Seismic performance of mechanically coupled reinforcing bars

Abstract

Seismic performance verification of a spiral thread mechanical reinforcement connection system for use in reinforced concrete structures was investigated by conducting both in-air component tests and structural subassembly tests. Current performance verification criteria listed in NZS 3101:2006 were found to be outdated and, following a review of various international protocols for testing mechanical connection systems, it was concluded that DIS 15835 protocols should instead be considered for adoption. Two external beam-column joint subassemblies having spiral thread mechanical reinforcement couplers installed at the column-joint interface were subjected to simulated seismic cyclic loading. It was found that bar curvature and the development of a non-uniform stress distribution around the perimeter of the reinforcement-coupler connection led to coupler slippage. However, the measured pinched hysteretic response owing to coupler slippage closely matched the response of companion tests where strength degradation was instead a result of excessive beam shear deformations. It was concluded that uniaxial tensile tests are unable accurately to demonstrate probable coupler performance in plastic hinge zones and that such tests should therefore not be used to predict likely ductile response in potential plastic hinge zones of reinforced concrete members.

Inelastic cyclic behaviour of RC members incorporating threaded reinforcement couplers

“…Such reduction in performance typically arise from the poor performance of the coupler-to-rebar connection, which may instigate rebar fracture at the coupler region. The relationship between the size/bulkiness factor λS=dcLc/(dbLb) depicted in Figure 1d and the ultimate rotation ratio θu,co/θu,cs for RC members incorporating rebar couplers and subjected to cyclic action, is extracted from previous studies [6,[9][10][11][30][31][32] and presented in Figure 16. The parameter θu,co represents the ultimate rotation of the member with couplers, whilst θu,cs represents the corresponding ratio in non-spliced counterparts, considering that these members have similar material properties and geometries; they were also subjected to the same loading procedure.…”

“…In contrast, precast columns provided with grouted sleeve couplers (GSC) [7,8] resulted in alteration of the distribution of plasticity within the potential plastic hinge region and reduced ductility in comparison to monolithic members. Other tests on members with bolt-lock couplers (BLC) and ribthreaded couplers indicated increase in capacity at the expense of reduction in ductility [9,10]. Observations indicate that members incorporating GSC and BLC generally exhibited up to 60% reduction in ductility levels compared to continuous reinforcement, whilst other forms may provide a more favourable inelastic performance, although this is based on limited test results [11].…”

Ductility considerations for mechanical reinforcement couplers

“…The relationship between the coupler-to-rebar diameter ratio dco/db and the displacement ductility ratio μδ,co/μδ,cs for RC members incorporating rebar couplers and subjected to reversed cyclic action [5][6][7][8][9][10][11][12] , is depicted in Figure 5. Paramter μδ,co represents the ratio between the ultimate δu to yield δy displacement of the member with couplers, whilst μδ,cs represents the same measure for the reference cast in situ members, all subjected to reversed cyclic loading.…”

“…In the case of BLC, the coupling system acted as additional reinforcement, hence enhancing the cross-section capacity and delaying failure 5 . On the other hand, for members with RTC couplers, the poor interlock at the coarse coupler-rebar thread led to rebar slippage inside the coupler 9 . Such dissipation mechanisms may become unreliable and incontrollable when significant non-linear behaviour develops in plastic hinges.…”

Monotonic and cyclic performance of threaded reinforcement splices

“…Mechanical couplers for reinforcement splicing are recognised as an effective alternative to lapped or welded bars in reinforced concrete (RC) members, as these can overcome congestion problems whilst reducing material and constructional costs [1][2][3][4][5][6]. The reinforcement congestion becomes particularly critical for situations in which ductile detailing is necessary.…”