Methods of Placing Concrete in Multi-Story Buildings

Multistory Tilt-Up Placement

• Tilt-up placement is most common for single-story structures but has enjoyed increasing popularity in construction of low-rise, multistory buildings as well. In this technique, workers pour the concrete on the horizontal, allowing the concrete to set and then lifting the wall with a crane and tilting it into place. Buildings up to three stories high are often assembled with single, full-height panels, whereas taller buildings may require stacked panels with horizontal panel joints a few feet above each supported floor.

Precast

• Precast concrete panels are poured and cast at the factory or production plant rather than on-site. This approach helps reduce cost while enabling engineers to precisely control the conditions under which the concrete is cured, achieving better results. The panels are then assembled on site. Precast construction is most appropriate in cases where the same panel design repeats or is reused throughout the structure.

Placement Boom

• Concrete can be pumped during work on a multistory building, as it would be elsewhere, although several special concerns apply. Often, the type pump used is called a placement boom, which is mounted or lifted by crane. The concrete should always be dropped along a true vertical line and free fall for a distance no greater than 4 feet. In cases where larger distances are involved, the concrete is dropped into a hopper with a flexible drop chute running down to the bottom of the form.

Considerations

• When pumping or pouring concrete rather than working with precast materials, the concrete is held in place by a structure called a form while it hardens. The form is removed afterwards. If the form is deep and narrow, the concrete’s consistency varies with higher water content towards the bottom and lower towards the top. Compacting the concrete with a vibrator is helpful, but the concrete should not be vibrated too long, nor should the vibrator be used to move concrete in a horizontal direction.