Research Paper Example on Beam-Column Joint Function

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1787 words
Sewanee University of the South
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Research paper
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According to Uma and Prasad (1996), the beam column joint operates as the most critical region in an armoured concrete moment resisting bar. This joint is usually exposed to enormous forces when a given structure is under extreme ground trembling and its overall behavior has a considerable impact on the overall structural reaction(Li & Kulkarni, 2010). The assumption of the overall and sustainable rigidity of joints fails to put into consideration the impact of excessive shear forces formed in the joint. This failure in shear is naturally fragile and an often unacceptablestructural behaviorparticularly during the onset of seismic tremors. The onset of seismic actions causes the beam-column joints to function in a manner deemed so unique in ensuring the continuous stability of the structure (Uma & Jain, 2006).

According to Hwang and Lee (2002), the overall stability of the structure originates from the ductility of the members while the secondone is attained through continuous inelastic revolutions. Inelastic rotations usually distribute over definite regions referred to as plastic hinges in the reinforced concrete members. The actual properties of the material usually exceed the elastic range during inelastic deformations causing damages in these regions (Walker, Yeargin, Lehman, & Stanton, 2012). Hence damages in form of plastic hinges occur in beams as opposed to columns in the seismic damages. The beam yielding mechanism is an attribute of the strong-column but weak-beam behavior whereby the obligated inelastic rotational demands are attained through appropriate beam detailing practices. Hence a structure in this behavior mode will automatically attain the expected inelastic response and ductility(Li & Kulkarni, 2010).

Types of Beam-Column Joint

Uma and Prasad (1996) define a beam-column joint as the typical part of the column found in the depth of the innermost beam that edges into the primary column. A frame in rotation displays usually demonstrates three different forms of beam-column joints at any given time. These joints include interior, exterior, and the corner joint.

Interior Joint

According to Li and Kulkarni (2010), interior joints are formed when four different beams edge into the perpendicular faces of a given column. Here, the shear forces in a frame going persistently through the joint often change from compression to tension resulting in a push-pull impact which causes a severe demand on the strength of the resisting bonds while necessitating sufficient development length within the joint in action (Uma & Jain, 2006). This development length must meet the conditions for compression with tension forces present in the same bar. Inadequate development length coupled with the distribution of forces in the splitting bar may crack into the joint core leading to the sliding of bars within the joint. This slippage phenomenon takes place when the bond responsible for limiting the shear forces is overpowered in the existing development length (Park & Milburn, 2015).

Exterior Joint

Uma and Jain (2006) aver that an exterior joint occurs when one ray extends into the perpendicular face of a column as two more but different planes edge into the column in the vertical direction. In this case, the framing of the beam and the verticalstrengthening into the column results in the termination of extension that may occur in the joint core. The deterioration of the bond instigated at the column face as a result of splitting cracks and yield penetration often continues towards the joint core after a little a few cycles of inflexible loading (Uma & Prasad, 1996).

Benavent-Climent (2007) adds that continuous loading results in the exacerbation of the situation coupled with a complete loss of bond up to the instigation of the portion of the bar may occur. The vertical reinforcement bar often gets pulled out as a result of continuous bond deterioration when terminated in a straight direction. The failure of the longitudinal bars of a given beam to pull out leads to complete loss of the strength of the beam to flex. This type of failure is usually intolerable at any given stage of bar extension. Thus appropriate anchorage of the longitudinal reinforcement bars of the beam within the joint core is extremely critical (Li and Kulkarni, 2010).

However, the failure of the bars to pull out in exterior joints can be stopped through the continuous installation of hooks or through the institutionalization of some positive anchorage (Benavent-Climent, Cahis, and Zahran, 2009). Hooks play a critical role in the provision of sufficient support for the extending beam especially when furnished with continuous extension of the tail of the bar and sufficient horizontal development length. This development length is often considered operational from the critical section beyond the zone of yield penetration due to the probability of the yield infiltration into the joint core (Walker, Yeargin, Lehman, & Stanton, 2012).

Corner Joint

Park &Mosalam (2013) asserts that a corner joint is created through the extension of beams into neighboring vertical planes of a column. The first type of corner joint is referred to as the floor joint usually experience the extension of different columns above the joint. Conversely, the second type of a corner joint is referred to as the roof or the knee joint does not experience the extension of the columns above the joint (Park & Milburn, 2015; Moehle&Mahin, 2011). The bond requirements of different longitudinal bars of beams often resemble those in an exterior joint despite the fact that there may are no unique code of requirements associated with bond for the knee joints in the case of a corner joint. Nonetheless, the functioning of these joints is considerably impacted by shear transverse cracks (Benavent-Climent, Cahis, and Zahran, 2009).

Difference of requirement between Hong Kong and New Zealand

There are mild differences of requirements in Hong Kong and New Zealand code of practices. The first code of practice in Hong Kong was formulated in 1987 before a comprehensive code was developed in 2004 and finally, the latest code produced in 2013 (Li, Lam, Cheng, Wu, & Wang, 2015 a). However, the New Zealand code of practice is similar to that of Australia and U.S and details all the appropriate requirements and guidelines that engineers have to follow when putting up a structure to grand stability and overall strengthening of the beam-column joint.

The current Hong Kong code of practice relied on the New Zealands while deriving the dynamic impacts of wind loads(Beres, El-Borgi, White, & Gergely, 2012). The Zealands code of practice was developed and published by the New Zealand Concrete Design Committee 1995 and can be summarized as NZS 3101: 1995. Hong Kongs wind code also made reference to the Code of Practice for Dead and Imposed Loads for Buildings 2011 for the determination of different characteristics of gravity loads for design. However, in Hong Kong, there is need for the designer to check and ascertain for the newly installed fire engines for the overall project of new builds, as stipulated by FSD (Hwang & Lee, 2002).

According to Wright and McCabe (2017), the 2013 code places emphasis on design loads for robustness which resemble the requirements outlined in the BS8110 Part 2 requirements. The requirements entail designing of the structure against a theoretical horizontal load amounting to 1.5% of the attributive dead weight at each and every level of the floor alongside vehicular impact loads. The small theoretical loads can be covered by wind loads when applied to the structure. Both New Zealand and Hong Kong calls for strict compliance and adherence to the existing code of practice and have put in place bodies responsible for implementation (Hwang & Lee, 2002).

Methods of strengthening Beam-Column Joint

Kim and LaFave (2008) ascertain that most of the joint in structures designed and built before the establishment of the contemporary design requirements need to be studied and evaluated in details to establish their effectiveness to develop appropriate techniques of connection repair and strengthening. This evaluation can play a critical role in understanding the most effective method of strengthening the existing beam-column joint to develop the required stability as a preventive measure against resultant risks, incidents, and accidents which may cause injuries (Ravichandran & Jeyasehar, 2012). Previous studies identify a range of techniques which play a significant role in the strengthening of beam-column joints regardless of their types and their overall location. Each and every strengthening technique has its unique characteristics as discussed below:

Epoxy Repair

According to Ravichandran and Jeyasehar (2012), the epoxy repair technique uses polyurethane mortar to rich in resin material to seal cracks occurring in the joints found on the floor of a given structure or protecting the overall joint from deterioration. The floor fix polymer resin and mortar made from resin and overall dried sand is usually the most efficient and fastest way for repairing a spall which comes as a result of cracked and deteriorating concrete. The epoxy technique also a sustainable beam-column joint strengthening technique used in protecting the joint when the slabs are immobile(Hwang & Lee, 2002).

Hwang and Lee (2002) add the epoxy repair technique involves filling of the deteriorating regions with polyuria joint filersthat results in the overall protection and strengthening of the side walls of the joints while bridging the gap allowing the traffic to beat up the joint. However, the results gathered from different experiments with epoxy repair techniques on one-way joints have demonstrated that the reliability of this method in the restoration of the initial attributes of the damaged joints is doubtable. The bond formed around the strengthening bars, once damaged, does not appear to be entirely restored through the injection of epoxy and resin materials (Ravichandran&Jeyasehar, 2012).

The ineffectiveness of the epoxy technique can be proved through the partial recovery of stiffness in the repaired joint and the pinching effect felt in the hysteresis loops (Li, Lam, Cheng, Wu, & Wang, 2015 b). The effectiveness of this technique is also limited by the overall access to the joint and the fact that the epoxy material cannot be successfully introduced in the joints surrounded by floor slabs and transverse beams. Shifting to vacuum impregnation technique may offer a possible solution to the limitations associated with epoxy. However, vacuum impregnation requires a high level of professional skills and technical experience among designers and the overall application may be hindered by the ambient temperatures experienced at the joint to be strengthened(Hwang & Lee, 2002).

Removal and Replacement Method

According to Beres, Pessiki, White, and Gergely (2016) the removal and replacement technique entails either partial or complete removal or replacement of heavily damaged joints characterized with distorted longitudinal bars, ruptured ties, and crushed concrete. The damaged structure must be put under temporary support to ensure stability before starting to remove the affected joints. Consequently, the designer needs to add considerable amounts of ties or longitudinal reinforcement depending on the proportion of concrete removed. The technique entails the use of non-shrink and high-strength concrete for replacement as the designer pays critical attention to attaining a good and sustainable bond between the new fitted concrete and the existing walls (Ravi...

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