▌ APPLICATION NOTE · OCTOBER 2026 · COUNTERWEIGHT BLOCKS Counterweight Blocks: Matching the Set to Jib Length and the Load Chart Counterweight is the quiet partner of the jib. The load on the working arm creates a moment that the mast must resist, and the counterweights on the counter-jib create an opposing moment that balances it. Change the jib length, and the correct counterweight changes with it. Fit the wrong set, and the crane’s load chart is no longer the one in the manual. This note explains how counterweight is matched to a crane, how blocks are made and secured, and what should be checked before erection. The crane maker’s load chart and manual govern the correct set; this note explains why that set matters.
01 THE BALANCE BEHIND THE LOAD CHART Every tower crane is designed around a balance between the jib and the counter-jib. The counterweights create a moment that offsets the load moment, reducing the bending in the mast and letting the crane lift its rated load across the working radius. The load chart that ships with the crane assumes a specific counterweight set for a specific jib length. That is why counterweight is not a matter of adding a little more for safety. More counterweight is not automatically better; it is simply a different loading on the mast and the slewing unit, and it may put the crane outside its design assumptions. ▌ BALANCE, NOT BALLAST Counterweight offsets load moment; it is a design value, not a safety margin. ▌ THE CHART ASSUMES A SET The load chart is only valid for the specified counterweight and jib length. ▌ MORE IS NOT SAFER Adding counterweight changes the loading on the mast and slewing unit. 02 MATCHING THE SET TO THE CRANE The correct counterweight set is defined by the crane maker for each jib length and configuration. It may be a number of blocks of a standard size, a specific total mass or a particular arrangement on the counter-jib platform. The manual and load chart show the combination. When a crane is re-configured, the counterweight should be re-checked at the same time. A crane that has had sections removed from its jib but kept its old counterweight is now over-counterweighted, and one that has been lengthened with the old set is under-counterweighted. Both are wrong. ▌ USE THE MAKER’S SET Counterweight is defined per jib length and configuration. ▌ RE-CHECK ON RE-CONFIGURATION Re-configuring the jib means re-checking the counterweight. ▌ BOTH ERRORS EXIST Too little and too much counterweight are both incorrect. 03 MAKING AND SECURING THE BLOCKS Counterweight blocks are usually cast concrete or cast iron, with lifting eyes and locating slots. They are stacked on the counter-jib platform in the arrangement shown in the manual and secured against movement during slewing. Lifting eyes are for handling during erection and dismantling, not for lifting the crane. Securing matters because the blocks are loaded dynamically as the crane slews and the jib moves. An unsecured block can shift, and a shift changes the balance and can damage the platform. The manual will show the securing arrangement. ▌ CAST CONCRETE OR IRON Blocks have lifting eyes and locating slots for correct stacking. ▌ SECURE AGAINST MOVEMENT Blocks must be restrained so they cannot shift during slewing. ▌ EYES ARE FOR HANDLING Lifting eyes are for erection handling, not for lifting the crane.
04 INSPECTION BEFORE ERECTION Before each erection, the counterweight set should be checked against the load chart: the right number of blocks, the right size and the correct arrangement. Blocks should be inspected for cracks, damaged lifting eyes and corrosion, and the platform and its securing points should be checked. A simple record of the counterweight fitted is useful, especially where a crane is reconfigured or moved between sites. It makes it obvious when the set no longer matches the machine. ▌ CHECK AGAINST THE CHART Confirm number, size and arrangement before every erection. ▌ INSPECT THE BLOCKS Look for cracks, damaged eyes and corrosion. ▌ RECORD THE SET A record of the fitted counterweight shows when it no longer matches. 05 WHAT GOES WRONG The most common error is a set that was correct for a previous configuration. The second is a missing block after a dismantle and re-erect, because nobody counted. The third is an improvised substitute, such as a block of a different size or a piece of site material, which changes the balance and may not be structurally suitable. None of these errors is dramatic at the time. They show up later as unexpected stress, a crane that behaves oddly under load or a load chart that no longer matches the machine. ▌ OLD CONFIGURATION A set left over from a previous jib length is a common error. ▌ MISSING BLOCKS Count the set after every dismantle and re-erect. ▌ NO SUBSTITUTES Improvised blocks change the balance and may not be structurally suitable. PROCUREMENT IMPACT ● Order counterweight to the crane maker’s jib length and configuration. ● Confirm the number, size and total mass of the set in writing. ● Specify the securing arrangement and lifting eyes as part of the set. ● Include a counterweight record sheet with the crane documentation. ● Ask for the load chart to be re-issued whenever the configuration changes. WHAT TO WATCH ● Watch for a set left over from a previous jib length. ● Watch the block count after every dismantle and re-erect. ● Watch improvised substitutes, which change balance and may not be suitable. ● Watch block condition, especially lifting eyes and cracks. ● Watch the load chart, which is only valid with the specified counterweight. ABOUT ZN Industrial (Shandong Zhinuo) designs and manufactures crane safety monitoring systems, positioning systems and mechanical auxiliary handling equipment for overseas construction, industrial and steel markets. Standards and regulations vary by market — local rules still govern your site. ▌ CONTACT shandongzhinuo@outlook.com +86 176 6371 0314 · en.znaqkj.com SOURCES · crane maker’s load chart and manual · EN 14439 · ISO 12480-1 |
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Counterweight Blocks: Matching the Set to Jib Length and the Load Chart
Counterweights balance the jib, and the wrong set changes the load chart. This note explains how counterweight is matched to jib length, how blocks are secured and what to check before erection.
