Block Shear : A Review

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Block Shear A Review

• Review of LRFD Rules
• Test Results
• LRFD rules v. test results
• Suggestions for improvement

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Block Shear Issues

• Gusset plates
• Coped beams
• Angles, tees

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An aside this is what were used to seeing
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But this is what actually happens (in gusset
plates)
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Failure mode in gusset plates
Failure is always by tensile fracture, regardless
of geometric proportions Shear yield along
vertical planes (through gross area, not
net) Failure is controlled by ductility not
strength.
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Another example of a gusset type test
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So, for gusset plates

• Use a model that combines
• tension fracture (on net tension area)
• shear yield (on gross shear area)

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G. Y. Grondin I did add the hole on the tension
face. If you dont want it, click on it and
delete. Your original line is behind.
Failure mode in coped beams
?y
?ult
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Coped Beam(holes in two lines)
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Coped Beam(single bolt line, slotted
holes)
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Some observations

• Mode of failure different for gusset plates v.
  coped beams (as would be expected)
• Does amount of rotation permitted in beam tests
  affect results?

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AISC LRFD Predictions

• Shear yield (Ag) tensile fracture (An) or
• Tensile yield (Ag) shear fracture (An)

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AISC rules contd
with an upper limit, which is tension rupture
(on net tension area) shear rupture (on net
shear area)
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Difficulties.

• The when statements are illogical
• The Commentary is in conflict with the equations
  (...use the larger)
• The equations predict a failure mode that does
  not exist in the tests
• The predictions are not in good agreement with
  the tests

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Gusset plate tests

• 117 tests from 6 different sources
• Good range of geometries represented
• Steel grades from 36 ksi to 100 ksi yield

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Gusset plate results
Source No. Tests Test / LRFD(1999) Comments
1 28 1.22 (0.08) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
2 1 1.18 (0.00) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
3 4 1.22 (0.07) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
4 3 1.35 (0.02) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
5 8 1.21 (0.04) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
6 73 1.18 (0.05) Std. dev. thus (0.07) Results always conservative Predicted failure mode usually wrong
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Coped beam tests

• 38 tests from 5 different sources
• Limited range of geometries represented (but,
  improving)
• Steel grades from 36 ksi to 115 ksi yield
• Amount of rotation a non-controlled variable
  (except in one test series)

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Coped beam results
Source No. Tests Test / LRFD(1999) Comments
1 7 0.70 (0.09) Std.dev. thus (0.19) Results often non-conservative
2 5 0.99 (0.19) Std.dev. thus (0.19) Results often non-conservative
3 1 0.95 (0.00) Std.dev. thus (0.19) Results often non-conservative
4 8 1.13 (0.08) Std.dev. thus (0.19) Results often non-conservative
5 17 1.06 (0.12) Std.dev. thus (0.19) Results often non-conservative
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What about angles and tees?

• Angles, tees
• 41 tests, 4 different sources
• The parameters involved now include shear lag
• Behave more like gussets than coped beams

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Angles and tees

• Researchers include Epstein, Gross, Orbison,
  Barthels (and their colleagues)
• Many more variables than for gusset plates and
  coped beams
• Variables include shear lag, use of staggered
  holes, and so on.

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A better model

• Gusset Plates tensile ultimate on net shear
  yield on gross
• Coped Beams ½ tensile ultimate on net shear
  yield on gross

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Results using new model
G. Y. Grondin For gusset plates, the mean is
1.19 and standard deviation 0.06 if we use what
has been adopted by S16-2001, i.e. we take the
least of yield on the gross shear area, Agv, or
ultimate on the net shear area, Anv. If you go
with what was originally proposed (yield on gross
shear), the numbers that you have are correct.

• Test / Predicted
• Gusset Plates 1.11 (0.10)
• Coped Beams 1.14 (0.13)

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Apply the suggested gusset model to tees and
angles

• Overall result (all four sources) is good
  test-to-predicted 0.93 (0.05)
• Results for Epstein stand out as inconsistent
  with the others
• Existing rules also give good agreement

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Concluding comments

• LRFD gives conservative results for gusset
  plates, non-conservative results for coped beams
• Degree of conservatism is inconsistent
• Predicted failure mode is often incorrect

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Satisfactory results using

• Gusset plates, angles
• Coped beam webs

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..with an upper limit
e.g., for gusset plates
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