the$simplified$method$of$shoring/reshoring$ · pdf...
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The Simplified Method of Shoring/Reshoring
• Some field measurements of loads suggest that the simplified method is accurate enough for prac9cal use. Other theore9cal studies consider variable s9ffness of the shores, or aspects of the slab-‐shore interac9on. Some recommend a correc9on factor of 5-‐15 percent to be used when using compressible shores – CommiFee 347 is preparing a report.
• Assump9on when using the Simplified Method 1. All Slabs are iden9cal – and shores/reshores are aligned one-‐on-‐one from floor to floor 2. Ground level is rigid, and shores are spaced closely enough to treat the shore reac9ons as
a distributed load. 3. Shores and reshores are infinitely s9ff rela9ve to the slab. 4. Slabs interconnected by shores all deflect equally when a new load is added, and carry a
share of the load in propor9on to their rela9ve s9ffness
SLAB 1 SLAB 1 SLAB 1
0 0
Step 1: Place level 1 concrete
0 1D
0 1D
0 2D
1D 0
1D 0
1D 0
1D 0
1D 0
1D 0
0 1D
1D 1D
1D 1D
.5D
.5D
1.5D 0
1D 0
Step 2: Place level 2 concrete Step 3: Remove shoring 1
Step 4: Re-‐shoring 1
Step 5: Place level 3 concrete Step 6: Remove shoring 2
SLAB 2
SLAB 1 SLAB 1 SLAB 1
SLAB 2 SLAB 2
SLAB 2 SLAB 2
SLAB 3 SLAB 3
Shoring/Reshoring: Simplified Analysis of Loads: Two levels of shoring, one level of re-‐shoring
½ load
½ load
full load
full load
OG load -‐1/2 transferred
References: Formwork for Concrete – Special Publica9on #4 Seventh Ed As per OSHA standards: Removal of the forms and shores should be specified by the engineer-‐architect for most major structures during construc9on.
Notes: once slab one is placed all load is transferred to the shoring
Notes: Slab 2 is placed, all load is transferred to the shoring 2, then load is transferred to shoring 1 because slab 1 can’t take load because the shoring doesn’t allow.
Notes: When shoring is removed both slab 1 and slab 2 deflect together allowing both to absorb there own weight
Notes: No change when reshoring is placed Notes: New slab is placed all the weight is transferred down through the shoring and reshoring
Notes: When you take away shoring 2 a major shia happens, half of the load that was carried by shoring 2 is shiaed to slab 3 and the other half is shiaed to slab 2. Shoring 3 is now carrying less of the load.
SLAB 1 SLAB 1 SLAB 1
SLAB 1
SLAB 2
.5D
.5D
1.5D 0
1D 0
0 1D
.83 1.17D
1.83D .34
1.34D 0
.59D
.41D
1.41D 0
1D 0
1D 0
0 1D
.92D 1.08D
1.74D .34D
1.34D 0
1D 0
Step 7: Place level 4 concrete, Reshore 2 with level 1 Step 8: Remove shoring 3
Step 10: Remove shoring 4
Step11: Place level 6 concrete, Reshore 4 with level 3
SLAB 2
SLAB 3
SLAB 4
SLAB 3
SLAB 2
SLAB 4 SLAB 4
SLAB 3
SLAB 2
Step 9: Place level 5 concrete, Reshore 3 with level 2
0 1D
.92D 1.08D
1.74D .34D
1.34D 0
1D 0
.54D
.46D
1.46D 0
1D 0
1D 0
1D 0
0 1D
.87D 1.13D
1.79D .34
1.34D 0
1D 0
1D 0
SLAB 1
SLAB 3 SLAB 3
SLAB 2
SLAB 4
SLAB 5
SLAB 4
SLAB 5
SLAB 6
SLAB 5
1/3 load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
½ load
½ load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
1/3 load ½ load
½ load
OG load -‐1/2 transferred
OG load -‐1/2 transferred
Notes: Now when a new slab is placed the load is shared among the other three slabs. This is high load impact on. Look at how much weight slab 2 has to carry.
Notes: Same method as step 6 Notes: Same method as step 7
Notes: Same method as step 7 Notes: Same method as step 6
Legend
Newly placed concrete slab
Fully cured concrete slab
Deflec9on of concrete is occurring
Transfer of load is occuring
SLAB 1 SLAB 1 SLAB 1
0 0
Step 1: Place level 1 concrete
0 1.6D
0 1.6D
0 2.7D
1.05D 0.05D
1.05D 0
1D 0.05D
1D 0
1D 0.05D
1D 0
0 1.6D
1.05D 1.6D
1.05D 1.6D
.52D
.58D
1.58D 0
1D 0
Step 2: Place level 2 concrete Step 3: Remove shoring 1
Step 4: Re-‐shoring 1
Step 5: Place level 3 concrete Step 6: Remove shoring 2
SLAB 2
SLAB 1 SLAB 1 SLAB 1
SLAB 2 SLAB 2
SLAB 2 SLAB 2
SLAB 3 SLAB 3
Shoring/Reshoring: Simplified Analysis of Loads: One levels of shoring, two level of re-‐shoring, assuming Construc9on Live loads(.5D) and shores and forms weigh(.1D)
½ load
½ load(1.05D)
full load
full load
OG load -‐1/2 transferred
References: Formwork for Concrete – Special Publica9on #4 Seventh Ed As per OSHA standards: Removal of the forms and shores should be specified by the engineer-‐architect for most major structures during construc9on.
Notes: once slab one is placed all load is transferred to the shoring
Notes: Slab 2 is placed, all load is transferred to the shoring 2, then load is transferred to shoring 1 because slab 1 can’t take load because the shoring doesn’t allow. Slab two has construc9on live load(CLL) and shores and forms weigh(SFW), slab just has SFW
Notes: When shoring is removed both slab 1 and slab 2 deflect together allowing both to absorb equally the remaining weight, which is just the self weight plus SFW of slab 2
Notes: No change when reshoring is placed Notes: New slab is placed all the weight is transferred down through the shoring and reshoring
Notes: When you take away shoring 2 a major shia happens, half of the load that was carried by shoring 2 is shiaed to slab 3 and the other half is shiaed to slab 2. Shoring 3 is now carrying less of the load. Also assume no CLL and only formwork on slab 3.
SLAB 1 SLAB 1 SLAB 1
SLAB 1
SLAB 2
.52D
.58D
1.58D 0
1D 0
0 1.6D
1.05 1.65D
2.11D .54D
1.54D 0
.6D
.50D
1.5D 0
1D 0
1D 0
0 1.6D
1.13D 1.57D
2.03D .54D
1.54D 0
1D 0
Step 7: Place level 4 concrete, Reshore 2 with level 1 Step 8: Remove shoring 3
Step 10: Remove shoring 4
Step11: Place level 6 concrete, Reshore 4 with level 3
SLAB 2
SLAB 3
SLAB 4
SLAB 3
SLAB 2
SLAB 4 SLAB 4
SLAB 3
SLAB 2
Step 9: Place level 5 concrete, Reshore 3 with level 2
0 1.6D
1.13D 1.57D
2.03D .54D
1.54D 0
1D 0
.56D
.54D
1.54D 0
1D 0
1D 0
1D 0
0 1.6D
1.09D 1.61D
2.07D .54
1.54D 0
1D 0
1D 0
SLAB 1
SLAB 3 SLAB 3
SLAB 2
SLAB 4
SLAB 5
SLAB 4
SLAB 5
SLAB 6
SLAB 5
1/3 load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
½ load
½ load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
1/3 load
1/3 load
Load -‐1
/3 load
2/3 Load -‐1
/3 load
1/3 load ½ load
½ load
OG load -‐1/2 transferred
OG load -‐1/2 transferred
Notes: Now when a new slab is placed the load is shared among the other three slabs. This is high load impact on. Look at how much weight slab 2 has to carry.
Notes: Same method as step 6. No CLL Notes: Same method as step 7
Notes: Same method as step 7 Notes: Same method as step 6, CLL is assumed removed
Legend
Newly placed concrete slab
Fully cured concrete slab
Deflec9on of concrete is occurring
Transfer of load is occuring