Federal Building and Fire Safety Invest

of the World Trade Center Disast

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

Strength and Impact Response 

October 19, 2004

Presented by John L. Gross

Prepared by Nicholas J. Carin
Disclaimer Disclaimer

Certain commercial entities, equipment, promaterials are identified in this presentation describe a procedure or concept adequatelthe history of the procedures and practices identification is not intended to imply recomendorsement, or implication that the entitiesmaterials, or equipment are necessarily the for the purpose. 
Effect of Impact on SFRM Protecte

Effect of Impact on SFRM Protecte

• Estimate of extent of dislodged SFRM is 

thermal-structural modeling

• Lack of available information on impact p

members protected with SFRM
Overview Overview

• In-place density and bond strength (Cafc• Laboratory static strength properties (Caf• Impact tests
Impact Damage Impact Damage

• SFRM was dislodged

3⁄4 Debris field3⁄4 Localized accelerations and deformations

• Estimate extent of dislodged SFRM

3⁄4 Measure static adhesive and cohesive tensile 3⁄4 Develop “failure criteria”3⁄4 Impact analysis and engineering judgment to 

dislodged SFRM
Laboratory Specimens Laboratory Specimens

• 8 x 16 x 1⁄4 in. plates

3⁄4 3⁄4 in. and 1-1/2 in. nominal thickness Cafco B3⁄4 With and without primer (Tnemec 99 Red)

• 1 x 20 in. bars

3⁄4 3⁄4 in. and 1-1/2 in. nominal thickness Cafco B3⁄4 With and without primer (Tnemec 99 Red)
March 25, 2004
March 24-25, 2004
Tensile strength properties of fibe

Tensile strength properties of fibe

SFRM

1. Adhesion to steel2. Cohesion normal to surface3. Cohesion parallel to surface (in-plane)

12
ASTM E 736 ASTM E 736 – Cohesion/Adhesion 

Cohesion/Adhesion 

Applied to Structural Members Applied to Structural Members (ado

(ado

SFRM

Bottle screw cap

Adhesive

0.06 in. Galvanized Steel Sheet


Limitations of ASTM Method Limitations of ASTM Method

• Failure area not well defined• Cannot measure both adhesive strength 

strength 

• No information on in-plane strength
Tensile Pull Tensile Pull-off Test for Adhesion 

off Test for Adhesion 

Cohesion Cohesion

SFRM

Aluminum plate

Adhesive

1⁄4 in. Steel plate

Adaptation of technique used to test overlays appconcrete (ASTM C 1583)

Saw 

Specimens for density and in-plane co

Specimens for adhesive/cohesive 
In-Plane Tensile Strength Plane Tensile Strength

• Prepare prism by sanding• Measure mass and dimensions• Compute density• Measure tensile strength

Tensile Pull Tensile Pull-off Test for Adhesion 

off Test for Adhesion 

Cohesion Cohesion

First Test Re-T

Adhesive failure Cohes

Cohesive failure Adhes
Test 1- Adhesive failure
Test 2- Cohesive failure
Results Results

• Tenant Alteration Audit reports for BZ-Type 

3⁄4 ASTM E 736 adhesive/cohesive strength 3⁄4 ASTM E 605 density

• Laboratory tests (BZ DC/F)

3⁄4 Density3⁄4 Adhesive strength3⁄4 Cohesive strength normal to surface3⁄4 Cohesive strength parallel to surface
PANYNJ Tenant Alteration Audit R

PANYNJ Tenant Alteration Audit R

• Average density: 18.9 pcf (sd = 3.2 pcf; COV 

• Average bond strength: 2.1 psi (sd = 0.6 psi• UL Design No. G805: Min. avg. = 13 pcf; m• Isolatek literature: Avg. bond strength 

≈ 1 ps

101520253035

75 80 85 90 95 100 105

WTC 1WTC 2

Density, pcf

Floor

012345

75 80 

WTWT

Bond, psi
Laboratory Density (BZ DC/F) Laboratory Density (BZ DC/F)

2526272829303132

0 2 4 6 8 10 

Density, pcf

Specimen

3/4 in. 1-1/2 in.
Laboratory Density (BZ DC/F) Laboratory Density (BZ DC/F)

Isolatek literature: Average minimum dens

1 1⁄2 in. 29.7 pcf 1.3 pcf 

3⁄4 in. 27.2 pcf 0.8 pcf 

Thickness Average Stand. Dev. 
Adhesive Strength Adhesive Strength

Poor adhesion to primed pl

3⁄4 in. Thickness 1 1⁄2 in
Adhesive Strength Adhesive Strength

Good adhesion to bare steel

3⁄4 in. Thickness 1 1⁄2 in
Laboratory Adhesive Strength Laboratory Adhesive Strength

01234567

0 5 10 15 

With PrimerNo Primer

Adhesive Strength, psi

Specimen

3/4 in.

1-1/2 in.
Laboratory Adhesive Strength Laboratory Adhesive Strength

Isolatek literature: Minimum bond strength f(ASTM E 736) with uncoated or galvanized (100 psf)

1 1⁄2 in. NP 4.6 psi 1.0 psi 1 1⁄2 in. P 1.2 psi* 1.4 psi 3⁄4 in. NP 3.1 psi 0.4 psi 3⁄4 in. P 1.3 psi 0.7 psi 

Average Stand. Dev. 

*For selected specimens; 2/3 of specimens had 0 bond 
Laboratory Cohesive Strength Nor

Laboratory Cohesive Strength Nor

Surface Surface

123456

0 5 10 15 

With PrimerNo PrimerASTM Cap

Cohesive Strength (N), psi

Specimen

3/4 in. 1-1/2 in.
Laboratory Cohesive Strength Nor

Laboratory Cohesive Strength Nor

Surface Surface

As expected, primer had no effec

1 1⁄2 in. NP 4.1 psi 1.1 psi 1 1⁄2 in. P 4.2 psi 1.0 psi 3⁄4 in. NP 2.6 psi 0.4 psi 3⁄4 in. P 3.0 psi 0.7 psi 

Average Stand. Dev. 
Comparison of Cohesive (N) and A

Comparison of Cohesive (N) and A

Strength for Unprimed Steel Strength for Unprimed Steel

No difference between adhesive and cohesive (N) s

1 1⁄2 in. Adhesive 4.6 psi 1.0 ps

1 1⁄2 in. Cohesive 4.1 psi 1.1 ps3⁄4 in. Adhesive 3.1 psi 0.4 ps3⁄4 in. Cohesive 2.6 psi 0.4 ps

Average Stand. D
Laboratory Cohesive Strength Par

Laboratory Cohesive Strength Par

Surface Surface

05

10152025

0 2 4 6 8 10 

Cohesive Strength (IP), psi

Specimen

3/4 in. 1-1/2 in.
Laboratory Cohesive Strength Par

Laboratory Cohesive Strength Par

Surface Surface

No reference values

1 1⁄2 in. 12.1 psi 3.8 psi 

3⁄4 in. 7.8 psi 2.7 psi 

Thickness* Average Stand. Dev. 

*Only specimens with primer
Impact Failure Impact Failure

• SFRM will dislodge when inertial tensile s

exceed strength

• Planar elements

3⁄4 Controlled by adhesive or cohesive strength, w

smaller

• Bar

3⁄4 Controlled by cohesive strength parallel to sur
Simple Models Simple Models

a

fb

fb

ρ t a =

t

Planar Substrate

ft

fb

4 ft (d

(do

a = 

Enc
Impact Tests Impact Tests

• Determine acceleration to dislodge SFRM• Correlate with static properties

Accelerometer

Acce

Plate Enc
Dislodged SFRM

Steel Plate
Summary Summary

• In-place density for BZ DC/F in laboratory 

than for BZ Type II from TAA reports 

• Laboratory cohesive (N) strength for BZ D

than in-place bond strength (ASTM E 736II from TAA reports

• Laboratory static strength tests

3⁄4 Primer reduces adhesive strength, especially 

3⁄4 In-plane cohesive strength greater than cohes

normal (N) to surface. (Dislodgment from planlikely than from encased bars.)

3⁄4 For unprimed specimens, cohesive strength (

adhesive strength.