Splice Length Research Articles

Bond-slip Behavior of Lapped Sand-Coated Deformed GFRP Rebars in UHPC under Double-Row Splice Test

Novel Ultra-High-Performance-Concrete (UHPC) structures reinforced with Fiber-Reinforced Polymer (FRP) rebars are promising candidates for applications in important infrastructures under exposed environments where normal concrete and steel rebars may falter. This paper aims to assess the bond-slip behavior between lapped sand-coated deformed Glass FRP (GFRP) rebars and UHPC using double-row splice tests, with parameters including bar diameter, splice length and lap clearance. Failure modes including the pullout of GFRP rebars and the splitting of UHPC were identified. For cases of pullout failure, the average bond strengths in samples with splice lengths of 5db were reduced by 17.6-22.1% compared to those of 2.5db. Increasing the lap clearance from 0 to 1db and 2db led to 11.1% and 30.2% increases in average bond strengths. Furthermore, average bond-slip models for lapped sand-coated deformed GFRP rebars in UHPC were developed. The predicted curves matched the experimental ones, showing errors within 20% for both average bond stresses and slips. When the cover is not less than 2db, the splice length is recommended to be at least 15db for sand-coated deformed GFRP rebars with diameters of 10mm to 16mm in UHPC, approximately 1.25 times the corresponding development length proposed by the existing research.

Strengthening of reinforced concrete beams with insufficient lapped splice length of reinforcing bars

The insufficient lapped splice length of reinforcing bars due to the design or construction errors reduces both the flexural strength and ductility of Reinforced Concrete (RC) beams. The defected RC beams need to be strengthened to allow structures to be ductile and robust in their design life. This paper reports experimental and numerical investigations into the flexural behavior of RC beams having insufficient lapped splice length of reinforcing bars strengthened by various techniques. Eleven RC beams have been tested to examine the effects of strengthening techniques and anchorage lengths of the strengthening materials on the performance of the beams. The test program and results are described on RC beam specimens strengthened by using the externally bonded stainless-steel (EBSS) sheets, the near surface mounted (NSM) steel bars, and the external prestressing system. Finite Element (FE) models are developed using ABAQUS to simulate the responses of strengthened RC beams in which the lapped splice length of reinforcement is inadequate. A parametric study is conducted using the validated FE models to examine the effects of the length of EBSS sheets and steel anchor bolts at the ends on structural behavior. An analytical model is proposed for calculating the ultimate capacity of beams strengthened by NSM technique. Experimental results reveal that the proposed strengthening methods can significantly improve both the cracking and ultimate loads of the defected beams. The application of the external prestressing method results in the largest increase in the cracking and ultimate loads of the defected beams calculated as 222 % and 213 %, respectively compared to the defected control beam. The ultimate load of the defected beam strengthened with EBSS sheet, NSM steel bars, and prestressing system with a length of 100D increases by 50 %, 109 %, and 182 %, respectively. It is shown that the developed FE models can accurately predict the behavior of strengthened beams having inadequate lapped splice length of reinforcing bars. The parametric study demonstrates that strengthening the entire clear span of the beam B-ESS-65D with EBSS sheet increases its ultimate load by 207 %. The failure mode of strengthened beams is ductile bending without debonding. The proposed analytical model is shown to yield accurate calculations of the ultimate loads of strengthened RC beams.

Flexural strengthening of reinforced concrete cantilever beams having insufficient splice length

Structural systems often undergo changes due to variations in the usage, the loading conditions, or the presence of defects in their elements. The problem can be exacerbated when there is insufficient overlap between reinforcing bars in critical moment zones. This article investigates the behavior of reinforced concrete cantilever beams exhibiting insufficient overlap between bars that used as main reinforcing steel bars in the negative moment zone. Various strengthening techniques were employed in order to improve these defected cantilever beams. Eleven beams underwent flexural testing until reaching failure. The experimental parameters encompassed the strengthening scenarios and the bonded length. Three strategies were used: the application of stainless-steel plates (SSPs) as externally bonded reinforcement, near surface mounted (NSM) reinforcement in which additional deformed steel bars were bonded utilizing engineering cementitious composites, and externally pre-stressing technique. The anchorage length was examined at 40, 50, and 60 times the internal bar diameter. It was noted that the most substantial improvement achieved with the NSM method, followed by the externally pre-stressing method. It is worth mentioning that most of the beams failed in a flexural manner, with partial debonding occurring in beams strengthened using external strengthening. Moreover, this article includes the development of a numerical model employing the finite element method to replicate the response observed from the experimentally tested beams. The accuracy of the model was confirmed through the comparison of its outcomes with the experimental data, demonstrating an acceptable level of accuracy with deviations of less than 4.4 %. This successful numerical investigation was also used to conduct a parametric study. From this study it is evident that the effect of debonding on SSPs can be reduced by adding steel anchors at the ends of these plates. Finally, an analytical method was proposed to calculate the ultimate load capacity of strengthened reinforced concrete beams.

Finite element analysis on non-contact lap splice connections in ultra-high-performance concrete

This study investigates the stress characteristics and failure modes of the lap splice region for non-contact lap-spliced rebar embedded in Ultra-High-Performance Concrete (UHPC), as well as the influence of lap parameters on these aspects. A series of refined finite element models of non-contact lap-spliced rebars embedded in UHPC were established and validated. The influences of UHPC mechanical properties, splice length, and clear spacing on lap region and the failure modes of specimens were studied. As the lap clear spacing increases from 0.5d to 4d, the ratio of principal compressive stress to principal tensile stress in the lap region of the elastic model decreases from 2.36 to 0.36. This trend indicates that with increasing clear spacing, the force transfer between rebars shifts from being dominated by compressive stress to tensile stress within the UHPC lap region. Consequently, the maximum load of the specimen transitions from being governed by compressive strength to being governed by tensile properties. With a clear spacing of 2d, the maximum load of the specimen increases with the splice length. The maximum load of 8d splice length specimen was increased by at least 27 % compared to the specimen with 0d splice length.

Experimental and numerical study on cyclic behavior of precast segmental railway bridge columns with lap-spliced rebar connections using UHPC wet joints

A novel lap-spliced connection with ultra-high performance concrete (UHPC) was proposed to connect precast railway bridge column segments with footings or cap beams. Two 1:3 scaled specimens were tested under cyclic loads. Specimen PC-LS was a precast column with lap-spliced rebar connection and UHPC wet joints. Specimen CIP was a monolithic column as a reference specimen. The test results revealed that the plastic hinge region of the precast specimen shafted to the upper surface of the UHPC wet joint. The failure mode of the precast specimen was exhibited as the crushing of the core concrete and the buckling/fracture of the longitudinal rebars. Specimen PC-LS experienced larger lateral force, initial stiffness, comparable ductility, and energy dissipation compared to specimen CIP. Additionally, the validated finite-element (FE) models considering the bond-slip effect between concrete and reinforcements were developed. The parametric studies were carried out to further investigate the cyclic behavior of specimen PC-LS. Analytical results demonstrated that the variation of the compressive and tensile strength of UHPC showed little influence on the cyclic behavior of the precast segmental column, which indicated that UHPC with natural curing and lower volume content steel fibers could be used as the wet joint. The precast segmental column had similar lateral force and stiffness with the cast-in-place column when the lap splice length was 10 times of the rebar diameter.

Experimental study on seismic performance of two-story two-bay. Precast concrete frame with UHPC-based connections

The UHPC-based connections, utilizing Ultra-high performance concrete (UHPC) to connect rebars within precast concrete structures, present the advantages of short splice length, simplified construction, and low cost due to the excellent bond property between UHPC and rebars. This investigation focuses on seismic performance of precast concrete frame (PCF) with UHPC-based connections. The UHPC-based connections were arranged strategically to the beam-column joints and column bases in PCF to connect longitudinal rebars of beams and columns, respectively. Two half-scale, two-story, two-bay reinforced concrete frames, including PCF and a monolithic concrete frame (MCF) for reference, were tested under cycle loading with axial compression ratios of 0.33 in the middle columns and 0.22 in the side columns. The results revealed that PCF exhibited a beam sway mechanism, with all beam hinges developed prior to column hinges, while MCF displayed a mixed sway mechanism, with part of beam hinges developed prior to column hinges. The hysteresis curves of the two frames were globally stable with minimal pinching, and PCF displayed greater energy dissipation compared to MCF. The load-carrying capacity of PCF was 9 % higher than that of MCF. The displacement ductility of PCF was 4.14, exceeding that of MCF by 10 %. The two frames showed similar laws of stiffness degradation. Overall, the precast concrete frame with the UHPC-based connections exhibited better seismic performance in comparison with the monolithic counterpart.

Seismic rehabilitation of RC frames with innovative precast U-shaped UHPC jackets: Experimental evaluation and computational simulation

The rehabilitation of post-earthquake reinforced concrete (RC) frames is crucial for both restoring structural integrity and enhancing seismic resilience against future seismic events. Ultra-high-performance concrete (UHPC) is distinguished by its exceptional strength, crack-control capabilities, ductility, and durability. Despite numerous studies on its use for structural retrofitting, its application in rehabilitating damaged RC frames remains limited. This study introduced a novel precast U-shaped UHPC jacket designed for the post-earthquake rehabilitation of RC frames. The jacketing method promotes composite action in rehabilitated members through lap splicing and dowel bars, complemented by cast-in-place connections using UHPC to minimize splice length and strengthen potential weak areas under external loads. The efficacy of this jacketing approach was rigorously evaluated through cyclic loading experiments on two RC frame specimens. Results indicated that the UHPC rehabilitation method not only recovered but significantly enhanced the seismic performance of the previously damaged frame, improving initial stiffness, yield strength, peak strength, displacement ductility, and energy dissipation capacity. However, the rehabilitated frame showed a reduced yield drift and increased residual displacement compared to the as-built frame. The experimental results also revealed the necessity of accounting for bond slip in structural rehabilitation analysis and design to prevent overestimating lateral stiffness. Furthermore, the study developed a computational model that incorporates flexure, bond slip, and shear responses, aiming to effectively simulate the load-displacement behavior of rehabilitated RC frames with reasonable accuracy.

Influence of finger joint length on the elastic modulus of reconstituted wood from Pinus taeda L.

The aim of this study was to evaluate the influence of three finger joint splice lengths on the dynamic modulus of elasticity of pieces of reconstituted wood from Pinus taeda L. Wooden specimens had finger joint splices of 5, 7 and 15 mm in length and were evaluated using the Stress Wave Time equipment, to analyze the wave propagation speed and dynamic modulus of elasticity, as well as the density of the pieces. As a result, increasing the finger joint’s length did not reduce the wave propagation speed through the wooden specimen. On the other hand, there was a reduction in the strength of the spliced wood as the much as the length of the finger joint increased. The density of the material may have influenced the reduction in the modulus of elasticity, even if it did not interfere with the wave propagation speed through the specimen.

Experimental investigation on retrofitting effects of circular steel rod damper systems on non-seismic detailed reinforced concrete frames

Existing non-seismically detailed low-rise reinforced concrete (RC) buildings are vulnerable to seismic attacks due to their insufficient seismic details including the spacing of transverse reinforcements and splice length at column critical regions. In order to mitigate those deficiencies, various retrofit strategies using externally-bonded reinforcing materials and adding external braced frames have been suggested, and adopted on the construction fields. Although various retrofit methods have been verified their retrofitting effects, there have been architectural concerns and difficulties in providing appropriate connections between supplemental structural systems and existing RC frames. One of the methods applying supplemental energy dissipating devices, this study introduces an externally retrofit method using circular steel rod dampers (CSRDs) which are installed between the existing RC frame and the external sub-frame. The existing RC frame have relatively long natural period and large displacement demand while the external sub-frame has short natural period and small displacement demand. Such relative displacement between two frames is a main mechanism acting the CSRDs. When the interaction of two frames occurs in the CSRD due to the seismic load, the load-transfer mechanism ensures stable hysteretic behaviors of the CSRD even during extreme earthquakes. To verify retrofitting effects of CSRD systems on non-seismically detailed RC frames, this study carried out component-level tests of CSRD systems and their hysteretic characteristics are investigated, especially in terms of their fatigue resistance. Then, full-scale cyclic tests are carried out with non-seismic detailed RC frames with and without CSRD systems in order to confirm the effectiveness of the introduced external retrofit method.

Investigating the efficiency and reliability of different lap-splice configurations in NSM BFRP rods for strengthening RC beams

The use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has shown great promise for flexural and shear strengthening of reinforced concrete (RC) members. However, the continuity of NSM FRP rods is often interrupted due to length constraints, necessitating lap splices to transfer forces between spliced rods. The performance of lap splices depends on design configuration factors, including anchorage shape, splice length, and connection method. This research describes an experimental investigation into the bond behaviour and failure mechanisms of various lap splice designs for NSM basalt FRP (BFRP) rods in RC beams. The parameters investigated were end anchorage shape (straight or Embedded Through-Section (ETS) anchors), and connection type (overlay rods or face-to-face with FRP sheet wrap). A total of 8 simply supported RC beams strengthened with different NSM BFRP lap splice configurations were tested under four-point bending. The load-deflection response, strain distribution, and failure modes were evaluated. Test results showed that beams with NSM FRP rods with ETS anchors exhibited higher bond strength and ductility than face-to-face connections. The outcomes of this study can help optimize lap splice design and detail provisions for NSM FRP systems in future strengthening applications.

Hysteresis Behavior of RC Beam–Column Joints of Existing Substandard RC Structures Subjected to Seismic Loading–Experimental and Analytical Investigation

Four exterior reinforced concrete beam–column joint subassemblages with poor reinforcement details and low-quality materials were constructed and subjected to cyclic lateral deformations under constant axial loading of the columns. The longitudinal rebars at the top of the beams were well-anchored in the joint region with a 90° hook and transversely welded to prevent premature slippage. The same was true for the longitudinal rebars at the bottom of the beam of the first specimen. Contrarily, the anchorage of the rebars at the bottom of the beam of the other three subassemblages was straight and of insufficient length. One of these specimens (the second) also had deficient lap splices of the column reinforcement, while the other three specimens had continuous column rebars. The third and the fourth subassemblage were designed with different joint aspect ratio and beam shear span/depth ratio values. The overall seismic performance of the specimens was evaluated and compared. The failure mode of the subassemblages was accurately predicted by the proposed analytical model. It was clearly demonstrated that the anchorage of the rebars, the length of the lap splices, the joint aspect ratio and the shear span/depth of the beam ratio value crucially affect the cyclic response of beam–column joints and, hence, may cause a severe detrimental impact to the overall structural integrity.

Experimental study on the flexural behaviour of lap-spliced rapid hardening concrete beams

Rapid-hardening concrete (RHC) has recently garnered significant attention because of its potential to expedite construction schedules and enhance structural performance. However, the flexural behaviour of lap-spliced RHC beams requires further investigation to provide valuable insights into the performance of this innovative construction material and splice technique. This study examined the flexural behavior of 22 lap-spliced RHC beams with varying lap splice lengths and compared them with four normal-strength concrete (NSC) beams. The key parameters investigated included lap splice length, concrete type, concrete cover, bar diameter, and splice end shape. The flexural performance of the beams was evaluated by analysing the load-deflection response, crack patterns, reinforcement strain distribution, and failure modes. Rapid-hardening concrete beams were tested three days after casting, whereas normal-strength concrete beams were tested 28 days later. The results of the study revealed that lap-spliced RHC beams exhibited increased ductility and load capacity by an average of 76 % and 32 %, respectively. In addition, the lap splice length in RHC beams could be reduced by up to 30 %.

Experimental investigation of bond behavior with lap splice for CFRP-steel composite bars in coral sea-sand aggregate seawater concrete

The pull-out tests on a total of 81 lap-spliced specimens in 27 groups were conducted to investigate the lap-spliced behavior and the appropriate splice length for CFRP-steel composite bars (C-FSCB) in coral sea-sand aggregate seawater concrete (CSSC). The test variables included the C-FSCB diameter (dc), splice length, concrete cover thickness, concrete strength, lap spacing, stirrup ratio, and materials type. Then, the influence of various test variables on the lap-spliced behavior of C-FSCB in CSSC was analyzed. The results showed that when the splice length was less than 17dc, the specimens exhibited pull-out and concrete splitting failure, while C-FSCB fracture failure occurred when the splice length exceeded 17dc. Severe shear damage was observed on the C-FSCB surface in the case of pull-out and concrete splitting failure. When the splice length was less than 14dc, the bond strength of the specimens was approximately 7.2 MPa. As the splice length increased beyond 14dc, the bond strength gradually decreased. After the cover thickness was greater than 4dc or the compressive strength of CSSC was greater than 30 MPa, the variation in bond strength of the specimens can be negligible. Increasing the stirrup ratio led to an increase in bond strength and a significant reduction in crack width. Compared to specimens with steel bars, the bond strength reduction for specimens with C-FSCB exceeded 25%. Based on the test results, calculation formulas for the bond strength and splice length of C-FSCB in CSSC were established. Furthermore, referring to the approach in the Chinese code GB 50010–2010, a simplified calculation formula for splice length was proposed.

Bond behaviour of staggered/non-staggered lap-spliced GFRP bars in concrete

This paper reports on the results of an experimental and analytical investigation into the bond behaviour of glass fibre-reinforced polymer (GFRP) splices in concrete. Eleven full-scale beam specimens in which GFRP bars were spliced within the constant-moment zone are examined. The study incorporates several key test variables, encompassing the ratio of bars lapped (33%, 50%, and 100%), surface characteristics (including sand-coated, ribbed, and wrapped bars), bar diameter (12 mm and 16 mm), and splice length (ranging from 30 to 40 times the bar diameter). The findings reveal a reduction in bond strength ranging from 12 to 24% for staggered bars when compared to their non-staggered counterparts. Furthermore, an increase in bar diameter is shown to decrease bond strength by 16%, whilst surface treatment also influences both bond strength and the pattern of cracking in the splice region. Increasing the splice length from 30 to 40 times the bar diameter enhances bar failure stress by 26%, but it also reduces the average bond strength by 9%. A new predictive equation for the design bond strength of fibre-reinforced polymer (FRP) bars is developed by utilizing a data base of 151 test results. The predicted bond strengths demonstrate greater consistency with experimental outcomes in comparison to previous models.

Data-Driven Approach for Selecting Mechanical Rebar Couplers Based on the Shape and Structural Characteristics of Reinforcing Bars for Sustainable Built Environment

Lap splices are the most commonly used method worldwide because they do not require specific equipment or skilled workers. However, lap splices incur high construction costs because of the long splice lengths required for large-diameter rebars in megastructures, as well as issues pertaining to material supply, labor costs, constructability, and project duration. Additionally, approximately 15% more rebar is required because of the overlap. Energy saving for a sustainable built environment is possible if the disadvantage of lap splices, which generate high CO2 emissions due to the excessive use of rebar, are resolved. Hence, mechanical rebar couplers (MRCs) have been developed. However, despite their advantages, they have not been widely applied in construction sites owing to concerns regarding safety, quality, and constructability. This is because data on MRC, including maintenance, and environmental impact, are not organized, making it difficult to select a coupler suitable for the environment during the construction stage. Therefore, a data-driven approach for selecting MRCs based on the reinforcing bar shape and structural characteristics is proposed in this study. The T-epoxy filled sleeve coupler was found to be the best in terms of seismic performance, durability, corrosion resistance, and long-term performance. In addition, using a data-driven MRC selection algorithm using the T-threaded coupler for one rebar over two floors resulted in 56% more efficient labor productivity, 15% shorter assembly time, 17% lower costs, and 26% lower CO2 emission. Using a developed algorithm, the appropriate MRC can easily and rapidly be selected for frequent design changes.

Structural behavior of jointed precast concrete beams reinforced with GFRP bars

This experimental research aims to reduce the joint length between the precast concrete elements reinforced with GFRP bars. The experimental work was divided into two stages. Stage (I) consists of twelve specimens made from GFRP bars and jointed together using GFRP or steel sleeves filled with epoxy resin. The specimens were tested under tension up to failure to investigate the tensile capacity of splice bars taking into consideration different parameters such as sleeve type, embedment length, bar size, and sleeve radial stiffness. While Stage (II) consists of ten reinforced concrete beams measuring 200 × 350 × 3300 mm. All beams were tested under a four-point bending load up to failure. The connection types for GFRP bars were investigated using two methods; (i) the optimum sleeve connector selected from stage I, (ii) using lap splice with different parameters such as splice length, joint compressive strength, and confinement lap-splice region with GFRP sheets. The test results show that an adequate bar embedment length and sleeve radial stiffness are required to achieve bar tensile strength. Whereas lap splice length can be reduced by increasing confinement of lap splice region with GFRP sheets. Finally, precast elements' joint length can be minimized by using a sleeve connector with adequate radial stiffness and embedment length equal to 15-times bar diameter or by confinement of the lap splice region to minimize its length to 40-times bar diameter.

Splice Length of Large Diameter Reinforcing Bars in Ultra-High-Performance Concrete

Potential exists for construction time savings through replacement of cast-in-place substructure columns, piers, or both, with prefabricated bridge elements and systems. Cast-in-place substructure construction requires forming, placing steel, and pouring concrete at the construction site. Using prefabricated elements would decrease the extent of work required at the site and potentially reduce concrete curing time. This research furthers the effort to use ultra-high-performance concrete (UHPC) as a joining material for prefabricated bridge substructure elements. UHPC has a high early strength, requires less development or splice length than conventional concrete, and has been used previously for accelerated construction projects, such as bridge deck replacement with precast units. UHPC also has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional concrete. Although UHPC has been researched extensively, previous research for reinforcing bar splice and development lengths has focused on #9 and smaller diameter bars. Typically, larger diameter bars are used for substructures. This research determined the required splice lengths for large diameter steel deformed reinforcing bars embedded in UHPC based on 127 individual tests. Three primary variables were included in the testing matrix: bar size, bar spacing, and concrete cover. To achieve at least 75 kips per square inch (ksi) (517 MPa) reinforcing bar stress in UHPC with an early age strength of 14 ksi (97 MPa), the required embedment length ranges from 8 to 13 times the bar diameter and the corresponding splice length varies from 6 to 11 times the bar diameter, depending on the bar size and concrete cover.

Flexural performance of rapid-hardening concrete (RHC) beams with tension lap splice

BackgroundRapid-hardening concrete (RHC) is a specialized type of concrete that gains strength at an accelerated rate, allowing for faster construction and reduced project timelines. The use of RHC in structural applications, such as in beams subjected to flexural loads, has gained significant attention due to its potential for improving construction efficiency. This study focuses on the flexural performance of RHC beams with tension lap splice, which is considered a common method for joining reinforcement bars in concrete structures.ResultsSeveral parameters were taken into consideration, such as concrete type, concrete cover, and reinforcement bar diameter. The loading test was performed on sixteen beams to show results of load capacities, moment–displacement response, energy absorption, and ductility. As a result, the flexural performance of RHC beams is compared to that of NC beams.ConclusionsResults indicate that RHC beams require 30 Φ splice length after 3 days of casting, while NC beams require 40 Φ splice length after 28 days. The RHC beam had higher load capacities, ductility, resilience, and toughness than NC beams, by 73%, 41%, 82%, and 88%, respectively. The bar diameter and concrete cover had a significant effect on increasing loads and resilience, while toughness decreased.

Lap splice assessment of GFRP rebars in reinforced concrete beams under flexure

To increase the knowledge and experience gained from the existing literature regarding the bond behavior of glass fiber-reinforced polymer (GFRP) rebars, a total of sixteen full-scale GFRP-reinforced concrete beams were subjected to a four-point bending test. The GFRP reinforcement comprised a single M16 (No.5) GFRP sand-coated bar without confinement reinforcement in the constant moment region. The research parameters encompassed three different lap-spliced lengths (i.e., 40-, 60- and 80-db) and two distinct concrete clear covers (i.e., 19 mm and 38 mm) to assess their impact on bond strength and failure modes. Strain gauges along the GFRP rebar and small potentiometers positioned at the end of the splice within the constant moment zone allowed detailed measurements. Rebar slippage in lap-spliced specimens was observed to have a limited impact on bond stress transfer capacity and member flexural stiffness until reaching maximum slippage. Concrete cover significantly influenced the behavior of lap-spliced GFRP-RC beams, with 38 mm-cc specimens exhibiting an average 21% higher capacity compared to 19 mm-cc specimens. The ACI expression exhibited an average overestimation of 24% for 19 mm-cc specimens, whereas for 38 mm-cc specimens, it offered a more accurate estimation, with only a 10% over-prediction. However, the computed lap splice length to achieve the required tensile stress was reduced from the one required by ACI due to extra factors implemented in the development length equation. This aligns with prior research findings that identified unconservative values of bond stress when employing the ACI provisions for specific combinations of parameters, highlighting the necessity for refinements in predictive models.

Seismic strengthening of deficient ground soft-story RC frames with inadequate lap splice using chevron brace

Deficient RC frames with ground soft-story irregularity have been constructed in many countries. Past earthquakes have shown that such structures are vulnerable and must be retrofitted. This study investigated the cyclic response of two one-bay, two-story, 1/2.5-scaled RC frames with inadequate lap splice length through experimental works and numerical simulations. One of the frames was kept as the reference, and the other was strengthened using a chevron brace system. The frames were subjected to displacement-controlled quasi-static cyclic loading, and their cyclic responses were recorded and compared. Besides, the lumped plasticity model was used to investigate the effect of the strength of infill walls on the force-displacement response of the retrofitted frame. The experimentally obtained results indicated that the employed chevron brace system significantly enhanced the cyclic response of the reference frame. The retrofitted frame exhibited a 171% greater ultimate strength than the reference frame. Besides, the retrofitted frame's initial and post-yield stiffness were 2.2 and 6.9 times greater than that of the reference frame. At a 3.5% drift ratio, the retrofitted frame dissipated 233% more energy than the reference frame. In small drift ratios, the retrofitted frame exhibited a faster decay in the lateral stiffness; however, at large drift ratios, both frames showed a comparable stiffness degradation rate. Numerical simulations showed that the infill wall's lateral strength could alter the retrofitted frame's failure mode and significantly affect its force-displacement response.