CUREe-Caltech Woodframe Project, Element 1 - Research

Meeting

Task 1.4.8.2 - Connections

Ken Fridley, Ted Ryan, David Pollock,

and Rafik Itani

Washington State University

January 12 & 13, 2001

OutlineI. Data Analysis

a. Scenario 1 first cyclic testb. Scenario 1 second cyclic test

II. Probabilistic Analysis of toe-nailed joint a. Derivationb. Results

III. Suggested modification of Scenarios 7 & 8a. Scenario 7b. Scenario 8

IV. Observations and Questions

I. Data Analysis

Scenario #1 Cyclic test number #1

Max absolute load: 6700 lbs..Displacement at max load: 0.73 in

Load vs. Interstory slip

--- Interstory slip

Scenario #1 Cyclic test number #2

Max absolute load: 6100 lbs.Displacement at max load: -0.84 in

Load vs. Interstory slip

--- Interstory slip

II. Probabilistic Analysis of toe-nailed joint

Wall Elevation View

Area of interest

Failure line

Procedure

• Use NDS Yield Equations and Monte Carlo Simulation to predict yield load.

• Bending yield strength of nails and dowel bearing strength of wood were considered as random variables. All other variables were assumed deterministic.

• Distributions were fit to random variables and a single nail yield value was produced using a Weibull distribution (for both random variables) based on best-fit.

• This was expanded to analyze the connection as a ductile parallel system.

NDS Yield Equations For Nailed Connections

)R3(1F2F

k2DZ

)R(2kFDtkZ

)2R(1kDpFkZ

kFDtZ

e

ybem

D

IV

eD

ems2IIIs

eD

em1IIIm

D

essIs

+=

+=

+=

=

Modes IIIs and IV generally control innailed connections

of this type

Parallel System Yield Equation

=

−+−=−

↔n

iZiZinZi

sys

11 )()(

1

1. Assuming same stiffness in each nailed connection2. Data ranked in increasing order

1,2

Predicted yield load (direct multiplication of single nail capacity

and probabilistic value) Using the yield limit equations without safety factors (but including

toenail factor):

Z = 364 lbs. Mode Is Toenail factor 0.83

Z = 215 lbs. Mode IIIm

Z= 144 lbs. Mode IIIs

Z = 132 lbs. Mode IV <== controls

There are 37 nails per connection (16 in rim joist and 3 in each of 7 floor joists)

connection capacity = (132 lbs./nail)*(37nails) = 4883 lbs.

Zsys(probabilistic method)=4249 lbs. (average over 1000 iterations)

III. Suggestions for modification of Scenarios 7 & 8

Original Scenario #7

Scenario #1 with a wall opening;rim joist serves as collector

This will be a modification of Scenario #3 instead of collector elements a different

size rim board will be used and comparedto that done in scenario #3

*Drawings courtesy of Kelly Cobeen and Jim Russell

ModifiedScenario #7

Original Scenario #8

Scenario #2 with a wall opening;double 2x6 Douglas fir header providedin wall system to serve as collector

*Drawings courtesy of Kelly Cobeen and Jim Russell

ModifiedScenario #8

This will be a modification of the baseline scenario with sheathing split at midpoint of

rim joist instead of below and above rim joistconnection

Conclusions

• NDS yield equations provide a conservative estimate of connection capacity.

• Preliminary data suggests that inter-story drift may need to be emphasized in building design provisions.

• Connection failure was consistent with controlling yield equation (ductile, yielding of nails).

• Probabilistic analysis provides a comparison to conventional deterministic design procedures.

Questions and Suggestions???