Introduction
The interaction of steel and reinforced concrete parts is critical in defining the structural behavior of moment-resisting frames. The joints in reinforced concrete constructions play a significant function in transmitting loads to the entire structure. Reinforced concrete structures use a variety of connections, including cast-in-place, dowel, mechanical connectors, and epoxy-bonding connections. When designing resistant moment frames out of reinforced concrete, it is essential to pick a joint connector that can withstand the loads placed on it without fail. There are benefits to using each joint connector type, but drawbacks must be weighed carefully before beginning construction. Based on the study of six research publications, this paper will analyze the benefits and drawbacks of these various joint connectors for reinforced concrete-resistant moment frames.
Cast-in-Place Connection
Advantages
One of the critical benefits of cast-in-place connection, as stated by Han et al. (2018), is that it creates a robust and rigid connection between precast members, which can withstand significant amounts of seismic stress. This method may result in better structural performance since the connections can be fine-tuned for optimal alignment and fit (Han et al., 2018). Cast-in-place connections also require less specialized materials and equipment, potentially cheaper than other connection methods like welding or bolting.
Disadvantages
Cast-in-place connections have their benefits, but they also have their drawbacks. Potential building delays due to concrete curing issues are a serious concern (Han et al., 2018). Delays in the overall building timeline can be both expensive and inconvenient. Quality control of the poured concrete is another concern, especially on a massive building site. Casting in place also requires a competent labor force, which can drive up wages and, thus, the project’s overall cost. While cast-in-place connections for reinforced concrete resisting moment frames have benefits like high strength and longevity, drawbacks include requiring a specialized labor force, construction delays, and quality control concerns. Cast-in-place connections are an option for building projects, but they require careful consideration of the abovementioned concerns.
Dowel Connection
Advantages
Joining steel beams to rebar-reinforced concrete columns with dowels is cost-effective and efficient (Vidjeapriya et al., 2014). They provide the connection with increased rigidity and strength with nothing in the way of specialized labor or tools, and they are also reasonably simple to build. Mechanical connections are made between precast concrete pieces using dowels in precast concrete construction, where dowel elements are kept apart yet joined together using jointing features such as welded or bolted plates. Dowel connections are a dependable and effective way to attach steel beams to columns made of reinforced concrete, and mechanical connections made with dowels are appropriate for precast concrete buildings. Dowel connections can be a valuable alternative for many projects because of their simple construction and inexpensive cost.
Disadvantages
Dowel connections have certain benefits but also have some disadvantages. Compared to other connections, they may provide less protection against earthquake and wind forces (Vidjeapriya et al., 2014). If dowel connections are not appropriately sealed, rust is another possibility to watch out for. When dowel connections are subjected to dynamic loading, especially in highly seismic regions, their behavior can degrade due to poor connections between the dowel connection elements and the lateral load-resisting systems. Alcocer et al. (2002) emphasize the importance of dowel connections in precast concrete construction, arguing that a deeper understanding of their behavior under dynamic loading circumstances is necessary to guarantee the reliability of precast concrete buildings in seismically active regions.
Mechanical Connectors
In order to join disparate building components, mechanical connections are commonly used. Bolts, screws, and other fasteners are typical examples of hardware used to make such connections. Despite the many benefits that mechanical connections provide, they have their own set of drawbacks.
Advantages
The robustness of mechanical connections is one of their main advantages. These connections can support heavy loads and provide a stable interaction among elements when properly planned and executed. Moreover, mechanical connections are typically straightforward to install and can be completed, saving both money and time on construction projects (Valikhani et al., 2021). Valikhani and coworkers (2012). They also have the advantage of being quickly demolished, allowing their use as impromptu shelters.
Disadvantages
Nevertheless, mechanical connections have their drawbacks. One of the biggest problems is that they need to be installed precisely right for them to work. The connection might fail due to improper alignment or torque, posing a safety risk and requiring expensive repairs. Valikhani et al. (2021) state that with time, corrosion and other forms of deterioration can weaken the binding between components where mechanical connections are used.
The influence of mechanical connectors on the shear strength of the interface between the concrete substrate and the ultra-high-performance concrete was studied experimentally and numerically by Valikhani et al. (2021). (UHPC). The shear strength of the two materials was found to be significantly improved by using mechanical connectors. However, the scientists emphasized that optimal outcomes required the connectors to be well-designed and installed (Ghayeb et al., 2020). They devised a design equation to guarantee the connectors’ proper installation and load-bearing capacity.
Epoxy-Bonding Connection
Advantages
Epoxy-bonding is a standard method of structural connection due to its many benefits over using screws or bolts. Because the bonding method produces such a robust and long-lasting joint, it is well-suited for use in structures like skyscrapers and bridges (Bouazaoui et al., 2008). There is less danger of fatigue failure since stress is distributed uniformly across the bonded region. Because the epoxy resin is so resistant to the elements, its connections are durable even in severe weather.
Disadvantages
Epoxy bonding has many benefits, but its lack of ductility can lead to brittle and unexpected failure. When designing buildings to withstand earthquakes, the capacity to deform and absorb energy is crucial to their success (Bouazaoui et al., 2008). Long-term bond strength loss owing to environmental conditions is another concern. Epoxy-bonded connections are durable, but the installation process can be difficult and time-consuming, which adds to the overall cost of a project and increases the likelihood of mistakes being made Although epoxy-bonded connections for reinforced concrete-resistant moment frames provide benefits like high durability and strength, drawbacks such a lack of ductility and the possibility of long-term bond strength loss owing to environmental variables must be considered. The benefits of this connection must be evaluated against the time and effort required for installation, which can drive up costs and the possibility of making mistakes.
Conclusion
Many considerations, including design criteria, cost, seismic performance, and corrosion resistance, influence the selection of joint connections for moment-resisting frames in reinforced concrete structures. Dowel connections are effective and affordable but have limitations in sustaining earthquake and wind loads. In contrast, cast-in-place connections are commonly recognized due to their reliability, safety, and cost-effectiveness. While mechanical connectors excel in seismic performance and corrosion resistance, they are prone to fatigue failure. Epoxy-bonding connections are solid and long-lasting but lack ductility and can be difficult to install.
Available research suggests that while choosing a joint connection for moment-resisting frames in reinforced concrete buildings, engineers and builders should consider unique design requirements, seismic performance, and environmental considerations. Dowel connections, commonly used in seismic regions, require more study to understand their behavior under dynamic stress circumstances fully. Mechanical connectors can cause problems like fatigue failure if not designed and placed correctly. As a final note, due to their lack of ductility and potential for long-term loss of bond strength, epoxy-bonding connections should be used with caution in seismic design.
References
Alcocer, S. M., Carranza, R., Perez-Navarrete, D., & Martinez, R. (2002). Seismic tests of beam-to-column connections in a precast concrete frame. PCI journal, 47(3), 70-89. https://www.pci.org/PCI_Docs/Publications/PCI%20Journal/2002/May-June/Seismic%20Tests%20of%20Beam-to-Column%20Connections%20in%20a%20Precast%20Concrete%20Frame.pdf
Bouazaoui, L., Jurkiewiez, B., Delmas, Y., & Li, A. (2008). Static behavior of a full-scale steel–concrete beam with epoxy-bonding connection. Engineering Structures, 30(7), 1981-1990. https://doi.org/10.1016/j.engstruct.2007.12.018
Ghayeb, H. H., Razak, H. A., & Sulong, N. R. (2020). Performance of dowel beam-to-column connections for precast concrete systems under seismic loads: A review. Construction and Building Materials, 237, 117582. https://doi.org/10.1016/j.conbuildmat.2019.117582
Han, W., Zhao, Z., Qian, J., Cui, Y., & Liu, S. (2018). Seismic behavior of precast columns with large-spacing and high-strength longitudinal rebars spliced by epoxy mortar-filled threaded couplers. Engineering Structures, 176, 349-360. https://doi.org/10.1016/j.engstruct.2018.09.007
Valikhani, A., Jahromi, A. J., Mantawy, I. M., & Azizinamini, A. (2021). Effect of mechanical connectors on interface shear strength between concrete substrates and UHPC: Experimental and numerical studies and proposed design equation. Construction and Building Materials, 267, 120587. https://doi.org/10.1016/j.conbuildmat.2020.120587
Vidjeapriya, R., Vasanthalakshmi, V., & Jaya, K. P. (2014). Performance of exterior precast concrete beam-column dowel connections under cyclic loading. International Journal of Civil Engineering, 12(1), 82-95. http://ijce.iust.ac.ir/article-1-708-en.html
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