moment connecting old beams to new columns
moment connecting old beams to new columns
(OP)
Hi, the office has received this retrofit project study where an old house with wooden joists and floors but concrete columns and beams and the neighbor has proven that there is a trespassing into his property line that is about 2 feet. This would put the perimeter columns directly at the neighbor property.
Has anyone actually tried replacing columns with new ones that are adjusted 2 feet shorter (instead of 18 feet beam span.. it becomes 16 feet)? This is a general question so even without knowing the layout you can imagine it
Some team members suggested putting new steel columns and putting the steel I-beams underneath the original concrete beam edge and welding the rebars of the original concrete beam to the steel i-beam then removing the original concrete columns that got trespassed. Would this work? But we are worried about lateral movement that can affect the interface. How would you design the interface (is there a industry standard for this).
Or has anyone tried putting a new concrete column by chipping away the old column-beam joint.. but a cold joint could form right at the face of the new joint.. would this be recommended?
If these are all not recommended or done anywhere. We'd jus advise client to demolish the entire house and build a new one (but he won't agree so we may just back out from the project). The neighbor won't accept any payments over the trespassed area because he need the critical space too. Thank you!
Has anyone actually tried replacing columns with new ones that are adjusted 2 feet shorter (instead of 18 feet beam span.. it becomes 16 feet)? This is a general question so even without knowing the layout you can imagine it
Some team members suggested putting new steel columns and putting the steel I-beams underneath the original concrete beam edge and welding the rebars of the original concrete beam to the steel i-beam then removing the original concrete columns that got trespassed. Would this work? But we are worried about lateral movement that can affect the interface. How would you design the interface (is there a industry standard for this).
Or has anyone tried putting a new concrete column by chipping away the old column-beam joint.. but a cold joint could form right at the face of the new joint.. would this be recommended?
If these are all not recommended or done anywhere. We'd jus advise client to demolish the entire house and build a new one (but he won't agree so we may just back out from the project). The neighbor won't accept any payments over the trespassed area because he need the critical space too. Thank you!






RE: moment connecting old beams to new columns
1) Install a steel or concrete column in the new location.
2) Assume a pinned beam connection at the new column.
3) Run some numbers to see if the beam can work without a fixed connection to the column.
As long as it's not a moment frame, I'd think that your odds are pretty good. Reconstituting a fixed connection between the beam and a new column would be pretty tough.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: moment connecting old beams to new columns
Moment resisting system would be mainly the columns & beams. The old house has no shear wall due to open spaces in the ground floor for parking space. Some practical tips how to moment connect the end of the beam and the new steel column or even steel beam?
Or perhaps just pinned beam connection at the new steel column fixed strongly at its foundation?
RE: moment connecting old beams to new columns
Reread your OP, and consider the fact that we can’t see it from here, we’re not looking at what you are. Then imagine that you get 10 responses, and I’ll wager you’ll get at least 10 guesses at what you are talking about and the arrangement and conditions you’re talking about; each requiring a different solution, layout and details. We know you are “replacing columns with new ones that are adjusted 2 feet shorter,” and ‘the beam span becomes 16', instead of 18'.’ And, we know “ This is a general question so even without knowing the layout you can imagine it.” Well... KootK gave you your general answer, since we can’t imagine what you are talking about. Get on the stick, if you want meaningful answers; some sketches, plans, details, dimensions, sizes, loads, etc. some info. for us to start to really understand your problem. Then, you might start getting some meaningful help. There are plenty of smart people here on E-Tips willing to help, but they don’t like wasting their time guessing at the unknown.
RE: moment connecting old beams to new columns
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: moment connecting old beams to new columns
Above shows the layout. 5 horizontal beams with span about 18 feet with columns at each end (no middle columns). The blue line indicates the actual property lines. So 6 columns will be removed all the way to second floor roof. All special moment frame seismic R=8. See actual picture of property.
Would like some tips for the following.
Rebars can be exposed after columns are demolished.. but there is a cold joint where new column would be moment connected to old beam (as can be seen above). What's the chipping pattern to recreate aggregate interlock? Would it be 100% aggregate interlock?
In the event of shoring failure or slip for instance in the 1/6 inch, would the right joint suffer crushing failure at bottom part of the joint or yielding failure at rebars above the joint? Or bending and failure of the column? Any video of actual tests?
How would you do the retrofit?
RE: moment connecting old beams to new columns
RE: moment connecting old beams to new columns
RE: moment connecting old beams to new columns
Canwesteng. The rule says splices can only be put at top of midspan due to the large amount of shear at support and if the mechanical splices were put at top of support.. there is a pulling action that could jeopardize the splice connection. Could mechanical splices be exempted from placement locations?
Have you guys seen any details of connecting old concrete beams to wide flange steel beam perpendicular to it below (this would be another idea where steel column and steel beam would be made first close to existing columns where they can carry the old beams prior to old columns removal. Think beam to beam connection)). How do you detail the moment connection between concrete beam and steel beam (below it carrying the concrete beam)? Someone suggested in cases like this. They put dowel to the old beams and weld this to the new steel beam (perpendicular... emphasis) below . But big question, has this been done anywhere before? How would it perform under seismic cyclic loading. Im afraid the bars connected to steel beam and old beam would break the old beam apart.
RE: moment connecting old beams to new columns
"Unable to establish robust special moment reconnection in multiple columns.
Initiate destruct (demolition) protocol"
Thanks a whole lot to Kootk for the very useful tips mentioned earlier.
For knowledge in case similar situation is encountered in the future. Do ACI, Eurocodes or any codes have guidelines for repair of special moment frame (such as replacing entire columns, beams and joints ) in situations such as this where the neighbor has encrouched on the property lines?
Has any of your actually done any such replacement? Please share how you do it. Thank you!
RE: moment connecting old beams to new columns
RE: moment connecting old beams to new columns
See page 14 of http://nehrp.gov/pdf/nistgcr8-917-1.pdf
"If beam longitudinal bars are lap-spliced, hoops are required
along the length of the lap, and longitudinal bars around the
perimeter of the cross section are required to have lateral support
conforming to ACI 318 - 7.10.5.3. Beam longitudinal bar lap
splices shall not be used (a) within the joints; (b) within a
distance of twice the member depth from the face of the joint;
and (c) where analysis indicates flexural yielding is likely due to
inelastic lateral displacements of the frame. Generally, if lap
splices are used, they are placed near the mid-span of the beam.
See Figure 5-11 for hoop spacing requirements."
Remember the beam-joint can have plastic rotations as it uses seismic reduction factor R=8 and the concrete can break apart with only the longitudinal bars and stirrups remaining. If they are spliced (even mechanical), they can be pulled apart. Also when you use sledge hammer or jackhammer on the concrete.. won't the bars suffer any micro brittle failure (supposed you would retain the original bars).
But the main problem is we cant put any shoring inside because of the 50 employees using the building. We need to do it with them inside so we backed out.
RE: moment connecting old beams to new columns
BA
RE: moment connecting old beams to new columns