CALCULATION & DRAFTING STANDARDS MANUAL PROCEDURE: C&D 525 Interior Ladder Standard REV 0.0 7/19/04

Transcription

1 BROWN MINNEAPOLIS TANK PAGE 1 OF 5 PURPOSE: Create, explain, and establish an interior ladder design standard, which will govern a BMT, supplied and/or installed typical interior ladder for welded steel field erected tanks. DESIGN STANDARD: Design Standard Commentary The BMT interior ladder is designed for rigid applications while maintaining safety and easy of use. The BMT interior ladder requires no maintenance. A BMT designed interior ladder meets AWWA D and OSHA 29 CFR Part 1910 requirements including but not limited to side rail dimensions, side rail spacing, rung diameter, and rung spacing. The interior ladder is coated with the same coating as the interior of the tank, which not only prevents rusting, but also will never interfere with the interior coating system of the tank. When used correctly the BMT designed interior ladder can prove to be an invaluable piece of equipment for access to the interior a full welded steel storage tank. In case of any kind of failure this interior ladder is covered under the standard BMT warranty for as long as the tank is covered. Specific Design Standards Only fabricate and install an interior ladder when an interior ladder has been required by the customer specifications, drawings, or by the BMT bid, unless specified All materials for the interior ladder will be A36 mild steel, unless specified All interior ladder side rails shall be fabricated from flatbar, which will be 3/8 thick x 2 wide, unless specified All interior ladders will be 1-4 from side rail to side rail, unless specified All interior ladder rungs shall be fabricated from roundbar, which will be ¾ x 1-4 long, unless specified All interior ladders will be 1-0 from rung to rung, unless specified All interior ladder braces shall be made from flatbar, which will be 3/8 thick x 3 wide, unless specified All interior ladder braces shall be a maximum of 6-0 apart, evenly spaced, unless specified All interior ladders shall maintain a 3 clearance from roof hatch skirt to interior ladder rungs, unless specified

2 BROWN MINNEAPOLIS TANK PAGE 2 OF 5 All interior ladder rungs shall be fillet welded to side rails, unless specified All interior ladders will be painted with the same coating as the tank, unless specified All interior ladders shall be centered with the same centerline as the roof hatch, unless specified The distance below roof hatch lid to last rung shall be 1-0 maximum, unless specified The distance above floor to first rung shall always be 1-0, unless specified The distance side rails extend past centerline of the rungs shall be 2, unless specified When a safety climb is required it shall always begin 2-0 ± from the floor. Even if an interior ladder type, size, dimension, material, or coating is specified otherwise, BMT shall submit the above design standard and wait for drawing comments before changing to anything other than the BMT standard, unless experience with certain engineers warrants supplying exactly what is shown on the customer s drawings or specifications. INTERIOR LADDER VARIABLES: The following are variables, which may require modifications to the interior ladder standard drawing. Even when considering the below variables the design standard shall be followed. 1. Interior Ladder Design Standard Variables: a. Knuckle: when a knuckle is encountered the braces shall be changed to L 2 x 2 x 1/4 b. Additional Safety Requirements: i. When a safety climb is required. ii. When anti-slip rungs are required.

3 BROWN MINNEAPOLIS TANK PAGE 3 OF 5 INDUSTRY STANDARDS & REQUIREMENTS: AWWA Requirements: AWWA D Section 5.5: If safety cages, rest platforms, roof-ladder handrails, or other safety devices in excess of OSHA (see Sec ) requirements are stipulated by the purchaser, or by state or local laws or other regulations, the purchaser shall so specify. None of these devices are advisable when submerged inside tanks in low-temperature climates. AWWA D Section 7.4.2: Inside tank ladders are not recommended for cold climates where ice may form. If an inside ladder is required, the side rails shall not be less than 2 x 3/8, with a spacing between side rails of not less than 1-4, and rungs shall not be less than ¾ round or square bars, spaced 12 apart on centers. DRAFTING INSTRUCTIONS: This drawing without any modification is the standard drawing for an interior ladder with a typical roof slope of ¾:12 and a typical 3 from interior ladder rung to roof hatch skirt. Step #1: For the next series of steps follow: Steps#1-#15 of the preceding standard C&D 510 Title Block Standard, skip Step#6. Step#16: Length of ladder from rung to rung. Press enter. Step#17: Ladder Brace Spacing. 6-0 maximum, braces must be evenly spaced. Press enter. Step#19: Select OK in the bottom left hand corner of the dialog box by clicking on it and you are done and ready to proceed with the rest of the drawing. Step#20: Type attedit into the command line of AutoCAD Step#21: Select the??a in the top right corner of the drawing by clicking on it. Step#22: Enter the drawing number followed by a large A in the piece mark A part of the dialog box, the default will be as follows??a. For example if this sheet happens to be sheet #23 of the drawing package the piece mark A will be as follows: 23A. It will be necessary to input the correct total weight for the interior ladder assembly. Step#23: It will be necessary to input the correct length and weight for the ladder side rails. Revise the description and weight for piece mark a with necessary data.

4 BROWN MINNEAPOLIS TANK PAGE 4 OF 5 Step#24: It will be necessary to input the correct number of pieces and weight for the ladder rungs. Revise the number of pieces and weight for piece mark b with necessary data. Step#25: It will be necessary to input the correct number of pieces and weight for the ladder braces. Revise the number of pieces and weight for piece mark c with necessary data. Step#26: Select OK in the bottom left hand corner of the dialog box by clicking on it. Step#27: If the interior ladder requires knurling for anti-slip rungs turn the layer called Anti- Slip Rungs on. If the interior ladder requires a safety climb turn the layer called Safety Climb on. With regards to all of the preceding options, both the drawing and the bill of materials will automatically revise with the appropriate information. Do not use these drawing functions unless the customer drawings or specifications explicitly call it out. Only follow steps #28-30 if the interior ladder has required a safety climb. Otherwise skip down to step #31 Step#28: Type attedit into the command line of AutoCAD Step#29: Select the d in the top right corner of the drawing by clicking on it. Step#30: It will be necessary to input the correct length for the ladder safety climb, input in the description the correct length for piece mark d with the necessary data. Step#31: You are done and ready to proceed with printing, saving, and closing the drawing. HISTORICAL DATA, REFERENCES, & NOTES: 1) Prior Design Standards Southwest Fabrication: Fillet weld, butt rung to side rail Northwest Fabrication: 13/16 hole in side rail, plug weld, insert rung through side rail Midwest West Fabrication: 13/16 hole in side rail, plug weld, insert rung through side rail West Fabrication: Fillet weld, butt rung to side rail 2) Rung Discussion The interior ladder rungs have been fillet welded to the side rails instead of punching the side rails since punching holes in the side rails it has been determined to be to labor intensive, and rarely approved by engineers. 3) Brace Spacing Discussion The braces are spaced 6-0 apart maximum because many engineers require this in the customer specifications or drawings. 4) Value Added Items A safety climb and anti-slip rungs are value added items. When these items have not been considered by the customer s contract drawings or specifications an additional charge will be assessed for supplying and installing the

5 BROWN MINNEAPOLIS TANK PAGE 5 OF 5 above mentioned items. When a galvanized safety climb has been required try to convince the customer it would be in their best interest to use a stainless steel safety climb instead.