Efficiency - Continuous cast connections

Efficient building industry – continuous structures and casting

By Marko Medjeral

September, 28, 2021

Concrete speed can be requirement in acute need, such as public service buildings or economic reasons. Bringing too much raw materials to the site and building everything from scratch wastes material and time. Hiding part of construction process inside factories keeps sites neat and clean and fitting to the milieu, as concrete pouring phase is offset. Can sites be neat and construction fast even if concrete is poured on site? Answer is naturally yes, here are few points to back this up.

Mechanical form or precast for long and high structure

Precast technology has helped keep messy industry and cozy urban milieu apart. There are however other ways to tidy up building process, especially, block-building can be difficult to lift conventionally when elements are especially large or complicated by shape.

Symmetricity and continuous cross-section can make bridge road and tower design and construction efficient. Regular shape in building helps also distributing loads more evenly and avoid complex solutions bracing or stiffening structures or joints locally. Mechanized construction can be applied locally or partially in a more complicated architectural designs (due environment etc.) or extremely long constructions, such as high-way bridges, for efficiency, easier process, and time-savings. (elevated road building, Figure 6)

Figure 1.Pylon slipform, precast bridge beam and shell casting

Especially tall (high-rise) buildings are subject to high sideways wind or seismic load, as they are many times as high as wide. This causes high flexure and shear over the height of the building, which is solved typically by building stiff “core”(-s) and wall-like shear stiff elements, leaving column-beam frame a supporting role transferring a portion of vertical loads to foundation.

If vertical elements lateral stability is taken care by monolithic or bracing structures, more flexibility is allowed in joints and connections. Continuous and high structures casting has attained reasonable speed using mechanical casting forms, that climb in various ways (Figure 2, example product). A comparison of different core forming options can be seen in Figure 3.

Figure 2. Climbing or sliding formwork allow limited discontinuity, but can be inventively allow even casting to shape

Hydraulic auto climbing systems can adapt to changing shape also (leftmost)

Figure 3. Main types of climbing formwork in comparison table (fib 73 bulletin – Tall buildings, p.49)

Horizontal frame member needs connection parts and recesses, that can pose a challenge of continuous core casting. Post-installed hidden corbels and threaded anchor bars allow undisrupted core casting and fast connection to slabs, either in-situ or precast (Figure 4).

Figure 4. Hidden corbels and recess-board anchors enable uninterrupted (smooth) core casting with beam or slab connections

Flat slabs make optimizes building space, benefit installations and consumption during usage. Apart from precast slim floors. It remains a practical challenge to lighten the floors. However, this has been addressed by installation techniques, such as tensioned bubble deck, utilizing simultaneous various types of sophisticated design, formwork, and reinforcement (Figure 5).

Figure 5. Bubble-deck eliminates ineffective concrete from deadweight, its capacity can be enhanced with post-tensioning and shear studs (on fast reinforcing rails) at critical zones, such as column tops, and lastly formwork systems make construction fast

Precast and cast-in situ techniques can work well together to accomplish optimized and beautiful modern constructions. The challenge is to manage various solutions and fit them together. This requires designers and constructors to familiarize solutions and understand their principles in advance.