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 slabshore interac9on. Some recommend a correc9on factor of 515 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 oneonone 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
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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
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
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