of girders will be increased by approximately 30% to 40%, anchorage requirements are minimal, drilling and chemical grouting of anchor bars is expected to be adequate. Shear stress is also expected to be within limits. 

All above of course, depends on achieving 100% composite action! Look forward to suggestions to ensure composite action.

------Original Message------

The Suggestion offered by Robert, are seen as most appropriate, which can take care of supplementing the shortfall in either Moment or Shear Capacities.

However the option in place of welding could be use of Shear Connector Bolts Stitching to Webs and Flared additional steel Plates, with the stiffeners welded to the Web plates, which could in some way, eliminate the need for control of welding temperature at interface of Steel plates and Concrete.

Yet another option could be " Carbon Fibre Wrap " or Carbon Plates attachments, though this will need very very high care in effective bonding to concrete and Fire Protection, since any fire during lifetime of Building, can otherwise destruct this Wrapping, almost instantly, and thereby negating the very input for strengthening, which may lead to a catastrophe

Are the additional loads as envisaged, for change of " User" too significant ? If from Residential to Commercial, the reduction in Partition Wall Loads of Floors, ( designed for Residential Floor ), and NOT needed for a Commercial Offices Use, in such a Scenario, may Not be a major issue.

In my experience, these Transfer Girders' Design, would be more " Shear-Critical,  rather than Bending Moments





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Satish Dhupelia A.M.ASCE
Consulting Structural Engineer
Mumbai MH
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Shashank:

The answers to your questions are Yes.
Since you must be in a large city, we can communicate directly rather than this route.
Please let me know and we will work it out.

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Gajanan Sabnis P.E., Dist.M.ASCE
Powai-Mumbai MH
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Thank you all for identifying various options. I liked Bruce's recommendations the best and intend to take them forward.


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Shashank Pendharkar Aff.M.ASCE
Pendharkar & Associates Ltd
Dar Es Salaam
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Hi. I think is required more geometric or system details in order to understand more deeply your situation. But in a more general basis sometimes use of carbon fiber or glass fiber can help you increase strength locally on girders. Also this solution can be used in conjunction with other strenghtening strategies.

Also helps in this situations run some staged construction analysis. This offer the chance to find out a more realistic moment diagram of this elements. At least it increases your judgement about what is happening in the element. 

Best regards

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Gustavo Porras Murillo Aff.M.ASCE
Structural Engineer
INGP
San Jose
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