3.6 Internal Climbing Collars & Top Climbing Units: Installation and Post-Climb Position
Key Takeaways
- Internal climbing transfers the crane's full vertical and horizontal load into the building through climbing collars, support beams, and floor wedges, so the supporting floors themselves become part of the crane's structural system.
- Floor wedges are the load-transfer element that locks a climbing collar's support beams against the floor opening; a loose or dislodged wedge is an inspection finding called out by name in 29 CFR 1926.1435(f)(4)(ii).
- A top climbing unit is a climbing cage on the outside of the mast that jacks the entire upper works up one mast section at a time while the mast is discontinuous at the splice.
- Tie-in collars, struts, and lower braces are the external counterpart to internal climbing collars, and both are 'structural supports' whose design is reserved to the manufacturer or a registered professional engineer under 1926.1435(b)(3).
- After climbing, the top climbing unit must be returned to the manufacturer-specified position with its load-transfer components disengaged and secured, so that operating loads pass through the completed mast splice as designed.
3.6 Internal Climbing Collars & Top Climbing Units: Installation and Post-Climb Position
Three blueprint items live in this section:
- D2.9 - Be familiar with proper installation of internal climbing collars, support beams, wedges, and climbing apparatus.
- D2.10 - Be familiar with proper installation of top climbing units and tie-in collars, struts, and lower braces.
- D2.11 - Know proper position of top climbing unit after climbing procedures in accordance with manufacturer's specifications.
The vocabulary is precise, and CCO tests the vocabulary. Getting collar, support beam, wedge, strut, and lower brace straight is half the work.
1. Internal Climbing: The Crane Lives Inside the Building
An internally climbing ("inside climbing") tower crane sits in a floor opening - typically an elevator shaft or a dedicated crane opening in the core - and is supported by the building rather than by a ground-level base.
The hardware, in load-path order
| Component | What It Does |
|---|---|
| Climbing collar (support frame) | A steel frame that clamps around the mast at a splice level. Two collars are normally in use at once, several floors apart. |
| Support beams | Heavy beams that span the floor opening and carry the collar's reactions out to the structural slab or shear walls. |
| Wedges | Tapered steel blocks driven between the support beams and the floor opening edges (or between beam and collar). They take up construction tolerance and lock the assembly tight so there is no free play. |
| Climbing apparatus / hydraulic jacking frame | The rams and pawls that raise the crane from the lower collar to the next floor level. |
Why two collars
The two collars work as a force couple. The mast is a cantilever that wants to rotate under the overturning moment. The upper collar pushes one direction and the lower collar pushes the other, and the vertical distance between them is the lever arm that resists the moment. That is why the spacing between collars is engineered, not chosen for convenience, and why a crane cannot operate on a single collar.
[!IMPORTANT] The supporting floors are part of the crane. This is the conceptual point behind 1926.1435(b)(7)(ii), which requires a registered professional engineer to verify that the host structure can sustain the forces imposed through the braces, brace anchorages and supporting floors. Concrete strength at the time of the jump, slab reinforcement at the opening, and shoring below are all crane-structural questions on an internal climb.
Installation discipline
- Collars are installed level and square to the mast, at the elevation the engineered drawing specifies - not at whichever floor is convenient.
- Support beams must bear on the designed bearing surfaces with the specified bearing length; packing plates are engineered items, not shims from the scrap pile.
- Wedges must be driven fully home and then secured, and re-checked after the first load cycles. A wedge that backs out lets the collar move under load, which converts a snug restraint into an impact load.
- Shoring below the supporting floors is installed per the engineer's design where the slab alone cannot carry the reaction.
2. Top Climbing: The Crane Climbs Its Own Mast
A top climbing unit (external climbing frame, "climbing cage") is a rectangular frame that surrounds the outside of the mast immediately below the slewing platform. It carries a hydraulic ram, guide rollers, and pawls/dogs that engage the mast section rungs or lugs.
The climb cycle, conceptually
- The crane is set to the manufacturer's climbing configuration - slew locked, trolley at the specified balancing radius, no production load.
- The upper works is transferred from the mast onto the climbing frame, and the mast splice bolts or pins at the top of the tower are released.
- The ram extends, pushing the upper works up. The pawls carry the load between strokes - which is why pawl seating is verified before every stroke.
- A new mast section is brought in on the monorail beam / introduction beam and rolled into the gap.
- The section is aligned, pinned or bolted, and torqued to the specified value in the specified sequence (Section 3.4).
- The upper works is lowered back onto the completed tower.
At step 3 the crane is at its most vulnerable state of its entire life. Everything in Section 3.2 - manufacturer prohibitions, wind limits, no personnel below, no production lifting - exists for this window.
3. Tie-In Collars, Struts, and Lower Braces
For an externally climbing crane running up the outside of a building, the mast is restrained by tie-in assemblies rather than internal climbing collars:
| Component | Function |
|---|---|
| Tie-in collar | Clamps the mast at a splice level and provides the connection points for the struts |
| Struts | Compression/tension members running from the collar to the building anchorages; typically two or three per tie-in, arranged to resist force in every horizontal direction |
| Lower braces | Additional members used where the geometry needs a second load path or where a single strut plane cannot triangulate the collar |
| Anchorages / embed plates | The engineered connection into the structure - cast-in embeds, through-bolted brackets, or clamped assemblies |
Strut length, angle, and the collar elevation are all engineered outputs. A strut that is cut short on site to "make it fit" changes the force distribution in every member of the assembly, and it is exactly the kind of field modification that 1926.1435(b)(3) forbids by reserving the design to the manufacturer or a registered PE.
4. Position of the Top Climbing Unit After Climbing (D2.11)
Blueprint item D2.11 asks a narrow question with a specific answer: after climbing, the top climbing unit must be in the position specified by the manufacturer.
Why it matters:
| Reason | Explanation |
|---|---|
| Load path | In the secured post-climb position the climbing frame's load-transfer components are disengaged, so operating loads pass down through the completed, torqued mast splice rather than through the climbing frame's pawls and rams. |
| Rated capacity | Load charts assume the crane in its normal operating configuration. Many machines derate capacity, or prohibit operation entirely, while the climbing unit remains in the climbing position. |
| Clearance | The frame must sit where the counter-jib, hoist rope, cable guides, and the next tie-in collar can clear it. |
| Inspection access | The specified position keeps the pawls, rollers, rams, hoses, and check valves accessible for the next climb and for periodic inspection. |
[!WARNING] A climbing unit left in the climbing (engaged) position is an out-of-service condition, not a cosmetic issue. On the exam, reject any answer that gives the operator, the A/D director, or the superintendent discretion over the climbing unit's parked position, and reject rules of thumb such as "as low as possible" or "immediately below the slew ring." The correct answer always points to the manufacturer's specifications.
5. Post-Climb Return-to-Service Checklist
Before the crane goes back to production after any climb, confirm:
- All new splice bolts torqued to value, in sequence, and match-marked; or all pins fully home with retention installed.
- Plumb re-verified by a qualified person - manufacturer tolerance, or at least 1:500 (about 1 inch in 40 feet) where the manufacturer is silent, per 1926.1435(b)(5).
- Top climbing unit in the manufacturer-specified position, load-transfer components disengaged and secured.
- Slew lock released and swing brake functional.
- Hoist upper limit and trolley travel limits re-set for the new mast height and confirmed by function test.
- Anti two-block device function verified.
- Any new tie-in collar, struts, lower braces, and anchorages installed per the engineered drawing and inspected; wedges (on an internal climb) driven home and secured.
- Hoist rope condition and drum spooling checked - the rope has just been reeved through a full climb cycle.
- Deficiencies documented, and the crane released only by the person authorized to do so.
On an internally climbing tower crane, what is the specific function of the wedges installed with the climbing collar assembly?
A climb is complete and the new mast section has been pinned and torqued. The climbing crew leaves the top climbing unit engaged in its climbing position because another jump is scheduled in two weeks. What is the correct assessment?
Which of the following correctly pairs a component with its role in a tower crane external tie-in assembly?