RC Specimen Research Articles

Seismic performance of HECC/RC beam–column external joint with no stirrup and reduced anchorage length in core region

In this paper, steel–polyethylene hybrid fiber-reinforced strain-hardening cementitious composites (HECC) are applied in beam–column external joint core region to form a novel HECC/reinforced concrete (RC) composite beam–column joint with reduced anchorage length of beam longitudinal rebar and eliminated transverse rebar, and thus to alleviate rebar congestion and simplify the construction process efficiently especially for precast RC frame structures. Five external beam–column joint specimens are constructed and tested under cyclic loading to illustrate the influences of the anchorage length of beam longitudinal rebar and longitudinal rebar ratio on the seismic performance of beam–column joint. The effects of design parameters on seismic performance, including hysteresis behavior, degradation of strength, energy dissipation capacity, and cracking patterns are discussed in detail. Experimental results indicate that the replacement of normal concrete with HECC in beam–column joint core region could apparently reduce the amount of stirrups in the joint core area while maintaining reliable seismic behavior. Remarkably, specimen with no stirrups in the core area exhibits nearly equivalent seismic behavior to that of the control RC specimen. Furthermore, the application of HECC in joint core area allows for a substantial reduction of the required anchorage length for the beam longitudinal rebar to 9d, which further simplifies the construction process considerably.

Experimental study on the progressive collapse resistance of emulative precast concrete beam-column subassemblies with various anchorage details

In this study, seven emulative precast concrete (PC) beam-column subassemblies with or without connecting bars and one concrete (RC) were fabricated and tested to investigate the effect of various types of anchorage detailing for reinforcing and connecting bars on the progressive collapse resistances. Two anchorage detailing formats for steel bars with bending and straight ends were used in the PC specimens for both the reinforcing and connecting bars. Test results show that, as found in the RC specimen, resisting mechanisms including pure flexure, compressive arch action (CAA) and tensile catenary action (TCA) were sequentially activated in all PC specimens. It is demonstrated that the connecting bars improved the progressive collapse resistance in both the CAA and TCA stages. The effect of the anchorage detailing was found to be negligible in CAA stage. However, in the TCA stage, the proper usage of the straight end for steel bars was helpful to improve the deformation capacity and thereafter enhanced the progressive collapse resistance. When the loading resistance, the deformation capacity as well as the construction flexibility are taken into account, the configuration consisting of both reinforcing and connecting bars with straight end as anchorage detailing is recommended for the design of precast beam-column connections in case a central column removal scenario is assumed.

An Assessment of the Structural Performance of Rebar-Corroded Reinforced Concrete Beam Members

This paper aims to determine the effects of local corrosion at three different corrosion areas, the (1) entire area, (2) the constant moment area, and (3) the constant shear area, on the flexural performance of RC beams. To analyze this, an experimental study was carried out to prepare two series of RC beams (200 × 300 × 2800 mm) created with three different degrees of corrosion, inducing local rebar corrosion. Furthermore, two series of experimental tests were conducted under different loading types: monotonic and cyclic loading. It was observed that the strength capacity reduction grew in the RC specimens with induced corrosion in the order of the (1) entire area > (2) the constant moment area > (3) the constant shear area, as the average corrosion rate increased. Our test results further showed that the yield and ultimate strength were kept nearly equivalent to the uncorroded RC specimen, with average corrosion rates of 10% and 15%, respectively. Over these corrosion rates, the yield strength and ultimate strength dropped significantly. Compared to the test results under a monotonic loading condition, the structural capacity under a cyclic loading condition decreased, with a more pronounced tendency for each corrosion case as the corrosion rate increased. Longitudinal cracks developed throughout and adjacent to the corrosion areas as the corrosion rate increased. Thus, we can infer that strength reductions may be strongly influenced by these longitudinal cracks.

Structural behavior of reinforced concrete tunnel linings with synthetic fibers addition

Fiber-reinforced-concrete has been widely used in underground structures in recent years, especially in tunnel linings. Compared with steel fiber reinforced concrete, synthetic fiber reinforced concrete not only has a considerable structural bearing capacity but also shows a better corrosion resistance and durability. However, most researchers focused on the cracking resistance property of synthetic fiber reinforced concrete instead of its mechanical contribution. Besides, experiments were carried out mostly on structural components such as beams or segments. There is little information about the performance of synthetic fiber reinforced concrete in full-scale tunnel lining rings. In this study, full-scale experiments were carried out for tunnel lining specimens with synthetic fiber reinforced concrete and traditional reinforced concrete. The experimental results are compared to evaluate the different structural behaviors between the fiber-reinforced and the steel-reinforced concrete specimens. The failure mechanism of the synthetic fiber reinforced concrete tunnel lining was investigated and compared to that of the traditional RC tunnel lining. The results show that the addition of synthetic fibers can delay the occurrence of yielding state and lead to a higher yielding load compared to the traditional RC specimen. The approach of reducing steel reinforcement by adding synthetic fibers appears to be a viable method to optimize the lining design. The differences in cracks, bearing capacity, stiffness, and other mechanical behaviors between the synthetic fiber reinforced concrete and the traditional reinforced concrete tunnel lining structures are also discussed. The results show that the synthetic fiber reinforced concrete tunnel lining structure has a different failure mechanism and better performance than the traditional RC tunnel lining structures. With a 47% reduction of steel reinforcement in the lining segments, the bearing capacity and other mechanical properties of the synthetic fiber reinforced concrete tunnel lining structure can still be comparable to those of the traditional RC tunnel lining structures.

Shear behaviour of beams strengthened using different Ni-Ti-Nb shape memory alloy wire configurations and design proposal based on the compression chord Capacity model (CCCM)

Shear strengthening of existing structures is often required in cases where shear strength is deficient because shear failures in RC members are associated with brittle collapse. In previous papers, the authors presented an innovative system for active strengthening shear critical-reinforced concrete (RC) beams using shape memory alloys (SMA) to take advantage of the shape memory effect. The authors also presented an approach to design this type of reinforcement based on the Compression Chord Capacity Model (CCCM). This model considers several shear transfer actions, including increased shear strength of the concrete compressed chord due to its confinement.This article presents an experimental study of RC beams with new types of SMA strengthening systems that also improve the shear behaviour of beams.The new types of tested shear strengthening systems are U-shaped external wires to facilitate the construction process by reducing initial imperfections; spiral active SMA wire implanted into a groove in the lower RC specimen part to see if it improves the dowel action effect; spiral active SMA wire only confining the compressed chord to check whether the CCCM predictions in this regard are adequate.

Corrosion level estimation by means of the surface crack width

Since the concrete cover cracking is the earliest visible manifestation of corrosion, a relationship between crack opening and corrosion level can be a useful non-destructive tool to estimate the degradation level of an existing RC member. In the present paper, the predictive formulations available in the scientific literature estimating the crack width due to a given corrosion level are accurately described and their reliability is evaluated by a statistical analysis of the error in the predictions. At this aim, an extensive dataset on crack openings of artificially corroded RC specimen reinforced with a single bar, or more bars with large spacing, has been collected. Finally, a novel relationship for the assessment of the corrosion degradation from the surface cracking is presented and validated.

Flexural Strength and Stiffness of Donut-Type Voided Slab

The voided slab system has been known as an effective technique to replace a heavy reinforced concrete slab system without the decrease in flexural strength. However, according to the previous studies, the flexural capacities such as flexural strength, stiffness and ductility of the voided slabs were practically lower than that of the solid slabs depending on the void shapes and details. Therefore, in this study, an analytical and experimental study were conducted to derive the optimal void shape and details focused on the flexural capacities of voided slabs. Based on a finite element (FE) analysis, a donut-type void shaper, which was a hexahedron with rounded edges and a hole penetrating the center, was suggested as the optimal shape in voided slabs, and an experimental study was conducted to verify flexural capacities of the donut-type voided slab. The flexural strength, stiffness and deflection of the donut-type voided slab were investigated by void shape and fixing method of void shaper as variables. The ductility of voided slab was also evaluated, because ductility is as important as strength for the safe design of slab member. The test results showed that the flexural strength of the donut-type voided slabs was equivalent to 98% and 105% that of the solid RC specimen, and the donut-type voided slab specimens had enough ductility for the flexural member. The stiffness of the donut-type voided slab was decreased about 8~9% compared with the solid slab, but it was improved up to 7% compared to the non-donut-type voided slab. Based on test results, the flexural design method of the donut-type voided slab associated with the void shape and fixing device of void shaper was suggested, and it was confirmed that the donut-type voided slab is one of the efficient alternatives to replace heavy flat plate slabs.

Experimental and numerical investigation of the progressive collapse of precast reinforced concrete frame substructures with wet connections

In precast reinforced concrete frame structures, beam-column joints suffer severe damage under large deformations, which may significantly influence their performance in resisting progressive collapse. A static progressive collapse test was conducted on one conventional reinforced concrete beam-column substructure (RC) and four precast reinforced concrete beam-column substructures with wet connections (PCWC). A quasi-uniformly distributed load was applied to the substructures to simulate gravity loads. The first group of PCWC specimens consisted of two specimens with different layouts of mechanical sleeves, in which the beam and column reinforcements were connected through mechanical sleeves and grout-filled coupling sleeves, respectively. In the second group of PCWC specimens, the beam and column reinforcements were joined through a 90° bend anchorage and lapping in grout-filled holes, respectively. In one of the PCWC specimens in this group, unbonded prestressed strands (UPS) were also adopted. For the first group, premature failure of the mechanical sleeve connections occurred, which reduced the collapse resistances of the PCWC specimens compared with that of the RC specimen. For the second group, the damage mode and collapse resistance of the specimen without UPS were similar to those of the RC specimen. Furthermore, the collapse resistance of the specimen with UPS, which generated additional axial force along the beam, was greater than that of the RC specimen. The connections of the column reinforcements in all PCWC specimens exhibited robustness under large deformations of progressive collapse, even though large horizontal deformations and slips along the grout-layer were observed in the specimen with UPS. An analytical model was then developed to study the collapse resistances of the specimens, particularly the contributions of the compressive arch action and the catenary action. Finally, numerical simulations were used to optimize the configurations of PCWC connections, namely the arrangements of the mechanical sleeves, levels of the UPS, and strength of the cast-in-situ concrete, to improve their performance in resisting progressive collapse.

Characterization of Application Methods for Textile-Based Composite Structures in Coastal Environments

Park, J.; You, J.; Park, S.-K.; Ryu, S.-C., and Hong, S., 2021. Characterization of application methods for textile-based composite structures in coastal environments. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 131-135. Coconut Creek (Florida), ISSN 0749-0208. Textiles exhibit many advantages including high strength/weight ratio and high corrosion resistance. Therefore, textiles can substitute steels in textile-reinforced concrete (TRC) and can strengthen existing RC structures, such as textile-reinforced mortar (TRM), in coastal environments. However, there is a difference in the structural performance of TRC and TRM so that it is important to clearly distinguish the behavior of textile-based composites. In this study, the flexural performance, serviceability, ductility, and fabrication process of TRC and TRM were analyzed and compared via two separate application. The results of the experiments were expressed as indexes, which were compared with that of the reference RC specimen. Finally, an efficient method for applying textile-based composite structures in a coastal environment was considered in terms of flexural strength, serviceability, ductility, and fabrication process. The TRM composite exhibited unstable behavior after the yield stage. The TRC composite exhibited stable behavior in all the loading stages and showed higher ductility than that of the TRM composites. The results of this study are expected to aid in the selection of an appropriate application method for conducting intensive durability verification.

Evaluating the effect of corrosion on shear-critical RC beams by integrated NDT

Integrated non-destructive testing (NDT) method consisting of acoustic emission (AE) and digital image correlation (DIC) was used to monitor and evaluate the load-behaviour of shear-critical reinforced concrete beams subjected to corrosion. Measurement data in the forms of mechanical load, deflection, surface strain and AE signals were processed and collectively analysed to facilitate interpretation of damage development and change of structural behaviour in a more comprehensive manner. Results show that when corrosion level increases, the failure mode of the beams changes from shear to flexure, leading to an increase in beam ductility. The steel-concrete bond deterioration caused the change of internal force transfer mechanism when beams were loaded, as indicated by DIC strain maps and AE b-value analysis. Integrated NDT method demonstrates the potential to intuitively and quantitatively indicate damage development of the RC specimen.

Response of low-percentage FRC slabs under impact loading: Experimental, numerical, and soft computing methods

Application of fiber reinforced concrete (FRC) has been increased in the past decade due to its enhanced structural performance. Therefore, it is important to fully characterize its static and dynamic behavior under different loading scenarios. In this paper, the effects of low-percentage steel fibers with four different fiber volume is investigated on the dynamic responses of concrete slabs. First, a series of experimental tests are conducted. Next, the results are used to validate a nonlinear finite element model under impact loading. Finally, a large dataset of numerical simulations are developed using appropriate design of experiments, and four soft computing techniques are used to predict the target responses.The findings show that application of low-percentages fiber increases the acceleration response of the concrete slabs subjected to impact load, on the average of 102%. The slab’s stiffness increases with an increase in fiber percentage. The dominant frequency, the damping ratio, as well as the slab’s cracking pattern, and the failure modes indicate that FRC slabs are stiffer than conventional RC specimen. The numerical simulations reasonably estimate the maximum acceleration. Outcome of the predictive meta-models can be used to estimate the dynamic behavior of similar slabs with no additional experimental and numerical costs.

PD42-01 RESIDUAL MUSCLE-INVASIVE DISEASE AT CYSTECTOMY IS NOT ACCURATELY PREDICTED BY POST-CHEMOTHERAPY RESTAGING PROTOCOLS INCLUDING DNA DAMAGE RESPONSE GENE MUTATION ANALYSIS

You have accessJournal of UrologyBladder Cancer: Basic Research & Pathophysiology III (PD42)1 Apr 2020PD42-01 RESIDUAL MUSCLE-INVASIVE DISEASE AT CYSTECTOMY IS NOT ACCURATELY PREDICTED BY POST-CHEMOTHERAPY RESTAGING PROTOCOLS INCLUDING DNA DAMAGE RESPONSE GENE MUTATION ANALYSIS Russell Becker*, Alex Baras, Alexa Meyer, Aaron Brant, Adam Reese, George Netto, Andres Matoso, Jean Hoffman-Censits, Noah Hahn, Woonyoung Choi, David McConkey, Phillip Pierorazio, Michael Johnson, Mark Schoenberg, Max Kates, and Trinity Bivalacqua Russell Becker*Russell Becker* More articles by this author , Alex BarasAlex Baras More articles by this author , Alexa MeyerAlexa Meyer More articles by this author , Aaron BrantAaron Brant More articles by this author , Adam ReeseAdam Reese More articles by this author , George NettoGeorge Netto More articles by this author , Andres MatosoAndres Matoso More articles by this author , Jean Hoffman-CensitsJean Hoffman-Censits More articles by this author , Noah HahnNoah Hahn More articles by this author , Woonyoung ChoiWoonyoung Choi More articles by this author , David McConkeyDavid McConkey More articles by this author , Phillip PierorazioPhillip Pierorazio More articles by this author , Michael JohnsonMichael Johnson More articles by this author , Mark SchoenbergMark Schoenberg More articles by this author , Max KatesMax Kates More articles by this author , and Trinity BivalacquaTrinity Bivalacqua More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000922.01AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The standard of care for eligible patients with muscle-invasive bladder cancer (MIBC) includes neoadjuvant cisplatin-based chemotherapy (NAC), followed by radical cystectomy and urinary diversion (RC). Deleterious DNA damage response (DDR) gene mutations have been correlated with favorable response to NAC. Several groups have proposed that including DDR mutation analysis in post-NAC restaging algorithms may help define a subset of favorable responders who can safely forego RC. We sought to test this hypothesis in a cohort of patients undergoing NAC and RC. METHODS: We identified patients in our institutional RC registry who underwent a prospective protocol of post-NAC restaging prior to RC, between 2003 and 2016. Tumor DNA was captured from pre-NAC tumor specimens, and sequenced for mutations in the DDR genes ATM, RB1, ERCC2, and FANCC by Illumina HiSeq. Pathologic stages based on post-NAC restaging findings (rT) and final pathologic evaluation of the RC specimen (pT) were categorized into ≤ T1 (including carcinoma in situ) or ≥ T2, as this represents a critical inflection point in both prognosis and management strategy. RESULTS: A total of 47 patients received adequate NAC followed by restaging and RC, and had tumor tissue available for sequencing. Of these, 31 (66%) had DDR mutations, with ATM mutations being the most prevalent (21/47, 45%). Restaging and pathologic T-stage categories were concordant in 38/47 patients overall (81%), and 24/31 DDR(+) patients (77%). For patients with ≤ rT1 on post-NAC restaging, final RC pathology revealed residual muscle-invasive disease (≥ pT2) in 7/25 patients overall (28%), and 5/15 DDR(+) patients (33%, Fisher’s exact test p=0.66). CONCLUSIONS: For some favorable responders, MIBC can be downstaged or even eradicated by NAC alone. However, current restaging protocols lack the precision to reliably identify these patients, as evidenced by the 7 patients falsely downstaged in our series. The addition of DDR gene mutation analysis to restaging protocols does not enhance their accuracy. Until better discriminators are developed, post-NAC restaging and DDR mutations should not be routinely used to guide management decisions. Source of Funding: none © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e827-e827 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Russell Becker* More articles by this author Alex Baras More articles by this author Alexa Meyer More articles by this author Aaron Brant More articles by this author Adam Reese More articles by this author George Netto More articles by this author Andres Matoso More articles by this author Jean Hoffman-Censits More articles by this author Noah Hahn More articles by this author Woonyoung Choi More articles by this author David McConkey More articles by this author Phillip Pierorazio More articles by this author Michael Johnson More articles by this author Mark Schoenberg More articles by this author Max Kates More articles by this author Trinity Bivalacqua More articles by this author Expand All Advertisement PDF downloadLoading ...

Punching shear resistance of supplementary cementitious concrete slab

This paper analyses the Punching shear resistance of RC slab using different mineral admixtures like Ground Granulated Blast Furnace (GGBS), Silica fume and Alkali resistant (AR) glass fibers. Here, silica fume and GGBS are partially replaced with cement at different proportions of 0, 10, 20, 30% and 0.5% of AR glass fibers are added to the total volume of concrete. Strength studies of Split tensile, Bending and Compressive strength done for M40 grade of concrete and compared to the control concrete. The optimum percentage obtained at 20% replacement of cement on these studies is used for designing of RC slab. RC specimen of (1000 × 1000 × 60 mm) of dimension was casted with optimum strength and subjected to single point loading with Discontinued on all the side conditions on loading frame. Cracking and deflection are analyzed experimentally. The loads, deflections and crack configurations of strengthened specimen were compared to the control specimen with same dimension to determine the behavior of slab.

Static load test on progressive collapse resistance of fully assembled precast concrete frame structure

The progressive collapse behavior of fully assembled PC structures using dry connections under explosion, uncontrolled fire, and vehicle impact loads has seldom been studied. In the present study, three half scale moment sub-structures including a conventional RC specimen and two PC specimens using dowel bars and corbel were tested to investigate the progressive collapse performance. Collapse of the moment frame specimens with two spans was generated by the mid-column removal scenario under static loading. The test result showed that the peak strength of the PC specimens was only 76–81% of that of the RC specimen in compressive arch action and the ultimate displacement of the mid-column was 72–77% of that of the RC specimen. Unlike the RC specimen, catenary action was not completely developed in the PC specimens showing lower ductility. The load-displacement relationship and failure modes of the specimens agreed well with the prediction by finite element analysis, and a parametric study was conducted addressing various connection details to improve the progressive collapse performance of the PC moment sub-structure.

Numerical Simulation on the Dynamic Splitting Tensile Test of reinforced concrete

The research for crack resistance was of RC was based on the split Hopkinson bar and numerical simulate software LS-DYNA3D. In the research, the difference of dynamic splitting failure modes between plane concrete and reinforced concrete were completed, and the change rule of tensile stress distribution with reinforcement ratio was studied; also the effect rule with the strain rate and the crack resistance was also discussed by the radial tensile stress time history curve of RC specimen under different loading speeds. The results shows that the reinforcement in the concrete can impede the crack extension, defer the failure time of concrete, increase the tension intensity of concrete; with strain rate of concrete increased, the crack resistance of RC increased.

Tumor heterogeneity of fibroblast growth factor receptor 3 (FGFR3) mutations in invasive bladder cancer: implications for perioperative anti-FGFR3 treatment

Fibroblast growth factor receptor 3 (FGFR3) is an actionable target in bladder cancer. Preclinical studies show that anti-FGFR3 treatment slows down tumor growth, suggesting that this tyrosine kinase receptor is a candidate for personalized bladder cancer treatment, particularly in patients with mutated FGFR3. We addressed tumor heterogeneity in a large multicenter, multi-laboratory study, as this may have significant impact on therapeutic response. We evaluated possible FGFR3 heterogeneity by the PCR-SNaPshot method in the superficial and deep compartments of tumors obtained by transurethral resection (TUR, n = 61) and in radical cystectomy (RC, n = 614) specimens and corresponding cancer-positive lymph nodes (LN+, n = 201). We found FGFR3 mutations in 13/34 (38%) T1 and 8/27 (30%) ≥T2-TUR samples, with 100% concordance between superficial and deeper parts in T1-TUR samples. Of eight FGFR3 mutant ≥T2-TUR samples, only 4 (50%) displayed the mutation in the deeper part. We found 67/614 (11%) FGFR3 mutations in RC specimens. FGFR3 mutation was associated with pN0 (P < 0.001) at RC. In 10/201 (5%) LN+, an FGFR3 mutation was found, all concordant with the corresponding RC specimen. In the remaining 191 cases, RC and LN+ were both wild type. FGFR3 mutation status seems promising to guide decision-making on adjuvant anti-FGFR3 therapy as it appeared homogeneous in RC and LN+. Based on the results of TUR, the deep part of the tumor needs to be assessed if neoadjuvant anti-FGFR3 treatment is considered. We conclude that studies on the heterogeneity of actionable molecular targets should precede clinical trials with these drugs in the perioperative setting.

Effect of steel and synthetic fibers on shear strength of RC beams without shear stirrups

This study presents the influence of the type and volume fraction of fibers in the concrete mix on the shear strength of RC beams. One RC (control) and six fiber reinforced concrete (FRC) beam specimens are tested under the gradually increasing monotonic loading. Both high-modulus (steel) and low-modulus (polypropylene) fibers of either 0.5% and 1% volume fraction in concrete are used in FRC specimens. Shear stirrups are completely eliminated in the half-span of the FRC specimens. A better post-peak residual strength response is noticed in case of all FRC beam specimens due to multiple cracking associated with the fiber bridging action. The main parameters investigated are shear strength, failure mechanism and displacement ductility. In the absence of shear stirrups, the peak shear resistance and mid-span displacement of the FRC specimen 1% of polypropylene fibers only reached about 70% and 50% of corresponding values for the RC specimen. The FRC specimens with combined steel and polypropylene fibers of minimum volume fraction of 0.5% in the concrete reached the same shear strength as RC specimen in the absence of shear stirrups. However, the shear resistance and deformability values are improved by 20% and 40%, respectively, when the polypropylene fibers of 1% of volume fraction were added to the concrete in addition to the steel fiber of 1% fiber content. Further, multiple cracks of smaller crack width are noticed at the failure stage of the CFRC specimens indicating the better fiber bridging action of combined metallic and nonmetallic fibers.

해상 프리캐스트 콘크리트 부유체 모듈 가접합을 위한 마이크로 실리카 혼입 수중용 에폭시 접합 성능 검토 : Part 2 - 구조 접합 성능 평가

ABSTRACT Recent studies to develop Very Large Floating Structure(VLFS) has shown that the construction procedure of the structure needs to acquire precast concrete module connection sy stem using prestressing. Howeve r, the loads occurring on water are complex combinations of various condition, so the safe and stable performance of the module joints and bonding materials are ke y to the success of the construction. Therefore, micro-silica mixed aqua-epoxy development was introduced in Part 1 using a bonding material developed in this study. The performance of the micro-silica mixed aqua-epoxy(MSAE) applied joint of concrete module specimens connected by prestressing tendon was evaluated to verify the usability and safety of the material. RC beam, spliced b eam connected by prestressing tendon and MSAE, and continuous prestressed concrete beam were tested for their initial cracking and maximum loads as well as cracking procedure and pattern. The results showed that the MSAE can control the stress concentration effect of the shear key and the crack propagation, and the maximum load capacity of MSAE joint specimens are only 5% less than that of continuous RC specimen. The details of the study are discussed in detail in the paper.

연성 강봉을 사용한 프리캐스트 콘크리트 보-기둥 접합부의 내진성능

Precast concrete (PC) beam-column connections using ductile rods are proposed for earthquake zone. An existing beam-column connection, two PC specimens designed by considering failure modes and a conventional RC specimen were tested under cyclic loading to evaluate the seismic performance. The specimens were designed to satisfy the requirements of current design code. The variables are the yield strength of longitudinal reinforcing bars of PC beams. The test results showed that the proposed system applying smaller yield strength of the longitudinal reinforcing bars at the PC beams than the ductile rods was satisfied with seismic criteria. The deformation capacity and energy dissipation capacity of the proposed PC beam-column connections were greater than those of the existing DDC system.

Influence of Steel and Polypropylene Fibers on Flexural Behavior of RC Beams

Seven full-scale concrete beam specimens are tested under gradually increasing monotonic loading to investigate their overall flexural response due to the addition of both metallic and nonmetallic fibers to the concrete. Steel and polypropylene fibers of 0.5% and 1.0% volume fraction are used in the fiber-reinforced concrete (FRC) beam specimens. No improvement is noticed in the compressive and splitting tensile strengths of concrete due to the addition of polypropylene fibers only. However, an improvement of 25-100% in the concrete splitting tensile strength is noticed when either steel or combined fibers are added to the concrete. Although an increase in fiber content in the combined FRC improves various mechanical properties, its influence on the peak load-resisting capacity of the full-scale beam specimens is rather limited. An increase of both steel and polypropylene fibers in excess of 0.5% volume fraction does not improve the ultimate flexural resistance of beams due to the uneven distribution of similar sizes of fibers in the presence of reinforcing steel bars. However, displacement ductility of the beam specimens is improved by 120% as compared with the RC specimen, when only polypropylene fibers of 1% volume fraction are added to the concrete. A better postpeak residual strength response is noticed in case of all FRC beam specimens due to multiple cracking associated with the fiber-bridging action.