This chapter covers the critical procedures of climbing, tying-in, and dismantling tower cranes. These operations represent the most dangerous phases of a tower crane's life cycle, with a disproportionately high accident rate relative to work hours. For the Red Seal exam, you must master not only the operational sequences, but also load calculations, Canadian regulatory requirements, and structural stability principles.
Fundamental Principles of Tower Crane Stability
The Overturning Moment
The stability of a tower crane relies on the balance between the overturning moment generated by the suspended load and the stabilizing moment provided by the counterweight, the crane's mass, and the tie-in system.
The overturning moment (Mᵣ) is calculated as follows:
Mᵣ = (Load + Weight of the jib) × Horizontal distance from the axis of rotation
The stabilizing moment (Mₛ):
Mₛ = (Counterweight × Counterweight distance) + (Counter-jib weight × Counter-jib distance) + (Tower weight × Distance from the axis)
For a free-standing tower crane (not tied in), stability depends on the base width (footprint) and the tower height. The rule of thumb: the maximum free-standing height of an untied tower is generally limited to approximately 20 to 25 times the base width, depending on the manufacturer.
Configuration
Maximum Free-Standing Height
Limiting Factor
Fixed base on slab
20 × base width
Soil/slab capacity
Base on piles
25 × base width
Tower deflection
Intermediate tie-ins
Up to 200 m
Tie-in strength
Climbing
Definition and Types of Climbing
Climbing is the operation of increasing the height of a tower crane's mast. There are two main methods:
18.Internal climbing (climbing cage): The crane climbs inside a hydraulic climbing cage installed around the mast, typically within a building under construction (central core).
20.External climbing: Uses a climbing section added to the base or top of the mast, with a hydraulic cylinder.
Internal Climbing — Detailed Procedure
Preparation Before Climbing
Before any climbing operation, the operator and supervisor must:
24.Verify that the load to be lifted is within the load chart limits for the current configuration
25.Position the jib in line with the prevailing wind direction or as per the manufacturer's instructions
26.Ensure the crane is in "climbing" mode (load limiter disabled or specifically adjusted)
27.Check the hydraulic oil level of the climbing system
28.Confirm that all tools and equipment are available (torque wrenches, cylinders, etc.)
29.Check weather conditions — climbing is prohibited if wind speed exceeds 72 km/h (20 m/s) per most manufacturers, but always consult the specific manual
Climbing Sequence
Step 1 — Crane Preparation:
Bring the jib to a 0° angle (horizontal)
Raise the hook to a safe height
Position the trolley (if a luffing jib crane) at the specified climbing position
Set down any load on the ground
Step 2 — Engaging the Climbing Cage:
Install the climbing cage around the mast, below the slewing platform
Verify that the hydraulic cylinders are correctly aligned with the climbing lugs on the mast
Engage the mechanical safety locks
Step 3 — Load Transfer:
Actuate the main cylinder to transfer the crane's weight from the mast to the cage
Verify that the mast is clear (no residual contact)
Open the cage gates to allow insertion of the new section
Step 4 — Section Insertion:
Lift the new mast section using the auxiliary crane or the climbing hoist
Insert it into the space created by the cylinder
Align the shear pins and bolts
Tighten the bolts to the specified torque (generally between 300 and 600 N·m depending on diameter)
Step 5 — Lowering and Locking:
Deactivate the hydraulic cylinder to lower the crane onto the new section
Verify full engagement of the locks
Permanently tighten all junction bolts
Remove the climbing cage
Climbing Calculations
Required Hydraulic Pressure
The hydraulic pressure required (P) for climbing is calculated:
P = (Total crane mass × 9.81) / (Piston area × Number of cylinders)
P = (120,000 × 9.81) / (0.0314 × 2) = 1,177,200 / 0.0628 = 18,745,223 Pa ≈ 18.7 MPa
Slab Capacity Verification
The pressure exerted on the slab (σ):
σ = Total crane weight / Support base area
σ = 1,177,200 N / 16 m² = 73,575 Pa = 73.6 kPa
This value must be compared to the allowable bearing capacity of the slab, typically specified in the engineering drawings.
Tying-In
Role of Tie-Ins
Tie-ins (or ties) connect the crane mast to the building structure to:
Transmit horizontal loads (wind, service loads)
Reduce the effective free-standing height of the mast
Increase the total achievable height
Control lateral deflections
Types of Tie-Ins
Type
Description
Typical Use
Rigid tie-in (collar)
Steel frame surrounding the mast, fixed to the structure
Reinforced concrete buildings
Articulated tie-in
Allows limited rotation
Steel structures
Tie-rod tie-in
Cables or bars tensioned between the mast and the structure
Large spans
Tie-In Spacing and Positioning
The maximum spacing between tie-ins is determined by:
Mast rigidity (section profile)
Local wind loads (per the National Building Code of Canada)
Manufacturer's recommendations
General rule: The first tie-in is placed at a height of 1.5 to 2 times the base width above the foundation, then every 20 to 30 metres (or per the manufacturer's specifications).
Tie-In Installation Procedure
81.Preparation: Verify that anchor inserts or plates were installed in the structure during concrete pouring (or check welded connections for steel structures)
82.Crane positioning: Orient the jib to facilitate access to the tie-in level
83.Frame installation: Secure the tie-in frame around the mast, ensuring the friction plates are in uniform contact
84.Structure connection: Bolt or weld the tie rods to the structure per the engineering drawings
85.Pre-tensioning: Apply the specified pre-tension to the tie rods (generally 10 to 20% of the maximum service load)
86.Verification: Check the mast alignment (typical tolerance: 1/500 of the height)
Loads on Tie-Ins
Tie-ins must resist:
Wind loads (dynamic pressure × projected area)
Service loads (overturning moments)
Seismic loads (in at-risk zones)
The wind load (F_w) is calculated per the NBCC:
F_w = q × C_e × C_g × C_p × A
Where:
q = reference dynamic pressure (varies by region)
C_e = exposure coefficient
C_g = gust coefficient
C_p = pressure coefficient
A = projected area
Dismantling
Dismantling Planning
Dismantling a tower crane is a high-risk operation that requires a written dismantling plan approved by an engineer. This plan must include:
103.The detailed sequence of operations
104.The loads at each step (verified against the load chart)
105.The location of the auxiliary crane (mobile or tower)
106.Exclusion zones and safety perimeters
107.Emergency procedures
108.Maximum weather conditions for each step
Dismantling Methods
Dismantling with a Mobile Crane
This is the most common method for tower cranes of moderate height (up to approximately 60 m). The mobile crane must have sufficient capacity to:
Dismantle the jib in sections
Remove the counter-jib and counterweights
Dismantle the mast in sections
Remove the slewing platform and mechanism
Critical calculation: The mobile crane must be able to reach the maximum height of the tower crane with a load corresponding to the weight of the heaviest section, at sufficient radius.
Dismantling with an Auxiliary Tower Crane (Derrick)
For high-rise towers, a small tower crane (or derrick) is installed on the slewing platform to dismantle the main crane in sections.
Dismantling by Reverse Climbing
The crane descends in stages using its own climbing mechanism, removing mast sections one by one from the base.
Typical Dismantling Sequence
122.Preparation:
Verify that all loads are removed from the hook
Position the jib in the dismantling direction
Install slings and restraint devices
126.Jib dismantling:
Dismantle jib sections from the tip toward the base
Lower each section with the auxiliary crane
Verify each section's weight against the load chart
130.Counter-jib dismantling:
Remove counterweights in stages (respecting the specified order)
Dismantle the counter-jib itself
133.Slewing platform dismantling:
Disconnect electrical and hydraulic cables
Remove the platform with the auxiliary crane
136.Mast dismantling:
Remove tie-ins progressively as you descend
Dismantle mast sections from top to bottom
Lower each section with the auxiliary crane
140.Base removal:
Dismantle the base and base counterweights
Clean up the site
Dismantling Calculations — Example
Assume a tower crane with a 50 m jib weighing 8,000 kg total, dismantled into 5 sections of 1,600 kg each. The dismantling mobile crane is positioned 20 m from the tower.
Capacity verification:
Heaviest section mass: 1,600 kg
Slings and accessories mass: 100 kg
Total load: 1,700 kg
Load moment: 1,700 kg × 20 m = 34,000 kg·m
The mobile crane must have a capacity of at least 34,000 kg·m at the 20 m radius, with a safety factor of 1.25 (per CSA standards) → required capacity: 42,500 kg·m.
Canadian Standards and Regulations
Applicable Standards
Standard
Application
**CSA Z248**
Tower Crane Code (primary standard)
**CSA Z150**
Mobile Crane Code (for auxiliary dismantling cranes)
**CSA S16**
Design of Steel Structures (for tie-ins)
**National Building Code of Canada (NBCC)**
Wind and seismic loads
**Canada Occupational Health and Safety Regulations (COHSR)**
Federal requirements for federally regulated worksites
**Canadian Electrical Code, Part I (CE Code)**
Electrical requirements for cranes (Rule 8-200 for grounding conductors)
Key CSA Z248 Requirements
Clause 4.2.1: Every tower crane must be designed, manufactured, and installed in accordance with the manufacturer's specifications and the requirements of the standard
Clause 6.3: Climbing operations must be supervised by a competent person
Clause 7.2: A written lift plan is required for any climbing, tying-in, or dismantling operation
Clause 9.1: Tie-ins must be designed by an engineer and installed per approved drawings
Clause 11.4: Pre-climb inspections must include verification of hydraulic cylinders, hoses, and mechanical locks
COHSR Requirements
Section 14.4: The employer must ensure that only trained and competent workers perform climbing and dismantling
Section 14.6: A record of all inspections and climbing operations must be maintained
Section 14.8: Weather conditions must be checked before any climbing or dismantling operation
Safety and Risk Management
Exclusion Zones
During climbing and dismantling, the following zones must be demarcated:
Tower fall radius (height × 0.5 minimum)
Jib rotation zone
Auxiliary crane working zone
Safe access and egress routes
Mandatory Personal Protective Equipment (PPE)
Safety helmet with chin strap
Safety harness with double lanyard (for work at height)
Steel-toe safety boots
Protective gloves
Safety glasses (for grinding and drilling)
Weather Limit Conditions
Operation
Maximum Wind Speed
Climbing
72 km/h (20 m/s)
Tying-in
50 km/h (14 m/s)
Dismantling
40 km/h (11 m/s)
Normal work
72 km/h (20 m/s) — automatic shutdown
These values are general references — always consult the manufacturer's manual and the supervisor's instructions.
Communication and Signals
During climbing and dismantling, communication must be:
By two-way radio (with prior channel verification)
By standardized hand signals (per CSA Z248)
In English or French, depending on the common language of the worksite
Common Pitfalls to Avoid
186.Ignoring the modified load chart during climbing: During climbing, the crane's capacity is reduced — often to 50% of normal capacity. Never lift a load during climbing.
187.Confusing overturning moment and load moment: The overturning moment includes the weight of the jib and counter-jib, not just the suspended load.
188.Forgetting to pre-tension tie rods: A tie-in without proper pre-tension can loosen under load and cause catastrophic failure.
189.Neglecting bolt re-torquing after the first load cycle: Mast junction bolts must be re-checked after the first hours of operation (typically 8 hours) and then at regular intervals.
190.Underestimating the wind effect on suspended mast sections: A suspended mast section acts like a sail — wind can cause it to rotate and collide with the structure.
191.Failing to verify slab or ground capacity under the dismantling mobile crane: The mobile crane exerts significant wheel loads that can exceed the soil bearing capacity.
192.Using damaged or uncertified slings: All slings must have a valid certification tag and be inspected before each use.
193.Forgetting to mechanically lock the climbing cylinder: The hydraulic cylinder must never be used as the sole support — mechanical locks must always be engaged.
194.Removing counterweights in the wrong order: The counterweight removal sequence is specified by the manufacturer to maintain stability — never improvise.
195.Working without a written lift plan: CSA Z248 requires a written plan for all climbing, tying-in, and dismantling operations — its absence is a regulatory violation.
Exam Tips
Memorize the limit values: Maximum wind speed for climbing (72 km/h), stability safety factor (1.5), alignment tolerance (1/500)
Understand moment calculations: Know how to calculate overturning moment and stabilizing moment
Know the standards: CSA Z248 is the primary standard — know its key clauses
Visualize the sequences: The exam may ask you to put the steps of a climb or dismantle in order
Pay attention to units: Calculations use the metric system (SI) — convert units correctly
Summary
Climbing increases the tower height by inserting new sections, either from the inside (climbing cage) or from the outside
Stability relies on the balance between the overturning moment and the stabilizing moment, with a minimum safety factor of 1.5
Tie-ins transmit horizontal loads to the structure and allow for increased total height — they must be designed by an engineer
Dismantling requires an approved written plan, a properly sized auxiliary crane, and a strict operational sequence
CSA Z248 is the primary standard governing tower cranes in Canada — it requires written plans, inspections, and competent supervision
Weather conditions limit operations: 72 km/h for climbing, 50 km/h for tying-in, 40 km/h for dismantling
Load calculations (hydraulic pressure, slab capacity, mobile crane capacity) are essential for safety and are part of the exam
Communication and exclusion zones are critical safety elements during all of these operations
Mastery of these procedures is essential not only to pass the Red Seal exam, but above all to ensure worker safety on construction sites. Every climbing, tying-in, or dismantling operation must be treated with the utmost seriousness, rigorously following written procedures and manufacturer's specifications.
