Cracks in ramped parking

[sag04]

Hi
In a high rise 25 storey residential building with 2 level parking, cracks have developed at every ramp beam column joints and at one place across the ramp slab within one weeks of construction. Why it is developed? is it design mistakes..
Ramp Width - 6m
Ramp slope 13%
Ground floor to first parking height is 4.85m
1 st park to 2 park height is 3.35m
Ramp support on side beams and columns,Parking slab - flat slab
Regards

 

[VoyageofDiscovery]

Hi sag04,

Could be shrinkage. The ramp slope is also high for maintaining sloped concrete during the pour.

Regards

VOD

 

[jike]

Much more info. is required to suggest some possible causes.

Was there a full time inspector or on-site structural engineer?
Was there photos taken of these areas with all rebar in place before the pour?
Was shoring removed?
Was it reshored?
Was the SEOR consulted on the cause?
How wide are the cracks?
Is there rebar running thru the cracks?
Was some rebar left out?
Who inspected the rebar before the pour?
How long (in feet) was the pour?
What is the distance between exp. joints?
What was the temperature variation during that period?
How was the slab cured and protected?
What part of the country is this in?

 

[Ron]

Very likely shrinkage at restraint points considering the timing of appearance. Good idea to go through jike's checklist though.

 

[sag04]

Hi jike
Was there a full time inspector or on-site structural engineer? - yes
Was there photos taken of these areas with all rebar in place before the pour? NO
Was shoring removed? YES
Was it reshored? NO
Was the SEOR consulted on the cause? NO
How wide are the cracks? HAIR LINE CRACKS
Is there rebar running thru the cracks? YES
Was some rebar left out? NO
Who inspected the rebar before the pour? SITE INSPECTOR
How long (in feet) was the pour? FIRST RAMP LENGTH IS 37.45M AND SECOND ONE 22.45M
What is the distance between exp. joints? THE BUILDING EXPANSION JOINT IS RUNNING ACROSS THE FIRST RAMP AT 17 M FROM THE STARTING POINT. SECOND RAMP STARTING EXACTLY FROM EXPANSION JOINT SO NO EAXPANSION JOINT. MOST SERIOUS CONCERN IS CONTRACTOR AND SITE INSPECTOR FORGOT TO MAKE THE EXPANSION JOINT IN FIRST RAMP. THEY POURED THE CONCRETE CONTINOUSLY WITH CONTINOUS REBAR THRU THE EXP JOINT.What was the temperature variation during that period? DAY TIME 48C AND NIGHT 32 C
How was the slab cured and protected? NORMAL - WATER spray CURING
What part of the country is this in? DUBAI

column spacing is 6m slab thickness 22 cm.
The site inspector is my friend and so please help me to give him some insight.
thank you all
Sag04

 

[Ron]

From additional info, still sounds like shrinkage cracking. Put some crack monitoring devices (Avongard or similar) and monitor for a while. You'll likely see little movement.

 

[jike]

It sounds like the cause might be shrinkage if it cracked within one week of construction. If it cracked before the shoring was removed then it is most likely shrinkage. If it cracked after the shoring was removed, then it could be either shrinkage or perhaps flexural in nature. Was the shoring removed too early?

It makes me a little suspicious that it cracked at every beam column joint although there must be some flexural cracking before the rebar takes over. What is the unreinforced concrete cracking moment at the beam column intersection? Does the dead load moment exceed this cracking moment?

The crack in the middle of the slab definitely sounds like shrinkage.

I highly recommend that you involve the SEOR. He is intimately familiar with the design of the structure and we can only guess (sometimes right and sometimes wrong) at a few of the possibilitites.