The steel fiber-reinforced polymer composite bars Known as (SFCB) are new kind of reinforcement, for concrete structures. A layer of glass fibers and reinforced polymer surrounding the steel bars ...resulting in the (GFRP), when used as concrete reinforcement contributes for enough, serviceability strength, and durability. Increasing the elastic modulus of GFRP bar, which have function of protecting corrosion in addition to reduce the initial cost of the FRP bar, is the purpose of hybridization. SFCB has the advantages of being noncorrosive, nonmagnetic nonconductive, and light in weight, along with high strength. This study presents the behavioral characteristics of RC beams, with tensile lap-spliced steel fibers-coated bars under flexure. Ten beam specimens were tested, with concrete cross-section of (25*40*420) cm and compressive strength of 30 MPa. One beam specimen, (R) was taken as reference as it was reinforced with no lap splice. Nine beam specimens were divided into three groups. Group (A) contained three beam specimens reinforced with SFCB of diameter 16 mm and lap splice of 50φ, one with stirrups, without stirrups and with staggered lap splice. Group(B) contains three beams reinforced with SFCB of 16 mm diameter and lap splice of 55 φ one with stirrups, without stirrups and with staggered lap splice. Group(C) contains three beam specimens reinforced with SFCB of 16 mm diameter and lap splice of 60 φ one with stirrups, without stirrups and with staggered lap splice. Beams were exposed to pure flexure. Crack patterns and results are presented along with stress-strain curves. Finally, conclusions are summarized and presented.
The advent of Ultra High Performance Concrete (UHPC) has led to strong interest in developing new structural applications for the material. While UHPC’s tensile and compression behaviors are ...relatively well understood, an in-depth analysis of UHPC’s behavior at the component level, specifically the bond strength between UHPC and steel bar reinforcement is lacking and the published data shows large scatter. In the presented study, a series of bar pull out tests was performed in order to characterize the bond strength of a non-proprietary UHPC blend. The tests were conducted using plain and epoxy-coated grade 60bars with nominal diameters of 13mm, 16mm, and 19mm. Other experimental parameters include three development lengths (50, 75 and 100mm), two casting orientations (longitudinal and transverse to the steel bar reinforcement), two steel fiber volume contents (1% and 2%) and early age bond strength at 1, 3 and 7days curing. Results from pull out testing show that bond strength decreases with increased embedment length suggesting a non-uniform distribution of bond strengths. Differences in steel fiber content yielded significant differences in bond strength of up to 36% when using 1% vs. 2% fiber volumes. Early age testing showed that 75% of compressive and bond strength in UHPC is developed within 7days of casting.
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.
•The tensile capacity of spliced bars increases by increasing radial stiffness of the GFRP sleeve connector.•The tensile capacity of steel sleeve spliced bars improved by increasing the bar embedment length, regardless of bar diameter.•Increasing confinement of the lap splice region with GFRP sheets can reduce the lap splice length.•The joint length of precast elements can be minimized by using a sleeve connector with adequate radial stiffness or by confinement of the lap splice region.
This study experimentally investigates the competing resistance mechanisms of reinforced concrete (RC) columns that are designed and constructed according to past standards and practices, which today ...are characterized as substandard; emphasis is given on testing the strength and the deformation capacity of lap-slices. Eight, 1:1 scale specimens of RC columns with substandard details were subjected to monotonic transverse loading, with or without the presence of axial compression, simulating column response to seismic excitation. Apart from axial loading, other parameters of study were the type of longitudinal reinforcement (smooth or ribbed) and the lap-slice configuration (straight or hooked, with dense or sparse stirrups). The experimental evidence served as proof-test of the Rapid Seismic Assessment system (RSA), which uses capacity prioritizing concepts to estimate the failure load of columns as the lowest strength among several competing mechanisms of resistance, such as flexure, shear, anchorage, or lap–splice.
•Experimental investigation of the response to transverse loading of 1:1 scale RC columns with details reflecting old construction practices.•Examination of detailing and axial loading effects on competing resistance mechanisms of RC columns.•Emphasis on lap-slice strength and deformation capacity.
The goal of the current research was to investigate – using the FE (finite element) modeling – the influence of externally attached CFRP (carbon FRP) U-wraps versus confining steel stirrups on ...enhancing the bond strength of substandard lap spliced GFRP (glass FRP) bars in concrete beams. The analysis incorporated modeling of the nonlinear response of concrete material and GFRP bars, bond-slip at the interface of concrete with GFRP bars, and contact between CFRP sheets and concrete substrate. Twenty-two concrete beams – internally reinforced with GFRP bars – were numerically studied in flexure. The studied variables involved the amount of confining steel stirrups, the number of CFRP layers, and the gap between spliced bars (0 and 1.5 times bar diameter). Besides two control beams, twenty beams had lap-spliced GFRP bars with a lap-splice length of 40 times bar diameter. Out of the 20 lap-spliced beams, two specimens were tested in flexure after being upgraded with externally attached CFRP laminates for the purpose of calibrating the FE modeling techniques. Based on the FE results, equations were suggested to compute the strain efficiency of the GFRP spliced bars in terms of the confining reinforcement index for both steel and CFRP-confined lap splice.
•Cyclic behavior of pre-damaged RC columns with deficient lap splice strengthened or retrofitted with UHPC and NSM was investigated.•The seismic performance of RC columns was significantly improved ...after strengthening or retrofitting with UHPC and NSM.•The design method addressing the pre-damage effect predicts well the flexural strength of RC columns and beams strengthened with UHPC.
Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.
Current design codes specify the bar development length empirically based on contact lap splice test results. The bar splice length of noncontact lap splices is not clearly specified due to limited ...test results. In the present study, the bond performance of noncontact lap splices was investigated. Lap splice tests were performed on 24 beam specimens under uniformly distributed moment or nonuniformly distributed moment with shear force. The test parameters were spacing of spliced bars, reinforcing bar diameter, transverse reinforcement, and moment distribution. The test results showed that the tensile stress of bar splices increased as the spacing of spliced bars increased in the specimens with stirrups. In the specimens under nonuniformly distributed moment with shear force, the bar splices exhibited better bond strength. The test results were compared with the predictions of current design codes. Keywords: lap splice; moment distribution; noncontact lap splice; reinforced concrete beam; reinforcing bar stress.
•Short lap splice of longitudinal reinforcement renders poor cyclic performance in columns with all shear span-to-depth ratios.•CFRP jacketing is effective to delay buckling of reinforcement, ...spalling and crushing of concrete, splitting cracks and shear failure in specimens with and without lap splices.•CFRP jacketing is effective to prevent gravity load collapse.•Nonlinear analysis based on multi-spring fiber section frame element can well simulate cyclic performances.
This paper presents an effective method for strengthening non-ductile reinforced concrete columns by applying an externally bonded Carbon Fiber Reinforced Polymer (CFRP) fabrics to enhance the shear capacity and confinement. Six rectangular reinforced concrete columns designed for gravity load only were tested under quasi-static cyclic loading. Three columns were provided with short lap-splice length of longitudinal reinforcements at the plastic hinge location to study the effect of lap splice. The experimental results indicate that, by means of CFRP jacketing, the shear strength under reversed cyclic loading is significantly improved as compared to the un-strengthened columns tested in the previous studies. In addition, owing to the confinement from CFRP, the columns exhibit a dramatically improved displacement capability. The nonlinear analysis of columns is also conducted by means of nonlinear fiber section frame element. The key attribute of the nonlinear analysis is to include the effect of lap splice of longitudinal reinforcement through the lap-spring spring model formulated according to the tri-uniform bond stress model. By combining the stress-strain models of concrete, steel reinforcement, lap-splice’s bond model, anchorage bond slip and nonlinear shear spring into the fiber section frame element, the numerical results shows a good agreement with experimental ones.
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 %.
•Rapid hardening concrete (RHC) achieved by using polycarboxlate ether-based.•Technique used to determine behavior of RHC and NC beams with tension splices.•An experimental test performed to determine adequate tension lap splice in RHC.•Comparison carried out between paper results and codes limits.
•Nine large-scale shear walls were tested including seven precast specimens and two cast-in-place specimens.•PC shear walls used lap splice that one of the spliced bar was embedded into a ...grout-filled hole reserved by metal bellow or expanded metal mesh.•A reasonable strut-and-tie model was proposed to investigate the force transfer mechanism of the specimens.
This paper discusses the seismic performance of nine full-scale shear walls including seven precast specimens and two cast-in-place specimens. The precast specimens were designed to emulate monolithic cast-in-place specimens. The precast upper shear wall and the base were connected at their interface through lap splice that one of the spliced bar was embedded into a grout-filled hole, which was reserved by metal bellow or expanded metal mesh. The geometries and reinforcement of precast specimens were identical with those of corresponding cast-in-place specimens in each group. But their stirrups were different. Based on the two types of grouted connections, the specimens were tested under low cyclic lateral loading to study their seismic performance by comparing their carrying capacities, crack patterns, ductility, hysteretic curves and energy dissipation. In general, shear walls with metal bellows at the joint exhibited better structural behaviour than the shear walls with expanded metal mesh due to their well confined effect on the spliced bars and surrounding concrete. Thus, this kind of precast connection may emulate cast-in-place connection. Lastly, a reasonable strut-and-tie model was developed based on ACI 318-14 code to investigate the force transfer mechanism of the precast shear wall. The calculated results were compared with the test results and the shear strength results calculated by empirical expression in the ACI 318-14 code.
