Pre-cast Concrete Walls
Generally pre-cast concrete walls are used to stabilize the pre-cast building. Pre-cast concrete walls have large in plane stiffness obtained by a combination of shear and flexure stiffness. Pre-cast concrete walls can be short or slender depending upon their geometry (Qian et al., 2011). Buckling should be checked of slender shear walls due to second order effects and flexibility of the foundation. In Slender shear walls buckling out of plane buckling is neglect so it must be checked within a story height(Jiaru et al., 2011). If in slender walls flexural stiffness dominates then such walls are called shear walls and they can resist horizontal loads. In the overall building the structural behavior and the stabilization between pre-cast floors and the shear walls is necessary. In pre-cast concrete walls diaphragm action is obtained by interaction of wall elements and the transfer of tensile and shear force across the joint is important(Sritharan et al., 2015). The most important factor in pre-cast shear wall is Stiffness. Stiffness is decreased if the cracks develop in the horizontal joints. Practically pre-cast shear walls are designed in that manner that tensile stresses are avoid in horizontal joints and only small tensile stresses are taken. It is also economical that all vertical loads must be taken shear walls to decrease tensile stresses. In the structure to have a good interaction of wall elements, all the elements must be connected to the foundation and the adjacent floors(Lowak et al., 2016). Pre-cast concrete walls have three layers first having 40mm to 60mm thick reinforcement constructed at pre-casting plant. This reinforcement is also known as leaves. The cavity in the leaves or reinforcement is filled with situ concrete. Criteria is that cavity is that cavity must be 100mm wide and must not be less than 70mm. In structures pre-cast concrete wall elements are used to construct impermeable concrete basement in groundwater with pressure head of six meter. Pre-cast concrete is economical in construction (Li et al., 2020). Pre-cast concrete walls are constructed concrete by using mold like casting concrete in wall mold or form which then cured in a controlled environment. After this process walls are transported to construction site and lifted into place. The basic purpose of pre-cast concrete walls is to speed up the construction. Concrete is used in construction from hundreds of years and it’s proven that a good building material(Scott III& Scott, 2019). Pre-cast concrete is used in every project now days like public buildings, infrastructure, commercial projects and residential projects. Pre-cast concrete has many benefits during and after the constructions. Pre-cast concrete walls are constructed in controlled conditions and quality and specification issues are deal with accuracy(Shumate, 2020). In construction of pre-cast concrete fabrication process do not depends upon weather but it mostly depends upon the skills and expertise of the labor. On the site of construction pre-cast members are quicker and simpler. There is no need of specialized skills for scaffolding. In big project use of pre-cast components reduce the cost of project and increased its speed. In pre-cast construction other activities are not disturbed such as electrician work, electricians can be hired just after erection and electrician don’t have to wait for curing(Sánchez-Roldán et al., 2016). Decorative activities can also be applied without waiting for curing. Pre-cast concrete is also an energy efficient material, Concrete walls absorb the heat during the warm day and it releases it during the night. Pre-cast concrete is good in terms of thermal mass and fire resistance. Pre-cast concrete is increasing its ability day-by-day, comparing to other materials it transmits WIFI signals more(Ahmed et al., 2017). So it is essential to use in educational and commercial projects and now pre-cast concrete is becoming first choice material for schools and colleges.
There many types of pre-cast concrete walls such as
1.1 Curtain Walls
Curtain walls are the type of pre-cast concrete walls mostly used for building envelopes. They are basically Non-load bearing walls used to oppose the wind and encase the space (Peng, Qian& Wang, 2016).
1.2 Load bearing Walls
This type of pre-cast concrete walls is used to oppose and exchange loads from different components and thistype of walls are not removed without influencing the quality of the building (Qian et al., 2011).
1.3 Shear Walls
Shear walls are mostly used in seismic buildings this type of pre-cast concrete walls is used to give parallel load opposing framework when joined with floor development (Jiaru et al., 2011).
Type of Joints
Type of Joints in Pre-cast concrete Walls
2.1 Bolted Connection
In fastest erection operation, bolted connections are the best and simplified. In bolted connection final alignment and adjustment can be done later without tying of the crane(Sritharan et al., 2015).But in bolted connections material should be according to designer and erection according to drawings.
2.2 Welded Connections
In pre-cast concrete construction mostly welded connections are used because welded connections are common and typical in the erection of pre-cast concrete. Welded connections are structurally efficient and adjusted according to field(Lowak et al., 2016). Welded connection undergoes the transfer of shear force. Welded connections come into action when they are mounted together a stabilizing system. This connection needs the fire resistance, higher durability and proper finish. To act as a shear wall the connection should be joined in that way to transfer shear force.
2.3 Dowel/Anchor Bolt Connection
In this type of connection strength of dowels in shear or tension depends upon the diameter of dowel, dowel length and the bond developed (Li et al., 2020).
Pre-cast construction is the modern type construction having many benefits. Pre-cast construction is efficient because of its insulation and energy efficiency. Basically pre-cast construction requires less labor to install. Simply walls are constructed at factory and transported and installed. There is no worry of material storage, preparing of concrete on site and worrying about the climate conditions. In brick construction or wet construction everything is to be kept in mind about the storage of material, climate change, workability of concrete, curing and all other operations are suspended till the curing of concrete. Many times it occurs that proper strength is not achieved and cracks appear on the wall. On other side pre-cast wall are constructed under controlled atmosphere so any worries about the workability, curing of concrete, handling of concrete and pre-cast construction is good in durability. Pre-cast concrete walls are good insulation and having less heat conduction. Pre-cast concrete walls go under quality control process. Pre-cast concrete walls require less maintenance and also decorate a wall with texture, colors and shapes. Pre-cast concrete construction is also fast construction comparison to brick or masonry construction and it requires less time for completion of project. If a contractor is selecting on site concrete poured walls construction than its having many disadvantages. The main disadvantage of on-site concrete poured walls is that quality is compromised. Climate, concrete mixture and skill of the pour technician also affect the quality of wall and without controlled climate it is impossible to improve quality. Other disadvantage of on-site concrete wall is that reinforcement is typically not included in on site poured concrete wall. During the cold weather ‘cold seem’ occur which cause crack in wall. On site poured concrete wall requires more time to complete and due to bad weather project is delayed also. If material is placed outside like concrete and rain occurs then there are chances of loss and project over runs. There are some benefits of poured concrete also like high density and no joints. Due to high density it has high compressive strength. But comparing all construction method pre-cast concrete construction is best and efficient. Pre-cast concrete construction require less labors and less maintenance. All the site expenses like storage cost, handling cost and labors are saved. Due to pre-cast completion time of project is reduced and cost efficient also.