• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.571-572
• /
• 2009

Current design codes regarding compression lap splice dose not utilize merits of the improved strength of ultra-high strength concrete. Especially, a compression lap splice can be calculated longer than a tension lap splice according to the codes because they do not consider effects of strength of concrete and transverse reinforcement. Design equation is proposed for compression lap splice in 40 to 70 MPa of compressive strength of concrete. The proposed equation is based on 51 specimens. Through two-variable non-linear regression analysis of measured splice strengths, a splice strength equation is derived, which is converted into a splice length equation.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3A
• /
• pp.227-234
• /
• 2011

Recently, a high strength concrete of more than 40 MPa has been increasingly used in practice. However, use of the high strength concrete may influence on design parameters, particularly stress distribution. This is very true since the current everyday practice employs equivalent rectangular stress distribution that is derived from normal strength concrete. Subsequently, the stress distribution seems to be reevaluated and then a new distribution with new parameters needs to be suggested for the high strength concrete. For this purpose, linear and multiple regression analyses have been carried out in term of using experimental data for the high strength concrete of 40 to 80 MPa available in literatures. Accordingly, new parameters associated with the stress distribution have been proposed and employed for the design of flexural and compressive members. Comparative design examples indicate that designs with new parameters reduce section dimensions compared to those with the current code parameters for concrete strengths of 40 to 70 MPa. In particular, for compressive members, design with new parameters exhibit conservative compressive force compared to those with the current code parameters.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.521-524
• /
• 2011

본 논문에서는 순환골재에 대하여 구조용 적용성 검증을 목표로 하였으며, 천연골재와 순환골재 치환율에 따른 압축파괴강도와 압축강도증가에 따른 파속도의 상관관계를 비교 분석하였다. 설계기준강도 21, 27, 35MPa에 순환굵은골재 치환율 0, 30, 50, 100%를 적용하여 설계기준강도에 따른 순환굵은골재 치환율의 배합을 총 12가지로 설정하였다. 재령160일까지의 압축파괴강도의 변화를 대기양생 공시체, 수중 양생공시체 그리고 코어공시체를 이용하여 비교하였고, 모의부재(800${\times}$800${\times}$200mm)를 통하여 재령160일까지의 초음파속도를 측정하였다. 압축파괴실험을 통하여 취득한 데이터를 비교해 본 결과 순환굵은골재 치환율에 따른 강도저하현상은 나타나지 않았다. 또한, 재령일에 따른 강도 증가와 함께 파속도도 같이 증가함을 알 수 있었다.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.4
• /
• pp.107-115
• /
• 2012

The present study evaluates the validity of different equations specified in code provisions and proposed by the existing researchers to predict the concrete tensile capacities (direct tensile strength, splitting tensile strength and modulus of rupture) using a comprehensible database including 361 lightweight concrete (LWC), 1,335 normal-weight concrete (NWC) and 221 heavy-weight concrete (HWC) specimens. Most of the equations express the concrete tensile strengths as a function of its compressive strength based on the limited NWC concrete test data. However, the present database shows that the concrete tensile capacities are significantly affected by its unit weight as well. As a result, the inconsistency between experiments and predictions by the different models increases when the concrete unit weight is below 2,100 kg/$m^3$ and concrete compressive strength is above 50 MPa. On the other hand, new models proposed by the present study considering the concrete unit weight predict the tensile strengths of concrete with more accuracy.

• Journal of the Korea Concrete Institute
• /
• v.27 no.5
• /
• pp.521-530
• /
• 2015

Design of fiber reinforced ultra-high strength concrete members should be verified with analytical or experimental methods for safety. Members with compressive strength larger than limitation of current design code usually be designed with analytical verification using stress-strain relation of concrete and reinforcements. For this purpose, mechanical characteristics of steel fiber reinforced ultra-high strength concrete were defined under uniaxial compression. Mix proportions of test specimens were based on reactive powder concrete and straight steel fibers were mixed with different volume fraction. Compressive strength of matrix were distributed from 80 MPa to 200 MPa. Effect of fiber inclusion were investigated : increase of compressive strength of concrete, elastic modulus and strain corresponding to peak stress. For the wide range application of investigation, previously tested test specimens were collected and used for investigation and estimation equation. Based on the investigation and evaluation of previous research results and estimation equation of mechanical characteristics of concrete, regression equations were suggested.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.2
• /
• pp.403-413
• /
• 2014

For the reliable design of the structural concrete by the strut-tie model approaches of current design codes, the effective strengths of concrete struts must be determined with sufficient accuracy. Many values and equations for the effective strengths have been suggested until now. As those are for the two-dimensional concrete struts, however, it is inappropriate to employ them in the strut-tie model designs of three-dimensional structural concretes. In this study, an approach, that determines the effective strengths of three-dimensional concrete struts consistently and accurately by reflecting the state of 3-dimensional stresses, the 3-dimensional failure criteria of concrete, the degree of cracks (or tensile strains of reinforcing bars crossing the struts), the strut's longitudinal length, the deviation angle between strut orientation and compressive principal stress flow, compressive strength of concrete, and the degree of concrete confinement by reinforcing bars, is proposed. To examine the validity of the proposed approach, the ultimate strength analyses of 115 reinforced concrete pile caps tested to failure by previous investigators were conducted by the ACI 318-11's strut-tie model approach with the existing and proposed effective strengths of concrete struts.

• Journal of the Korea Institute of Building Construction
• /
• v.14 no.4
• /
• pp.336-342
• /
• 2014

Shear strengths of reinforced high strength concrete beams without web reinforcement are studied with experimental analysis of 10 specimen with 2.4 shear span-to-depth ratio (a/d) beams for 4 stages of concrete compressive stength over 60MPa comparing ultimate loads and shear stresses of ACI363R and KCI code equations. Expecially, concrete compressive strengths used in shear design were essentially limited to 10,000 psi (69MPa) by ACI363R and KCI Code. The modified Code equation's shear stresses of the specimen without the limit are compared with test results. The comparison between the modified exist Code equations results and test results are expected to show an available scope to apply in construction field and to give considerations of design and contraction.

• Journal of the Korea Institute of Building Construction
• /
• v.18 no.6
• /
• pp.543-550
• /
• 2018

The RC buildings which are constructed on the seaside are followed by KBC(2016) to achieve the minimization of durability damage. To control the corrosion of the reinforcing steel bar by salt attack, W/C should be under 0.4 and specified concrete strength is higher than 35MPa in the concrete/building construction standard specification. Even though it has been proved that the concrete mixed with mineral admixture such as blast furnace slag and fly ash etc. have high strength and durability in previous researches, the beneficial informations are not applied to the codes. Ready-mixed concretes which usually include the admixtures in Busan were tested to certify the salt attack durability. In the same specified concrete strength, remarkable salt attack durability was evaluated in comparison to OPC. For economical and reliable durability design, chloride ion diffusivity should be measured before applying to new building construction.

• Journal of the Korea Concrete Institute
• /
• v.29 no.4
• /
• pp.335-343
• /
• 2017

This paper aims at investigating the bending strength of high-strength concrete beams with compressive strength of 80 MPa. The experimental parameters included nominal yielding strength of rebar with 400 and 600 MPa, rebar ratio ranging from 0.98 to 1.97%, and shear span-effective depth ratios (a/d) of 6.0 and 4.8. Experimental results were discussed regarding load-deflection relationship, ductility, bending strength, and prediction of bending strength of beams. Test results indicate that the use of high-strength rebar increased bending strength but decreased ductility. As span-effective depth ratio increased, the ductility of test beams decreased. In addition, test results of bending strength were compared with predictions from the current KCI code, Eurocode 2 and Korean Highway Design Specification (KHDC). The design code predictions for bending strength underestimated the experimental results. Therefore, the current design code predictions for bending strength of high-strength concrete beams would provide conservative design. Predictions of bending strength from KCI code using strength reduction factors and those from Eurocode 2 as well as KHDC using material factors were similar each other.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.6
• /
• pp.206-215
• /
• 2017

An experimental program was carried out to investigate the mechanical properties of high-strength concrete. High-strength concrete with compressive strengths of 80 to 120 MPa was tested. Test results are presented regarding effect of water-binder ratio on compressive strength and compressive strength gain. In addition, the effect of curing methods on compressive strength, elastic modulus, splitting tensile strength, and modulus of rupture is investigated. Test results of elastic modulus, splitting tensile strength, and modulus of rupture are compared with predictions from the current design recommendations. Predictions of elastic modulus by using KCI recommendation has good agreement with test results. However, predictions of modulus of rupture by using KCI recommendation underestimate the test results. ACI 363R recommendations predict well test results of splitting tensile strength and modulus of rupture. ACI 363R recommendations for predicting splitting tensile strength and modulus of rupture can be used for high-strength concrete with compressive strengths up to 120 MPa.