Expansion Joint in Slab-on-Grade 1

[FiniteElemet]

Hi,

Can a key and groove joint in a slab be treated as expansion joint such that the bars (both top and bottom) extending into second pour are terminated in second pour and greased viz. they can slide during expansion and contraction.

Do we have a code recommendation for such a system.


Thanks

 

[fcu45]

Floor slab or raft foundation?

Why don't you actually place the expansion joint? then to cover it with the special expansion joints capping?

In general, as I know, building may extend up to 60 meters without an expansion joint.

 

[dik]

I don't often use keyways for slabs; I usually transfer the load via smooth dowels secured on one side and lubricated on the other. Reinforcing is terminated at each side of the joint. The dowels are secured in place using dowel 'baskets' that provide proper support, spacing and location. Care has to be taken so that the dowels are all parallel and a dowel basket helps with this. Some of the problems with this are alleviated by using 'diamond' plate dowels.

For dowels to work, they must be smooth, I'm not sure if you were planning on using non-deformed bars.

Dik

 

[FiniteElemet]

This will be an external slab approximately 280 Ft x 180 ft. Is it right to say that groove and key joint with terminating greased bar as described by Dik will account for expansion joint?

 

[fcu45]

I have seen what dik mentioned in base slab of underpass "highway tunnel"
informative link

http://www.everything-about-concrete.com/concrete-construction-joints.html

 

[dik]

How thick is the slab?

Dik

 

[hokie66]

Dik's recommendation is the usual solution for control joints in slabs on grade. Slabs on grade do not need expansion joints. Keyed joints fail due to the outer parts of the key breaking. Avoid them if there are any significant wheel loads on the slab.

 

[dik]

Can you make the pour as a continuous pour and just use sawcuts? or are you planning on two 140'x180' panels?

Dik

 

[asixth]

I use smooth dowels and not a key as mentioned above. For a slab on grade internal to a building such as the basement of an enclosed building I don't used expansion joints because the temperature variation will be minimal and the ground will help control the expansion and contraction. General working hours will only allow 10,000 sq.ft to be placed per day so this sequencing helps early age shrinkage to be mitigated.

For an external slab which can really feel the temperature I would recommend expansion joints but not by having deformed bar crossing the joint. I would use a smooth dowel and a sleeve.

 

[hokie66]

If control joints (contraction joints) work as intended, I contend that expansion joints are not required and cause problems of their own, due to differential vertical movement of the joints. For the control joints to work, they have to be well maintained so that debris does not enter the joints. That may be an unrealistic expectation, but debris in the joints is the only reason that thermal change causes the slabs to move horizontally.

 

[Ron]

Agree with hokie66...expansion joints are not necessary. Control joints and construction joints are necessary. If slab is to receive traffic, such as forklift or other industrial traffic, then treat as dik noted.

More important to control slab thickness and make sawcuts at proper time than to provide for "expansion".

 

[dik]

My slab on grade general notes... modify as needed... I have other SOG notes elsewhere in my general notes, sawcutting, joint filler, etc. Conc strength, slump and time of cutting are critical... can cut earlier with specialised saw.

Dik



SLAB ON GRADE

THE MODULUS OF SUB-GRADE REACTION IS ASSUMED TO BE 200 PCI. THE CONTRACTOR, THROUGH THE CLIENT IS RESPONSIBLE FOR OBTAINING A GEOTECHNICAL REPORT TO CONFIRM THIS DESIGN ASSUMPTIONS. THE [CONSULTANT | ENGINEER] ASSUMES NO LIABILITY FOR THESE DESIGN ASSUMPTIONS OR FOR ANY FOUNDATION REDESIGN NECESSITATED BY DIFFERING SOIL CONDITIONS

TEMPERATURE DIFFERENTIAL BETWEEN THE GRANULAR BASE AND THE TOP OF THE CONCRETE SLAB SHALL BE MINIMISED

SLAB FINISHING SHALL BE DELAYED AS LONG AS POSSIBLE

THE IS DESIGNED FOR [LIGHT | MEDIUM | HEAVY] DUTY USE ONLY

THE EXPOSED SUB-GRADE FOR SLAB ON GRADE SHALL BE PROOF ROLLED. SOFT SPOTS SHALL BE EXCAVATED, BACK-FILLED WITH GRANULAR FILL AND COMPACTED TO 95% [SPDD | MPDD]. GRANULAR FILL AND COMPACTION METHODS TO BE APPROVED BY THE [CONSULTANT | ENGINEER]

PROVIDE MIN [6 IN | 150 MM] CMPT GRAN 'A' BASE COURSE BENEATH SLAB-ON-GRADE U/N. CMPT TO 95% [SPDD | MPDD] U/N

PROVIDE MIN [6 IN | 150 NN] CMPT GRAN 'B' SUB-BASE COURSE BENEATH BASE COURSE U/N. CMPT TO 100% [SPDD | MPDD] U/N

THE COMPACTED GRANULAR FILL SHALL PROVIDE A UNIFORM SURFACE WITH NO ABRUPT CHANGES IN LEVEL. MAX DEVIATION IN LEVEL SHALL NOT EXCEED [0.5 IN | 12 MM]

INSTALL [6 MIL | 0.15 MM] PEVB MEMBRANE CONFORMING TO CAN3-51.33-M80 BTN SLAB AND FILL WITHIN THE AREA OF THE BUILDING

LAP PEVB JOINTS [12 IN | 300 MM] MIN AND SEAL WITH MASTIC CEMENT

U/N REINF FOR SLAB-ON-GRADE SHALL BE (0.2%):
DEPTH REINF
5 10M@16 TEW
6 10M@13 TEW
6 15M@24 TEW
7 15M@22 TEW
8 15M@19 TEW
8 10M@20 T&BEW

U/N REINF FOR SLAB-ON-GRADE SHALL BE (0.25%):
DEPTH REINF
5 10M@12 TEW
6 15M@20 TEW
7 15M@17 TEW
8 15M@15 TEW
8 10M@16 T&BEW


U/N REINF FOR SLAB-ON-GRADE SHALL BE (0.3%):
DEPTH REINF
5 15M@20 TEW
6 15M@16 TEW
7 15M@14 TEW
8 15M@12 TEW
8 15M@24 T&BEW

U/N REINF FOR SLAB-ON-GRADE SHALL BE:
DEPTH REINF
125 10M@400 TEW
150 10M@330 TEW
175 15M@550 TEW
200 15M@510 TEW
200 10M@510 T&BEW

LAP WELDED WIRE FABRIC, ONE FULL MESH AT SPLICES

REINF STEEL TO BE LOCATED [2 IN | 50 MM] BELOW TOP OF FINISHED FLR SLAB U/N

SUPPORT SLAB TOP REINF ON HIGH CHAIRS AND/OR 15M SUPPORT BARS WHERE REQUIRED. ALL BARS AND CHAIRS MUST BE SECURELY TIED TOGETHER

PROVIDE SUFFICIENT CHAIRS AND SUPPORT BARS TO MAINTAIN CONC PROTECTION AS SPECIFIED

CUTTING OF CONTROL JOINTS SHALL BEGIN AS SOON AS THE CONC SURFACE HAS HARDENED SUFFICIENTLY TO RESIST RAVELLING AS THE CUT IS MADE. SAWCUTTING SHOULD COMMENCE APPROX 6 TO 8 HOURS AFTER FINISHING SLAB

SAWCUT SLABS INTO PANELS NOT EXCEEDING 20' IN ANY DIRECTION. MAX CONTROL JOINT SPACING SHALL PREFERABLY NOT EXCEED 30 TIMES THE SLAB THICKNESS AND SHALL NOT EXCEED 36 TIMES THE SLAB THICKNESS. THE LENGTH TO WIDTH RATIO OF THE CONTROL JOINT PANELS SHALL NOT EXCEED 1.5. IF A SAWCUT INTERSECTS ANOTHER SAWCUT, THE SMALLER ANGLE OF INTERSECTION SHALL NOT BE LESS THAN 50 DEGREES

CONTRACTOR SHALL PROVIDE SHOPDRAWING SHOWING THE PROPOSED CUTTING PATTERN AND THE PROPOSED SAWCUTTING PROCEDURE WELL IN ADVANCE OF PLACING THE CONCRTE FOR THE SLAB ON GRADE

CONC SLAB-ON-GRADE HAS BEEN DESIGNED FOR THE FOLLOWING:
WHEEL LOAD XXXX POUNDS
INFLATION PRESSURE XXX PSI

DIM A XXX
DIM B XXX
DIM C XXX

LOAD REPETITIONS XXXXX THOUSAND
SAFETY FACTOR XXX

IF DIM A=0 THEN VEHICLE AXLE HAS SINGLE WHEELS
IF DIM B=0 THEN VEHICLE HAS SINGLE AXLE ONLY


SLAB FLATNESS

SLAB FLATNESS SHALL BE [ 20/15 | 25/20 | 35/25 | 45/35 | 65/40 | 100/50 | FM1 | FM2 | FM3 ]

U/N FLOORS SHALL HAVE A DEGREE OF FLATNESS DEFINED BY THE FACE FF/FL NUMBER THAT SHALL NOT BE LESS THAN:
20/15 MECHANICAL ROOMS, PARKING STRUCTURES, ETC.
25/20 CARPETED AREAS OF COMMERCIAL OFFICE BUILDINGS
35/25 TYPICAL WAREHOUSE FOR MODERATE/HEAVY RANDOM TRAFFIC, FACTORY, ETC.
45/35 CONSIDERED 'FLAT' TYPICAL WAREHOUSE WITH AIR PALLET USE, ICE RINKS, ETC.
65/40 CONSIDERED 'VERY FLAT'
100/50 CONSIDERED 'SUPER FLAT'

ALTERNATIVELY,

THE MAX VERTICAL DEVIATION OVER A [24 | 600] WIDTH SHALL NOT EXCEED
2.5mm (quality FM1)
3.5mm (quality FM2)
5.0mm (quality FM3)

THE MAXIMUM VERTICAL DEVIATION OVER A [10FT | 3.0M] WIDTH SHALL NOT EXCEED
3.0mm (quality FM1)
6.0mm (quality FM2)
8.0mm (quality FM3)

FLATNESS TESTING MAY COMMENCE 16 HOURS AFTER SLAB FINISHING. FLATNESS TESTING SHALL BE COMPLETED WITHIN 72 HOURS OF SLAB FINISHING

 

[FiniteElemet]

Thanks for the response.
So my exterior slab is 34" thick. It s 300 ft x 180 ft approx. I have divided the slab into sections seperated by tongue and groove contraction joints. To allow for the potential expansion, I have greased the bars protuding from first into second pour at construction joints typically 70 ft - 115 ft O.C.
ACI 224 recommends that shrinkage / contraction is more of an issue than expansion. ACI does not refer to any sort of calulation for expansion within slab on grade. So to account for the worst of both worlds, In the absence of much guidance from ACI on the matter, I am leaned towards recommending a joint such as described above. I am concerned that if I provide expansion joint with filler, there may be a vertical movement between the slab....Opinion about the solution much appreicated.

Thanks

 

[BAretired]

Wow! That is one hefty slab on grade. Because it is outside, I would have concerns about heaving due to expansion, particularly if the outside edges are not free to expand.

BA

 

[spats]

What kind of loading would require a slab that thick? I designed a slab for a rocket assembly building at the Cape some years back, and it wasn't half that thickness. Must be some serious sh**.

 

[cvg]

spats, agreed, we design slabs for airport aprons for 747's (and larger) and the entire structural section including agg base is usually less than 30 inches. usually about 12-14 inch thick concrete. no keyways or expansion joints needed. all joints doweled and edges fully reinforced.