US. Deportment 

of Transportotioo 

Federal Highway 

Administration 

Mr. Chris Brookes 

Work Zone Delivery Engineer 

Michigan Department of Transporlation 

P.O. Box 30050 

Lansing, MT 48909 

Dear Mr. Brookes: 

This Jetter is in response to your request for the Federal Highway Administration (f.'HW A) to 

review a roadside safety system for eligibility for reimbursement under the FederaJ-aid highway 

program. 

April 22, 20 l 4 

1200 New Jersey Ave., SE 

Washington, D.C. 20590 

In Reply Refer To: 

HSST/SS-36A 

Name of system: Breakaway wood sign supports with lag screws 

Type of system: Ground mounted breakaway sign support 

Test Level: NCHRP Report 350 Test Level 3 

Testing conducted by: (Federal Outdoor Impact Laboratory) 

Task Force 13 Designator: PDP20-24 

Date of request: January 23. 2014 

Date of completed package: April 3. 2014 

Decision 

The following device is eligible. with details provided in the form which is attached as an 

integral part of this letter: 

• Breakaway wood sign supports with lag screws in lieu of through bolts. 

Based on a review of crash test results certifying the device described herein meets the crash test 

and evaluation criteria of the National Cooperative Highway Research Program (NCHRP) 

Report 350, the device is eligible for reimbursement under U1e Federal-aid highway program. 

E)jg.ibility for reimbursement under the Federal-aid highway program does not establish approval 

or endorsement by the FHWA for any particular purpose or use. 

The FHWA, the Department of Transportation, and the United States Government do not 

endorse products or services and the issuance of a reimbursement eligibility letter is not an 

endorsement of any product or service. 
2 

Requirements 

To be found eligible for Federal-aid funding, roadside safety devices should meet the crash test 

and evaluation criteria contained in the NCHRP Report 350 or the American Association of State 

Highway and Transportation Officials' Manual for Assessing Safety Hardware (MASH). 

Description 

The device and supporting documentation are described in the attached form and "Lag Screw 

and Through Bolt Connections." 

Summary and Standard Provisions 

Therefore, the system described and detailed in the attached form is eligible for reimbursement 

and may be installed under the range of conditions tested. 

Please note the following standard provisions that apply to FHW A eligibility letters: 

• This letter provides a AASHTO/ARTBNAGC Task Force 13 designator that should 

be used for the purpose of the creation of a new and/or the update of existing Task 

Force 13 drawing for posting on the on-line 'Guide to Standardized Highway Barrier 

Hardware' currently referenced in AASHTO Roadside Design Guide. 

• This finding of eligibility does not cover other structural features of the systems, nor 

conformity with the Manual on Uniform Traffic Control Devices. 

• Any changes that may influence system conformance with NCHRP Report 350 

criteria will require a new reimbursement eligibility letter. 

• Should the FHW A discover that the qualification testing was flawed, that in-service 

performance reveals safety problems, or that the system is significantly different from 

the version that was crash tested, we reserve the right to modify or revoke this letter. 

• You are expected to supply potential users with sufficient information on design and 

installation requirements to ensure proper performance. 

• You are expected to certify to potential users that the hardware furnished has the 

same chemistry, mechanical properties, and geometry as that submitted for review, 

and that it will meet the crash test and evaluation criteria of the NCHRP Report 350. 

• To prevent misunderstanding by others, this letter of eligibility is designated as 

number SS-36A and shall not be reproduced except in full. This letter and the test 

documentation upon which it is based are public information. All such letters and 

documentation may be reviewed at our office upon request. 
• This letter shall nol be construed as authorization or consent by the FHW A to use, 

manufactu re, or sell any patented system for which Lhe applicant is not the patent 

holder. The FHW A does not become involved in issues concerning patent law. 

Patent issues, if any, are to be resolved by the applicant. 

Enclosures 

Sincerely yours, 

Michael S. Griffith 

Director, Office of Safety Technologies 

Office of Safety 

3 
Version 7.0 (3/13) 

Page 1 of 2 

Request for Federal Aid Reimbursement Eligibility 

Of Highway Safety Hardware 

Date of Request: , /23/2014 \New \ :Resubmission 

Name: Chris Brookes Work Zone Delivery Er Signature: c::-C- /J---- .. Company: cu Michigan Department ofTransportatoin 

.~ Address: E Brookesc@michlgan.gov Phone: 517-636~0300 Cell: 517-242-6486 .c 

:J Country: Ill USA 

Michael S. Griffith, Director To: FHWA, Office of Safety Technologies 

I request the following devices be considered eligible for reimbursement under the Federal-aid 

highway program. 

System Type Submission Type Device Name I Variant Testing Criterion Test 

Level 

'SS': Breakaway Sign 

Supports, Mailboxes, & 

other small sign supports 

~Physical Crash Testing 

C FEA & V&V Analysis 

Lag screw to fasten signs 

on wood posts 

NCHRP Report 350 TL3 

By submitting this request for review and evaluation by the Federal Highway Administration, I certify 

that the product(s) was (were) tested in conformity with the NCHRP Report 350 (Report 350) and that 

the evaluation results meet the appropriate evaluation criteria in the Report 350. 

Identification of the Individual or organization responsible for the product: 

Contact Name: Chris Brookes Work Zone Delivery Engineer Same as Submitter [gJ 

Company Name: Michigan Department ofTransportatoln Same as Submitter [gJ 

Address: Brookesc@mlchlgan.gov Phone: 517-636-0300 Cell: 517-242-6486 Same as Submitter [gJ 

Country: USA Same as Submitter [gJ 

PRODUCT DESCRIPTION 

Modification to Existing Hardware null 

The Michigan Department ofTransportation is requesting FHWA's approval to use 3/8 lag screws in substitution 

of a 3/8 through bolts on a 1 :1 basis on 4x6 wood post/sign conflguratlon. The Attached Excel spreadsheet 

with calculations shows that for a Oto +/-1 O degree crash angle range, 3/8 lag screws substituted for 3/8 

through bolts on a 1 :1 basis Is expected to have no adverse effects on the crashworthiness of the 4x6 wood 

post/sign configuration. The document also contains the Mathcad worksheet for reference. 

CRASH TESTING 

A brief description of each crash test and its result: 

Required Test 

Number 

Narrative 

Description Evaluation Results 

3-60 (820() WAIVER REQUESTED 
Version 7.0 (3/13) 

Page 2 of 2 

Required Test 

Number 

Narrative 

Description Evaluatlon Results 

S3-60000C) WAIVER REQUESTED 

NCHRP Report 350 does not contain a pass/fall requirement for 

3·61 (8200 ground-mounted sign supports. Therefore the substitution of 

fasteners Is allowed If the altematlve Is shown to have equivalent WAIVER REQUESTED 

holding strength. 

53-61 0000 WAIVER REQUESTED 

Full Scale Crash Testing was done In compliance with Report 350 by the following accredited crash test 

laboratory (cite the laboratory's accreditation status as noted In the crash test reports.): 

Laboratory Name: Federal Outdoor Impact Laboratory 

Laboratory Contact: Same as Submitter O 

Address: Same as Submitter O 

Country: Same as Submitter 0 

Accreditation Certificate 

Number and Date: 

· ISO 17025; Cert.# AT-1565 

A TI ACHlvfENTS 

Attach to this form: 

1) A copy of the full test report, video, and a Test Data Summary Sheet for each test conducted In 

support of this request. 

2) A drawing or drawings of the devlce(s) that conform to the Task Force-13 Drawing Specifications 

(Hardware Gulde Drawing Standards]. For proprietary products, a single isometric line drawing Is 

usually acceptable to Illustrate the product, with detailed specifications, Intended use, and contact 

Information provided on the reverse. Additional drawings (not In TF-13 format) showing details that 

are key to understanding the performance of the device should also be submitted to facllltate our 

review. 

FHWA Offlc!al Byslness On bf: .... 

Ellgiblllty Letter AASHTOTF13 

Number Date Designator Key Words 

Wood Sign Supports SS-36A Aprll 10, 2014 Lag Screw 
Calcμlation sheet to determine acceptable use limits or lag screw substituted sign connections for temporary signs mounted to wood posts 

Prepared by S. Kahl 1/22/2014 

Description Value Source 

3/8 lag screw O.L.Y. strength (lb) 418 from mathcad sheet 

3/8 lag screw withdrawal load (lb) 3461 from mathcad sheet 

3/8 bolt O.LY. strength (lb) 1573 from mathcad sheet 

3/8 bolt withdrawal load (lb) 1702 from ma thcad sheet 

sign mass {slug) 3.1 assumed 100 lb weight 

car mass (slug) 61.6 NCHRP report 553 section 8.4 vehicle weight l,984 lb with occupant 

Maximum delta V after impact {ft/s) 16.4 NCH RP report 350 maximum occupant collision velocity 

Notes: Impact force= m•dv/dt, where m =post mass, dV =change in velocity, and dt =vehicle transit time for a 3.5 in wood post (0.29 

ft) at Impact velocity. Impact velocity and delta v taken from test re.suits outlined in fHWA approval letter HNG·l4/SS·36 

head·On 

head·on impact crash test post Vat Impact dV after dt Impact force II bolts # lag screws 

configuration 

single unmodified 

(ft/s) impact {ft/s) (transit time, s) (lb) Odcgrees Odegrees 

30.3 13.2 0.010 4269 2.51 l.23 

89.3 5.0 0.003 4774 2.80 1.38 

dual-modified (holes drilled) 

dual-modified (holes drilled), one 

post hit 

29.3 8.6 0.010 2698 1.59 0.78 

85.9 

31.4 

7.5 0.003 6890 4.05 1.99 

7.4 0009 2487 1.46 0.72 

88.8 3.0 0.003 2847 1.67 0.82 

test case for angled Impact angle {degrees) sin angle lateral force (lb) II lag screws target 

6.5 01132 483 1.16 

ao 01392 594 1.42 

10.0 01736 741 1.n 

single unmodifled, 30.3 h/s 12.0 0.2079 888 2.12 2 

15.0 0.2588 1105 2.64 

20.0 0.3420 1460 3.49 

25.0 0.4226 1804 4.32 

6.S 0.1132 540 1.29 

8.0 0.1392 664 1.59 

10.0 0.1736 1129 l.98 

single, unmodified, 89.3 ft/s 12.0 0.2079 992 2.37 2 

15.0 0.2588 1235 2.96 

20.0 0.3420 1633 391 

25.0 0.4226 2017 4.83 

65 01132 305 0.73 

8.0 01392 375 0.90 

10.0 01736 468 1.U 

dual,modlfied (holes drilled), 29.3 ft/s 12 0 02079 561 1.34 4 

15.0 0.2588 698 1.67 

200 03420 923 2.21 

25.0 0.4226 1140 2.73 

6.5 0.1132 780 1.87 

8.0 0.1392 959 2.29 

10.0 0.1736 1196 2.86 

d ual,modified (holes drill ed), 85.9 ft/s 12.0 0.2079 1433 3.43 4 

15.0 0.2588 1783 4.27 

20.0 0.3420 2357 5.64 

25.0 0.4226 2912 6.97 

65 01132 780 187 

a.o 01392 959 2 29 

10.0 01736 1196 2..86 

dual, modified (holes drilled), one post hit, 31.4 ft/s 12 0 0.2079 1433 3.43 4 

15.0 0.2588 1783 4.27 

20.0 0.3420 2357 5.64 

25.0 0.4226 2912 6.97 

6.5 01132 780 1.87 

8.0 0.1392 959 2.29 

10.0 0.1736 1196 2.86 

dual, modified (hol es drilled), one post hit, 88.8 ft/s 12.0 0.2079 1433 3.43 4 

15.0 0.2588 1783 4.27 

20.0 0.3420 2357 5.64 

25.0 0.4226 2912 6.97 

Green shaded area rl!tlttSents 1ntlclpated acce11uble lltfformance with lag wew subst1tut1on for siRn to oost connection. 
TYPE lJ AHO DPE 111 SIGHS 

TOP vmr 

TIPE I SIGH 

_, - .t(IW .... ( tfAAUll ' Jrlf •• tl.:M 

Steven Kahl P.E. Lag Screw and Through Bolt 

Connections 

07-16-13 

Page 1of4 

This solver is intended to provide the equivalent strength of lag bolts as compared to through bolts for 

temporary sign on wood posts on the typical WZD-100 page 9 of 11 . References: 1. Forest Products 

Laboratory 'Wood handbook- Wood as an engineering material.• General Technical Report 

FPL-GTR-190. Madison, WI:, U.S.Department of Agriculture, Forest Service, Forest Products Laboratory. 

April 2010. 2. NOS 2001, American Forest and Paper Association, the American Wood Council. 

Figure 1. Illustration of temporary sign details from WZD-100 page 9 

Input section (highlighted = user input) 

D 0 375 in D = Lag screw shank diameter 

Dr ·= 0.271 in Dr = Lag screw root diameter, 0.271 in for 3/8 in., and 0.371 for 1/2 in. 

Db := 0.375 in Db = bolt diameter 

Liag = 4.5·in L1ag = nominal length of lag screw. For all posts, use 4-1/2 in. This length is 

sufficient for the full embedment of the threaded portion, and such that the 

withdrawal load will not exceed the tensile strength of the lag screw. 

Lboll :: 5.Sin Lbolt is the bolt length in bearing against the wood surface, 5.5 in for a 4x6 post, 

and 7.5 in for a 6x8 post. This assumes the bolt is installed through the front 

face. 

lb Fyb ·= 45000· - Minimum bending yield strength of lag screw and,ASTM A307 Grade A (36 ksi . 2 

tn Fy) bolt. Reference AITC lechnical note 8. 

F : 60000~ Tensile strength of ASTM A307 Grade A bolts and lag screws. 1 2 in

0- Lag screw threaded length (T) from NOS Appendix L (T = 1/2 x nominal length+ L1 _..!_ in J 2 ag 2 1/2 in) 

Lt = 2.75in 

ts : 0.50·in ts is sign member thickness, 0.080 in. for aluminum sheet for Type Ill sign, or 

0.50 in. for plywood Type II. 

G = specific gravity of wood based on overdry weight and volume at 12% 

Q..= 0.55 moisture content (unitless). Southern Pine is actually comprised of 4 primary 

mixes, longleaf, slash, loblolly, and shortleaf pine. G is averaged for Southerin 

Pine from the above species in Table 5-3b of FPL wood handbook. 
Steven Kahl P.E. Lag Screw and Through Bolt 

Connections 

07-16-13 

Page 2 of 4 

F 

cperp ·.

-

- ( 790 + 960 820 1020 ~ 

4 in2 Southern Pine (12% moisture) compressive strength is 

averaged from individual species for both perpendicular to 

Fcpar := 7130 + 8470 + 7270 + 8140 ~ grain and parallel to grain. FPL wood handbook table 5-3b. 

4 in2 

Section 1: ultimate withdrawal load (direct tension) 

LPun := , 7.0 if G ~ 0.61 Penetration length (LPu1t) of the threaded part to develop 

the lag screw tensile (ultimate) strength, 7 times the shank 7-D + 26.3·(0.61 - G)in otherwise 

diameter for G ~ 0.61, and 10 to 12 times the shank 

diameter for G < 0.42. with interpolation between. FPL 

wood handbook pages 8-12 and 8-13. LPult = 4.203in 

1. 5 . Penetration length of the lag screw threaded portion. subtracting the 

L := L lag-ts --rn - - rn P aluminum or plywood sign thickness. 1/4 in. washer thickness. and the 4 16 

5/16 in. tapered portion of the threads (dimension E from NOS 

Appendix L). Pullout resistance does not include tapered part of LP = 3.438in .. 

Check := I 

threads 

"OK" if LP s LPuu In determining the withdrawal resistance, the allowable tensile strength 

of the lag screw al the net (root) section should not be exceeded (FPL 

"NG" otherwise wood handbook page 8-12). 

Check = "OK" 

3 3 Pult is the ultimate withdrawal load (lb). FPL wood handbook 

2 4 lb equation 8-14b. The tensile strength (Ft) of the lag screw at the net 

p It := 81DO·G ·D ·Lp·- - (root) section is exceeded if the use ratio (U) > 1.0, indicating failure u in 1.75 

of bolt before pullout. Note that the leading constant is different from 

NOS Equation 11 .2-1, as the FPL equation gives ultimate withdrawal 

load versus NOS allowable design withdrawal loads. Pult = 5442 lb 

Pult lb 

C1:=-- C1 = 94355- u = 1.573 

. 2 or2 1n 71·-

4 

Pult P1ag is the adjusted lag screw withdrawal load based on the limiting 

P1ag== u tensile strength of the lag screw. 

P1ag = 3461 lb 

Used for calculating long to short bolt bearing stress ratios (FPL wood handbook Lbolt = 14.667 figures 8-9 through 8-11 ). Ob 

Pbolt calculates bolt withdrawal load based on the net 

2 2 cross section area (wood bearing area) multiplied by ·= .[ (1 .251n) - (0.4060in) ·O . .F 71 5 0 40 l the adjusted parallel to grain compressive strength . Pbolt · · · CparJ 4 Fepa, Reductions of 0.50 and 0.40 from FPL wood 

handbook Figure 8-9 are applied. The bearing area 

Pbolt is assumed to be the 3/8 in washer (i.d. 0.4060 in, = 1702 lbf 

o.d. 1 250 in). 
Model.., Mode 1. Mode II 

Mode Ill,.. Mode Ill, Mode IV 

Figure 2. FPL wood handbook Figure 8-5, showing various failure 

modes for wood-bearing and fastener-bending yields. 

Steven Kahl P.E. Lag Screw and Through Bolt 

Connections 

07-16-13 

Page 3 of 4 

Section 2: Lateral resistance (shear) 

Fe:= 16600·G 84 .~ Fe is the dowel bearing strength of wood and is empirically related to the specific . 2 

In gravity. FPL wood handbook Equation 8-3b. 

lb Fe = 5526- . 2 

In 

Fem := Fe Setting the dowel bearing strength of the main member equal to the bearing 

strength of the wood post 

lb Fes := 3350- The dowel bearing strength of Aluminum is 56,000 psi. For plywood signs, set . 2 

In Fes equal to 3350 psi (NOS Table 11 .3.28). 

R ·= Fem Re is the ratio of dowel bearing strength of the main member to the side member . ..!$;· Fes 

2 2·(1 + Re) Fyb ·(2 + Re)-Or k3 is a constant in the offset lateral yield strength equation. k3 := - 1 + + --'---'-- --'---

2 Re 2 ·Fem·ts

k3 = 1.753 

Ps := Lp - Lt P 5 is the penetration length of the unthreaded portion of the shank, Lp 

accounts for the sign and washer thickness. 

Ps 

Rp: Rp is t11e ratio of penetration distance of shank into wood post to the = o 

shank diameter. Ratios greater than 1.0 allow for increase in the offset 

RP = lateral yield strength. The strength multiplier S is calculated from FPL 1.833 

wood handbook Table 8-12. 

1.0 if RP ~ 1.0 

2 - 0.9881 ·RP + 13.083·Rp - 4.4286] 

1.0 + ( otherwise 

100 

s = 1.162 

Z1 := S·Dr·tS·Fes 

Z1 = 528 1b 

Z3 := S·k3·Dr·ts·Fem 

2+ Re 

Z3=418 1b 

:= S·Dr2. 1.75·Fem·Fyb 24 

3(1 +Re) 

Z4 = 6321b 

min(Z1 .Z3 .Z4) = 418 lb 

Z1 , Z3, and Z4 are the lag screw offset lateral yield strength wood 

bearing/fastener bending failure modes. Z1 is for mode Is, Z3 is for mode 

Ills, and Z4 for mode IV. See Figure 2. All three evaluated for controlling 

(lowest strengh) mode. See FPL wood handbook Table 8-5. Also refer to 

NOS Table 11 .3.1A, Yield Limit Equations. 
Steven Kahl P.E. 

Bolts Pbt calculates perpendicular-to-grain loading, by multiplying the 

species compression perpendicular-to-grain proportional limit stress Pbt := Fcperp·1.7·0.50·LboirDb (Fc.perp) by (a) the appropriate factor from Figure 8-11 , (b) the 

appropriate factor from Figure 8- 10, and (c) Lboll x Db. FPL wood 

Pbt = 1573 lbf handbook, page 8-15. 

Lateral force required to shear Type II plywood sign 

Fply := 3350psi-0.50in·D Dowel bearing strength of plywood (3,350 psi) multiplied by the sign 

F ply = 628 lbf thickness x lag screw diameter. This will be the limiting failure loading in 

lateral offset yield, as the sign will tear away from the connection. 

min(Pbt. Fply) = 628 lbf 

Lateral force required to shear Aluminum sign 

Falum := 56000psi ts·D Dowel bearing strength of Al multiplied by the sign thickness x lag screw 

diameter. this will be the limiting failure loading in lateral offset yield, as the 

Falum = 105001bf sign will tear away from the connection. 

min(Pbt. Falum) = 1573 lbf 

Summary 

Lag Screw and Through Bolt 

Connections 

07-16-13 

Page 4 of 4 

offset lateral yield offset lateral yield Lag Screws Lag Screws 

strength (lb) - Type strength (lb) - Type required per bolt required per bolt 

withdrawal load (lb) II signs Ill signs Type II signs Type Ill signs 

Fastener Type diameter (in) 4x6 post 6x8 post 4x6 post 6x8 post 4x6 post 6x8 post xxxxxxxxxxxxxxxxxxxxxx 

0.375 3461 3461 418 418 715 715 this section not 

Lag Screw (4.5 applicable in. length) 0.500 6486 6486 694 694 1249 1249 

xxxxxxxxxxxxxxxxxxxxxx 3/8 in. Bolt 0.375 1702 1702 628 628 1573 1680 

*NOS 11.1.3 requires predrilling for lag screws with diameter greater than 3/8". Lag screws must 

meet ANSl/ASME Standard 818.2.1 or ASTM A307 Grade A, with a minimum bending yield strength of 

45,000 psi.