Crack in Concrete Bearing Wall at Opening
Crack in Concrete Bearing Wall at Opening
(OP)
Wondering if some one could point me in the right direction as in determining when the cracking as seen in the attached photo will occur. I am not sure on this, but can one use the standard shear stength equation (ACI 11-1) for this type of shearing failure. The bearing area seen in the picture supports a precast floor system and the specified bearing length of 4" was a judgement call for the size of the load. The resulting crack was a 3.5" horizontal by 15" vertical bearing failure at the concrete wall end. Any assistance would be greatly appreciated.






RE: Crack in Concrete Bearing Wall at Opening
The other scenarion is that the support area is too little for the load seen. You would have to run the numbers.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Crack in Concrete Bearing Wall at Opening
It appears there is a steel HSS column adjacent to the wall. Is it capable of carrying all of the load by itself?
Is it possible to determine how much load goes to the HSS and how much to the concrete wall? Any sudden change in temperature will affect the amount of load carried by the steel because steel will respond to temperature change faster than concrete.
Also, there may be horizontal forces present due to temperature and shrinkage of the floor structure.
If the wall is needed to carry gravity load, it will be necessary to tie the bearing plate and the triangular chunk of concrete back to the wall to engage more wall reinforcement.
BA
RE: Crack in Concrete Bearing Wall at Opening
The crack initiated under shear force as you surmise, with or without restraint of the embed by structure above. The crack stopped moving once the reinforcement was mobilized. If the reinforcement/DBAs were stressed significantly, but within yield, the crack would widen under load and then squeeze back together when unloaded.
I agree that the design of the support, and the size and placement of the embed may have been inadequate for the forces involved. But, if the reinforcement is adequate and there is sufficient shear friction developed by aggregate interlock, this member may still be serviceable. Is there any vertical displacement? And do you have shops for the embed?
RE: Crack in Concrete Bearing Wall at Opening
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Crack in Concrete Bearing Wall at Opening
If one assumes that no strength is provided by reinforcement in design (plain concrete shear strength), is it correct to assume that the shear failure plane will propogate from the center of the bearing plate to the outside of the wall at a 45 degree angle during design? When looking at the crack in the picture, the shear plane goes from the back side of the bearing plate at a approx. 60 degree angle to the outside of the wall.
RE: Crack in Concrete Bearing Wall at Opening
The angle would vary depending on the magnitude of horizontal tension in the floor system.
BA
RE: Crack in Concrete Bearing Wall at Opening
If the beam and connection seat were not designed to take drag forces, the beam should have had horizontally eleongated holes for the bolts provided for longitudinal movement/slippage. If they were not, therein lies the problem.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Crack in Concrete Bearing Wall at Opening
John Southard, M.S., P.E.
http://www.pdhlibrary.com/