AttachmentA.pdf

Chant Engineering Co. Inc.

59 Industrial Drive New Britain, PA 18901 P: 215.230.4260 F: 215.230.4261 www.chantengineering.com

CAGE Code 7K419

December, 15th, 2016

STRUCTURAL ANALYSIS

for

TENSILE TEST TOWER UPGRADE

Rev. B

Contract # N00174-16-P-0238

NSWC IHEODTD

NSWC – Picatinny Det. Bldg. #61N Picatinny Arsenal, NJ 07806-5000

Chant Job # 30204

Prepared by:

David Crane, M.E.

Reviewed by:

Dylan Garges, M.E.

Approved by:

David Patrick, P.E

Tensile Test Tower Evaluation Report for Contract # N00174-16-P-0238

The report below contains information obtained from the evaluation performed on the Tensile Test Tower on October 25th, 2017 to effectively increase the load capacity from 50,000 pounds to 100,000 pounds. The purpose of the evaluation was to determine if the existing tower structure and concrete anchor pad are capable of having a Safe Working Load (SWL) of 100,000 pounds and a proof-test load equal to 125% of the SWL.

The evaluation was conducted by David Crane, M.E., of Chant Engineering and witnessed by Ryan Broderick of Picatinny Arsenal. Chant Engineering is already very familiar with this machine as we have upgraded, dismantled, transported, and rebuilt it in the past. This experience helped us complete a comprehensive analysis of the existing structure. In the calculations below, we followed the recommendations presented, assuming all structural steel to be A-36 and all bolts to be A-325 High Strength Steel.

Picatinny Tower, As-Is

Cylinder Bearing Beam

Tower Leg, Typ

Leg Brace

Angle Bolting Plate

Cylinder Bearing Beam in Bending:

Beam Material: W18 x 106

Stress at Critical Point:

Where: W = Maximum Load = 100,000 lbs or 125,000 lbs l = Distance between Supports = 113.2 in y = Distance from neutral axis to extreme fiber = 9.37 in

Z = Section Modulus = I/y, where I = Moment of Inertia about loaded axis.

= 1,910 in4 / (9.37 in) = 203.8 in3

= 13,886 psi

Factor of Safety (FoS): 36,000 psi /13,886 psi = 2.59:1

At W = 125,000 lbs:

Figure 1 – W18 x 106 Section Properties (units in inches) Figure 2 – Beam Loading Condition

125,000 113.2

4 203.8 3

= 17,357 psi

FoS: 36,000 psi /17,357 psi = 2.07:1

Cylinder Eye Attachment to Cylinder Beam:

Bolt Dia: 1” Assume Grade 5 (A325 Bolts)

Where:

W = Maximum Load for Bolt σtensile = Maximum Tensile Stress = 120,000 psi

At = Tensile Stress Area of Bolt = 0.606 in2

Solving for W, 120,000psi x .606in2 = 72,700 lbs Total Capacity: (4 plcs) 72,700 lbs = 290,800 lbs

At 100,000 lbs:

FoS: 290,800 lbs / 100,000 lbs = 2.91:1

At 125,000 lbs:

FoS: 290,800 lbs / 125,000 lbs = 2.32:1

Angle Bolting Plate Bolts (3/4-10 A325 Bolts)

While the Angle Bolting Plates which support the cylinder attachment beam are 4, in quantity, for a total of 16 bolts, we conservatively analyzed the Angle Plates as having 12 bolts, total, due to several issues, such as the non-direct load path for the upper angles, deflection at load of bearing points, and potential material degradation with time and exposure.

Bolt Properties:

o Ultimate Tensile Strength = Tmin:

40,100 lbs o Cross Sectional Bolt Area = A [2]:

0.334 in o Minimum Shear Stress = τmin

120,000 psi o R = Ratio between Shear and Tensile Stress (for homogeneous, isotropic material) [4]:

0.577

Maximum Allowed Stress:

120,000 psi 0.577

69,240 psi

Calculated Stress on Bolts (Assuming maximum load ( ) of 125,000 lbs):

o Force on each Bolt:

10,417 lbs hole o Stress on each Bolt:

31,187 psi bolt

Calculated Safety Factors:

o FoS at 125,000 lbs:

FoS

FoS 2.22 o FoS at 100,000 lbs:

FoS

FoS 2.77

Angle Bolting Plates Bearing Stress (Assuming A36 Steel):

Angle Properties:

o Profile: Angle, 6” x 3 ½” x ½” o Yield Strength of A36 Steel [3]:

Material Yield Strength 36,000 psi o Hole Dimensions:

2 plates Assume two plates of 4 bearing load

Bearing Area 2

Maximum Allowed Force Before Yield:

o Compressive Yield Load:

Maximum Compressive Load Before Yield

Calculated Safety Factors o FoS at 125,000lbs:

432,000lbs 125,000lbs

3.45:1

Support Columns Analysis

Column Properties:

o Dimensions Profile: W14×48

Depth: d=8.03in=2y

Elastic Section Modulus: 11.26 in

Length: 47 3 ” 567.375 in o Material [3]:

A36 Steel

o Radius of Gyration = Rx:

1.909 o Slenderness Ratio:

567.375in 1.909in

297.16

Note: if Slenderness Ratio is greater than 100, use the Euler formula for buckling.

Euler Formula for Ultimate Load:

F = n π2 E I / L2

Where;

F = allowable load n = factor accounting for the end conditions

E = modulus of elasticity (steel) = 29 x 106psi

L = length of column = 567.38in

I = Moment of inertia = 51.4 in4

Fsingle leg = 1 (π2) (29x106 psi) (45.2in4) = 45,700 lbs (567.38in)2

Ftotal = 45,700 lbs x (4 Legs) = 182,800 lbs

Angle Between Load and Beam = Approx. 6.5° Resolved Axial Load Used for Buckling = 125,808 lbs

125,000 cos 6.5°

125,808

Factor of Safety: 182,800 lbs / 125,808 lbs = 1.45:1

However, if we assume that the lateral bracing, approximately half-way up the tower is rigid enough in both axes, we can examine the tower supports at a shorter effective length, greatly increasing the frame buckling load:

Euler Formula for Ultimate Load:

F = n π2 E I / L2

Where L = ½ Overall Length

Fsingle leg = 1 (π2) (29x106 psi) (51.4 in4) = 176,142 lbs (289 in)2

Ftotal = 176,142 lbs (4 legs) = 704,568 lbs

Factor of Safety at 125,808 lb load: 704,568 lbs/125,808 lbs = 5.6:1

Power Head (Cylinder Eye Attachment Point)

The cylinder attaches to the power head using a threaded eye screwed to the cylinder rod. With the current cylinder in place, we are at the limit to the size of the eye that can be pinned-in to the powerhead as-is. To fit a larger eye into the powerhead will require substantial modifications.

Any necessary upgrades would be performed to bring the assembly to appropriate factors of safety for the higher capacities at that time.

Concrete Anchor Pad Capacity (Concrete is 4,000 psi concrete per USACOE Drawing S- 304):

Assumptions:

* All 4 Legs of Tower bear directly on full-depth foundation.

* Tower Legs have centers of 153” x 146”

* Test-Area concrete has uniform depth of 3ft.

Test Slab Bending Stress:

For 100,000 lb load applied to center of slab, assuming the full width of the slab contributes to resisting the load. Perform Transformed-Section Analysis to determine independent stress level in concrete:

Slab: 15ft Wide, by 36” Deep Rebar; #6 on 10” Centers Rebar Area: 0.44in2 Es = 29 x 106 psi Ec = 3.6 x 106 psi

Calculate Ratio of Elasticities:

n = Es/Ec = 29 x 106 psi / 3.6 x 106 psi = 8.06 nAs = 8.06 (0.44in2) = 3.55 in2

The neutral axis of the slab passes through the centroid of the transformed section. Summing moments of the transformed area about the neutral axis;

10x (x/2) – 3.55(36 – x) = 0 x = 5.97”

The moment of inertia of the transformed section is:

I = 1/3 (10”)(5.97”)3 + (3.55 in2)(36-5.97”)2 = 4,541.8 in4

Maximum Stress in Concrete:

s = Mc/I = (300,000 in-lbs)(5.97”)/(4541.8in4) = 360 psi

This is the maximum stress in the slab, at 100,000 lbs. Because the load is applied upward on the slab, it is in tension at the top of the slab and compression at the bottom of the slab. As the slab is comprised of both concrete and rebar, we would like to see how much stress the concrete is subjected to, as the tension handling ability of concrete is negligible.

Guidelines say the tensile strength of concrete should be in the range of 10-15%. For 4,000 psi concrete, this value would be 400-600 psi.

The ACI Code Recommendation for concrete in tension is:

fr = 7.5 √fc

Where fr = Rupture Stress

Here, Fr = 474 psi

The predicted value of 360 psi is below the limit of 474 psi.

While it is never ideal to have concrete in tension, this value seems to be acceptable for operation at the load indicated.

Evaluation Summary

Following the SOW guidelines and review suggestions, the Tower structure has achieved significantly higher factors of safety (FoS). The lowest FoS, operating at 125,000 lbs. is 2.07:1, in the cylinder bearing beam. While this factor of safety would normally fall within an acceptable range, a 2:07 factor of safety on this machine is not high enough to recommend operation at that load. The decades this machine has spent outdoors coupled with the potential for unknown degradation makes it difficult, if not impossible for us to guarantee material performance, despite visual appearance. We recommend a minimum 2.5:1 factor of safety due to the history of the machine and the potential for serious operator injury or death if anything were to go wrong.

The 2.5 FoS also meets, or exceeds recommendations from the Crane Manufacturer’s Association of America (CMAA) for Allowable Stresses, section 3.4, Case 1. Shear stress (0.35 , Allowable Bearing Stress (0.75 , and Allowable Tension Stress (0.60 .

Also, the limit for deflection of an unsupported beam, less than 1/600 span, is met.

Mandating a 2.5: 1 FoS would result in a Proof Test Load of 100,000 lbs. This excludes the Power Head, which would need to be fitted with a larger cylinder, load cell, and necessary components to work at this load.

Certification

Taking the above Evaluation Summary into account, Chant Engineering Co. Inc. certifies this tower in its current “as-built” condition to a SWL of 50,000 lbs., due in part to the existing cylinder and power head.

However, as our analysis has indicated, the structure and concrete anchor pad could sustain a higher SWL of 80,000 lbs. (100,000 lbs. proof test load). As such, the tower capacity could be increased to these values if the cylinder & powerhead were replaced.

References

[1] "Structural A36 steel wide flange I beam section properties table sizes W14 to W25 -Â engineers edge," in Engineers Edge, 2016. [Online]. Available:

http://www.engineersedge.com/standard_material/Steel_ibeam_properties_2.htm.

Accessed: Oct. 19, 2016.

[2] "Proof load Tensile strength for grade 2, 5, & 8," in Alma Bolt Company & Prime Fasteners, 2006. [Online]. Available:

http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm. Accessed: Oct. 19, 2016.

[3] "ASTM A36 steel, bar," in MatWeb. [Online]. Available:

http://www.matweb.com/search/datasheet_print.aspx?matguid=d1844977c5c8440cb9a3a 967f8909c3a. Accessed: Oct. 19, 2016.

[4] R. O. Ritchie, J. F. Knott, and J. R. Rice, "On the relationship between critical tensile stress and fracture toughness in mild steel," Journal of the Mechanics and Physics of Solids, vol. 21, no. 6, pp. 395–410, Nov. 1973.