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In this article, we will discuss precast walls.
|The precast concrete walls possess higher in-plane stiffness adding higher stability for the precast buildings. They gain larger in-plane stiffness due to the addition of flexural and shear stiffness.
Depending on the geometry, the precast walls can be made short or slender. When assuming slender walls for construction, it is essential to verify them for global in-plane buckling.
These are due to the flexibility in foundations or other second-order effects. The buckling due to out-of-plane stiffness is neglected. But the verification for the same has to be carried out for at least a single-story height.
The slender precast concrete walls control their flexural stiffness and they are called shear walls. This is because they have a higher ability to withstand horizontal loads.
1. Precast Wall
A suitable interaction between the precast floors and the stabilizing shear wall is very much essential to advance the whole structural behavior and stabilization of the structure. Suitable interaction will be facilitated only if the connection between the floors and the precast walls is properly connected.
The interaction of wall elements assists in carrying diaphragm action enabling the transfer to shear and tensile joints across the joints. This shows the necessity of proper joint design.
The strut and tie models are employed to understand the equilibrium system of the overall arrangement. The joint design is carried out depending on the desired structural behavior. The precast concrete walls are put through higher axial loads and stresses when compared to precast floor diaphragms. An essential property of shear walls is stiffness.
2. Structural Actions of Precast Walls
Any evolution of cracks in the wall will affect the stiffness of the wall structure. Hence, the design has to be carried out in such a way that no tensile stresses are allowed in the horizontal joints of the wall or to verify that only lesser tensile stress will take place. Having more vertical loads on the walls is the most economical solution to decrease the tensile stresses on the walls.
The parts are best suggested to be attached to the foundation, to the adjacent floor diaphragms as well as to each other in order to have a good interaction. The walls employed in the precast shafts can be designed like an individual shear wall or they can be attached along the vertical joints.
This will hence make a closed or an open cross-section. This will form the shaft work as a single and stabilized system. The incorporation of the interaction of walls in the system requires attachment along the vertical joints. This is to resist the shear forces.
3. Connection Between the Precast Wall Units
The most common selection of connections is welding and concrete-filled joints. Another connection process is by the interlock elements. These interlocking bonds tend to supply higher shear capacity.
There is a deformation of connection in the vertical joint when these are loaded in shear. This is mainly dependent on the stress versus slip characteristics. This deformation will directly influence the whole structural response.
Depending on how good the connections are to withstand the shear deformation, the wall component interaction can be split into partial or full.
There are mainly two connections available for the precast concrete walls:
a. Cast in situ concrete joints
b. Welded connection
a. Cast-in-Situ Concrete Joints
The cast in situ concrete connection has transverse reinforcement which provides continuous shear transfer along the joint. The concrete poured can be either plain or castellated.
There can be well-distributed or concentrated transverse reinforcement in the horizontal joints. These are stiffer and stronger compared to welded connections when their difficulty to employ at corners is neglected.
b. Welded Connection
The welded connection suffers from the intermittent transfer of shear force. They come into action once they are mounted together as a stabilizing system. These connection demand fire resistance, higher durability, and proper finish. Painting or grouting will help as protection for welded connections.
These are less stiff compared to concrete or interlocking connections. Employing standing multi-story wall elements or laying story height wall elements assist in establishing the facade elements. These components can hold vertical loads or can act as nonbearing cladding.
Both the above connection can be either prepared as a shear wall or not as a shear wall. To work as a shear wall, the connection has to be connected in such a way as to move the shear force. If no moving has to be done, just a non-structural filling must be done as a way of climatic resistance.
When a structure consists, of both stabilizing and unstabilizing walls, a sufficient study of the stiffness of the building has to be researched. The attraction of load by an unstabilizing wall will provide unfavorable outputs and structural behavior.
4. Advantages of Precast Walls
The advantages of precast walls are as follows:
b. Flexibility in use
c. More Durable than real masonry
d. Optimum use of material
e. Protection of environment
5. Disadvantages of Precast Walls
The disadvantages of precast walls are as follows:
a. Very heavy members
b. Connections may be difficult.
c. Cranes are required to lift concrete panels
Read Also: Road Lines
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