Platform Analysis Report Rev -.pdf

USACE ESSAYONS

PEDESTAL CRANE ACCESS PLATFORM ANALYSIS

REVISIONS

REV SHEET DESCRIPTION DATE APPROVED

‐ ALL INITIAL ISSUE 11/22/19

DRAWING NO. REV SHEET NO.

354‐F399‐02 ‐ 1

USACE Essayons Pedestal Crane Access Platform Analysis

Table of Contents

Section: Page

1.0 References

2.0 Background

3.0 Method/Assumptions

4.0 Loads and Safety Factors

5.0 Results

6.0 Conclusion

Figures:

Figure 1 - Platform FE Model Figure 2 - Platform FE Model – Under Deck Figure 3 – Fixed End Restraints on Model Figure 4 – Case 1 Loaded Area Figure 5 – Case 2 Loaded Area Figure 6 – Case 3 Loaded Edge Figure 7 - Von Mises Stress Contours – Case 1 Figure 8 - Von Mises Stress Contours – Case 1 – Close Figure 9 - Von Mises Stress 26.5 ksi Criteria – Case 1 – Close Figure 10 - Von Mises Stress Contours – Case 2 Figure 11 - Von Mises Stress Contour – Case 2 – Close Figure 12 - Von Mises Stress 26.5 ksi Criteria – Case 2 – Close Figure 13 - Von Mises Stress Contours – Case 3 Figure 14 - Von Mises Stress Contour – Case 3 – Close Figure 15 - Von Mises Stress 26.5 ksi Criteria – Case 3 – Close

Tables:

Table 1 - Allowable Stresses

USACE Essayons Pedestal Crane Installation Analysis

1.0 References:

1.1 Dwg. 354-F330-02 Pedestal Crane Access Modifications

1.2 ABS Steel Vessel Rules 2019

2.0 Background:

A new main pedestal crane is being installed on the hopper dredge Essayons to replace the existing crane. The existing crane and ancillary equipment are located on the hopper top (46’-6” ABL) on centerline between frames 74 and 78. The new crane will be installed in the same location. The existing crane access will be removed and replaced with a new access platform.

This report addresses the structural requirements necessary for the installation of the new pedestal crane access platform.

Three separate load cases were considered to analyze the platform. In case 1, the entire platform is loaded with a standard uniform personnel load of 65 psf. This case represents the platform holding personnel at a standard density of 1 person per 3 square feet across the entire platform.

In case 2, the longest unsupported span of platform is loaded with 200 psf for a total load of about 5000 lb. across the span. This is the worst-case concentrated load that the fiberglass grating can handle on the longest unsupported span of the platform. In case 3, the forward edge of the platform is loaded with 100 lb./ft. for a total load of approximately 3100 lb. This is the worst case scenario of standing personnel lining the railing (for example a crew picture).

3.0 Method/Assumptions:

A finite element model (FEM) of the pedestal and surrounding area was developed based on Ref. 1.1. The structure was modeled in FEMAP Version 12.0.0, copyright © 2018 Siemens Product Lifecycle Management Software, Inc. The solver is Autodesk Nastran Version 10.3.0.716, copyright © 2016 Autodesk, Inc. NASTRAN is a large-scale structural Finite Element Analysis package that is widely used by industry for a variety of FEA solutions. The model is solved with a linear static analysis.

3.1 Model: The model consists of the platform and stanchions, and a section of the crane pedestal. The model consists of 2D PLATE elements representing the platform angle, stanchions, crane pedestal, and grating. The mesh size is generally 2 inches throughout the model to maintain at least 2 elements per side on 4x4 angle iron and 4x4 square tube.

The model contains approximately 32,400 nodes and 32,200 elements. The coordinate system used throughout the modeling process matches the coordinate system used in the structural drawing. The X-axis is oriented longitudinally with positive forward, the Y-axis is oriented transversely with positive to port, and the Z-axis is oriented vertically with positive upward from baseline. All units in the model are US units (in, lbs, sec, psi).

Figures 1 and 2 show the platform structure.

Figure 1 - Platform FE Model

Figure 2 - Platform FE Model – Under Deck

3.2 Boundary Conditions: In this FE model, nodes are constrained at the deck connections as well as the top and bottom of the pedestal section. The constraints are shown in Figure 3.

Figure 3 – Fixed End Restraints on Model

4.0 Loads and Safety Factors:

4.1 Loads: The platform structure is analyzed using three load cases. In case 1, the entire platform is loaded with a downward force of 65 psf. The platform area loaded in this case is shown in Figure 4. In case 2, a local area of the platform is loaded with 200 psf.

The areas loaded in this load case are shown in Figure 5. In case 3, the forward edge of the platform is loaded with 100 lb./ft. downward. The extents of the loaded edge are shown in Figure 6.

Figure 4 – Case 1 Loaded Area

Figure 5 – Case 2 Loaded Area

Figure 6 – Case 3 Loaded Edge

4.2 Allowable Stress: The structure in the area of concern consists only of ordinary strength steel. Allowable stress for all materials is 78% of yield per Reference 1.1.

Maximum allowable stresses are shown in Table 1.

Table 1 - Allowable Stresses

Material Allowable Stress (PSI)

OSS 26,500

The stresses of concern in this analysis are von Mises stresses, which arise from distortion energy theory. The use of von Mises stresses is quite accurate in predicting failure of steel parts. Von Mises stresses shown throughout the report indicate the maximum of surface stresses on either side of the plate elements. The von Mises stress is defined as:

σ

Where σ1 and σ2 are the principal stresses.

All steel is modeled with a modulus of elasticity (E) of 29,000 ksi, a Poisson’s Ratio (ѵ) of 0.29, and a density (ρ) of 7.324 x 10-7 kips-s2/in4.

5.0 Results:

The following stress plots show the von Mises stress results from the finite element analyses of the access platform.

5.1 Case 1: Figures 7, 8, and 9 show the von Mises stress plots of the access platform in load case 1. The stress contour scale ranges from 0 psi (magenta) to the OSS allowable stress of 26,500 psi (red).

Figure 7 - Von Mises Stress Contours – Case 1

Figure 8 - Von Mises Stress Contours – Case 1 – Close

Figure 9 - Von Mises Stress 26.5 ksi Criteria – Case 1 – Close

There are no elements that exceed the allowable stress; therefore, the stresses are acceptable.

5.2 Case 2: Figures 10, 11, and 12 show the von Mises stress plots of the access platform in load case 2. The stress contour scale ranges from 0 psi (magenta) to the OSS allowable

Figure 10 - Von Mises Stress Contours – Case 2

Figure 11 - Von Mises Stress Contour – Case 2 – Close

Figure 12 - Von Mises Stress 26.5 ksi Criteria – Case 2 – Close

5.3 Case 3: Figures 13, 14, and 15 show the von Mises stress plots of the access platform in load case 2. The stress contour scale ranges from 0 psi (magenta) to the OSS allowable

Figure 13 - Von Mises Stress Contours – Case 3

Figure 14 - Von Mises Stress Contour – Case 3 – Close

Figure 15 - Von Mises Stress 26.5 ksi Criteria – Case 3 – Close

6.0 Conclusions:

This analysis demonstrates that the structural modifications detailed in Reference 1.1 are adequate to support personnel based on the guidance provided in Reference 1.2. The structural stresses are less than the allowable stress for ordinary strength steel in all three worst case load cases. There are no individual elements that do not meet the stress criteria.