In this study, the flexural behavior of noncompact and slender concrete-filled U-section (CFU) beams was investigated focusing on local buckling of U-section walls and shear transfer across the beam-to-slab interface. Seven large-scale CFU beam specimens were tested under negative bending. The width-to-thickness ratios of U-section walls (i.e., flanges and webs) and stiffening details for preventing local buckling were considered as the test variables. The tests showed that, due to excessive slab reinforcement, all specimens were failed by shear failure at the composite interface of beam and slab after flexural yielding. The ultimate strength and deformation capacity of CFU beams were degraded by flange and web local buckling. Buckling modes of U-section walls were affected by the stiffening details. The ultimate strengths of noncompact and slender CFU beams were compared with the nominal strengths calculated in accordance current standards. In addition, the flexural behavior of CFU beams affected by the local buckling and partial debonding of U-section walls and slip behavior at the composite interface was further investigated through fiber-based section analyses based on the effective stress-strain models of materials.

고층 RC 벽식 건축물의 성능기반설계에서 RC 벽체의 전단모델은 극한전단거동을 탄성거동으로 가정하고 있지만, 이러한 가정은 RC 벽체의 전단거동을 합리적으로 묘사한다고 보기 어렵다. 따라서 본 연구에서는 최근 개정된 “철근콘크리트 건축구조물의 성능기반 내진설계지침”에서 제안한 RC 벽체의 이선형 전단모델을 기존 실험결과와의 비교를 통해 유효성을 정량적으로 검증하였다. 또한, 비선형 지진이력해석을 통해 상기 모델을 적용했을 때 건축물의 거동특성변화를 시스템적 측면에서 분석하였다. 비선형 지진이력해석 시 해석 변수는 섬유요소모델에 적용되는 전단모델로 탄성전단모델(0.5G, 1.0G)과 이선형 전단모델이다. 해석결과, 이선형 전단모델을 적용할 경우에 층별 밑면 전단력이 감소하고 벽체의 전단력이 재분배되어 특정 벽체에 집중되었던 전단응력이 완화되었다. 이를 통해 제안된 이선형 전단모델을 고층 RC 벽식구조물 벽체 모델링에 적용한다면 합리적이고 경제적인 성능기반 내진설계가 가능하다.

이 연구에서는 SD600 철근을 사용한 외부 보-기둥 접합부의 내진성능을 조사하였다. 보 항복 메커니즘을 보이도록 설계된 6개의 실험체에 대하여 횡하중 반복가력시험을 수행하였다. SD600 보 철근이 90도 표준갈고리로 정착된 보-기둥 접합부에서는 전단보강을 위하여 직사각형 나선철근이 사용되었다. 실험변수로는 콘크리트 압축강도(32.2 및 52.2 MPa), 철근 항복강도(442 및 662 MPa), 및 강섬유콘크리트 사용 등이 고려되었다. 실험 결과, 조인트 깊이가 크지 않은 접합부에서 설계기준에서 요구하는 SD600 철근의 정착길이를 만족하지 못하였지만, 대부분의 실험체에서 부착슬립 및 정착파괴가 발생하지 않았다. 변형능력은 변위비 5 % 이상이었지만, 5개 중 3개의 실험체에서 불량한 경화거동으로 인한 SD600 고강도철근의 인장파단이 발생하였다. 접합부에서 부착 및 전단 거동은 더 높은 압축강도의 콘크리트와 강섬유 콘크리트를 사용함으로써 개선되었다.

이 연구에서는 수평증축 리모델링을 고려 중인 내력벽 아파트의 격막 해석 및 설계 방법을 제안하였다. 격막 모델링 및 분석 절차를 수립하기 위해 기존 설계기준 및 기술지침을 검토하였다. 수평증축 리모델링을 고려 중인 18층 내력벽 아파트에 대해 컴퓨터해석을 수행하여, 격막거동 및 격막연결부를 통한 힘 전달을 조사하였다. 해석 결과, 격막거동에 의한 슬래브 면내응력은 벽체 근처에서 많이 증가하였고, 특히 격막전달력은 셋백으로 인해 바닥면적의 일부가 감소한 최상층 2층 바로 아래 바닥층에서 벽체 불연속으로 인해 많이 증가하는 것으로 나타났다. 이러한 분석 결과를 바탕으로 수평증축 리모델링을 위한 격막연결부의 설계 고려사항을 논의하였다. 또한 콘크리트 전단키와 부착식 앵커철근을 사용하여 기존 및 신설 격막 슬래브를 연결하기 위한 계면전단접합방법을 제안하였다.

This study investigated the compressive behavior of concrete-encased high-strength steel angle columns (F-y = 718 MPa). Axial compressive tests were performed on six composite columns with different angle sections and confinement details. The results showed that the failure mode of the columns was local buckling of the angle legs and crushing of the confined core. Local buckling and concrete confinement significantly affected the compressive strength and ductility. The test strengths were compared with the theoretical strengths computed using the plastic stress distribution method. For analytical investigation, effective stress-strain models of the steel angle and concrete are proposed to account for the local buckling, spalling, and confinement. Through the strain-compatibility analysis based on the proposed models, the contributions of the angles, unconfined cover, and confined core to the compressive strength varying with deformation were investigated. Based on the investigation results, recommendations for the design and detailing of concrete-encased high-strength steel angle columns are given. (C) 2021 American Society of Civil Engineers.

세장한 강재 트러스부재의 좌굴성능을 향상시키기 위하여 개발된 모르타르 충전 각형강관 부재가 최근들어 지붕트러스의 대각재와 현재에 사용되고 있다. 본 연구에서는 이러한 모르타르가 충전된 각형강관의 압축성능을 실험적으로 검증하였다. 단면 100 ㎜×100 ㎜ 크기의 소형 각형강관 부재에 대해 총 6개의 압축실험을 수행하였다. 각형강관의 두께, 관통철근 보강, 단부강판 크기를 주요변수로 고려하였다. 실험결과, 모든 실험체는 휨 좌굴에 의해 파괴가 발생하였다. 각형강관의 유효 축강성과 압축강도는 각형강관의 두께에 주로 영향을 받았다. 현행설계기준에서 제시하는 압축력을 받는 충전형 합성기둥의 공칭압축강도와 실험결과가 잘 일치하는 결과를 보였다.

ABS T R A C T This study investigated the behavior of bolted end plate connection for structural angle sections. For the splice of angles under tensile loading, thick end plates attached to the end of angles are connected by one single high-tension bolt. To improve connection performance and reduce required plate thickness, plate washers made of the same material as that of the end plates are used under the bolt head and nut. Tensile tests of twenty-two specimens with different connection details were conducted. The tests showed that the governing failure mode was bolt rupture and the connection performance was affected by the thickness of the plates. The minimum thickness of end plate and plate washer determined by the yield line theory was conservative. Due to prying action, the connection strength (i.e., the tensile load of angles) was reduced to about 85% of the tensile strength of high-tension bolt. The force transfer behavior of the end plate connection with and without plate washer was investigated in detail through finite element analysis.

This study investigated the seismic resistance of thin, lightly reinforced walls strengthened in the out-of-plane direction by thick jacketing. To connect the thin existing wall and thick strengthening jacket, a tee shear connector consisting of one T-shaped steel section and several dowel bars and anchor bolts was used. Cyclic tests of four jacketed wall specimens were performed under out-of-plane lateral loading. The tests showed that the strength of the strengthened walls by thick jacketing was significantly enhanced. During the initial behavior, the tee shear connector performed well, not only as the shear connector; but also as the flexural tension reinforcement. However: as concrete damage increased during repeated load cycles, band failure occurred early in the tee shear connector under flexural tension. The flexural strengths of the strengthened walls by thick jacketing were computed based on full and partial composite action of the tee section, and the bond and shear resistances of the tee shear connector were estimated in accordance with the provisions of ACI 318-19.

이 연구에서는 아파트 지하주차장의 바닥시스템으로 개발된 PC 보 및 이음부의 구조성능을 조사하였다. PC 보는 PC 벽기둥 상부 또는 영모멘트 위치에서 이음되며, 이음부에서는 구조적인 일체성을 높이기 위하여 접합되는 PC 보의 단면 일부에 홈을 팠고, 철근을 배치하였으며, 그런 다음 현장타설 콘크리트로 접합하였다. 또한 별도의 토핑 콘크리트를 현장타설하여 PC 보 및 토핑 콘크리트를 연속된 바닥구조로 설계하였다. 휨거동 및 전단거동을 분석하기 위하여 4개의 PC 보 이음실험체에 대하여 4점 재하 보실험을 수행하였다. 실험 결과, PC 보 이음부의 휨거동은 홈 내부 콘크리트 접합면의 부착성능(즉, 홈 길이)에 영향을 받았다. 홈의 크기가 충분히 큰 실험체는 공칭강도 이상의 휨성능을 발휘한 반면, 홈 길이가 불충분한 실험체는 홈 내부 및 토핑에서 휨균열 이후 발생하는 부착쪼갬균열에 의한 콘크리트 전단파괴가 발생하였다.

The seismic performance of exterior beam-column joints in low-rise buildings with limited ductility details was investigated. Seven exterior beam-column connection specimens were prepared for cyclic loading tests, and the major test parameters were the column depth and joint shear reinforcement details. In the specimens, joint shear failure occurred before beam or column yielding. The shear strength of the exterior joints increased as the column depth (i.e., joint depth) and the area of shear reinforcements increased. Despite the nonseismic reinforcement details, U-shaped bars and 90 degrees-hooked hoops with a spacing of one-third of the column depth increased the joint shear strength. As a result, flexural beam yielding occurred in several specimens. The joint shear strengths were compared with the predictions by current design codes, and the effects of the test parameters were investigated. Based on the results, a shear strength equation for exterior joints was proposed that is applicable to nonseismic details. (C) 2019 American Society of Civil Engineers.

In earthquake design of columns, 135-degree hook anchorages are required in peripheral hoops and crossties to assure the ductility of columns. However; 135-degree hook anchorages frequently cause difficulty in reinforcing bar placement. In the present study, V-shaped ties were studied to partially replace conventional transverse reinforcement. Their details and layout were also proposed. To verify the effect of V-ties, cyclic lateral loading tests were performed for six columns using conventional transverse reinforcement or V-ties. The test results showed that V-ties successfully restrained buckling of longitudinal reinforcement and provided lateral confinement to the core concrete. However; the deformation capacities of columns with V-ties were slightly less than those of columns with crossties because V-ties do not provide shear resistance. Thus, for special moment frames with high shear demand and ductility demand, the vertical spacing of perimeter hoops should be reduced. On the basis of the test results, design considerations for columns with V-ties were recommended.

이 연구에서는 편심압축력을 받는 철근콘크리트 벽체의 전단거동을 조사하였다. 형상비가 2.0인 6개의 켄틸레버 벽체에 대하여 전단실험을 수행하였다. 벽체에 가해진 압축력의 크기와 편심이 설계변수로 고려되었다. 실험결과에 따르면, 편심재하된 벽체의 파괴모드와 전단강도는 편심에 의하여 크게 영향을 받는다. 편심이 증가할 경우, 벽체의 파괴모드는 복부의 사인장균열파괴에서 휨전단균열파괴로 바뀌며, 그로 인하여 전단강도가 감소한다. 벽체의 실험강도는 ACI318-14 및 KCI 2012의 규정에 따라 예측한 전단강도와 비교하였다. 비교 결과, 사인장균열파괴와 휨전단균열파괴에 근거한 기존의 벽체 및 기둥 전단강도 평가방법은 편심재하된 벽체의 전단강도를 크게 저평가하는 것으로 나타났다.

In 2017 Pohang Earthquake, a number of residential buildings with pilotis at their first level were severely damaged. In this study, the results of an analytical investigation on the seismic performance and structural damage of two bearing wall buildings with pilotis are presented. The vibration mode and lateral force-resisting mechanism of the buildings with vertical and plan irregularity were investigated through elastic analysis. Then, based on the investigations, methods of nonlinear modeling for walls and columns at the piloti level were proposed. By performing nonlinear static and dynamic analyses, structural damages of the walls and columns at the piloti level under 2017 Pohang Earthquake were predicted. The results show that the area and arrangement of walls in the piloti level significantly affected the seismic safety of the buildings. Initially, the lateral resistance of the piloti story was dominated mainly by the walls resisting in-plane shear. After shear cracking and yielding of the walls, the columns showing double-curvature flexural behavior contributed significantly to the residual strength and ductility.

A new lateral force-resisting structural system for concrete high-rise buildings, distributed belt wall system, is proposed. Unlike conventional belt structures, the belt walls infilling the space between perimeter columns are distributed separately along the overall building height. In this study, the force transfer mechanism and performance of the distributed belt walls, acting as virtual outriggers under lateral load, are investigated. For the reinforcement of the belt walls subjected to high shear demand, a reinforcing method using high-strength prestressing strands (i.e. PSC belt wall) is suggested, and the shear strength of the PSC belt walls is estimated based on the compression field theory. By performing nonlinear finite element analysis, the shear behavior of the PSC belt walls, including cracking and yield strengths, is investigated in detail. Based on these investigations, recommendations for the shear design of the belt walls reinforced by high-strength prestressing strands are given.

This study investigates a bolted end-plate splice of steel angles for encased composite columns. For the splice, two end plates, each of which is welded at the end of the spliced angle, are butted to each other, and connected in tension by one or three high-strength bolts. Since the centroids of the angle and bolt sections do not coincide, the deformation and prying force occurring at the connection need to be considered for design. Thus, the minimum thickness of end plate is proposed based on the yield line theory, and the tensile strength of the connection decreased by the prying force is estimated. The strength and failure mode of the connection are investigated through the direct tension tests of bare angle splice, and flexural tests of encased composite column with angle splice. The tests have shown that the connection is susceptible to slip and fracture in the threaded portion of bolt. In addition, the proposed minimum end-plate thickness and connection strength agree well with the test results.

Reinforced concrete structural walls with T-shaped cross sections (or T-shaped walls) have been used as an efficient lateral force-resisting system for building structures. Such T-shaped walls are subjected to axial compression and combined bending moments about two orthogonal axes. In the present study, a straightforward design method for biaxially loaded T-shaped walls is developed by modifying the existing load contour method. First, a strain compatibility section analysis method that can estimate the biaxial bending resistances of arbitrary wall sections is developed and its validity is verified through comparisons with test results. Then, a parametric study is performed to investigate the interaction of biaxial moments at a constant axial load in T-shaped walls. The parametric results show that, due to the unsymmetrical geometry of T-shaped sections, the biaxial interaction depends significantly on the direction of moments and the magnitude of axial compression. Based on the results, the non-dimensional contour equations of biaxial moments for T-shaped walls are proposed and a design procedure of T-shaped walls is established.

The seismic performance of reinforced concrete beam-column connections is degraded by yield penetration, bond failure, and slip deformation at the joint. In the present study, reinforcement details for the beam-column joints were developed. 45° bent bars and 90° hooked bars were used passing through the joints in order to secure a longer development length of re-bars at the joints and relocate the severe plastic hinge of beams away from the joint interface. Cyclic loading tests on six cruciform beam-column connections were performed. The earthquake resistance including the strength, ductility, energy dissipation capacity, and failure mode were evaluated. In the specimens with the joint-reinforcing details, plastic hinges developed at the beam ends as intended. Thus, re-bar yield penetration and bond slip deteriorating the seismic performance of the joint were substantially decreased. The specimens with the proposed joint-reinforcing details satisfied the performance requirements of ACI 374.1-05 on strength, stiffness, energy dissipation, and ductility. Keywords: RC Beam-column Joint, Seismic Performance Test, Joint Reinforcement, Ductility, Energy Dissipation Capacity