The spreader bar is used for lifting and placing ACB mats. ACB mats can weigh 29,000 pounds on the high end and 4,200 pounds on the low end. Because of the wide spectrum in mat weight, the appropriate bar must be specified for each project. In some cases multiple spreader bars may be required to unload and place, simultaneously.
It is very important to inspect the spreader bar prior to lifting any loads. Diagram 1 below indicates what areas should be checked.
- Lifting Block
- Bridle Quality (8 on each end)
- Swivel and Release Mechanism
- Extension Bars
- Extension Pins
- Structural Frame Supports
- Lifting Hooks**
- Guide Ropes
|Lx = Mat Length Capability of the Bar:|
|Weight of Bar|
** A "jumper" may also be required when lifting shorter mats. This device simply attaches to the existing lift hook and extends the length for shorter mats.
Mats can only be lifted one (1) at a time. The reasons for this are:
- Lifting more than one mat with the bar places stresses on the concrete and causes cracking and breaking of the block.
- The hardware used to assemble the mats become overstressed when trying to lift more than one mat.
- The spreader bar itself is designed for handling single mats.
Revetment mats should be lifted in a manor that will minimize the bowing of the mat. A properly adjusted spreader bar, and/or properly sized jumpers (if required) are necessary to maintain as flat a profile as possible when lifting the mats. Minimizing the bowing of the mats during lifting reduces the stress on the blocks that may cause cracking, breaking, and ultimate failure.
When lifting mats, all personnel should be well clear of the underside of the mat. Only those personnel holding the guide ropes at the four corners should be in the area.
When using a "friction band" type crane, the operator must take caution not to "snap" the load with the brake when lowering it into position. The high inertia forces generated by "snapping" the load can be detrimental to the wire ropes, concrete masonry units, spreader bar, and the crane itself.
Spreader Bar | Subgrade Preparation | Geotextile Installation | Loading and Unloading Cabled Mattresses
Placement of ACBs | Cabling, Anchoring and Crimping | Grouting | Bibliography