Bar Anchorage Research Articles

Seismic behavior of single plate shear connection between steel-concrete composite beam and RC column

This paper aims to investigate the seismic behavior of single plate shear (SPS) connection between steel–concrete composite (SCC) beam and reinforced-concrete (RC) column. A total of four SCC beam to RC column composite joints were fabricated: one specimen was tested under monotonic loading, and three specimens were tested under cyclic loading. The failure modes, hysteretic and skeleton curves, strain distribution of anchor bars, RC slab and longitudinal reinforcement, ductility, energy dissipation and stiffness degradation were discussed, and the influence of longitudinal reinforcement ratio ρsl and the type of embedded parts on the seismic performance of joint were studied. The results indicated that the joint exhibited good seismic behavior. With the increase of ρsl, the initial stiffness, hogging moment and rotation capacities increased, while the ductility and energy dissipation capacity decreased slightly. The type of embedded parts had influence on the failure modes and initial stiffness, but had little effect on the moment and rotation capacities, ductility and energy dissipation capacity of joint. Finally, based on the Zhang’s model, considering the composite action of the floor slab and the contribution of additional bending moment, a calculation method was proposed to predict the ultimate sagging moment capacity of the joint, and the strength of the embedded parts of all specimens in this study and open literature were checked. The results showed that the Zhang’s model and the proposed model have a good prediction accuracy, and it is suggested that when designing the embedded parts of the joint under sagging moment, the cross-sectional area of anchor bars should be checked to avoid early failure.

Experimental study on the bond behaviour between steel bars and 3D printed concrete

The effects of the steel bar direction, steel bar anchorage length, and incorporation of recycled sand and fibre on the bond behaviour of 3D printed concrete specimens were investigated with pull-out tests. The steel bar was placed and covered by multiple printed concrete layers in this study. Compared with mould-cast concrete specimens, the bond failure pattern was similar when the steel bar was pulled out for the 3D printed concrete specimen. However, because the 3D printed concrete specimens had multiple internal interfaces, the probability of splitting failure was higher, and the failure patterns were clearly different. In general, the bond strengths of the 3D printed concrete specimens were lower than those of mould-cast specimens, and there were differences in the bond strength when the steel bars were placed in various directions. Moreover, the modified bond strength model proposed in this study agrees well with the test results and can be used to predict the bond strength between steel bars and 3D printed concrete.

Seismic behavior of hybrid coupled shear wall with replaceable U-shape steel coupling beam using terrestrial laser scanning

The hybrid coupled shear wall (HCW) with replaceable coupling beam (CB) is an optimal component to recover buildings promptly after a severe earthquake. However, the reinstallation may be difficult or impossible with an identical CB because of the inelastic relative dislocation between two wall piers. This study proposes a novel HCW with different reinforcement ratios in the connection, which was tested under cyclic loading. After the test, the bolt holes can be located through terrestrial scanning, which is then utilized to fabricate a new CB that can accommodate the deformation between two wall piers. The newly replaced HCW system was also tested. As a result, all virgin test specimens fail in web fracture and show a significant inelastic chord rotation of 0.2 rad, exhibiting an excellent energy dissipation capacity. Meanwhile, the new method to locate the bolt holes after the test is feasible. The replaced HCW fails in the pull-off of anchor bars and shows poor seismic behavior due to the unpatched concrete cover in the connection. To improve the energy dissipation for the replaced HCW, high-strength grouting in the connection can be used and high-strength material can be used to replace the usual anchor bolts.

Influence of internal defects of semi grouted sleeve connections on the seismic performance of precast monolithic concrete columns

To investigate the influence of internal defects of semi-grouted sleeve connections on the seismic performance of precast monolithic columns, four specimens of precast monolithic concrete columns with semi-grouted sleeves connecting reinforcement bars were fabricated, including one specimen (PC-D0) with no internal defect and three specimens (PC-D10, PC-D20, PC-D30) with 10%, 20%, 30% of internal defects respectively by controlling the length of anchor bars inside the semi grouting sleeve. The behavior of the columns as well as the failure modes, hysteresis loops, skeleton curves, degradation of rigidity, ductility and energy dissipation capacity were studied based on the data obtained by a low cycle reciprocating test. The results indicate that (1) the precast columns are all damaged by bending and the grouting layer of the assembled columns can be pulled apart easily; (2) the seismic energy dissipation capacity of the column without defects is higher than that of the columns with defects; (3) the existence of internal defects reduces the horizontal bearing capacity, rigidity, ductility and energy dissipation capacity of the assembled columns. However, the peak load for PC-D10, PC-D20 and PC-D30 reaches values respectively equal to 94%, 90% and 84% of that exhibited by PC-D0; (4) the energy dissipation capacity of the defective column with 30% of internal defects is significantly lower than those reached by other columns with defects, a feature that indicates that the influence of internal defects on the energy dissipation capacity of assembled columns is not linear. In conclusion, the results provide an insight into the influence of internal defects of semi grouted sleeve connections on the seismic performance of precast monolithic columns.

Cyclic performance of emulative precast beam to column con-nection with corbel using dowel bar

The objective of this study is to examine the seismic performance of exterior and interior types of an emulative precast beam to column connection, constructed with grouted steel dowel bar and cast-in-situ concrete under quasi-static reversed cyclic loading. The dowel bar connection between the precast structural elements is achieved by inserting the dowel bar into the column corbel's holes and the precast portion of the beam. To secure the dowel bar's anchorage, these holes are packed with non-shrinkage grout and then cast-in-situ concreting is done in the joint core and the entire upper segment of the precast beam. In the past, particularly after an earthquake in the Emilia-Romagna region of Italy in May 2012 (Ercolino, Magliulo, & Manfredi, 2016), witnessed damage to precast reinforced concrete structures was more likely to occur in the precast beam-column joint section. Hence, it’s essential to improve the performance of the beam-column joint to withstand all possible lateral load combinations, which are to be included in the design and detailing of the precast structural components. This study analyzed an eight-story RC frame building for earthquake loading using Staad.Pro software. The exterior and interior types of proposed beam-column connections were designed and detailed using the design forces and moments computed by the Staad.Pro analysis, in accordance with the Indian standard codes (IS 456, 2000), (IS 1893, 2016)and (IS 13920, 2016). The beam-column joint behavior under quasi-static cyclic loading was studied using one-third scaled-down test specimens, i.e., monolithic (MBC-EJ & MBC-IJ) and emulative beam-column (EBC-EJ & EBC-IJ) exterior and interior joints. In that proposed emulative connection, the structural continuity and compatibility between the precast elements were achieved through the corbel with the dowel bar and cast-in-situ concreting. The test specimen’s ultimate and yield load carrying capacity, energy dissipation capacity, stiffness degradation, and ductility parameters were determined based on the obtained load-displacement hysteresis relationship. Based on the findings, the precast exterior joint specimens (EBC-EJ) were found to be 14.36% more ductile and 13.23% more energy dissipative than monolithic exterior joint specimens (MBC-EJ). Similarly, precast interior joint specimens (EBC-IJ) outperformed monolithic interior joint specimens (MBC-IJ) by 6.27% more ductility and 16.86% more energy dissipation. Therefore, the experimental results confirmed that using grouted dowel bars and wet concreting in the joint area enhances rigidity and structural continuity, as well as improves the ultimate strength of precast connections to a level that closely resembles typical monolithic beam-column joints.

Urocleidoides spp. (Monogenea: Dactylogyridae) from the gills of Parodon nasus (Characiformes: Parodontidae) from a Brazilian stream with descriptions of two new species.

Urocleidoides spp. are reported from the gills of 20 specimens of Parodon nasus (standard length 8.512 cm), from the Indiana stream, Tiet River, Upper Paran River basin, municipality of Botucatu, So Paulo State, Brazil. Urocleoidoides tenuis and two new species were found. Urocleidoides indianensis n. sp. differs from its congeners mainly by the morphology of the vaginal sclerite that is robust, sickle-shaped, and forked at the distal end; and by the bulbous-shaped accessory piece of the male copulatory complex. Urocleidoides parodoni n. sp. resembles U. tenuis by presenting male copulatory organ with approximately 7 counterclockwise rings, but differs by the morphology of the accessory piece (lobate with a small hook-like projection versus pincer-shaped), vaginal sclerite (thumb-like subterminal projection vs. presence of a distal hook), vaginal tube (conspicuously sclerotized vs. slightly sclerotized), shape of the ventral bar (bowed vs. wide V-shaped), ventral and dorsal anchors (robust base and short shaft vs. considerably less robust base and long shaft), and hooks (slender shank with a weakly sclerotized subunit at base vs. dilated shank). Sequences of the partial 28S rDNA gene of the dactylogyrids found in this study are provided. Phylogenetic analyses showed Urocledoides spp. from Parodontidae clustering together with strong support values. This study increases the number of valid Urocleidoides species to 39, and the number of species described from parodontid hosts to four.

Cover Picture: Geomechanics and Tunnelling 6/2021

AbstractThe Borth underground salt mine with an annual production volume in the range of 2 m t of halite is amongst the largest underground mines in Central Europe. All mined halite is transported to the central hoisting shaft with belt conveyor systems. To ensure a safe and efficient operation of the main conveyor belt, precautionary support measures in geotechnically stressed areas of various stopes were necessary. For the rehabilitation measures, an innovative anchoring system was applied using 3.7 to 5.7 m long hollow bar anchors which were first anchored mechanically in a borehole, pre‐stressed and then fully grouted with resin.

Comparative Test on the Bond Damage of Steel and GFRP Bars Reinforcing Soft Rock Slopes

Soft rock slopes were anchored with traditional steel bars and new Glass Fibre Reinforced Polymer (GFRP) bars. The difference in the anchorage performance of the two kinds of anchorage elements in soft rock and expansive soil was studied by an in-situ test. The results show that cyclic load can aggravate the bond damage of the interface between grouting body and both kinds of bars used in soft rock. Compared with the number of cyclic loads applied, the previous maximum load is the main factor that influences the bond damage of the anchorage bar. Under constant loading, the interface bond behaviour of GFRP bar is better than the steel bar. Because of the small difference in elastic modulus between the GFRP bar and the grouting body, the interface bond around the GFRP bar can invoke more resistance of the grouting body efficiently which demonstrates its more effective anchorage performance than the steel bar under the same conditions. The anchorage structure of steel bar in soft rock can generate larger interfacial relative displacement with increasing load than the GFRP bar in the anchorage section, even though the elastic modulus of steel is much larger than GFRP. In the expansive soil, the anchorage structure deformations of steel and GFRP bars are almost the same because of the weaker bond at the interface of the grouting body and the surrounding soil than that of the bar interface. Under the ultimate loading of the anchorage structure in soft rock, the steel bar with 450 MPa which is less than its ultimate strength shows the failure of the bar body pulling-out, and the GFRP bar with 508 MPa which is larger than its ultimate strength shows the failure of the bar body by fracture. The steel bar anchorage structure in soft rock is destroyed at the interface around the grouting body. The results show that the GFRP bar performs more efficiently than the steel bar.

Seismic behavior of hybrid coupled wall system with replaceable endplate-steel coupling beam

The hybrid coupled wall (HCW) with steel coupling beam (CB) has been widely used in high-rise buildings due to its good ductility and energy dissipation capacity. The HCW with replaceable CB is an optimal component to recover buildings promptly after a severe earthquake. However, the seismic behavior of the HCW with replaceable CB and the reasonable reinforcement ratio in connections to satisfy the design concept of replaceable structure have not been investigated. In this study, a novel HCW subassembly with replaceable endplate-steel CB having different reinforcement ratios in the connections was proposed and tested under cyclic loading. Then, an identical CB was reinstalled and the replaced HCW system was also tested. The results showed that increasing the horizontal or vertical reinforcement ratio in connections significantly enhanced the seismic behavior of HCWs, ensuring the CB to act as a fuse during the test. Increasing the vertical reinforcement ratio could effectively provide a constraint effect on anchor bars and ensure the wall pier to remain elastic, thus satisfying the replaceable requirements. Additionally, the replaced HCW showed similar seismic behavior to the virgin one. Lastly, relevant design methods and recommendations are proposed for the HCW with replaceable CB according to the test results.

Experimental study on bond and anchorage of steel bars in precast concrete structures with new-to-old concrete interface

In monolithic precast concrete structures, the connection between precast components with extended reinforcing bars usually encounters problems regarding conflicts in reinforcement placement. In particular, the problem of reinforcement conflicts is more prominent for precast slabs in China. In order to solve reinforcement conflicts encountered during practical construction, a novel connecting approach for precast members is proposed. This new approach involves setting notches at the end of precast components and anchoring reinforcing bars at the specially designed notches. This new approach ensures that the structural performance of the joints for precast members is similar to that of cast-in-place structures while minimizing the protrusion of reinforcement at the end of the member. In order to investigate the force transfer mechanism of the proposed method and its applicability to precast slabs, a total of 54 specimens with and without notches are designed and tested using pull-out experiments. Based on the experimental analysis, it is found that the existence of the new-to-old concrete interface changes the anchorage strength of steel bars in the notches. The effect of new-to-old concrete interface on the bond strength of steel bars and the desirable anchorage length of steel bars at the concrete interface are analyzed. The influences of steel bar diameter, anchorage length, concrete strength and reinforcement ratio of the concrete cover on the structural performance are discussed and compared in depth. Through the experimental results, the main factors affecting the bond strength of steel bar anchorage in the notched connection are identified. The physical mechanism of force transfer of the proposed method is developed and described. Preliminary calculation and design methods are presented to guide the practical application of the proposed method and to further facilitate the construction process of the precast structures.

Experimental investigation of steel-concrete composite beam to reinforced-concrete column joints with single plate shear connection

This paper focused on the behavior of steel–concrete composite beam (SCCB) to reinforced-concrete (RC) column exterior joint with single plate shear (SPS) connection under monotonic loading. Four SCCB to RC column exterior joints were constructed, and the test parameters were the longitudinal reinforcement ratio and high-strength bolt diameter. The failure modes, moment-rotation responses, strain distribution along composite beam depth, strain distribution of anchor bar and the influence of parameters were investigated. Compared with open literature, the influence of RC slab was also discussed. Finally, a calculation model accounting for the influence of RC slab was proposed to evaluate the yield moment and ultimate moment capacity of the joint under hogging moment. The test results showed that the longitudinal reinforcement ratio (ρsl), high-strength bolt diameter (db) and the RC slab effect had a great influence on static behavior of the SCCB to RC column joints with SPS connection. When ρsl was increased from 0.57% to 0.98%, the ultimate moment was increased by 40.3%. When db was increased from 16 mm to 20 mm, the ultimate moment was increased by 10.9%. Compared with the joints without RC slab, the ultimate moment of joints with RC slab was increased by 118% to 254%. Moreover, the proposed model provided a good prediction and laid a foundation for the design of SCCB to RC column joints with SPS connection.

UNIFIED CALCULATION METHOD FOR SHEARING STRENGTH OF NEW-TO-OLD CONCRETE INTERFACE WITHOUT ANCHOR BARS BASED ON THREE-DIMENSIONAL ENERGY YIELD CRITERION

There are two types of calculation methods for the shear strength of the existing new-to-old concrete interface without anchor bars: considering normal stress and without considering normal stress. These methods lack theoretical support and need to improve the calculation accuracy. A unified calculation formula that takes into account both normal stress and zero normal stress has not been reported. According to the shear test failure phenomenon and the new-to-old concrete interface mechanism, the failure mechanism of a new-to-old concrete interface without anchor bars is analyzed. Based on the three-dimensional energy yield criterion, on virtual work principle and, on plastic limit analysis theory, the theoretical calculation formula of shear strength of new-to-old concrete interface without anchor bars is derived. The comprehensive coefficient considering the influence of normal stress and of roughness is introduced. The theoretical formula is modified using three-dimensional curve fitting based on the existing shear test data of new-to-old concrete interface without anchor bars. A unified calculation formula of shear strength of new-to-old concrete interface without anchor bars is obtained. Based on 27 groups of compressive (tensile) shear test specimens and on 30 groups of pure shear test specimens of the new-to-old concrete interface without anchor bars, different methods are used to calculate the shear strength, and a comparative analysis is conducted. The results show that: for the compressive (tensile) and shear test specimens, the deviation between the calculated values and experimental values of the method is generally less than 15%, and the calculation accuracy of the unified formula is higher than that of the existing calculation methods considering normal stress. For pure shear test specimens, the deviation rates of the calculated values of the method proposed are mostly within 20%. Except for the large deviation rate of low strength concrete specimens, the calculation accuracy of the unified formula is much higher than that of the existing calculation formula without considering the normal stress. The unified calculation method has a sufficient theoretical basis and is simple in computation. It can be applied to compressive (tensile) shear composite members and pure shear members. Meanwhile, the calculation accuracy is better than that of the existing calculation methods.

Anchorage and lap capacity of square twisted reinforcement for assessment of existing structures

AbstractAlthough square twisted section reinforcement is no longer used in new construction, there remain many older structures still in service that were built with such bars. The increasing need for assessment of existing construction means there remains a continuing need for information on performance over older types of reinforcement. Research into plain surface bars essentially ceased when ribbed bars became the norm, and plain bars have consequently been bypassed in developments in understanding of bond since 1960. The basis through which margins of safety are introduced for design has also changed as formal methods for analysis of reliability have developed. An analysis of test data on bond of square twisted bars, also termed Type 1 deformed or Ransome type bars is presented, and a new semi‐empirical formulation for anchorage capacity of straight square twisted bars in R.C. structures consistent with the reliability‐based approach included in the forthcoming second generation of Eurocodes is derived. The expression parallels that for ribbed bars in the fib Model Code 2010. A comparison with provisions of some historical international design codes suggests that in some cases the margin of safety against failure of straight plain bar anchorages may have been lower than would be required by current norms. Implications for practice are briefly discussed.

Local bond behavior of bundled bars: Experimental investigation

AbstractThe use of bundled bars in highly loaded concrete members instead of individual bars can reduce or even avoid reinforcement congestion, allowing easier placing and compaction of concrete, since bundles (with two or more side‐by‐side bars) are less obstructive to fresh‐concrete flow. However, there is still a lack in knowledge of the fundamental phenomena related to the bond behavior of bars in bundles. Therefore, design code rules for anchorages and splices differ significantly among International Standards (Eurocode 2, fib Model Code 2010, and ACI 318–19). The present paper reports the results of more than 100 pullout tests with short embedded length with the aim of comparing the local bond behavior of bundles with that of corresponding notional individual bars. Among the three criteria usually introduced to compare bundled and individual bars, based on the concepts of “equivalent sectional area,” and “minimum or maximum sectional perimeter,” the first and the second are introduced in this paper. Experimental results show that both criteria are suitable methods for evaluating the bearing capacity of bundled bar anchorages, even if equivalent area criterion seems to be slightly more conservative. The experimental results provide also information on the bursting forces generated by the wedge action of the ribs which clearly increases with bar diameter. Finally, experimental results are compared with design rules for anchorage strength of bundled bars as prescribed by fib‐Model Code 2010.

Cast-in and post-installed rebar anchorage systems in RC column foundation joints: Experimental investigations

This paper discusses an experimental program aimed at comparing different reinforcing bar (rebar) anchorage systems in reinforced concrete (RC) column-to-foundation joints (CFJ). A total of 13 tests on full scale CFJ are presented. Within the test matrix, cast-in straight (CIS), cast-in with bent-in hook (CIH) and post-installed rebar (PI) systems are employed for anchorage of the column main rebar in the foundation concrete. The specimens were designed to trigger different failure modes (and their combinations) specific to the rebar anchorage zones. This paper provides the details of the test program, specimens, test procedure and the results. Behavioral perspectives for different rebar anchorage systems (CIH, CIS and PI) are discussed based on the test observations. A discussion of the test results within the framework of expectations outlaid in design of the test specimens is also presented. The study highlights that high bond strength offered by PI system used in the present investigation resulted in flexural yielding of column at lower anchorage length in comparison to the CIS reinforcement. It is also shown that concrete breakout failure typically considered in fastening technology is also applicable in case of cast-in anchorages with bent in hooks, although it manifests in a slightly different manner.The test data presented in this paper offers the necessary benchmark data required for system specific assessment and design approach for the rebar anchorage zones in CFJ. A proposal for system specific assessment and design approach and its comparison with the available assessment and design approaches in the light of experiments presented in this paper and also those available from the literature will be presented in another paper.

Locator versus stress free implant bar attachments for two -implants immediately loaded by mandibular overdentures. A one year randomized study

Aim: The purpose of this short-term randomized trial was to study clinical and radiographic outcomes of Locators and SFI bar attachments used for two -implants immediately loaded by mandibular overdentures Material and method: Twelve edentulous participants (6 males and 6 females) received new maxillary and mandibular dentures and wore them for 3 months to increase muscular control. Two fixtures were installed in the canine regions of the mandible and immediately loaded by mandibular overdentures using Locator (group 1) or SFI bar (group 2) attachments. Plaque index (PI), gingival index (GI), probing depth (PD), stability of the implants (IS), and marginal bone resorption (BL) were measured at base line (insertion), 6 and 12 months later. Results: The implant survival was 91.7% and 100% for Locator and SFI bar groups respectively. PI, PD and BL increased significantly with time in both groups. SFI bar group showed significant higher PI and PD than Locator group after 6 and 12 months. On the other hand, Locator group showed significant higher BL than bar group at 6 and 12 months. No significant difference in GI and IS between observation times or between groups was noted Conclusion: Within limitation of this study, it is concluded that both Locators and SFI bar anchors are recommended for immediately loaded 2 inter-foraminal implants by mandibular overdentures. However, Locators may be favorable regarding improved peri-implant soft tissue conditions and SFI bar may be favorable regarding reduced marginal bone loss around the implants

Pullout behavior of lap splice connections between double-steel-plate composite walls and RC raft foundation in nuclear engineering

Considering the flexibility of construction and convenience of transportation, the lap splice connection using dowel or lapped bars between double-steel-plate composite (DSC) walls and reinforced concrete (RC) raft foundation is becoming increasingly popular in nuclear engineering. Because the anchorage of dowel or lapped bars in RC members has already been stipulated by many codes, this study mainly focus on the portion in DSC wall of this connection. Eight 1/2 scaled DSC wall – RC foundation connection specimens were tested with monotonic tensile loading to study the pullout mechanism of this connection and provide solid basis for design. The investigated variables are the locations of lapped bars and tie configuration including the spacing and diameter of tie bars. A new tie form using internal steel webs instead of tie bars is also proposed. The test results are analyzed and discussed in terms of crack pattern, load-displacement relations, strains of key components including steel faceplates, tie bars and lapped bars. Based on the experimental findings and previous research, five possible failure modes are concluded and the steel faceplates yielding is regarded as the design target. To avoid the other failure modes, design recommendations on tie bars, lapped bars and shear studs are given. Particularly, a new formula is proposed to design the tie bars to avoid splitting failure based on the nonlinear strain distribution along the length of connection. In addition, the internal steel webs are recommended as a promising alternative forms of tie bars, which has shown better mechanical performance as well as more convenient construction process.

Research on Anchorage of GFRP Anchor Bolts and Heads

GFRP is an abbreviation of Glass Fiber Reinforced Polymer. It is an inorganic non-metallic material made of glass fiber reinforced material, synthetic resin as matrix material, and compounded by a certain process. Although the glass fiber reinforced polymer anchor can fundamentally solve the problem of poor corrosion resistance of the steel bar anchor, in the anchor system, the force on the surface layer or the waist beam needs to be transmitted to the shaft through the anchor head. At present, the pull-out strength of domestic GFRP anchors is far away from the tensile strength of GFRP tendons. This may cause the anchorage system of anchors to fail due to anchorage failure, and the tensile strength of GFRP tendons cannot be fully exerted. When ordinary clip-type anchorages are used, there is a huge clamping force on the ribs in the anchorage zone, which may result in the shear failure of ribs.Based on this, this article uses a high-strength impregnated reinforcement material to carry out the tensile failure test of a GFRP anchored anchorage with a diameter of 18cm. The study found that the use of high-strength reinforced concrete can make the GFRP anchor achieve the maximum tensile strength, and with the increase of curing time, the ability of the high-strength reinforcement to limit the displacement of the anchorage end is stronger.

Design and Evaluation of a New Resin-Filled GFRP Pipe Connection System for Butt Splicing of FRP Bars.

Fiber-reinforced polymer (FRP) bars are one of the promising alternatives for steel bars used in concrete structures under corrosion or non-magnetic environments due to the unique physical properties of FRP materials. When compared with steel bars, FRP bars are difficult to be spliced in field application due to their anisotropy and low shear and compressive strengths. In view of this, the paper presents a new non-metallic connection system (i.e., resin-filled glass fiber-reinforced polymer (GFRP) pipe connection system) for the butt splicing of FRP bars. With the proposed connection system and a simplified trilinear interfacial bond-slip model, a set of design formulas were derived based on the requirement that the proposed connection system should provide a load transfer capacity beyond the tensile capacity of the spliced FRP bars (i.e., to fulfill the high tensile strength of FRP materials). Besides, considering the fabrication error-induced load transfer capacity reduction of the connection system in field application, a correction factor was introduced in the paper to compensate for the reduced load transfer capacity by increasing the FRP bar anchorage length. At last, to estimate the effectiveness of the proposed connection system and the derived design formulas, nine specimens were fabricated with a kind of commercially available basalt fiber-reinforced polymer (BFRP) bars and the designed connection system and tested under unidirectional tension to study their tensile performance. With the comparison between the tested and theoretical results, the effectiveness of the proposed connection system and the derived design formulas are verified.

Moment redistribution and flexural performance of RC continuous T-beams strengthened with NSM FRP or steel bars

This paper discusses the flexural strengthening of continuously reinforced concrete (RC) beam constructions in hogging or sagging regions using near-surface mounted (NSM) technique. The main difficulties in strengthening RC continuous beams in hogging are the vertical middle column which prevents continuity of the NSM reinforcement bars and end anchorage of the NSM reinforcement. A test program consisted of seven two-span T-beams was used; one control beam, which was used for comparison, four beams were strengthened at the hogging region, and two beams were strengthened at the sagging regions. Two types of strengthening material were adopted in this study, carbon fiber reinforced polymers (CFRP) rebars, and high tensile steel bars. An RC column loaded with a constant load (120 kN) was used as the middle support. The main test parameters were the type of the reinforcement bars, continuous NSM bars beside the middle column, or NSM bars anchored inside the middle column, as well as the strengthened region. Besides, the impact of using embedded through-section (ETS) end anchorage of NSM CFRP bars was investigated as well. The experimental results were evaluated for the effects of strengthening technique and materials on the load-carrying capacity of beams, deformation, ductility index, and moment redistribution. The experimental results showed that strengthening with NSM steel bars could improve the service load carrying capacity by 23–40%, whereas the NSM CFRP rebars improved the service loads by 33–36%. The ETS end anchorage at the hogging region and the NSM steel bars at the sagging region helped to achieve the flexural rigidity by a very significant amount relative to the other strengthened beams and control beam by 270%. The moment redistribution achieved after the beam cracking load until the failure load varies in accordance with the strengthening region and the strengthening material type.