AREMA UNLOADING PIT CALCULATIONS

Transcription

1 AREMA UNLOADING PIT CALCULATIONS AUTHORS Steven P. Lorek, PE (Principal Author) HDR Engineering, Inc Carver Road, Suite 200 Cincinnati, OH Phone: Fax: ABSTRACT The paper submitted for publication will document the process taken to revise the unloading pit section of the AREMA manual. The original section on unloading pits was incorporated into the Manual in Upon review of Section 8.4 for reaffirmation in 2010, it was determined that the figures in section were developed prior to the implementation of the alternate loading and the concrete figures should be removed from Chapter 15. Figures and were reviewed in relation to current live load and fatigue criteria specified in Section 1. The documentation will include commentary of the history of the section, steps take to revise the section, and the detailed calculations required to make the table changes. AREMA MANUAL OF RECOMMENDED PRACTICE PUBLICATION ARCHIVE ARCHIVE REASON: TABLE CALCULATIONS UPDATE PUBLICATION YEAR: 2012 COMMITTEE: SUBCOMMITTEE: REVISION: ATTACHMENTS: 15 - Steel Structures 08 Painting & Special Construction Figure Unloading Pit Fifteen Foot Maximum Span Executive Summary AREMA MRE Figure (2011) Letter Ballot AREMA MRE Figure (2014) Calculations AREMA

2 EXECUTIVE SUMMARY In order to determine the capacity of both the supporting steel beams and concrete structure of the unloading pits under alternate loading, a preliminary analysis was performed. The unloading pit can be found in the 2011 American Railway Engineering and Maintenance (AREMA) Chapter 15 Section 8.4. The current tables of the beam requirement and concrete pit reinforcing were developed under E80 loading. The following is a summary of the findings and analysis of the unloading pit under alternate loading. SUPPORTING BEAM Using a MathCAD template, the supporting beams were analyzed for the alternate loading in both bending and shear. The investigation used the same steel beam section with respect to the varying span length as that of the AREMA - Figure We used the same design requirements such as A.S.T.M A36 structural steel and live impact of 28%. As shown on the enclosed table most of the supporting steel beams were determined deficient for the alternate loading condition. All other design assumptions are included with this document. A summary is enclosed. CONCRETE PIT STRUCTURE A structural analysis (computer model) was performed on the concrete pit structure. The walls are design per foot and the footing length varied with respect to wall height at a 1:1 ratio to sustain the applied loads. The pit was analyzed using the same restrictions and design requirements stated in the AREMA section It is determined that the proposed reinforcing would not work for the E80 or alternate loading conditions. A complete wall model will need to be developed in order to obtain an exact result for the proposed reinforcing listed in AREMA figure Enclosed in this document is the model used to evaluate the concrete pit. A spreadsheet with the number of proposed iteration is also included in order to full analyze the pit as the span length the wall height the wall thickness and footing thickness varies. CONCLUSIONS Supporting Beam - The enclosed table demonstrates that three beam sections would still work for the alternate loading with the respective listed span length; HP12X74 for 8 and 9 feet spans, W16X89 for 12ft span and W21X101 for 15ft span. All other beams are deficient in either bending or shear or both. For these failing sections, larger sections would need to replace the present proposed beams, given that their structural capacity does not permit the alternate loading at the stated span length. Concrete Pit Structure - The concrete pit structure needs further analysis by the committee in order to accurately determine the capacity of the reinforcing as the wall height and span varies. AREMA

3 AREMA MRE Figure (2011) AREMA

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6 Letter Ballot Number: Title: Proposed Revisions to for alternate live load criteria Proposed Letter Ballot: Proposed revisions to the section include updates to the following figures: Figure (Sheet 2 of 3) revision. (See attached) Figure (Sheet 3 of 3) revision. (See attached) Rationale: Table is being revised to accommodate the alternate live loading criteria. Figure Unloading Pit Fifteen Foot Maximum Span To comply with the current live load criteria specified in Section 1, the beam supported superstructure is being upgraded to accommodate the current alternate live loading. In addition, the welded diaphragm connection to the main supporting beams of Figure is being revised to represent a bolted diaphragm connection. This will improve the fatigue category and extend service life while allowing for a reduced beam section. AREMA

7 Letter Ballot Number: AREMA

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11 CALCULATIONS DESIGN ASSUPMTIONS: Design Method: (Steel) Sevice Load Design - Steel Beam Structural Steel Yield Strength: Fy = 36 ksi Live Load: AREMA - Alternate Live Load Impact ( Steel Beams only) : 28% Maximum Speed on tracks: 10 MPH Design Method: (Concrete) Load Factor Design - Concrete Pit Concrete Compressive Strength: f'c = 3 ksi Reinforcing Steel Yield Strength: fy = 60 ksi Unit Weight of Soil: w s = 120 pcf Angle of Internal Friction Φ = 0 Horizontal Earth Pressure: E = 1/2*w s *h^2 AREMA (Case 6) Horizontal Live Load Surcharge: h' = h*q AREMA (Case 6) Surchage Load q = 4 ksf Reference :- Chapter 15 - Section Unloading Pit Structural Steel Beam Structural Steel (Fatigue) Diaphragm Connection Simple Beam Fatigue was evaluated assuming that the channel-section diaphragm is bolted to the web of the Unloading Pit beam at mid-depth with matched angles or a T-section. The bolted detail is evaluated at the bolt furthest from mid-depth according to AREMA Table , Section 2 for bolted connections. (See figures, below) W8x67, C5x6.7, WT3x12.5 W14x132, C10x15.3, WT3x12.5 W10x57, C6x8.2, WT3x12.5 W16x100, C12x20.7, WT3x12.5 AREMA

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