Designing a crane-rail connection

The Crane-rail connection type (Wizard group Hangers & bearing, mark prefix CR) details a crane rail on the top flange of a runway girder: how the rail is fastened to the girder, and how two rail lengths are joined. It follows the AISC Steel Construction Manual, 16th Edition, Part 15 (Crane Rail Connections, pp. 15-5 to 15-9), the rail dimensions of Table 1-21 and the crane-rail notes of Part 2 (p. 2-26), with AISC Design Guide 7, 3rd Edition (Industrial Building Design: crane loads, CMAA service classes, rail attachments, rail joints, crane stops and runway tolerances) and the CMAA 70 crane specification (70-2020 where it is on file, else 70-1983).

Part 15 describes crane-rail connections as detailing practice. It gives recommendations, not design equations. ILX therefore reports most of its checks as recommendations: they quote the Manual and are flagged when not met, but they do not make the connection Not adequate. The strength checks are the AISC 360-22 checks of the bolts that hold the fastenings to the girder, for a crane lateral force that you enter or that ILX computes from the crane data by Design Guide 7.

Crane-rail inputs #

• Loads: the crane lateral force H per fastening pair (service dead and crane live loads, required strength, ASCE 7 combinations or load cases). The Manual leaves the spacing of the fastenings and the force each one takes to the crane supplier or the structural engineer (p. 15-7), so you enter it from the crane data or the design criteria, or you let ILX compute it (Crane data, below).
• Rail, girder and crane: the rail from Table 1-21 (ASCE 30 to 100 lb, ASTM A759 104 to 175 lb), the W-shape runway girder and its material, the CMAA crane service class A to F (or, when not entered, the crane service duty, low or heavy), the runway length and the rail eccentricity to the girder web centerline (default 0). With a class, ILX reads Classes A, B and C as light duty and D, E and F as heavy-duty cycle cranes (DG7 14.7.1).
• Crane data (Design Guide 7): tick Crane loads from the crane data to replace the load input. Enter the criteria (ASCE/SEI 7-16, default, or AIST TR-13), the crane operation (cab or remote, pendant, powered monorail, hand geared), for AIST the crane type of Table 3.2, the rated capacity, the bridge weight with end trucks, the trolley and hoist weight, the number of wheels (default 4), and optionally the maximum wheel load from the crane data and the driving wheels (default half the wheels). The defaults are the crane of DG7 Example 14.1.1 (20 tons, bridge 57.2 kips, trolley and hoist 10.6 kips, 4 wheels). ILX computes:
  • the maximum wheel load: the bridge shared by all wheels, the trolley, hoist and lifted load by the wheels of one end truck (DG7 Example 14.1.2); an entered wheel load replaces it for service and ASD; LRFD is always 1.2 × the crane weights + 1.6 × the lifted load (DG7 Chapter 12);
  • the vertical impact: ASCE 7 25 % (cab, remote, powered monorail), 10 % (pendant), 0 (hand geared); AIST 25 % (20 % for motor room maintenance cranes);
  • the side thrust: ASCE 7 20 % of the capacity plus trolley and hoist (none for hand-geared cranes); AIST the greatest of Table 3.2, 20 % of the lifted load plus trolley and 10 % of the lifted load plus the crane (40 % and 15 % for stacker cranes), or 20 % of the load on the driving wheels for pendant cranes. It is shared equally by the wheels (DG7 Example 14.1.1);
  • the tractive force per rail: ASCE 7 10 % of the maximum wheel loads on the rail; AIST 20 % of the load on its driving wheels;
  • the bumper force: entered, or for a spring bumper DG7 Eq. 14-3, F = W V² / (g ct), with V = 50 % of the rated bridge speed and ct the stroke, or the DG7 default, the greater of twice the tractive force and 10 % of the crane weight.

  The lateral force per fastening pair is your share of a wheel's lateral force (default 1.0, one pair takes it all: DG7 calls the design of rail attachments "largely empirical" and gives no distribution). It is a crane live load: LRFD 1.6 (DG7's recommendation), ASD 1.0. Fatigue inputs from the service class (default on) sets the cycles from DG7 Table 11-1 (A 20,000; B 50,000; C 100,000; D 500,000; E 1,500,000; F over 2,000,000, taken as an indefinite life) times the stress cycles per crane passage (default 1), and cycles half the side thrust (DG7 12.7, AIST fatigue loads). Turn it off to enter your own fatigue inputs.

• Rail fastening: the type, the spacing of the pairs along the rail, the hook-bolt offset, the bolt gage across the rail, bolts per clip or clamp and their pitch, the clamp end distance, the clamp plate and filler thicknesses (filler 0 = the rail toe thickness n of Table 1-21), the tight-clamp adjustment, the floating-clamp float, an optional manufacturer's available lateral strength per fastening, and the elastomeric rail pad.
• Fastener bolts: grade (default ASTM F3125 Grade A325: DG7 recommends high-strength bolts for clamps; Fig. 15-6 shows a machine bolt), diameter and threads.
• Rail splice: bolted joint bars (splice, angle or joint bars of Fig. 15-3), the gap between the rail ends (default 1/16 in., the CMAA 70-2020 maximum), the bolts (track bolts or fully tensioned high-strength bolts), whether the bars are welded to the rail, clips or clamps at each end of the splice; or a flash-butt, thermite or electric-arc welded joint. Then the distance from the joint to the nearest girder end or splice, the stagger of the joints on the two rails (at least 1 ft, DG7 14.8), the crane wheel spacing and your minimum difference between the two (neither the Manual nor DG7 gives a number), the rail length and the shortest odd length. The joint bar length, the splice bolts per rail end and their diameter are for the drawing only.

Crane-rail checks #

Strength (AISC 360-22), with H applied by statics: the rail bears on the fastening on the side it is pushed toward, so that clip or clamp carries all of H.

• Bolt shear of the clip or clamp bolts, H / n per bolt (J3.7, Table J3.2).
• Bearing and tearout at the bolt holes in the girder flange, toward the flange tip (J3.11, Eqs. J3-6a and J3-6c).
• Hook bolt in tension: one hook bolt of a pair, the one hooked on the far flange edge, carries H (J3.7).
• Manufacturer's rating, when entered, against H.

Detailing: the rail base fits on the flange; the bolt holes clear the rail base and lie within the flange (Not feasible otherwise); the edge distance from the bolts to the flange tip and the clamp end distance (Table J3.4); the bolt pitch in a clamp (J3.4).

Recommendations (Manual Part 15 and Part 2, Design Guide 7, CMAA 70): the fastening limits in the table above; the splice gap of 1/8 in. or less (Manual) and 1/16 in. or less (CMAA 70-2020 1.4.5); splice bars not welded to the rail; clips or clamps next to each end of the splice; rail joints at least 5 ft from the girder ends and not at girder splices; joints staggered at least 1 ft between the two rails and the stagger not equal to the wheel spacing; odd rail lengths of 10 ft or more; the rail lengths available (40 lb: 30 ft; 60 lb: 30, 33 or 39 ft; standard rails: 33 or 39 ft; crane rails up to 80 ft); the rail centered on the girder within 3/4 of the web thickness (DG7 Chapter 15); a lateral float of 1/32 in. or less on rail pads. Notes repeat the guidance on welded joints (AREMA, DG7 14.8), heavy cranes, keeping bolted joints tight, the rail selection by the crane manufacturer, the rail pad, never welding rails to girders, and the RCSC Commentary on pretensioned bolts in buildings with cranes.

With a CMAA class, a note gives the class, the duty ILX reads from it and the DG7 Table 11-1 design life (CMAA 70-1983 definitions; the current edition is 70-2020, confirm the class against it). With the crane data, notes give the crane loads with every step, the forces the runway girder must take (wheel load with impact, lateral force per wheel, tractive force per rail, bumper force, DG7's deflection limits) and the crane stop guidance. ILX reports these forces; it does not design the girder or the stop.

Crane-rail drawings #

Section A-A cuts across the girder: the top flange with the web broken below it, the rail profile from Table 1-21 (on the pad when there is one), and the fastening on both sides with its bolts. The gage and flange width are dimensioned below and the rail depth at the right. The elevation at the rail joint shows the girder broken at both ends, the two rail ends with the joint bars and the splice bolts on the Table 1-21 gage line (or the welded joint), and the fastenings at their spacing. The bar length and the spacing are dimensioned above the rail.

Crane-rail limits #

• Neither Part 15 nor Design Guide 7 gives a bearing length through the rail for web local yielding or crippling (J10.2, J10.3) under a crane wheel, so ILX does not check them. DG7 checks web sidesway buckling (J10.4) under the wheel load with impact as part of the runway girder design, which ILX does not do (biaxial bending, deflection, fatigue of the girder details). The rail itself and the clip, clamp plate, filler or hook as components are not checked either (by the supplier or the engineer). The rail is selected by the crane manufacturer.
• Fatigue (Appendix 3). Tick Cyclic loading (fatigue) and enter the cycle count and the cyclic range (a fraction of the live lateral force HL, or the range of H), or let the crane data set them from the service class; see Fatigue (Appendix 3). Hook bolts: the bolt in tension (Table A-3.1 Case 8.5, Category G, on the tensile stress area; not pretensioned, so the whole range). Clips and clamps carry H in shear: bolts in shear are not checked (Section 3.4(a)), and their holes in the girder top flange are details of the runway girder under its own stress range, which ILX does not design; the result says so.
• The distribution of the crane lateral force to the fastenings is your input (DG7 gives none).
• The CMAA 70 class definitions come from the 1983 edition and the 2020 preview; the full 2020 edition is not on file. AIST TR-13 is quoted only as DG7 quotes it.
• There is no published numeric example of a crane-rail connection. The tests check the Table 1-21 data as printed, the AISC 360-22 bolt strengths by hand (backend/tests/test_crane_rail.py), and the crane loads against DG7 Examples 14.1.1 and 14.1.2 and Table 12-2 (backend/tests/test_crane_rail_dg7.py). See research/63_crane_rail_connections.md.